KINETICS AND MECHANISM OF OXIDATION OF TRIS(ETHYLENEDIAMINE)-CHROMIUM(III) BY N-BROMOSUCCINIMIDE

In aqueous solutions, [Cr(en)(3)](3+) aquates to [Cr(en)(2)(H2O)(2)](3+). A kinetic study of the oxidation of [Cr(en)(3)](3+) by N-bromosuccinimide (NBS) in aqueous solutions and water-alcohol solvent mixtures was performed. The reaction is first order with respect to both total [Cr-III] and [NBS]. The rate is inversely dependent upon [H+] in the 7.0-7.9 pH range, and varies with the co-solvent according to the order: MeOH > EtOH > PrOH. An appropriate mechanism, in which the deprotonated [Cr(en)(2)(OH)(H2O)](2+) is the reactive species, is suggested. Thermodynamic activation parameters have been calculated.