Mesoionic compounds. Part 5. The acid-catalysed hydrolysis of diarylisosydnones

Abstract

The acid-catalysed hydrolyses and protonation behaviour of some 4-(para-substituted phenyl)-5-phenylisosydnones have been studied in aqueous solutions of mineral acids. For perchloric and sulphuric acid, plots of the first-order rate coefficients k₁ against [H⁺] show maxima which arise from extensive protonation of the substrates. Analyses of the kinetic data by Bunnett and Bunnett–Olsen criteria are consistent with a bimolecular mechanism. Oxygen-18 tracer studies establish that the acid-catalysed hydrolyses of diarylisosydnones proceed through two different pathways involving attack of water at both the C-5 and the C-2 carbonyl carbon atom.