(1) Assemble a mechanical stirrer, thermometer, and constant pressure dropping funnel in a 500mL three-necked flask. 35g of maleic anhydride (0.357 mol) and 100mL of acetone were added to the flask and stirred at 20°C until completely dissolved. Meanwhile, a clear solution was prepared by dissolving 49 g of p-aminobenzoic acid (0.357 mol) in 250 mL of acetone. Subsequently, the acetone solution of p-aminobenzoic acid was slowly added dropwise through a constant pressure dropping funnel into a three-necked flask. After the dropwise addition, the reaction was continued with stirring for 1 hour. After completion of the reaction, filtration was carried out (recovery of solvent), and the solid product was washed with an appropriate amount of solvent, followed by recrystallization and drying to give 77.28 g of yellow crystalline N-(4-carboxyphenyl)maleimidic acid in 92% yield and 99.3% purity (HPLC analysis).
