The reaction of carbon disulfide and o-phenylene diamine catalyzed by tetrabutylammonium bromide (QBr) was carried out in an alkaline solution of KOH/organic solvent two-phase medium. The main reaction was observed to occur in the organic solution in which the reaction of the active intermediate (HOCS(2)(-)Q(+)) and o-phenylene diamine (C6H4(NH2)(2)) is the rate-determining step of the entire reaction. Water was added to dissolve the solid potassium hydroxide prepared for the reaction with QBr catalyst to form the reactive tetrabutylammonium hydroxide (QOH). The reaction rate is dramatically enhanced by adding an appropriate amount of potassium hydroxide and tetrabutylammonium bromide. The water-soluble potassium salt of 2-mercaptobenzimidazole (product) is easily separated through precipitation by adding an acidic compound using o-phenylene diamine of a limited amount. A reaction mechanism is proposed to account for the kinetic model. The reaction is simplified and described by a pseudo-first order rate law. The effects of the operating conditions and parameters are studied. Satisfactory explanations are obtained describing the enhancement of the reaction of carbon disulfide and o-phenylene diamine by tetrabutylammonium bromide, which exceeded the enhancement with potassium hydroxide alone.