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The following reaction will be used for the synthesis:
aspirilabelinreaction.jpg

  1. Place 5 cm3of distilled water in a clean boiling tube and place in a bucket of ice to cool. This will be used in step 7.
  2. Weigh 0.25 g of salicylic acid into dry boiling tube
  3. Add 0.5 cm3 14C-labelled salicylic acid
  4. Using a disposable pipette, carefully add 1 drop conc. sulphuric acid
  5. Shake and then heat in the dry bath in the fume hood for ~15 min
  6. Cool the boiling tube in the basin of ice and add 5 cm3of distilled H2O to form a slurry
  7. Filter this through a Buchner funnel then wash with 1 - 2 cm3of ice-cold distilled water to minimise solution of the product – keep filtrate for later (see step 11)
  8. Dry the filter paper using the vacuum pump to pull air through, then scrape the crystals off the filter paper into a 3rdclean boiling tube. Make sure you are working only in the white tray so that no crystals are dropped on the bench. Change your gloves after doing this.
  9. Add 1-2 cm3of toluene and place in the dry bath for 5-10 min to dissolve the crystals
  10. Place the boiling tube in the ice bucket for 20 min to allow to cool, stirring occasionally to form small crystals
  11. Refilter through a 2nd Buchner funnel
  12. Transfer the filter paper onto an aluminium planchette and dry to constant weight under the infrared lamp in the fume hood – when weight stops changing it is at constant weight – you will need to record this final weight – keep this filter paper to use in step 17
  13. The original filtrate (from step 7) contains a small amount of dissolved product which can be recovered by scavenging with inactive aspirin (acetyl salicylic acid) and will give 2nd product with lower specific activity
  14. 4. Add 0.15 g of inactive aspirin to a 4th boiling tube, then add filtrate, warm in the dry bath for 5-10 min and then stand in ice with occasional shaking – the dissolved and undissolved aspirin will exchange – this will become fairly solid
  15. Filter through Buchner funnel – if solid then scrape out with spatula – to collect the aspirin
  16. Transfer filter paper to planchette and dry to constant weight as previously – record weight
  17. Scrape the crystals from each of your 2 filter papers into separate plastic 20 ml scintillation vials and record weight (20 – 40 mg if possible – there may be very little on the filter paper) – record the weight
  18. Add 10 ml of scintillation fluid to each of these vials, and also add 10 ml of scintillation fluid a 3rd empty vial to give the background count, securely tighten the lids and vortex for 30 sec
  19. Count in the scintillation counter using programme no. 2