Lab Report: Synthesis and Purification of Acetaminophen

Categories: Chemistry

Abstract

In this experiment, the synthesis and purification of acetaminophen were performed. Initially, crude acetaminophen was obtained with a 58.7% yield through the reaction of p-aminophenol with acetic anhydride. The crude acetaminophen was then decolorized, resulting in purified acetaminophen with a 13.5% yield. The purity of the final product was assessed through qualitative observations of coloration and comparison of melting point ranges with pure acetaminophen. The experiment highlighted the importance of minimizing product loss and impurities in the synthesis and purification process.

Introduction

Acetaminophen, also known as paracetamol, is a widely used over-the-counter pain reliever and fever reducer.

It can be synthesized from p-aminophenol through a chemical reaction with acetic anhydride. The resulting crude acetaminophen can contain impurities, and the goal of this experiment is to purify the product. This process involves decolorization and crystallization to obtain a purified form of acetaminophen.

Materials and Methods

Materials:

  • p-Aminophenol (0.150g)
  • Acetic anhydride (0.165ml)
  • Water (0.450ml)
  • Alumina block
  • Conical vial
  • Spin vane
  • Air condenser
  • Ice bath
  • Hirsch funnel
  • Sodium dithionite (0.2g)
  • Methanol

Methods:

  1. Weigh out 0.150g of p-aminophenol and place it in a 5ml conical vial.
  2. Add 0.450ml of water and 0.165ml of acetic anhydride to the conical vial.
  3. Heat the reaction with an alumina block at about 120°C while stirring gently. After complete dissolution of the solid precipitate, heat for an additional 20 minutes.
  4. Remove the vial from heat and allow it to cool to room temperature.
  5. Remove the spin vane and air condenser from the conical vial and let it cool further.
  6. Place the mixture in an ice bath for 15-20 minutes to allow for crystallization.

    Get to Know The Price Estimate For Your Paper
    Topic
    Number of pages
    Email Invalid email

    By clicking “Check Writers’ Offers”, you agree to our terms of service and privacy policy. We’ll occasionally send you promo and account related email

    "You must agree to out terms of services and privacy policy"
    Write my paper

    You won’t be charged yet!

  7. Collect the crystals through vacuum filtration using a Hirsch funnel for 5-10 minutes to allow air to pass through.
  8. Weigh the crude product and determine its melting point range (166.8-167.6°C) compared to the known melting point range of pure acetaminophen (169.5-171°C).
  9. Dissolve 0.2g of sodium dithionite in 1.5ml of water in a 5ml conical vial.
  10. Add the crude product to the vial and heat the mixture at about 100°C for 15 minutes.
  11. After heating, the crude product should completely dissolve, producing a light tan translucent solution.
  12. Cool the mixture in an ice bath for about 10 minutes.
  13. Collect the crystals by vacuum filtration with the Hirsch funnel, and weigh the purified acetaminophen (0.060g).
  14. Crystallize the material from a solvent mixture composed of 50% water and 50% methanol by volume.
  15. Set up the Craig tube apparatus and dissolve the product in hot solvent.
  16. Allow the solution to cool by inserting the inner plug of the Craig tube and place it in an ice bath.
  17. Collect the crystals using a centrifuge, weigh the final product (0.028g), and determine its melting point range (166.1-169.8°C).

Calculations

The percent yield of crude acetaminophen was calculated as follows:

Percent Yield of Crude Acetaminophen = (Weight of Crude Acetaminophen / Weight of p-Aminophenol) x 100

Percent Yield of Crude Acetaminophen = (0.122g / 0.150g) x 100 = 58.7%

The percent yield of the final crystallized acetaminophen was calculated as follows:

Percent Yield of Final Crystallized Acetaminophen = (Weight of Final Crystallized Acetaminophen / Weight of Crude Acetaminophen) x 100

Percent Yield of Final Crystallized Acetaminophen = (0.028g / 0.207g) x 100 = 13.5%

Observations

During the experiment, the following observations were made:

  • p-Aminophenol is a dark purple powder containing few small grains.
  • Addition of water formed a dark purple viscous mixture, with most p-aminophenol dissolved.
  • Addition of acetic anhydride to the mixture produced a dark brown mixture, and a brown precipitate seemed to have formed at the bottom of the vial.
  • Crude acetaminophen was light brown in color.
  • Purified acetaminophen was slightly light tan/pink, almost white.
  • Crystallized acetaminophen resulted in whiter, shiny, fine crystals with no apparent odor.

Results

The results of the experiments are as follows:

Crude Acetaminophen:

  • Percent Yield: 58.7%
  • Melting Point Range: 166.8-167.6°C

Final Crystallized Acetaminophen:

  • Percent Yield: 13.5%
  • Melting Point Range: 166.1-169.8°C

Discussion

Through the main reaction between 0.150g of p-aminophenol with acetic anhydride, 0.122g of crude acetaminophen was produced along with some acetic acid. This indicates a 58.7 percent yield of crude acetaminophen. This is a fair percent yield considering a slight amount of p-aminophenol was lost due to spillage in the transferring process into conical vail and slight amount of crude acetaminophen was lost when trying to remove crystallized crude acetaminophen from conical vial.

Percent yield is 58.7% indicating loss of reactants or spillage of products. There is possible error when performing suction filtration; too much washing of product can cause product to fall through filter ultimately decreasing overall percent yield. also overheating may have caused a loss of product; some of the product may have been splattered out of the reaction vessel when heating. 1005 yield would mean that one has carried out the lab activities perfectly producing the predicted amount of product. Given the 58.7% yield actually obtained, it is evident that experimental procedures be accurately followed for further improvement. It is in the transferring process of p-aminophenol to a 5mL conical vial. Where error is most critical and product can be readily lost.

After decolorization process, 0.060g of decolorized/purified acetaminophen was obtained indicating a significant loss of product. Prior to decolorization process, 0.122g of crude acetaminophen solid was present, meaning half of product was lost in the decolorization process. It is important to note that a significant amount of product was lost due to spillage when transferring crude acetaminophen into conical vial to decolorization. Error may also be present if mixture is overheated and product is evaporated off.

After crystallization process of purified acetaminophen, 0.028g of white final acetaminophen resulted indicating a 13.5% yield. this is a poor percent yield. this indicates slightly less than half of 0.060g of purified acetaminophen was lost. Such a low percent yield can be attributed to the loss of product throughout the crystallization process. It is important o note that a significant amount of product was lost within supernatant after centrifugation, also, product was lost when trying to remove product from Craig tube and plug.

Purity of final product of acetaminophen was tested through qualitative observation of coloration and by comparing obtained melting point ranges of crude and final acetaminophen to the literature melting point range of pure acetaminophen. Because crude solid acetaminophen contains dark impurities carried along with p-aminophenol we can qualitatively compare the level of impurity before and after decolorization. As for the second test for impurity, the melting point range of the crude acetaminophen, 166.8-167.6°C is slightly depressed when compared to the known melting point range of pure acetaminophen 169.5-171°C. Crude acetaminophen melting point range is depressed by 2.7°C. A difference of less than 5°C indicates a good melting point range was obtained for crude acetaminophen this indicating a minimal amount of impurity present. The melting point range of final crystallized acetaminophen, 166.1-169.8°C is slightly depressed and elongated when compared to the known melting point range of pure acetaminophen 169.5-171°C.

It is depressed by 3.4°C and elongated by 2.2°C. A difference of less than 5°C indicates a good melting point range was obtained, though impurities may still be present. When crystals are isolated by filtration from a solvent, it is important to allow complete drying/evaporation of the solvent in order to minimize impurities and get a good melting range. Residual solvent may also function as an impurity and will depress/broaden the melting range for acetaminophen. When two chemicals are mixed, side reactions may take place and produce by-products which can serve as impurities ultimately lowering and elongating the melting point range. For further reference, one must meticulously carry out experimental procedures to ensure that neither reactants nor product is lost and higher percent yield is obtained.

Conclusion

The synthesis and purification of acetaminophen resulted in a crude product with a 58.7% yield and a final crystallized product with a 13.5% yield. The low yields indicate the loss of product during various stages of the experiment, including transfer, heating, and purification steps. The presence of impurities was confirmed through melting point analysis. Further refinement of the experimental procedures is necessary to improve yield and purity.

Recommendations

To enhance the efficiency and yield of the synthesis and purification processes, the following recommendations are made:

  1. Exercise caution and precision during the transfer of chemicals to minimize spillage and product loss.
  2. Avoid overheating to prevent product evaporation and splattering.
  3. Minimize loss during vacuum filtration and centrifugation by ensuring complete drying and collection of product.
  4. Consider alternative purification methods or solvent systems to improve product purity.
Updated: Dec 29, 2023
Cite this page

Lab Report: Synthesis and Purification of Acetaminophen. (2016, Mar 16). Retrieved from https://studymoose.com/document/isolation-of-crude-acetaminophen

Lab Report: Synthesis and Purification of Acetaminophen essay
Live chat  with support 24/7

👋 Hi! I’m your smart assistant Amy!

Don’t know where to start? Type your requirements and I’ll connect you to an academic expert within 3 minutes.

get help with your assignment