Mechanism of the liquid phase homogeneous oxidation of alkylaromatic hydrocarbons by cobalt salts

Abstract

The mechanism of the liquid phase oxidation of alkylaromatic hydrocarbons by molecular oxygen in the presence of cobalt as catalyst, is discussed with special reference to the oxidation of durene. In the absence of strong acid, pyromellitic acid produced in the reaction is associated with cobalt as insoluble aggregates of complex structure. Cobalt atoms are themselves associated to give either highly active cobaltic species or mixed-valence species which are less active as oxidizing agents but which appear to be involved in the regeneration of cobalt(III). The action of promoters such as acetaldehyde or methylethylketone in such reactions is discussed. In the presence of strong perhalogenated carboxylic acids, new active cobaltic species are produced wherein these strong acids are subtituted for pyromellitic acid which precipitates as such from the reaction mixture. Under such conditions, durene is readily transformed into pyromellitic acid in an almost quantitative yield at temperatures lower than 100°C.