Catalytic activity studies of some new transition metal complexes in the oxidation of ascorbic acid to dehydroascorbic acid

Abstract

Certain new Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes of the Schiff bases derived from quinoxaline-2-carboxaldehyde have been screened for their catalytic activity towards the oxidation of ascorbic acid. Results of the screening studies indicate that among the various metal complexes synthesised, only the Cu(II) complexes are highly efficient catalysts towards oxidation of ascorbic acid although a few other complexes also exhibit slight activity. The kinetics of oxidation of ascorbic acid in the presence of Cu(II) complex of the Schiff base quinoxaline-2-carboxalidene-2-aminophenol have been studied in detail in methanol water mixtures. These studies indicate that the reaction is first order in catalyst and zero order in ascorbic acid. Added ligand retards the reaction. A suitable mechanism has been proposed to explain these results.