Practical 6 - Synthesis of a solid organic product

Question 1

Aim

Answer 1

To synthesise 2-acetoxybenzenecarboxylic acid (aspirin) from 2-hydroxybenzenecarboxylic acid and ethanoic anhydride, purify the product using recrystallization and determine its melting point

Question 2

Method

Answer 2

1. Weigh out 1.0 g of 2-hydroxybenzenecarboxylic acid and transfer to a pear shaped flask.
2. Add 2 cm of (CH CO)20 and 8 drops of concentrated H3PO4 solution.
3. Connect the reflux condenser and place in a fume hood.
4. Warm the mixture in a hot water bath until all of the solid dissolves then warm for a further 5 minutes.
5. Carefully add 5 cm’ of cold deionised water to the solution and stand the flask in a bath of iced water until precipitation appears to be complete. It may be necessary to stir vigorously with a glass rod to start the precipitation process.
6. Filter the mixture under reduced pressure to obtain the impure derivative and wash with a little cold water.
7. Using a boiling tube in a water bath, dissolve the impure product in the minimum amount of warm ethanol.
8. Add 5 cm of warm water drop-wise. If the solution becomes cloudy, heat until it becomes clear again.
9. Place the boiling tube into ice water for 15 minutes or until the crystals stop forming.
10. Filter the purified derivative under reduced pressure.
11. Dry the purified product using filter paper.
12. Collect your sample in a dry, pre-weighed sample vial and calculate the mass of the product. Use this information to calculate the percentage yield of the product.
13. Measure the melting point of the product.