In this experiment, the objective was to establish the temperature at the reaction that allows for the synthesis of aspirin and collection of purest aspirin product occurs. The experiment has two parts wherein the first part aspirin is made and the second part is where the made aspirin is analyzed. Typically, aspirin has two components; Salicylic Acid (C7H6O3) and Acetic Anhydride (C4H6O3) (Poyraz 120). These components react to yield Acetic Acid (C2H4O2) and Acetyl Salicylic Acid (C9H8O4). Also, there is the use of phosphoric acid (H2SO4) in this experiment. Some side reactions are expected to occur at various temperatures depending on the purity of the aspirin made. Caution is taken with the procedure as contact with water can destroy the ethanol and acetic anhydride used in the experiment. For the other part of the experiment, the melting point of aspirin will be established. Gao, Jihong and Yuzhen mentions that typically aspirin melts in between 135-136 degrees Celsius (1910). The impure aspirin will have lower and broader melting point range. Ultimately, a Thin Layer Chromatography (TLC) will be carried out will be carried out to compare aspirin synthesized with pure aspirin, and salicylic acid.
In this part, a water bath is prepared by heating to boiling 100ml water in a 400ml beakers. Exactly 13.8 grams of salicylic acid is measured and placed in a 12ml Erlenmeyer flask, and 14 ml of acetic anhydride is added to the flask. The flask is then placed in cold water. After that, 6-8 drops of phosphoric acid are added to the flask then swirled with caution not to spill the content. The next step is putting the flask in boiling water bath with occasional swirling. Once all the solid is completely dissolved and a clear solution observed, the flask is heated in a water bath for another 5 minutes. It is then removed, and 40ml cold distilled water is added, stirred to mix well and then cooled in 150 ml water and ice mixture. The cooled slurry impure product is poured into a Buchner funnel collecting the solid. The reaction flask is rinsed twice with 20ml distilled water with each rinse poured on the funnel. Suction is then applied until the dry product is collected.
There are four crucial steps in this recrystallization (Bica, Christiaan and Mark 2014). 10ml of ethanol is heated on a hot pad and the beaker with the crude product with care not to let it reach a boil. The boiling ethanol is then transferred to the beaker with the crude product and together heated for another 10 minutes. The beaker with the product is placed on an ice bath until crystals begin to form.
Melting Point Determination
The mass of the recrystallized product is noted. The recrystallized aspirin product is placed into a closed-ended capillary tube and tapped to get the recrystallized product into the bottom. A melting point determinator is then used to find the melting point range of the product using a thermometer.
Thin Layer Chromatography
10 ml of acidified Ethyl Acetate is added with the use of a graduated cylinder into a developing jar. A pencil mark is drawn, about 1cm from the bottom of TLC plate. This will help in the spotting of recrystallized aspirin, salicylic acid, and pure aspirin. Recrystallized aspirin is converted to a liquid by placing some of it on a watch glass and adding a half ethanol half dichloromethane mixture then stirred until ground to fine liquid. The half ethanol half dichloromethane mixture will be added to salicylic acid as well. Pure aspirin is already in liquid form. Each substance is carefully spotted on the TLC plate and lets in the developing jar to develop. After developing, a solvent line is drawn and observed under UV light and develop in iodine jar so that TLC data can be observed. The values are then calculated.
The melting point technique in this experiment revealed that the crude aspirin was not as pure as its melting point did not fall within the 1 degree Celsius of the actual melting point of pure aspirin. The thin layer chromatography equally revealed that the synthesized crude aspirin was not similar to pure aspirin since thy has different retention factors. The percentage yield recorded in the experiment showed the highest yield of 65%. However, the percentage yield never affected the recrystallization percentage as there was no small melting point range. This indicates that the aspirin was impure.
In conclusion, it is correct to say that the synthesized aspirin in the lab was impure. However, the findings from this experiment cannot make strongly stand to this. There could be possible errors that occurred initially perhaps in overheating the melting apparatus. Also, the recorded melting point could be higher than the observed one. Vacuum filtration could be a source for additional errors. However, it could be generally assumed that the experiment was successful.
BIBLIOGRAPHY Bica, Katharina, et al. "In search of pure liquid salt forms of aspirin: ionic liquid approaches with acetylsalicylic acid and salicylic acid." Physical Chemistry Chemical Physics 12.8 (2010): 2011-2017.
Gao, Lin, Sun Jihong and Li Yuzhen. "Functionalized bimodal mesoporous silicas as carriers for controlled aspirin delivery." Journal of Solid State Chemistry 184.8 (2011): 1909-1914.
Poyraz, M. "Synthesis, structural characterization and biological studies of novel mixed ligand Ag (I) complexes with triphenylphosphine and aspirin or salicylic acid." Inorganica Chimica Acta 375.1 (2011): 114-121.
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