General procedure for the synthesis of 3-bromo-2-iodothiophene from 3-bromothiophene: In a 100 ml four-necked flask, 3-bromothiophene (10 g, 61.3 mmol), iodine (5.61 g, 22.1 mmol), iodic acid (2.27 g, 12.9 mmol), acetic acid (20 ml), cyclohexane (30 ml), water (8 ml) and concentrated sulfuric acid (0.4 mL). The reaction mixture was stirred at 40°C for 17 hours. After completion of the reaction, the mixture was cooled to room temperature and then extracted by adding saturated aqueous sodium bicarbonate (40 mL) and diethyl ether (30 mL). The organic phase was washed sequentially with aqueous sodium hydroxide-sodium sulfite solution (30 mL) and saturated sodium chloride solution (30 mL) for 10 min each. The washed organic phase was dried with magnesium sulfate, filtered and concentrated. The crude product obtained was purified by distillation under reduced pressure (about 125 °C/9 torr) to give 3-bromo-2-iodothiophene (15.6 g, 88% yield) as an almost colorless liquid.
