To a beaker immersed in an ice bath add 30 mL of 100% fuming nitric acid and slowly with stirring start the addition of 20 g of barbituric acid while maintaining the temperature below 40°C. Continue the stirring for 1h after the addition, then pour 430 mL of water to the solution and cool the mixture down to 10°C, filter and wash with 50 mL of cold water. Dry the crude product at 110°C for 2-3h to remove the nitric acid and water, recrystallize the crude product from warm acetone.
Nitration of the barbituric acid
The mixture after the addition of the water
Filtration of the mixture
The dry crude product