0.30 g of m-chloroperbenzoic acid (purity of 68%) was added to a mixture of 0.20 g of 3-ethylsulfanyl-N-(5-trifluoromethylpyridin-2-yl)picolinamide (Compound of Present Invention 2) and 3 mL of chloroform under ice cooling, and the mixture was stirred at room temperature for 2 hours. A saturated aqueous sodium bicarbonate solution and a saturated aqueous sodium thiosulfate solution were poured to the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to obtain 0.11 g of 3-ethylsulfonyl-N-(5-trifluoromethylpyridin-2-yl)picolinamide (hereinafter, referred to as Compound of Present Invention 3).
