KINETICS AND MECHANISM OF THE OXIDATION OF L-ASCORBIC ACID BY POTASSIUM TRISOXALATOFERRATE (III) TRIHYDRATE IN AQUEOUS HYDROCHLORIC ACID MEDIUM

Abstract

The kinetics of the oxidation of K3[Fe(C2O4)3].3H2O by L-ascorbic acid has been studied in aqueous acidic medium. The stoichiometric studies showed that 1 mole of H2A was oxidized for every 2 moles of Fe(C2O4)33- reduced. Under pseudo-first order conditions of H2A >> Fe(C2O4)33-, the reaction was found to have first order dependence on each of the reactants, giving second order overall. The reaction rate was found to be directly dependent on acid concentration and increased with increase in ionic strength of reaction system. It was also evident that increase in dielectric constant of the reaction medium (D) enhanced the reaction rate and addition of CH3COO-, HCOO-, Mg2+and Li+ catalyzed the rate of the reaction. The oxidation of L-ascorbic acid by potassium trisoxalatoferrate (III) trihydrate is rationalized in terms of absence of ion pair complex formation with outer-sphere reaction pathway characteristics.