Kinetic Studies of the Oxidation of L-Ascorbic Acid by the Peroxodisulfate Ion, and of Copper(II)-catalysis

Article abstract of DOI:10.1246/bcsj.55.2068

Kinetic studies of the oxidation reaction of L-ascorbic acid by the peroxodisulfate ion(S2O8^2-) are carried out in an aqueous solution over the pH range of 3.4-4.6 at various ionic-strengths from 0.071 to 1.07 M (1 M=1 mol dm^-3) with NaClO4, and at four temperatures between 15 and 30 deg C, at an ionic-strength of 1.07 M.The variations in the rate of the oxidation with the hydrogen-ion concentrations are consistent with the reaction schemes involving two pH-related species; ascorbic acid H2A (k₁=0.032 M^-1 s^-1 at 25 deg C, ΔH^<*>₁=17 kJ mol^-1, ΔS^<*>₁=-220 J deg^-1 mol^-1) and the ascorbic anion HA^- (k₂=0.43 M^-1 s^-1 at 25 deg C, ΔH^<*>₂=45 kJ mol^-1, ΔS^<*>₂=-102 J deg^-1 mol^-1).A relationship of log k₂=-1.47+2.17 I^1/2/(1+I^1/2) is found with the ionic-strength (I) at 25 deg C.The reaction rate is greatly catalyzed by the presence of trace amounts of the copper(II) ion; the mechanisms of the copper(II)-catalyzed reaction are discussed.