Oxidation of thiocyanate with H2O2 catalyzed by [RuIII(edta)(H2O)]−

Abstract

The [Ru^III(edta)(H₂O)]⁻ (edta⁴⁻ = ethylenediaminetetraacetate) complex is shown to catalyze the oxidation of thiocyanate (SCN⁻) with H₂O₂ mimicking the action of peroxidases. The kinetics of the catalytic oxidation process was studied by using stopped-flow and rapid scan spectrophotometry as a function of [Ru^III(edta)], [H₂O₂], [SCN⁻], pH (3.2–9.1) and temperature (15–30 °C). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which hydrogen peroxide reacts directly with thiocyanate coordinated to the Ru^III(edta) complex. Catalytic intermediates such as [Ru^III(edta)(OOH)]²⁻ and [Ru^V(edta)(O)]⁻ were found to be non-reactive in the oxidation process under the specified conditions. Formation of SO₄²⁻ and OCN⁻ was identified as oxidation products in ESI-MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented.