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Investigate the formation of an Ester through the reaction of an alcohol with a carboxylic acid, where the ester formation is promoted by the presence of concentrated sulphuric acid acting as a catalyst.


Time Allocation: 45 Minutes

An ester is a chemical compound used to make many fragrances in the cosmetic industry as well as artificial flavours for the food industries. What is also surprising about the commercial uses for esters is the use of them as ester based fluids in transformers at some electric power plants. In recent times the short comings of mineral oil are being realized as flammability, poor environmental performance, low moisture tolerance and corrosive sulphur which pose production issues. The solution to all these problems is to use an ester based fluid, since they are fire safe, readily biodegradable, and free from corrosive sulphur compounds, they have excellent moisture tolerance. Ester fluids have also been shown to extend the life of cellulose insulation, bringing further benefits to operators.

Synthetic esters are manufactured from carefully selected raw materials to give a finished product that is tailored to the specific application. Natural esters are derived directly from natural sources. These are not easily tailored to fit application needs unlike synthetic esters.

Production of Esters

An ester is a reaction product from the combination of an acid and an alcohol. This process is called an acid-catalysed condensation or Esterification of a carboxylic acid. The reaction produces an Ester and water as reaction products.


 The first part of the ester name takes its prefix from the alcohol, with suffix –yl. The second part of the ester takes its prefix from the carboxylic acid with the ester suffix –oate.  For example the ester ethyl ethanoate is created from the combination of the alcohol portion of ethanol with the carboxylic acid portion of Ethanoic acid.

An ester has the functional group  , which is also known as an ester link. The reaction is called a condensation reaction because two molecules link up by the elimination of a small molecule between them, in this case water.

The use of sulphuric acid the catalyst as well as a dehydrating agent is present in these reactions. Reactions like esters can take place without a catalyst, however the rate of reaction will be extremely slow. Some examples such as the aroma of Oranges, is attributed to octyl ethanoate (formed from octanol and ethanoic acid) and apricots have an aroma because of the presence of pentyl butanoate (formed from pentanol and butanoic acid).


  • Test Tube Rack
  • 3 x Glass Test Tubes
  • 3 x Glass Beakers 400ml
  • Gas stove
  • Thermometer
  • 25g Salicylic acid
  • 100ml Methanol
  • 100ml Propanol
  • 100ml Butanol
  • 10ml Sulphuric Acid 98%
  • 100ml Distilled water
  • 5 x 5ml graduated pipettes
  • 1 x glass stirring rod
  • 1 x stainless steel spatula
  • 3 x metal test tube tongs


  1. Work in groups of 3.
  2. Ignite the gas burner and place a wire gauze over it.
  3. Take the 400ml beaker and fill it with 200ml of tap water and place it over the burner on top of the wire gauze.
  4. Place the thermometer inside the beaker and monitor it as it will gradually heat up between 60˚C – 70˚C, do not allow them to reach boiling point, switch it off as it reaches above 70˚C.
  5. Take 3 test tubes and label them A to C.
  6. Place them in the test tube rack.
  7. Take 3 vials containing 2g Salicylic acid and place each vials content into one of each test tube.
  8. Using the first pipette measure 4ml of methanol and add it to beaker A.
  9. Use a second new pipette and measure 4ml of propanol and add it to beaker B.
  10. Using the third pipette measure 4ml of butanol and add it to beaker C.
  11. Use the last pipette to place 8 drops of concentrated Sulphuric acid into each of the test tubes.
  12. Shake the contents of the test tubes to allow the contents to mix.
  13. Once has reached 60˚C – 70˚ take all 3 test tubes, hold them with the tongs and place them in the water bath with the tongs attached to weigh them down, if the water boils you will not be able to keep the test tubes stable.
  14. Ensure the water level is enough to submerge the contents of the test tubes so they heat effectively.
  15. Leave them in the water bath for 15 minutes, shake regularly, record any smells coming off the beakers in the process without directly smelling them, also note down what you observe as they heat.
  16. While waiting, take the second beaker and add 200ml cold tap water into it.
  17. After 15 minutes remove the test tubes from the hot water bath and transfer them to the cold water bath to cool.
  18. As the test tubes are cooling, take the hot water bath beaker, empty its contents as well as the one remaining clean beaker, fill it with normal cold tap water up to 200ml.
  19. Label the beakers A and B, as you remove the test tubes from the cold water bath label the cold water bath beaker C do not empty this beaker.
  20. Decant each corresponding letter test tube into each of its labelled beakers.
  21. Have one student hold the beaker and the other lightly blow over the top of the beaker toward the next student in order to get the smell of the ester.
  22. Do this for all 3 beakers.
  23. Note down the test tubes and your observations on the table below for record purposes before you start the practical.


There should be different aromas produced in each test tube, adding them water allows the ester to form a thin film over the top of the solution as it is slightly insoluble. Sulphuric acid is an ideal catalyst as it is hygroscopic, meaning it attracts water compounds in the reaction speeding up the reaction rate as it removes the water molecule where the ester linkage will occur.

Draw a table to record your results, the table should have 2 columns with the following headings and 3 rows for your labelled test tube results.



  • Wear safety goggles at all times.
  • Avoid skin contact with any chemicals – wear gloves and protective clothes at all times when handling chemicals.
  • Avoid eye contact with Acids and Alcohols– In case of contact with eyes, wash with cold water and get medical help.
  • Sulphuric Acid is corrosive and causes severe skin irritation and burns.
  • In case of skin contact, rinse with a lot of cold water.
  • Do not directly sniff the acids or esters you will be making.
  • All Alcohols are toxic; methanol can cause blindness, coma and even death.
  • Ethanol is a severe nerve poison.
  • Alcohols and Esters have high vapour pressure and are extremely flammable, therefore keep a fire extinguisher on stand-by