Synthesis of 2-mercaptobenzimidazole [ MBI) was carried out by reacting o-phenylene diamine and carbon disulfide catalyzed by tertiary amine ( R , N ) in a homogeneous solution Dichloromethane. chlorobenzene, chloroform, toluene, and benzene were employed as the organic solvent. The advantage of using such organic solvents is that MBI precipitates from the organic solution Only mechanical separation processes, such as filtration and centrifugation, can be used to obtain the MBI product of high purity. Based on the reaction mechanism, a kinetic model, which included two steps of reactions in the organic phase, was proposed, i.e ( i ) a chemical equilibrium of the reaction of CS, and R,N to produce an active intermediate [ R, N-CS,) was built up within a short period of time and [ i i ) this active intermediate further reacted with o-phenylene diamine to produce the desired MBI product A combination of the zeroth order and pseudo-first-order rates law was used to describe the kinetic data. However, the reaction follows pseudo-first-order rate law at higher temperature, and the reaction follows zeroth-order rate law at lower temperature. The effects of the operating conditions on the conversion of o-phenylene diamine were also investigated C I 1996 lohn Wiiey G Sons. Inc