Kinetics and mechanism of the addition of benzylamines to β-nitrostyrenes in acetonitrile

Abstract

The kinetics and mechanism of the addition of benzylamines to β-nitrostyrenes in acetonitrile at 25.0 °C have been investigated. The addition reaction proceeds by two pathways, uncatalyzed (k₂) and catalyzed (k₃) paths. The kinetic isotope effects (k_H/k_D) involving deuterated benzylamine nucleophiles support the proposal that proton transfer from the amine to the β-carbon occurs concurrently with addition of the amine to the α-carbon. The transition state is predicted to have four- (I) and six-membered (II) cyclic structures for the k₂ and k₃ paths, respectively, with a tighter and more rigid structure for the uncatalyzed process. The cross-interaction constants, ρ_XY, are negative (−0.90 and −0.54 when the fall-off factor is taken into account) and the magnitude is larger for the uncatalyzed path than for the normal backside attack S_N2 reaction of benzyl derivatives with anilines (−0.6 to −0.8).