Chemistry of isocyanides. Part 2. Nucleophilic addition of hydroxide to aromatic isocyanides in aqueous dimethyl sulphoxide. Correlations of rate with a nucleophilicity function

Abstract

A range of aromatic isocyanides has been found to undergo nucleophilic addition of hydroxide in aqueous dimethyl sulphoxide (DMSO) over the composition range 0–98.67 mol% DMSO. The rate of reaction increases as the aqueous content of the solutions is decreased. At compositions low in DMSO correlations of log k_obs with H_–+ log a_w are linear with slopes of 0.47–0.50, while at higher levels of DMSO correlations are also linear, but with slopes of 0.73–0.90. The results are discussed in terms of a solvent-induced switch from a concerted to a stepwise mechanism. An unusually enhanced reactivity of m-nitrophenyl isocyanide is observed and possible explanations for this are considered.