Kinetics and Mechanism of the Addition of Benzylamines to Benzylidenemalononitriles in Acetonitrile

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Abstract
Nucleophilic addition reactions of benzylamines (BA) to benzylidenemalononitrile (BMN) have been studied in acetonitrile at 15.0 °C. The rate is first-order with respect to both BA and BMN and no base catalysis is observed. The rate decreases as the electron-withdrawing power of the substituent (Y) in the substrate increases (ρY < 0). This is in contrast to the similar reactions of β-nitrostyrenes (NS) with BAs in acetonitrile and the addition reactions of NS and BMN in aqueous solution (ρY > 0). This sign change of ρY is considered to result from the strong electron-withdrawing power of the (CN)2 group in BMN, which leads to polarization of Cαδ+Cδ-(CN)2 in the transition state. The mechanism of amine addition to BMN in acetonitrile is radically different from that in water. The reaction is predicted to proceed concertedly in a single step with a hydrogen-bonded, four-center cyclic transition state.

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