2-Bromo-4-chloroaniline (10 g, 48 mmol) was suspended in hydrochloric acid water (50 mL of concentrated hydrochloric acid and 35 mL of water), and the suspension was cooled on a dry ice/methanol bath at -15°C. A sodium nitrite aqueous solution (3.6 g, 52 mmol, 1. 1 eq. /20 mL) was gradually added dropwise to it over 20 minutes, and the mixture was stirred from -15°C to 0°C for 30 minutes, thereby preparing a diazonium salt. The reaction solution was gradually added dropwise to a potassium iodide aqueous solution (73 g, 0.44 mol, 9 eq. /220 mL) at room temperature for 10 minutes. The reaction mixture was stirred at room temperature for 6 hours and then allowed to stand overnight. Dichloromethane (200 mL) was added to the reaction mixture, and subsequently, sodium hydrogensulfite (2 g) was added, deactivating the generated iodine. An organic layer was aliquoted, washed with a 10 % sodium hydrogensulfite aqueous solution (100 mL) and saturated salt water (30 mL) and dried over anhydrous magnesium sulfate. The solvent was then distilled off to obtain a red liquid. This was purified using column chromatography (silica gel/hexane) to obtain a white needle crystal 2-Bromo-4-chloro-1-iodobenzene (12.4 g, 81 %).
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