Reactivity of ions and ion pairs in the nucleophilic substitution reaction on methyl p-nitrobenzenesulfonate

Abstract

Nucleophilic substitution on methyl p-nitrobenzenesulfonate has been studied with a series of chloride salts with different structures and solvations: Bu₄NCl, PPNCl or KCl complexed by 18-crown-6 or Kryptofix 2,2,2 as well as with a bromide salt (PPNBr) for comparison purposes. The rate constants and the activation parameters are in accordance with an S_N2 mechanism. The treatment of the data, following the Acree equation, shows that the process takes place by way of two reaction paths: the first, due to the chloride ion, has the same rate for all the salts, while the second slower path, involving the ion pair, has a rate related to the dissociation constant of the salts.