Molecular-Radical Catalysis of the Chain Reaction of Quinone Imine with Hydroquinone under the Action of Aromatic Amines

Abstract

Secondary aromatic amines are catalysts of the chain reaction (v = 103 units) of N-phenyl-1,4-benzoquinone monoimine with 2,5-di-tert-butyl-1,4-hydroquinone. A complex mechanism of amine catalysis reveals that the rate of the chain reaction may increase, decrease, or remain unchanged in the presence of these compounds. In that case the product composition does not change, and amines are not consumed. The effects of temperature and the nature of para substituents (six species) on the activity of aromatic amines as catalysts were studied. A mechanism was proposed for the catalytic reaction; it implies the coupled occurrence of chain and catalytic processes. An expression for the rate of the catalytic reaction was obtained. The rate constants of individual steps with the participation of a catalyst and its radicals were calculated using the method of crossing parabolas. With the use of these data, a theoretical calculation of the dependence of the reaction rate on catalyst concentration was performed; the results were in good agreement with experimental data. The mechanism of the catalytic reaction was discussed; the similarities and distinctions between this mechanism and the mechanisms of other coupled chain reactions were demonstrated.