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aminobenzene, phenylamine, C6 H5 NH2, the simplest aromatic amine; a colorless liquid with a slight odor; melting point -6.15°C; boiling point 184.4°C; density at 20°C 1,017 kg/m3; refractive index nD20 1.5863. Aniline is soluble in water (3.4 g in 100 g water at 20°C); miscible in all respects with alcohol, ether, and benzene; forms metallic derivatives—for example, C6H5NHNa—with a series of metals (potassium, sodium, calcium, magnesium, and others). Aniline has the same basic, but less pronounced, characteristics as aliphatic amines (dissociation constant K = 4.5 × 10-10). With mineral acids, aniline forms salts—for example, aniline hydrochloride, C6H5NH3Cl, which is used in fabric printing. The interaction of aniline with organic acids, chloroanhydrides, or anhydrides yields anilides; for example, aniline reacting with acetic acid forms acetanilide:
C6H5—NH2 + CH3COOH → C6H5NHCOCH3 + H2O
Anilides are produced on an industrial scale and are used in the production of n-nitroaniline, one of the important intermediate products in the manufacture of dyes.
In industry the methylation of aniline (with methyl chloride, methanol, or dimethyl ether) yields mono- or dimethyl anilines, which are widely used in the manufacture of dyes and explosives:
C6H5NH2 + (CH3)2O → C6H5N(CH3)2 + H2O
Phenylglycine, C6H5NHCH2COOH, a product of the alkyla-tion of aniline with chloracetic acid, is used in the synthesis of indigo. Heating aniline with aniline hydrochloride at high temperature and pressure in industry yields diphenylamine, (C6H5)2NH, an important intermediate in the production of a dye (so-called aniline black). During catalytic hydrogenation aniline produces cyclohexylamine (C6H11NH2). A very important reaction of aniline widely used in industry is diazoti-nation; phenyl diazonium chloride [C6H5—N≡N]Cl formed by this reaction serves as a basic intermediary of azo dyes.
Aniline is widely used in the manufacture of developers for photography (para-aminophenol and others) and accelerators for the vulcanization of rubber and in the production of explosives, pharmaceuticals, and so on.
The basic method for producing aniline is the reduction of nitrobenzene during heating with rubber shavings in the presence of a small quantity of hydrochloric acid:
4C6H5NO2 + 9Fe + 4H2O → 4C6 H5NH2 + 3Fe3O4
Other methods, including the reduction of nitrobenzene with copper carbonate as a catalyst and treatment of chloroben-zene with ammonia, are also used. Aniline was discovered by several chemists working independently of one another; it was first synthesized in 1842 by N. N. Zinin, who reduced nitrobenzene with ammonium sulfide.
Aniline, a poison, affects the central nervous system, causes the formation of methemoglobin in the blood, degenerative changes in erythrocytes, and hemolysis, which results in an oxygen deficiency in the organism. Aniline enters the organism through the breathing apparatus in the form of vapors and is also absorbed through the skin and mucous membranes. The absorption rate increases at high air temperature and with the use of alcohol. Critical and chronic aniline poisoning are possible; the latter is known as anilism. Weakness, dizziness, headaches, and blueing of the lips, outer ear, and nails are signs of minor aniline poisoning. In critical cases these symptoms are accompanied by nausea, sometimes vomiting, and an unsteady walk; the pulse is increased. Severe cases of poisoning are extremely rare. Chronic cases of poisoning lead to toxic hepatitis, nervous and psychiatric disorders, disturbed sleep, reduction of memory, and so on.
First aid in aniline poisoning calls for the removal of the victim from the source of poisoning; the body should be washed with water (not hot!); oxygen mixed with carbon dioxide should be administered. Bloodletting, antidotes (methyl blue), cardiovascular techniques, and rest are also prescribed.
Aniline poisoning can be prevented by the mechanization of production in a hermitic environment, ventilation, and strict observance of industrial safety methods and industrial sanitation. Maximum permissible air concentration of aniline in a working zone is 3 mg/m3. Methods of individual protection include using a filtering gas mask brand “A,” impermeable to aniline; special clothing; a shower and change of clothing after work; and a required medical examination for those working with aniline. Maximum permissible concentration of aniline in vats during their industrial heating is 0.1 mg/1 (100 mg/m3).
REFERENCESJukel’son, I. I. Tekhnologia osnovnogo organicheskogo sinteza. Moscow, 1968.
Professional’nye bolezni, 2nd ed. Moscow, 1964.
Vrednye veshchestva v promyshlennosti, 5th ed. Edited by N. V. Lazarev. Moscow-Leningrad, 1965. Chapter 1, p. 575. (Bibliography.)