The Melting Point Analysis of Crude and Recrystallized Acetaminophen Synthesized


...Start of the The Melting Point Analysis of Crude and Recrystallized Acetaminophen Synthesized ...

Acetic Anhydride and p-Aminophenol were heated in a vial attached to an air condenser to synthesize crude acetaminophen, resulting in 0.097 grams (47.48% yield). The crude acetaminophen was then recrystallized in a solvent of water and methanol over heat resulting in 0.082 grams (39.61% yield) of pure acetaminophen. Melting points of both crude and pure acetaminophen were taken, and found to be 165.9 – 170.9°C and 168.2 – 171.5°C, respectively. The literature melting point of acetaminophen is 169.5 – 171.0°C, indicating that our final product was pure. The synthesis of acetaminophen involves the attraction of the electrophilic carbonyl group of acetic anhydride to the nucleophilic NH2 of the p-aminophenol. This occurs because the NH2 group is a better nucleophile than the OH group attached on the opposite side of the p-aminophenol. A new nitrogen-carbon bond is formed, producing acetaminophen with acetic acid as a byproduct. During the synthesis of acetaminophen, it is necessary to dissolve all solid material, and heat the reaction at a high enough temperature and for a long enough time period to ensure completion.


...Middle of the The Melting Point Analysis of Crude and Recrystallized Acetaminophen Synthesized ...

The product was placed in a Craig tube and several drops of hot (100°C) solvent (50% water, 50% methanol, by volume) was added and heated until all of the crystals dissolved. The Craig tube was plugged and set in an Erlenmeyer flask to cool. Crystallization was induced once the mixture was at room temperature by scratching the inner wall of the tube. It was then placed into an ice bath for ten minutes until crystallization was complete. The tube was then centrifuged for 3 minutes to remove the liquid. The crystals were collected on a watch glass and allowed to air dry. The resulting crystals (o.o82g) were pale brown in color. Melting points were taken for both the crude (165.9 – 179.9°C) and the pure (168.2 – 171.5°C) acetaminophen. Results and Calculations .


...End of the The Melting Point Analysis of Crude and Recrystallized Acetaminophen Synthesized ...

The low percent yields of both the crude product and the recrystallized product could have been caused by several factors. Some of both products could have been lost when transferred to the watch glass to be weighed. The hot plate that the reactions occurred on was also very unstable, and the temperature fluctuated throughout the reaction. This may have effected how much product was formed, as more side products would have resulted from a higher temperature. The crude crystals were also not allowed enough time to adequately dry before recrystallization occurred. Had they been allowed more time to dry, the percent yield of pure acetaminophen may have increased. Overall, however, the experiment was successful, as pure acetaminophen was synthesized. The melting point of the product confirmed the high level of purity, and the difference between the crude and recrystallized products could be easily observed.


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