STOPPED-FLOW KINETIC-STUDY OF THE FORMATION AND DECAY OF THE 4,4'-(DIMETHYLAMINO)DIPHENYLMETHANE RADICAL-CATION IN AQUEOUS-SOLUTION

The oxidation kinetics of 4,4'-(dimethylamino)diphenylmethane (DMADPM) by Ce-IV, by the oxoanions, MnO4- and Cr2O72-, by peroxides, namely, peroxomonosulfate, peroxodisulfate and H2O2, and by halogens viz., Cl- 2, Br-2 and I-2, to the radical cation, DMADPM(.+) along with further oxidation to the product monocation DMADPM(+) have been studied by the stopped-flow technique. The first- and second-stage oxidations have b een followed by monitoring the formation and decay of DMADPM(.+) via t he absorption at 610 nm. Both formation and decay of DMADPM(.+) obey t otal second-order kinetics, first-order each with respect to [DMADPM] or [DMADPM(.+)] and [oxidant]. The effects of pH and temperature have also been investigated on the formation and decay of DMADPM(.+) and th e kinetic and transition-state parameters have been evaluated and disc ussed with suitable reaction mechanisms. DMADPM(.+) was converted back into the DMADPM by the following reducing agents; ascorbic acid, dith ionite, metabisulfite, sulfite and thiosulfate. The rate constants for these reactions were estimated. The experimentally determined rate co nstants for the oxidative electron-transfer reactions were correlated theoretically using Marcus theory and the observed and calculated rate constants show good agreement.