KINETICS OF OXIDATION OF COPPER(I) BY MOLECULAR OXYGEN IN PERCHLORIC ACID-ACETONITRILE SOLUTIONS

Spectrophotometry and polarographic methods were used to study the oxidation of Cu(I) by dissolved O2 in HCIO4-CH3CN solutions of ionic strength 0.1 M. The reaction follows the rate law -d[Cu(CH3CN)2+]/dt = d[Cu2+]/dt = kc[Cu(CH3CN)2+][O2][H+]/[CH3CN]2, where kc = 6.9 ± 0.3 X 107 M-2 sec-1 at 30°. The activation energy for the process is 8.4 ± 0.4 kcal/mole in the temperature range 9.8-48°. The data are interpreted in terms of a bimolecular reaction between a hypothetical CuO2+ complex and H+ in the rate-limiting step of a sequence which involves the prior rapid dissociation of the Cu(CH3CN)2+ complex followed by the formation of the oxygenated intermediate. The stoichiometry of the reaction indicates that under the reported conditions Cu(I) reacts more slowly with H2O2 than with O2. A small amount of the Cu(I) ion can be detected at the conclusion of O2 uptake, at which time the addition of a complexing agent preferential for Cu(I) results in the relatively slow formation of the Cu(I) complex in a pH-dependent reaction. Although the reaction sequence implies the participation of free-radical oxygen intermediates, attempts to obtain evidence for the appearance of these reactive species by the ability of the reaction mixture to hydroxylate benzoic acid were unsuccessful. In addition the ultraviolet spectra for the acetonitrile and aquo complex ions of Cu(I) were obtained; attempts to detect the CuO2+ intermediate spectroscopically failed. © 1969, American Chemical Society. All rights reserved.