Preparation method of cyhalofop-butyl

The invention relates to a preparation method of cyhalofop-butyl. The method comprises the following steps: by using (R)-2-(4-hydroxyphenoxy)propionic acid and 3,4-difluorobenzonitrile as raw materials and an inorganic alkali as an acid-binding agent, adding an organic alkali and a phase-transfer catalyst, carrying out etherification reaction under milder conditions within a short time to generate an intermediate (R)-2-[4-(2-fluoro-4-cyano)-phenoxy]-propionic acid, and carrying out esterification reaction for dehydration, wherein the total yield of the two reactions can reach 94% or above, and the optical purity is greater than 99%. The method lowers the etherification reaction temperature, shortens the etherification reaction time, enhances the reaction selectivity, completely maintains the chirality, and increases the product yield, thereby saving the energy consumption and lowering the cost. Besides, in the esterification reaction, the used dehydration solvent can lower the byproduct content, thereby omitting the refinement operation of the product, reducing the discharge amount of three wastes, and being beneficial to environmental protection.