SCH4C          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

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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.

Apparatus:

250 mL beaker wire gauze
bunsen burner pipettes
ring stand 2 iron rings
test tubes distillation apparatus as per previous labs

Materials:
ethanol (ethyl alcohol)  or methanol (methyl alcohol)
acetic acid or salicylic acid
concentrated sulphuric acid

Procedure:
1. 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.
2. While the water is heating prepare a clean dry large test tube.
3. In the test tube place 10 mL of one of the alcohol and 10 mL of one of the acids.   Set this aside.
4. Using a dropper pipette get some concentrated sulphuric acid.  CAUTION:  concentrated sulphuric acid is extremely corrosive to skin and clothing.
5. 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.
6. Boil the reaction for 5 minutes.
7. To a clean distilling flask, add  50 mL of distilled water and the contents of your large test tube.
8. 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.
9. Your ester is the distillate.  Packing the outside of the receiving flask with ice will help condense your ester.

Questions:
1.    What can you say about the effect of sulfuric acid on the reaction between the alcohol and carboxylic acid?  Explain your answer.

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.