Aniline
Aniline or aminobenzene (C6H5NH2) is a primary aromatic amine consisting of a benzene ring and an amino group. The structure of aniline is shown at the right.
Synthesis
Aniline can be produced from benzene in two steps. First, benzene is nitrated (reacted with nitric acid, a form of electrophilic substitution reaction) to give nitrobenzene. Second, the nitrobenzene is reduced to give aniline. A variety of reducing agents are effective for the reduction, including H2 (with a catalyst), hydrogen sulfide, iron, zinc, or tin.
Many derivatives of aniline can be prepared similarly.
Properties
Aniline is a carcinogen. It is oily and although colourless, it can be slowly oxidized in air to form impurities which can give it a red-brown tint. Its boiling point is 184 °C and its melting point is -6 °C.
Chemically, aniline is a weak base. It reacts with strong acids to form salts, and reacts with acyl halides (such as acetyl chloride, CH3COCl) to form amides. The amides formed from aniline are sometimes called anilides, for example CH3-CO-NH-C6H5 is acetanilide.
Like phenols, aniline derivatives are highly reactive in electrophilic substitution reactions. For example, sulfonation of aniline produces sulfanilic acid, which can be converted to sulfanilamide. Sulfanilamide is one of the sulfa drugs which were widely used as antibacterials in the early 20th century.
Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium ions. Through these, the -NH2 group of aniline can be conveniently converted to -OH, -CN, or a halogen.
Uses
Aniline is used to make a wide range of synthetic products, most notably dyes.
History
Aniline was first isolated from indigo in 1826 by Otto Unverdorben. In 1855, an inexpensive means of producing aniline from coal tar was discovered by August Wilhelm von Hofmann.
Its first industrial-scale use was in the manufacture of mauveine, a purple dye discovered in 1856 by William Henry Perkin.
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