Abstract: A novel esterification process of 2-keto-L-gulonic acid is provided to obtain an improve degree of esterification. According to the process, 2-keto-L-gulonic acid anhydrous crystals are formed from its monohydrate crystals in water-soluble alcohol solvent. The anhydrous 2-keto-L-gulonic acid is esterified with lower alcohol to obtain a lower alkyl ester of 2-keto-L-gulonic acid. The resultant ester is lactonized to obtain a metal L-ascorbate.

Abstract: A method of purifying L-ascorbic acid which comprises: bringing an acidic aqueous solution of L-ascorbic acid which contains a cationic surfactant into contact with active carbon activated by chemicals.The method is in particular useful for removing a cationic surfactant from a reaction mixture of diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid with a mineral acid in the presence of an inert solvent and a cationic surfactant, to produce L-ascorbic acid.

Abstract: A method of purifying L-ascorbic acid which comprises: subjecting an acidic aqueous solution of L-ascorbic acid which contains salts of an inorganic acid to electrodialysis to remove the salt therefrom.The method is in particular useful for removing salts of an inorganic acid from an aqueous mixture of L-ascorbic acid and the inorganic salt resulting from the production of L-ascorbic acid in which diacetone-2-keto-L-gulonic acid or 2-keto-L-gulonic acid is heated in the presence of an inorganic acid, or an alkyl ester of 2-keto-L-gulonic acid is enolized and lactonized in the presence of a base.