Copper(II)-catalyzed decomposition of hydrogen peroxide: Catalyst activation by halide ions

The catalytic action of Cu(II) on the decomposition of H2O2 in near-neutrality aqueous solutions is activated by halide ions. The activation energies amount to 113+/-7 (parent reaction) and 69.9+/-1.4 (chloride-activated reaction) kJ (.) mol(-1). Free-radical chain mechanisms are proposed for both the parent reaction and the halide-activated reaction. The catalyst activation caused by halide ions is explained in terms of coordination of halide ligands by both Cu(II) and Cu(I), the coordination causing a higher stabilization of Cu(I) than of Cu(II). At low concentrations, Br- causes an inhibition of the Cu(II)/H2O2 reaction. This is explained in terms of an increase of the rate of termination of the chain reaction due to the scavenging effect of OH radicals caused by Br-.