Process for the synthesis of fipronil

A process for preparing a compound of formula I trifluoromethylsulfinylpyrazole, ** ** Formula wherein R1 and R2 contain halogen elements respectively, and R3 is a perhaloalkyl; said method comprising: a) halogenating an aromatic compound of formula II: Formula ** ** wherein R is a halogen and R3 is a perhaloalkyl, to obtain a compound of formula III polyhalogenated perhalogenoalquilbenceno of; ** ** Formula where R, R2 respectively contain elements halogen group; and R3 is a perhaloalkyl, b) reacting, in a polar solvent selected from a group consisting of N-methylpyrrolidone, dimethyl sulfone, N, N'-dimethylimidazolidinone and diphenylsulfone, preferably N-methylpyrrolidone, the compound of formula III with anhydrous ammonia in the presence of an alkali halide, preferably potassium fluoride; at a temperature of about 200C to 300C, preferably in the range of 235 ° C to 250 ° C; and a pressure of about 1.96 MPa (20 kg / cm2) to about 4.90 MPa (50 kg / cm2), preferably in the range of 2.45 MPa (25 kg / cm2) to about 4.11 MPa ( 42 kg / cm2) to obtain a compound of halogeno-perhalogenoalquilanilina of formula IV: ** ** formula wherein R2 is halogen and R3 is a perhaloalkyl. c) reacting the compound of halogeno-perhalogenoalquilanilina of formula IV with at least one halogenating agent selected from a group consisting of chlorine, sulfuryl chloride, thionyl chloride and phosphorus pentachloride; preferably sulfuryl chloride, in a chlorinated solvent selected from a group consisting of chloroform, dichloroethane, dichloromethane, chlorobenzene and o-dichlorobenzene, to obtain a product mixture containing the compound of formula V polyhalogenated perhalogenoalquilanilina; ** ** Formula wherein R1 and R2 respectively contain elements halogen group; and R3 is a perhaloalkyl; d) isolating the compound of formula V polyhalogenated perhalogenoalquilanilina of the product mixture, preferably by fractional distillation; e) diazotising the compound of polyhalogenated aniline of formula V with isolated nitrosyl sulfuric acid in the presence of an acid solvent to form a diazotized derivative of the compound V; ** ** Formula f) reacting the diazotized derivative of the compound V with derivative cyano-alkyl propionate and ammonia to a temperature in the range of 0 to 25 for about obtain a reaction mixture containing the pyrazole compound of formula VII; ** ** formula