Aniline

Aniline

Aniline is the common, and the systematic, name given to aminobenzene. It is, therefore, the phenyl-substituted derivative of ammonia. The empirical formula of aniline is C₆H₇N, although it is more commonly written as either C₆H₅NH₂ (aminobenzene) or PhNH₂ (phenylamine). It is an example of an aromatic primary amine. At standard temperature and pressure it is a colorless, oily liquid with an unpleasant odor that turns brown due to slow oxidation by air. It has a melting point of 22°F (-6°C) and a boiling point of 326°F (184°C). Aniline is manufactured by reduction of nitrobenzene, using hydrogen gas and a copper catalyst, or using iron, water, and hydrochloric acid for the reduction.

Aniline is an industrially important compound. It is used in the manufacture of antioxidants, pharmaceuticals, dyes, and in the vulcanization of rubber. Production of this chemical in the United States was at a level of 400,000 tons annually in the late 1990s.

Aniline is a weakly basic compound that gives water soluble salts with the mineral acids. When aniline is reacted with excess acetic (ethanoic) acid under dehydration conditions a white, crystalline material is formed, acetanilide. Acetanilide, C₆H₅NHC(O)CH₃, is formed by acylation of the aniline by the acetic acid with loss of water. Acetanilide is used in the manufacture of rubber and dyes. Dyes are prepared by a nitration addition reaction to aniline, followed by reduction of the nitro group using sodium sulfide. The products from these reactions are used in the production of an important class of dyes, the azo dyes. The azo dyes are used for wool, cotton, and color photography. They are an acid fast category of dyes.

Phenol can be produced from aniline by reacting aniline with a mixture of sodium nitrite and hydrochloric acid to give benzene diazonium chloride, that when heated gently, gives off nitrogen to leave phenol. The diazonium group can also be replaced by halogen, cyano, or pseudohalogen groups or atoms in a double decomposition reaction called Sandmeyer's reaction. The benzene diazonium chloride is treated with (e.g.) copper chloride to yield nitrogen gas and chlorobenzene. The diazonium salt can also be reacted and joined to phenolic groups and amines to give azo compounds.

Halogenation occurs readily with aniline by electrophilic aromatic substitution. For example, bromine water is rapidly discolored and a precipitate of 2,4,6-tribromoaniline is obtained.

Heating aniline with a variety of compounds yields a wide range of products. Heating with alkyl chlorides gives a mixture of the mono and the dialkyl aniline. Skraup's reaction (the addition of sulfuric acid and glycerol to aniline) gives quinoline which is used in the manufacture of dyes and pharmaceuticals. Quinaldine can be made by reacting aniline, hydrochloric acid, and paraldehyde. This compound can be used in the manufacture of photosensitive dyes.

Aniline is an arylamine that has a large industrial usage in the manufacture of various dyes for a wide range of applications as well as being a precursor for the manufacture of a number of pharmaceutical compounds.