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BACKGROUND
Principle:
The synthesis of barbituric acid is effected by condensation of diethyl malonate with urea in the presence of sodium ethoxide which may be prepared by reacting Na metal with ethanol and it undergo cyclization reaction with diethyl malonate.1
Aim: To prepare barbituric acid from urea and dimethyl malonate.
Reaction:
Mechanism:
Use:
Itself not active pharmacologically, buts its derivatives are used as sleeping pills and sedatives.
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REQUIREMENTS
Chemicals: Sodium metal
Ethanol
Diethyl malonate
Urea
Calcium chloride
Concentrated hydrochloric acid
Apparatus: Round bottom flask – 2000 ml
Reflux condenser
Beaker
Buchner funnel
Measuring cylinder
Filter paper
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PROCEDURE
Assemble a double surface reflux condenser with a 2 litre round bottomed flask, place 11.5 g (0.5 mol) of clean sodium. Mix 250 ml of absolute ethanol in a portion and if the reaction is unduly vigorous, immerse the flask within ice. When all the sodium has completed reaction, add diethyl malonate 80 g (76 ml, 0.5 mol), followed by a solution of dry urea 30 g (0.5 mol) in 250 ml of hot (70 °C) absolute ethanol. Shake the mixture thoroughly, attach a calcium chloride guard tube to the top of the condenser, start reflux of the mixture for 7 h in an oil bath and heat to 110 °C. A white solid will be separated. Treat the reaction mixture with hot (50 °C) water 450 ml and then with concentrated hydrochloric acid, with constant stirring, until the solution will be acid (about 45 ml). Filter the resulting almost clear solution and leave it in the refrigerator overnight. Filter the solid at the pump, wash it with 25 ml of cold water, drain well and then dry at 100 °C for 4 hours. The yield of barbituric acid is 50 g (78%). It melts with decomposition at 245 °C.
Calculation:
Here limiting reagent is diethyl malonate; hence yield should be calculated from its amount taken.
Molecular formula of diethyl malonate = C7H12O4
Molecular formula of barbituric acid = C4H4N2O3
Molecular weight of diethyl malonate = 160 g/mole
Molecular weight of barbituric acid = 128 g/mole
Theoretical yield:
160 g diethyl malonate forms 128 g barbituric acid
Therefore, 80 g diethyl malonate will form …….? (X) g barbituric acid
X =( 128 ×80)/160 = 64 g
Theoretical yield = 64 g
Practical yield = ————- g
% Yield = (Practical Yield)/(Theoretical Yield) × 100
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CONCLUSION
Barbituric acid was synthesized and the percentage yield was found to be………..%
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REFERENCES
- Vogel’s Textbook of Practical Organic Chemistry by Brian S. Furniss, Antony J. Hannaford, Peter W. G. Smith & Austin R. Tatchell; Fifth Edition; Page No. 1176.
