Process for synthesis of fipronil

A process for the preparation of a trifluoromethylsulfinylpyrazole compound of formula I,

• said process comprising:
• a) halogenating an aromatic compound of formula II:
• wherein, R is a halogen and R3 is a perhaloalkyl, to obtain a polyhalogenated perhaloalkyl benzene compound of formula III;
• wherein, R and R2 are halogen independently selected from the group consisting of F, Cl, Br, and I;
• and R3 is a perhaloalkyl;
• b) reacting in a polar solvent selected from the group consisting of N-methyl pyrrolidone, dimethylsulfone, N,N′-dimethyl imidazolidinone and diphenylsulfone;
• the compound of formula III with anhydrous ammonia in the presence of an alkali halide;
• at a temperature of about 200° C. to 300° C.;
• and a pressure of about 20 kg/cm2 to about 50 kg/cm2 to obtain a halo-perhaloalkyl aniline compound of formula IV,
• wherein R2 is halogen and R3 is a perhaloalkyl;
• c) reacting halo-perhaloalkylaniline compound of formula IV with at least one halogenating agent selected from the group consisting of chlorine, sulfuryl chloride, thionyl chloride and phosphorus pentachloride, in a chlorinated solvent selected from the group consisting of chloroform, dichloroethane, dichloromethane, chlorobenzene and o-dichlorobenzene to obtain a product mixture containing polyhalogenated perhaloalkylaniline compound of formula V,
• wherein, R1 and R2 are halogen independently selected from the group consisting of F, Cl, Br, and I;
• and R3 is a perhaloalkyl;
• d) isolating polyhalogenated perhaloalkylaniline compound of formula V from the product mixture;
• e) diazotizing the isolated polyhalogenated aniline compound of formula V with nitrosyl sulfuric acid in the presence of an acid solvent to form a diazotized derivative of compound V;
• f) reacting the diazotized derivative of compound V with cyanoalkyl propionate derivative and ammonia at a temperature range of about 0° C. to 25° C. to obtain a reacted mixture containing pyrazole compound of formula VII,
• wherein, R1 and R2 are halogen independently selected from the group consisting of F, Cl, Br, and I;
• and R3 is a perhaloalkyl;
• g) isolating the pyrazole compound of formula VII from the reacted mixture with a halogenated aliphatic hydrocarbon solvent followed by evaporating the solvent to yield crude pyrazole compound VII;
• h) sulfenylating the crude pyrazole compound VII with a sulfenylating agent in a halogenated aliphatic hydrocarbon solvent to obtain a product mixture containing thiopyrazole compound of formula IX,
• wherein, R1 and R2 are halogen independently selected from the group consisting of F, Cl, Br, and I;
• and R3 is a perhaloalkyl;
• followed by isolating the thiopyrazole compound from the product mixture;
• i) oxidizing the isolated thiopyrazole compound of formula IX at a temperature 10° C. to 30° C. in a reaction medium comprising an oxidizing agent which is a peroxide compound selected from the group consisting of hydrogen peroxide, tert-butyl hydrogen peroxide, benzoyl peroxide and sodium peroxide;
• a solvent system comprising in various ratios at least two solvents selected from a group of halogenated solvents consisting of trichloroacetic acid, di chloroacetic acid, mono bromoacetic acid, di bromoacetic acid, tri bromoacetic acid, chlorobenzene, dichloromethane and dichloroethane;
• and a corrosion inhibitor, to yield a product mixture containing trifluoromethyl sulfinyl pyrazole compound of formula I;
• and
• j) optionally purifying trifluoromethyl sulfinyl pyrazole compound of formula I by at least one process selected from the process consisting of crystallization which is carried out using at least one solvent selected from the group consisting of toluene, chlorobenzene and ethyl acetate;
• and leaching which is carried out using at least one solvent selected from the group consisting of toluene, chlorobenzene and ethyl acetate.