PROCESS FOR THE PREPARATION OF FIPRONIL AND ANALOGUES THEREOF

The present invention relates to a new and efficient process for preparing 5-amino-1-(2,6-dichloro-4-(trifluo-romethyl)phenyl)-4-(trifluoromethylthio)-IH-pyrazole-3-carbonitrile (hereinafter referred to as compound of formula I), which is useful as an intermediate for the antiparasitic agent fipronil, and a process for preparing 5-amino-3-cyano-1-(2,6-dichloro-4-tri-fluoromethylphenyl)-4-trifluoromethyl sulfinylpyrazole (hereinafter referred to as compound of formula II or fipronil). In one aspect, there is provided a process for preparing fipronil comprising: a) a step of reacting CF3S( O)ONa with the compound of formula (III) in the presence of a reducing/halogenating agent; and b) a step of oxidizing the compound of formula (I) obtained in step a) in the presence of a selective oxidizing agent, under suitable conditions, wherein the selective oxidizing agent selectively effects oxidation of (I) to the corresponding sulfoxide, Fipronil. In certain exemplary embodiments, the selective oxidizing agent is MHSO5, wherein M is an alkaline metal cation.