Oxidation of Ascorbic Acid and Dehydroascorbic Acid by Superoxide Ion in Aprotic Media

Article abstract of DOI:10.1021/ja00387a020

In dimethylformamide, superoxide ion (O2^-) oxidizes ascorbic acid (H2A) to dehydroascorbic acid (A).The rate-limiting step is first order for each reactant and has a second-order rate constant (k) of 2.8 x 10⁴ M^-1 s^-1; the overall stoichiometry is 3H2A molecules per 2O2^- ions.Addition of O2^- to dehydroascorbic acid (A) results in its rapid oxidation (k = 3.3 x 10⁴ M^-1 s^-1), with an overall stoichiometry of 2O2^- per A.The major products of the process are oxalate ion and the anion of threonic acid.On the basis of the reaction stoichiometries, kinetics, and products, self-consistent mechanisms are proposed for the oxidation of ascorbic acid and dehydroascorbic acid.