Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 5. Solvent effects

Abstract

First- and second-order rates for the reactions of 1-methyl-, 1-isopropyl-, 1-s-butyl-,1-benzyl-, and 1-p- methoxybenzyl-2,4,6-triphenylpyridiniums with piperidine in chlorobenzene in protic and dipolar aprotic solvents are reported. For the 1-isopropyl, 1-s-butyl and 1-p-methoxybenzyl derivatives the bimolecular reaction is accompanied by a unimolecular process in all solvents. Second-order rate constants for the 1-methyl and for the 1-benzyl compounds are correlated with the E_T solvent parameter. Principal component analysis of second-order rates provided a three-component model. The first component differentiates aprotic solvents from protic ones, while the second component is linearly related to the basicity parameter B for aprotic solvents.