Synthesis of Aspirin

DISCUSSION

As a product of an acidcatalyzed or esterification reaction between salicylic acid and acetic anhydride, aspirin was produced. The alcohol group from the salicylic acid reacted with an acetic anhydride causing a chemical reaction that turned salicylic acid's hydroxyl group into an acetyl group which yielded aspirin and acetic acid as a byproduct. Small amounts of phosphoric acid were as a catalyst. Acetic anhydride was used since it could be easily decomposed by the addition of water and it could also be reused. In Table 1, you can see the observations as actions were taken.

Below is the detailed mechanism showing how phosphoric acid catalyzes the formation of acetylsalicylic acid.

Figure 1. Reaction mechanism of the formation of aspirin

Table 2 shows how much acetylsalicylic acid was yielded. The theoretical yield of acetylsalicylic acid based on the amount of salicylic acid used for the reaction should be equal to the amount of salicylic acid yielded since there is a 1:1 ratio between the two. In the experiment, this is not the case. It was shown that 7.36g of the sample was harvested when 2.52g of salicylic acid was used. Though the sample’s not yet recrystallized, it is very much obvious that the impurities are present in high amounts. One reason could have been because of the product not dried well.

During the recrystallization of aspirin, Table 3 shows some observations. EtOH which serves as a good solvent for the purification of aspirin was used. Petroleum ether was added to the aspirin-EtOH mixture which led to the displacement and precipitation of aspirin, leaving behind impurities which were dissolved in the petroleum ether-EtOH mixture. The mixture was subjected to heat in a water bath in which a temperature of no higher than 80°C was maintained. This temperature is necessary to control the aspirin crystal formation and its rate of reaction. If the temperature is raised any further beyond 80°C, the aspirin might get...