aniline

aniline

(ăn`əlĭn), C₆H₅NH₂, colorless, oily, basic liquid organic compound; chemically, a primary aromatic amine whose molecule is formed by replacing one hydrogen atom of a benzene molecule with an amino group. Aniline boils at 184°C; and melts at −6°C;. It is of great importance in the dye industry, being used as the starting substance in the manufacture of many dyes—e.g., indigo—and as an aid in the manufacture of others. For this reason many dyes have the word aniline in their common name, such as aniline black (one of the best black dyes known), aniline red, yellow, blue, purple, orange, green, and others. Today these synthetic dyes have largely replaced the natural ones. Aniline is prepared commercially by the reduction of nitrobenzene, a product of coal tar, or by heating chlorobenzene with ammonia in the presence of a copper catalyst. Sulfonation of aniline yields sulfanilic acid, the parent compound of the sulfa drugs. Aniline is also important in the manufacture of rubber-processing chemicals and antioxidants.

Aniline

 

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 n_D²⁰ 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, C₆H₅NHN_a—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).

REFERENCES

Jukel’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.)

aniline

[′an·əl·ən]

(organic chemistry)

C₆H₅NH₂ An aromatic amine compound that is a pale brown liquid at room temperature; used in the dye, pharmaceutical, and rubber industries.

aniline

a colourless oily pungent poisonous liquid used in the manufacture of dyes, plastics, pharmaceuticals, and explosives. Formula: C₆H₅NH₂