2 Practical 1
Health and safety
Concentrated sulfuric(VI) acid and nitric acid are both corrosive; nitric(V) acid is also oxidising.
Wear protective nitrile gloves when using these chemicals or the nitrating mixture.
Make sure that all apparatus is dry before use.
Methyl benzoate is harmful. Do not inhale its vapour and avoid contact with skin.
Ethanol is highly flammable and harmful. Keep away from all sources of ignition.
In particular, use recently boiled water from an electric kettle to warm the ethanol for recrystallisation.
Dispose of all ethanol safely before determining the melting point of the product.
Safety goggles must be worn at all times.
Introduction
In this experiment, you will be nitrating a benzene compound, methyl benzoate.
This reaction is a safer alternative to the nitration of benzene itself, which is a class 1 carcinogen.
The equation for the reaction is shown below.
O O
O + HNO
3
NO
2
     
O
+ H
2
O methyl benzoate + nitric acid   
2
   methyl 3-nitrobenzoate + water
The procedure consists of three stages:
A preparation of the crude product
B purification of the product by recrystallisation and filtration
C testing the purity of the product, by melting-point determination.
Apparatus per student or group
• concentrated sulfuric(VI) acid
• concentrated nitric acid
• methyl benzoate
• ice
• ethanol
• distilled water
• access to an electric kettle
• top-pan balance measuring to 2 decimal places
• melting-point apparatus
• protective nitrile gloves
• safety goggles
• 400 cm 3 beaker
• 250 cm 3 beaker
• three 100 cm 3 conical flasks
• 25 cm 3 measuring cylinder
• two 10 cm 3 measuring cylinders
• two boiling tubes
• eight graduated droppers
• Büchner funnel and flask
•
•
• filter pump or large syringe filter papers small thermometer
Original material © Cambridge University Press 2005, 2007, 2009
1 COAS Chemistry 2 Teacher Resources

2 Practical 1
Procedure
A: Preparation of crude product
1 Prepare an ice bath in a small trough or 400 cm 3 beaker.
2 Add 10 cm 3 of concentrated sulfuric acid ( CORROSIVE ) to a clean, dry boiling tube and place the tube in the ice bath. Leave for 5 minutes while you carry out the next part of the experiment.
3 In another clean, dry boiling tube, prepare a mixture of 3 cm 3 of concentrated sulfuric acid and
3 cm 3 of concentrated nitric acid ( CORROSIVE , OXIDISING ). Label the tube ‘nitrating mixture’ and cool it in the ice bath.
4 Place the 10 cm 3 measuring cylinder on the top-pan balance and add 4 cm 3 of methyl benzoate
( HARMFUL ). Record the mass of the liquid.
5 Add the methyl benzoate to the concentrated sulfuric acid ( not the nitrating mixture) and continue to cool it in the ice bath.
6 Using a clean, dry dropping pipette, add the nitrating mixture drop by drop to the acidified methyl benzoate. Carefully swirl the tube after each addition and make sure the temperature stays in the range 5–15

C.
7 After all the nitrating mixture has been added, leave the mixture to stand at room temperature for
10 minutes. Meanwhile cool 15 cm 3 of distilled water and 10 cm 3 of ethanol, ready for steps 11 and 12 respectively.
8 Crush up some ice and transfer about 40 g of it to a 250 cm 2 beaker.
9 Add the reaction mixture to the ice and stir until the product solidifies.
10 Filter the product using a Büchner flask and suction filtration.
11 Wash the solid product with three 5cm 3 portions of cold distilled water.
12 Change the collection flask for a clean, dry conical flask and wash the product with two 5 cm 3 portions of cold ethanol.
B: Purification of the product
1 Transfer the product to a 100 cm 3 conical flask, add 20 cm 3 of ethanol (
HIGHLY FLAMMABLE
,
HARMFUL ) and place the flask in a 400 cm 3 beaker of almost boiling water from an electric kettle.
2 When the solid dissolves, remove the flask from the hot water bath, filter its contents into a clean flask and allow to cool in the ice bath.
3 Measure and record the mass of a dry filter paper. Using this paper, filter off the solid and allow it to dry overnight.
4 Weigh the solid and filter paper. Calculate the mass of solid produced, and hence the percentage yield.
C: Checking the purity of the product
1 Using the melting-point apparatus, measure the melting point of the purified product.
(Pure methyl 3-nitrobenzoate melts at 77.5

C.)
2 As an extension activity, carry out thin-layer chromatography on the purified solid and the ethanolic filtrate from step 12 .
COAS Chemistry 2 Teacher Resources
Original material © Cambridge University Press 2005, 2007, 2009
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