Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Kinetics of the Oxidation of Ascorbic Acid by the Copper (II) Ion in an Acetate Buffer Solution
Katumitu HayakawaShoko MinamiSumio Nakamura
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1973 Volume 46 Issue 9 Pages 2788-2791

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Abstract

The kinetics of the oxidation of ascorbic acid by the copper(II) ion has been studied spectrophotometrically by a stopped-flow technique. At pH 4–6, the initial rate of the decrease in the monohydroascorbate anion is of the second-order with respect to the total concentration of the copper(II) ion and of the first-order with respect to the concentrations of the monovalent and divalent ions of ascorbic acid:
-(d[HA^-]/dt)_t=0=k_1[Cu(II)]_T^2[HA^-]+k_2[Cu(II)]_T^2[A^2-]
where HA and A2− are the monovalent and divalent ions of ascorbic acid respectively. k1, k2, and the activation parameters are obtained as follows: k1=3.1×104, k2=6.1×1010 M−2 s−1, ΔH\ eweq=17 kcal/mol, ΔS\ eweq=8.3 cal/deg mol, and ΔG\ eweq=15 kcal/mol. The EPR signal from the ascorbate radical is not observed in the kinetic run by either a flow technique or a quenching technique. Some discussions of the mechanism of the reaction are given.

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