Quantitative approach to the Menschutkin reaction of benzylic systems

Article abstract of DOI:10.1002/poc.574

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_N2 reactions. In particular, the reaction of strongly activated benzyl derivatives with tertiary amines in acetonitrile reveals a more advanced bond breaking like S_N1 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