Synthesizing Acetylsalicylic Acid

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Synthesizing Acetylsalicylic Acid from Salicylic Acid

Shultz, Joshua T.

Chemistry 2210L


Figure 1. Esterification of Salicylic Acid to Yield Acetylsalicylic Acid

Figure 2. Acetyl Group Table 1. Reference Data, Experimental Volumes, Yields, and Melting Points
Melting Point of Salicylic Acid 158° C
Melting Point of Acetylsalicylic Acid 138° C - 140° C
Initial Mass of Salicylic Acid 0.510 g
Theoretical Yield of Acetylsalicylic Acid 0.665 g
Experimental Yield of Acetylsalicylic Acid 0.524 g
Percent Yield 78.8%
Melting Point of Initial Salicylic Acid 158° C - 160° C
Melting Point of Recovered Acetylsalicylic Acid 139° C - 146° C

Calculation 1. Theoretical Yield of Acetylsalicylic Acid with Salicylic Acid as the Limiting Reagent
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Salicylic acid’s hydroxyl group readily reacts with acetyl groups in a process called acetylation. The resulting substitution reaction replaces the hydrogen in salicylic acid’s hydroxyl group with an acetyl group thereby forming an ester functional group. This esterification of salicylic acid produces acetylsalicylic acid, or aspirin. Figures 1 and 2 above show the reagents and products involved in the experiment’s esterification of salicylic acid. With excess acetic anhydride and a concentrated acid, 0.510 g of salicylic acid should have yielded approximately 0.665 g of acetylsalicylic acid. Unfortunately, small quantities of the reagents and products adhered to the sides of the flask and filter paper during the experimental process. In the end, an actual yield of 0.524 g resulted from the experimental procedures. This quantity equated to a 78.8 % yield. The purity of both the salicylic acid used and the acetylsalicylic acid recovered appeared high according to their observed and theoretical melting points. Both substances melted over ranges matching their theoretical melting points, most likely indicating an absence of impurities. Recrystallization of the acetylsalicylic acid in ethyl acetate likely contributed to the recovery of a purer sample of acetylsalicylic acid. The recovered acetylsalicylic acid, with a theoretical melting point of 138° C - 140° C, melted between 139° C and 146° C. Deviations from the theoretical melting points most likely resulted from difficulties viewing and pinpointing the exact point at which the products melted in the Mel-Temp apparatus. Regardless, the esterification of salicylic acid produced a 78.8 % yield of relatively pure acetylsalicylic

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