Semi‐continuous gas‐liquid catalyzed reaction of o‐phenylene diamine and carbon disulfide by tertiary amines

Abstract

A semi‐continuous reactor was used to carry out the catalyzed reaction of o‐phenylene diamine and carbon disulfide to synthesize 2‐mercaptobenzimidazole (MBI) in a gas‐phase/alkaline solution two‐phase medium. Tertiary amines, which are relatively less expensive than quaternary ammonium salts, were used as the catalysts to promote the reaction rate. In addition, gas‐phase carbon disulfide of higher temperature was introduced into the reactor to react. 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. Also, the reaction is carried out at a higher rate in the absence of potassium hydroxide. Carbon disulfide, which is first dissolved in the organic phase, reacts with tertiary amine in the organic‐phase solution to produce an active intermediate (R₃N‐CS₂). Second, this active intermediate (R₃N‐CS₂) further reacts with o‐phenylene diamine to produce the desired product MBI. Based on the experimental observation, a reaction mechanism is proposed, and a kinetic model, which considers the two‐step reaction is developed. A pseudo‐first order rate law is sufficient to describe the reaction. The effects of the reaction conditions, including the amount of tertiary amines (TEA, TPA and TBA) and ammonia (NH₃), agitation speed, initial concentration of carbon disulfide, flow rate of gas phase, amount of o‐phenylene diamine and temperature, on the apparent rate constant (k_app) are investigated in detail.

Key words:

• synthesis of 2‐mercaptobenzimidazole
• gas‐liquid reaction
• semi‐continuous reactor
• catalyzed reaction

Notes

Corresponding author. (Tel: [phone] ext. 4160; Fax: [phone]; Email: [email protected])