Aspirin is the most widely used over-the-counter drug
in the world. The average tablet contains about 325 milligrams of acetylsalicylic acid with an inert binding material such as starch. Aspirin is used to relieve pain, reduce inflammation, and lower fever. Aspirin originally was derived by boiling the bark of the white willow tree. Although the salicin in willow bark has analgesic properties, purified salicylic acid was bitter and irritating when taken orally. Salicylic acid was neutralized with sodium to produce sodium salicylate, which was better-tasting but still irritated the stomach. Salicylic acid could be modified to produce phenylsalicylate, which was better tasting and less irritating, but released the toxic substance phenol when metabolized. Felix Hoffman and Arthur Eichengrün first synthesized the active ingredient in aspirin, acetylsalicylic acid, in 1893.
In this laboratory exercise, you can prepare aspirin (acetylsalicylic acid) from salicylic acid and acetic anhydride using the following reaction:
salicylic acid (C7H6O3) + acetic anhydride (C4H6O3) --> acetylsalicylic acid (C9H8O4) + acetic acid (C2H4O2)