Preparation Method of 5-Amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole

5-Amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole is an important intermediate used in the process for preparation of Fipronil and has the following chemical structure shown herein below,as structure:

The synthetic route is accompanied with various drawbacks such as generation of large amounts of acidic effluent, several reaction steps, and difficulty in dealing with the waste acid, use of toxic reagents, low purity, and low yield of product. Thus, there is felt need for a process for preparing 5-Amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole in high yield in a simple, economical and environment friendly manner.

To ameliorate one or more of the above mentioned problems, the present disclosure envisages a process for the preparation of aminopyrazole, 5-Amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole, wherein the step of diazotization is carried out by using a mixture of spent acids. One of process is described herein below:

Gharda Chmicals Limited provides a process for the preparation of aminopyrazole. The aminopyrazole is particularly, 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)  pyrazole. The process steps involve the step of reacting 2,6 dichloro-4-trifluoromethylaniline (DCTFMA) with a mixture of spent HCl and spent H2SO4 in at least one fluid medium and in at least one wetting agent to obtain a slurry comprising the salts of 2,6-dichloro-4-trifluoromethyl aniline. To the slurry, NaNO2 solution is added for diazotizing the salts of 2,6-dichloro-4-trifluoromethyl aniline, over a period of 30 minutes to 180 minutes under stirring at a temperature in the range of 15℃ to 25℃ to obtain a suspension comprising diazotized salt of 2,6-dichloro-4-trifluoromethylaniline followed by diluting it with water to obtain a mixture. A dicyanopropionic acid ester is added to the mixture while stirring it for 10 hours to 12 hours to obtain a biphasic system. The organic phase is separated from the biphasic system and the separated organic phase is treated with an aqueous alkali solution and cooled to a temperature in the range of 80 C. to 100 C. to obtain a precipitate comprising aminopyrazole compound. The so obtained precipitate is filtered to obtain a cake, which is washed with water and dried it under vacuum to obtain aminopyrazole.

Xiaojun Shan put forward a preparation method of high-purity pesticide fipronil with the content of 98-99%. The preparation method specifically comprises the following steps: firstly adopting low-content 93-95% 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl) pyrazol to prepare 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl) pyrazol with the content up to 99.8% by selecting an appropriate reducing agent, and then enabling reaction with 98% trifluoromethyl sulfinyl chloride to obtain the fipronil of which the content can reach 98%-99%. Therefore, the preparation method solves the preparation problem of high-purity fipronil, the process route that the high-content fipronil is unlikely to be obtained by using the raw material of low-content fipronil to purify is avoided, and the disadvantages existing in an existing preparation technology are overcome. The raw materials adopted in the whole synthesis and purification method are easily obtained, the process conditions are simple and convenient, and the product is excellent in quality.

References

[1]Xiaojun shan, Yunshan Chen, Lidong Xu, et al. High-purity fipronil preparation method.China Patent No.104557713B
[2]Hiroshi Kodama. Wakayama; Yasuhiro, etc. SYNERGISTICTERMITICIDAL COMPOSITION OF PYRETHROD AND NPHENYL-PYRAZOLE.United State Patent No. 5747519
[3]Keki Hormusji Gharda, Mumbai (IN), Laxminarayan Subraya Shet. PROCESS FOR PREPARATION OF AMINOPYRAZOLE.United State Patent No.10202352B2

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