Aspirin Synthesis

Preparing Aspirin is a classic lab synthesis performed in university and school. Here is how to make Aspirin yourself:

Key Takeaways

  • Aspirin or ASA (acetylsalicylic acid) can be synthesized by turning the hydroxyl group of salicylic acid into an ester group (R-OH → R-OCOCH3)
  • In the body, however, aspirin is again metabolized to salicylic acid, which is the active ingredient
  • The product can be tested for purity, by adding ferric chloride to an aqueous solution. If salicylic acid is present, the test will turn a deep purple color

Chemicals needed to make Aspirin

How to synthesize Aspirin

  1. Add all chemicals to the round-bottomed flask and setup the heating bath
  2. Add a magnetic stirring bar to the flask and begin heating the mixture.
  3. Heat the water bath to boiling and keep it at this temperature for around 10 minutes
  4. Add 2ml of distilled water to destroy remaining acetic anhydride
  5. After a minute, remove the flask from the water bath and add 20 mL of distilled water. Let the flask cool to room temperature. As the solution cools, crystals of aspirin will appear.
  6. A “purified product” can be obtained through recrystallization of the crude product in hot ethanol.

Aspirin Synthesis Equation

Aspirin is the common name for the compound acetylsalicylic acid, widely used as a fever reducer and as
a pain killer. Salicylic acid, whose name comes from Salix, the willow family of plants, was derived from
willow bark extracts.

To prepare aspirin, salicylic acid is reacted with an excess of acetic
anhydride. A small amount of a strong acid is used as a catalyst that speeds up the reaction. In this
experiment, phosphoric acid will be used as the catalyst. The excess acetic acid will be quenched with
the addition of water. The aspirin product is not very soluble in water so the aspirin product will
precipitate when water is added. The synthesis reaction of aspirin is shown below:

The spectroscopic analysis of aspirin will involve the complexing of iron(III) to the deprotonated form of
salicylic acid (salicylate ion) to give a purple solution. Only the salicylate ion complexes to iron(III).

Experiment Video