REACTIONS INVOLVING COPPER(I) IN PERCHLORATE SOLUTION . KINETICS AND MECHANISM OF COPPER(2) CATALYSIS OF VANADIUM(3) REDUCTIONS OF COBALT(3) COMPLEXES

Copper(II) catalyzes the oxidation of V3+ to VO2+ by the cobalt(III) complexes Co(NH3)5Br2 +, Co(NH3)5C12+, and trans-Co(en)2Cl2+. The rate equation is -d[V3+]/dt = (g + A/[H+])[Cu2 +][V3+], independent of [Co(III)]. At 25.0˚ and μ = 3.00 M (L1C1O4), the values are g = 0.018 ± 0.002 M-1ec-1 and h = 0.336 ± 0.001 sec-1. The activation parameters for h are δH = 19.4 ± 0.1 kcal mole-1 and δS = 4.4 + 0.4 eu. The rate was also studied with NaC1O4 as the added electrolyte and at μ = 1.00 M (liCIO4). The rate-determining step is proposed to be the rapid reaction of V3+ and Cu2+, followed by the rapid reoxidation of the Cu+ so formed by Co(III). The role of Cu(I) in the catalytic cycle is discussed, and some “direct” measurements of the V3+ + Cu2+ rate are presented. The relation of the present results to those on the reverse reaction, VO2+ + Cu+, is considered. Arguments are advanced for a mechanism in which the inner-sphere reaction of VOH2+ and Cu2+ is the main rate-determining step. © 1969, American Chemical Society. All rights reserved.