Step 2: Synthesis of 3,4-difluorobenzenesulfonamide (a-3); A solution of anhydrous dichloromethane (1.5 L) of crude 3,4-difluorobenzene-1-sulfonyl chloride (a-2) (200 g, 0.92 mol) was vented with ammonia (NH3) at -30 °C. After 10 minutes of venting, formation of a white viscous substance was observed. After 30 minutes of reaction, thin layer chromatography (TLC) analysis (unfolding agent ratio of ethyl acetate: petroleum ether = 1:2) showed completion of the reaction. Subsequently, the reaction mixture was concentrated under vacuum to give the crude product. The crude product was purified by column chromatography (eluent gradient of ethyl acetate: petroleum ether = 1:5 to 1:2, and finally pure ethyl acetate) to afford the pure 3,4-difluorobenzenesulfonamide (a-3) (170 g, yield ca. 92.8%) as a white solid, which could be used in the subsequent reaction without further purification.1H NMR (400 MHz, DMSO-d6): δ 7.82 (t , J=Hz, 1H), 7.67 (m, 2H), 7.52 (s, 1H).
