Synthesis of Aspriin

In this lab, the objective was to obtain acetylsalicylic acid from salicylic acid and acetic anhydride. An IR was taken after the impurities were removed to see if the desired product was in fact synthesized.

The acetic anhydride and salicylic acid were combined in a tube. The phosphoric acid and heat were added as catalysts because the reaction would either not have happened or been very slow without them. As a catalyst, the phosphoric acid lowered the amount of activation energy needed to complete the reaction. The heat sped up the reaction so that it was completed faster. Once the reaction was completed, water was added to decompose any leftover acetic anhydride. In this reaction the salicylic acid was the limiting reagent, so it was used up first. Some acetic anhydride remained, which the water attacked. The acetic anhydride is a symmetrical diester, so the central oxygen atom was a very strong electrophile. The water acted as a nucleophile and cleaved the molecule in half to create two molecules of acetic acid. The acetic acid didn’t react with any of the remaining products, and more water was added to quench the reaction.

To decrease the solubility of the desired product, the test tube was cooled. Scratching the side provided a seed for the crystals to begin to precipitate on. The product was filtered, and a small amount of cold water was used to make sure the entire acetylsalicylic acid crude product was removed from the tube. It was important that the water be cold so that the product will be less likely to go back into solution before it could be vacuum filtered. Hot ethanol was then used to resuspend the product and separate out the impurities. The ethanol was used the second time because it is less polar than water but still polar enough to put the product into solution with a minimal amount. A final product was then filtered and obtained.

A melting point analysis was taken for the product. For the given sample a melting point of...