Nitration and oxidation of substituted benzaldehydes in solutions of dinitrogen pentaoxide or nitronium trifluoromethanesulfonate in nitric acid

Abstract

The competition between oxidation to the corresponding benzoic acid and nitration in the aromatic ring of some substituted benzaldehydes has been probed by kinetic and product studies. Nitrodeformylation was not detected. 4-Carboxybenzaldehyde is nitrated but nitro- and dinitro-substituted benzaldehydes are predominantly oxidised. Rapid reversible gem-dinitrate formation occurs in concentrated solutions of dinitrogen pentaoxide in nitric acid, and the equilibrium extent of formation of dinitrato-(4-nitrophenyl)methane from 4-nitrobenzaldehyde is reported. Both species are oxidised in processes in which α-hydrogen loss is at least partially rate determining, as shown by kinetic hydrogen isotope effects. There is evidence for the intrusion of radical mechanisms in concentrated solutions of dinitrogen pentaoxide.