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 250 mL of anhydrous ethanol into a RBF, add 11.5 g of sodium and wait until all of the sodium has reacted with the ethanol to form sodium ethoxide. Add 80 g of dry ethyl malonate to the solution. Heat 250 mL of ethanol to near boiling point and dissolve 30 g of dry thiourea into it. Add the ethanolic thiourea solution to the first solution and reflux for 5 h, with magnetic stirring. Neutralize the solution with hydrochloric acid. Add water with heating to recrystallize the thiobarbituric acid.
Sodium metal reacting with the ethanol
Sodium ethoxide mixture
Addition of the HCl and water
The crystallized thiobarbituric acid