A fast kinetic study of the formation and decay of N,N,N′,N′-tetramethyl-p-phenylenediamine radical cation in aqueous solution

Abstract

The oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) by S₂O^2–₈, HSO^–₅, H₂O₂, MnO^–₄, Cr₂O^2–₇, Ce^IV and molecular bromine and iodine has been studied. The fast kinetics of formation of the diamine radical cation and its further oxidation at a longer time scale, or with a higher concentration of the oxidants at a shorter time scale, were studied by following the absorption and decay of the radical cation, TMPD^˙+ at 565 or 615 nm. The reaction was found to be second-order overall, but first-order with respect to [TMPD] and [oxidant]. The values of the second-order rate constants for the formation and decay of the radical cation were found to be in line with the oxidation potentials of the oxidants. Reduction of the radical cation by dithionite was found to regenerate the diamine, and the rate constant for this reaction was also determined.