Heat all the glassware to dry them first. Make sure that your reflux apparatus is protected by calcium chloride tube, water will make your yield smaller. Pour 50 mL of anhydrous ethanol into a conical flask, add 2.2 g of sodium and wait until all of the sodium has reacted with the ethanol to form sodium ethoxide. Add 15 mL of dry diethyl malonate and 6 g of dry urea dissolved in 50 mL of hot anhydrous ethanol to the solution and reflux for 10h, with magnetic stirring. Be careful not to exceed 120°C Cool the mixture down, add 50 mL of 50°C water and neutralize the solution with hydrochloric acid. Cool the mixture down in a freezer, filter and wash with a little of cold water. Recrystallize the barbituric acid from boiling water.
The crystallized barbituric acid