An in depth session on simple aromatic molecules, and the analytical techniques needed understand them

This session should take seven hours.

Suggested timings

  • 09.45 Arrival
  • 10.15 Lecture on chirality and its importance in chemistry, biology and pharmacology
  • 10.45 Lecture looking at the discovery of new medicines
  • 11.30 Break
  • 11.45 Careers lecture – why study chemistry?
  • 12.30 Lunch
  • 13.15 Organic practical session
  • 14.00 Groups are taken to analyse the starting material by either MS, NMR or IR. Try to finish by 14.45.
  • 14.50 Groups are taken to analyse their product by either MS, NMR or IR.
  • 15.10 Another group is taken to analyse the product using mass spectrometry.
  • 15.45 Break
  • 16.00 Lecture on up to date research being done at the university
  • 17.00 Finish

Equipment

  • Eye protection
  • Gloves
  • Apron
  • Crushed ice 
  • Ice baths
  • Thermometers
  • Dropping pipettes (eg ‘calibrated’ plastic)
  • Buchner flasks
  • Buchner funnels and suitable sized filter paper
  • Ethanol 
  • Steam baths
  • Melting point apparatus
  • Conical flasks
  • Beakers
  • Stirring rods
  • Water bottles
  • Large filter papers

Chemicals

  • Concentrated sulfuric acid
  • Concentrated nitric acid
  • Methyl benzoate
  • Deionised water

Health, safety and technical notes 

  • Read our standard health and safety guidance here.
  • Wear protective goggles, gloves, and apron.
  • Perform a risk assessment.
  • For safety information on sulfuric acid, see CLEAPSS Hazcard HC098a
  • For safety information on nitric acid, see CLEAPSS Hazcard HC067
  • Acids should be measured in a fume cupboard. 
  • No naked flames should be present whilst ethanol is being used.

Procedure

  1. Measure 2.5 cm3 of methyl benzoate into a small conical flask and then dissolve it in 5cm3 of concentrated sulfuric acid. When the liquid has dissolved, cool the mixture in ice.
  2. Prepare the nitrating mixture by carefully adding 2 cm3 of concentrated sulfuric acid to 2 cm3 of concentrated nitric acid. Cool this mixture in ice.
  3. Add the nitrating mixture – drop by drop from a teat pipette – to the solution of methyl benzoate. (NB: Do not allow the nitrating mixture to get into the rubber teat.) Stir the mixture with a glass rod and keep the temperature below 10 °C. When you have completed the addition, leave the mixture to stand at room temperature for another 15 minutes.
  4. After 15 minutes, pour the reaction mixture on to about 25 g of crushed ice and stir until all the ice has melted and the crystalline nitro derivative forms.
  5. Filter the crystals using a Buchner funnel, wash thoroughly with cold water, and then transfer to a small beaker.
  6. Recrystallise the product from hot ethanol. The idea of recrystallisation is to dissolve the impure product in the minimum possible volume of hot solvent. When you cool the solution, the product that you want crystallises out of solution. This is because there is not enough solvent to dissolve it all at the lower temperature. However, the impurities stay behind in solution, because there are less of these impurities there is enough solvent to keep them dissolved. You then filter off the crystals of the product from the remaining solution.
  7. Put 15 cm3 of ethanol in a boiling tube. Warm it to about 50 °C on the steam bath. Dissolve all the crystals in the minimum possible volume of this hot ethanol. Allow the solution to cool to room temperature, then immerse the beaker in ice to complete the crystallisation.
  8. Filter the crystals and dry them between filter paper. If there is time, measure the melting point of the crystals.

 

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