Coupled Catalytic and Autocatalytic Oxidation Reactions Linked by a Feedback Reaction Part 1. The Mechanism of the Superadditive Oxidation of p-Phenylenediamines by Iron(III)aq and Hexacyanoferrate

Kinetics and Mechanism of the Heterogeneous Oxidation of N-Substituted-p-Phenylenediamines over Supported Zinc Oxide

The kinetics and mechanism of the oxidation of some N-substituted-p-phenylenediamines over ZnO supported with some transition metal sulfates were investigated at 25 °C. The rate of reaction decreased in the following order; N,N,N´,N´-tetramethyl-p-phenylenediamine, TMPPD > N,N-diethyl-p-phenylenediamine, DEPPD > N,N-di-methyl-p-phenylenediamine, DMPPD, due to the positive inductive effect of alkyl groups. For the oxidation of DEPPD, the rate of reaction was observed to have the order: Cu(II) > Fe(III) > Ni(II) > Cr(III) > Mn(II) > Co(II). The initial rate of reaction was decreased with decreasing pH as a result of the protonation of the diamine nitrogen atoms. Also, it follows a first order dependence of the initial concentration of the diamine and attained a maximum at higher concentrations. Moreover, it increased with increasing amount of the oxidant. Greater amounts, however, reduced the rate of reaction as a result of the adsorption of the formed p-semiquinonediimine, S