Permanganate Oxidation mechanisms of Alkylarenes

Permanganate oxidation of benzaldehyde and p-nitrobenzaldehyde goes by two paths, i.e. a major one which is responsible for the normal oxidation giving good second order kinetic and minor path which involves a very small percent of a radical species formed by hydrogen atom abstraction by the permanganate ion. A mechanism involving Hydrogen atom abstraction by permanganate from the alkoxide ion is thus favoured in the permanganate oxidation of p-nitrophenyltrifluoromethylcarbinol. Oxidations of alkylarenes by nBu4NMnO4 in toluene solvent. Toluene is oxidized to benzoic acid and a small amount of benzaldehyde.The kinetics of the reactions, monitored by UV/vis spectrometry; show that the initial reactions are first order in the concentrations of both nBu4NMnO4 and substrate. No induction periods are observed. The rate-limiting step in all of the reactions is hydrogen atom transfer from the substrate to a permanganate oxo group. The ability of permanganate to abstract a hydrogen atom is explained on the basis of its ability to form an 80 ± 3 kcal/mol bond to H•, as calculated from a thermo chemical cycle. Rates of H• abstraction by nBu4NMnO4 correlate with rates of abstraction by oxygen radicals.