CHEMISTRY OF ISOCYANIDES .2. NUCLEOPHILIC-ADDITION OF HYDROXIDE TO AROMATIC ISOCYANIDES IN AQUEOUS DIMETHYL-SULFOXIDE - CORRELATIONS OF RATE WITH A NUCLEOPHILICITY FUNCTION

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.