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

摘要

The oxidation of 4,4'-diaminodiphenylmethane(DADPM)by metal ion(Ce~(4+));oxoanions [MnO_4~-and Cr_2O_7~(2-)],peroxides [peroxomonosulfate(PMS),peroxodisulfate(PDS)and H_2O_2],and halogens [Cl_2,Br_2 and I_2],to the radical cation DADPM~(centre dot+),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 second-order kinetics,first-order each with respect to the [DADPM] or [DADPM~(centre dot+)] and [oxidant].In addition,the radical cation DADPM~(centre dot+)oxidizes sulfite(SO_3~(2-)),thiosulfate(S_2O_3~(2-)),dithionite(S_2O_4~(2-))and metabisulfite(S_2O_5~(2-))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(MnO_4~ > Cr_2O_7~(2-)> Ce(IV))and peroxides(S_2O_8~(2-)> HSO_5~-> H_2O_2)which is in agreement with the redox potentials,while the reactivity trend for halogens is found to be I_2 > Br_2 > Cl_2 which is not in agreement with the redox potentials.The observed rate constants for electron transfer have been correlated theoretically using Marcus theory.