Example 1 Synthesis of 5-amino-2,4,6-triiodoisophthalic acid
In a 250 mL three-necked round-bottomed flask equipped with a thermometer, condenser, and magnetic stirrer, 5-aminoisophthalic acid (I) (3.86 g, 27.6 mmol) was dissolved in water (129.42 g), and pH was adjusted with 96% sulfuric acid (2 mL, 35.3 mmol) to 1. Subsequently, solid iodine (8.42 g, 33.2 mmol) was added, and the mixture was heated to 72 °C in an oil bath. An 18.65% (w/v) aqueous iodic acid solution (20 mL, 21.2 mmol) was slowly added via syringe pump over 5.2 h (addition rate 3.8 mL/h). After continuing the reaction at 72 °C for 1 h (total reaction time 6.2 h), the reaction mixture was cooled to room temperature and filtered. The resulting solid was washed with water and dried to afford 5-amino-2,4,6-triiodoisophthalic acid (II) (12.74 g, 22.8 mmol) as a pale pink solid in 82.6% yield. The product was analyzed by HPLC and compared with the standard to confirm that it meets the analytical specification of industrially produced 5-amino-2,4,6-triiodoisophthalic acid.
