Aniline is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile starting material for fine chemical synthesis. Its main use is in the manufacture of precursors to polyurethane, dyes, and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds.
Chemically, it is considered an electron-rich benzene derivative, and as a consequence, reacts rapidly in electrophilic aromatic substitution reactions. Likewise, it is also prone to oxidation: while freshly purified aniline is an almost colorless oil, exposure to air results in gradual darkening of the sample (to yellow or red) due to the formation of strongly colored, oxidized impurities. Aniline can be diazotized to give a diazonium salt, which can then undergo various nucleophilic substitution reactions.
Like other amines, aniline is a base (pKaH = 4.6) and nucleophile, although it is a weaker base and poorer nucleophile than structurally similar aliphatic amines.
Aniline is predominantly used for the preparation of methylenedianiline and related compounds by condensation with formaldehyde.
The diamines are condensed with phosgene to give methylene diphenyl diisocyanate, a precursor to urethane polymers.
Other uses include rubber processing chemicals (9%), herbicides (2%), and dyes and pigments (2%).As additives to rubber, aniline derivatives such as phenylenediamines and diphenylamine, are antioxidants. The principal use of aniline in the dye industry is as a precursor to indigo, the blue of blue jeans.