Combine fine powders of 70 g of phthalic anhydride with 23 g of urea, pour the mixture 1 L RBF, heat the mixture strongly. After 15-20 minutes the mixture turns into a foam then the reaction is complete. Cool down the mixture until it is warm and add 300 mL of hot water, break up the lumps. Pour the contents into a beaker, wash the RBF with 200 mL of hot water, stir the mixture well to break up all the lumps. Filter and wash twice with warm water. Dry the product at 150°C for 2h.
Start to heat strongly, some of the anhydride will sublime out
The mixture started to melt and boil
The reaction is now complete
Add the water and break the lumps
Start to break the lumps and stir well
Filter and wash with warm water