Reaction of o-phenylene diamine and carbon disulfide by potassium hydroxide at higher temperature

A semi-continuous reactor was employed to study the reaction of o-phenylene diamine and carbon disulfide in a gas-liquid (KOH solution/organic solvent) two-phase medium to produce potassium salt of 2-mercaptobenzimidazole (C6H4(N)(NH)CS−K+, ArS−K+). Gas-phase carbon disulfide of higher temperature is continuously introduced to the reactor for reaction. The main advantage of the present system is that the reaction can be carried out at a relatively higher temperature in the semi-continuous reactor. No quaternary ammonium salt is also required to obtain the desired reaction rate and the conversion. The conversion of o-phenylene diamine is low in the absence of potassium hydroxide. Potassium hydroxide does not directly participate in the reaction with o-phenylene diamine and carbon disulfide to synthesize 2-mercaptobenzimidazole (MBI). It merely reacts with the product 2-mercaptobenzimidazole to form ArSK, and reacts with hydrogen sulfide which is a byproduct from the reaction of synthesizing 2-mercaptobenzimidazole. Nevertheless, the reaction is greatly enhanced in the presence of potassium hydroxide of an appropriate amount. Based on the experimental observation, a simple reaction mechanism is proposed, and a pseudo-first-order rate law is employed to describe the reaction. The effects of the reaction conditions, such as the amount of potassium hydroxide, the agitation speed, the initial concentration of carbon disulfide, the flow rate of gas-phase, the amount of o-phenylene diamine and the temperature on the apparent rate constants (kapp) are investigated in detail.