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

초록

Nucleophilic addition reactions of benzylamines(BA) to benzylidenemalonitrile(BMN) have been studied in acetonitrile at 15.0℃. 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 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-bondes, four-center cyclic transition state.