The Synthesis Processes Of Herbicide's Intermediates 5-chloro-2,3-difluoropyridine

This paper gives a overall description of Fluoro-containing pesticide, especially herbicide. And further review the synthesis of fluoro-containing herbicide chodinafop-propargyl and its intermediate 5-chloro-2,3-difluoropyridine. With references to lots of papers related, we chose a route to synthesize from 2-amidopyridine, through chloroination, diazotization, a second chloronation, fluorination to give 5-chloro-2,3-difluoropyridine. Time, temperature, solvent, catalyst and treatment dependence were studied. Results are satisfactory.In the synthesis of 2,3,5-trichloropyridine, 2-aminopyridine was firstly chloridized to 2-amino-3, 5-dichloropyridine, and then sodium nitrite solution was added with the existence of hydrogen chloride to diazotize the 2-amino-3,5-dichloropyridine. After the diazotization, a mixture of 2,3,5-trichloropyridine and 3, 5- dichloropyridine-2-ketone was got as a result of Sandmeyer reaction. Lastly, Thionyl chloride was used to chloridize the mixture. And the product 2,3,5-trichloropyridine was got after necessary purification processes. The yield of the product is about 84.7%Consequently, we used 2,3,5-trichloropyridine as the reactant for the syntheis of 5-chloro-2,3-difluoropyridine. NMP was chosen to be the solvent. A mixture of KF and CsF was added as fluridizer. The reaction was carried out at a high temperature to produce 5-chloro-2,3-difluoropyridine. According to the GC test, the yield was approximately 34.5%.The route we have chosen requires only easily available and cheap resources, concise steps and is easy to operate with a yield of 29.2% of intermediate.