Explore some of the most important principles of chemistry with this session that shows learners how to isolate a physiologically active organic compounds

This session should take six hours. 

Session timings

  • 9.00 Students arrive
  • 9.30 General introduction and explanation of why the experiments in the activity are useful.
  • 10.00 Laboratory session
  • 14.00 Lunch break
  • 14.15 Summary of what the students have learnt during the day. Careers talk from a university academic or an industrialist.
  • 15.00 Finish

Equipment

  • Separating funnel, 100 cm3 
  • Round bottomed flask, 100 cm3 
  • Test tube rack and three test tubes
  • Filter funnel
  • Filter paper
  • Spatula
  • Melting point tube
  • Thin layer chromatography (tlc) plate
  • Jar for running tlc
  • Capillaries for tlc
  • Wash bottle of deionised water

Chemicals

  • Paracetamol tablets x 4
  • Ethyl acetate 100 cm3
  • Deionised water
  • Dilute HCl (approx 2 cm3 per student)
  • Dilute NaOH (approx 2cm3 per student)
  • Anhydrous MgSO4 (for drying)

Health, safety and technical notes 

  • Read our standard health and safety guidance here.
  • Wear eye and clothing protection if desired.
  • For safety information on ethyl acetate, see CLEAPSS Hazcard HC043a
  • For more information on hydrochloric acid, see CLEAPSS Hazcard HC047a
  • For more information on sodium hydroxide, see CLEAPSS Hazcard HC091a

Procedure

Isolation procedure

  1. Weigh out four tablets and place them in a small beaker containing 20 cm3 of distilled water. Observe what happens.
  2. After the tablets have disintegrated, transfer the contents of the beaker to a separating funnel and add 20 cm3 of ethyl ethanoate
  3. Shake the funnel vigorously until everything has dissolved. Allow the solvents to separate and run off the lower aqueous layer (including any emulsion at the interface) into the beaker. Keep this fraction.
  4. Run off the remaining ethyl ethanoate layer into a dry 100 cm3 conical flask.
  5. Put the aqueous layer back into the separating funnel and extract it once more with a fresh 20 cm3 of ethyl ethanoate. Combine this ethyl ethanoate extract with the previous one to give a combined organic extract. Keep the aqueous layer!
  6. Dry the ethyl ethanoate solution by adding a heaped spatula of anhydrous magnesium sulfate to it, and gently swirl the flask. 
  7. After 10–15 minutes, filter off the drying agent into a round bottom flask which has been previously weighed. 
  8. Evaporate the solution to dryness on a rotary evaporator and weigh the flask again.
  9. Record the weight of your solid on the report sheet.
  10. At the end of the experiment wash the aqueous extract down the sink with plenty of tap water.

Preliminary investigation of the white solid (X)

  1. Record the infrared (IR) spectrum of X, with the help of a demonstrator.
  2. Run a thin layer chromatography (tlc) analysis of X using ethyl ethanoate as the eluent.
  3. Measure the melting point of X and record it on the report sheet.
  4. Investigate the solubility of X by adding small samples to approximately 1 cm3 of the following solvents. Give each test about 2–3 minutes for something to happen. Record your observations on the report sheet: 

Notes

The students do not know that the compound they are isolating is paracetamol. It is important that they do not know the identity of the compound before starting the experiment.

A compound with an odd number of nitrogen atoms has a molecular mass that is also an odd number

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