Kinetics and mechanism of the copper(II) catalyzed oxidation of N-substituted p-phenylenediamines by 2,3,9,10-tetramethyl-1,4,5,7,8,11,12,14-octaazacyclotetradeca-1,3,8,10-tetraenecopper(II)

The kinetics of oxidation of N,N-dimethyl- and N,N,N',N'-tetramethyl-p-phen ylenediamines, to the corresponding semiquinonediimine radical and the quin onediimine, with a macrocyclic copper(II)-complex were studied at pH less t han or equal to 7. Under pseudo-first order conditions, the reaction rate f or the N,N,N',N'-tetramethyl derivative was much faster than for N,N-dimeth yl-p-phenylenediamine, due to the increased probability of electron transfe r. The reaction rate decreases with increasing acidity of the medium as a r esult of protonation of the amine nitrogen atoms. The rate constants and ac tivation parameters were evaluated and the reaction was found to be enthalp y controlled. Furthermore, kinetic measurements revealed a remarkable super additive effect when CuCl2 solution was added, even at concentrations lower than that of the copper complex. This observation was used for the kinetic determination of copper ions at concentrations < 10(-5)M.