Ramdon, Dwight C.; Dixon, Donovan A.; Dasgupta, Tara P.
Author Affiliation, Ana.
Department of Chemistry
Mechanism of reduction of chromium (VI) ion by 2-mercaptosuccinic acid in aqueous solution
Inorganica chimica acta
Date of Publication
The kinetics of the reduction of the chromium (VI) ion by 2-mercaptosuccine acid (thiomalic acid) were studied by rapid scanning stopped flow spectrophotometry. The conditions used were [Cr(VI)]T = 0.20 mM, [MSA]T = 5-90 mM, 3.0 £ pH £ 5.6 in citric acid-phosphate buffer, or 3.3 £ pH £ 5.4 in 0.40 M acetic acid-acetate buffer, 20.0 £ T £ 35.0 °C at I = 0.50 M (NaClO4). Spectrophotometric titration at 350 nm indicates the stoichiometry of the reaction to be 1:3. The kinetics of both formation and decay of the intermediate chromium (VI) thioester were followed at lmax=425 nm and rate expressions, specific rate constants and corresponding activation parameters were derived from the proposed mechanism. The acetic acid-acetate buffer was found to catalyze the formation but not the decay rate of the intermediate. The citric acid-phosphate buffer and dissolved oxygen did not have any significant effect on the reaction rates. The justification of the mechanism was discussed in terms of standard biological conditions.....