Examples of Chemical Processing Operations

Published in 104. Guide to Chemicals

Wednesday, 03 August 2011 00:17

Aromatic Amino Compounds

The aromatic amino compounds are a class of chemicals derived from aromatic hydrocarbons, such as benzene, toluene, naphthalene, anthracene and diphenyl by the replacement of at least one hydrogen atom by an amino –NH₂ group. A compound with a free amino group is described as a primary amine. When one of the hydrogen atoms of the –NH₂ group is replaced by an alkyl or aryl group, the resultant compound is a secondary amine; when both hydrogen atoms are replaced, a tertiary amine results. The hydrocarbon may have one amino group or two, more rarely three. It is thus possible to produce a considerable range of compounds and, in effect, the aromatic amines constitute a large class of chemicals of great technical and commercial value.

Aniline is the simplest aromatic amino compound, consisting of one –NH₂ group attached to a benzene ring and its derivatives are most widely used in industry. Other common single-ring compounds include dimethylaniline and diethylaniline, the chloroanilines, nitroanilines, toluidines, the chlorotoluidines, the phenylenediamines and acetanilide. Benzidine, o-tolidine, o-dianisidine, 3,3'-dichlorobenzidine and 4-aminodiphenyl are the most important conjoined ring compounds from the point of view of occupational health. Of compounds with ring structures, the naphthylamines and aminoanthracenes have attracted much attention because of problems of carcinogenicity. Strict precautions necessary for handling carcinogens apply to many members of this family.

Azo and diazo dyes

Azo dye is a comprehensive term applied to a group of dyestuffs that carry the azo (–N=N–) group in the molecular structure. The group may be divided into subgroups of monoazo, diazo and triazo dye and further in accordance with the number of the azo group in the molecule. From a toxicological perspective, it is important to take into account that the commercial grade dyestuffs usually contain impurities up to 20% or even higher. The composition and quantity of the impurities are variable depending on several factors such as the purity of the starting materials for the synthesis, the process of synthesis employed and the requirements of the users.

Production

Azos dyes are synthesized by diazotization or tetrazotization of aromatic monoamine or aromatic diamine compounds with sodium nitrite in the HCl medium, followed by coupling with dye intermediates such as various aromatic compounds or heterocyclic compounds. When the coupling component carries an amino group, it is possible to produce long-chained polyazo dye by the repetition of diazotization and coupling. The generalized structural formulae for the first three members of the family are:

R–N=N–R' monoazo dye

R–N=N–R'–N=N–R" diazo dye

R–N=N–R'–N=N–R"–N=N–R"' triazo dye

Tetrazotization of benzidine and coupling with naphthionic acid yields the very popular dye Congo Red.

Uses

Aromatic amino compounds are primarily used as intermediates in the manufacture of dyes and pigments. The largest class of dyestuffs is that of the azo colours, which are made by diazotization, a process by which a primary aromatic amine reacts with nitrous acid in the presence of excess mineral acid to produce a diazo (–N=N–) compound; this compound is subsequently coupled with a phenol or an amine. Another important class of dyestuffs, the triphenylmethane colours, is also manufactured from aromatic amines. In addition to serving as chemical intermediates in the dyestuffs industry, several compounds are employed as dyes or intermediates in the pharmaceutical, fur, hairdressing, textile and photography industries.

o-Aminophenol is used for dyeing furs and hair. It is also a developer in the photography industry and an intermediate for pharmaceuticals. p-Aminophenol is used in dyeing textiles, hair, furs and feathers. It finds use in photographic developers, pharmaceuticals, antioxidants and oil additives. 2,4-Diaminoanisole provides an oxidation base for dyeing fur. o-Toluidine, p-phenylenediamine, diphenylamine and N-phenyl-2-naphthylamine find additional uses as antioxidants in the rubber industry.

Diphenylamine is also employed in the pharmaceutical and explosives industries and as a pesticide. N-Phenyl-2-naphthylamine serves as a vulcanization accelerator, a stabilizer for silicone enamels and a lubricant. It is a component of rocket fuels, surgical plaster, tin-electroplating baths and dyes. 2,4-Diaminotoluene and 4,4'-diaminodiphenylmethane are useful intermediates in the manufacture of isocyanates, basic raw materials for the production of polyurethanes.

The major use of benzidine is in the manufacture of dyestuffs. It is tetrazotized and coupled with other intermediates to form colours. Its use in the rubber industry has been abandoned. Auramine is used in printing inks and as an antiseptic and a fungicide.

o-Phenylenediamine is a photographic developing agent and a hair dye component while p-phenylenediamine is used as a photographic chemical and a dyeing agent for fur and hair. However, p-phenylenediamine has been banned for use as an oxidation dye for hair in some countries. p-Phenylenediamine is also a vulcanization accelerator, a component of gasoline antioxidants. m-Phenylenediamine has numerous functions in the dyestuffs, rubber, textile, hairdressing and photography industries. It finds use in rubber curing agents, ion exchange and decolorizing resins, urethanes, textile fibers, petroleum additives, corrosion inhibitors and hair dyes. It is used as an promoter for adhering tire cords to rubber.

Xylidine serves as a gasoline additive as well as raw material in the manufacture of dyes and pharmaceuticals. Melamine is used in moulding compounds, textile and paper treating resins, and in adhesive resins for gluing lumber, plywood and flooring. In addition, it is useful in organic synthesis and in leather tanning. o-Tolidine is a reagent for the detection of gold.

Anilines

The anilines are primarily used as intermediates for dyes and pigments. Several compounds are intermediates for pharmaceuticals, herbicides, insecticides and rubber processing chemicals, as well. Aniline itself is widely used in the manufacture of synthetic dyestuffs. It is also used in printing and cloth marking inks and in the manufacture of resins, varnishes, perfumes, shoe blacks, photographic chemicals, explosives, herbicides and fungicides. Aniline is useful in the manufacture of rubber as a vulcanizing agent, as an antioxidant, and as an antiozone agent. A further important function of aniline is in the manufacture of
p,p'-methylenebisphenyldiisocyanate (MDI), which is then used to prepare polyurethane resin and spandex fibers and to bond rubber to rayon and nylon.

Chloroaniline exists in three isomeric forms: ortho, meta and para, of these only the first and the last are important for manufacturing dyes, drugs and pesticides. p-Nitroaniline is a chemical intermediate for antioxidants, dyes, pigments, gasoline gum inhibitors and pharmaceuticals. It is used in diazotized form to retain fastness of dyes after washing. 4,4'-Methylene-bis(2-chloroaniline), MbOCA, is used as a curing agent with isocyanate-containing polymers for the manufacture of solid abrasion-resistant urethane rubbers and moulded semi-rigid polyurethane foam articles with a hardened skin. These materials are used in an extensive range of products, including wheels, rollers, conveyor pulleys, cable connectors and seals, shoe soles, antivibration mounts and acoustic components. p-Nitroso-N,N,-dimethylaniline and 5-chloro-o-toluidine are used as intermediates in the dyestuffs industry. N,N-Diethylaniline and N,N-dimethylaniline are used in the synthesis of dyestuffs and other intermediates. N,N-Dimethylaniline also serves as a catalytic hardener in certain fibreglass resins.

Azo compounds

Azo compounds are among the most popular groups of various dyes including direct dyes, acid dyes, basic dyes, naphthol dyes, acid mordant dyes, disperse dyes, etc., and are extensively used in textiles, fabrics, leather goods, paper products, plastics and many other items.

Hazards

The manufacture and use in industry of certain aromatic amines may constitute a grave and sometimes unexpected hazard. However, since these hazards have become better known, there has, over recent years, been a tendency to substitute other substances or to take precautions which have reduced the hazard. Discussion has also taken place concerning the possibility of aromatic amines having health effects either when they exist as impurities in a finished product, or when they may be restored as the result of a chemical reaction taking place during the use of a derivative, or—and this is a totally different case—as the result of metabolic degradation within the organism of persons who may be absorbing more complex derivatives.

Absorption pathways

Generally speaking, the principal risk of absorption lies in skin contact: the aromatic amines are nearly all lipid-soluble. This particular hazard is all the more important because in industrial practice it is one often not sufficiently appreciated. In addition to skin adsorption, there is also a considerable risk of absorption by inhalation. This may be the result of inhaling the vapours, even though most of these amines are of low volatility at normal temperatures; or it may result from breathing in dust from the solid products. This applies particularly in the case of the amine salts such as sulphates and chlorohydrates, which have a very low volatility and lipid solubility: the occupational hazard from the practical point of view is less but their over-all toxicity is about the same as the corresponding amine, and thus the inhalation of their dust and even skin contact must be considered dangerous.

Absorption by way of the digestive tract does represent a potential danger if inadequate eating and sanitary facilities are provided or if workers do not exercise excellent person hygiene practices. Contamination of food and cigarette smoking with dirty hands are two examples of possible ingestion routes.

Many of the aromatic amines are flammable and represent a moderate fire hazard. Combustion products can often be highly toxic. The primary health danger of industrial exposure to aniline arises from the ease with which it can be absorbed, either by inhalation or from skin absorption. Because of these absorptive properties, prevention of aniline poisoning requires high standards of industrial and personal hygiene. The most important specific measure for the prevention of spillage or contamination of the work atmosphere with aniline vapour is proper plant design. Ventilation control of the contaminant should be designed as close to the point of generation as possible. Work clothing should be changed daily and facilities for an obligatory bath or shower at the end of the working period should be provided. Any contamination of skin or clothing should be washed off immediately and the individual kept under medical supervision. Both workers and supervisors should be educated to be aware of the nature and extent of the hazard and to carry out the work in a clean, safe manner. Maintenance work should be preceded with sufficient attention to removal of possible sources of contact with the offending chemicals.

Since many cases of aniline poisoning result from contamination of the skin or clothing that leads to absorption through the skin, contaminated clothing should be removed and laundered. Even when intoxication results from inhalation, the clothing is likely to be contaminated and should be removed. The entire body surface, including hair and fingernails, should be carefully washed with soap and tepid water. Where methaemoglobinemia is present, appropriate emergency precautions should be taken and the occupational health service must be fully equipped and trained to handle such emergencies. Laundry workers should be provided with adequate precautions to avoid contamination from the aniline compounds.

Metabolism

The amines undergo a process of metabolization within the organism. Generally the active agents are the metabolites, some of which induce methaemoglobinaemia, while others are carcinogenic. These metabolites generally take the form of hydroxylamines (R-NHOH), changing to aminophenols (H₂N-R-OH) as a form of detoxification; their excretion provides a means of estimating the degree of contamination when the level of exposure has been such that they are detectable.

Health effects

Aromatic amines have various pathological effects, and each member of the family does not share the same toxicological properties. While each chemical must be evaluated independently, certain important characteristics are prominently shared by many of them. These include:

cancer of the urinary tract, particularly of the urinary bladder

danger of acute poisoning, particularly methaemoglobinaemia, which may ultimately have adverse effects on the red cells

sensitization, notably of the skin, but sometimes respiratory.

Toxic effects are also related to chemical characteristics. For example, although an aniline salt has a very similar toxicity to aniline itself, it is not water or lipid soluble and hence not readily absorbed through the skin or by inhalation. Thus, poisoning by aniline salts from industrial exposure are rare.

Acute poisoning generally results from the inhibition of haemoglobin function through the formation of methaemoglobin, leading to a condition called methaemoglobinemia, which is discussed more fully in the Blood chapter. Methaemoglobinemia is more often associated with the single-ring aromatic amino compounds. Methaemoglobin is normally present in the blood at a level of about 1 to 2% of the total haemoglobin. Cyanosis at the oral mucosae begins to become apparent at levels of 10 to 15%, though subjective symptoms are normally not experienced until methaemoglobin levels of the order of 30% are reached. With increases above this level, the patient's skin colour deepens; later, headache, weakness, malaise and anoxia occur, to be succeeded, if absorption continues, by coma, cardiac failure and death. Most cases of acute poisoning react favourably to treatment and the methaemoglobin disappears completely after two to three days. The consumption of alcohol is conducive to and aggravates acute methaemoglobin poisoning. Haemolysis of the red blood cells can be detected after severe poisoning, and is followed by a process of regeneration which is demonstrated by the presence of reticulocytes. The presence of Heinz bodies in the red blood corpuscles may sometimes also be detected.

Cancer. The potent carcinogenic effects of the aromatic amines were first discovered in the workplace as a result of the abnormally high incidence of cancer employees in a dye factory. The cancers were described as "dye cancer", but further analysis very soon pointed to their origin being in the raw materials, of which the most important was aniline. They then became known as "aniline cancers". Later, further definition was possible and β-naphthylamine and benzidine were considered to be the “culprit” chemicals. Experimental confirmation of this was long in coming and difficult. Experimental work on many members of this family has found a number to be animal carcinogens. Since insufficient human evidence is available, they have been classified by the International Agency for Research on Cancer (IARC) for the most part as 2B, probable human carcinogens, that is, having sufficient evidence for animal carcinogenicity but insufficient for human carcinogenicity. In some cases, laboratory work has lead to the discovery of human cancer, as in the case of 4-aminodiphenyl, which was first shown to be carcinogenic for animals (in the liver), after which a number of cases of bladder cancer in humans were brought to light.

Dermatitis. Because of their alkaline nature, certain amines, particularly the primary ones, constitute a direct risk of dermatitis. Many aromatic amines can cause allergic dermatitis, such as that due to sensitivity to the "para-amines" (p-aminophenol and particularly p-phenylenediamine). Cross-sensitivity is also possible.

Respiratory allergy. A number of cases of asthma due to sensitization to p-phenylenediamine, for example, have been reported.

Haemorrhagic cystitis can result from heavy exposure to o- and p-toluidine, particularly the chlorine derivatives, of which chloro-5-o-toluidine is the best example. These haematuria appear to be short-lived and the relationship to development of bladder tumours is not established.

Liver injuries. Certain diamines, such as toluenediamine and diaminodiphenylmethane, have potent hepatotoxic effects in experimental animals but serious liver damage resulting from industrial exposure has not been a widely reported. In 1966, however, 84 cases of toxic jaundice were reported from eating bread baked from flour contaminated with 4,4'-diaminodiphenylmethane, and cases of toxic hepatitis have also been reported after occupational exposure.

Some of the toxicological properties of the aromatic amines are discussed below. Because the members of this chemical family are very numerous, it is not possible to include them all, and there may be others, not included below, which also have toxic properties.

Aminophenols

Neither o- nor p-aminophenol isomers, which are crystalline solids of low volatility, are readily absorbed through the skin, although both may act as skin sensitizers and cause contact dermatitis, which appears to be the greatest hazard arising from their use in industry. Although both isomers can cause serious, even life-threatening methaemoglobinaemia, this seldom arises from industrial exposure, since their physical properties are such that neither compound is readily absorbed into the body. p-Aminophenol is the major metabolite of aniline in humans and is excreted in the urine in conjugated form. Bronchial asthma from the ortho isomer has been reported as well.

p-Aminodiphenyl is considered a confirmed human carcinogen by IARC. It was the first compound in which the demonstration of carcinogenic activity in experimental animals preceded the first reports of bladder tumours in exposed workers, where it was used as an antioxidant in rubber manufacture. The substance is clearly a potent bladder carcinogen since in one plant with 315 workers, 55 developed tumours as did 11% of 171 workers in another plant manufacturing 4-aminodiphenyl. The tumours appeared 5 to 19 years after initial exposure, and survival ranged in duration from 1.25 to 10 years.

Aniline and its derivatives

It has been demonstrated experimentally that aniline vapour can be absorbed via the skin and respiratory tract in approximately equal amounts; however, the rate of absorption of the liquid through the skin is about 1,000 times greater than that of the vapour. The most frequent cause of industrial poisoning is accidental skin contamination, either directly through accidental contact, or indirectly through contact with soiled clothing or footwear. The use of clean and suitable protective clothing and rapid washing in case of accidental contact constitute the best protection. While the US National Institute for Occupational Health and Safety (NIOSH) recommends that aniline be treated as a suspected human carcinogen, IARC has rated it as a Group 3 chemical, meaning insufficient evidence of animal or human carcinogenicity.

p-Chloroaniline is a potent methaemoglobin-former and eye irritant. Animal experiments have provided no evidence of carcinogenicity. 4,4'-Methylene bis(2-chloroaniline), or MbOCA, can be absorbed from contact with dust or from fume inhalation, and in industry, skin absorption may also be an important route for uptake. Laboratory studies showed MbOCA or its metabolites may cause genetic damage in a variety of organisms. In, addition, long-term subcutaneous administration in rats resulted in liver and lung tumours. Thus, MbOCA is regarded as an animal carcinogen and a probable human carcinogen.

N,N-Diethylaniline and N,N-dimethylaniline are readily absorbed through the skin, but poisoning may also occur through inhalation of vapours. Their hazards may be considered as similar to those of aniline. They are, in particular, potent methaemoglobin-formers.

Nitroanilines. Of the three mono-nitroanilines, the most important is p-nitroaniline. All are used as dye intermediates, but the o- and m- isomers only on a small scale. p-Nitroaniline is readily absorbed through the skin and also by inhalation of dust or vapour. It is a powerful methaemoglobin-former, and is alleged, in serious cases, also to bring about haemolysis, or even liver damage. Cases of poisoning and cyanosis have been reported following exposure while cleaning up spills. The chloronitroanilines are also potent methaemoglobin-formers, leading to haemolysis, and are hepatotoxic. They may give rise to dermatitis by sensitization.

p-Nitroso-N,N-dimethylaniline possesses both primary irritant and skin sensitizing properties, and it is a common cause of contact dermatitis. Although, occasionally, workers who develop dermatitis may subsequently work with this compound without further trouble, most will suffer a severe recurrence of the skin lesions on re-exposure, and, in general, it is wise to transfer them to other work to avoid further contact.

5-Chloro-o-toluidine is readily absorbed through the skin or by inhalation. Although it (and some of its isomers) may cause methaemoglobin formation, the most striking feature is its irritant effect on the urinary tract, resulting in haemorrhagic cystitis characterized by painful haematuria and frequency of micturition. Microscopic haematuria may be present in men exposed to this compound before the cystitis is manifest, but there is no carcinoenic hazard to humans. However, laboratory experiments have cast doubts on the carcinogenicity of other isomers for certain species of animals.

Benzidine and derivatives

Benzidine is a confirmed carcinogen, the manufacture and industrial use of which has caused many cases of papilloma and carcinoma of the urinary tract. Among some working populations, more than 20% of all workers have developed the disease. Recent studies indicate that benzidine may raise the rate of cancer at other sites but there is not agreement on this as yet. Benzidine is a crystalline solid with a significant vapour pressure (that is, it forms vapours readily). Penetration through the skin seems to be the most important pathway for the absorption of benzidine, but there is also a hazard from the inhalation of vapour or fine particles. The carcinogenic activity of benzidine has been established by the many reported cases of bladder tumour in exposed workers and by experimental induction in animals. It is a Group1 confirmed human carcinogen according to IARC ratings. The use of benzidine has been discontinued in most places.

3,3'-Dichlorobenzidine is a probable human carcinogen (IARC Class 2B). This conclusion is based on a statistically significantly increased tumor incidence in rats, mice and dogs and positive data on its genotoxicity. The structural relationship to benzidine, a known, powerful human bladder carcinogen, lends further weight to the probability that it is a human carcinogen.

Diamino-4,4'-diaminodiphenylmethane. The most striking example of the toxicity of this compound was when 84 persons contracted toxic hepatitis as a result of eating bread baked from flour that was contaminated with the substance. Other cases of hepatitis were noted after occupational exposure through skin absorption. It may also give rise to allergic dermatitis. Animal experiments have led to its being a suspected potential carcinogen, but conclusive results have not been obtained. Diaminodiphenylmethane derivatives have been shown to be carcinogens for laboratory animals.

Dimethylaminoazobenzene. The metabolism of DAB has been extensively studied and it has been found that it involves reduction and cleavage of the azo group, demethylation, ring hydroxylation, N-hydroxylation, N-acetylation, protein binding and binding of nucleic acids. DAB shows mutagenic properties after activation. It has carcinogenic power by various routes in the rat and mouse (liver carcinoma), and by oral route it causes carcinoma of the bladder in the dog. The only occupational health observation in humans was of contact dermatitis in factory workers handling DAB.

Technical measures should prevent any contact with the skin and mucous membranes. Workers exposed to DAB should wear personal protective equipment and their work should be carried out only in restricted areas. Clothing and equipment after use should be placed in an impervious container for decontamination or disposal. Pre-employment and periodical examinations should focus on liver function. In the US, DAB has been included by OSHA among the cancer suspect agents for humans.

Diphenylamine. This chemical can be mildly irritating. It appears that under ordinary industrial conditions it offers little hazard, but the potent carcinogen 4-aminodiphenyl may be present as an impurity during the manufacturing process. This may be concentrated to significant proportions in the tars produced at the distillation stage and will constitute a hazard of bladder cancer. While modern manufacturing procedures have enabled the amount of impurities in this compound to be considerably reduced in the commercial product, appropriate prevention must be taken to prevent unnecessary contact.

Naphthylamines

The naphthylamines occur in two isomeric forms, a-naphthylamine and b-naphthylamine.
α-Naphthylamine is absorbed through the skin and by inhalation. Contact may cause burns to the skin and eyes. Acute poisoning does not arise from its industrial use, but exposure to commercial grades of this compound in the past has resulted in many cases of papilloma and carcinoma of the bladder. It is possible that these tumours were attributable to the substantial β-naphthylamine impurity. This matter is not merely of academic interest, as α-naphthylamine with greatly reduced levels of β-naphthylamine impurity is now available.

β-Naphthylamine is a known human bladder carcinogen. Acute poisoning results in methaemoglobinemia or acute haemorrhagic cystitis. Although at one time extensively used as an intermediate in the manufacture of dyestuffs and antioxidants, its manufacture and use has been almost entirely abandoned throughout the world, and it has been condemned as too dangerous to make and handle without prohibitive precautions. It is readily absorbed through the skin and by inhalation. The question of its acute toxic effects does not arise because of its high carcinogenic potency.

Phenylenediamines

Various isomeric forms of the phenylenediamines exist but only the m- and p-isomers are of industrial importance. While p-phenylenediamine can act as a methaemoglobin-former in vitro, methaemoglobinaemia arising from industrial exposure is unknown. p-Phenylenediamine is notorious for its sensitizing properties of the skin and respiratory tract. Regular skin contact readily causes contact dermatitis. Acne and leukoderma have also been reported. The former problem of "fur dermatitis" is much less frequent now owing to improvements in the dyeing process having the effect of removing all traces of p-phenylenediamine. Similarly, asthma, at one time common among fur dyers using this substance, is now relatively rare after improvements in the control of airborne dust. Even with controls, a preliminary skin test is useful prior to possible occupational exposure. m-Phenylenediamine is a strong irritant to the skin and causes eye and respiratory irritation. Conclusions drawn from experiments conducted on the phenylenediamines and their derivatives (e.g. N-phenyl or 4- or 2-nitro) relating to their carcinogenic potential are, up to the present time, either insufficient, inconclusive or negative. Chlorine derivatives that have been tested seem to have a carcinogenic potential in animal tests.

The carcinogenic potential of commercial mixtures in the past was of great concern because of the presence of β-naphthylamine, which had been found to exist as an impurity in considerable quantities (running into tens or even hundreds of ppm) in some of the older preparations, and by the discovery, in the case of N-phenyl-2-naphthylamine, PBNA, of β-naphthylamine as a metabolic excretion, though in infinitesimal quantities. The experiments point to a carcinogenic potential for the animals tested but do not permit a conclusive judgment to be made, and the degree of significance of the metabolic findings is not yet known. Epidemiological investigations on a large number of persons working under different conditions have not shown any significant increase in the incidence of cancer among workers exposed to these compounds. The amount of β-naphthylamine that is present in the marketed products today is very low—less than 1 ppm and frequently 0.5 ppm. At the present time it is not possible to draw any conclusions as to the true cancer hazard, and for this reason every precaution should be taken, including the elimination of impurities that may be suspect, and technical protective measures in the manufacture and use of these compounds.

Other compounds

Toluidine exists in three isomeric forms but only the o- and p- isomers are of industrial importance. o-Toluidine and p-toluidine are readily absorbed through the skin, or inhaled as dust, fume or vapour. They are powerful methaemoglobin-formers, and acute poisoning may be accompanied by microscopic or macroscopic haematuria, but they are much less potent as bladder irritants than 5-chloro-o-toluidine. There is sufficient evidence of carcinogenicity in animals to classify o-toluidine and p-toluidine as suspected human carcinogens.

Toluenediamines. Among the six isomers of toluenediamine the one most frequently encountered is the 2,4- which accounts for 80% of the intermediate product in the manufacture of toluene diisocyanate, a further 20% being the 2,6- isomer, which is one of the basic substances for the polyurethanes. Attention was drawn to this compound following the experimental discovery of a carcinogenic potential in laboratory animals. Data on humans are not available.

Xylidines. Results of animal experiments indicate that they are primarily liver toxins and act secondarily on the blood. However, other experiments have demonstrated that methaemoglobinaemia and Heinz body formation were readily induced in cats, though not in rabbits.

Azo Dyes

In general, azo dyes as a group represent a relatively low order of general toxicity. Many of them have an oral LD₅₀ of more than 1 g/kg when tested in rats and mice, and the rodents can be given lifetime laboratory diets containing more than 1 g of the test chemical per kg of diet. A few may cause contact dermatitis but usually with only mild manifestations; in practice, it is rather difficult to determine whether the dye per se or co-existing material is responsible for the observed skin lesion. In contrast, increasing attention has been focused on the carcinogenic potentials of the azo dyes. Although confirmative epidemiological observations are as yet rare, the data from long-term experiments have accumulated to show that some azo dyes are carcinogenic in laboratory animals. The main target organ under such experimental conditions is the liver, followed by the urinary bladder. The intestine is also involved in some cases. It is, however, very problematic to extrapolate these findings to humans.

Most of the carcinogenic azo dyes are not direct carcinogens, but pre-carcinogens. That is, they require conversion by in vivo metabolic activation through proximate carcinogens to be ultimate carcinogens. For example, methylaminoazobenzene first undergoes N-hydroxylation and N-demethylation at the amino group, and then sulphate conjugation takes place with the N-hydroxy derivative forming the ultimate carcinogen which is reactive with the nucleic acid.

It should be noted that benzidine-derived diazo dyes may be transformed to the highly carcinogenic chemical benzidine by the body’s normal metabolic processes. The body reduces two azo groups in vivo or by the activity of intestinal bacteria, to benizidine. Thus azo dyes should be handled with prudence.

Safety and Health Measures

The most important specific measure for the prevention of spillage or contamination of the work atmosphere by these compounds is proper plant design. Ventilation control of the contaminant should be designed as close to the point of generation as possible. Work clothing should be changed daily and facilities for an obligatory bath or shower at the end of the working period should be provided. Any contamination of skin or clothing should be washed off immediately and the individual kept under medical supervision. Both workers and supervisors should be educated to be aware of the nature and extent of the hazard and to carry out the work in a clean, safe manner. Maintenance work should be preceded with sufficient attention to removal of possible sources of contact with the offending chemicals.

Aromatic amino compounds tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Wednesday, 03 August 2011 00:15

Amines, Aliphatic

Aliphatic amine compounds are formed when one or more hydrogen atoms in ammonia (NH₃) are replaced by one, two or three alkyl or alkanol radicals. The lower aliphatic amines are gases like ammonia and freely soluble in water, but the higher homologues are insoluble in water. All the aliphatic amines are basic in solution and form salts. The salts are odourless, non-volatile solids freely soluble in water.

According to the number of hydrogens substituted, the amines may be primary (NH₂R), secondary (NHR₂) or tertiary (NR₃).

Uses

Aliphatic amines are found in the chemical, pharmaceutical, rubber, plastics, dye-stuff, textile, cosmetics and metal industries. These chemicals are used as intermediates, solvents, rubber accelerators, catalysts, emulsifiers, synthetic cutting fluids, corrosion inhibitors and flotation agents. Several are used in the manufacture of herbicides, pesticides and dyes. In the photography industry, triethylamine and methylamine are used as accelerators for developers. Diethylamine is a corrosion inhibitor in the metal industries and a solvent in the petroleum industry. In the tanning and leather industries, hexamethylenetetramine is used as a tanning preservative; methylamine, ethanolamine and diisopropanolamine are softening agents for hides and leather.

2-Dimethylaminoethanol functions as a control agent for the acidity of boiler water treatment. Triethanolamine, isopropanolamime, cyclohexylamine and dicyclohexylamine are used in dry-cleaning soaps. Triethanolamine is used extensively in industry for the manufacture of surface-active agents, waxes, polishes, herbicides and cutting oils. It is also used to recover hydrogen sulphide from sour natural gas and sour crude petroleum. Ethanolamine extracts both carbon dioxide and hydrogen sulphide from natural gas.

Ethylamine acts as a stabilizer for rubber latex and as a dye intermediate, while butylamine is a pesticide and a strong alkaline liquid used in the rubber, pharmaceutical and dye-stuff industries. Ethylenediamine is another strongly alkaline liquid used in the preparation of dyes, rubber accelerators, fungicides, synthetic waxes, pharmaceuticals, resins, insecticides and asphalt wetting agents. Dimethylamine and isobutanolamine find use in the rubber industry as vulcanization accelerators. Dimethylamine is also used in the tanning industry and in the manufacture of detergent soaps.

Ethylenimine is an important compound found in the paper, textile, petroleum, lacquer and varnish, cosmetics and photography industries. Diethanolamine is a scrubbing agent for gases, a chemical intermediate, and an emulsifier in agricultural chemicals, cosmetics and pharmaceuticals. Other widely used emulsifying agents include isobutanolamine, isopropanolamine and cyclohexylamine.

Hazards

Since the amines are bases and may form strongly alkaline solutions, they can be damaging if splashed in the eye or if allowed to contaminate the skin. Otherwise they have no specific toxic properties, and the lower aliphatic amines are normal constituents of body tissues, so that they occur in a large number of foods, particularly fish, to which they impart a characteristic odour. One area of concern at present is the possibility that some aliphatic amines may react with nitrate or nitrite in vivo to form nitroso compounds, many of which are known to be potent carcinogens in animals, as is discussed more fully in the accompanying box.

Allylamine. The vapour is intensely irritating. In animals there is evidence of effects on the heart and circulatory system. Myocardial and vascular legions have been observed. Some of allylamine’s toxicity has been attributed to the formation of acrolein in vivo. There is also a definite risk of explosion over a wide range of concentrations in air.

Butylamine is the most important isomer commercially. Its vapour has been observed to have severe effects on the central nervous system (CNS) of animals exposed to it. It has intense effects on humans. It is extremely irritating to the eyes and respiratory tract. It also affects the CNS and can cause depression and even unconsciousness. Chest pains and severe coughing have also been reported. Butylamine is readily absorbed through the skin. Any absorbed butylamine is readily metabolized.

A main toxic effect of cyclohexylamine is to act as an irritant. It may damage and sensitize the skin. Cyclohexylamine is also a weak methaemoglobin inducer. This amine is also a principal metabolite of cyclamate.

Diethanolamine is irritating to the skin and mucous membranes. Exposure can lead to nausea and vomiting.

Dimethylamine vapours are both flammable and irritating. The solutions which it forms are strongly alkaline.

Ethanolamine may be weakly irritating but is not associated with major toxic effects on humans.

Ethylamine can cause eye irritation. Corneal damage may occur in those exposed to the vapour. The compound is excreted unchanged by humans.

Ethylenediamine damages the eyes, skin and respiratory tract. Sensitization may follow vapour exposure.

Methylamine a stronger base than ammonia, and the vapour is irritating to the eyes and respiratory tract. Cases of sensitization (bronchial) have been reported. The warning properties of this chemical are not good, since olfactory fatigue can set in.

Propylamine vapour may be injurious to the eyes and respiratory tract. Transitory visual disturbances have been reported.

Triethanolamine is of low human toxicity and is commonly added to many cosmetics and similar products.

Aliphatic amines tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Case box!!

Published in 104. Guide to Chemicals

Wednesday, 03 August 2011 00:11

Amides

The amides are a class of organic compounds which can be regarded as having been derived from either acids or amines. For example, the simple aliphatic amide acetamide (CH₃–CO–NH₂) is related to acetic acid in the sense that the –OH group of acetic acid is replaced by an –NH₂ group. Conversely, acetamide can be regarded as being derived from ammonia by replacement of one ammonia hydrogen by an acyl group. Amides can be derived not only from aliphatic or aromatic carboxylic acids but also from other types of acids—for example, sulphur- and phosphorus-containing acids.

The term substituted amides may be used to describe those amides having one or both hydrogens on the nitrogen replaced by other groups—for example, N,N-dimethylacetamide. This compound could also be regarded as an amine, acetyl dimethyl amine.

Amides are generally quite neutral in reaction compared with the acid or amine from which they are derived, and they are occasionally somewhat resistant to hydrolysis. The simple amides of aliphatic carboxylic acids (except formamide) are solids at room temperature, while the substituted aliphatic carboxylic acid amides may be liquids with relatively high boiling points. The amides of aromatic carboxylic or sulphonic acids are usually solids. A wide variety of methods are available for the synthesis of amides.

Uses

The unsubstituted aliphatic carboxylic acid amides have wide use as intermediates, stabilizers, release agents for plastics, films, surfactants and soldering fluxes. The substituted amides such as dimethylformamide and dimethylacetamide have powerful solvent properties.

Dimethylformamide is primarily used as a solvent in organic synthesis. It is also used in the preparation of synthetic fibres. It is a selective medium for the extraction of aromatics from crude oil and a solvent for dyes. Both dimethylformamide and dimethylacetamide are ingredients in paint removers. Dimethylacetamide is also used as a solvent for plastics, resins and gums, and in many organic reactions.

Acetamide is used for denaturing alcohol and as a solvent for many organic compounds, as a plasticizer, and an additive in paper. It is also found in lacquers, explosives and soldering flux. Formamide is a softener for paper and glues, and a solvent in the the plastics and pharmaceutical industries.

Some unsaturated aliphatic amides, such as acrylamide, are reactive monomers used in polymer synthesis. Acrylamide is also used in the synthesis of dyes, adhesives, paper and textile sizing, permanent press fabrics, and sewage and waste treatment. It is utilized in the metal industry for ore processing, and in civil engineering for the construction of dam foundations and tunnels. The polyacrylamides find extensive use as flocculants in water and sewage treatment, and as strengthening agents during paper manufacture in the paper and pulp industry. Aromatic amide compounds form important dye and medicinal intermediates. Some have insect repellent properties.

Hazards

The wide variety of possible chemical structures of amides is reflected in the diversity of their biological effects. Some appear entirely innocuous—for example, the longer-chain simple fatty acid amides such as stearic or oleic acid amides. On the other hand, several of the members of this family are classified as Group 2A (probable human carcinogens) or Group 2B (possible human carcinogens) by the International Agency for Research on Cancer (IARC). Neurologic effects have been noted in humans and experimental animals with acrylamide. Dimethylformamide and dimethylacetamide have produced liver injury in animals, and formamide and monomethylformamide have been shown experimentally to be teratogens.

Although a considerable amount of information is available on the metabolism of various amides, the nature of their toxic effects has not yet been explained on a molecular or cellular basis. Many simple amides are probably hydrolyzed by non-specific amidases in the liver and the acid produced excreted or metabolized by normal mechanisms.

Some aromatic amides—for example, N-phenylacetamide (acetanilide)—are hydroxylated on the aromatic ring and then conjugated and excreted. The ability of a number of amides to penetrate the intact skin is especially important in considering safety precautions.

Neurological effects

Acrylamide was initially made in Germany in 1893. Practical use of this compound had to wait until the early 1950s, when commercial manufacturing processes became available. This development occurred primarily in the United States. By the mid-1950s it was recognized that workers exposed to acrylamide developed characteristic neurologic changes primarily characterized by both postural and motor difficulties. Reported findings included tingling of the fingers, tenderness to touch, coldness of the extremities, excessive sweating of the hands and feet, a characteristic bluish-red discolouration of the skin of the extremities, and a tendency toward peeling of the skin of the fingers and hands. These symptoms were accompanied by weakness of the hands and feet which led to difficulty in walking, climbing stairs and so on. Recovery generally occurs with cessation of exposure. The time for recovery varies from a few weeks to as long as 1 year.

Neurologic examination of individuals suffering from acrylamide intoxication shows a rather typical peripheral neuropathy with weakness or absence of tendon reflexes, a positive Romberg test, a loss of position sense, a diminution or loss of vibration sense, ataxia, and atrophy of the muscles of the extremities.

Following recognition of the symptom complex associated with acrylamide exposure, animal studies were carried out in an attempt to document these changes. It was found that a variety of animal species including rat, cat and baboon were capable of developing peripheral neuropathy with disturbance of gait, disturbance of balance and a loss of position sense. Histopathologic examination revealed a degeneration of the axons and myelin sheaths. The nerves with the largest and longest axons were most commonly involved. There did not appear to be involvement of the nerve cell bodies.

Several theories have been advanced as to why these changes occur. One of these has to do with possible interference with the metabolism of the nerve cell body itself. Another theory postulates interference with the intracellular transport system of the nerve cell. An explanation is that there is a local toxic effect on the entire axon, which is felt to be more vulnerable to the action of acrylamide than is the cell body. Studies of the changes taking place within the axons and myelin sheaths have resulted in a description of the process as a drying back phenomenon. This term is used to describe more accurately the progression of changes observed in the peripheral nerves.

While the described symptoms and signs of the characteristic peripheral neuropathy associated with acrylamide exposure are widely recognized from exposure in industry and from animal studies, it appears in humans that, when acrylamide has been ingested as a contaminant in drinking water, the symptoms and signs are of involvement of the central nervous system. In these instances drowsiness, disturbance of balance, and mental changes characterized by confusion, memory loss and hallucinations were paramount. Peripheral neurological changes did not appear until later.

Skin penetration has been demonstrated in rabbits, and this may have been a principal route of absorption in those cases reported from industrial exposures to acrylamide monomer. It is felt that the hazard from inhalation would be primarily from exposure to aerosolized material.

Hepatotoxic effects

The good solvent action of dimethylformamide results in drying and defatting of the skin on contact, with resultant itching and scaling. Some complaints of eye irritation have resulted from vapour exposure in industry. Complaints by exposed workers have included nausea, vomiting and anorexia. Intolerance to alcoholic beverages after exposure to dimethylformamide has been reported.

Animal studies with dimethylformamide have shown experimental evidence of liver and kidney damage in rats, rabbits and cats. These effects have been seen from both intraperitoneal administration and inhalation studies. Dogs exposed to high concentrations of the vapour exhibited polycythemia, decrease of the pulse rate, and a decline in systolic pressure, and showed histologic evidence of degenerative changes in the myocardium.

In humans this compound is capable of being readily absorbed through the skin, and repeated exposures can lead to cumulative effects. In addition, like dimethylacetamide, it may facilitate the percutaneous absorption of substances dissolved in it.

It should be mentioned that dimethylformamide will readily penetrate both natural and neoprene rubber gloves, so that prolonged use of such gloves is inadvisable. Polyethylene provides better protection; however, any gloves used with this solvent should be washed after each contact and discarded frequently.

Dimethylacetamide has been studied in animals and has been shown to exhibit its principal toxic action in the liver on repeated or continued excessive exposure. Skin contact may cause the absorption of dangerous quantities of the compound.

Carcinogenesis

Acetamide and thioacetamide are prepared by heating ammonium acetate and aluminium sulphide, and are used in the laboratory as analytical reagents. Both compounds have been shown to produce hepatomas in rats on prolonged dietary feeding. Thioacetamide is more potent in this respect, is carcinogenic also to mice, and can also induce bile duct tumours in rats. While human data on these chemicals are not available, the extent of the experimental animal data is such that both of these substances are now considered possible human carcinogens. (Thioacetamide can also be found in the article “Sulphur compounds, organic” in this chapter.) Dimethylformamide is also classified as a Group 2B possible human carcinogen by IARC.

Acrylamide is classified as a probable human carcinogen (Group 2A) by IARC. This decision is supported by the results of bioassays in mice by several routes and yielding multiple sites of cancer, by data on genotoxicity, and by acrylamide’s ability to form adducts. The chemical structure of acrylamides also supports the probability that the chemical is a human carcinogen.

Safety and Health Measures

The potential toxic properties of any amide should be carefully considered before use or exposure commences. Owing to the general tendency of amides (especially those of lower molecular weight) to be absorbed percutaneously, skin contact should be prevented. Inhalation of dusts or vapours should be controlled. It is desirable that persons with exposure to amides be under regular medical observation with particular reference to the functioning of the nervous system and liver. The possible or probable cancer status of some these chemicals dictates that extremely prudent working conditions are needed.

Amides tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3- Physical and chemical hazards.

Published in 104. Guide to Chemicals

Wednesday, 03 August 2011 00:05

Alkaline Materials

This article discusses ammonia, sodium, potassium, calcium and lithium, and their compounds. With the exception of ammonia, these are the most common alkali and alkaline earth metals.

Uses

Ammonia is an important source of various nitrogen-containing compounds. An enormous quantity of ammonia is used in the production of ammonium sulphate and ammonium nitrate, which are used as fertilizers. Ammonia is further used for oxidation into nitric acid, for the production of synthetic urea and soda, and for the preparation of water solutions used in chemical and pharmaceutical industries. It is employed in the explosives industry, in medicine and in agriculture. In refrigeration, ammonia is used to lower temperatures below the freezing point and for the manufacture of synthetic ice.

Ammonium hydroxide is employed in the textile, rubber, pharmaceutical, ceramics, photography, detergent and food industries. It is also used in extracting such metals as copper, nickel and molybdenum from their ores. Ammonium hydroxide is useful for removing stains and bleaching. It is a household cleansing agent as well as a solvent for casein in the pulp and paper industry. Diammonium phosphate is used for fireproofing textiles, paper and wood products. It is found in fertilizers and in flux for soldering metals. Ammonium chloride is used in flux for coating sheet iron with zinc, in safety explosives, medicine, and in cement for iron pipes. In addition, it is utilized in tinning, dyeing, electroplating and tanning.

Calcium is the fifth most abundant element and the third most abundant metal; it is widespread in nature as calcium carbonate (limestone and marble), calcium sulphate (gypsum), calcium fluoride (fluorspar) and calcium phosphate (apatite). Calcium minerals are quarried or mined; the metallic calcium is obtained by the electrolysis of molten calcium chloride or fluoride. Metallic calcium is used in the production of uranium and thorium and in the electronics industry. It serves as a deoxidizer for copper, beryllium and steel, and as a hardener for lead bearings. In addition, calcium is an industrial catalyst for polyester fibres.

Calcium chloride is obtained as a waste product in the Solvay ammonia-soda process. It is used as a pavement de-icer, a refrigerant, and as a drying agent in air-conditioning systems. Calcium chloride is utilized in the production of barium chloride, metallic calcium and various dyes. It is also used to prevent dust formation during road construction, to accelerate concrete curing times, and to inhibit spontaneous combustion of coal in coal mines. Calcium nitrate is used in agriculture as a fertilizer and in match manufacture as an oxidizing agent. It is also found in the explosives and pyrotechnics industries. Calcium sulphite is used as a reducing agent in the production of cellulose. Calcium carbide is used for the industrial production of acetylene and in the manufacture of calcium cyanamide. It is employed in the pyrotechnics industry and in acetylene generators for acetylene lamps. Calcium carbide is also used for oxyacetylene welding and cutting.

Lime is a general term for the products of calcined limestone—for example, calcium oxide and calcium hydroxide. Calcium oxide is used as a refractory material, as a flux in steelmaking, a binding agent in the building industry and as the raw material for chlorinated lime bleaching powder. It is employed in the pulp and paper, sugar refining, agriculture and leather tanning industries. Calcium hydroxide is used in building and civil engineering for mortars, plasters and cements. It is used for soil treatment, dehairing hides and fireproofing. Calcium hydroxide also finds use in lubricants and in the pulp and paper industry.

Lithium is used as a “getter” in vacuum tubes, a constituent of solder and brazing alloys, a coolant or heat exchanger in reactors, and as a catalyst in the manufacture of synthetic rubber and lubricants. It finds use in the manufacture of catalysts for polyolefin plastics and in the metal and ceramics industries. Lithium is also used in special glasses and in fuels for aircraft and missiles. Lithium chloride is used in the manufacture of mineral waters and for soldering aluminium. It is employed in the pyrotechnics industry and in medicine as an antidepressant. Lithium carbonate is utilized in the production of glazes on ceramic and electrical porcelain and for the coating of arc-welding electrodes. It is found in luminescent paints, varnishes and dyes. Lithium carbonate is also used in medicine as a mood-stabilizing drug and antidepressant. Lithium hydride is a source of hydrogen and a nuclear shielding material.

Potassium is used in the synthesis of inorganic potassium compounds. It is found in agriculture as a component of fertilizers. Potassium is also employed in sodium-potassium alloy for heat transfer in nuclear reactor systems and in high-reading thermometers.

Potassium hydroxide is used for the manufacture of liquid soap, for absorbing carbon dioxide, mercerizing cotton, and for the production of other potassium compounds. It finds use in electroplating, in lithography and as a mordant for wood. Potassium hydroxide is also used in paint and varnish removers and in printing inks.

Other potassium compounds include potassium bromate, potassium chlorate, potassium nitrate, potassium perchlorate and potassium permanganate. They are used in the pyrotechnics, food and explosives industries, and they serve as oxidizing agents. Potassium chlorate is a component of match tips, a bleaching agent and a dyeing agent for furs, cotton and wool. It is also used in the dye-stuffs and pulp and paper industries. Potassium chlorate is used in the manufacture of explosives, matches, pyrotechnics and dyes.

Potassium bromate is a dough conditioner, a food additive, an oxidizing agent and a permanent wave compound. Potassium nitrate is used in fireworks, fluxes, gunpowder and in the glass, match, tobacco and ceramics industries. It is also used for pickling meats and for impregnating candle wicks. Potassium nitrate acts as a fertilizer in agriculture and as an oxidizer in solid rocket propellants. Potassium perchlorate is used in the explosives, pyrotechnics and photography industries. It serves as an inflating agent in automobile safety air bags. Potassium permanganate is used as an oxidizing agent, a disinfectant and a bleaching agent in the leather, metal and textile industries. It is also employed in metal cleaning, separation and purification in mining. In addition, potassium permanganate is a tanning agent in the leather industry.

Sodium is used in the manufacture of sodium compounds and in organic syntheses. It serves as a reducing agent for metals and as a coolant in nuclear reactors. Sodium is also found in sodium lamps and in electric power cable. Sodium chlorate is an oxidizing agent in the dye-stuffs industry and an oxidizing and bleaching agent in the pulp and paper industry. It is used for dyeing and printing fabrics, tanning and finishing leather, and uranium processing. It is also employed as an herbicide and a rocket fuel oxidant. Sodium chlorate finds additional uses in the explosives, match and pharmaceutical industries.

Sodium hydroxide is used in the rayon, mercerized cotton, soap, paper, explosives, dye-stuffs and chemical industries. It is also used in metal cleaning, electrolytic extraction of zinc, tin plating, laundering and bleaching. Trisodium phosphate finds use in photographic developers, in detergent mixtures and in the paper industry. It it used for clarifying sugar, removing boiler scale, softening water, laundering, and for tanning leather. Trisodium phosphate is also a water-treatment agent and an emulsifier in processed cheese. Disodium phosphate is used in fertilizers, pharmaceuticals, ceramics and detergents. It is used for weighting silk, dyeing and printing in the textile industry, and for fireproofing wood and paper. Disodium phosphate is also a food additive and a tanning agent. Sodium hypochlorite is a household and laundry bleaching agent, and a bleaching agent in the paper, pulp and textile industries. It is employed as a disinfectant for glass, ceramics and water as well as a sanitizer in swimming pools. Sodium chloride is used for metalworking, curing hides, highway de-icing, and preserving food. It also finds use in the photography, chemical, ceramic and soap industries, and in nuclear reactors.

The salts of carbonic acid (H₂CO₃), or carbonates, are widespread in nature as minerals. They are used in the construction, glass, ceramics, agriculture and chemical industries. Ammonium bicarbonate is used in the plastics, ceramics, dye-stuffs and textile industries. It finds use as a blowing agent for foam rubber and as a leavening agent in the production of baked goods. Ammonium bicarbonate is also used in fertilizers and in fire extinguishers. Calcium carbonate is used primarily as a pigment and is employed in the paint, rubber, plastics, paper, cosmetics, match and pencil industries. Calcium carbonate also finds use in the manufacture of Portland cement, foods, polishes, ceramics, inks and insecticides. Sodium carbonate is widely used in the manufacture of glass, caustic soda, sodium bicarbonate, aluminium, detergents, salts and paints. It is utilized for the desulphurization of pig iron and for the purification of petroleum. Sodium bicarbonate is used in the confectionery, pharmaceutical, non-alcoholic beverage, leather and rubber industries, and for the manufacture of fire extinguishers and mineral waters. Potassium carbonate is widely used in potash fertilizers and in the textile industry for dyeing wool. It also finds use in the glass, soap and pharmaceutical industries.

Alkalis

Alkalis are caustic substances which dissolve in water to form a solution with a pH substantially higher than 7. These include ammonia; ammonium hydroxide; calcium hydroxide and oxide; potassium; potassium hydroxide and carbonate; sodium; sodium carbonate, hydroxide, peroxide and silicates; and trisodium phosphate.

Health hazards

In general, the alkalis, whether in solid form or concentrated liquid solution, are more destructive to tissues than most acids. The free caustic dusts, mists and sprays may cause irritation of the eyes and respiratory tract, and lesions of the nasal septum. Strong alkalis combine with tissue to form albuminates, and with natural fats to form soaps. They gelatinize tissue to form soluble compounds which may result in deep and painful destruction. Potassium and sodium hydroxide are the most active materials in this group. Even dilute solutions of the stronger alkalis tend to soften the epidermis and emulsify or dissolve the skin fats. First exposures to atmospheres slightly contaminated with alkalis may be irritating, but this irritation soon becomes less noticeable. Workers often work in such atmospheres without showing any effect, while this exposure will cause coughing and painful throat and nasal irritation in unaccustomed persons. The greatest hazard associated with these materials is the splashing or splattering of particles or solutions of the stronger alkalis into the eyes.

Potassium hydroxide and sodium hydroxide. These compounds are very dangerous to the eyes, both in liquid and solid form. As strong alkalis, they destroy tissues and cause severe chemical burns. Inhalation of dusts or mists of these materials can cause serious injury to the entire respiratory tract, and ingestion can severely injure the digestive system. Even though they are not flammable and will not support combustion, much heat is evolved when the solid material is dissolved in water. Therefore, cold water must be used for this purpose; otherwise the solution may boil and splatter corrosive liquid over a wide area.

Carbonates and bicarbonates. The principal carbonates are: calcium carbonate (CaCO₃), magnesite (MgCO₃), soda ash (NaCO₃), sodium bicarbonate (NaHCO₃) and potash (K₂CO₃). The normal carbonates (with the anion CO₃) and the acid or bicarbonates (with the anion HCO₃) are the most important compounds. All bicarbonates are water-soluble; of the normal carbonates only the salts of alkaline metals are soluble. Anhydrous carbonates decompose when being heated before reaching the melting point. Carbonate solutions give rise to alkaline reactions because of the considerable hydrolysis involved. The bicarbonates are converted to normal carbonates by heating:

2 NaHCO₃ = Na₂CO₃ + H₂O + CO₂

The normal carbonates are decomposed by strong acids (H₂SO₄, HCl) and set free CO₂.

The sodium carbonates occur in the following forms: soda ash—anhydrous sodium carbonate (Na₂CO₃); crystallized soda— sodium bicarbonate (NaHCO₃); and sodium carbonate decahydrate (Na₂CO₃·10 H₂O).

Alkaline carbonates may cause harmful irritation of the skin, the conjunctivae and the upper airways during various industrial operations (handling and storage, processing). Workers who load and unload bagged carbonates may present cherry-sized necrotic skin portions on their arms and shoulders. Rather deep ulcerated pitting is sometimes observed after the black-brown scabs have fallen off. Prolonged contact with soda solutions may cause eczema, dermatitis and ulceration.

Calcium and compounds. Calcium is a well-known essential constituent of the human body, and its metabolism, alone or in association with phosphorus, has been widely studied with special reference to the musculoskeletal system and cellular membranes. Several conditions may lead to calcium losses such as immobilization, gastrointestinal disturbances, low temperature, weightlessness in space flights and so on. The absorption of calcium from the work environment by inhalation of calcium compounds dust does not increase significantly the calcium daily intake from vegetables and other food (usually 0.5 g). On the other hand, metallic calcium has alkaline properties, and it reacts with moisture, causing eye and skin burns. Exposed to air it may present an explosion hazard.

Calcium carbide. Calcium carbide exerts a pronounced irritant effect due to the formation of calcium hydroxide upon reaction with moist air or sweat. Dry carbide in contact with skin may cause dermatitis. Contact with moist skin and mucous membranes leads to ulceration and scarring. Calcium carbide is particularly hazardous to the eyes. A peculiar type of melanoderma with strong hyperpigmentation and numerous telangiectases is often observed. Burns caused by hot calcium carbide are common. The tissues are generally damaged in depths of 1 to 5 mm; the burns evolve very slowly, are difficult to treat, and often require excision. Injured workers may resume work only after the burnt skin surface is completely scarred. Persons exposed to calcium carbide frequently suffer from cheilitis characterized by dryness, swelling and hyperaemia of the lips, intense desquamation, and deep radial fissures; erosive lesions with a tendency to suppuration can be observed in the mouth angles. Workers with a long professional history often suffer from nail lesions—that is, occupational onychia and paronychia. Eye lesions with pronounced hyperaemia of the lids and conjunctiva, often accompanied by mucopurulent secretions, are also observed. In heavy cases the sensitivity of the conjunctiva and cornea is strongly reduced. While the keratitis and keratoconjunctivitis evolve first without symptoms, they may later degenerate into corneal opacities.

In calcium carbide production, impurities may produce additional hazards. Calcium carbide contaminated with calcium phosphate or calcium arsenate may, when moistened, give off phosphine or arsine, both of which are extremely toxic. Calcium carbide itself, when exposed to damp air, gives off acetylene, which is a moderate anaesthetic and asphyxiant, and a considerable fire and explosion hazard.

Calcium chloride has a powerful irritant action on the skin and mucous membranes, and cases have been reported, amongst workers packing dry calcium chloride, of irritation accompanied by erythema and peeling of facial skin, lacrimation, eye discharge, burning sensation and pain in the nasal cavities, occasional nose bleeding and tickling in the throat. Cases of perforation of the nasal septum have also been reported.

Calcium nitrate has an irritating and cauterizing action on skin and mucous membranes. It is a powerful oxidizing agent and presents a dangerous fire and explosion hazard.

Calcium sulphite. Cases of occupational calcium sulphite poisoning do not appear to have been reported. Accidental ingestion of a few grams may produce repeated vomiting, violent diarrhoea, circulatory disorders and methaemoglobinaemia.

Ammonia

Ammonia is present in small amounts in the air, water, earth, and particularly in decomposing organic matter. It is the product of normal human, animal and plant metabolism. Muscular effort and excitement of the nervous system result in the formation of an increased amount of ammonia, an accumulation of which in the tissues would result in poisoning. Endogenous formation of ammonia increases also in the course of many diseases. Through vital processes it is combined and excreted from the organism, mainly via urine and sweat, in the form of ammonium sulphate and urea. Ammonia is also of primary importance in the nitrogen metabolism of plants.

Ammonia is lightly reactive, easily undergoing oxidation, substitution (of hydrogen atoms) and additional reactions. It burns in air or in hydrogen to form nitrogen. An example of substitution would be the formation of amides of alkaline and alkaline-earth metals. As a result of addition it forms ammoniates (e.g., CaCl₂·8NH₃, AgCl₃NH₃) and other compounds. When ammonia dissolves in water, it forms ammonium hydroxide (NH₄OH), which is a weak base and dissociates as follows:

NH₄OH → NH₄⁺ + OH^-

The radical NH₄⁺ does not exist in free form since it decomposes into ammonia and hydrogen when an attempt is made to isolate it.

Ammonia poisoning may occur in the production of ammonia and in the manufacture of nitric acid, ammonium nitrate and sulphate, liquid fertilizers (ammoniates), urea and soda, in refrigeration, synthetic ice factories, cotton printing mills, fibre dyeing, electroplating processes, organic synthesis, heat treatment of metals (nitriding), chemical laboratories, and in a number of other processes. It is formed and emitted into the air during the processing of guano, in the purification of refuse, in sugar refineries and tanneries, and it is present in unpurified acetylene.

Industrial poisoning is usually acute, while chronic poisoning, although possible, is less common. The irritant effect of ammonia is felt especially in the upper respiratory tract, and in large concentrations it affects the central nervous system, causing spasms. Irritation of the upper respiratory tract occurs at concentrations of above 100 mg/m³, while the maximum tolerable concentration in 1 hour is between 210 and 350 mg/m³. Splashes of ammonia water into the eyes are particularly dangerous. The rapid penetration of ammonia into the ocular tissue may result in perforation of the cornea and even in death of the eyeball. Particular health hazards exist in each section of an ammonia plant. In the sections where the gas is generated, converted (oxidation of CO to CO₂), compressed and purified, the main problem is the emission of carbon monoxide and hydrogen sulphide. Considerable quantities of ammonia may escape during its synthesis. Escaping ammonia in the atmosphere may reach explosive limits.

Chlorates and perchlorates

Chlorates and perchlorates are the salts of chloric acid (HClO₃) and perchloric acid (HClO₄ ). They are strong supporters of combustion, and their main hazard is associated with this property. The potassium and sodium salts are typical of the group and are those most commonly used in industry.

Fire and explosion hazards. Chlorates are powerful oxidizing agents, and the main dangers are those of fire and explosion. They are not themselves explosive but they form flammable or explosive mixtures with organic matter, sulphur, sulphides, powdered metals and ammonium compounds. Cloth, leather, wood and paper are extremely flammable when impregnated by these chlorates.

Perchlorates are also very strong oxidizing agents. Heavy metal salts of perchloric acid are explosive.

Health hazards. Chlorates are harmful if absorbed by ingestion or by inhalation of the dust, which can provoke sore throat, coughing, methaemoglobinaemia with bluish skin, dizziness and faintness, and anaemia. In case of large absorption of sodium chlorate an increased sodium content in the serum will be seen.

Perchlorates may enter the body either by inhalation as dust or by ingestion. They are irritant to skin, eyes and mucous membranes. They cause haemolytic anaemia with methaemoglobinaemia, Heinz bodies in the red cells, and liver and kidney injuries.

Alkaline materials tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Tuesday, 02 August 2011 23:58

Aldehydes and Ketals

Aldehydes are members of a class of organic chemical compounds represented by the general structural formula R–CHO. R may be hydrogen or a hydrocarbon radical—substituted or unsubstituted. The important reactions of aldehydes include oxidation (whereby carboxylic acids are formed), reduction (with the formation of alcohol), aldol condensation (when two molecules of an aldehyde react in the presence of a catalyst to produce a hydroxy aldehyde), and the Cannizzaro reaction (with the formation of an alcohol and the sodium salt of an acid). Ketals, or acetals, as they are also called, are diesters of aldehyde or ketone hydrates. They are produced by reactions of aldehydes with alcohols.

Uses

Because of their high chemical reactivity, aldehydes are important intermediates for the manufacture of resins, plasticizers, solvents and dyes. They are used in the textile, food, rubber, plastics, leather, chemical and health care industries. The aromatic aldehydes and the higher aliphatic aldehydes are used in the manufacture of perfumes and essences.

Acetaldehyde is primarily used to manufacture acetic acid, but it is also used in the manufacture of ethyl acetate, peracetic acid, pyridine derivatives, perfumes, dyes, plastics and synthetic rubber. Acetaldehyde is utilized for silvering mirrors, hardening gelatin fibers, and as an alcohol denaturant and a synthetic flavoring agent. Paraldehyde, a trimer of acetaldehyde, is used in the dyestuff and leather industries and as a hypnotic agent in medicine. Industrially it has been used as a solvent, rubber activator and antioxidant. Metaldehyde is used as a fuel in portable cooking stoves and for slug control in gardening. Glycidaldehyde has been used as a cross-linking agent for wool finishing, for oil tanning, and for fat liquoring of leather and surgical sutures. Propionaldehyde is utilized in the manufacture of polyvinyl and other plastics and in the synthesis of rubber chemicals. It also functions as a disinfectant and as a preservative. Acrolein is used as a starting material for the manufacture of many organic compounds, including plastics, perfumes, acrylates, textile finishes, synthetic fibres and pharmaceuticals. It has been used in military poison gas mixtures and as a liquid fuel, an aquatic herbicide and biocide, and a tissue-fixative in histology.

Formaldehyde has an extremely wide range of uses related to both its solvent and germicidal properties. It is used in plastics production (e.g., urea-formaldehyde, phenol-form-aldehyde, melamine-formaldehyde resins). It is also used in the photography industry, in dyeing, in the rubber, artificial silk and explosives industries, tanning, precious metal recovery and in sewage treatment. Formaldehyde is a powerful antiseptic, germicide, fungicide and preservative used to disinfect inanimate objects, improve fastness of dyes on fabrics, and preserve and coat rubber latex. It is also a chemical intermediate, an embalming agent and a fixative of histological specimens. Paraformaldehyde is the most common commercial polymer obtained from formaldehyde and consists of a mixture of products with different degrees of polymerization. It is used in fungicides, disinfectants, bactericides and in the manufacture of adhesives.

Butyraldehyde is used in organic synthesis, mainly in the manufacture of rubber accelerators, and as a synthetic flavoring agent in foods. Isobutyraldehyde is an intermediate for rubber antioxidants and accelerators. It is used in the synthesis of amino acids and in the manufacture of perfumes, flavorings, plasticizers and gasoline additives. Crotonaldehyde is used in the manufacture of n-butyl alcohol and crotonic acid and in the preparation of surface active agents, pesticides and chemotherapeutic agents. It is a solvent for polyvinyl chloride and acts as a shortstopper in vinyl chloride polymerization. Crotonaldehyde is used in the preparation of rubber accelerators, the purification of lubricating oils, leather tanning, and as a warning agent for fuel gases and for locating breaks and leaks in pipes.

Glutaraldehhyde is an important sterilizing agent effective against all microorganisms, including viruses and spores. It is used as a chemical disinfectant for cold sterilization of equipment and instruments in the health care industry and as a tanning agent in the leather industry. It is also a component of embalming fluid and a tissue fixative. p-Dioxane is a solvent in pulping of wood and as a wetting and dispersing agent in textile processing, dye-baths, stain and printing compositions. It is used in cleaning and detergent preparations, adhesives, cosmetics, fumigants, lacquers, paints, varnishes, and paint and varnish removers.

Ketals are used in industry as solvents, plasticizers, and intermediates. They are capable of hardening natural adhesives like glue or casein. Methylal is used in ointments, perfumes, special purpose fuel, and as a solvent for adhesives and coatings. Dichloroethyl formal is used as a solvent and as an intermediate for polysulphide synthetic rubber.

Safety Precautions

Many aldehydes are volatile, flammable liquids which, at normal room temperatures, form vapours in explosive concentrations. Fire and explosion precautions, as described elsewhere in this chapter, must be most rigorous in the case of the lower members of the aldehyde family, and safeguards with respect to irritant properties must also be most extensive for the lower members and for those with an unsaturated or substituted chain.

Contact with aldehydes should be minimized by attention to plant design and handling procedure. Spillages should be avoided where possible and, where they occur, adequate water and drainage facilities should be available. For those chemicals labelled as known or suspected carcinogens, routine precautions for carcinogens, described elsewhere in this chapter, must be applied. Many of these chemicals are potent eye irritants and approved chemical eye and face protection should be mandatory in the plant area. For maintenance work, plastic face shields should also be worn. Where conditions require, suitable protective clothing, aprons, hand protection and impervious foot protection should be provided. Water showers and eye irrigation systems should be available in the plant area and, as with all protective equipment, operators must be fully trained in their use and maintenance.

Health Hazards

Most of the aldehydes and ketals are capable of causing primary irritation of the skin, eyes and respiratory system—a tendency which is most pronounced in the lower members of a series, in members that are unsaturated in the aliphatic chain, and in the halogen-substituted members. The aldehydes can have an anaesthetic effect, but the irritant properties of some of them may force a worker to limit exposure prior to having sufficient exposure to suffer anaesthetic effects. The irritating effect on the mucous membranes may be related to the ciliostatic effect where the hairlike cilia that line the respiratory tract and provide essential clearance functions are disabled. The degree of toxicity varies greatly in this family. Some of the members of the aromatic aldehydes and certain aliphatic aldehydes are rapidly metabolized and are not associated with adverse effects and thus have been found to be safe for use in foods and as flavourings. However, other members of the family are known or suspected carcinogens and due caution must be exercised in all situations in which contact may be possible. Some are chemical mutagens and several are allergens. Other toxic effects include the ability to produce an hypnotic effect. More detailed data on specific family members are included in the text which follows and in the accompanying tables.

Acetaldehyde is a mucous membrane irritant and also has general narcotic action of the central nervous system. Low concentrations cause irritation of the eyes, nose and upper respiratory passages, as well as bronchial catarrh. Extended contact can damage the corneal epithelium. High concentrations cause headache, stupor, bronchitis and pulmonary oedema. Ingestion causes nausea, vomiting, diarrhoea, narcosis and respiratory failure; death may result from damage to kidneys and fatty degeneration of the liver and heart muscle. Acetaldehyde is produced in the blood as a metabolite of ethyl alcohol, and will give rise to facial flushing, palpitations and other disagreeable symptoms. This effect is enhanced by the drug disulphiram (Antabuse), and by exposure to the industrial chemicals cyanamide and dimethylformamide.

In addition to its acute effects, acetaldehyde is a Group 2B carcinogen, that is, it has been classified as possibly carcinogenic to humans and a carcinogen in animals by the International Agency for Research on Cancer (IARC). Acetaldehyde induces chromosomal aberrations and sister-chromatid exchange in a variety of test systems.

Repeated exposure to the vapours of acetaldehyde causes dermatitis and conjunctivitis. In chronic intoxication, the symptoms resemble those of chronic alcoholism, such as loss of weight, anaemia, delirium, hallucinations of sight and hearing, loss of intelligence and psychic disturbances.

Acrolein is a common atmospheric pollutant which is produced in the exhaust fumes of internal combustion engines, which contain many and varied aldehydes. Acrolein concentration is increased when diesel oil or fuel oil is used. In addition acrolein is found in tobacco smoke in considerable quantities, not only in the particulate phase of the smoke, but also, and even more, in the gaseous phase. Accompanied by other aldehydes (acetaldehyde, propionaldehyde, formaldehyde, etc.) it reaches such a concentration (50 to 150 ppm) that it seems to be among the most dangerous aldehydes in tobacco smoke. Thus acrolein represents a possible occupational and environmental hazard.

Acrolein is toxic and very irritating, and its high vapour pressure may result in the rapid formation of hazardous atmospheric concentrations. Vapours are capable of causing injury to the respiratory tract, and the eyes can be injured by both liquid and vapours. Skin contact may produce severe burns. Acrolein has excellent warning properties and severe irritation occurs at concentrations less than those expected to be acutely hazardous (its powerful lacrimatory effect in very low concentrations in the atmosphere (1 mg/m³) compels people to run away from the polluted place in search of protective devices). Consequently, exposure is most likely to result from leakage or spillage from pipes or vessels. Serious chronic effects, such as cancer, however, may not be completely avoided.

Inhalation presents the most serious hazard. It causes irritation of nose and throat, tightness of the chest and shortness of breath, nausea and vomiting. The bronchopulmonary effect is very severe; even if the victim recovers from acute exposure, there will be permanent radiological and functional damage. Animal experiments indicate that acrolein has a vesicant action, destroying respiratory tract mucous membranes to such an extent that respiratory function is fully inhibited within 2 to 8 days. Repeated skin contact may cause dermatitis, and skin sensitization has been observed.

The discovery of the mutagenic properties of acrolein is not recent. Rapaport pointed it out as long ago as 1948 in Drosophila. Research has been carried out to establish whether cancer of the lung, whose connection with the abuse of tobacco is unquestionable, can be traced to the presence of acrolein in the smoke, and whether certain forms of cancer of the digestive system that are found to have a link with the absorption of burnt cooking oil are due to the acrolein contained in the burnt oil. Recent studies have shown that acrolein is mutagenic for certain cells (Drosophila, Salmonella, algae such as Dunaliella bioculata) but not for others (yeasts such as Saccharomices cerevisiae). Where acrolein is mutagenic for a cell, ultrastructural changes can be identified in the nucleus which are reminiscent of those caused by x rays in algae. It also produces various effects on the synthesis of DNA by acting on certain enzymes.

Acrolein is very effective in inhibiting the activity of the cilia of the bronchial cells that help to keep the bronchial tree clear. This, added to its action favouring inflammation, implies a good probability that acrolein can cause chronic bronchial lesions.

Chloroacetaldehyde has very irritant properties not only with regard to mucous membranes (it is dangerous to the eyes even in the vapour phase and can cause irreversible damage), but also to the skin. It can cause burnlike injuries on contact at 40% solution, and an appreciable irritation at 0.1% solution on prolonged or repeated contact. Prevention should be based on the avoidance of any contact and the control of atmospheric concentration.

Chloral hydrate is mainly excreted in humans first as trichloroethanol and then, as time progresses, as trichloroacetic acid, which may reach up to half the dose in repeated exposure. On severe acute exposure chloral hydrate acts like a narcotic and impairs the respiratory centre.

Crotonaldehyde is a strongly irritant substance and a definite corneal burn hazard, resembling acrolein in toxicity. Some instances of sensitization in workers have been reported and some assays for mutagenicity have produced positive results.

In addition to the fact that p-dioxane is a dangerous fire hazard, it has also been classified by IARC as a Group 2B carcinogen, that is, an established animal carcinogen and possible human carcinogen. Inhalation studies in animals have demonstrated that p-dioxane vapour can cause narcosis, lung, liver and kidney damage, irritation of the mucous membrane, congestion and oedema of the lungs, behavioural changes and elevated blood counts. Large doses of p-dioxane administered in drinking water have led to the development of tumours in rats and guinea pigs. Animal experiments have also demonstrated that dioxane is rapidly absorbed through the skin producing signs of incoordination, narcosis, erythema as well as liver and kidney injury.

Experimental studies with humans have also shown eye, nose, and throat irritation at concentrations of 200 to 300 ppm. An odour threshold as low as 3 ppm has been reported, although another study resulted in an odour threshold of 170 ppm. Both animal and human studies have demonstrated that dioxane is metabolized to β-hydroxyethoxyacetic acid. An investigation in 1934 of the deaths of five men working in an artificial silk plant suggested that the signs and symptoms of dioxane poisoning included nausea and vomiting followed by diminished and finally absence of urine output. Necropsy findings included enlarged pale livers, swollen haemorrhagic kidneys and oedematous lungs and brains.

It should be noted that unlike many of the other aldehydes, the irritant warning properties of p-dioxane are considered poor.

Formaldehyde and its polymeric derivative paraformaldehyde. Formaldehyde polymerizes readily in both liquid and solid state to form the mixture of chemicals known as paraformaldehyde. This polymerization process is delayed by the presence of water and, consequently, commercial formaldehyde preparations (known as formalin or formol) are aqueous solutions containing 37 to 50% formaldehyde by weight; 10 to 15% methyl alcohol is also added to these aqueous solutions as a polymerization inhibitor. Formaldehyde is toxic by ingestion and inhalation and it may also cause skin lesions. It is metabolized into formic acid. The toxicity of polymerized formaldehyde is potentially similar to that of the monomer since heating produces depolymerization.

Exposure to formaldehyde is associated with both acute and chronic effects. Formaldehyde is a proven animal carcinogen and has been classed as a 1B probable human carcinogen by IARC. Consequently, when working with formaldehyde, appropriate precautions for carcinogens must be taken.

Exposure to low atmospheric concentrations of formaldehyde causes irritation, especially of the eyes and respiratory tract. Due to the solubility of formaldehyde in water, the irritant effect is limited to the initial section of the respiratory tract. A concentration of 2 to 3 ppm causes slight formication of the eyes, nose and pharynx; at 4 to 5 ppm, discomfort rapidly increases; 10 ppm is tolerated with difficulty even briefly; between 10 and 20 ppm, there is severe difficulty in breathing, burning of the eyes, nose and trachea, intense lacrimation and severe cough. Exposure to 50 to 100 ppm produces a feeling of restricted chest, headache, palpitations and, in extreme cases, death due to oedema or spasm of the glottis. Eye burns can also be produced.

Formaldehyde reacts readily with tissue proteins and promotes allergic reactions, including contact dermatitis, which has also arisen from contact with formaldehyde-treated clothing. Asthmatic symptoms may occur due to allergic sensitivity to formaldehyde, even at very low concentrations. Kidney injury may occur in excessive and repeated exposure. There have been reports of both inflammatory and allergic dermatitis, including nail dystrophy due to direct contact with solutions, solids or resins containing free formaldehyde. Inflammation follows even after short-term contact with large quantities of formaldehyde. Once sensitized, the allergic response may follow contact with only very small quantities.

Formaldehyde reacts with hydrogen chloride, and it was reported that such reaction in humid air could yield a non-negligible amount of bis(chloromethyl) ether, BCME, a dangerous carcinogen. Further investigations have shown that at ambient temperature and humidity, even at very high concentrations, formaldehyde and hydrogen chloride do not form bis-(chloromethyl) ether at the detection limit of 0.1 ppb. However, the US National Institute for Occupational Safety and Health (NIOSH) has recommended that formaldehyde be treated as a potential occupational carcinogen because it has shown mutagenic activity in several test systems and has induced nasal cancer in rats and mice, particularly in the presence of hydrochloric acid vapours.

Glutaraldehyde is a relatively weak allergen which can cause allergic contact dermatitis and the combination of irritant and allergen properties are suggestive of the possibility of respiratory system allergies as well. It is a relatively strong irritant to the skin and the eyes.

Glycidaldehyde is a highly reactive chemical which has been classified by IARC as a group 2B possible human carcinogen and established animal carcinogen. Thus precautions appropriate for the handling of carcinogens must be exercised with this chemical.

Metaldehyde, if ingested, may cause nausea, severe vomiting, abdominal pain, muscular rigidity, convulsions, coma and death from respiratory failure. Ingestion of paraldehyde ordinarily induces sleep without depression of respiration, although deaths occasionally occur from respiratory and circulatory failure after high doses or more. Methylal can produce liver and kidney impairment and acts as a lung irritant on acute exposure.

Aldehydes and ketals tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Tuesday, 02 August 2011 23:53

Alcohols

Alcohols are a class of organic compounds formed from hydrocarbons by the substitution of one or more hydroxyl groups for an equal number of hydrogen atoms; the term is extended to various substitution products which are neutral in reaction and which contain one or more of the alcohol groups.

Uses

Alcohols are used as chemical intermediates and solvents in the textile, dye-stuff, chemical, detergent, perfume, food, beverage, cosmetics, and paint and varnish industries. Some compounds are also used in denaturing alcohol, cleaning products, quick-drying oils and inks, antifreeze, and as frothing agents in ore flotation.

n-Propanol is a solvent found in lacquers, cosmetics, dental lotions, printing inks, contact lenses and brake fluids. It is also an antiseptic, a synthetic flavouring agent for non-alcoholic beverages and food, a chemical intermediate and a disinfectant. Isopropanol is another important industrial solvent, which is used in antifreeze, quick-drying oils and inks, denaturing alcohol and perfumes. It is used as an antiseptic and a substitute for ethyl alcohol in cosmetics (i.e., skin lotions, hair tonics and rubbing alcohol), but cannot be used for pharmaceuticals taken internally. Isopropanol is an ingredient in liquid soaps, window cleaners, a synthetic flavouring additive for non-alcoholic beverages and food, and a chemical intermediate.

n-Butanol is employed as a solvent for paints, lacquers and varnishes, natural and synthetic resins, gums, vegetable oils, dyes and alkaloids. It is used as an intermediate in the manufacture of pharmaceuticals and chemicals, and employed in industries producing artificial leather, textiles, safety glass, rubber cement, shellac, raincoats, photographic films and perfumes. sec-Butanol is also used as a solvent and chemical intermediate, and is found in hydraulic brake fluids, industrial cleaning compounds, polishes, paint removers, ore-flotation agents, fruit essences, perfumes, dye-stuffs, and as a chemical intermediate.

Isobutanol, a solvent for surface coatings and adhesives, is employed in lacquers, paint strippers, perfumes, cleaners and hydraulic fluid. tert-Butanol is used for the removal of water from products, as a solvent in the manufacture of drugs, perfumes and flavours, and as a chemical intermediate. It is also a component of industrial cleaning compounds, a denaturant for ethanol, and an octane booster in gasoline. The amyl alcohols are frothing agents in ore flotation. Numerous alcohols, including methylamyl alcohol, 2-ethylbutanol, 2-ethylhexanol, cyclohexanol, 2-octanol and methylcyclohexanol, are used in the manufacture of lacquers. In addition to their numerous uses as solvents, cyclohexanol and methylcyclohexanol are useful in the textile industry. Cyclohexanol is employed in finishing textiles, leather processing, and as a homogenizer for soaps and synthetic detergent emulsions. Methylcyclohexanol is a component in soap-based spot removers and a blending agent for special textile soaps and detergents. Benzyl alcohol is used in the preparation of perfumes, pharmaceuticals, cosmetics, dye-stuffs, inks and benzyl esters. It also serves as a lacquer solvent, a plasticizer, and as a degreasing agent in rug cleaners. 2-Chloroethanol finds use as a cleaning agent and as a solvent for cellulose ethers.

Ethanol is the raw material for numerous products, including acetaldehyde, ethyl ether and chloroethane. It is an antifreeze agent, food additive and yeast growth medium, and it is used in the manufacture of surface coatings and gasohol. The production of butadiene from ethyl alcohol has been of great importance to the plastics and synthetic rubber industries. Ethyl alcohol is capable of dissolving a wide range of substances, and for this reason it is used as a solvent in the manufacture of drugs, plastics, lacquers, polishes, plasticizers, perfumes, cosmetics, rubber accelerators and so on.

Methanol is a solvent for inks, dyes, resins and adhesives, and is used in the manufacture of photographic film, plastics, textile soaps, wood stains, coated fabrics, unshatterable glass and waterproofing formulations. It is a starting material in the manufacture of many chemical products as well as an ingredient of paint and varnish removers, dewaxing preparations, embalming fluids and antifreeze mixtures.

Pentanol is used in the manufacture of lacquers, paints, varnishes, paint removers, rubber, plastics, explosives, hydraulic fluids, shoe cement, perfumes, chemicals, pharmaceuticals, and in the extraction of fats. Mixtures of the alcohols perform well for many of the solvent uses, but for chemical syntheses or more selective extractions, a pure product is often required.

Next to allyl chloride, allyl alcohol is the most important of the allyl compounds in industry. It is useful in the manufacture of pharmaceuticals and in general chemical syntheses, but the largest single use of allyl alcohol is in the production of various allyl esters, of which the most important are diallyl phthalate and diallyl isophthalate, which serve as monomers and repolymers.

Health Hazards

Methanol

Among the synthetic processes by which methyl alcohol is produced is the Fischer-Tropsch reaction between carbon monoxide and hydrogen, from which it is obtained as one of the by-products. It can also be produced by the direct oxidation of hydrocarbons and by a two-step hydrogenation process in which carbon monoxide is hydrogenated to methyl formate, which in turn is hydrogenated to methyl alcohol. The most important synthesis, however, is the modern, medium-pressure, catalytic hydrogenation of carbon monoxide or carbon dioxide at pressures of 100 to 600 kgf/cm² and temperatures of 250 to 400 °C.

Methyl alcohol has toxic properties under acute and chronic exposure. Injury has occurred amongst alcoholics from ingestion of the liquid, and to process workers from inhalation of the vapour. Animal experiments have established that methyl alcohol can penetrate the skin in sufficient quantity to cause fatal intoxication.

In cases of severe poisoning, most commonly following ingestion, methyl alcohol has a specific effect on the optic nerve, causing blindness as a result of optic nerve degeneration accompanied by degenerative changes of the ganglion cells of the retina and circulatory disturbances in the choroid. Amblyopia is commonly bilateral and may occur within a few hours of ingestion, whilst total blindness usually requires a week. The pupils are dilated, the sclera is congested, there is pallor of the optic disc with central scotoma; breathing and cardiovascular function are depressed; in fatal cases the patient is unconscious but coma may be preceded by delirium.

The consequences of industrial exposure to methyl alcohol vapour may vary considerably among individual workers. Under varying conditions of severity and duration of exposure, indications of intoxication include irritation of the mucous membranes, headache, ringing in the ears, vertigo, insomnia, nystagmus, dilated pupils, clouded vision, nausea, vomiting, colic and constipation. There may be skin injuries arising from the irritant and solvent action of methyl alcohol and from the harmful effects of stains and resins dissolved in it, and these are most likely to be located on the hands, wrists and forearms. In general, however, these harmful effects have been caused by prolonged exposures to concentrations very much in excess of limits recommended by authorities on methyl alcohol vapour poisoning.

Chronic combined exposure to methanol and carbon monoxide has been reported as a causative factor of cerebral atherosclerosis.

The poisonous action of methyl alcohol is attributed to its metabolic oxidation into formic acid or formaldehyde (which have a specific dangerous effect on the nervous system), and possibly to a severe acidosis. This oxidation process may be inhibited by ethyl alcohol.

Ethanol

The conventional industrial hazard is exposure to the vapour in the vicinity of a process in which ethyl alcohol is used. Prolonged exposure to concentrations above 5,000 ppm causes irritation of the eye and nose, headache, drowsiness, fatigue and narcosis. Ethyl alcohol is quite rapidly oxidized in the body to carbon dioxide and water. Unoxidized alcohol is excreted in the urine and expired in air, with the result that the cumulative effect is virtually negligible. Its effect on the skin is similar to that of all fat solvents and, in the absence of precautions, dermatitis may result from contact.

Recently another potential hazard in human exposure to synthetic ethanol was suspected because the product was found to be carcinogenic in mice treated at high doses. Subsequently, epidemiological analyses have revealed an excess incidence of laryngeal cancer (on average five times greater than expected) associated with a strong acid ethanol unit. Diethyl sulphate would appear to be the causative agent, although alkyl sultones and other potential carcinogens were also involved.

Ethyl alcohol is a flammable liquid, and its vapour forms flammable and explosive mixtures with air at normal temperature. An aqueous mixture containing 30% alcohol can produce a flammable mixture of vapour and air at 29 °C. One containing only 5% alcohol can produce a flammable mixture at 62 °C.

While ingestion is not a likely consequence of the use of industrial alcohol, it is a possibility in the case of an addict. The danger of such illicit consumption depends upon the concentration of ethanol, which above 70% is likely to produce oesophageal and gastric injuries, and upon the presence of denaturants. These are added to make the spirit unpalatable when it is obtained free of tax for non-potable purposes. Many of these denaturants (e.g., methyl alcohol, benzene, pyridine bases, methylisobutylketone and kerosene, acetone, gasoline, diethylphthalate and so on) are more harmful to a drinker than the ethyl alcohol itself. It is important therefore to ensure that there is no illicit drinking of the industrial spirit.

n-Propanol

Ill effects from the industrial usage of n-propanol have not been reported. In animals it is moderately toxic via inhalation, oral and dermal routes. It is an irritant of the mucous membranes and a depressant of the central nervous system. After inhalation, slight irritation of the respiratory tract and ataxia may occur. It is slightly more toxic than isopropyl alcohol, but it appears to produce the same biological effects. There is evidence of one fatal case after ingestion of 400 ml of n-propanol. The pathomorphological changes were mainly brain oedema and lung oedema, which have also been often observed in ethyl alcohol poisoning. n-Propanol is flammable and a moderate fire hazard.

Other compounds

Isopropanol in animals is slightly toxic via dermal and moderately toxic via oral and intraperitoneal routes. No case of industrial poisoning has been reported. An excess of sinus cancers and laryngeal cancers has been found among workers producing isopropyl alcohol. This could be due to the by-product, isopropyl oil. Clinical experience shows that isopropyl alcohol is more toxic than ethanol but less toxic than methanol. Isopropanol is metabolized to acetone, which can reach high concentrations in the body and is in turn metabolized and excreted by the kidneys and lungs. In humans, concentrations of 400 ppm produce mild irritation of the eyes, nose and throat.

The clinical course of isopropanol poisoning is similar to that of ethanol intoxication. The ingestion of up to 20 ml diluted with water has caused only a sensation of heat and slight lowering of the blood pressure. However, in two fatal cases of acute exposure, within a few hours after ingestion respiratory arrest and deep coma were observed and also hypotension, which is regarded as a bad prognostic sign, was also observed. Isopropanol is a flammable liquid and a dangerous fire hazard.

n-Butanol is potentially more toxic than any of its lower homologues, but the practical hazards associated with its industrial production and use at ordinary temperature are substantially reduced by its lower volatility. High vapour concentrations produce narcosis and death in animals. Exposure of human beings to the vapour may induce irritation of the mucous membranes. The reported levels at which irritation occurs are conflicting and vary between 50 and 200 ppm. Transient mild oedema of the conjunctiva of the eye and a slightly reduced erythrocyte count may occur above 200 ppm. Contact of the liquid with skin may result in irritation, dermatitis and absorption. It is slightly toxic when ingested. It is also a dangerous fire hazard.

The response of animals to sec-butanol vapours is similar to that to n-butanol, but it is more narcotic and lethal. It is a flammable liquid and a dangerous fire hazard.

At high concentrations the action of isobutanol vapour, like the other alcohols, is primarily narcotic. It is irritating to the human eye above 100 ppm. Contact of the liquid with the skin may result in erythema. It is slightly toxic when ingested. This liquid is flammable and a dangerous fire hazard.

Although tert-butanol vapour is more narcotic to mice than that of n- or isobutanol, few industrial ill effects have as yet been reported, other than occasional slight irritation of the skin. It is slightly toxic when ingested. In addition, it is flammable and a dangerous fire hazard.

Although headache and conjunctival irritation may result from prolonged exposure to cyclohexanol vapour, no serious industrial hazard exists. Irritation to the eyes, nose and throat of human subjects results at 100 ppm. Prolonged contact of the liquid with the skin results in irritation, and the liquid is slowly absorbed through the skin. It is slightly toxic when ingested. Cyclohexanol is excreted in the urine, conjugated with glucuronic acid. The liquid is flammable and a moderate fire hazard.

Headaches and irritation of the eye and upper respiratory tract may result from prolonged exposure to the vapour of methylcyclohexanol. Prolonged contact of the liquid with the skin results in irritation, and the liquid is slowly absorbed through the skin. It is slightly toxic when ingested. Methylcyclohexanol, conjugated with glucuronic acid, is excreted in urine. It is a moderate fire hazard.

Other than temporary headache, vertigo, nausea, diarrhoea and loss of weight during exposure to a high vapour concentration resulting from a mixture containing benzyl alcohol, benzene and ester solvents, no industrial illness is known from benzyl alcohol. It is slightly irritating to the skin and produces a mild lacrimating effect. The liquid is flammable and a moderate fire hazard.

Allyl alcohol is a flammable and irritant liquid. It causes irritation in contact with the skin, and absorption through the skin gives rise to deep pain in the region where absorption has occurred in addition to systemic injury. Severe burns may be caused by the liquid if it enters the eye. The vapour does not possess serious narcotic properties, but it has an irritant effect on the mucous membranes and the respiratory system when it is inhaled as an atmospheric contaminant. Its presence in a factory atmosphere has given rise to lacrimation, pain in the eye and blurred vision (necrosis of the cornea, haematuria and nephritis).

Amyl alcohols

Pentyl alcohols exist in several isomeric forms, and of the eight possible structural isomers, three also have optical active forms. Of the structural forms, four are primary alcohols—1-pentanol (amyl alcohol), 2-methyl-1-butanol, isopentyl alcohol (3-methyl-1-butanol, isoamyl alcohol) and neopentyl alcohol (2,2-dimethyl-1-propanol); three are secondary alcohols—2-pentanol, 3-pentanol and 3-methyl-2-butanol; and the final one is a tertiary alcohol—tert-pentyl alcohol (2-methyl-2-butanol).

Pentyl alcohol is irritating to the mucous membranes of the eyes, nose and throat at or somewhat above 100 ppm. Although it is absorbed by the gastrointestinal tract and the lungs, and through the skin, the incidence of industrial illness is quite low. Mucous membrane irritation occurs readily from the crude product because of the volatile extraneous materials present. The complaints from systemic illness include headache, dizziness, nausea, vomiting, diarrhoea, delirium and narcosis. Since pentyl alcohol is frequently used as the impure technical material and in conjunction with other solvents, distinctive symptoms and findings cannot be ascribed to the alcohol with any certainty. The ease with which the alcohols are metabolized is in the decreasing order of primary, secondary and tertiary; more tertiary is excreted unchanged than the others. Although toxicity varies with the chemical configuration, as a general estimation it can be said that a mixture of pentyl alcohols is about ten times as toxic as ethyl alcohol. This is reflected in the recommended exposure limits of the two alcohols—100 ppm and 1,000 ppm, respectively. The fire hazard from the amyl alcohols is not particularly great.

Alcohols tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Tuesday, 02 August 2011 23:48

Acids and Anhydrides, Organic

Organic acids and their derivatives cover a wide range of substances. They are used in nearly every type of chemical manufacture. Because of the variety in the chemical structure of the members of the organic acid group, several types of toxic effects may occur. These compounds have a primary irritant effect, the degree determined in part by acid dissociation and water solubility. Some may cause severe tissue damage similar to that seen with strong mineral acids. Sensitization may also occur, but is more common with the anhydrides than the acids.

For the purpose of this article, organic acids may be divided into saturated monocarboxylic and unsaturated monocarboxylic acids, aliphatic dicarboxylic acids, halogenated acetic acids, miscellaneous aliphatic monocarboxylic acids and aromatic carboxylic acids. Many carboxylic acids are of importance because of their use in food, beverages, drugs and a range of manufacturing processes. The following are among the most common: adipic acid, azelaic acid, fumaric acid, itaconic acid, maleic acid, malic acid, malonic acid, oxalic acid, pimelic acid, sebacic acid, succinic acid, tartaric acid and thiomalic acid.

The long-chain saturated monocarboxylic acids are the fatty acids and are in the main derived from natural sources. Synthetic fatty acids may also be manufactured by air oxidation of paraffins (aliphatic hydrocarbons) using metal catalysts. They are also produced by the oxidation of alcohols with caustic soda.

Uses

Organic acids are employed in the plastics, tanning, textile, paper, metal, pharmaceutical, food, beverage and cosmetics industries. Organic acids are also found in perfumes, herbicides, dyes, lubricants and cleaners.

Formic acid and acetic acid are the major industrial chemicals in the group of saturated monocarboxylic acids. Formic acid is primarily used in the textile and leather industries. It acts as a dye-exhausting agent for a number of natural and synthetic fibres and as a reducing agent in chrome dyeing. Formic acid is used as a deliming agent and a neutralizer in the leather industry, and as a coagulant for rubber latex. It also finds use in the manufacture of fumigants and insecticides. Acetic acid serves as a chemical intermediate, a deliming agent during leather tanning, a solvent, and an oil-well acidizer. In addition, it is an additive for various foods and glazes as well as a catalyst and a finishing agent in the dye-stuff and textile industries.

Weak concentrations of acetic acid (vinegar contains about 4 to 6%) are produced by aerobic fermentation (Acetobacter) of alcohol solutions. Acetic acid is one of the most widely used organic acids. It is employed in the production of cellulose acetate, vinyl acetate, inorganic acetates, organic acetates and acetic anhydride. Acetic acid itself is used in the dyeing industry, pharmaceutical industry, the canning and food preserving industry and pigment production.

Chloroacetic acid is used in the pharmaceutical, dye-stuffs and chemical industries as a chemical intermediate. Salicylic acid acts as another chemical intermediate used in the synthesis of aspirin and in the rubber and dye-stuffs industries. Benzoic acid, nonanoic acid, ascorbic acid and oleic acid (9-octadecenoic acid) are other useful compounds found in the food, beverage and pharmaceutical industries.

Palmitic acid and stearic acid have a wide application in soaps, cosmetics, detergents, lubricants, protective coatings and intermediate chemicals. Propionic acid is used in organic synthesis. It is also a mould inhibitor and a food preservative. Acrylic acid, methacrylic acid and crotonic acid are employed in the manufacture of resins and plasticizers in the paper, plastics and paint industries. In addition, acrylic acid is an ingredient in floor-polish formulations. Crotonic acid finds use in the manufacture of softening agents for synthetic rubber. Lactic acid, butyric acid and gallic acid are employed in the leather-tanning industry. Lactic acid is also used in adhesives, plastics and textiles. It serves as a food acidulant and as an agent in oil-well acidizing. Glycolic acid is used in the leather, textile, electroplating, adhesives and metal-cleaning industries.

The dicarboxylic acids (succinic acid, maleic acid, fumaric acid, adipic acid) and the tricarboxylic acid (citric acid) are useful in the food, beverage and pharmaceutical industries. Succinic acid is also used in the manufacture of lacquers and dyes. Maleic acid is used in the manufacture of synthetic resins and in organic syntheses. Maleic acid acts as a preservative for oils and fats; its salts are used in the dyeing of cotton, wool and silk. Fumaric acid is used in polyesters and alkyd resins, plastics surface coatings, food acidulants, inks and organic syntheses. The majority of adipic acid is utilized for nylon production, while smaller quantities are used in plasticizers, synthetic lubricants, polyurethanes and food acidulants.

Oxalic acid is a scouring agent in textile finishing, stripping and cleaning, and a component of household formulations for metal cleaning. It also finds use in the paper, photography and rubber industries. Oxalic acid is used in calico printing and dyeing, bleaching straw hats and leather, and cleaning wood. Aminoacetic acid is used as a buffering agent and in syntheses. Peracetic acid is used as a bleach, catalyst and oxidant.

Commercial naphthenic acid is usually a dark-coloured malodourous mixture of naphthenic acids. Naphthenic acids are derived from cycloparaffins in petroleum, probably by oxidation. Commercial acids are usually viscous liquid mixtures and may be separated as low- and high-boiling fractions. The molecular weights vary from 180 to 350. They are used principally in the preparation of paint dryers, where the metallic salts, such as lead, cobalt and manganese, act as oxidizing agents. Metallic naphthenic acids are used as catalysts in chemical processes. An industrial advantage is their solubility in oil.

Organic acid anhydrides

An anhydride is defined as an oxide which, when combined with water, gives an acid or a base. Acid anhydrides are derived from the removal of water from two molecules of the corresponding acid, such as:

2HMnO₄ → Mn₂O₇ + H₂O

Industrially, the most important anhydrides are acetic and phthalic. Acetic anhydride is used in the plastics, explosives, perfume, food, textile and pharmaceutical industries, and as a chemical intermediate. Phthalic anhydride serves as a plasticizer in vinyl chloride polymerization. It is also used for the production of saturated and unsaturated polyester resins, benzoic acid, pesticides, and certain essences and perfumes. Phthalic anhydride is employed in the production of phthalocyanine dyes and alkyd resins used in paints and lacquers. Maleic anhydride has a significant number of applications as well.

Propionic anhydride is used in the manufacture of perfumes, alkyd resins, drugs and dyes, while maleic anhydride, trimellitic anhydride and acetic anhydride find use in the plastics industry. Trimellitic anhyide (TMA) is also utilized in the dye-stuff, printing and automotove upholstery industries. It is used as a curing agent for epoxy and other resins, in vinyl plasticizers, paints, coatings, dyes, pigments and a wide variety of other manufactured products. Some of these products find applications in high-temperature plastics, wire insulation and gaskets.

Hazards

Monocarboxylic acids

The low-molecular-weight monocarboxylic acids are primary irritants and produce severe damage to tissues. Strict precautions are necessary in handling; suitable protective equipment should be available and any skin or eye splashes irrigated with copious amounts of water. The most important acids of this group are acetic acid and formic acid.

The long-chain saturated monocarboxylic acids (the fatty acids) are non-irritant and of a very low order of toxicity. They appear to pose few problems in industrial use.

Unsaturated monocarboxylic acids are highly reactive substances and are recognized as severe irritants of the skin, eye and respiratory tract in concentrated solution. Hazards appear to be related to acute rather than cumulative exposures.

The majority of these acids appear to present minimal hazard from low-level chronic exposure, and many are normally present in human metabolic processes. Primary irritant effects are present with a number of these acids, however, particularly in concentrated solutions or as dusts. Sensitization is rare. As the materials are all solids at room temperature, contact is usually in the form of dust or crystals.

Acetic acid. Acetic acid vapour may form explosive mixtures with air and constitute a fire hazard either directly or by the release of hydrogen. Glacial acetic acid or acetic acid in concentrated form are primary skin irritants and will produce erythema (reddening), chemical burns and blisters. In cases of accidental ingestion, severe ulceronecrotic lesions of the upper digestive tract have been observed with bloody vomiting, diarrhoea, shock and haemoglobinuria followed by urinary disorders (anuria and uraemia).

The vapours have an irritant action on exposed mucous membranes, particularly the conjunctivae, rhinopharynx and upper respiratory tract. Acute bronchopneumonia developed in a woman who was made to inhale acetic acid vapours following a fainting attack.

Workers exposed for a number of years to concentrations of up to 200 ppm have been found to suffer from palpebral oedema with hypertrophy of the lymph nodes, conjunctival hyperaemia, chronic pharyngitis, chronic catarrhal bronchitis and, in some cases, asthmatic bronchitis and traces of erosion on the vestibular surface of the teeth (incisors and canines).

The extent of acclimatization is remarkable; however, such acclimatization does not mean that toxic effects will not also occur. Following repeated exposure, for example, workers may complain of digestive disorders with pyrosis and constipation. The skin on the palms of the hands is subject to the greatest exposure and becomes dry, cracked and hyperkeratotic, and any small cuts and abrasions are slow to heal.

Formic acid. The principal hazard is that of severe primary damage to the skin, eye or mucosal surface. Sensitization is rare, but may occur in a person previously sensitized to formaldehyde. Accidental injury in humans is the same as for other relatively strong acids. No delayed or chronic effects have been noted. Formic acid is a flammable liquid, and its vapour forms flammable and explosive mixtures with air.

Propionic acid in solution has corrosive properties towards several metals. It is irritant to eye, respiratory system and skin. The same precautions recommended for exposure to formic acid are applicable, taking into account the lower flashpoint of propionic acid.

Maleic acid is a strong acid and produces marked irritation of the skin and mucous membranes. Severe effects, particularly in the eye, can result from concentrations as low as 5%. There are no reports of cumulative toxic effects in humans. The hazard in industry is of primary irritation of exposed surfaces, and this should be averted where necessary by the provision of appropriate personal protective equipment, generally in the form of impermeable gloves or gauntlets.

Fumaric acid is a relatively weak acid and has a low solubility in water. It is a normal metabolite and is less toxic orally than tartaric acid. It is a mild irritant of skin and mucous membranes, and no problems of industrial handling are known.

Adipic acid is non-irritant and of very low toxicity when ingested.

Halogenated acetic acids

The halogenated acetic acids are highly reactive. They include chloroacetic acid, dichloroacetic acid (DCA), trichloroacetic acid (TCA), bromoacetic acid, iodoacetic acid, fluoroacetic acid and trifluoroacetic acid (TFA).

The halogenated acetic acids cause severe damage to the skin and mucous membranes and, when ingested, may interfere with essential enzyme systems in the body. Strict precautions are necessary for their handling. They should be prepared and used in enclosed plant, the openings in which should be limited to the necessities of manipulation. Exhaust ventilation should be applied to the enclosure to ensure that fumes or dust do not escape through the limited openings. Personal protective equipment should be worn by persons engaged in the operations, and eye protective equipment and respiratory protective equipment should be available for use when necessary.

Fluoroacetic acid. Di- and trifluoroacetic acids have a lower level of toxicity than monofluoroacetic acid (fluoroacetic acid). Monofluoroacetic acid and its compounds are stable, highly toxic and insidious. At least four biological plants in South Africa and Australia owe their toxicity to this acid (Dichapetalum cymosum, Acacia georginae, Palicourea marcgravii), and recently more than 30 species of Gastrolobium and Oxylobrium in Western Australia have been found to contain various amounts of fluoroacetate.

The biological mechanism responsible for the symptoms of fluoroacetate poisoning involves the “lethal synthesis” of fluorocitric acid, which in turn blocks the tricarboxylic acid cycle by inhibiting the enzyme aconitase. The resultant deprivation of energy by stopping of the Krebs cycle is followed by cellular dysfunction and death. It is impossible to be specific about the toxic dose of fluoroacetic acid for humans; a likely range lies between 2 and 10 mg/kg; but several related fluoroacetates are even more toxic than this. A drop or two of the poison by inhalation, ingestion and absorption through skin cuts and abrasion or undamaged skin can be fatal.

From a study of hospital case histories, it is apparent that the major toxic effects of fluoroacetates in humans involve the central nervous system and cardiovascular system. Severe epileptiform convulsions alternate with coma and depression; death may result from asphyxia during a convulsion or from respiratory failure. The most prominent features, however, are cardiac irregularities, notably ventricular fibrillation and sudden cardiac arrest. These symptoms (which are indistinguishable from those frequently encountered clinically) are usually preceded by an initial latent period of up to 6 h characterized by nausea, vomiting, excessive salivation, numbness, tingling sensations, epigastric pain and mental apprehension; other signs and symptoms which may develop subsequently include muscular twitching, low blood pressure and blurred vision.

Chloroacetic acid. This material is a highly reactive chemical and should be handled with care. Gloves, goggles, rubber boots and impervious overalls are mandatory when workers are in contact with concentrated solutions.

Other acids

Glycolic acid is stronger than acetic acid and produces very severe chemical burns of the skin and eyes. No cumulative effects are known, and it is believed to be metabolized to glycine. Strict precautions are necessary for its handling. These are similar to those required for acetic acid. Concentrated solutions can cause burns of the skin and eye. No cumulative effects are known. Personal protective equipment should be worn by persons handling concentrated solutions of this acid.

Sorbic acid is used as a fungicide in foods. It is a primary irritant of the skin, and individuals may develop sensitivities to it. For these reasons contact with the skin should be avoided.

Salicylic acid is a strong irritant when in contact with skin or mucous membranes. Strict precautions are necessary for plant operatives.

Anhydrides

Acid anhydrides have higher boiling points than the corresponding acids. Their physiological effects generally resemble those of the corresponding acids, but they are more potent eye irritants in the vapour phase, and may produce chronic conjunctivitis. They are slowly hydrolyzed on contact with body tissues and may occasionally cause sensitization. Adequate ventilation should be provided and suitable personal protective equipment should be worn. In certain circumstances, particularly those associated with maintenance work, suitable eye protection equipment and respiratory protective equipment are necessary.

There have been reports of conjunctivitis, bloody nasal excreta, atrophy of the nasal mucosa, hoarseness, cough and bronchitis in workers employed in the production of phthalic acid and anhydride. It has been recognized that phthalic anhydride causes bronchial asthma, and skin sensitization has been reported following prolonged exposure to phthalic anhydride; the lesion is usually an allergic dermatitis. A specific IgE to phthalic anhydride has also been identified.

Phthalic anhydride is flammable and constitutes a moderate fire hazard. Its toxicity is comparatively low in relation to other industrial acid anhydrides, but it acts as a skin, eye and upper respiratory tract irritant. Since phthalic anhydride has no effect on dry skin, but burns wet skin, it is probable that the actual irritant is phthalic acid, which is formed on contact with water.

Phthalic anhydride must be stored in a cool, well-ventilated place away from open flames and oxidizing substances. Good local and general ventilation are required where it is handled. In many processes phthalic anhydride is used not as flakes but as a liquid. When so used, it is brought to the plant in tanks and directly pumped into the pipe system, preventing contact as well as contamination of the air with dust. This has led to the complete disappearance of manifestations of irritations among the workers in such plants. However, vapours liberated from liquid phthalic anhydride are as irritating as the flakes; care must, therefore, be taken to avoid any leakage from the pipe system. In case of spillage or contact with the skin, the latter should be washed immediately and repeatedly with water.

Workers who are handling phthalic derivatives must be under medical supervision. Special attention should be paid to asthma-like symptoms and skin sensitization. If any such symptoms are noticed, the worker should be moved to another job. Skin contact is to be avoided under all circumstances. Suitable clothing, such as rubber hand protection, is recommended. Pre-employment examinations are necessary to ensure that persons with bronchial asthma, eczema or other allergic diseases are not exposed to phthalic anhydride.

Acetic anhydride. When exposed to heat, acetic anhydride can emit toxic fumes, and its vapours can explode in the presence of flame. It can react violently with strong acids and oxidizers such as sulphuric acid, nitric acid, hydrochloric acid, permanganates, chromium trioxide and hydrogen peroxide, as well as with soda.

Acetic anhydride is a strong irritant and has corrosive properties on contact with eyes, usually with delayed action; contact is followed by lacrimation, photophobia, conjunctivitis and corneal oedema. Inhalation can cause nasopharyngeal and upper respiratory tract irritation, with burning sensations, cough and dyspnoea; prolonged exposure may lead to pulmonary oedema. Ingestion causes pain, nausea and vomiting. Dermatitis can result from prolonged skin exposure.

When contacts are possible, protective clothing and goggles are recommended and eyewash and shower facilities should be available. Chemical cartridge respirators are appropriate for protection against concentrations up to 250 ppm; supplied air respirators with a full eyepiece are recommended for concentrations of 1,000 ppm; self-contained breathing apparatus is necessary in case of fire.

Butyric anhydride is manufactured by catalytic hydrogenation of crotonic acid. Butyric anhydride and propionic anhydride present hazards similar to those of the acetic anhydride.

Maleic anhydride can produce severe eye and skin burns. These may be produced either by solution of maleic anhydride or by flakes of the material in the manufacturing process coming into contact with moist skin. Skin sensitization has occurred. Strict precautions should be taken to prevent contact of the solution with skin or eyes. Suitable goggles and other protective clothing must be worn by plant operatives; ready access to eye irrigation solution bottles is essential. When suspended in air in a finely divided condition, maleic anhydride is capable of forming explosive mixtures with the air. Condensers in which the sublimed material settles in the form of fine crystals should be situated in a safe position outside an occupied room.

Trimellitic anhydride has been reported to have caused pulmonary oedema in workers after severe acute exposure, and airways sensitization after exposure periods of weeks to years, with rhinitis and/or asthma. Several incidents involving the occupational effects of exposure to TMA have been reported. Multiple inhalation exposures to an epoxy resin containing TMA being sprayed on heated pipes was reported to have caused pulmonary oedema in two workers. Exposure levels were not reported but there was no report of upper respiratory tract irritation while the exposures were being experienced, indicating that a hypersensitive reaction might have been involved.

In another report, 14 workers involved in the synthesis of TMA were observed to have respiratory symptoms resulting from sensitization to TMA. In this study three separate responses were noted. The first, rhinitis and/or asthma, developed over an exposure duration of weeks to years. Once sensitized, exposed workers exhibited symptoms immediately after exposure to TMA, which ceased when the exposure was stopped. A second response, also involving sensitization, produced delayed symptoms (cough, wheezing and laboured breathing) 4 to 8 hours after exposure had ceased. The third syndrome was an irritant effect following initial high exposures.

One study of adverse health effects, which also involved measurements of air concentrations of TMA, was conducted by the US National Institute for Occupational Safety and Health (NIOSH). Thirteen workers involved in the manufacture of an epoxy paint had complaints of eye, skin, nose and throat irritation, shortness of breath, wheezing, coughing, heartburn, nausea and headache. Occupational airborne exposure levels averaged 1.5 mg/m³ TMA (range from “none detected” to 4.0 mg/m³) during processing operations and 2.8 mg/m³ TMA (range from “none detected” to 7.5 mg/m³) during decontamination procedures.

Experimental studies with rats have demonstrated intra-alveolar haemorrhage with subacute exposures to TMA at 0.08 mg/m³. The vapour pressure at 20 °C (4 × 10^-6 mm Hg) corresponds to a concentration slightly more than 0.04 mg/m³.

Oxalic acid and its derivatives. Oxalic acid is a strong acid which, in solid form or in concentrated solutions, can cause burns of the skin, eyes or mucous membranes; oxalic acid concentrations as low as 5 to 10% are irritating if exposure is prolonged. Human fatalities have been recorded following ingestion of as little as 5 g of oxalic acid. The symptoms appear rapidly and are marked by a shock-like state, collapse and convulsive seizures. Such cases may show marked renal damage with precipitation of calcium oxalate in the renal tubules. The convulsive seizures are thought to be the result of hypocalcaemia. Chronic skin exposure to solutions of oxalic acid or potassium oxalate have been reported to have caused a localized pain and cyanosis in the fingers or even gangrenous changes. This is apparently due to a localized absorption of the oxalic acid and a resultant arteritis. Chronic systemic injury from inhalation of oxalic acid dust appears to be very rare, although the literature describes the case of a man who had been exposed to hot oxalic acid vapours (probably containing an aerosol of oxalic acid) with generalized symptoms of weight loss and chronic inflammation of the upper respiratory tract. Because of the strongly acid nature of the dust of oxalic acid, exposure must be carefully controlled and work area concentrations held within acceptable health limits.

Diethyl oxalate is slightly soluble in water; miscible in all proportions in many organic solvents; a colourless, unstable, oily liquid. It is produced by esterification of ethyl alcohol and oxalic acid. It is used, as are other liquid oxalate esters, as a solvent for many natural and synthetic resins.

The symptoms in rats following ingestion of large quantities of diethyl oxalate are those of respiratory disturbances and muscle twitchings. Large quantities of oxalate deposits were found in the renal tubules of a rat after an oral dose of 400 mg/kg. It has been reported that workers exposed to 0.76 mg/l of diethyl oxalate over a period of several months developed complaints of weakness, headache and nausea together with some slight alterations in the blood count. Because of the very low vapour pressure of this substance at room temperature, the reported air concentrations may have been in error. There was also some use of diamyl acetate and diethyl carbonate in this operation.

Safety and Health Measures

All acids should be stored away from all sources of ignition and oxidizing substances. Storage areas should be well ventilated to prevent the accumulation of dangerous concentrations. Containers should be of stainless steel or glass. In the event of leakage or spillage, acetic acid should be neutralized by application of alkaline solutions. Eyewash fountains and emergency showers should be installed for dealing with cases of skin or eye contact. Marking and labelling of containers is essential; for all forms of transport, acetic acid is classified as a dangerous substance.

To prevent damage to the respiratory system and mucous membranes, the atmospheric concentration of organic acids and anhydrides with high vapour pressure should be kept below maximum permissible levels using standard industrial hygiene practices such as local exhaust ventilation and general ventilation, backed up by periodic determination of atmospheric acetic acid concentrations. Detection and analysis, in the absence of other acid vapours, is by means of bubbling in an alkaline solution and determination of residual alkali; in the presence of other acids, fractional distillation used to be necessary; however, a gas chromatographic method is now available for determination in air or water. Dust exposures should be minimized as well.

Persons working with the pure acid or concentrated solutions should wear protective clothing, eye and face protection, hand and arm protection and respiratory protective equipment. Adequate sanitary facilities should be provided and good personal hygiene encouraged.

Organic acids and anhydrides tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Tuesday, 02 August 2011 23:41

Acids, Inorganic

An inorganic acid is a compound of hydrogen and one or more other element (with the exception of carbon) that dissociates or breaks down to produce hydrogen ions when dissolved in water or other solvents. The resultant solution has certain characteristics such as the ability to neutralize bases, turn litmus paper red and produce specific colour changes with certain other indicators. Inorganic acids are often termed mineral acids. The anhydrous form may be gaseous or solid.

An inorganic anhydride is an oxide of metalloid which can combine with water to form an inorganic acid. It can be produced by synthesis such as: S + O₂ → SO₂, which can be transformed into an acid by the addition of a water molecule (hydration); or by eliminating water from an acid, such as:

2HMnO₄ → Mn₂O₇ + H₂O

Inorganic anhydrides share in general the biological properties of their acids, since hydration can readily occur in watery biological media.

Uses

Inorganic acids are used as chemical intermediates and catalysts in chemical reactions. They are found in a variety of industries, including metal- and woodworking, textile, dye-stuff, petroleum and photography. In metalworking they are often used as cleaning agents before welding, plating or painting. Sulphamic acid, sulphuric acid and hydrochloric acid are used in electroplating, and perchloric acid is used in metal plating.

Hydrochloric acid, sulphuric acid, perchloric acid and sulphamic acid are widely used in industry. Hydrochloric acid, or hydrogen chloride in aqueous solution, is used for industrial acidizing, for refining ores of tin and tantalum, for converting cornstarch to syrup, and removing scale from boilers and heat-exchange equipment. It is also a tanning agent in the leather industry. Sulphuric acid is used in parchment paper and in various processes including purification of petroleum, refining vegetable oil, carbonization of wool fabrics, extraction of uranium from pitchblende, and iron and steel pickling. Sulphuric acid and perchloric acid are used in the explosives industry. Sulphamic acid is a flame retardant in the wood and textile industries and a bleaching agent and bactericide in the pulp and paper industry. It is also used for chlorine stabilization in swimming pools.

Nitric acid is used in the manufacture of ammonium nitrate for fertilizer and explosives. In addition, it is used in organic synthesis, metallurgy, ore flotation, and for reprocessing spent nuclear fuel.

Hazards

The specific hazards of the industrially important inorganic acids will be found below; however, it should be noted that all these acids have certain dangerous properties in common. Solutions of inorganic acids are not flammable in themselves; however, when they come into contact with certain other chemical substances or combustible materials, a fire or explosion may result. These acids react with certain metals with the liberation of hydrogen, which is a highly flammable and explosive substance when mixed with air or oxygen. They may also act as oxidizing agents and, when in contact with organic or other oxidizable materials, may react destructively and violently.

Health effects. The inorganic acids are corrosive, especially in high concentrations; they will destroy body tissue and cause chemical burns when in contact with the skin and mucous membranes. In particular, the danger of eye accidents is pronounced. Inorganic acid vapours or mists are respiratory tract and mucous membrane irritants, although the degree of irritation depends to a large degree on the concentration; discolouration or erosion of the teeth may also occur in exposed workers. Repeated skin contact may lead to dermatitis. Accidental ingestion of concentrated inorganic acids will result in severe irritation of the throat and stomach, and destruction of the tissue of internal organs, perhaps with fatal outcome, when immediate remedial action is not taken. Certain inorganic acids may also act as systemic poisons.

Safety and Health Measures

Wherever possible, highly corrosive acids should be replaced by acids which present less hazard; it is essential to use only the minimum concentration necessary for the process. Wherever inorganic acids are used, appropriate measures should be instituted concerning storage, handling, waste disposal, ventilation, personal protection and first aid.

Storage. Avoid contact with other acids and combustible or oxidizable materials. Electrical installations should also be of the acid-resistant type.

Storage areas should be separated from other premises, well ventilated, sheltered from sunlight and sources of heat; they should have a cement floor and contain no substances with which an acid might react. Large stocks should be surrounded by kerbs or sills to retain the acid in the event of leakage, and provisions for neutralization should be made. A fire hydrant and a supply of self-contained respiratory protective equipment for emergency or rescue purposes should be provided outside the storage premises. Spillages should be dealt with immediately by hosing down; in the event of a large leakage, personnel should vacate the premises and then, having donned emergency equipment, return to neutralize the acid with water or calcined sand. Electrical equipment should be of the waterproof type and resistant to acid attack. Safety lighting is desirable.

Containers should be kept tightly closed and should be clearly labelled to indicate the contents. Decompression measures should be taken where necessary. Piping, couplings, gaskets and valves should all be made of material resistant to nitric acid. Glass or plastic containers should be adequately protected against impact; they should be kept off the floor to facilitate flushing in the event of leakage. Drums should be stored on cradles or racks and chocked in position. Gas cylinders of gaseous anhydrous acid should be stored upright with the cap in place. Empty and full containers should preferably be stored apart. Maintenance and good housekeeping are essential.

Handling. Wherever possible acids should be pumped through sealed systems to prevent all danger of contact. Wherever individual containers have to be transported or decanted, the appropriate equipment should be employed and only experienced persons allowed to undertake the work. Decanting should be done by means of special syphons, transfer pumps, or drum or carboy tilting cradles and so on. Cylinders of anhydrous acid gas require special discharge valves and connections.

Where acids are mixed with other chemicals or water, workers must be fully aware of any violent or dangerous reaction that may take place. For example, a concentrated acid should be slowly added to water, rather than vice versa, in order to avoid the generation of excessive heat and violent reactions which can cause splashes and skin or eye contact.

Ventilation. Where processes produce acid mists or vapours, such as in electroplating, exhaust ventilation should be installed.

Personal protection. Persons exposed to dangerous splashes of inorganic acids should be required to wear acid-resistant personal protective equipment including hand and arm protection, eye and face protection and aprons, overalls or coats. Provided safe working procedures are adopted, the use of respiratory protective equipment should not be necessary; however, it should be available for emergency use in the event of leakage or spillage.

When workers are required to enter a tank that has contained inorganic acids in order to carry out maintenance or repairs, the tanks should first be purged and all precautions for entry into enclosed spaces, as described elsewhere in the Encyclopaedia, should be taken.

Training. All workers required to handle acids should be instructed about their hazardous properties. Certain work activities, such as those involving enclosed spaces or handling of large quantities of acids, should always be done by two persons, one being ready to come to the other’s aid in case of need.

Sanitation. Personal hygiene is of utmost importance where there is contact with inorganic acids. Adequate washing and sanitary facilities should be provided and workers encouraged to wash thoroughly before meals and at the ends of shifts.

First aid. Essential treatment for inorganic acid contamination of skin or eyes is immediate and copious flushing with running water. Emergency showers and eyewash fountains, baths or bottles should be strategically located. Splashes in the eye should be treated with copious irrigation with water. Contaminated clothing should be removed and other appropriate emergency skin treatment procedures should be in place and personnel trained in their administration. Neutralization of the acid in the affected area with an alkaline solution such as 2 to 3% sodium bicarbonate, or 5% sodium carbonate and 5% sodium hyposulphite, or 10% triethanolamine is a standard procedure.

Persons who have inhaled acid mists should be removed immediately from the contaminated zone and prevented from making any effort. They should be put in the care of a physician immediately. In the event of accidental ingestion, the victim should be given a neutralizing substance, and gastric lavage should be carried out. In general, vomiting should not be induced since this may make the injury more widespread.

Medical supervision. Workers should receive pre-employment and periodic medical examinations. The pre-employment examination should be particularly directed at the detection of chronic respiratory, gastro-intestinal or nervous diseases and any eye and skin diseases. Periodic examinations should take place at frequent intervals and should include a check on the condition of the teeth.

Water pollution. This should be prevented by ensuring that wastewater containing spent acid is not emptied into watercourses or sewage systems until the pH (acidity) has been brought to a level that is between 5.5 and 8.5.

Hydrochloric acid

Anhydrous hydrogen chloride is not corrosive; however, aqueous solutions attack nearly all metals (mercury, silver, gold, platinum, tantalum and certain alloys are exceptions) with release of hydrogen. Hydrochloric acid reacts with sulphides to form chlorides and hydrogen sulphide. It is a very stable compound, but at high temperatures it decomposes into hydrogen and chlorine.

Hazards. The special hazards of hydrochloric acid are its corrosive action on skin and mucous membranes, the formation of hydrogen when it contacts certain metals and metallic hydrides, and its toxicity. Hydrochloric acid will produce burns of the skin and mucous membranes, the severity being determined by the concentration of the solution; this may lead to ulcerations followed by keloid and retactile scarring. Contact with the eyes may produce reduced vision or blindness. Burns on the face may produce serious and disfiguring scars. Frequent contact with aqueous solutions may lead to dermatitis.

The vapours have an irritant effect on the respiratory tract, causing laryngitis, glottal oedema, bronchitis, pulmonary oedema and death. Digestive diseases are frequent and are characterized by dental molecular necrosis in which the teeth lose their shine, turn yellow, become soft and pointed, and then break off.

Safety and health measures. In addition to the general measures described above, the acid should not be stored in the vicinity of flammable or oxidizing substances, such as nitric acid or chlorates, or near metals and metal hydrides which may be attacked by the acid with the formation of hydrogen. (The explosive limits of hydrogen are 4 to 75% by volume in air.) Electrical equipment should be flameproof and protected against the corrosive action of the vapours.

Nitric acid

Nitric acid is highly corrosive and attacks a large number of metals. Reactions between nitric acid and various organic materials are often highly exothermic and explosive, and reactions with metals may produce toxic gases. Nitric acid will cause skin burns, and the vapours are highly irritant to the skin and mucous membranes; inhalation of significant quantities will produce acute poisoning.

Fire and explosion. Nitric acid attacks most substances and all metals except the noble metals (gold, platinum, iridium, thorium, tantalum) and certain alloys. The rate of reaction varies depending on the metal and the concentration of the acid; the gases produced during the reaction include the nitrogen oxides, nitrogen and ammonia, which may have a toxic or asphyxiating effect. When in contact with sodium or potassium, the reaction is violent and dangerous, and nitrogen is released. However, in the case of certain metals, a protective oxide film is formed which prevents further attack. Nitric acid may react explosively with hydrogen sulphide. Nitrates obtained by the action of the acid on various bases are powerful oxidizing agents.

Even in dilute concentrations, nitric acid is a powerful oxidizing material. Solutions of a concentration higher than 45% may cause the spontaneous ignition of organic materials such as turpentine, wood, straw and so on.

Health hazards. Solutions of nitric acid are highly corrosive and will produce lesions of the skin, eyes and mucous membranes, the severity of which will depend on the duration of contact and the acid concentration; the lesions range from irritation to burns and localized necrosis following prolonged contact. Nitric acid mists are also corrosive to the skin, mucous membranes and dental enamel.

Nitric acid vapours will always contain a certain proportion of other gaseous nitrogen compounds (e.g., nitrogen oxides), depending on the concentration of the acid and the type of operation. Inhalation may produce acute poisoning and peracute poisoning. Peracute poisoning is rare and can be fatal. Acute poisoning generally comprises three phases: the first consists of irritation of the upper respiratory tract (burning in the throat, cough, feeling of suffocation) and of the eyes with tearing (lacrimation); the second phase is misleading, since pathological signs are absent for a period of up to several hours; in the third phase, the respiratory disorders reappear and may develop rapidly into acute pulmonary oedema, often with serious outcome.

Accidental ingestion will produce severe damage in the mouth, pharynx, oesophagus and stomach, and may have serious sequelae.

Safety and health measures. Depending on the quantities and concentrations involved, nitric acid should be stored in stainless steel, aluminium or glass containers. Glass carboys or winchesters should be protected by a metal envelope to provide resistance to impacts. However, nitric acid containing any fluorinated compounds should not be stored in glass. Organic materials such as wood, straw, sawdust and so on, should be kept away from operations involving nitric acid. When nitric acid is to be diluted with water, the acid should be poured into the water, and localized heating should be avoided.

Sulphuric acid

Sulphuric acid is a strong acid which, when heated to above 30 °C, gives off vapour and, above 200 °C, emits sulphur trioxide. When cold, it reacts with all metals including platinum; when hot, reactivity is intensified. Dilute sulphuric acid dissolves aluminium, chromium, cobalt, copper, iron, manganese, nickel and zinc, but not lead or mercury. It has a great affinity for water, absorbs atmospheric moisture, and abstracts water from organic materials, causing charring. It decomposes salts of all other acids except silicic acid.

Sulphuric acid is found in the native state in the vicinity of volcanoes, in particular in the volcanic gases.

Hazards. The action of sulphuric acid on the body is that of a powerful caustic and general toxic agent. Introduced into the body in liquid or vapour form, it causes intense irritation and chemical burns of the mucous membranes of the respiratory and digestive tract, the teeth, eyes and skin. On contact with the skin, sulphuric acid causes violent dehydration. It releases heat in sufficient quantities to produce burns that are similar to thermal burns and may be classified accordingly as first, second or third degree. The depth of the lesions depends on the concentration of the acid and the length of contact. Inhalation of vapours produces the following symptoms: nasal secretion, sneezing, a burning feeling in the throat and retrosternal region; these are followed by cough, respiratory distress, sometimes accompanied by spasm of the vocal cords, and a burning sensation in the eyes with lacrimation and conjunctival congestion. High concentrations may cause bloody nasal secretion and sputum, haematemesis, gastritis and so on. Dental lesions are common; they affect mainly the incisors and present as brown staining, enamel striation, caries and rapid and painless destruction of the tooth crown.

Occupational exposures to strong inorganic acid mists, such as sulphuric acid mists, have been classified by the International Agency for Research on Cancer (IARC) as being carcinogenic to humans.

Chemical burns are the injury most commonly encountered in sulphuric acid production workers. Concentrated solutions cause deep burns of mucous membranes and skin; initially the zone of contact with the acid is bleached and turns brown prior to the formation of a clearly defined ulcer on a light red background. These wounds are long in healing and may frequently cause extensive scarring that results in functional inhibition. If burning is sufficiently extensive, the outcome may prove fatal. Repeated skin contact with low concentrations of acid causes skin desiccation and ulceration of the hands, and panaris or chronic purulent inflammation around the nails. Splashes of acid in the eyes may have particularly serious consequences: deep corneal ulceration, kerato-conjunctivitis and palpebral lesions with severe sequelae.

The general toxic action of sulphuric acid causes alkaline depletion of the body (i.e., an acidosis which affects the nervous system and produces agitation, hesitant gait and generalized weakness).

Safety and health measures. The most effective measures are the total enclosure of processes and the mechanization of handling procedures to prevent all personal contact with sulphuric acid. Particular attention should be devoted to acid storage, handling and application procedures, the ventilation and lighting of workplaces, maintenance and good housekeeping, and personal protective equipment. In addition to the general precautions given above, sulphuric acid should not be stored in the vicinity of chromates, chlorates or similar substances in view of the fire and explosion hazard involved.

Fire and explosion. Sulphuric acid and oleum are not flammable per se. However, they react vigorously with numerous substances, especially organic materials, with the release of sufficient heat to produce a fire or explosion; in addition, the hydrogen released during reaction with metals may form an explosive mixture in air.

Catalysts. Where a vanadium catalyst is used in the contact process, workers should be protected against exposure to emissions of ammonium vanadate or vanadium pentoxide, which are employed on a diatomite or silica gel support.

Inorganic acids, tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Published in 104. Guide to Chemicals

Tuesday, 02 August 2011 23:07

General Profile

Jump to Acknowledgements or Notes on the Tables

The Guide to Chemicals is designed to be a quick reference guide to approximately 2,000 chemicals which are of commercial interest. The chemicals have been divided into chemical "families" based on their chemical formulae. This division is somewhat arbitrary in that many chemicals can be classified into more than one family.

The reader who is searching for a particular chemical is advised to consult the chemical substances index in this volume to determine whether a chemical is covered and its location. The chemical substances index will also provide references to other chapters in the Encyclopaedia in which discussion of the chemical may also be found. The reader is referred to the chapters Metals: Chemical properties and toxicity and Minerals and agricultural chemicals for a systematic discussion of those elements and compounds and to the chapter, Using, storing and transporting chemicals for information on safe handling, usage, storage and transport of chemicals.

Each chemical family has a brief discussion of relevant toxicologic, epidemiologic or chemical safety information and four types of tables which summarize chemical, physical, safety and toxicologic data in a consistent format.

Because of page constraints, references for primary literature for the preparation of the textual materials are not provided here. The reader will be able to locate most primary data sources by referring to the Hazardous Substances Database (HSDB), produced by the US National Library of Medicine. In addition to the 3rd edition of this Encyclopaedia and the general scientific literature, the HSE Reviews published by the UK Health and Safety Executive served as a source of information. The Resources: Information and OSH chapter in this Encyclopaedia and the chapters mentioned above provide other general references.

The data on industrial uses of chemicals have been adapted from the 3rd edition of the Encyclopaedia and the HSDB. (For discussions of specific chemical industries, see the chapters Chemical processing, Oil and natural gas, Pharmaceutical industry and Rubber industry.)

Acknowledgements

This chapter is a collection of materials, some from articles in the 3rd edition of the Encyclopaedia of Occupational Health and Safety, which have been updated and consistently placed in tabular form.

The 4th edition contributors are:

Janet L. Collins Pia Markkanen

Linda S. Forst Debra Osinsky

David L. Hinkamp Beth Donovan Reh

Niels Koehncke Jeanne Mager Stellman

Kari Kurppa Steven D. Stellman

Chemical structure diagrams which are given in the chemical identification tables were created using CS ChemDraw Pro and obtained from the ChemFinder Web Server, courtesty of CambridgeSoft Corporation (www.camsoft.com).

The 3rd edition contributors are:

M. V. Aldyreva M. Lob

Z. Aleksieva L. Magos

D. D. Alexandrov K. E. Malten

G. Armelli M. M. Manson

Z. Bardodej P. Manu

E. Bartalini J. V. Marhold

F. Bertolero D. Matheson

G. W. Boylen, Jr. T. V. Mihajlova

W. E. Broughton A. Munn

E. Browning S. Nomura

G. T. Bryan K. Norpoth

D. D. Bryson E. V. Olmstead

S. Caccuri L. Parmeggiani

B. Calesnick J. D. Paterson

N. Castellino F. L. M Pattison

P. Catilina M. Philbert

A. Cavigneaux J. Piotrowski

W. B. Deichmann J. Rantanen

D. DeRuggiero D. W. Reed

P. Dervillee G. Reggiani

E. Dervillee C. F. Reinhardt

J. Doignon V. E. Rose

H. B. Elkins H. Rossmann

M. Evrard V. K. Rowe

D. Fassett N. I. Sadkovskaja

A. T. Fenlon T. S. Scott

L. D. Fernandez-Conradi G. Smagghe

I. Fleig G. C. Smith

V. Foá J. Sollenberg

A Forni M. J. Stasik

E. Fournier R. D. Stewart

I. D. Gadaskina W. G. Stocker

E. Gaffuri F. W. Sunderman, Jr.

J. C. Gage O. N. Syrovadko

P. J. Gehring J. Teisinger

H. W. Gerarde A. M. Thiess

W. G. Goode A. A. Thomas

A. R. Gregory T. R. Torkelson

P. Hadengue T. Toyama

H. I. Hardy D. C. Trainor

H. Heimann J. F. Treon

E. V. Henson R. Truhaut

A. Iannaccone E. C. Vigliani

M. Ikeda P. L. Viola

M. Inclan Cuesta N. I. Volkova

T. Inoue M. Wassermann

N. G. Ivanov D. Wassermann

W. H. Jones N. K. Weaver

F. Kaloyanova-Simeonova D. Winter

B. D. Karpov C. M. Woodbury

K. Knobloch R. C. Woodcock

H. Kondo S. Yamaguchi

E. J. Largent J. A. Zapp, Jr.

J. Levèque M. R. Zavon

A. L. Linch J. B. Zuzik

Notes on the Tables

The four types of tables found in each family are:

1. Chemical identification

These tables list chemical names, synonyms, UN codes, CAS-numbers and chemical or structural formulae. An attempt has been made to use the same chemical name for each substance throughout the discussions in this Guide and this Encyclopaedia, to the extent possible. No attempt has been made, however, to use only the nomenclature system of the International Union of Pure and Applied Chemistry (IUPAC). Oftentimes the IUPAC name will be unfamiliar to those who work in a commercial setting and a less cumbersome and/or more familiar name is used. Thus the name which appears as the chemical name in the tables of each family is more often a "familiar" name than the IUPAC name. The list of synonyms given in these tables is not exhaustive but is a sample of some of the names which have been applied to the chemical. The CAS Registry Number (RN) is a numerical identifier used in each of the tables for consistent identification. The CAS number is unique and is applied to both chemicals and mixtures and is used universally and is in the format xxx-xx-x, which permits efficient database searching. The Chemical Abstracts Service is an entity within the American Chemical Society, a professional society of chemists headquartered in the United States.

2. Health Hazards

The data on short-term exposure, long-term exposure, routes of exposure and associated symptoms are adapted from the International Chemical Safety Cards (ICSC) series produced by the International Programme on Chemical Safety (IPCS), a cooperative programme of the World Health Organization (WHO), the International Labour Organization (ILO) and the United Nations Environment Programme (UNEP).

The abbreviations used are: CNS = central nervous system; CVS = cardiovascular system; GI = gastrointestinal system; PNS = peripheral nervous system; resp tract = respiratory tract.

The remaining data on target organs and routes of entry and their associated symptoms are taken from the NIOSH Pocket Guide to Chemical Hazards published by the US National Institute for Occupational Safety and Health (1994, NIOSH Publication No. 94-116).

The following abbreviations are used: abdom = abdominal; abnor = abnormal/abnormalities; album = albuminuria; anes = anesthesia; anor = anorexia; anos = anosmia (loss of the sense of smell); appre = apprehension; arrhy = arrhythmias; aspir = aspiration; asphy = asphyxia; BP = blood pressure; breath = breathing; bron = bronchitis; broncopneu = bronchopneumonia; bronspas = bronchospasm; BUN = blood urea nitrogen; [carc] = potential occupational carcinogen; card = cardiac; chol = cholinesterase; cirr = cirrhosis; CNS = central nervous system; conc = concentration; conf = confusion; conj = conjunctivitis; constip = constipation; convuls = convulsions; corn = corneal; CVS = cardiovascular system; cyan = cyanosis; decr = decreased; depress = depressant/depression; derm = dermatitis; diarr = diarrhea; dist = disturbance; dizz = dizziness; drow = drowsiness; dysfunc = dysfunction; dysp = dyspnea (breathing difficulty); emphy = emphysema; eosin = eosinophilia; epilep = epileptiform; epis = epistaxis (nosebleed); equi = equilibrium; eryt = erythema (skin redness); euph = euphoria; fail = failure; fasc = fasiculation; FEV = forced expiratory volume; fib = fibrosis; fibri = fibrillation; ftg = fatigue; func = function; GI = gastrointestinal; gidd = giddiness; halu = hallucinations; head = headache; hema = hematuria (blood in the urine); hemato = hematopoietic; hemog = hemoglobinuria; hemorr = hemorrhage; hyperpig = hyperpigmentation; hypox = hypoxemia (reduced oxygen in the blood); inco = incoordination; incr = increase(d); inebri = inebriation; inflamm = inflammation; inj = injury; insom = insomnia; irreg = irregularity/ irregularities; irrit = irritation; irrty = irritability; jaun = jaundice; kera = keratitis (inflammation of the cornea); lac = lacrimation (discharge of tears);lar = laryngeal; lass = 1assitude (weakness, exhaustion); leth = lethargy (drowsiness or indifference); leucyt = leukocytosis (increased blood leukocytes); leupen = leukopenia (reduced blood leukocytes); li-head = lightheadedness; liq = liquid; local = localized; low-wgt = weight loss; mal = malaise (vague feeling of discomfort); malnut = malnutrition; methemo = methemoglobinemia; monocy = monocytosis (increased blood monocytes); molt = molten; muc memb = mucous membrane; musc = muscle; narco = narcosis; nau = nausea; nec = necrosis; neph = nephritis; ner = nervousness; numb = numbness; opac = opacity; palp = palpitations; para = paralysis; pares = paresthesia; perf = perforation; peri neur = peripheral neuropathy; periorb = periorbital (situated around the eye); phar = pharyngeal; photo = phtophobia (abnormal visual intolerance to light); pneu = penumonia; pneuitis = pneumonitis; PNS = peripheral nervous system; polyneur = polyneuropathy; prot = proteinuria; pulm = pulmonary; RBC = red blood cell; repro = reproductive; resp = respiratory; restless = restlessness; retster = retrosternal (occurring behind the sternum); rhin = rhinorrhea (discharge of thin nasal mucus); salv = salivation; sens = sensitization; sez = seizure; short = shortness; sneez = sneezing; sol = solid; soln = solution; som = somnolence (sleepiness, unnatural drowsiness); subs = substernal (occurring beneath the sternum); sweat = sweating; swell = swelling; sys = system; tacar = tachycardia; tend = tenderness; terato = teratogenic; throb = throbbing; tight = tightness; trachbronch = tracheobronchitis; twitch=twitching; uncon = unconsciousness; vap = vapor; venfib = ventricular fibrillation; vert = vertigo (an illusion of movement); vesic = vesiculation; vis dist = visual disturbance; vomit = vomiting; weak = weakness; wheez=wheezing.

3. Physical and chemical hazards

The data on physical and chemical hazards are adapted from the International Chemical Safety Cards (ICSC) series produced by the International Programme on Chemical Safety (IPCS), a cooperative programme of the World Health Organization (WHO), the International Labour Organization (ILO) and the United Nations Environment Programme (UNEP).

The risk classification data are taken from Recommendations on the Transport of Dangerous Goods, 9th edition, developed by the United Nations Committee of Experts on the Transport of Dangerous Goods and published by the United Nations (9th edition, 1995).

The following codes are used: 1.5 = very insensitive substances which have a mass explosion hazard; 2.1 = flammable gas; 2.3 = toxic gas; 3 = flammable liquid; 4.1 = flammable solid; 4.2 = substance liable to spontaneous combustion; 4.3 = substance which in contact with water emits flammable gases; 5.1 = oxidizing substance; 6.1 = toxic; 7 = radioactive; 8 = corrosive substance.

The Recommendations are addressed to governments and international organizations concerned with the regulation of the transport of dangerous goods. They cover principles of classification and definition of classes, listing of the principal dangerous goods, general packing requirements, testing procedures, marking, labelling or placarding, and transport documents. Special recommendations address particular classes of goods. They do not apply to dangerous goods in bulk which, in most countries, are subject to special regulations. The following UN classes and divisions are frequently found in the chemical tables in this Guide to chemicals and in the chapter Metals: Chemical properties and toxicity:

Class 2—Gases

Division 2.3—Toxic gases: Gases which (a) are known to be so toxic or corrosive to humans as to pose a hazard to health or (b) are presumed to be toxic or corrosive to humans because they have an LC₅₀value equal to or less than 5,000 ml/m³ (ppm) when tested in accordance with 6.2.3. Gases meeting the above criteria owing to their corrosivity are to be classified as toxic with a subsidiary corrosive risk.

Class 4—Flammable solids; substances liable to spontaneous combustion; substances which in contact with water emit flammable gases

Division 4.2—Substances liable to spontaneous combustion: Substances which are liable to spontaneous heating under normal conditions encountered in transport, or to heating up in contact with air, and being then liable to catch fire.

Division 4.3—Substances which in contact with water emit flammable gases: Substances which, by interaction with water, are liable to become spontaneously flammable or to give off flammable gases in dangerous quantities.

Class 5—Oxidizing substances; organic peroxides

Division 5.1—Oxidizing substances: Substances which, while in themselves not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material.

Class 6—Toxic and infectious substances

Division 6.1—Toxic substances: These are substances liable either to cause death or serious injury or to harm human health if swallowed or inhaled or by skin contact.

Class 8—Corrosive substances

These are substances which, by chemical action, will cause severe damage when in contact with living tissue, or, in the case of leakage, will materially damage, or even destroy, other goods or the means of transport; they may also cause other hazards.

UN Codes, identification numbers assigned to hazardous materials in transportation by the United Nations Committee of Experts on the Transport of Dangerous Goods, are used to readily identify hazardous materials in transportation emergencies. Those preceded by "NA" are associated with descriptions not recognized for international shipments, except to and from Canada.

4. Physical and chemical properties

Relative density is measured at 20°C/4°C, ambient and water temperature, respectively, unless otherwise specified.

The following abbreviations are found: bp = boiling point; mp = melting point; mw = molecular weight; sol = soluble; sl sol = slightly soluble; v sol = very soluble; misc = miscible; insol = insoluble; pvap = vapour pressure; inflam. limit = inflammability limit (vol-% in the air); ll = lower limit; ul = upper limit ; fl. p = flashpoint; cc = closed cup; oc = open cup; auto ig. p = auto ignition point