Nitration process of 2-(2,4-dichlorophenyl)-4-(difluoromethyl)-5-methyl-1,2,4-triazol-3-one in a microreactor

In a continuous flow microreactor system, a continuous nitration process of 2-(2,4-dichloro-5-nitrophenyl)-4-(difluoromethyl)-5-methyl-1,2,4-triazol-3-one which is the key intermediate for the synthesis of important triazolinone herbicide Sulfentrazone was developed. The effects of molar ratio of mixed acids, molar ratio of nitric acid to substrate, reaction temperature, total flow rate and residence time in the microreactor on nitration reaction were studied. The results showed that when the flow rate of the material was 60 mL/min, the molar ratio of nitrate to sulfur mixed acid was 1:6, the molar ratio of nitric acid to raw material was 1.1:1, the reaction temperature was 60 ℃, and the residence time was 30 s, the product can be obtained in 97% yield. Compared with the results of nitration process using traditional batch reactors, the use of continuous flow microreactors improved reaction efficiency and achieved higher yields. A characterization kinetics study was conducted on this reaction, and the pre-exponential-factor and activation energy for 2-(2,4-dichlorophenyl)-4-(difluoromethyl)-5-methyl-1,2,4-triazol-3-one nitration were obtained. The activation energy of the reaction is 40.204 kJ/mol. The continuous flow microreactor system greatly increased liquid-liquid two phases mass transfer efficiency, while accurately controlling the reaction temperature and residence time in the reactor.