Chlorpyrifos was synthesized by reacting of 3,5,6-trichloro-2-pyridinol sodium(1 mol) with O,O-diethyl phosphorochloridothioate(1 mol) via aqueous phase(pH=11-13) reaction and benzyltrimethyl ammonium chloride as catalyst at 60 °C for 3 hrs,and the yield and purity of chlorpyrifos were over 94% and 97%,respectively.

The route of intermediate 3,5,6-trichloro-2-pyridinol sodium was discussed The chlorpyrifos was synthesized by reaction of O,O-diethyl phosphorochloridothioate with 3,5,6-trichloro-2-pyridinol sodium prepared from 2,3,5,6-tetrachloropyridine and caustic sodium as the starting materials.