Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). Much of this is believed to be due to decreased production of prostaglandins and thromboxanes. Aspirin’s ability to suppress the production of prostaglandins and thromboxanes is due to its irreversible inactivation of the cyclooxygenase (COX) enzyme. Cyclooxygenase is required for prostaglandin and thromboxane synthesis.
Aspirin acts as an acetylating agent where an acetyl group is covalently attached to a serine residue in the active site of the COX enzyme. The synthesis of aspirin is classified as an esterification reaction. Salicylic acid is treated with acetic anhydride, an acid derivative, causing a chemical reaction that turns salicylic acid’s hydroxyl group into an ester group (R-OH > R-OCOCH3). This process yields aspirin and acetic acid, which is considered a byproduct of this reaction. Small amounts of sulfuric acid (and occasionally phosphoric acid) are almost always used as a catalyst.
This method is commonly employed in undergraduate teaching labs. Formulations containing high concentrations of aspirin often smell like vinegar because aspirin can decompose through hydrolysis in moist conditions, yielding salicylic and acetic acids. The acid dissociation constant (pKa) for acetylsalicylic acid is 3. 5 at 25°. Chemical Reactions Discussion of Results 3 grams of Salicylic Acid is equal to 0. 0217 mol of the compound. The stoichiometric relationship between Salicylic Acid and Acetylsalicylic Acid is 1:1 therefore the moles of Acetylsalicylic Acid (Aspirin) is 0.
0217 mol. In the overall reaction, 3 grams of Salicylic Acid will theoretically yield 3. 909 grams of Aspirin. 3g S. A. x (1mol S. A. /138. 118g) x (1mol A. A. / 1mol S. A. ) x (180. 15g A. A / 1mol A. A. ) = 3. 909 g Aspirin The measured weight of Aspirin in the experiment is 3. 5267 grams. The percentage yield is 90. 48%. Large amount of Aspirin was yielded but it is only an impure Aspirin this will lessen when recrystallization takes place. (3. 5267 g / 3. 9092g) x 100% = 90. 48%.