Kinetics and mechanism of oxidation of 3,6-dioxa-1,8-octanedithiol and dl -dithiothreitol by a platinum(IV) complex

A Pt(IV) complex [PtCl 2 (en)(heda)]Cl 2 (heda = N -(2-hydroxyethyl)-ethylenediamine) has been synthesized and characterized by ESI–MS, 1 H NMR, elemental analysis, and X-ray crystal structure analysis. Oxidations of dithiol compounds 3,6-dioxa-1,8-octanedithiol (DODT) and dl -dithiothreitol (DTT) by this complex were studied. The oxidation products were characterized as ten- and six-membered ring compounds for DODT and DTT, respectively, both containing an intramolecular disulfide bond. The kinetics of the oxidation reactions was followed by stopped-flow spectrophotometry over a wide pH range. The oxidations display an overall second-order character, being first-order each in [Pt(IV)] and in [dithiol]. A mechanism involving three parallel rate-determining steps is proposed, and the rate constants of the rate-determining steps have been evaluated.