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sulfanilic acid[¦səl·fə¦nil·ik ′as·əd]
(or p-aminobenzenesulfonic acid), a colorless crystalline compound that decomposes at 280°–300°C. It is sparingly soluble in water; 1 g dissolves in 100 g of water at 20°C.
Sulfanilic acid is an inner salt, in which the amino group is neutralized by the sulfo group. Therefore, the acid does not form salts with mineral acids, but its sulfo group may be neutralized by
bases—for example, with the formation of the sodium salt H2N—C6H4SO3Na.
Sulfanilic acid is produced by heating aniline sulfate, C6H5NH2·½H2SO4, at 180°–200°C. Diazotization of sulfanilic acid yields diazobenzenesulfonic acid, , which is widely used in the production of azo dyes. The amide of sulfanilic acid, H2H—C6H4—SO2NH2 (sulfanilamide), is used in medicine, where it is called Streptocid album. Some of the derivatives of sulfanilamide, including Albucid, sulfonamide (Sul’gin), Sulfidine, sulfamethazine, and sulfazole, or sulfamethylthiazole, are also used in medicine. In the laboratory, sulfanilic acid is used for the determination of nitrites and the detection of several metals, such as osmium and ruthenium.