Study On The Synthesis Of High-effective Herbicide Glufosinate-ammonium

Glufosinate-ammonium(Ammonium 2-amino-4-(hydroxymethyl phosphinyl)butanoate)is a high-effective,low toxicity and non-selective herbicide which was widely used in many crops,especially in the genetically modified glufosinate-tolerant crops.The history of herbicides and the application prospect of glufosinate-ammonium were reviewed in this dissertation.The various processes for the preparation of glufosinate-ammonium and its key intermediate methylphosphorus dichloride were summarized based on the current literatures.Then,the new synthetic route of methylphosphorus dichloride and glufosinate-ammonium was devised and optimized in this paper.An improved synthesis method of methylphosphorus dichloride was disclosed which using methy chloride and phosphorous trichloride as a starting material,including reaction with aluminum chloride via CH3PCl4-AlCl3,then reduced by aluminum and removed aluminium chloride with a total yield of 76.2%.In comparison with the traditionary synthesis method of methylphosphorus dichloride,the improved method has the advantages of higher purity,less wastes,mild reaction conditions and low cost.Then,another intermediate diethyl methylphosphonate was obtained in 96.0%yield by the reaction of methylphosphorus dichloride with sodium ethylate.The currently manufacture of glufosinate in china has the following disadvantage:(a)low purity of the product,(b)a large amounts of ammonium chloride and difficult to deal with,(c)use of high toxicity material.Then,another process for preparing glufosinate was disclosed in this paper.Glufosinate-ammonium was obtained by the reaction of diethyl methylphosphonate with 5-bromoethylhydantoin via 5-(2-(ethoxymethylphosphinyl)ethyl)hydantoin,subsequent hydrolysis and amination with ammonia solution.The method avoided the use of sodium cyanide and has a higher purity of the product.But,the wastes haven’t reduced effectively in the process caused by the lengthy synthesis route of 5-bromoethylhydantoin.A new process for the synthesis of glufosinate-ammonium was disclosed in the paper,which using diethyl methylphosphonate as a starting material,comprising 4 steps including reaction with acrolein via(3-acetoxy-3-ethoxy)methylphosphinic ethyl ester,subsequent reaction under the conditions of a Burcherer-Bergs synthesis,hydrolysis of 5-(2-(ethoxymethylphosphinyl)ethyl)hydantoin and finally salification by ammonia solution to give the final product with total yield of 70.4%.The new method has strong practicability and can avoid the use and generation of ammonium chloride,which not only decreases the wastes,but also simplifies the purification process of the product.Another new process was devised which the instable material diethyl methylphosphonate was replaced by methyl-phosphinic acid monoisobutyl ester.And the ultraviolet-light was used as catalyst in the reaction of methyl-phosphinic acid monoisobutyl ester with 1,1-diacetoxy-2-propene to give the intermediate[3,3-bis(acetyloxy)propyl]methylphosphinic acid isobutyl ester.Then the intermediate was followed by the Burcherer-Bergs reaction and then hydrolysed led to glufosinate.The new synthesis of glufosinate-ammonium via a hydantoin intermediate has the advantages of simple operation,little waste and high purity of the product,which was suitable for industrial production.