Lab Report COM 100
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Napolitano 1 Aspirin Synthesis Lab #7 Ashlyn Napolitano October 19, 2015 Abstract The goal of this experiment was to perform a synthesis of a pure sample of acetylsalicylic acid from salicylic acid. This synthesis produced was a somewhat low 33.2% yield. The synthesis first consisted of the reaction of salicylic acid and acetic anhydride, which produced acetylsalicylic acid and the byproduct acetic acid once it was heated. The reaction was followed by isolation of the product by cooling and filtration with water, and purification by recrystallization with ethanol. Then the recrystallized product was characterized from the melting point and analyzing the infrared spectrum taken. This synthesis was found to be successful because the IR Spectrum characterized the recrystallized product as acetylsalicylic acid. Napolitano 2 Introduction Chemical synthesis is used in labs to create new structures with properties that are important and specific for everyday life. The purpose of this lab is to practice a simple synthesis of acetylsalicylic acid by creating a reaction, then isolating, purifying, identifying and characterizing the product. This synthesis is important because acetylsalicylic acid is aspirin, which is a very important drug that people use to reduce fever, relieve moderate pain, and reduce swelling. It can also be used to prevent blood clots, or decrease the risk of stroke or heart attack (“Aspirin Oral”). Overall synthesis is important in organic chemistry because it converts simple starting structures into complex structures through series of breaking bonds and forming chemical reactions. In order to perform a synthesis of aspirin, multiple steps need to be made. The chemical reaction shown in Equation 1 is used to break and make bonds for the reaction of the synthesis. Equation 1 Salicylic Acid+Acetic Anhydride→ AcetylSalicylicAcid+AceticAcid Reactant+Reagent→Product+ByProduct Napolitano 3 Specific bonds need to be broken before making bonds. In order to break the bonds, the activation energy needs to be reached by adding heat as a source of energy to make the reaction go faster. Phosphoric Acid is also added as a catalyst to increase the rate of the reaction. Salicylic acid is the reactant that is transformed in the reaction, and acetic anhydride is the reagent that is needed in order to break and make the bonds in the reactant. Salicylic acid is transformed into the product, acetyl salicylic acid. Acetic acid is the byproduct because it is the product that isn’t derived from the reactant. After the reaction, the product is isolated by simple crystallization and the product is purified by recrystallization from ethanol. Finally, the product is identified by the melting point and the infrared spectrometry as Aspirin. Calculating the yield is an important part of synthesis because it determines how efficient the synthesis is. A low product yield is often because the reaction didn’t react completely, it reacted side products, or if the product isn’t isolated efficiently. In order to find product yield, the moles of the product is compared to the moles of the reactant. After the reaction, isolation, and purification, the product should be identified as acetylsalicylic acid. In order to identify this product the melting point is expected to range from 134 to 136 ℃ . If the product is pure it should have a narrow melting point with a range of only 2 degrees. Finally, an infrared spectrum of the product is recorded. The results show peaks −1 above 1500 cm that correlate to specific bonds in functional groups, and peaks below 1500 −1 are compared to an authentic sample. The product is identified as acetylsalicylic acid if cm the infrared spectrum of the sample closely resembles that of the authentic compound. Experimental Napolitano 4 According the Aspirin Synthesis Package provided by Gould, the reaction was performed by adding 0.5mL of acetic anhydride to the weighed 0.261g of salicylic acid in a test tube. Four drops of 85% phosphoric acid was added to the test tube to catalyze the reaction. Then, the test tube was placed in a beaker of water at 55 ℃ so the reaction was at the right conditions to react. The test tube was shook throughout the 15 minutes it was heated to ensure that the reactant dissolved completely. Once the reaction was performed, the test tube was removed from the beaker and the product was isolated by adding 1.5mL of deionized water (hydrophobic effect). Once the solution in the test tube was cooled to room temperature, the sides of the test tube were scratched so crystals would form, and then placed into an ice bath to further the crystallization. Once more crystals were formed, the solution was quickly filtered in the Hirsch funnel and washed with half a mL of deionized water that was also cooled in the ice bath. Then the crystals were dried on the filter paper for another 10 minutes. Once the crystals were dry, they were weighed and a small portion was used to take the melting point in the Digimelt Machine. Once the product was isolated, it was purified by recrystallization. Less than half of a mL of ethanol was heated and added to the solution to dissolve the crude product. Once it was dissolved and cooled, the sides of the test tube were scratched with a spatula and put into an ice bath to increase the amount of crystal formation. Then, the crystals were isolated by centrifugation and then dried on a drying plate. Once dry, the crystals were weighed and a small portion was used to take the melting point in the Digimelt Machine. Finally, the crystals were identified as acetylsalicylic acid by using the infrared spectrum of the pure product, and comparing the diagnostic and fingerprint region of the spectrum to an authentic spectrum of acetylsalicylic acid. Napolitano 5 Results In this experiment the starting weight of salicylic acid was taken before the reaction. After isolating the crude product, the weight and melting point was measured, and finally after purification, the isolated recrystallized weight and melting point of the product was measured. These measurements are shown in Table 1 below. Table 1 Chemical(s) Weight (g) Melting Point ( ℃ ) Starting Salicylic Acid 0.261g N/A Isolated Crude Product 0.219g 122.1125.5 ℃ Isolated Recrystallized 0.113g 121.3128.2 ℃ Product Table 1 shows the weight and melting point that was measured throughout the experiment. Once all of the measured data was recorded, the percent yield was calculated. In order to calculate the percent yield, the weight of the reactant and products was converted to moles. The number of moles of reactant is the weight of the reactant divided by the molecular weight of the reactant as shown in Equation 2. Equation 2 Weightof Reactantg ) Molesof Reactant= Molecular Weightof Reactant g (mol 0.261g −3 ¿ =1.89×10 mol 138.12 g (mol Napolitano 6 Similarly, the number of moles of product is the weight of the product divided by the molecular weight of the product as shown in Equation 3. This equation was used to find both the moles of crude product and the moles of recrystallized product. Equation 3 Weightof Product(g) Molesof Product= MolecularWeightof Product g (mol 0.219g −3 CrudeProduct= =1.22×10 mol 180.16 g (mol 0.113g Recrystallized Product= =6.27×10 mol g 180.16(mol Once the amount of moles of the reactant and products were calculated, the percent yield was found by comparing the number of moles of product to the reactant for both the crude product and recrystallized product as shown in Equation 4. Equation 4 ¿Moles of Product PercentYield= ¿Molesof Reactant×100 −3 CrudeProduct Percent Yield=1.22×10 mol ×100=64.6 1.89×10 mol −4 Recrystallized Product PercentYield=7×10 mol ×100=33.2 1.89×10 mol The infrared spectrum of the solid crystal was also taken to identify the product. The −1 −1 spectrum shown in Figure 1 shows peaks above 15cm and below 1500 cm . Table 2 Napolitano 7 shows the infrared frequencies and percent transmission of the sample and authentic aspirin. The authentic sample that is compared to the recrystallized product sample is shown in Figure 2. Table 2 Sample Product Sample Product Authentic Bond Vibration Functional Peak ( cm ¿1 Peak % T Sample Peak ( Group cm ¿ 2831.85 86.39% ~3000 Broad OH Alcohol 1749.77 57.76% 1754 C=O Carboxylic Acid 1681.60 43.19% 1693 C=O Ketone 1454.04 61.70% 1469 N/A N/A 1303.67 52.46% 1308 1218.51 54.72% 1222 1182.50 27.57% 1190 915.49 37.44% 918 753.73 43.02% 766 666.43 57.33% 706 Table 2 shows the wavenumber and percent transmission of the sample product and authentic sample peaks −1own in the IR Spectrum in Figure 1. For the peaks in the diagnostic region above 1500(cm ¿ , the bond vibration and functional group is also identified. Figure 1 Napolitano 8 Figure 1 is the infrared spectrum of the recrystallized sample product with the functional −1 groups and bond vibrations labeled above 1500( cm ¿ . Figure 2 F igure 2 is the infrared spectrum of the authentic sample that the recrystallized sample is being compared to. Discussion Napolitano 9 In this experiment, the reaction along with the mechanism of the reaction performed is shown in Figure 3. During this reaction, bonds had to break in the reactant and reagent in order to make bonds in the product and by product. In order for this reaction to react, phosphoric acid was added to the reactant and reagent; salicylic acid and acetic anhydride. Then the solution was heated to the right condition to give the reaction enough energy to reach the activation energy that broke the bonds in the reactant, reagent, and catalyst. After the reaction, the product was isolated by cooling and filtration. Finally the product was purified by recrystallization and characterized by the product’s melting point and infrared spectrum. Figure 3 Figure 3 is the reaction mechanism of the reaction performed in the synthesis of aspirin. Napolitano 10 In order to identify the recrystallized product as aspirin, the infrared spectrum of the product shown in Figure 1, was compared to the authentic sample shown in Table 2. The peaks above 1500 cm−1 indicated bond vibrations of the functional groups, while the peaks below −1 1500 cm were in the fingerprint region that identified specific molecules. Specific and major peaks were selected for comparison between the two spectrums. The three major functional groups that were found in the recrystallized product were alcohol, carboxylic acid, and ketone. Some of the peaks that differ slightly could be because of impurities in the recrystallized product. Overall, the sample product showed similar bond vibrations, frequencies, and functional groups as aspirin. The unknowns were also identified by their melting points, which increased the certainty of their identity. The crude product melting point ranged from 122.1 ℃o 1, and the recrystallized product melting point ranged from 121.3℃28.. These melting points were also compared to the authentic melting point of acetylsalicylic acid, which ranges from 134 to 136 ℃ . Since the melting points from the reaction are slightly lower and broader than the authentic sample, it implies that there might be some impurities in the sample products. The identity was confirmed by comparing the melting points and IR Spectrum of the sample product to the authentic aspirin. The percent yield of crude product as 64.6% and the recrystallized product as 33.2% is practical because there could have been losses during the reaction if it didn’t react, isolate, or recrystallize completely. After conducting this lab, it has demonstrated multiple steps that are included in a synthesis of organic compounds. It has introduced the reaction mechanism that takes place during a synthesis. It also included practicing isolation, filtration, recrystallization, purification, Napolitano 11 and characterization. The most useful part of this lab was learning how to characterize the products because it involved understanding the infrared spectrum and melting point of compounds. Finally, this lab showed how to calculate percent yield and that it isn’t expected to always receive a high percent. Conclusion The purpose of this lab was to practice the synthesis of acetyl salicylic acid from salicylic acid, and to ensure it was made with efficiency by the percent yield. After isolation, purification, and recrystallization the percent yield was 33.2%. Isolation was performed by cooling the solution and filtering it. Purification was performed by recrystallizing the product with ethanol. Finally, the recrystallized product was identified by comparing the infrared spectrum to an authentic spectrum, and the melting point of the product was taken. It was determined that the synthesis of aspirin was successful because the IR spectrum of the recrystallized product showed similar major peaks, bond vibrations, and functional groups of the authentic sample. Works Cited in MLA "Aspirin Oral: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing WebMD." WebMD. WebMD, n.d. Web. 19 Oct. 2015. Gould, Richard. "Aspirin Synthesis Package." (n.d.): n. pag. Arizona State University: CHM 237: Organic Chemistry Lab: Fall 2015. Web. 20 Oct. 2015.
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