Lab #13 - Preparation and Purification of an Ester
Introduction: The reaction between
a carboxylic acid with an alcohol results in the formation of an ester.
The reaction is carried out in an concentrated acid, such as sulphuric to
help remove the water from between the acid and alcohol
Many esters are pleasant-smelling substances and are, in fact, responsible
for the fragrances of many flowers and fruits. In this experiment
you will prepare and ester and then fractionally distill it to purify
and strengthen the aroma. This will be accomplished by first pouring
the reaction mixture into distilled water. The polar carboxylic acid,
alcohol and sulphuric acid will dissolve into the water and the less soluble
ester should float to the surface where it will be removed as the first distillate.
|250 mL beaker
||2 iron rings
||distillation apparatus as per previous labs
ethanol (ethyl alcohol) or methanol (methyl alcohol)
acetic acid or salicylic acid
concentrated sulphuric acid
||Heat 20 mL of water in a 250 mL beaker to the boiling
point using a hot plate. DO NOT use the bunsen burner as there are
flammable alcohol being used openly in the lab.
||While the water is heating prepare a clean dry large
||In the test tube place 10 mL of one of the alcohol
and 10 mL of one of the acids. Set this aside.
||Using a dropper pipette get some concentrated sulphuric
acid. CAUTION: concentrated sulphuric acid is extremely corrosive
to skin and clothing.
||Place the large test tube in the boiling water.
Add 10 drops of the sulphuric acid to the alcohol, carboxylic acid mixture
in the test tube.
||Boil the reaction for 5 minutes.
||To a clean distilling flask, add 50 mL of distilled
water and the contents of your large test tube.
||Set up your distilling apparatus and distill the ester
from the distillation flask mixture. It should be the first substance
that comes off. Record the temperatures every 30 seconds after the
temperature of the mixture starts to climb quickly.
||Your ester is the distillate. Packing the outside
of the receiving flask with ice will help condense your ester.
1. What can you say about the effect of sulfuric
acid on the reaction between the alcohol and carboxylic acid? Explain
2. What substance produces the odour of your
ester. Give it a proper name and chemical formula.
3. What is the complete chemical equation for
the reaction that occurred?
4. What substance, besides a carboxylic acid
and an alcohol, is required to prepare the ester?
5. How would you prepare an ester from acetic
acid and butan-1-ol? Give an equation for the reaction.
6. On the basis of this experiment, suggest
a likely commercial use for esters.