Method for purifying pendimethalin

Abstract

The invention discloses a method for purifying pendimethalin, which comprises the following steps of: adding coarse product of pendimethalin, thiocyanate and hydrochloric acid into a reaction container according to a mass ratio of 7-10:1:3-5; performing reflux reaction at the temperature of between 75 and 81 DEG C for 6 to 15 hours under normal pressure, adding the thiocyanate again in the reaction process for continuous reaction until the content of N-nitrosamine compound is less than 10ppm, and taking an oil layer after the reaction is finished; and washing the oil layer with water, alkali and water in turn and controlling the temperature to between 60 and 90 DEG C under the vacuum condition for removing a solvent so as to obtain the pendimethalin. The method for purifying the pendimethalin has the advantages that: due to the existence of the aid thiocyanate, the speed of the reaction for removing the N-nitrosamine compound is high, and the content of the N-nitrosamine compound is less than 20ppm; because the reaction temperature is controlled at the reflux temperature, the method does not need to be operated under the pressure condition, and can reduce the operating difficulty and equipment requirement and improve the operating safety.

Description

technical field [0001] The invention relates to a method for purifying herbicides, in particular to a method for purifying pendimethalin. Background technique [0002] Pendimethalin, its chemical name: N-(ethylpropyl)-3,4-dimethyl-2,6-dinitroaniline; is a dinitroaniline herbicide, applicable Annual grasses and some broadleaf weeds. Because pendimethalin products have good weeding effect and high safety, they have been widely popularized and applied. [0003] The current process uses 3,4-dimethylnitrobenzene as the starting material, undergoes hydrogenation reduction, alkylation reaction with 3-pentanone, nitration reaction, and denitrosation reaction to obtain the product pentamethylpentane spirit. It is recorded in US Patent No. 4,136,117 and US Patent No. 4,621,157 that about 20% of toxic N-nitroso by-products will be produced during the nitration reaction of this process. It is described in Adv. Cancer. Res. 1967.10: 163 (Frontier Cancer Research, October 1967, p. 163...

AI Technical Summary

Problems solved by technology

Relevant scientific research institutions and production enterprises in all countries in the world have conducted research on this. U.S. Patent 5196585 and others have introduced the generation of tissue by-products such as sulfite and dithionate in the nitrification process, but after adopting this method, N- The content of nitrosamine compounds is still more than 10%; U.S. Patent No. 4,136,117 and other reports use sulfamic acid and 37.7% hydrochloric acid to react for 6 hours under the conditions of 80-82°C after nitration, and the content of N-nitrosamine compounds can reach 0.1 %; U.S. Patent US5922915 and other reports increase the temperature of the material to 170~180°C in the presence of urea and nitrogen, which can reduce the content of N-nitrosamine compounds, but cause the decomposition of the target product under high temperature conditions, reducing the product dimethyl The purity of pentane; in the US patent US4391992, 3-pentanone and concentrated hydrochloric acid are used to react with the nitrated material at a temperature of 80-88 °C and a pressure of 1-2 kg / cm 2 The content of N-nitrosamine compounds can be reduced under certain conditions

However, due to the requirement to reach this pressure under the hydrochloric acid medium, the condition of the equipment material is harsh, which increases the difficulty of operation and the safety of operation