The study investigates the content of transposition impurities in chlorpyrifos and explores ways to reduce the formation of the impurity in chlorpyrifos synthesis,the optimal process parameters of synthesizing O-ethyl-S-ethyl-O-(3,5,6-trichloro-2-pyridinyl)phosphate ester were identified.The target product was synthesized in a five-step process,including substitution,ammonification,condensation,acylation and a final condensation,starting from phosphorus trichloride and ethanol.The yields for each step were as follows:substitution 82.3%,ammonification 90.3%,condensation 96.0%,acylation 97.1%,and final condensation 96.7%,leading to an overall yield of 67.0%.Chromatographic analysis showed that the normalized area of the synthesized product reached 98%.
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