| In the 21st century, agrochemicals are still the main body of the crop protection. Green agrochemicals are needed to harmonize the relationship between pesticide and environment. Exploring green agrochemicals includes two aspects: green products and clean processes. Fluthiacet-methyl (1), as a super-effective, wide-spectral and safe herbicide, is one of the called green agrochemicals. However, the reported producing processes of 1 are complicated, with a lot of environmental trouble.In this paper, an economically inexpensive, operationally simple and environmentally friendly synthetic process is developed, basing on analyzing and improving the literature synthetic methods and creating new synthetic methods of the product 1 and its intermediates.1 is prepared by reacting 4-chloro-2-fluoro-5-(methoxycarbonylmethylthio)-phenylisothiocyanate (2) with hexahydropyridazine hydrochloride salt (11) and than bis(trichloromethyl)carbonate (BTC). In comparison with the literature methods, the method has such advantages as that the solid 11 is more easily prepared in higher purity and more convenient for handling than the volatile liquid hexahydropyridazine (10) used in the reported processes; and has such advantages as operationally safe and environmentally friendly by replacing the high toxic gaseous phosgene by BTC.The intermediate 2 is synthesized by reacting methyl 5-amino-2-chloro-4-fluoro-phenylthioacetate (12) with CS2 and BTC sequentially. By using CS2 to replacethiophosgene and using BTC to replace chloroformate, the synthesis is operationally safe and environmentally friendly.The intermediate 12 is prepared by three methods: In route 1, N-acetyl-4-chloro-2-fluoroaniline (13) is chlorosulfonated, reduced, hydrolyzed, and then reacted with methyl chloroacetate to give 12. The red P/h method is better than the zinc method for the reduction reaction. In route 2, 13 is nitrified, reduced, diazotized and nucleophilic substituted with thioglycolic acid, and then methanolyzed and esterifed to give 12. Instead of the reported iron method, the reduction is carried out by catalytic hydrogenation, which is advanced in high yield, simple treatment and environmentally friendly reaction. The one-pot method of methanolysis and esterification is a clean process with simple operations, good yield and little waste. The route 6 is a new method for the preparation of 12, using 3,4-dichloronitrobenzen (33) as the starting material, comprising 6 steps such as nucleophilic substitution by thioglycolic acid, esterification by methanol, catalytic hydrogenation, Schiemann reaction, nitrification and catalytic hydrogenation again, in a 42% total yield. In this method, the raw materials are readily available and inexpensive, the procedures are operationally convenient, and the raw materials and by-products are low toxic and safe to environment. In a word, the method is a relatively clean process for the preparation of the intermediate 12.The route 6 is selected as one of the main parts of the industrial process of the compound 1, because of its advantages such as economic, convenient and environmentally friendly, in accordance with the results of comparing the above-mentioned three routes in three aspects such as material cost, atom-economy and operational safety.The intermediate 11 is synthesized from hydrazine hydrate, involving the reaction with formic acid, followed by the reaction with dichlorobutane and methanolysis. The process is economic, simply handlable, readily realizable in industrial scale, and environmentally friendly.In conclusion, the environmentally friendly herbicide Fluthiacet-methyl is successfully synthesized with readily available and environmentally friendly materialsby 12 reacting steps, all of which are operationally simple and safe and most of which are relatively atom economic reactions. In addition, the analysis methods of the intermediates and product, the mid-control methods and waste treatment methods are recommended. The work has built a firm base for the future industrial manufactur...
|
PDF Full Text Request