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: 1. CH3CH2OH + C6H4OHCOOH > C6H4OHCOOCH2CH3 + H2O The Product of a reaction using salicylic acid and ethanol would be an ester, namely ethyl salicylate. This ester is a compound formed when an alcohol (the ethanol) reacts with an acid (the salicylic acid) with water being the by-product.
The catalyst in this reaction would be the Cu, which is added to complex the carboxyl group and make for an easier ester formation reaction. 2. +[H2SO4] > +CH3COOH 3. a) Using 4mL of acetic anhydride instead of 5mL would result in a lower yield of ASA. b) At higher temperatures (warm water), molecules have more kinetic energy and collide with each other more often to interact with water molecules, increasing the solubility of the aspirin. The ice bath slowed the molecules, allowing them to more easily stick together and “fall out” of solution or crystallize. Discussion of the Results:
Although my partner and I were not able to get a high percent yield we were satisfied with our results. We were able to successfully create aspirin product. Our percent yield was low at 45% and there could have been a multitude of different reasons why we did not get results that we were expecting. The first problem would be that our hot plate was not working properly, and therefore it took far longer than necessary to heat our water to 75 C or above. This may have resulted in a different Salicylic acid + acetic anhydride [H2SO4] aspirin + acetic acid reaction, and our results were definitely delayed.
We also noticed that our water was very cloudy and murky when we filtered the crystals for impurities. Furthermore, we lost crystals in our transportation from the filter to the watchglass which significantly change our numbers. Conclusions: I would call this experiment a tentative success. Although we had a low percent yield at 45% a large % error at 59. 25%, we were able to successfully create aspirin through our procedure and through our methods. The crystals that we did acquire were somewhat pure, and I was able to understand and comprehend reactions of esters, and the effects of hydrolysis.