Kinetics and mechanism of the formation of diaryliodonium salts by sulphuric acid catalysed reaction of substituted phenyl iodosoacetates with aromatic hydrocarbons in acetic acid solution

Abstract

The reaction of substituted phenyl iodosoacetates with toluene under pseudo-first-order conditions is first-order in both components. The marked catalysis by sulphuric acid is explicable by two mechanisms: one depends on the ion pair Phl⁺HSO₄, HSO₄^– and involves base-catalysis, the other on ionisation parallel to the J₀ function. There is a primary hydrogen isotope effect and the reaction is highly substrate-selective between toluene and benzene. The isomer specificity of the reaction is attributed to different stabilisation of the Wheland intermediates for ortho- and para-substitution rather than to steric effects.