Synthesis of fipronil sulfide, an active metabolite, from the parent insecticide fipronil

A convenient procedure for the synthesis of fipronil sulfide, one of several active metabolites identified from the insecticide fipronil, has been developed. Reduction of fipronil with trifluoroacetic anhydride–sodium iodide in acetone, followed by flash chromatography afforded fipronil sulfide in 60% yield and >99.9 percent purity. This represents the first direct synthesis of this key metabolite from fipronil.