(509au) Kinetic Study Of S-Alkylation Of 2-Mercaptobenzimidazole Catalyzed By Tetrabutylammonium Bromide

The S-alkylation of 2-mercaptobenzimidazole (MBI) by á-bromo-m-xylene under phase transfer catalytic reaction condition was successfully carried out in an alkaline solution of KOH/organic solvent two-phase medium. No product was obtained from N-alkylation during or after the reaction period by using a limited quantity ofá-bromo-m-xylene. The reaction is greatly enhanced by adding a small amount of tetrabutylammonium bromide (TBAB) and/or potassium hydroxide. Based on the experimental evidence, a rational reaction mechanism is proposed. A kinetic model is derived from which a pseudo-steady-state hypothesis (PSSH) is applied to the reaction system. The kinetic behaviors and the characteristics of the reaction are sufficiently described by the pseudo-first order rate law. There is detailed investigation for the effects of the reaction conditions, including the agitation speed, the amount of TBAB catalyst, the amount of KOH, quaternary ammonium salts, volume of water, volume of dichloromethane, amount of 2-mercaptobenzimidazole, the amount of á-bromo-m-xylene, inorganic salts, organic solvents and temperature on the conversion of the reactant and the apparent rate constants (kapp). Rational explanations satisfactorily account for the observed phenomena from experimental results.