Kinetics of oxidation of Cr(III)-organic complexes by H2O2

Oxidation of Cr(III)-organic complexes by H2O2 was examined in laboratory scale experiments. Ascorbate, glutamate, histidine, cysteine, serine, mandelate, citrate, pyruvate, oxalate and EDTA were selected as model organic ligands. The oxidation of Cr(III)-organic complexes by H2O2 was first order with respect to [OH-] (pH 7-8.8), [H2O2] (from 0.0002 to 0.3 M), and [Cr(III)-L] (where L is the organic ligand). The concentration of Cr(III) was from 19 mM to 288 mu M and organic ligands ranged from 76 to 1152 mu M. Oxidation of Cr(III)-organic complexes by H2O2 was found to be significantly slower than oxidation of inorganic Cr(III) species. At pH 8.0 and 25 degrees C and [H2O2] 0.1 mu M, the t(0.5) varied from 51 years (Cr(III)-mandelate complex) to 3164 years (Cr(III)-histidine complex) except for Cr(III)-cysteine and Cr(III)citrate complexes. When [H2O2] is lower than 0.02 M, The oxidation of most Cr(III)-organic complexes is extremely slow.