General procedure for the synthesis of 5-hydroxy-2-iodobenzoic acid from 2-amino-5-hydroxybenzoic acid: 2-amino-5-hydroxybenzoic acid (1.99 g, 1.33 mmol) was dissolved in water (20 mL), then concentrated hydrochloric acid (10 mL) and sodium nitrite (NaNO2, 1.08 g, 45.6 mmol) were added slowly. The reaction mixture was stirred at 0 °C for 30 min for the diazotization reaction. Subsequently, potassium iodide (KI, 3.24 g, 19.5 mmol) and water (5 mL) were added to the reaction system. The resulting mixture was stirred at 90 °C for 30 min for iodination reaction. After completion of the reaction, the mixture was extracted with ethyl acetate, and the organic layer was washed sequentially with water, dried over anhydrous magnesium sulfate (MgSO4), and then concentrated under reduced pressure. The crude product was purified by silica gel column chromatography to afford 5-hydroxy-2-iodobenzoic acid (2.15 g, 88% yield) as a brown solid with a melting point of 180°C. The product was purified by IR (KBr). The product was analyzed by IR (KBr) showing characteristic absorption peaks: νmax= 3293, 1700, 1666, 1583, 1477, 1427, 1307, 1265, 1241, 1222, 1018, 933, 877, 827, 782 cm-1. 1H NMR (500 MHz, DMSO-d6) data: δ= 6.69 (1H, d, J = 8.5 Hz), 7.13 (1H, s), 7.71 (1H, d, J = 8.5 Hz), 9.9 (1H, s).13C NMR (DMSO-d6) data: δ= 80.5, 117.8, 120.6, 137.9, 141.7, 157.8, 168.3.High-resolution mass spectrometry (HRMS. APCI) analysis: the calculated value of [M + H]+ for C7H5O3I was 264.9361 and the measured value was 264.9377.
