Acetylsalicylic Acid

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Experiment 8: Acetylsalicylic Acid
Post lab:
Restatement of experiment:
Aspirin (acetylsalicylic acid) is a derivative of salicylic acid with the same medicinal values but fewer side effects. It is used widely as a pain killer and anti-inflammatory. In this experiment, aspirin was synthesized from salicylic acid and acetic anhydride. To determine the product’s purity, the melting point of aspirin was then measured using a Thomas-Hoover Uni- Melt device. The product had a low percent yield and was found to be impure due to its low melting point. Result:

Percentage yield (%)
Compound Theoretical yieldActual yield Percent yield
Acetylsalicylic acid0.16g0.21g76.29%

Table 1. The theoretical yield of acetylsalicylic acid based on the amount of salicylic acid used for the reaction. Compound Observed M.PReal M.P
Acetylsalicylic acidImpure: 135 – 136
Pure : 133 - 136138
Table 2. The observed melting point of acetylsalicylic acid compared to its literature melting point. Calculation of mass of crude product before recrystallization of aspirin: Mass of 125mL Erlenmeyer flask = 25.32g

Mass of flask w/ crude product = 25.48g
(Mass of flask w/ crude product) – (Mass of flask) = Mass of crude product 25.48g – 25.32g = 0.16g crude product
Table 1 shows how much acetylsalicylic acid was synthesized compared to how much salicylic acid was used. Since there is a 1:1 ratio between the two, then the amount of salicylic acid used should be equal to the amount of acetylsalicylic acid recovered at the end of the experiment. As Table 1 shows, this is not the case, for 0.21g of acetylsalicylic acid was harvested when 0.16g of salicylic acid was used. This could have some effect on the purity; for the melting point of the harvested acetylsalicylic acid was not close to the literature melting point (see Table 2). Since the final product was determined not to be very pure, it is highly likely that less than 0.21g of the product was acetylsalicylic acid....
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