SULFONIC ACID

sulfonic also spelled Sulphonic, any of a class of organic acids containing sulfur and having the general formula RSO3H, in which R is an organic combining group. The sulfonic acids are among the most important of the organic sulfur compounds; the free acids are widely used as catalysts in organic syntheses, while the salts and other derivatives form the basis of the manufacture of phenolic compounds, detergents, water-soluble dyes, sulfonamide pharmaceuticals, and ion-exchange resins. The aromatic sulfonic acids are particularly useful as intermediates or starting materials in synthesis. The aromatic sulfonic acids are obtained generally by treating aromatic compounds with concentrated sulfuric acid, the process being called sulfonation (q.v.). Because the acids are frequently used in the form of their sodium salts, sulfonation is usually followed by neutralization with sodium hydroxide or sodium carbonate. Such operations are conducted on a manufacturing scale in the preparation of the sodium salts of benzenesulfonic acid for the manufacture of phenol, those of alkylated benzenesulfonic acids used as synthetic detergents, and that of anthraquinonesulfonic acid used in the manufacture of alizarin and other dyes. The aliphatic sulfonic acids are generally less important and more difficult to prepare than the aromatic sulfonic acids. Among the various methods used to prepare aliphatic sulfonic acids are the oxidation of other organic sulfur compounds and the reaction of alkyl halides and metallic sulfites.