Nucleophilic substitution in the side chain of 5-membered heterocycles—I : Reactions of furfuryl, 2-thenyl and benzyl chlorides with aniline in acetonitrile and in benzene

The reaction kinetics of furfuryl, 2-thenyl and benzyl chlorides with aniline has been studied in acetonitrile and benzene solutions, The reactions are third order overall, first order with respect to the chloromethyl compound and second order with respect to aniline. In benzene solutions the kinetics at high aniline concentrations (≥0·8 M) deviate from the third order equation. The remarkable increase in k₃, not depending on the polarity of the reaction medium, is ascribed to the association of aniline in benzene. The reactions in acetonitrile are faster than in benzene; in both solvents furfuryl chloride reacts faster than 2-thenyl and benzyl chlorides, the latter being the less reactive. The large negative activation entropies, consistent with an ordered and highly polar transition state, determine the observed rate sequence. The rate constants were correlated with the polar constants for heterocycles.