Nitration of Methyl Benzoate

Benzene rings are components of many important natural products and other useful organic compounds. 
Therefore, the ability to put substituents on a benzene ring, at specific positions relative to each other, is a very 
important factor in synthesizing manyorganic compounds. The two main reaction types used for this are both 
substitutions: Electrophilic Aromatic Substitution (EAS) and Nucleophilic Aromatic Substitution (NAS). The 
benzene ring itself is electron-rich, which makes NAS difficult, unless there are a number of strongly electron-withdrawing substituents on the ring. EAS, on the other hand, is a very useful method for putting many different 
substituents on a benzene ring, even ifthere are other substituents already present. Electrophilic Aromatic 
Substitution chapter describes the factors involved in the regioselectivity for EAS reactions using benzene rings, 
which already have substituents on them. 
In this experiment you will put a nitro (—NO2) group on a benzene ring, which already has an ester group, 
attached to it (methyl benzoate). The actual electrophile in the reaction isthe nitronium ion (NO2+), which is 
generated in situ("in the reaction mixture" HNO3/H2SO4) using concentrated nitric acid and concentrated sulfuric 
acid. 

Reaction mechanism
The carbomethoxy group (-CO2CH3) directs the aromatic substitution reaction to the position that are meta to it. 
As a result the m-nitrobenzoate is the principal product from this reaction. Formation of dinitro products from this 
reaction is unlikely under the conditions in which you carryout your reaction. The reason for this is that both 
carbomethoxy groups as well as the nitro group (on the mono nitrated product)are deactivating groups making the 
second nitration less favorable. 

Concentrated sulfuric acid is the solvent for this reaction and is involved in the formation of nitronium ion (NO2+) 
from concentrated nitric acid. Water has a retarding effect on the nitration since it interferes with the nitric acid-sulfuric acid equilibrium (shown below) that generates the required nitronium ion 
Temperature also has an effect on the product distribution from this reaction. Higher the temperature, greater will 
be the amounts of dinitration products formed from this reaction. 
Safety Note
Caution:Avoid contact with the acids used in this experiment and the reaction product. 
Prevent contact with the skin, eyes, and clothing; work in the hood. An acid spill is 
neutralized using solid sodium carbonate or bicarbonate. The reaction is highly 
exothermic. A vigorous reaction will occur if the acid mixture is added too rapidly to the methyl benzoate. 
Concentrated nitric acid and concentrated sulfuric acid are both strong oxidizers, and strongly corrosive--wear gloves while handling them, and avoid breathing their vapors. 
Methyl benzoate and methyl m-nitrobenzoate are irritants-- wear gloves while handling them. Methanol is a flammable liquid,and is toxic -- no flames will be allowed in lab, 
wear gloves while handling it, and avoid breathing its vapors.

Experimental Procedure


Chemicals              Materials

                       150 – mL beaker 

Methyl benzoate        400-mL beaker 

Sulfuric acid (conc.)  125-mL flask 

Nitric acid (conc.)    Stirring rod 

Ice                    

Methanol              Suction filtrationfunnel 

In a 125-mL. Erlenmeyer flask mix 1.5 mL of methyl benzoate and approximately 4.0 mL of concentrated 
sulfuric acid (drop-wise), and chill it in an ice bath. Continue to cool the mixture in the ice bath to reduce the heat, 

which produced in the reaction. After complete addition of sulfuric acid, add approximately 2.0 mL concentrated 

nitric acid (measured in 10- mL graduated cylinder) drop- wise using a small graduated plastic pipette and mix by 
gentle swirling. Continue to cool the reaction mixture. Allow the reaction mixture to stand at room temperature for 
about five minutes. 
Float the 125-mL flask in a 400-ml beaker hot water bath. Remove the flask occasionally and swirl the content 
carefully. After fifteen minutes heating pour the reaction mixture in 100-ml ofice water contained in a 150- mL 
beaker, with stirring. 
Product Isolation- Isolate the product by vacuum filtration, wash the product with (ice) cold water (20 mL). 
Note- Proper washing removes the more soluble orthoisomer. The crude material may be purified by 
recrystallization from a small volume ( ~ 10 mL) of hot methanol (optional). The crude product is pressed dry. 
You may need to air dry (or hand dry using paper towels) the product. Discard the aqueous filtrate down the drain 
with lots of water. 

Synthesis of Methyl 3-nitrobenzoate  2
Notes: 
A.  The methyl benzoate is soluble in the sulfuric acid at this step and should produce a clear colorless solution. 
A yellow solution may indicate an unclean flask or an impurity introduced inadvertently. 
B.  For convenience, two or more students can share a larger batch of 50:50 conc. H2SO4and HNO3prepared in 
separately. 
C.  The nitration of methyl benzoate runs smoothly at nearly the rate that the HNO3is added. It is essential to 
keep the temperature within the specified limits, otherwise the yield falls; at 50°C the yield drops to about 
70%, while at 70°C the yield drops to about 50%. 
D.  It is not necessary to weigh the cracked ice. The density of cracked ice is about 0.5 g/mL. Hence, 15 grams 
of cracked ice is equivalent to about 30 mL. Do not take more ice than this because a filtration step comes 
after this and the presence of a large excess of ice will make the isolation of solid product more difficult. 
E.  The methanol wash will contain by-products of the reaction. These will include methyl 2-nitrobenzoate and 
traces of dinitrobenzbenzoic ester. There will also be some methyl 3-nitrobenzoateproduct in the methanol 
as well which will reduce your yield. The amount of this loss should be only a small percentage of your 
yield depending on your technique. Keep the methanol cold to minimize loss of your product. 
F.  Methanol has a bp 65°C so use a small beaker and an appropriate setting on the hot plate. Cover the small 
beaker with a small square of aluminum foil to reduce vapor loss as the methyl m-nitrobenzoate dissolves. 
Turn the hot plate off as soon as the methanol reachesboiling and a clear pale yellow solution is obtained. 
Place the hot flask on a paper towel on your desk, not directly on a cold surface.Also place a larger 
inverted beaker over the recrystallizing beaker to isolate cold drafts. Better crystals result when the hot 
solution cools slowly undisturbed. 
G.  The recrystallization of methyl 3-nitrobenzoate typically results in about a 15% loss of product compared to 
the yield at the crude product stage. This mechanical loss can be higher if you are careless in handling and 
leave significant solid on surfaces in the recrystallization procedure.