The kinetics and mechanism of reactions of nanomolar concentrations of Cu(I) and Cu(II) with H2O2 in 0.7 M NaCl and 2 mM NaHCO3 solution over the pH range from 4.0 � 8.0 have been revisited. While the rate of Cu(I) peroxidation did not vary considerably with varying pH, the kinetics of reaction of Cu(II) with H2O2 showed a strong pH dependence with both the Cu(II) reduction rate and the overall production of oxidative intermediates observed to increase with increasing pH. Measurements of both the formation of the hydroxylated phthalhydrazide chemiluminescent product and the degradation of radiolabelled formate in the absence and presence of known hydroxyl radical scavengers in the Cu(II)/H2O2/O2 system indicated that a higher oxidation state of copper, Cu(III), is the key oxidative intermediate at high pH. At low pH, Cu(III) becomes less stable decomposing by generation of the more reactive hydroxyl radical (HO?) with a rate constant of 100 s-1 at pH 6.5 and 455 s-1 at pH 4.0. A kinetic model has been developed that satisfactorily describes the experimental data over a range of conditions, demonstrating that the hydroperoxyl anion (HO2�) is likely to be the major species that contributes to the observed pH dependency of the oxidative characteristics of the Cu(II)/H2O2/O2 system.

pH-Dependency of oxidative intermediate production by copper-catalyzed decomposition of hydrogen peroxide

248th National Meeting (2014)

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