Example 2: General procedure for the synthesis of 2,4-dioxo-5,5-diphenylimidazoline-1-sodium salt from 5,5-diphenylglycolide urea: 5,5-diphenylglycolide urea (20 g) was dissolved in 120 mL of deionized water and sodium hydroxide solution (3.56 g in 22.5 mL of water), and stirred in a 250 mL four-necked round-bottomed flask at 25-30 °C until complete dissolution. The reaction mixture was filtered. The reaction mixture was filtered, the clarified filtrate was collected and sodium chloride solution (4 g in 10 mL of water) was added to it. The reaction mixture was cooled to 5-10 °C under nitrogen protection and stirred for 60 min. The solid product was filtered under vacuum and washed with 20 mL of cold water. The solid was dried under nitrogen atmosphere at 50-60°C to give 18.5 g of dry 2,4-dioxo-5,5-diphenylimidazoline-1- sodium salt in about 85% yield.
Example 3: 5,5-Diphenylglycolide (25 g) was dissolved in 150 mL of deionized water and sodium hydroxide solution (4.45 g in 25 mL of water) in a 250 mL four-necked round-bottomed flask with stirring at 25-30 °C until completely dissolved. The reaction mixture was filtered, the clarified filtrate was collected and sodium chloride solution (7.5 g in 22 mL of water) was added to it. The reaction mixture was cooled to 5-10°C under nitrogen protection and stirred for 60 minutes. The solid product was filtered under vacuum and washed with 20 mL of cold water. The solid was dried under nitrogen atmosphere at 50-60°C to give 25.3 g of dry 2,4-dioxo-5,5-diphenylimidazoline-1- sodium salt in about 93% yield.
Example 4: 5,5-Diphenylglycolide (25 g) was dissolved in 150 mL of deionized water and sodium hydroxide solution (4.45 g in 25 mL of water) in a 250 mL four-necked round-bottomed flask with stirring at 25-30 °C until completely dissolved. The reaction mixture was filtered, the clarified filtrate was collected and sodium chloride solution (10 g in 28 mL of water) was added to it. The reaction mixture was cooled to 5-10°C under nitrogen protection and stirred for 60 minutes. The solid product was filtered under vacuum and washed with 20 mL of cold water. The solid was dried under nitrogen atmosphere at 50-60°C to give 25.9 g of dry 2,4-dioxo-5,5-diphenylimidazoline-1- sodium salt in about 95.3% yield.
Example 5: Potassium hydroxide (152 g) was dissolved in 96 mL of deionized water in a 3L round-bottomed flask, methanol (480 mL) was added at 25-30°C and cooled to 0-5°C. The mixture was then purified by addition of urea. Urea (49.5 g) and diphenylethylenedione (100 g) were added at 0-5 °C. The reaction mixture was refluxed for 60 min. The reaction mixture was refluxed for 60 min, 144.0 mL of water was added and cooled to 0 °C. The reaction mixture was then cooled to 0 °C. 10 g of diatomaceous earth and 10 g of activated carbon were added and stirred at 0-5 °C for 30-60 min. The reaction mixture was filtered through a bed of diatomaceous earth, washed with cooled 100 mL of water, and the filtrate was collected in a 3L round bottom flask. The pH was adjusted to 6.0-7.0 with concentrated hydrochloric acid at 30-45 °C. The slurry was stirred for 30 min, filtered and washed with 1000 mL of hot water to give 178.1 g of wet 5,5-diphenylglycolide with a moisture content of 38.7% and an anhydrous weight of 109.2 g. Wet 5,5-diphenylglycolide (178 g) was dissolved in 600 mL of deionized water and a solution of sodium hydroxide ( 16.7 g was dissolved in 105 mL of water) in a 2L round-bottomed flask and stirred at 30-40 °C until complete dissolution. The reaction mixture was filtered, the clarified filtrate was collected and sodium chloride solution (2 g in 32 mL of water) was added to it. The filtrate was cooled to 5-10°C under nitrogen protection and stirred for 60 minutes. The solid product was filtered under vacuum and washed with 100 mL of cold water. The solid was dried under nitrogen atmosphere at 50-60°C to give 102.6 g of dry 2,4-dioxo-5,5-diphenylimidazoline-1- sodium salt.
