Research On The Synthesis Of Acephate

Acephate (O,S-dimethyl acetylphosphoramidothioate) is a new type of organophosphate insecticides, which has a number of advantages such as low toxicity, low residue. While, there exists some weak points such as low yield, complex operations, high cost and pollution to the environment in the current synthesis methods. The byproduct which obtained in the process of producing O,O-dimethyl phosphorochloridothioate, O,O,O-trimethyl phosphorothioate, represents a major disposal problem on the purity of the acephate. Therefore, it is of great significance to improve the synthesis technic of acephate.The evolvement and synthetic methods of acephate are introduced and summarized. Reviewed synthetic techniques are optimized and improved in this paper. The aim product is obtained with a total yield80.3%using phosphorothioyl trichloride as raw material by two esterifications, ammonification, isomerization and acetylation. The improved technical route is as follows:1. Firstly, phosphorothioyl trichloride reacted with methanol at-5℃after0,0,0-trimethyl phosphorothioate with a mole ratio of1:0.05put in the flask. Then, the reaction was continued without further treatment, using50%methanol sodium solution. At last, ammonia was added to yield the intermediate O,O-dimethyl phosphoramidothioate with95.7%yield.2. The final product acephate was prepared via isomerization and esterification from the intermediate O,O-dimethyl phosphoramidothioate, with the yield of80.3%(65.4%in the literature) based on phosphorothioyl trichloride. An optimized reaction condition was given as follows:O,O-dimethyl phosphoramidothioate and dimethyl sulfate at a mole ratio of1:0.05were at50℃; methamidophos, acetic anhydride and sulphuric acid at a mole ratio of1:1.15:0.03were at25℃. With the water-free reaction system, the target product could be obtained through successive esterification and amination without water washing process, therefore the waste water produced was reduced. On the other hand, the byproduct, O,O,O-trimethyl phosphorothioate, was also suppressed to0.7%(literature10%) by recycling about5%of it to the reaction system.This experiment also has studied the conversion of thiophosphoryl (P=S) compounds to corresponding oxo (P=O) compounds by oxidation reaction with O,O,O-trimethyl phosphorothioate at50℃.We have used ozone as the oxidizer to yield92.1%trimethyl phosphate after4h.The structure of the products in every step were confirmed by GC-MS,1H-NMR and13C-NMR.