2-methyl-4-chlorophenoxyacetic acid preparation method

Abstract

The invention provides a 2-methyl-4-chlorophenoxyacetic acid preparation method, which comprises: carrying out a condensation reaction on sodium o-cresolate and sodium chloroacetate under the catalysis of a trimethylamine catalyst to obtain 2-methyl sodium phenoxyacetate, acidifying, and chlorinating to obtain 2-methyl-4-chlorophenoxyacetic acid. According to the present invention, under the catalysis of the trimethylamine catalyst, sodium o-cresolate and sodium chloroacetate can be subjected to the condensation reaction in the near-neutral environment with the temperature of lower than 70 DEGC, such that the main side reaction for hydrolyzing sodium chloroacetate into sodium glycolate is greatly reduced, the produced wastewater contains less o-methylphenol and glycolic acid (or sodium glycolate) so as to easily meet the nationally acceptable emission standards at a low treatment cost, the resource utilization of the waste acid solution can be achieved, the cost of the raw materials and the three-waste treatment cost are reduced, the purity of 2-methyl-4-chlorophenoxyacetic acid is higher than 95%, and the total yield is higher than 93%.

Description

technical field [0001] The invention belongs to the technical field of organic synthesis, and relates to a preparation method of 2-methyl-4-chlorophenoxyacetic acid. Background technique [0002] There are many types of herbicides currently on the market, and the production and use of phenoxyacetic acid herbicides rank second only to glyphosate in the world. Due to the different substituents and substitution positions on the benzene ring, and the different numbers of carbon atoms of the carboxylic acid, different phenoxycarboxylic acid herbicides are formed. 2-methyl-4-chlorophenoxyacetic acid (common name: dimethyltetrachloride) is a hormone-type systemic phenoxycarboxylic acid herbicide developed and promoted by Imperial Chemical Industries in 1945. It has strong physiological activity and is easily absorbed and conducted by roots and leaves. At low concentration, it can stimulate the growth of crops, prevent flower and fruit drop, form seedless fruit, promote fruit ripe...

AI Technical Summary

Problems solved by technology

However, in this process, the reaction temperature of the condensation of chloroacetic acid solution and sodium o-cresol is controlled at a temperature of 110°C-130°C, and there are following defects: at this temperature, the reaction rate of sodium chloroacetate self-hydrolysis into sodium glycolate Fast, resulting in insufficient sodium chloroacetate condensed with o-cresol sodium, o-cresol sodium can not react completely, due to resource conservation and rigid environmental protection requirements, in the later stage of the reaction, it is necessary to detect the reaction kettle through the platinum resistance thermometer set in the condensation reaction kettle The temperature in the body, when it is higher than the preset 90 ℃, control the enamel reactor connected to the condensation reactor to heat the still body, and finally obtain the o-cresol that needs to be recovered through the enamel condenser connected to the enamel reactor; in addition, Sodium hypochlorite is used to chlorinate sodium 2-methylphenoxyacetate. Theoretically, the ratio of 2-methylphenoxyacetate to sodium hypochlorite solution is 1:1. In order to make the chlorination reaction better, CN103351295B discloses The technology will ensure that the ratio of sodium 2-methylphenoxyacetate and sodium hypochlorite solution is 1:6. This has the following defects: after the chlorination is finished, there is still a large amount of sodium hypochlorite that has not been consumed in the reaction solution, and additional reducing agent is needed. or other suitable methods for decomposition or harmless treatment, not only increases the production cost of dimethyltetrachloride, but also requires a large amount of wastewater to be treated, which also poses a great challenge to the continuous and stable production of dimethyltetrachloride

In the third step of the process, in the condensation reaction between sodium o-cresolate and sodium chloroacetate, the reaction temperature is controlled at 110-120°C, and the condensation reaction at such a high temperature also has the following defects: sodium chloroacetate itself is hydrolyzed into hydroxyl The reaction speed of sodium acetate is fast, causes the sodium chloroacetate that condenses with o-cresol sodium to be insufficient, and o-cresol sodium cannot react completely; Therefore, for resource conservation and rigid environmental protection requirements, in the third step, dropwise addition of sodium chloroacetate is adopted. Dephenolized water at the edge of the solution, continue the operation of dephenolized water after adding sodium chloroacetate solution dropwise

In the fourth step of the process, sulfone chloride is used as the chlorination reagent in the chlorination of o-methylphenoxyacetic acid. The reaction is an anhydrous reaction, and the reaction temperature is 30-50°C. The advantage is that the generation of a large amount of phenol-containing wastewater is reduced. Reduce energy consumption; But there is following defect: after sulfone chloride is chlorinated o-methylphenoxyacetic acid, will produce the mixed gas of hydrogen chloride and sulfone dioxide of two molar equivalents, to this highly poisonous, highly corrosive mixed gas The collection, utilization or harmless treatment of waste is also a big challenge in technology, and more resources need to be invested to solve it properly