A Kinetic Study of the Oxidation of Hydroxo(ethylenediaminetetraacetato)chromate(III) and Hydroxo[N'-(2-hydroxyethyl)ethylenediamine-N, N, N'triacetato]chromate(111) by Hydrogen Peroxide in Aqueous Ammonia

Abstract

The kinetics and mechanism of the oxidation of hydroxo(ethylenediaminetetraacetato)chromate (III) (1) and hydroxo[N'-(2-hydroxyl)ethypethylenediamine-N, N, N'-triacetato]chromate(III) (2) by hydrogen peroxide in aqueous ammonia were studied by means of visible, UV and ESR spectroscopy and chemical ananlysis. The results were compared with th ose of previous works dealing with hexaaquachromium(III) and tris(oxalato)chromate(III) complexes. The coordination of H₂O₂ to the complex (1) or (2) is the primary step and CrO₄^-2 is the final product. The coordination rates in these complexes are much greater than that in tris(oxalato)chromate(III), suggesting that the lability of these complexes were enhanced by the existence of hydroxyl. These complexes are oxidized to CrO₄^2- via detectable Cr complexes. The Cr ^v intermediates in this work retain the amino acid ligands of the parent Cr^III complexes and do not seem to coordinate H₂O₂ molecules. The rate-determining step is presumed to be the liberation of ligands from the Cry complexes, followed by the rapid coordination of EH2O2and by further oxidation.