Synthesis and stability of L-ascorbate 2-sulphate

Abstract

L-Ascorbate 2-sulphate (I) has been isolated in 75–80% yield by two methods. In a modified conventional procedure, tertiary amine salts of 5,6-acetal derivatives of L-ascorbic acid were sulphated with an amine–sulphur trioxide complex in a dipolar aprotic solvent. In an alternative procedure, L-ascorbate (II) was sulphated rapidly and almost quantitatively by treatment with trimethylamine–sulphur trioxide in alkali (pH 9·5–10·5) at 70°. L-Ascorbate 2-sulphate (I) was 20 times more stable than L-ascorbate to oxygen (air) in boiling water. In boiling alkali (pH 13·0) it had a half-life of 21 h, whereas in boiling acid (pH 1·0) its half-life was 4·7 min. Loss of sulphate from L-ascorbic acid 2-(hydrgen sulphate)(III) was 1500 times faster in 99% methanol than in water at 50°.