Copper-catalyzed Oxidation of Ascorbic Acid

Abstract

Copper-catalyzed oxidation of ascorbic acid was investigated in various environments by using the conventional Warburg manometric technique. The rate of the oxidation, expressed by the consumption of molecular oxygen, depends on pH and the concentration of ascorbic acid. From the pH dependence of the reaction, it was deduced that the dissociated monoionic ascorbic acid was a molecular species susceptible to the oxidation. Inorganic ligand including buffer anion influenced the oxidation. Nitrate, sulfate and acetate ions, which have a little ability to complex with copper ion, reduce a little the catalytic efficiency. The retardation by acetate ion was ascribed to the formation of copper tetraacetate. Halide, pyrophosphate, thiocyanate and cyanide ions, which complex preferably with cuprous ion thereby change the redox potential between cupric and cuprous ions, retards the oxidation markedly. © 1969, The Pharmaceutical Society of Japan. All rights reserved.