This lab primarily aims to synthesize aspirin. Melting point, heat, and ferric chloride tests are conducted to determine the purity of the sample of the lab aspirin to that of the commercial. The percentage yield of the product is obtained to be 25%. Also, the melting point of the first and second recrystallization are obtained to be 135.6 oC and 138.3 oC respectively.
Introduction
Aspirin is simply a common name for referring to the compound acetylsalicylic acid. This acid is widely used for reducing fever and also as a painkiller (Huang 7). The preparation of aspirin first involves reacting the salicylic acid with an acetic anhydride which is in excess. Moreover, a small quantity of strong acid playing a significant role in speeding up the reaction as it acts as a catalyst. One of the best material to be used as a catalyst is phosphoric acid (Lee 4).
The separation of acetic acid from the product of aspirin is easily carried out because it is very soluble in water. In this step, the aspirin isolated is the "crude product." It is possible to obtain a “purified product” through the crude product’s recrystallization in hot ethanol. Here, the desired material is the crude product. Subsequently, the crude product’s percentage yield is determined for this reaction. The product’s purity is also analyzed as well. The methods for analyzing the product include titration, melting point, and spectroscopic assay (Huang 9).
Experimental Data
A centigram balance was used to weigh a 50 mL Erlenmeyer flask. Afterwards, about 2 grams of salicylic acid was placed in the flask and weighed again. About five drops of catalyst (phosphoric acid) were added to the flask before clamping it in a beaker of tap water. Water was then heated to boiling after which the flame was shut off. At this time, the flask was kept in the hot water bath for about ten more minutes.
About 2 mL of distilled water was added to the flask for decomposing any excess acetic anhydride. A watch glass and the filter paper were then weighed on the centigram balance. Both the filter paper and the aspirin were transferred to a pre-weighed watch glass for allowing it to air dry. The filtrate was then discarded down the sink with water.
Results/ Discussion
Table 1: Data Sheet
Moles of salicylic acid used
0.0146 moles
Mass of salicylic acid used
2.011g
Volume of acetic anhydride used
5.40 mL
Mass of acetic anhydride used
5.83g
Moles of acetic anhydride used
0.057 moles
Actual mass of crude aspirin recovered
2.6g
Percent yield of aspirin before recrystallization
58.8%
Mass of recrystallized aspirin
0.64g
Percent yield of pure product
25%
Melting point after the first recrystallization
135.6 °C
Melting point after the second recrystallization
138.3 °C
Table 2: Result and Interpretation of Ferric Chloride Test
Color
Intensity
Salicylic Acid
purple
High
Your product
Pale purple
Low
Commercial Aspirin
Pale yellow
Low
Control
clear
low
As shown in Table 1, the melting point after the first and the second recrystallizations are 135.6 °C and 138.3 °C respectively. Such values are not very far from the theoretical melting point which ranges between 138 °C and 140 °C. The percentage purity can be calculated as follows, % purity = (the acid’s actual moles/ aspirin’s theoretical moles) x 100. In this case, the percentage yield of the aspirin before recrystallization and that of the product are 58.8% and 25% respectively. Apart from salicylic acid which has high intensity, all other materials had low intensity. They also depicted different colors as shown in Table 2.
Conclusion
Evidently, the lab achieved its primary objective of synthesizing aspirin even though there was some presence of errors. The addition of water helped in quenching the excess acetic acid. It is also used to precipitate the aspirin because of the low solubility of the product. The melting point after the first and the second recrystallization did not deviate so much from the theoretical value.
Works Cited
Huang, Gangliang. "Synthesis and Biological Activities of Galactose–Aspirin Conjugate Prodrug Designed for ADEPT and PMT." Medicinal Chemistry Research, 2017, Springer Nature, doi:10.1007/s00044-017-2094-4.
Lee, Jaechun. "Aspirin Desensitization as A Treatment for Aspirin-Sensitive Chronic Spontaneous Urticaria." Dermatologic Therapy, vol. 28, no. 1, 2014, pp. 4-6. Wiley-Blackwell, DOI:10.1111/dth.12171.
