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Synthesis of Acetaminophen Lab Report...

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The Synthesis of Pure and Crude Acetaminophen From P-Aminophenol and Acetic Anhydride Name: Student ID: Partner: TA: Experiment Performed on: CHEM 120L Section 007 Friday 2:30 p.m. - 5:20 p.m., STC 4019

Introduction Chemical synthesis is used to create a new substance, usually in one or multiple step reactions (“Chemical Synthesis”, n.d.). Mostly organic molecules are created using chemical synthesis (“Chemical Synthesis”, n.d.). The bond of a certain substance is broken and in turn creates a new product that does not naturally occur in nature (“Chemical Synthesis”, n.d.). Synthesis reactions are widely used in industrial settings to produce large quantities of a certain substance (“Chemical Synthesis”, n.d.). Chemical synthesis is useful to determine the reaction mechanism and physical and chemical properties of the substance created (“Chemical Synthesis”, n.d.). For example, the quantity of energy required to make the desired product, how much reactant was used and what was the most efficient way to make a product (“Chemical Synthesis”, n.d.). The objective of this lab was to synthesize 100% of the acetaminophen from paminophenol through the recrystallization and vacuum filtration techniques and record the crude and purified melting point temperatures respectively using a melting point apparatus. Acetaminophen, most commonly known as Tylenol, is an over the counter drug used for pain and fever (“National Center for Biotechnology Information”, n.d.). Taking increased doses of acetaminophen can lead to liver injury and possibly liver failure (“National Center for Biotechnology Information”, n.d.). Acetaminophen is apart of the phenol group, 4-aminophenol (“National Center for Biotechnology Information”, n.d.). The hydrogen atoms attached to the amino group of 4-aminophenol can be replaced with an acetyl group to form acetic acid (“National Center for Biotechnology Information”, n.d.). The chemical equation for this reaction is as follows:

Figure 1: Complete Chemical Reaction of P-Aminophenol and Acetic Acid to Acetaminophen and Acetic Acid

(“Synthesis Reaction of Acetaminophen”, n.d.)

Figure 1 describes the process of how acetaminophen is synthesized for the experiment. Paminophenol and acetic anhydride are heated to catalyze the formation of the crude and pure product which was obtained through recrystallization.

Experimental Procedure The experimental procedure used for this experiment was outlined in CHEM 120L lab manual, experiment #4. All steps were followed without deviation.

Experimental Observations Table 1: Physical and Chemical Properties for Pure and Crude Acetaminophen Chemicals Used

Physical Description of Chemicals Used

Weight (g)

Melting Point Range (°C )

% Yield

P- Aminophenol

White dry powder, opaque

3.03 g

N/A

N/A

Pure Acetaminophen

Small colourless crystals, slightly transparent

2.69 g

167.5°C - 172.48°C

59.8%

Crude Acetaminophen

White wet powder, opaque, clumpy

2.51 g

170.4°C - 173.6°C

65.10%

* The weight of pure acetaminophen was obtained from lab student ....

Results and Calculations Figure 1: Complete Chemical Reaction of P-Aminophenol and Acetic Anhydride to Acetaminophen and Acetic Acid

(“Synthesis Reaction of Acetaminophen”, n.d.)

Theoretical Yield for P-Aminophenol and Pure and Crude Acetaminophen

Calculation for the Moles of P-Aminophenol 3.03 g of p-aminophenol x

1 mol / 109.14 g/mol = 0.027762506 mol

Calculation for the Moles of Crude Acetaminophen 2.51 g of crude acetaminophen x 1 mol / 151.163 g = 0.016604592 mol Calculation for the Moles of Pure Acetaminophen 2.69 g of pure acetaminophen x 1 mol / 151.163 g = 0.017795359 mol Percentage Yield of Pure and Crude Acetaminophen % Yield of crude acetaminophen = 0.016604592 mols of crude acetaminophen / 0.027762506 mols of p-aminophenol x 100% = 59.81% % Yield of pure acetaminophen = 0.017795359 mols of pure acetaminophen / 0.027762506 mols of p-aminophenol x 100% = 65.10% Calculating the Limiting Reagent Moles of P-Aminophenol = 0.27762506 mol Moles of Acetic Anhydride Given : Volume of acetic anhydride: 4.0 mL Density of acetic anhydride: 1.08 g/mL P=m/v 1.08mL = m / 4.0mL = 4.32 g , Mass of acetic anhydride: 4.32 g m = moles of acetic acid/molar mass of acetic anhydride 4.32 = n / 60.052 g = 0.071937654 mols Moles of acetic anhydride: 0.071937654 mols

Therefore, the limiting reagent in this synthesis reaction is P-Aminophenol

Discussion

The results obtained from the synthesis of acetaminophen revealed that not 100% of the product was obtained at the end of the experiment. The percentage yield for the crude product was 59.81% and 65.10% for the pure respectively. An ideal result would have been a 100% of both the crude and pure products were obtained using vacuum filtration. Since 3.03 g of paminophenol was used as one of the reactants to convert into acetaminophen, the moles of the crude and pure product were divided by the moles of p-aminophenol to obtain the theoretical yield of how much of the reactant was successfully converted to the product. In this experiment, acetic acid was a by-product and had no significant contribution to the overall reaction. A similar experiment performed by the Department of Medicine and Pharmacology at the University of Colorado Medical Center, synthesized acetaminophen- d4 in order to observe its side effects that cause hepatic necrosis when overdosed (Freed and Murphy, 1978). Hepatic necrosis, which contains hepatic cytochrome P-450 is activated when metabolite is oxidized, causing it to become very reactive and is essentially trapped by glutathione (Freed and Murphy, 1978). Acetaminophen metabolite will release glutathione and bind to hepatocyte molecules (Freed and Murphy, 1978). The experiment used a benzene-ring deuterated acetaminophen to isolate the metabolite (Freed and Murphy, 1978). P-aminophenol was mixed with hydrochloric acid (HCL) and recrystallized to form rod-like crystals (Freed and Murphy, 1978). The percentage yield for the experiment was 92% (Freed and Murphy, 1978). Similar to the synthesis of acetaminophen, the experiment yielded more than half of the pure and crude product. Obtaining 100% of product after synthesis is highly unlikely due to product being lost during transferring and vacuum filtration. Melting point determination was recorded using a MelTemp. A MelTemp can provide precise melting points for up to three substances up to a maximum of 500°C (“Mel-Temp

Capillary Melting Point Apparatus, n.d.). A glass mercury thermometer was inserted into the apparatus to accurately determine when the crude and purified acetaminophen melted (“MelTemp Capillary Melting Point Apparatus, n.d.). According to the Merck Index, the melting point temperature range of acetaminophen is 169°C-170.5°C (“The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals”, 1996). Compared to the results obtained from the lab, the melting temperature range for pure acetaminophen was between 167.5°C-172.48°C, and 170.4°C - 173.6°C for crude. The results were in the same range as the actual melting temperature of acetaminophen provided by the Merck Index. Since both products melted at a fast rate, a human error was encountered and the temperature range although similar to the Merck Index, the purified product should have had a higher temperature range. Molecular symmetry affects the melting temperature of crystalline substance in that when a product is purified, it exhibits a higher melting point when compared to the molecular symmetry of crude products which have similar structures and lower symmetry exhibit a lower melting point (Pinal, 2004). A purified product has the ability to acquire multiple arrangements of the same structure while crude products can only form a few structural arrangements (Pinal, 2004). In order to break the bonds of p-aminophenol and acetylate the amine group and form an amide group, p-aminophenol was mixed with acetic anhydride which activated the reaction. A recrystallization technique was used, which heated the solute for 5 minutes and immediately cooled for another 10 minutes in order to isolate the precipitate of acetaminophen. To further isolate the acetaminophen precipitate, vacuum filtration was used to obtain as much of the precipitate as possible. At this step, much of the solid acetaminophen was stuck to the filter paper which limited the ability to obtain 100% of acetaminophen. Acetaminophen may have also been

lost during the transferring of the precipitate from the erlenmeyer flask to the vacuum filtration funnel.

Conclusion Overall, the experiment succeeded when obtaining enough crude and purified acetaminophen from 3.03 g of p-aminophenol to record its respective melting point temperatures using a melting point apparatus. The percent yield for this experiment was 59.8% of pure and 68.10% of crude product, indicating that about half of p-aminophenol was obtained at the end of the experiment. Human error was accounted for the loss of some p-aminophenol that prevented a 100% yield. For melting temperatures, the Merck Index was used to compare the exact melting point temperature of acetaminophen, which was between 169°C-170.5°C (“The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals”, 1996). Compared with the results recorded during the lab, the values were between the range provided by the Merck Index. Purified products have significantly higher melting points compared to crude products due to the molecular symmetry, but due to human error, the results exhibited a higher melting point range for the crude product. The techniques in the experiment provided somewhat accurate results in the synthesis of acetaminophen was successful.

References

Synthesis Reaction of Acetaminophen; University of Missouri-St. Louis.

National Center for Biotechnology Information. PubChem Database. Acetaminophen, CID=1983, https://pubchem.ncbi.nlm.nih.gov/compound/Acetaminophen (accessed Nov 22, 2019).

Chemical Synthesis. https://www.britannica.com/science/chemical-synthesis (accessed Nov 22, 2019).

Freed, C. R.; Murphy, R. C. Synthesis of Acetaminophen‐d4. Journal of Labelled Compounds and Radiopharmaceuticals 1978, 15 (S1), 637–638.

Mel-Temp Capillary Melting Point Apparatus. https://www.sigmaaldrich.com/catalog/product/aldrich/z289051?lang=en®ion (accessed Nov 22, 2019).

The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, 12th ed.; Budavari, S.; O'Neal, M.J.; Smith, A.; Heckelman, P. E.; Kinneary, J. F., Eds.; Merck & Co.: Whitehouse Station, NJ, 1996; entry 4857.

Pinal, R. Effect of Molecular Symmetry on Melting Temperature and Solubility. Organic & Biomolecular Chemistry 2004, 2 (18), 2692.

Stathopulos, S. CHEM 120L Laboratory Manual; University of Waterloo: Waterloo, ON, 2019; p. 53-55....