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Example 1 Preparation of 4-iodo-3-nitrobenzoic acid (Compound V): 45 g (0.25 mol) of 4-amino-3-nitrobenzoic acid, 400 mL of deionized water and 100 mL of concentrated hydrochloric acid were added to a reaction flask. Stirring was turned on and the reaction mixture was cooled to 0 to 5 °C before 50 mL of an aqueous solution containing 25.9 g (0.38 mol) of sodium nitrite was slowly added dropwise. Gradual dissolution of the solid was observed. After the dropwise addition was completed, the reaction was maintained at 0 to 5°C and continued for 1 hour. Subsequently, 200 mL of an aqueous solution containing 88 g (0.5 mol) of potassium iodide was slowly added dropwise at the same temperature. After completion of the dropwise addition, the reaction mixture was stirred at room temperature for 2 hours, during which time a solid precipitated. The solid product was collected by filtration, washed with deionized water and dried to give 65 g (0.22 mol) of 4-iodo-3-nitrobenzoic acid (compound V) in 89.7% yield.