Determination of pKa value, kinetic studies of decomposition and oxygen transfer for chromium(VI) peroxide

The determination of pKa value for the unstable chromium(VI) peroxide, CrO(O2)2(H2O) in aqueous solution is presented. The pKa value is found to be (1.55 ± 0.03). The kinetic decomposition of chromium(VI) peroxide is dependent on the concentration of hydrogen peroxide in the pH range between 2.5 and 4.0. We have proposed the possible explanation for the formation of triperoxo chromium complex of hydrogen peroxide which is dependent on decomposition. Activation of coordinate peroxide in chromium(VI) peroxide observed in the kinetic studies is by reduction of thiolato–cobalt(III) complex. The rate constant (M−1 s−1, 15 °C) for the oxygen atom transfer reaction from CrO(O2)2(OH)− to (en)2Co(SCH2CH2NH2)2+ is found to be (25.0 ± 1.3).