aniline [key], 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℃ and melts at −6℃. 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.
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