Fremgangsmåde til fremstilling af natrium- eller kalium-L-ascorbat

In the described process for the preparation of sodium or potassium L-ascorbate, 2-keto-L-gulonic acid monohydrate is esterified with methanol. The esterification is only carried out partially, i.e. not to attainment of the esterification equilibrium. In an intermediate step, unesterified 2-keto-L-gulonic acid and any impurities are precipitated and removed by addition of sodium bicarbonate or of potassium bicarbonate in an amount essentially adequate for neutralising the ester solution. Subsequently, the lactonisation of the methyl 2-keto-L-gulonate formed is facilitated by addition of further bicarbonate. To achieve a high yield the unesterified 2-keto- L-gulonic acid from the bicarbonate precipitation can be subsequently esterified using the same process, preferably in parallel, and likewise converted into ascorbate. The process enables the preparation of very pure sodium or potassium ascorbate suitable for pharmaceutical purposes in an economical manner.