Kinetics and mechanism of chromate reduction with hydrogen peroxide in base

[(CrO4)-O-VI](2-) is reduced to [Cr-V(O-2)(4)](3-) by hydrogen peroxide in strongly basic media where the acid dissociation of H2O2 (pK(a) = 11.65) is appreciable. The reaction is first order in chromium(VI) and inhibited by hydroxide. The hydrogen peroxide dependence is defined by the form of the effective pseudo-first-order rate constant: k(eff) = [H2O2](3)/(K-1 + K-2[H2O2] + K-3[HO2-]) with K-1 = 175(43) s(.)M(3), K-2 = 403(18) s(.)M(2), and K-3 = 1422(34) s(.)M(2). Hydrogen peroxide anion initially attacks chromate, and subsequent equilibrium steps that exchange oxo groups for three peroxo groups precede a rate-determining, one-electron, intramolecular reduction step.