The general procedure for the synthesis of 1,4-diiodo-2-nitrobenzene from 4-iodo-2-nitroaniline was as follows: first, 4-iodo-2-nitroaniline (6.60 g, 0.025 mol) was suspended in a mixture of water (19 mL) and glacial acetic acid (17.5 mL). After cooling the mixture to 0 °C, sulfuric acid (17.5 mL, 0.328 mol) was slowly added. The mixture was continued to be cooled to -5°C and a solution of NaNO2 (1.90 g, 0.028 mol) in water (7.5 mL) was added dropwise at a rate not exceeding 0°C. After the dropwise addition was completed, the mixture was stirred for 30 minutes. Subsequently, the mixture was added in small portions to a boiling solution of sodium iodide (22.33 g, 0.149 mol) in water (7.5 mL) (Note: Nitrogen is violently released during the reaction). The reaction mixture was kept at 60°C for 1 hour, after which it was cooled to room temperature. Extraction was carried out by adding ether (500 mL), the ether layer was separated and washed twice each with water (150 mL) and saturated NaHCO3 solution (150 mL). The organic phase was dried with Na2SO4 and concentrated in vacuum to give a solid product. Finally, purification by ethanol recrystallization afforded 1,4-diiodo-2-nitrobenzene (9.30 g, 99% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 8.15 (d, 1H, J = 2.0 Hz), 7.75 (d, 1H, J = 8.3 Hz), 7.56 (dd, 1H, J = 8.3 and 2.0 Hz).
