CHEM 234: Laboratory Procedure
ELECTROPHILIC AROMATIC SUBSTITUTION
Nitration of Methyl Benzoate
Benzene and somewhat less reactive aromatic compounds such as methyl benzoate can be nitrated with
a mixture of nitric and sulfuric acids that ionizes completely to generate the nitronium and hydronium ions:
+
-
HNO3 + 2H2SO4 NO2 + 2HSO4 + H3O
+
Hot concentrated nitric acid is also a good oxidizing agent. For example, benzoin is oxidized easily to
benzil. Activated aromatic compounds such as amines and phenols can be nitrated using just
concentrated nitric acid:
+
-
2HNO3 NO2 + NO3 + H2O
1,3,5-Trinitrobenzene cannot e prepared by nitration of m-dinitrobenzene, even with the use of heat,
concentrated sulfuric acid, and fuming nitric acid because the two nitro groups strongly deactivate the
benzene ring.
In the present experiment, sulfuric acid serves as the solvent:
O
O
CH3
C
+ H2SO4
H
O
+
C
O
CH3 H
+
O
O
CH3
C
+ HSO4-
and nitration occurs at the meta position because of the partial positive charges residing at the ortho and
para positions.
Nitration of Methyl Benzoate
NO2+ + 2HSO4- + H3O+
HNO3 + 2H2SO4
Nitronium ion
COOCH3
Hydronium ion
COOCH3
HNO3
H2SO4
NO2
Methyl benzoate
MW 136.16
o
Methyl 3-nitrobenzoate
bp 199.6 C
MW 181.15
den 1.09
mp 78oC
In a 125-mL Erlenmeyer flask cool 12 mL of concentrated sulfuric acid to 0°C and then add 6.1 g of
methyl benzoate. Again cool the mixture to 0-10°C. Now add dropwise, using a Pasteur pipette, a cooled
mixture of 4 mL of concentrated sulfuric acid and 4 mL of concentrated nitric acid. During the addition of
the acids, swirl the mixture frequently and maintain the temperature of the reaction mixture in the range of
5-15°C.
When all the nitric acid has been added, warm the mixture to room temperature and after 15 min pour it
on 50 g of cracked ice in a 250 mL beaker. Isolate the solid product by suction filtration using a small
Buchner funnel and wash well with water, then with two 10-mL portions of ice-cold methanol. A small
sample is saved for a melting point determination. The remainder is weighed and crystallized from an
equal weight of methanol.
Cleaning Up
Dilute the filtrate from the reaction with water, neutralize with sodium carbonate, and flush down the drain.
The methanol from the crystallization should be placed in the organic solvents container.