Background of the invention

The invention relates to novel processes for preparing compounds of Formula I, particularly intermediate 5-amino-3-cyano-l-(2,6,-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide a potential intermediate for the preparation of pesticide, Fipronil.

WO0130760 describes the preparation of compound of 5-amino-l-(2,6-dichloro-4-trifluoromethylphenyl)-3-cyanopyrazol-4-yl disulfide from 5-amino-l-(2,6-dichloro-4-trifluoromethylphenyl)-3-cyanopyrazole with sulfur monochloride at 35°C. This process reported involves two-stage synthesis and results in formation of significant amount of the mono sulfide II as the byproduct.

EP 0374061 and J-L. Clevel et al in J. Chem. Soc. Perkin I, (1992), 3371-3375 describes the preparation of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide.

However, this patent also involves two stage of the process for disulfide synthesis leading to tedious workups and lower reaction yields.

Detailed Description of the invention

In order to overcome the problems faced in the prior art and to develop a industrially viable process for synthesis of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide, or the derivatives, a simple facile and a single pot reaction is reported in the present invention; this surpasses the formation of the byproduct as impurity i.e., the monosulfide II. The above 2-step procedure is inefficient for an industrial process, and a one-pot synthesis clearly outweighs the disadvantages of the earlier reported procedures.

It is an object of the present invention to provide a convenient process for preparing Formula I a pesticidal intermediate, which is an important intermediate for the synthesis of Fipronil. In this process, compound of Formula I is obtained in high yield and high purity. This process utilizes readily available materials, allows efficient isolation of the product and does not require additional purification.

According to one aspect of the invention, 2,6-dichloro-4-trifluoromethylphenyl aniline was reacted with sulfuric acid and sodium nitrite, preferably in the presence of acetic acid, followed by the addition of ethyl dicyano propionate, acetic acid and water. These additions are carried out at temperatures 5- 15°C preferably at 15°C. Sulfur monochloride was added to the same reaction pot obtain 5-amino-3-cyano-l-(2,6-dichloro-4-trifiuoromethyl phenyl) pyrazol-4-yl disulfide. The addition is carried out at temperatures between 20- 40°C, preferably at 35-40°C.

The above described aspect of the invention may be extended to the other derivatives of anilines as starting compounds to yield the corresponding intermediates of Formula I and is not limited to the preparation of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide.

Example

Synthesis of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide I:

2,6-Dichloro-4-trifluoro methyl aniline was taken in solution containing cone. Sulfuric acid and Sodium nitrite and Acetic acid at 15°C for 10 min. This was cooled and added to ethyl-2,6-dicyano propionate solution in acetic acid-water at 10 °C for 15 min. The formed pyrazole was dissolved in dichloroethane, dehydrated and sulfur monochloride was added at 35-40°C and the resultant precipitate was filtered off to get 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide compound in 85% yield with 94-96% purity.

We Claim:

1. A single pot synthesis of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide from 2,6-Dichloro-4-trifluoro methyl aniline and ethyl-2,6-dicyano propionate.

The process of claim 1 which involves the following stages:

a) 2,6-Dichloro-4-trifluoro methyl aniline was taken in solution containing cone. Sulfuric
acid and Sodium nitrite and Acetic acid at 15°C for 10 min

b) This was cooled and added to ethyl-2,6-dicyano propionate solution in acetic acid-water at 10 °C for 15 min

c) The formed pyrazole in dichloroethane was dehydrated by addition of dichloroethane, and sulfur monochloride was added at 35-40°C

d) 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethyl phenyl) pyrazol-4-yl disulfide
compound is formed in 85% yield with 94-96% purity.