Isolation of Crude Acetaminophen

EXPERIMENT 9: ACETAMINOPHEN

REACTION:

PROCEDURE:

Reaction Mixture:

We started the experiment by placing 1.5grams of p-aminophenol, 1.7 mL of acetic anhydride and 4.5 mL of water in a 50 mL Erlenmeyer flask. Using a magnetic stir bar and a hot plate, the reaction mixture was heated to 100 degrees Celsius until the solid p-aminophenol was completely dissolved. The mixture was then heated for an additional period of time to ensure the reaction was completed.

Isolation of Crude Acetaminophen:

After heating, the flask was removed from the hot plate and cooled to room temperature. During this time, crystal formation was initiated by using a stirring rod to scrape the inside of the flask. Further cooling the mixture in an ice bath for 10 minutes completed the crystallization process. From there, the crystals were collected through vacuum filtration and remained in the Buchner funnel to dry. After 10 minutes in the funnel, we removed the sample and allowed it to dry more efficiently on a watch glass for an additional 10 minutes. The crystals were weighed and a small sample of the crude product was removed for melting point determination and a color comparison after the last step.

Decolorization of Crude Acetaminophen:

My partner and I used 15 mL of water to dissolve 2.0g of sodium dithionite in a clean, 50mL Erlenmeyer flask. Our crude acetaminophen product was added to this flask and heated to 100 degrees Celsius for 15 minutes. After heating, the flask was placed in an ice bath for 10 minutes in order to reprecipitate any decolorized acetaminophen that was dissolved during the heating process. The purified product was then obtained through vacuum filtration and dried on the Buchner funnel for 10 minutes before being weighed.

Crystalization of Acetaminophen:

A 50-50 percent mixture of water and methanol was used to crystalize our purified acetaminophen. We transferred our product into a 50 mL Erlenmeyer flask and filled the water/methanol mixture just above the surface of the purified acetaminophen. The flask was heated until the product dissolved and was cooled slowly to room temperature, ensuring maximum and quality crystallization. Placing the product in an ice bath for 15 minutes completed this process. The final collection was filtered with our Buchner funnel before being air-dried and weighed.

RESULTS

* Crude product weight: 1.062g

* Purified product weight: 1.523g

* Purified product Percentage Yield:

* Melting Point Range: 165-171oC

DISCUSSION

In this experiment p-aminophenol was reacted with acetic anhydride to form the amide, acetaminophen along with the by-product acetic acid. Through crystalizing and filtrating the reaction mixture, a crude product weighing 1.762g was collected. Upon collection of the crude acetaminophen, it was observed that it appeared brown in color. This discoloration is due to the oxidation of the phenol group in p-aminophenol during the chemical reaction. As shown below, Figure 1 is a photograph of the crude acetaminophen that was obtained after vacuum filtration and Figure 2 illustrates the oxidation of p-aminophenol (Resulting in the