Step 1: 6-Chloropyridin-3-ol (112 g, 868 mmol) was used as a raw material and dissolved in a solvent mixture of THF (800 mL) and water (800 mL). Sodium carbonate (92.0 g, 1.736 mol) and iodine (244.2 g, 1.04 mol) were subsequently added. The reaction mixture was stirred at room temperature for 4 hours. Upon completion of the reaction, the aqueous and organic phases were separated and the product was mainly present in the aqueous phase. The aqueous phase product was washed with hexane (400 mL x 2) to remove impurities. Next, the pH of the aqueous phase was adjusted to 7 with hydrochloric acid and extracted with ethyl acetate (500 mL x 4). The organic layers were combined, dried with anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure to obtain the crude product, which was washed with ethyl acetate to give a final 6-chloro-2-iodopyridin-3-ol 163 g in 75% yield. The structure of the product was confirmed by 1H NMR (DMSO, 400 MHz): δ 11.13 (s, 1H, OH), 7.31 (dd, J = 8.4,12.8 Hz, 2H).
