GB384558A - Improvements in the purification and decolorisation of aromatic hydroxy-carboxylic ac - Google Patents

Abstract

Aromatic hydroxycarboxylic acids, more particularly salicylic and the cresotinic acids, are purified by treatment of a solution of a salt of the acid with a precipitated oxide, hydroxide or carbonate, including basic carbonates, of zinc or aluminium, which may be either formed in the solution by precipitation or precipitated separately and introduced moist into the solution. The process may be used in conjunction with known purification methods. According to examples, (1) crude sodium salicylate in a solution made slightly acid is heated with decolorizing carbon, zinc dust, and crystallized zinc sulphate, followed by the addition of sodium carbonate, filtering, adding sodium sulphite and precipitation in the usual manner; (2) crude sodium o-cresotinate is first treated by precipitation by acid from aqueous solution, dissolved in caustic alkali, rendered slightly acid, and treated with decolorizing carbon and the procedure of example (1). The Provisional Specification refers in general to the use of insoluble carbonates, hydroxides, or oxides of metals of groups II and III of the Periodic System for purifying aromatic hydroxycarboxylic acids and their homologues and derivatives