Stopped-flow kinetic investigations of one-electron transfer reactions of 4,4ʹ-diaminodiphenylmethane and its radical cation in aqueous solution

Abstract

The oxidation of 4,4'-diaminodiphenylmethane (DADPM) by metal ion (Ce⁴⁺); oxoanions [MnO4ˉ and Cr₂O₇²ˉ), peroxides [peroxomonosulfate (PMS), peroxodisulfate (PDS) and H₂O ₂], and halogens [Cl₂, Br₂ and I₂], to the radical cation DADPM^•+, and further oxidation to the product monocation DADPM⁺ by the above mentioned oxidants has been investigated by stopped-flow technique. A probable mechanism has been proposed. The reactions follow a total secondorder kinetics, first-order each with respect to the [DADPM] or [DADPM^•+] and [oxidant]. In addition, the radical cation DADPM^•+oxidizes sulfite (SO₃^2-), thiosulfate (S₂O₃^2-), dithionite (S₂O₄^2-) and metabisulfite (S₂O₅^2-)<i> </i>to regenerate the parent compound DADPM. The rate constants for these reactions have also been estimated. Reactivity for the formation of DADPM follows the decreasing order in the case of oxoanions (MnO₄ˉ > Cr₂O₇²ˉ > Ce(IV)) and peroxides (S₂O₈^2-> HSO₅ˉ > H₂O₂) which is in agreement with the redox potentials, while the reactivity trend for halogens is found to be I₂> Br₂ > Cl₂ which is not in agreement with the redox potentials. The observed rate constants for electron transfer have been correlated theoretically using Marcus theory.