Ravi R.,Osmania University |
Sanjeev R.,Mizan Tepi University Tepi |
Jagannadham V.,Osmania University
International Journal of Chemical Kinetics | Year: 2013
The rates of reactions of N-substituted benzyl amines with benzyl bromide were measured using a conductivity technique in methanol medium. The reaction followed a total second-order path. The end product of the reaction is identified as dibenzyl alkyl amine (C6H5CH 2N(R)CH2C6H5). The rates increased with a decrease in the electron-donating capacity or with an increase in the Taft σ* value of electron-donating alkyl substituents (R) such as t-butyl (σ* = -0.3), i-propyl (σ* = -0.19), n-butyl (σ* = -0.13), and ethyl (σ* = -0.1) on nitrogen of the amine until the Taft σ* value becomes zero for the methyl group (σ CH 3* = 0.00), and then the rates decreased with an increase in the electron-withdrawing capacity or with an increase in the Taft σ* value of electron-withdrawing substituents (R) such H and C6H 5 (σH* = 0.49 and σC6H5= 0.6). The locus of the Taft polar free energy relationship has a maximum near the point for N-methyl benzyl amine, showing that there is a sharp change in the rate-determining step. A mechanism involving formation of an SN2-type transition state between the amine nucleophiles and the benzyl bromide and its subsequent decomposition is proposed. Activation parameters were calculated and are discussed. © 2013 Wiley Periodicals, Inc.