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Process for preparing ascorbic acid
| Details |
Inventors: Le Fur, Isidore; Richard, Jean-Paul; Wolff, Gerard;
Assignee: Rhone Poulenc Rorer S.A. (FR)
Primary Examiner: Ivy; C. Warren
Assistant Examiner: Trinh; Ba K.
Attorney, Agent or Firm: Morgan & Finnegan
Process for preparing 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 lactonization 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. |
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DETAILED DESCRIPTION OF THE INVENTION It has now been found, and this forms the subject of the present invention, that practically pure, that is greater than 99.
5%, ascorbic acid may be obtained after purification on acidic and basic resins of the ascorbic acid obtained by the action of a strong acid on sodium ascorbate, preferably isolated beforehand, which is itself obtained from 2-keto-L-gulonic acid or one of its alkali metal salts.
Practically pure ascorbic acid may be obtained by crystallization in water, in an alcohol such as methanol or in an aqueous-alcoholic medium such as an aqueous-methanolic solution.
According to the present invention, 2-keto-L-gulonic acid, optionally in salt form, is esterified by means of an alcohol in the presence of a strong acid, and the ester obtained is then converted, optionally in situ, by the action of a base in alcoholic solution, in the amount needed for quantitative consumption of the 2-keto-L-gulonic acid ester, to an alkali metal salt of ascorbic acid, which is isolated and then neutralized by the action of a strong acid, working in a solvent in which the alkali metal salt of the strong acid is insoluble and ascorbic acid is soluble.
After separation of the alkali metal salt of the strong acid, the ascorbic acid is isolated from its solution.
The esterification of 2-keto-L-gulonic acid is carried out by means of an alcohol such as methanol or butanol, in the presence of a strong acid such as hydrochloric acid, sulfuric acid or sulfonic acids.
The esterification is performed in the presence of an amount of strong acid which is preferably in the region of 2 mol % relative to the 2KLG-H employed, or by monitoring the apparent pH of the medium, which is maintained in the vicinity of 0.
5 when hydrochloric acid or sulfuric acid is used.
Using an alkali metal salt of 2-keto-L-gulonic acid, preferably the sodium salt, it is necessary to use an amount of strong acid permitting the liberation of 2-keto-L-gulonic acid in situ and catalysis of the esterification reaction
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Molecular Biology 
