Making Aspirin
Carboxylic Acids Worksheet
Synthesis Reactions
1. Salicylic acid is the common name for 2-hydroxybenzoic acid (2-hydroxybenzenecarboxylic acid). It can be used to make aspirin and oil of wintergreen.
a) Draw the structure of salicylic acid.
b) Write an equation for the formation of aspirin from salicylic acid.
c) Write an equation for the formation of oil of wintergreen from salicylic acid.
d) Outline the mechanism for the reaction between salicylic acid and ethanoyl chloride.
Production & Purification
2. During the production of aspirin, salicylic acid is reacted with ethanoic anhydride.
a) Suggest why ethanoic anhydride was used instead of ethanoyl chloride.
The reaction using ethanoic anhydride is less exothermic than the reaction using ethanoyl chloride, and it doesn’t produce HCl, which is toxic.
b) Once the aspirin has been made, it has to have any impurities removed.
i. Describe the process used to remove any insoluble impurities. Include a diagram in your answer.
- The impure aspirin is dissolved in the minimum quantity of hot solvent.
- It is then filtered in a Buchner Funnel using reduced pressure.
- It is then cooled down to increase the amount of crystals formed, and increase the rate at which they form.
ii. Describe the process used to remove soluble impurities.
- The crystals are placed in a Buchner funnel.
- The crystals are compressed (using a bung).
- The crystals are washed with ice cold solvent and left to dry.
Purity Testing
3. Once the purification process has taken place, the purity can be tested.
a) Describe a method for how to determine the purity of the aspirin and suggest how the results would differ.
- Place a small sample in a capillary tube.
- Place the capillary tube in a melting point apparatus.
- Gradually increase the temperature until the sample melts.
- Note the temperature at which it melts.
Pure aspirin would melt at a single temperature.
Impure aspirin would melt over a range, which would be lower than the melting point of pure aspirin.
b) Describe how the pure aspirin would differ in appearance to impure aspirin.
Pure aspirin would have bigger crystals.