Synthesis of Acetaminophen Utilizing

Recrystallization Techniques

Armaan Gill
20777133
Partner: Brittney Persad
TA: Yuxing
Experiment Performed: November 6, 2018
CHEM 120L Section 009

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 Introduction
The objective of this experiment was to retrieve a crude and pure product of

acetaminophen, and determine the melting point ranges of both products. The main purpose of

this experiment was to produce a pure product of acetaminophen through a recrystallization

technique. Acetaminophen is an organic medicinal drug which aids in relieving pain and

reducing fevers. This drug is created by reacting p-aminophenol with acetic anhydride to produce

acetaminophen and acetic acid. The amine group of p-aminophenol is acetylated by acetic

anhydride to construct an amide group. This results in acetic acid being one of the by–products.

After this reaction takes place, acetaminophen is precipitated out of solution due to the solubility

of the products. Acetic acid is highly soluble whereas acetaminophen is highly insoluble in

water, which results in the two products separating and acetaminophen solid forming. In this

experiment, the vacuum filtration, and recrystallization techniques are utilized along with warm

and cool water baths to aid in reactions. The warm water bath was used to dissolve the

crude/pure product in its solvent, distilled water. The ice water bath was used to allow the

crude/pure product to precipitate out of the solution. The vacuum filtration technique filters out

all of the acetic acid, leaving the solid crude or pure product. A sample of both the crude and

pure product are collected to determine their melting temperature ranges. Theoretically, the crude

product should have a lower melting temperature then the pure product due to the fact that the

crude product is less pure. This means the crude product contains more foreign elements to the

precipitate which lowers the energy within its bonds. A pure product has stronger bonds than an

impure product which causes it to have a higher melting temperature.

Procedure
The experimental procedure used for this experiment was outlined in CHEM 120L lab manual,

Experiment #4. All steps were followed without deviation.

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 Experimental Observations
Stage Observations
Round bottom flask -3.24 grams p-aminophenol and 10 mL deionized water heated at 70oC
(warm bath) -4.00 mL pure acetic anhydride added, giving the solution a yellow color,
and continued heating
-All p-aminophenol dissolved 6 minutes after pure acetic anhydride added
-Solution cooled at room temperature for 10 minutes while stirring
Round bottom flask -Yellow solution cooled for 15 minutes
(ice-water bath) -White precipitate formed at the bottom of flask
Vacuum filtration -Solid kept under vacuum for 5 minutes
(crude product) -Aqueous solution filtered out
-3.92 grams of white powdery substance (crude product) obtained
Recrystallization -3.92 grams of crude product and 39.2 mL of deionized water added to
(warm water bath) Erlenmeyer flask
-Mixture heated till dissolved then cooled at room temperature
Recrystallization -Clear solution cooled for 10 minutes
(ice-water bath) -White substance recrystallized at bottom of flask
Vacuum filtration -Solid kept under vacuum for 5 minutes
(pure product) -Aqueous solution filtered out
-3.44 grams of shiny white powdery substance (pure product) obtained
Melting -Product started melting at 163oC
temperature for -Product finished melting at 165oC
crude product
Melting -Product started melting at 163oC
temperature for -Product finished melting at 168oC
pure product

Results and Calculations

p-Aminophenol + Acetic Anhydride  Acetaminophen + Acetic Acid

Theoretical yield of acetaminophen:

Percent Yield:
% Yeild = Actual Yield – Theoretical Yield x 100%
Theoretical Yield

% Yeild = 3.44g – 4.49g x 100% = 23.4%

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 Discussion
In this experiment, a p-aminophenol was taken through a series of reactions to ultimately

form a pure product of acetaminophen. This experiment accomplished the production of the

crude product, the pure product, and from these two products, the melting temperature ranges of

each were measured. From 3.24 grams of p-aminophenol, 3.92 grams of crude product was

produced and 3.44 grams of pure product was produced. The melting temperature range of the

crude product was 163oC to 165oC and the pure product was 163oC to 168oC. The accepted value

of the melting temperature of acetaminophen is 169 oC to 170oC. (NIST, 2018). The experimental

temperature range of the pure acetaminophen was only a few degrees below the accepted

temperature range. This means that the experiment was extremely effective and efficient as the

accepted temperature range is for a purified acetaminophen. However, even though the

acetaminophen in the experiment was a pure product, it was not completely pure. There was a

percent error of 23.4% which means that the pure product obtained was not 100% pure. This

error could have been the cause of some of the acetaminophen remaining dissolved in the

solution separated from the precipitate. As predicted, the purer substance has a higher melting

temperature than an impure version of the same substance. Since the pure product produced in

the experiment was not completely pure, it resulted in a temperature range lower than the

expected. However, the temperature range was extremely close which means the experiment was

conducted with a high degree of effectiveness.

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 Questions
1. In this experiment crude acetaminophen was purified using the technique of
recrystallization; answer the following questions regarding this technique:
a. What could happen if 5 mL of water was added for every 1 g of crude product?
Adding 10 mL of water per every 1 g of crude product was instructed because this would result

in a saturated solution where no more solute can dissolve. If 5 mL of water was used instead, it

would have resulted in a supersaturated solution where there is a much higher solute

concentration than the solvent which could possibly lead to the formation of some crystals.

b. What could happen if 15 mL of water was added for every 1 g of crude product?
If 15 mL of water was used for every 1 g of crude product, the solution would have become

unsaturated where more solute can dissolve. Adding 10 mL or 15 mL may give you the same

results because if the solute can dissolve in 10 mL, it can also dissolve in 15 mL. In this case, the

extra 5 mL of water is just excess water.

c. Cold solvent was used to aid in the transfer of the recrystallized product. What could
happen if room temperature solvent was used?
Higher temperatures result in a higher rate of dissolving as the molecules begin to move faster

with more energy. Since room temperature is higher than the temperature of the cold solvent,

some of the recrystallized product could have dissolved due to the warmer room temperature.

That is why the cooler solvent was used.

d. What is the purpose of scratching the inner walls of the round bottom flask?
This causes small particles of glass from the flask to get scratched off and react with the solution

as nuclei for crystal growth. The glass particles act as a seed allowing crystals to form around the

seed from the dissolved solution. This induces crystallization in the solution.

2. How is measuring the melting points of your samples help to assess the purity?
An impure sample melts faster than a pure sample due to the impurities in the structure of the

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 solid. A pure substance has more tightly packed molecules than an impure substance. This fact

means that the pure substance requires more energy to break apart the bonds between molecules

than an impure substance. This allows the impure substances to have lower melting temperatures

than the pure substances as less energy is required. That is also the result achieved in the

experiment, the pure product had a higher melting temperature than the crude product.

3. Research a product a product (other than acetaminophen) that is created using organic
synthesis. Write a short paragraph (200 words or less) summarizing your research. Some
things to think about: What product is synthesized? What are the reagents used? What is
the process of synthesis? How has this product changed the world we live in?
One product produced using organic synthesis is aspirin. The two main reagents used to

create this product were salicylic acid and acetic anhydride. (Olmsted, 1998). The products of

this synthesis reaction are acetylsalicylic acid (aspirin) and acetic acid. Acetic acid is highly

soluble and acetylsalicylic acid is highly insoluble. This causes the aspirin to simply precipitate

out of the solution.

Aspirin has changed the world by being one of the many drugs that aid to reduce fever and

act as a pain killer. Salicylic acid, one of the ingredients of making aspirin, it is used to create a

variety of products using organic synthesis as it is a plant hormone. (Olmsted, 1998). Relative to

health treatment, salicylic acid comes from willow bark which is another reagent that is a

headache remedy. Salicylic acid has similar functions to aspirin except is much easier for the

body to consume.

4. Find one organic amine (other than p-Aminophenol) and one organic amide (other than
acetaminophen), draw the structure for each and clearly indicate the amine/amide group.

Amine: Methylamine Amide: Methanamide

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 Conclusion
The main objectives of this experiment consisted of creating a crude product of

acetaminophen, and then using that to create a pure product. Another objective of this experiment

was to determine the temperature ranges of each, crude and pure product. The objectives

regarding this experiment were achieved as the crude and pure products were produced and the

melting temperature ranges were determined. The initial mass of the p-aminophenol used was

3.24 grams. The mass of the crude product produced was 3.92 grams and that was recrystallized

to produce 3.44 grams of the pure product. Samples of the crude and pure product were used to

measure melting temperature ranges for both products. It was predicted that the pure product

would have a higher melting temperature range due to the product having stronger bonds than

the less pure, crude product. These predictions were correct, as the melting temperature range of

the crude product was 163oC to 165oC and the pure product was 163oC to 168oC. Looking at the

experimental yield, 3.44 grams of pure product was obtained. However, the calculated theoretical

yield for the acetaminophen was 4.49 grams. This resulted in a percent error of 23.4%. This was

an extremely reliable experiment as there were very few reactions, and more steps involving

changes of state and isolating the precipitate. However, the experimental yield was lower than

the theoretical yield. This could have been due to the dissolving step. When the acetaminophen

was precipitated out of solution and separated out of the solution using vacuum filtration, some

of the acetaminophen could have still been dissolved in solution and didn’t precipitate out. This

could be the main reason for the experimental yield being lower than the theoretical yield.

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 References

NIST Chemistry WebBook, SRD 69. https://webbook.nist.gov/cgi/cbook.cgi?

ID=C103902&Mask=FFFF (accessed Nov 20, 2018).

Olmsted, J. A. Synthesis of Aspirin: A General Chemistry Experiment.

https://pubs.acs.org/doi/abs/10.1021/ed075p1261 (accessed Nov 20, 2018).

Stathopulos, S. CHEM 120L Laboratory Manual; Waterloo, 2018.

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