General procedure for the synthesis of 5-bromopyridine-3-sulfonyl chloride from 5-bromopyridine-3-sulfonic acid: a mixture of 5-bromopyridine-3-sulfonic acid (7.14 g, 30 mmol), phosphorus pentachloride (9.68 g, 47 mmol), and phosphorus trichloride (20 mL) was heated to reflux, and the reaction was carried out for 4 h. (Ref: J. Org. Chem. 1989, 54(2) , 389). Upon completion of the reaction, the mixture was concentrated to dryness to give a yellow semi-solid. The semi-solid was dissolved in a solvent mixture of ice water and tert-butyl methyl ether, and saturated aqueous NaHCO3 solution was added slowly until neutralized. Subsequently, the organic and aqueous phases were separated by saturating the solution with solid NaCl. The organic phase was dried with anhydrous Na2SO4. Finally, the solvent was removed in vacuum to give a yellow solid 5-bromopyridine-3-sulfonyl chloride (7.57 g, 98% yield). The mass spectrum (EI) showed m/z of 254.9 [M+], 256.9 [M+2]+, and 258.9 [M+4]+; the melting point was 64 °C. The analytes were analyzed in aqueous phase and in the presence of aqueous phase.
