Synthesis of Acetylsalicylic Acid (Aspirin)

Introduction:
The purpose of this experiment is to carry out the synthesis of acetyl salicylic acid (aspiring via the esterification of salicylic acid by the reaction with acetic anhydride un acidic conditions;


According to the above reaction, Salicylic acid is treated with acetic anhydride causing the reaction that converts the hydroxyl group on salicylic acid into and ester functionality. The product of this reaction will be acetyl salicylic acid (aspirin) and acetic acid. Sulphuric acid or phosphoric acid will be used as a catalyst.


Results:

Mechanism:

Physical Properties:

Discussion:

Initially, 138 mg of salicylic acid is mixed with 0.3 ml of acetic anhydride and one drop of phosphoric acid;

As the solution is being mixed under heating (90 °C) water is added dropwise until acetic anhydride is eliminated from the reaction mixture. The reaction is exothermic therefore the temperature should be carefully monitored. (1)


Once the reaction is complete, it is cooled in an ice bath to room temperature. The mixture will then crystallize. In some instances, crystallization may not occur but it can be encouraged by scratching the bottom of the reaction flask with a glass stirring rod which in turn creates nucleation sites. To further purify the product, recrystallization from hexanes mixture is possible.(1) The product is then collected via vacuum filtration and then left to dry on the filter paper. The mass, HNMR and melting points can then be measured.

Reference
1. Synthesis of Acetylsalicylic Acid, http://courses.chem.psu.edu/chem36/SynFa06Web/Expt80.pdf