General procedure for the synthesis of 2-iodo-3-hydroxypyridine using 3-hydroxypyridine as starting material: sodium carbonate (Na2CO3, 11.6 g, 109.72 mmol) and iodine (I2, 13.3 g, 52.57 mmol) were added sequentially to a solution of 3-hydroxypyridine (5.0 g, 52.57 mmol) in water (400 mL). The reaction mixture was stirred at room temperature for 2 hours. After completion of the reaction, the pH was adjusted to 4 with 1 M hydrochloric acid (HCl) solution. the precipitate was collected by filtration, washed with cold water and dried to give 2-iodo-3-hydroxypyridine (10.7 g, 92% yield) as a white powder. The product characterization data were as follows: melting point 189-190 °C (neat); thin layer chromatography (TLC) Rf = 0.33 (unfolding reagent dichloromethane/ethanol, 97/3, v/v); infrared spectroscopy (IR, KBr pressed) νmax (cm-1): 2851, 2722, 2573, 2345, 1560, 1455, 1301, 1189, 1121, 794, 668; nuclear magnetic resonance hydrogen spectrum (1H NMR, 400 MHz, DMSO-d6): δ10.88 (s, 1H, OH), 7.87 (dd, 1H, J1 = 1.6 Hz, J2 = 4.4 Hz, H-6), 7.24 (dd, 1H, J1 = 4.4 Hz, J2 = 8.0 Hz, H-5), 7.18 (dd, 1H, J1 = 1.6 Hz, J2 = 8.0 Hz, H-4); nuclear magnetic resonance carbon spectrum (13C NMR, 100 MHz, DMSO-d6): δ 154.0, 141.8, 124.3, 121.3, 110.9; high resolution mass spectrometry (HRMS) calculated value of C5H4INO [M + H]+ 221.9410, measured value 221.9416.
