Abstract: Introduction/Objective: Prepare and analyze aspirin from salicylic acid and acetic anhydride, and calculate the percent yield of the synthesized aspirin. Materials and Methods: This experiment called for the synthesis of acetylsalicylic acid, or aspirin, by using salicylic acid, acetic anhydride, sulfuric acid, and vacuum filtration. The salicylic acid and the acetic anhydride were mixed in a flask. Sulfuric acid was used as a catalyst to speed up the decomposition rate of salicylic acid. Vacuum filtration as then used to remove all water from the aspirin sample.
Afterward, the aspirin was analyzed by using chromatography which confirmed the purity of the aspirin. Results: The results of this experiment showed that the aspirin synthesized was not completely pure since there were miniscule traces of salicylic acid present in the aspirin sample. This was evident after analyzing the chromatographic paper under UV light. The calculated yield of the dried aspirin sample was 74. 09 percent totaling a mass of 2. 03 grams of aspirin with a theoretical yield of 2. 74 grams.Discussion: There may have been some room for error in this experiment.
After adding the acetic acid anhydride and the sulfuric acid into the flask, the flask could have been swirled for a longer period of time to increase the chance of all the salicylic acid being dissolved. Also, the sample could have been kept on the aspirator for a longer period of time to ensure that all water was removed from the aspirin sample before weighing it. Introduction: Purpose/Objective: Experiments like these are important since the right amount of salicylic acid and acetic anhydride must be mixed in order to synthesize pure aspirin.
Aspirin is an important supplement to take to relieve pain, fevers, and reduce the risk of possible heart attacks. Theory: In order to make the results of this experiment meaningful, there is some background knowledge that needs to be known such as using laboratory equipment properly. Also, it must be known that sulfuric acid acts as a catalyst in the experiment. There needs to be very precise measurements of salicylic acid, acetic anhydride, and sulfuric acid in order to create the purest aspirin sample possible. And lastly, there needs to be careful calculations of mass and moles in order to obtain accurate yields.
Equations: There are several equations used in this lab. Equation 1 was used to calculate the number of moles of salicylic acid: (mass of salicylic acid, g)(1mol salicylic acid/138. 12 g salicylic acid). Equation 2 was used to calculate the mass of acetic anhydride: (Volume of acetic anhydride, m)(Density of acetic anhydride, g/mL). Equation 1 was also used to calculate the number of moles of acetic anhydride: (grams of acetic anhydride)(1mol acetic anhydride/102. 09 g acetic anhydride). Equation 3 was used to calculate the theoretical yield: (Number of moles of limiting reactant)(1mol aspirin/1mol limiting reactant)(180.15 g aspirin/1 mol aspirin).
Equation 4 was used to calculate the percent yield: (actual yield, g)/(Theoretical yield, g)(100%). Notice that equation 1 was used to calculate the number of moles of both salicylic acid and acetic anhydride. Method: The key components in the experiment are salicylic acid, acetic anhydride, sulfuric acid, and chilled distilled water. The Buchner funnel was used to vacuum filtrate the water from the synthesized aspirin through a filter paper. In analyzing the sample, the technique used was chromatography. This process was used to determine the purity of the aspirin sample that was synthesized.
Acetic anhydride is corrosive. Concentrated sulfuric acid, NAOH, and HCL are toxic and corrosive oxidants that cause severe burns. Phenolphthalein is flammable and toxic. Extreme precaution must be used with these chemicals. This is why all of these are handled under the fume hood. Methods:The first step taken in the experiment was putting together the aspirator that would be used to vacuum filter the aspirin sample. Also, the filter paper in the Buchner funnel was weighed and its mass recorded.Once that was finished, ice was collected in a 400-mL Beaker.
It was filled half way with ice and then tap water was added to the beaker to create an ice bath. Next, 60-mL of distilled water was transferred into a 150-mL beaker and placed in the ice bath to cool. Next, a piece of weighing paper was weighed and the mass was recorded. A spatula was used to add 2. 1 g of salicylic acid to the weighing paper. Then the weighing paper with the salicylic acid was weighed and the mass was recorded. Afterward, the sample of salicylic acid was placed into a 50-mL Erlenmeyer Flask.Afterward, in the fume hood, a Pasteur Pipet was used to transfer 4. 0-mL of acetic anhydride to the flask with the salicylic acid.
The acetic anhydride and the salicylic acid were mixed and the volume was recorded. After a few seconds of mixing, five drops of concentrated sulfuric acid was added into the flask and it was swirled until a solid white substance appeared at the bottom of the flask. Next, using a 10-mL graduated cylinder, 10-mL of chilled distilled water was slowly added into Erlenmeyer flask. This was used to decompose any un-reacted acetic anhydride. Afterward, a clean glass rod was used to break up any bumps in the mixture.The aspirator was now turned on. Next, the filter paper was moistened with some distilled water.
The supernatant fluid was decanted from the flask with the help of the rubber policeman on the glass rod onto the filter paper in the Buchner Funnel. Afterward, 15-mL of distilled water was added onto the funnel and the aspirator was allowed to run for ten minutes in order to dry the aspirin sample. •Next, a clean watch glass was weighed and its mass was recorded. The aspirin crystals and the filter paper were transferred to the glass watch and weighed. The mass was recorded.Lastly, everything needed to be cleaned and disposed of. The pipers were cleaned by flushing water through them.
Three drops of phenolphthalein were added into the flask with the water filtrated in the Buchner funnel. Afterward, Hydrochloric acid was added into the flask to neutralize the solution. It was then poured into the drain. Then all glassware was thoroughly washed in the sink. Results:Synthesis: After having the aspirin sample on the aspirator for ten minutes, it was places on a glass watch, weighed, and the mass was recorded. The mass of the sample that was calculated was 3. 73 g. The percent yield was also calculated and it was found to be 136 percent. The theoretical yield was only 2. 74 g.
The sample of aspirin was left to dry for a week. After a week, the sample was once again weighed and the mass recorded. This time, the calculated mass of the aspirin was 2. 03 g. This was a difference of 1. 7 g. The percent yield dropped to 74. 09 percent. This indicates that there was water left over in the sample after filtration. If the sample would have been left on the aspirator for a longer period then perhaps any excess water would have been filtered out. Table 1: Synthesis of Aspirin Data Name of ChemicalGramsMolesPercent Yield Salicylic Acid2. 1 g1. 52 x 10-2 mol- Acetic Anhydride4. 3 g4. 20 x 10-2 mol-Acetyl Salicylic Acid (Wet)3. 73 g2. 07 x 10-2 mol136% Acetyl Salicylic Acid (Dry)2. 03g1. 13 x 10-2 mol74. 09%.
Analysis: After the aspirin sample was weighed and the mass recorded, a chromatogram was preformed. This test was used to find the purity of aspirin. A TLC plate was placed in a beaker with 10-mL of chromatography solvent (Ethyl acetate/Hexanes/Acetic acid). The solvent was allowed to run up the TLC plate and then removed. Afterward, the plate was examined under UV light. It was found that the aspirin sample was almost completely pure. There were miniscule levels of salicylic acid present in the synthesized aspirin.
Table 2: Analysis of Synthesized Aspirin SpotDistance from Starting LineCalculated Rf Solvent Front4. 5 cm1. 00 Salicylic Acid 3. 3 cm. 73 Pure Aspirin2. 8 cm. 62 Student Aspirin2. 8 cm. 62 Salicylic Acid in Student Aspirin3. 3 cm. 73 Discussion: When aspirin was first synthesized, it was weighed and found to have a mass of 3. 73g. This totaled to 136 percent yield from a theoretical yield of 2. 74g. After a week, the aspirin was weighed again and was found to have a mass of 2. 03g with a yield of 79. 04 percent. It was clear that the aspirin was not left on the aspirator long enough.
If it would have been left on longer, then all the water may have been filtered out. It is evident that there was water left since there was a difference of 1. 7g. Also, although unlikely, there could have been room for error while the aspirin dried. Since the sample was kept in a locker, it is possible, although unlikely, that some of the sample was lost, knocked out of the weighing glass, while in the locker. Like mentioned, this error is very unlikely but it still needs to be considered.In the analysis of the aspirin, it was found that the sample was almost pure. There were very small levels of salicylic acid present in the sample.
This could have been prevented if the salicylic acid, sulfuric acid, and acetic anhydride were better mixed in the flask. This could have been done by swirling the flask for a longer period of time. This would have broken down any leftover bumps in the flask and thus broken down any unreacted salicylic acid.
References: 1. Mann, C. C. ; Plummer, M. L. The aspirin wars: Money, medicine, and 100 years of rampant competition. Knopf, New York; 1991. 2. Feinman, S. E. (Ed. ). Beneficial and toxic effect of aspirin. CRC Press, Boca Raton, FL; 1993. 3. March, J. Advanced Organic Chemistry, Fourth Edition. John Wiley & Sons, New York, NY; 1992.