Continuous-flow diazotization of slightly soluble dichlorobenzidine

3, 3'-Dichlorobenzidine (DCB) diazonium salt aqueous solution was synthesized from slightly soluble 3,3'-dichlorobenzidine hydrochloride by continuous-flow method via a collision mixer. The concentration of DCB diazonium salt was evaluated by spectrophotometry and the yield of diazotization was calculated. The effects of mass concentration of 3,3'-dichlorobenzidine hydrochloride, feed temperature, flow rate, dosage of hydrochloric acid on the yield of diazotization were investigated. A yield of 98.3% was achieved under the optimized reaction conditions of mass concentration of DCB 70 g/L, feed temperature 20℃, flow rate 1.1 m/s, n(HCl):n(DCB)=4:1. Compared with a batch process, the continuous-flow process requires less hydrochloric acid, improves reaction efficiency, and can carry out at room temperature (20℃), which significantly reduces energy consumption and has great potential in industrial applications. © 2020, Editorial Office of FINE CHEMICALS. All right reserved.