3,5-Diiodo-4-hydroxybenzaldehyde was prepared as follows: in a 100 mL round bottom flask, 4-hydroxybenzaldehyde (1.0 g, 8.19 mmol), sodium periodate (1.75 g, 8.19 mmol), and NaCl (957 mg, 16.38 mmol) were dissolved in acetic acid (30 mL). H2O (3 mL) was added at room temperature. The reaction mixture was stirred at room temperature for 10 min, then potassium iodide (2.72 g, 16.4 mmol) was added and the reaction mixture was stirred at room temperature for 96 hours. The reaction mixture was diluted with EtOAc (25 mL) and 1 M aqueous sodium thiosulfate. The solution (25 mL) was added and the resulting mixture was stirred for 15 minutes. The solution was poured into 250 mLErlenmeyer and washed with EtOAc (50 mL) and 1 M aqueous sodium thiosulfate. solution (50mL) and the resulting solution was stirred for another 15 minutes. The organic layer was separated and the aqueous phase was further extracted with EtOAc (3 x 50 mL). The combined organic layers were washed with brine (100 mL), dried over Na2SO4, filtered and concentrated to dryness to afford 4-hydroxy-3,5-diiodobenzaldehyde (2.91 g, 95% yield) as a light yellow solid.
