experimental+procedure+for+radiolabelling+of+aspirin

Back to Main The following reaction will be used for the synthesis:


 * 1) Place 5 cm 3 of 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 cm 3 14 C-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 cm 3 of distilled H 2 O to form a slurry
 * 7) Filter this through a Buchner funnel then wash with 1 - 2 cm 3 of 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 3 rd clean 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 cm 3 of 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 2 nd 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 2 nd product with lower specific activity
 * 14) 4. Add 0.15 g of inactive aspirin to a 4 th 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 3 rd 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