Microscale Synthesis of Acetylsalicylic Acid

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Synthesis of Aspirin

Ling Tecson Gamido, Mitchiko Mariel M. Mizukami

Acetylsalicylic acid, or also known as aspirin is known to be a drug that relives people of pain and is commonly used even today. It is synthesized from salicylic acid and ethanoic anhydride, both of small quantities. Phosphoric acid was used as a catalyst in the synthesis to speed up the process. Esterification is involved and the final product is aspirin with the presence of acetic acid as the byproduct. In order to create the powder form of aspirin, the process of crystallization was conducted and was run through vacuum filtration. After running through the help of an electronic instrument, the result that was achieved in this experiment was met due to the presence of esters in the graph in Figure 5; with a peak of 1297.89 at 1300-1100. There is also a match of 35.48 with ethyl salicylate. The objective, which is to create aspirin, has been completed due to the results shown by the data provided by an electronic instrument.A recommendation would be a more exact amount of reactants to be used. In this experiment, there was an excess of water and more acetic anhydride was used due to the salicylic acid not being able to dissolve at the amount of 0.3mL. Overall, this was a successful experiment where aspirin was synthesized properly. The melting point, using the meltemp, was at 146º-158 º.


Aspirin is among the most fascinating and a versatile drug known to medicine and it is among the oldest. The first known use of an aspirin-like preparation can be traced to ancient Greece and Rome. Salicigen, an extract of willow and poplar bark, has been used as a pain reliever (analgesic) for centuries. In the middle of the last century it was found that salicigen is a glycoside formed from a molecule of salicylic acid and a sugar molecule. Acetylsalicylic acid (Aspirin) has been used as a drug that would lessen small pains within the body. It is considered as a salicylate drug. Aspirin is the product of synthesis between salicylic acid and ethanoic anhydride. Acetic acid is the byproduct of the reaction.


138 mg of salicylic acid, which is in powder form, is placed inside a test tube. After that, a boiling chip and a small drop of 85% phosphoric acid was added. In order to wash down the excess salicylic acid, 0.3mL of acetic anhydride was used. The test tube containing the substance was shook to mix the substance. The reaction tube was heated in a steam bath for five minutes. The temperature of the steam bath and the substance stayed constant at 90ºC.0.2mL of water was added to the mixture for decomposition of excess acetic anhydride. 0.3mL of water was also added after the signs of reaction within the test tube. The test tube is placed in an ice bath. Crystallization took place; this is visible by the appearance of small diamond-like crystals floating within the mixture. After the crystallization is complete, vacuum filtration was done by pouring the mixture into a filter flask leaving the crystals from the crystallization of the mixture.

Fig. 1

Figure 1. Aspirin Formation. This equation shows the main process of synthesis of acetylsalicylic acid. Salicylic acid + Ethanoic anhydride -> Aspirin + Acetic acid.

Fig. 2

Figure 2. Carbocation Formation.This shows the esterification of the Ethanoic anhydride with H+ causing the formation of a carbocation. This process is in equilibrium.

Fig. 3

Figure 3. Formation of aspirin from carbocation. Due to the presence of the carbocation in Ethanoic anhydride, this caused a reaction with salicylic acid, hence creating the final product of Aspirin with acetic acid as its by product. Fig. 4

Figure 4. Crystallization. In this picture, the test tube containing the mixture is placed in an ice bath throughout the duration of the crystallization process.

Fig. 5

Figure 5. Dehydration. The powder within the cone is the aspirin collected...
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