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Chemistry in Medicine

Aspirin: synthesis and analysis

  • 3 things to know
  • Unit A2 2

Overview

Recall questions on the synthesis from salicylic acid with ethanoic anhydride and why that reagent is chosen, the catalyst and the equation, purification by recrystallisation and checking purity by melting point, why aspirin is supplied as the sodium salt, determining its concentration by titration with phenolphthalein, and why the solution must be fresh.

What you need to know

Answer each one before you reveal it.

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Key term

From what is aspirin synthesised?

Key term

Write the equation for the synthesis of aspirin from salicylic acid and ethanoic anhydride

Key term

What catalyst is used in the synthesis of aspirin?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    From what is aspirin synthesised?

    Model answer

    Salicylic acid, also called 2-hydroxybenzoic acid.

  2. 2

    What reagent converts salicylic acid to aspirin?

    Model answer

    Ethanoic anhydride.

  3. 3

    Write the equation for the synthesis.

    Model answer

    C₆H₄(OH)COOH + (CH₃CO)₂O → C₆H₄(OCOCH₃)COOH + CH₃COOH.

  4. 4

    Why is ethanoic anhydride used rather than ethanoic acid?

    Model answer

    It is far more reactive, so the reaction goes to completion rather than reaching an equilibrium.

  5. 5

    Why is ethanoic anhydride preferred to ethanoyl chloride industrially?

    Model answer

    It is cheaper, less readily hydrolysed and does not release corrosive hydrogen chloride.

  6. 6

    What catalyst is used?

    Model answer

    A few drops of concentrated sulfuric or phosphoric acid.

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