连续流硝酸氧化制备2,4二氯邻硝基苯甲酸

Continuous flow process for the preparation of 2,4-dichloro-o-nitrobenzoic acid through nitric acid oxidation

釜式反应器中2,4二氯邻硝基甲苯硝酸氧化制备2,4二氯邻硝基苯甲酸的过程存在放热量大、腐蚀性强、安全性差、反应周期长、产物收率低等诸多问题。本文开发出一种连续流制备2,4二氯邻硝基苯甲酸的新工艺,考察反应温度、停留时间、硝酸质量分数、原料质量比、体系压力对氧化过程的影响。结果表明:在温度180℃、总流速2 mL/min、硝酸与2,4二氯邻硝基甲苯质量比5∶1、停留时间45 min、体系压力2.5 MPa时,2,4二氯邻硝基苯甲酸的纯度约为99%,硝酸的质量分数可降低至35%,氧化反应速率可提高20倍,反应过程稳定,选择性和转化率分别为98%和99%。

The preparation of 2,4-dichloro-o-nitrobenzoic acid by nitric acid oxidation of 2,4-dichloro-o-nitrotoluene in the batch reactor exhibits problems with high heat release,strong corrosion,poor safety,long reaction cycle and low product yield.In this paper,a new process of continuous flow preparation of 2,4-dichloro-o-nitrobenzoic acid was developed.The effects of reaction temperature,residence time,nitric acid mass fraction,mass ratio of raw material and system pressure on oxidation process were investigated.Results revealed that the optimal reaction conditions was that reaction temperature of 180℃,total flow of 2 mL/min,mass ratio of nitric acid to 2,4-dichloro-o-nitrotoluene of 5∶1,residence time of 45 min,and system pressure of 2.5 MPa.In general,the continuous flow process featured with high conversion and selectivity reaction(98%and 99%,respectively)with a 35%(mass fraction)dilute nitric acid,and the purity of 2,4-dichloro-o-nitrobenzoic acid was 99%,while the oxidation reaction rate could be increased by 20 times.