OXIDATION OF THIOGLYCOLIC ACID AND GLUTATHIONE BY (TRANS-CYCLOHEXANE-1,2-DIAMINE-N,N,N',N'-TETRAACETATO)MANGANATE(III) IN AQUEOUS-MEDIA

The kinetics of the electron-transfer reactions of the manganese(III) complex of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetate (cdta4-) with two thiols thioglycolic acid and glutathione has been investigated at 30-degrees-C in aqueous media in the range pH 2.0-10.33 with varying reductant concentrations at constant ionic strength, I = 0.20 mol dm-3 (NaClO4). The reactions are first order both in complex and reductants and follow the general rate law, -d[Mn(III)(cdta)-]/dt = k(obs)[Mn(III)(cdta)-] = k[Mn(III)(cdta)-][reductant]. Both the reactions have been assumed to proceed via an inner-sphere mechanism with support for this coming from the observation of a rapid initial increase in absorption followed by a slower decay. This indicates the formation of an inner-sphere associated species which decomposes unimolecularly leading to the transfer of the electron from the thiol to the oxidant. Additional support for this mechanism comes from a comparison of the water-exchange rate of [Mn(cdta) (H2O)]- with the higher limit of the electron-transfer rates. The pH-rate profiles are bell-shaped curves and were successfully modelled by fitting the experimental data to a computer-fitted program thereby evaluating the reactivity of all the reacting species of the reductants.