Quantitative approach to the Menschutkin reaction of benzylic systems

Abstract

Abstract The quaternization reactions of substituted (Z)‐benzyl (X)‐benzenesulfonates with substituted (Y)‐pyridines were investigated in acetonitrile at 35 °C. The magnitudes of the Hammett reaction constants ρ X , ρ Y and ρ Z indicate that a stronger nucleophile leads to a lesser degree of bond breaking. In addition, a better leaving group is accompanied by a lesser degree of bond formation. Application of multi‐Hammett interactions, | ρ YZ | >| ρ XY | >| ρ XZ |, predicts that these Menschutkin‐type reactions are dissociative S N 2 reactions. In particular, the reaction of strongly activated benzyl derivatives with tertiary amines in acetonitrile reveals a more advanced bond breaking like S N 1 reactions. The predicted mechanism for the benzylation of pyridines with benzylic systems is evident from More O'Ferrall–Jencks diagram and the semi‐empirical MO calculations with the AM1 method. Copyright © 2002 John Wiley & Sons, Ltd.