Formation of L-Threonolactone and Oxalic Acid in the Autoxidation Reaction of L-Ascorbic Acid.

The autoxidation of i-ascorbic acid (ASA) in methanol without heavy metal ion catalysts led to the formation of dehydro-L-ascorbic acid (DASA), the main oxidation product, together with minor oxidation products, L-threonoIactone (THL) and oxalic acid (OXA), which had been reported as the major oxidation products in the reaction of ASA with singlet oxygen. The facts suggested the possible involvement of the C(2) oxygen adduct of ASA as an important intermediate compound in this autoxidation process, and it was also supported by the semi-empirical molecular orbital calculation.