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