Practical Experiment 4: Benzyl from benzoin

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, 5 th 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. 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. CALCULATIONS :- Molecular weight of benzoin = 212.24gm/M Molecular weight of benzil = 210.23gm/M Weight taken of benzoin= 1 gm/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%

6. Calculation: TLC: Structure:    Formula:   C 14 H 10 O 2 Theorotical Yield:   0.99gm Practical Yield:   0.92gm % Yield:   92% Melting/Boiling Point:   94.8 c /346.8 c R f Value:   0.83