General procedure for the synthesis of 5-chloro-2-iodophenol from 2-amino-5-chlorophenol: 2-amino-5-chlorophenol (5.7 g, 40 mmol) was dissolved in a mixed solvent of DMSO/water/H2SO4 (200/60/140 mL) and the solution was cooled to 0 °C. A solution of sodium nitrite (4.1 g, 60 mmol) in water (20 mL) was slowly added at 0 °C and the reaction mixture was continuously stirred for 1 hour. Subsequently, a solution of potassium iodide (19.9 g, 120 mmol) in water (20 mL) was added to the reaction system and the mixture was stirred at room temperature for 1 hour. The same amount of potassium iodide (19.9 g, 120 mmol) in water (20 mL) solution was added again and the mixture continued to be stirred at room temperature for 1 hour. After completion of the reaction, the reaction mixture was diluted with ethyl acetate and washed sequentially with water, saturated aqueous sodium sulfate solution and brine. The organic phase was dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The resulting residue was purified by fast chromatography (Biotage Si65M, 20% ethyl acetate/hexane) to afford 5-chloro-2-iodophenol 8.09 g (79% yield) as a pink solid. gC-MS m/e 254 [M]-.
