preparation process of ascorbic acid

Process for the preparation of pure ascorbic acid from 2-keto-L-gulonic acid or its sodium salt, by carrying out the following successive steps: - esterification of 2-keto-L-gulonic acid or its sodium salt, - lactonisation to sodium ascorbate - optional separation of the sodium ascorbate - displacement of the ascorbic acid from its salt - separation of the sodium sulphate - separation and purification of the ascorbic acid from its methanolic or aqueous-methanolic solution.