Nitrate esters as intermediates in the oxidation of toluenes by ammonium cerium(IV) nitrate

Abstract

Reports have appeared that substituted toluenes can be oxidised by ammonium cerium(IV) nitrate in dilute nitric acid solution to the corresponding benzaldehydes in high yield. We find that the major primary reaction product is a benzyl nitrate ester, and that the outcome of the reaction is dependent on the rate of hydrolysis of this nitrate ester, which is followed by rapid oxidation of the substituted benzyl alcohol. Aliphatic hydrocarbon solvents greatly reduce the concentration of nitrate ester in the aqueous phase and prevent hydrolysis. In the absence of solvents toluene is eventually oxidised to benzaldehyde but o-xylene gives 2-methylbenzyl nitrate as the major oxidation product. The nitrate insertion reaction acts in parallel with a hydroxide insertion reaction which yields a substituted benzyl alcohol as an alternative primary reaction product : the small amount of o-tolualdehyde obtained from the oxidation of o-xylene is probably formed from this latter reaction rather than by hydrolysis and further oxidation of the nitrate ester.