Practical Experiment 4: Benzyl from benzoin
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The document summarizes an experiment to synthesize benzyl from benzoin. Benzoin is reacted with concentrated nitric acid, which oxidizes the alcohol group to a ketone, forming benzil. This is done by heating a mixture of benzoin and nitric acid on a water bath for 1.5 hours. The benzil product is purified by crystallization and has a melting point of 94-96°C. The percentage yield of benzil obtained is calculated to be 92% based on the theoretical and practical yields.
![Title: Synthesis of Benzyl from Benzoin
Aim: To synthesize and submit Benzyl from Benzoin.
Procedure: [Ref: B. S. Furniss, A. J. Hannaford, P. W. G. Smith, Vogel’s textbook of practical
organic chemistry, 5th edition, Co published in the United States with John Wiley & Sons,
Inc., New York Page No. 1043-1045]
Place 1 g (0.0047 mol) of crude benzoin and 5 ml of concentrated nitric acid in a 250-ml
round-bottomed flask. Heat on a boiling water bath (in the fume cupboard) with occasional
shaking until the evolution of oxides of nitrogen has ceased (about 1.5 hours). Pour the
reaction mixture into 50-100 ml of cold water contained in a beaker, stir well until the oil
crystallizes completely as a yellow solid. Filter the crude benzyl at the pump, and wash it
thoroughly with water to remove the nitric acid. Recrystallize from ethanol or rectified
spirit (about 2.5 ml per gram). The yield of pure benzyl, m.p. 94-96 °C, is______ g.](https://image.slidesharecdn.com/exp4benzylfrombenzoin-210626113118/85/Practical-Experiment-4-Benzyl-from-benzoin-2-320.jpg)
Practical Experiment 4: Benzyl from benzoin
- 1. Experiment 4: To synthesize and submit Benzyl from benzoin. Presented By…. Prof. Sonali R. Pawar Medicinal Chemistry I B. Pharmacy IV semester
- 2. Title: Synthesis of Benzyl from Benzoin Aim: To synthesize and submit Benzyl from Benzoin. Procedure: [Ref: B. S. Furniss, A. J. Hannaford, P. W. G. Smith, Vogel’s textbook of practical organic chemistry, 5th edition, Co published in the United States with John Wiley & Sons, Inc., New York Page No. 1043-1045] Place 1 g (0.0047 mol) of crude benzoin and 5 ml of concentrated nitric acid in a 250-ml round-bottomed flask. Heat on a boiling water bath (in the fume cupboard) with occasional shaking until the evolution of oxides of nitrogen has ceased (about 1.5 hours). Pour the reaction mixture into 50-100 ml of cold water contained in a beaker, stir well until the oil crystallizes completely as a yellow solid. Filter the crude benzyl at the pump, and wash it thoroughly with water to remove the nitric acid. Recrystallize from ethanol or rectified spirit (about 2.5 ml per gram). The yield of pure benzyl, m.p. 94-96 °C, is______ g.
- 3. Theory: Here alcohol group of benzoin is oxidized to ketone group forming benzil in the presence of concentrated nitric acid. Nitration of aromatic ring is not occurring as sulphuric acid is totally absent in the whole process. What is the role of nitric acid in conversion of benzoin to benzil? The synthesis of benzil involves reacting benzoin from the previous lab with nitric acid through an oxidation reaction. An oxidation reaction is a type of reaction that involves a transfer of electrons. In this experiment nitric acid is used as the oxidizing reagent to oxidize benzoin. Uses: Benzil is commonly used as pharmaceutical intermediates, insecticide and curing agent. It is used in organic synthesis. Its main use is as a photoinitiator in polymer chemistry. It is used in the free-radical curing of polymer networks.
- 4. C H C O OH O C O C O Benzoin (a-hydroxyketone) Benzil (diketone) Principle: Oxidation of the a-hydroxyketone with concentrated nitric acid, or by catalytic amounts of copper(n) salts in acetic acid solution which are regenerated continuously by ammonium nitrate, yields the diketone that is benzil.
- 5. O OH N O HO O O O H N OH O O O O H N HO OH O O O + N OH HO O HO OH N O H -H2O O N O Nitrogrn (IV) Oxide
- 6. CALCULATIONS :- Molecular weight of benzoin = 212.24gm/M Molecular weight of benzil = 210.23gm/M Weight taken of benzoin=1gm/M Practical yield = 0.92gm X(theoretical yield )=molecular weight benzil x weight of benzoin taken molecular weight of benzoin =210.23g/M x 1g/212.23g/M = 0.99gm Percentage yield = practical yield /theoretical yieldx100% Percentage yield =0.92/0.99x100% Percentage yield = 92%
- 7. Calculation: TLC: Structure: Formula: C14H10O2 Theorotical Yield: 0.99gm Practical Yield: 0.92gm % Yield: 92% Melting/Boiling Point: 94.80c /346.80c Rf Value: 0.83