How is salicylic acid converted into aspirin?

Aspirin can be made by reacting salicylic acid with acetic acid in the presence of an acid catalyst. The phenol group on the salicylic acid forms an ester with the carboxyl group on the acetic acid. However, this reaction is slow and has a relatively low yield.

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 which 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.

Aspirin is prepared from salicylic acid via an esterification reaction, which involves forming an ester (ASA) from an alcohol (salicylic acid) and carboxylic acid derivative (acetic anhydride), in the presence of a catalyst (H2SO4).

For the preparation of aspirin, salicylic acid is reacted with an excess of acetic anhydride. Small amount of strong acid is used as a catalyst in these reactions which enhances the speed of reaction acid used is phosphoric acid. Excess acetic acid will be extinguished with the addition of water.

Salicylic acid is subjected to acetylation with the help of acetic anhydride to yield acetylsalicylic acid (commonly known as aspirin) and acetic acid as the final product. It can be noted that acetic anhydride is also used as an acetylating agent in the synthesis of THC acetate ester and diacetylmorphine.

Salicylic acid should not be used by someone allergic to aspirin. Both ingredients may cause dryness and irritation when you first start using them. Allergic reactions are rare, but they are possible. You should seek emergency medical attention if you develop extreme swelling or have trouble breathing.