Preparation of 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole Nitrosyl sulfuryl prepared from 7 g of sodium nitrite and 27.5 mL of concentrated sulfuric acid The suspension was diluted with acetic acid, and 50 mL of acetic acid solution of 21.2 g of 2,6-dichloro-4-trifluoromethylaniline was added dropwise at 25 to 32 °C, the temperature was raised to 55 °C, heated for 20 min, and poured into 2,3-dicyano In a solution of ethyl propionate in acetic acid (60 mL) and water (125 mL), after stirring for 15 min, water was added, the oil layer was separated, extracted with dichloroethane, the oil layers were combined, washed with ammonia water to pH 9, layered, water, dilute hydrochloric acid Washed, dried, filtered, evaporated in vacuo, and the oil was recrystallized from toluene and hexane, yield 70.9%. Preparation of 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-trifluoromethylsulfanylpyrazole Trifluoromethylsulfanyl chloride was added within 1 h (10.8 g) of the dichloromethane solution was added dropwise to the dichloromethane solution containing 20 g of the product of the previous step. The mixture was stirred at room temperature overnight, washed with water, dried, filtered and desolubilized to obtain 26.3 g of a solid, which was recrystallized to obtain the product with a yield of 92%. Under stirring for the synthesis of fipronil, the dichloromethane solution of 10 g of the product of the previous step was treated with 4.5 g of m-chloroperoxybenzoic acid, and after stirring overnight, 2 parts of 1.6 g of m-chloroperoxybenzoic acid were added and left for 2d. Diluted with ethyl acetate, washed with sodium sulfite solution, sodium carbonate solution and water in turn, dried, filtered, desolubilized, eluted with dichloromethane on SiO2 chromatographic column and purified to obtain fipronil 6.0g, yield 57.8 %.
