aniline, 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.

One of the most important organic bases, parent substance for many dyes and drugs. Pure aniline is a highly poisonous, oily, colourless liquid with a distinctive odour. First obtained (1826) from indigo, it is now prepared synthetically. It is a weakly basic primary aromatic amine and participates in many reactions with other compounds. It is used to make chemicals used in producing rubber, dyes and intermediates, photographic chemicals, urethane foams, pharmaceuticals, explosives, herbicides, and fungicides as well as to make chemicals used in petroleum refining.

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