Formation Mechanism of Monodehydro-L-ascorbic Acid and Superoxide Anion in the Autoxidation of L-Ascorbic Acid

Abstract

The oxidation of L-ascorbic acid (ASA) by molecular oxygen was studied in the absence of heavy metal ion catalysts. The formation of superoxide anion was confirmed during the autoxidation of ASA not only in aqueous solution but also in MeOH. The formation mechanism of superoxide anion was discussed based on both experimental and molecular orbital (MO) calculation results. It was proposed that ASA autoxidation proceeded via the C(2) okygen adduct of ASA, and superoxide anion would be directly released from the C(2) oxygen adduct of ASA, forming monodehydro-ASA (MDASA).