KINETICS OF QUATERNIZATION BETWEEN N, N-DIMETHYLANILINE AND BENZYL CHLORIDE IN POLAR SOLVENTS-A REVISIT TO MENSHUTKIN REACTION

Abstract

This work reports an extension of Menshutkin reaction and involves the studies on kinetics of quaternization reaction between N,N-Dimethylaniline and benzyl chloride in acetone and in other various solvents at 300 K. The progress of the reaction was followed by measuring the conductance of the product formed at regular intervals of time. The effect of [benzyl chloride] and [N,N-Dimethylaniline] on reaction rate was studied under pseudo-first order condition and the rate showed first order dependence on both [benzyl chloride] and [N,N-Dimethylaniline]. The effect of dielectric constant of the medium on reaction rate was studied by employing various solvents such as methyl ethyl ketone, isopropyl alcohol, ethyl alcohol, methyl alcohol and acetonitrile and the rate is found to increase with increase in dielectric constant of the medium. The linear plot with a negative slope on plotting log k2 against 1/D where D is the dielectric constant of the medium indicates the existence of a highly charged or a polar transition state during the progress of the reaction. The quaternization reaction was also carried out at different temperatures so as to compute the various thermodynamic parameters like activation energy, enthalpy of activation, entropy of activation and Gibb’s free energy change. The higher value of activation energy is attributed for a slower reaction which is sterically controlled rather than thermodynamically controlled. The negative value of entropy of activation (ΔS*) indicates some sort of surrendering of disorder in the transition state on its formation which proves that it is highly ordered with sufficient charge separation and polar in character. The product after purification was analysed by melting point and infra-red spectral analysis and is proved to be N-Benzyl-N,N-dimethylphenylmethanaminium chloride. A plausible mechanism in accordance with the obtained experimental results is reported.