Specific and non‐specific solvent effects on aromatic nucleophilic substitution. Kinetics of the reaction of 1‐fluoro‐2,6‐dinitrobenzene and homopiperidine in binary solvent mixtures

Abstract

AbstractThis paper presents a comparative study of the solvent effects on the kinetics of the reactions between 1‐fluoro‐2,6‐dinitrobenzene and hexahydro‐1H‐azepine in ethyl acetate + chloroform or acetonitrile and acetonitrile + chloroform binary solvent mixtures. The purpose was to asses the contribution of each molecular‐microscopic solvent property to the overall solvation effect of the reaction critical state. The influence of the dipolarity/polarizability, hydrogen‐bond donor acidity and hydrogen‐bond acceptor basicity of the solvent mixtures on the reaction rate was analyzed by the application of the multiparametric approach of Kamlet, Abboud and Taft. The evaluation of the correlation coefficients shows that the solvation effects are dominated by the non‐specific interactions. Moreover, the incidence of the hydrogen‐bond acceptor solvent ability is more important than that corresponding to the hydrogen‐bond donor character, except for the reactions that manifest kinetic retarding effects. The influence of the solvation effects on the base catalysis was analyzed, describing the response patterns of the partial rate coefficients to the mixture composition and also to each solvent property. The application of a preferential solvation model to the kinetic results yields information on the preferential solvation of the reaction critical state by any of the pure solvents, or by the hydrogen‐bonded complexed media. Copyright © 2002 John Wiley & Sons, Ltd.