Mesoionic compounds. Part IV. Acid catalysed hydrolysis and protonation behaviour of 4,5-diarylisosydnones

Abstract

The acid catalysed hydrolyses of some 5-(para-substituted phenyl)-4-phenylisosydnones have been studied in aqueous solutions of mineral acids over a wide range of acidities. For perchloric and sulphuric acids plots of the first-order rate coefficients k₁ against [H⁺] show maxima which are caused by extensive protonation of the substrate. Analysis of these data by Bunnett and Bunnett–Olsen criteria, solvent deuterium isotope effects, and substituent effects are consistent with an A-2 mechanism.