Method for recovering pure metahydroxybenzoic acid

摘要

A method for recovering purified m-hydroxybenzoic acid from crude m-hydroxybenzoic acid alkali metal salt. The method comprises dissolving the crude m-hydroxy benzoic acid alkali metal salt in water at a ratio of between about 13 and 20 milliliters of water per gram of pure m-hydroxybenzoic acid alkali metal salt contained in the crude salt; acidifying the resulting solution to a pH of below 2 with a mineral acid to neutralize all alkali metal hydroxide present and to convert the m-hydroxybenzoic acid alkali metal salt to free m-hydroxybenzoic acid; and cooling the solution to from about 0 DEG C. to about 15 DEG C. for a sufficient time to crystallize purified m-hydroxybenzoic acid from the solution. The method is particularly effective for removing impurities of parahydroxybenzoic acid, alkali metal hydroxide and water soluble inorganic salts.