Synthesis And Process Improvement Of 2,5-Dimethylphenylacetic Acid

Spirotetramat is the second generation of quaternary ketoic acid insecticide developed by Bayer,Germany.It is a new type of insecticide with high efficiency,broad spectrum,low toxicity and environmental friendliness.It has a good market prospect and application prospect both at home and abroad.At present,there are mainly six synthesis routes of 2,5-dimethylphenylacetic acid in literature.In this paper,a lot of research has been done on the process route of preparing 2,5-dimethyl phenylacetic acid from p-xylene through chloromethylation,cyanidation,alkaline hydrolysis and acidification,and continuous industrial production has been achieved.The main research contents and achievements are as follows:1)Preparation of 2,5-dimethyl benzyl chloride.By studying the ratio of raw materials,reaction temperature and stirring speed,the reaction conditions were optimized to solve the problems of low yield and large dissubstituted impurities in the synthesis of benzyl chloride.The yield was as high as 95%and the purity as high as 99.8%.Through the investigation of the reaction pressure holding and the recovery and reuse of hydrochloric acid,the difficulties of process co-industrialization such as the large amount of hydrogen chloride waste gas and the difficult treatment of hydrochloric acid by-product were solved,the cost was saved and the pressure of environmental protection was reduced.2)Preparation of 2,5-dimethyl benzyl chloride.By investigating the ratio of raw materials,reaction temperature and drop acceleration of 2,5-dimethyl benzyl chloride,the synthesis scheme was optimized to solve the situation of intense material accumulation and exothermic heat release during the synthesis process,and the reaction yield was increased to more than 99%.In addition,the one-pot synthesis with the next hydrolysis reaction reduced the unit operation.It avoids the generation of waste salt in the waste water in this step,and avoids the poisoning risk of the workers caused by the leakage of residual~-CN of the reaction system in the form of HCN gas in the process of material separation.3)Synthesis of 2,5-dimethylphenylacetic acid.By studying the amount of alkali,water consumption and reaction temperature,the feeding proportion of raw and auxiliary materials was optimized to solve the problem of long hydrolysis process time.The shortest reaction time was 0.5h.At the same time,the separation of the reaction products was studied,which solved the problem of large residual of the dissubstituted impurities and improved the product quality.The dissubstituted impurities only accounted for about 0.1%and the yield was as high as 93%(calculated by 2,5-dimethyl benzyl chloride).In addition,through the study of high pressure reaction synthesis,the-CN in the reaction system was almost completely hydrolyzed,which solved the problem of post-treatment safety.Through the absorption of ammonia and the treatment of waste water and salt,the recycling of waste water and the by-product of waste gas and salt are realized,and the pressure of environmental protection is reduced.4)The continuous synthesis of 2,5-dimethylbenzyl chloride into 2,5-dimethyl-phenylacetic acid was investigated according to the intermittent feeding ratio and reaction parameters.The continuous synthesis of 2,5-dimethylbenzyl chloride was investigated.The feed rate was optimized and the continuous synthesis was realized by investigating the material retention time in the series backmixing reactor during the reaction process.Thus greatly reduce the safety of each step in the process of reaction,save labor costs,easier to realize automation,product yield up to 90%.The total molar yield of this process is more than 88%,The optimized synthetic route is not only cheap,safe and easy to obtain raw materials,but also mild reaction conditions,simple operation,and most importantly,high yield and less waste,suitable for industrial production.The synthesis and optimization study of this process solves the problem of difficulty in purchasing 2,5-dimethylphenylacetic acid in the market due to environmental problems,which is of great significance for the production of spironethyl ester and lays the foundation for the mass production of spironethyl ester.