Reaction pathways in the decomposition of hydrogen peroxide catalyzed by copper(II)

The kinetics of the decomposition Of H2O2 catalyzed by Cu(II) has been studied by the initial-rate method in aqueous phosphate media at near physiological pH. The activity of the catalyst is increased by [Fe(CN)(6)](3-) and decreased by VO3-, CrO42- and Zn(II). Three reaction pathways are involved in the Cu(II)-H2O2 reaction, the kinetic orders of the catalyst being 1 (rate constant k(1)), 2 (rate constant k(2)) and 3 (rate constant k(3)). The three pathways present fractional apparent orders (> 1) in H2O2 and base catalysis. The apparent activation energies associated to rate constants k(1), k(2) and k(3) are 102 +/- 4, 65 +/- 8 and 61 +/- 5 kJ mol(-1). Free-radical chain mechanisms are proposed for the three pathways. (C) 2003 Elsevier Inc. All rights reserved.