Kinetics of displacement reactions with pyridines as both leaving group and nucleophile

Abstract

Kinetic rates are determined for the transfer of N-benzyl, methyl, and ethyl groups from a pyridinium cation to a substituted pyridine. Rates (and equilibrium constants) vary significantly with alkyl group, nucleophilicity of the substituted pyridine, and with solvent. Transfer rates for methyl and ethyl depend on the anion showing that the corresponding alkyl iodides and bromides are intermediates. Exploratory experiments designed to catalyse electrophilic substitution in substituted heteroaromatics are described.