Carboxylic Acids and Derivatives

Question 1

State why ethanoic anhydride is preferred to ethanoyl chloride for the preparation of aspirin

Answer 1

ethanoic anhydride is less corrosive

Question 2

Describe the recrystallisation process used to purify the aspirin

Answer 2

• dissolve crude product in hot solvent (water and ethanol) of minimum volume
• filter (hot to remove insoluble impurities)
• cool to recrystallise
• filter under reduced pressure/with Buchner apparatus
• wash with cold solvent and dry

Question 3

State the physical property that is measured to check the purity of aspirin. Describe two ways the result would show that the product is impure.

Answer 3

• melting point
  1. if it melted at a lower temperature than data book value
  2. melts over a wide range of temperature rather than a narrow range if pure