Specific features of oxidation of ferrocenylacetic acid with molecular oxygen in the absence and in the presence of Brønsted acids

Abstract

Comparative analysis of the specific features of autooxidation of ferrocenylacetic acid (FcCH2COOH) in organic solvents at 30–50°C in the absence and in the presence of trifluoroacetic acid (processes 1 and 2 respectively) was carried out. It was shown that both reactions proceed as a sequence of two macrostages, the molecular and the chain radical oxidation of the metal complex. Introduction of acid (HX) in the reaction mixture leads to a significant increase in the rate of the process, in the amount of oxygen per one mole of metal complex absorbed by the reaction mixture, and to the change in the yields of main reaction products like hydroxymethylferrocene, formylferrocene, ferrocenylpyruvic acid, and CO2. On the basis of results of the investigation performed, the kinetic and thermodynamic analysis of primary reactions of the process probable mechanisms of both macrostages in both processes were suggested. The significant effect of approach and orientation on the rate of the molecular oxidation of complex as the bifunctional reagent was noted. An assumption was made that the acid takes place in the molecular oxidation of FcCH2COOH according to two alternative mechanisms differing by the way of its coordination with O2 and the metal complex in the prereactional intermediates. The oxidative transformation of these intermediates leads to the generation of radicals of different nature, Fc+·CH2C(O)OO· and HO2· which initiate the chain radical oxidation of the metal complex.