Experiment #4
Preparation of Aspirin

Purpose: To prepare aspirin by preparing the active ingredient acetylsalicylic acid through careful calculation through the procedure listed.

Procedure: To conduct this experiment we first weighed out salicylic acid into a flask. We mixed thix with acetic anhydride that was located under the hood and added a few drops of 85% phosphoric acid to serve as a catalyst. We clamped the flask in place within a beaker of water on a hot plate. We were to maintain this temperature for approximately fifteen minutes to complete the reaction. To decompose any excess acetic anhydride we added distilled water to the flask which gave off some vapors. We removed the flask from the water and submerged it in an ice bath to let sit for a few minutes to hasten crystallization and increase yield of product. Because our product was so slow to manifest crystals, we used a stirring rod to scratch inside of the flask. After weighing out our filter paper and watch class we collected the aspirin. We did this by filtering distilled water through a cold Buchner funnel using suction. We repeated the suction process multiple times until we felt that most of the impurities were washed out. We then transferred the solution onto a large watch glass and allowed to dry in my partner's drawer for the weekend. Returning on Monday we weighed the product and recorded the results after receiving instructions on the use of the melting point apparatus.

Data:
1. Balance Used: #4
2. Weight of Salicylic Acid: 2.16 g
3. Volume acetic anhydride added:
Initial: 7.49 mL
Final: 12.59 mL
TOTAL: 5.10 mL
4. Phosphoric acid drops: 5 drops
5. Description of mixture during heating:
Took an extra long time (over ten minutes) to heat water to 75 C. We suspected it was from a faulty hot plate. This, in turn, took extra long for crystals to appear. We rinsed the crystals out of the Erlenmeyer glass three times. In addition, some of the crystals got stuck and hardened at the bottom of the flask, making them difficult to get out. The remaining water was cloudy and some of our product got suctioned through the filter and the filter paper. After putting distilled water in, the solution bubbled and the vapor was astringent and had the pungent scent of vinegar.
6. Weight of watchglass + paper: 56.09 g
7. Description of crystals:
White, almost powdery and the appearance of snow, it stuck to the bottom of the flask. It made the whole solution that we suctioned off cloudy. Lost some crystals transferring from filter to watchglass.
8. Weight of watchglass/filter/aspirin: 57.25 g
9. Melting point of aspirin: 134.2 C
10. Literature melting point: Merck index.

Calculations: 1. Calculate the molar mass of:
Salicylic Acid (C7H6O3): 7(12.0107) + 6(1.00794) + 3(15.9994) = 138.121 g/mol
Acetic Anhydride (C4H6O3): 4(12.0107) + 6(1.00794) + 3(15.9994) = 102.09 g/mol
ASA (C9H8O4): 9(12.0107) + 8(1.00794) + 4(15.994) = 180.157 g/mol 2. Calculate the number of moles of salicylic acid and acetic anhydride used in the experiment.
Salicylic Acid: 2.16 g/138.121 g/mol = 0.0156 mol
Acetic Anhydride: 5.10 mL/102.09 g/mol = 0.0499 mol 3. Identify the limiting reagent in your reaction
Salicylic Acid 4. Give the number of moles of ASA expected if the reaction gave a 100% yield.
C7H6O3 + C4H6O3 → C9H3O4 + HC2H3O2 = 0.0145 mol ASA 5. Calculate the moles of ASA actually obtained from the grams of product in your reaction.
1.17 g/180.157 g/mol = 6.494 mol ASA 6. Calculate the % yield
1.17 g/2.6 g = 45% 7. Calculate the % error in your melting point, compared to the accepted one.
134.2-135= 0.8/135=5.925 x 100= 59.25%

Report Table:
% Yield
Accepted Melting Point
Determined Melting Point
% Error
45%
135
134.2 C
59.25%

Discussion Questions: