The Kinetics of the Reaction between the Chromium(III) Ion and the Ethylenediamine-N,N,N′,N′-tetraacetate Ion in the Presence of Hydrogen Peroxide

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Abstract
The rate of the reaction between chromium(III) ion and ethylenediamine-N,N,N′,N′-tetraacetate was found to be accelerated upon the addition of a large excess of hydrogen peroxide. Under such a condition the rate of CrIII(edta)(H2O)− formation shows a first-order dependence on the concentrations of hydrogen peroxide and chromium(III) ions, but is independent of the concentration of EDTA. The rate of CrIII(edta)(H2O)− formation catalyzed by the hydrogen peroxide increases with an increase in the pH and decreases with an increase in the acetate ion concentration. The kinetic study suggested that the initiation of the reaction takes place as follows: Cr(III)+H2O2→Cr(IV)+OH·+OH− The reaction mechanism of the hydrogen-peroxide catalysis is discussed in terms of the formation of the chromium(IV)– and /or the chronium(V)–EDTA complex in the course of the reaction. It was found that monohydroxochromium(III) is much more reactive than the chromium(III) ion toward hydrogen peroxide.