Sulfanilic Acid

sulfanilic acid [¦səl·fə¦nil·ik ′as·əd]

(organic chemistry)

C₆H₄NH₂·SO₃H·H₂O Combustible, grayish-white crystals slightly soluble in water, alcohol, and ether, soluble in fuming hydrochloric acid; chars at 280-300°C; used in medicine and dyestuffs and as a chemical intermediate.

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Sulfanilic Acid 

(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.