Preparation method of penoxsulam

The invention provides a preparation method of penoxsulam, and belongs to the technical field of pesticide synthesis. The penoxsulam is prepared through condensation reactions between 2-(2,2-difluoroethoxy)-6-trifluoromethyl benzene sulfonyl chloride (I) and 5,8-dimethoxy-[1,2,4]triazole[1,5-c]pyrimidine-2-amine (II) in the presence of a non-nucleophilic alkali or weakly-nucleophilic alkali. The synthesis time is reduced from reported 4 hours or more to 30 to 60 minutes, the product yield is 84 to 96%, and thus the production efficiency and product yield are prominently improved. Furthermore, the raw material prices are low, and the production cost is low. In the reaction process, no highly-toxic raw material or medicament is used, the material post treatment is simple, the generation amount of waste gas, waste liquid, and waste solid is small, and the treatment on the wastes is convenient, so the provided method is accord with the environment protection requirements and is suitable for industrial production and applications.