Laboratory Report: Synthesis of Aspirin

Abstract

The purpose of this experiment was to synthesize aspirin (Acetylsalicylic acid) using a method similar to industrial manufacturing. Salicylic acid and acetic anhydride were reacted in the presence of concentrated sulfuric acid as a catalyst.

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The theoretical yield of aspirin was calculated, and the percent yield was determined based on the actual yield obtained. The experiment identified the limiting reagent as salicylic acid and assessed the purity of the synthesized aspirin through a Ferric chloride test. The results showed that the aspirin produced was approximately 97.

5% pure, indicating a partial reaction and impurities in the final product. Potential sources of error were discussed, including the possibility of a stalled reaction or insufficient catalyst concentration.

Introduction

The synthesis of aspirin (Acetylsalicylic acid, ASA) is a common laboratory experiment that mimics industrial processes. ASA is widely used as an analgesic and anti-inflammatory drug. In this experiment, ASA was synthesized from salicylic acid and acetic anhydride in the presence of sulfuric acid as a catalyst. The reaction is represented as follows:

Salicylic acid + Acetic anhydride + Sulfuric acid → Aspirin + Acetic acid

The expected outcome was the successful synthesis of pure aspirin from the mixture of reactants. The limiting reagent in the reaction was determined through calculations, and the purity of the synthesized aspirin was assessed using a Ferric chloride test.

Materials and Methods

The following materials and equipment were used in the experiment:

Safety precautions: Concentrated sulfuric acid is corrosive and flammable.

All transfers were performed in a fume hood to avoid inhaling vapors. Proper personal protective equipment (PPE) was worn when handling chemicals. In case of skin or clothing contact, immediate washing with copious amounts of water was required, and any spills were reported to the lab instructor.

Procedure

1. Half-filled a 400mL beaker with tap water and heated it to 45-50°C on a hot plate to serve as a hot bath.
2. Weighed approximately 2.000g of salicylic acid and recorded the mass.
3. Transferred the salicylic acid to a 125mL Erlenmeyer flask under a fume hood.
4. Measured approximately 5mL of acetic anhydride and recorded the volume.
5. Added the acetic anhydride to the Erlenmeyer flask containing the salicylic acid and swirled.
6. Added 4 drops of concentrated sulfuric acid to catalyze the reaction.
7. Placed the flask in the hot water bath and heated for 10 minutes, stirring until the salicylic acid dissolved.
8. Removed the flask from the hot water bath and allowed it to cool to room temperature, allowing aspirin to precipitate.
9. Prepared an ice water bath using a 400mL beaker with a 1:1 ratio of ice and water.
10. Added 50mL of tap water to the beaker and gradually added ice until the water level reached 100mL.
11. Placed the flask into the ice water bath and allowed it to cool until aspirin stopped precipitating.
12. Added 20mL of ice-chilled distilled water to the reaction flask in 5mL increments, stirring after each addition, and returned the flask to the ice water bath to cool.

Vacuum Filtration

1. Assembled the filtration apparatus with the following steps:
   • Inserted the Buchner funnel into the rubber stopper in the filter flask.
   • Clamped the filter flask to the ring stand.
   • Attached the vacuum tubing to the flask side arm and vacuum aspirator.
   • Placed the filter paper inside the Buchner funnel and moistened it with distilled water to prevent drying out.
   • Turned on the vacuum aspirator to verify the filter paper created a proper seal on the bottom of the funnel.
2. Transferred the reaction mixture into the Buchner funnel with the vacuum aspirator activated to collect the solid product (aspirin).
3. Rinsed the Erlenmeyer flask with distilled water and poured it into the Buchner funnel to ensure all aspirin precipitate was collected.
4. Rinsed the solid aspirin twice with small amounts of cold water to remove residual impurities.
5. Continued to draw air through the crystals in the funnel until they were dry.

Ferric Chloride Test

1. Placed about 5mL of distilled water in the first test tube and added a small amount of aspirin (about the size of a pen tip).
2. Placed about 5mL of distilled water and a small amount of salicylic acid (about the size of a pen tip) in the second test tube.
3. Added about 5mL of the filtrate from the filter flask to the third test tube.
4. Added 10 drops of 1% Ferric chloride to each test tube and stirred.
5. Compared the color changes in each reaction.

Data Tables

Table 1: Class Raw Data

Table 2: Class Salicylic Acid Data

Table 3: Class Acetic Anhydride Data

Table 4: Class Yields of Aspirin (ASA)

Observations

The following observations were made during the experiment:

• The dry Salicylic acid crystals were white in color.
• Both the Acetic anhydride and Sulfuric acid were clear and colorless.
• Upon introduction of the Acetic anhydride and Sulfuric acid to the flask containing the Salicylic acid crystals, the mixture became white and cloudy.
• Once the aspirin formed, it appeared to be white and crumbly.
• An odor of vinegar developed during the filtration process.
• The 1% Ferric chloride was clear and yellow-orange in color.
• Upon introduction of the Ferric chloride to the first test tube with Salicylic acid, the mixture turned to a dark purple color.
• Upon introduction of the Ferric chloride to the second test tube with the product (aspirin), the mixture became light purple and clear.
• Upon introduction of the Ferric chloride into the third test tube with the filtrate mixture, the mixture turned into a dark purple.

Calculations

Several calculations were performed to analyze the experiment results:

1. The moles of salicylic acid_CHO were determined using the following equation:

^Moles = ^{Mass (g)} / _{Molar Mass (g/mol)}

2. The moles of acetic anhydride_CHO were calculated using the same equation.

3. The ratio of moles of salicylic acid_CHO to moles of acetic anhydride_CHO was determined to identify the limiting reagent.

4. The theoretical yield of aspirin (ASA) was calculated using the limiting reagent's moles:

^{Theoretical Yield (g)} = ^{Moles of Limiting Reagent} × _{Molar Mass of ASA (g/mol)}

5. The percent yield of aspirin was determined using the following equation:

^{Percent Yield} = ^{(Actual Yield) / (Theoretical Yield)} × 100

Results

The experiment yielded a personal synthesis of 2.855g of aspirin, while the theoretical yield was calculated to be 2.926g. This resulted in a percent yield of approximately 97.5%.

Discussion

The experiment successfully synthesized aspirin from salicylic acid and acetic anhydride. The limiting reagent was identified as salicylic acid based on the mole ratio calculation, with a ratio of 1:3.3 indicating an excess of acetic anhydride. The percent yield of approximately 97.5% indicated a partial reaction and the presence of impurities in the final product, as confirmed by the Ferric chloride test.

Possible sources of error included a stalled reaction, non-ideal reaction temperatures, or insufficient catalyst concentration. To improve the experiment's accuracy, the inside of the Erlenmeyer flask could be scraped with a glass stirring rod to restart the reaction if it stalls. Additionally, ensuring the reaction is conducted at optimal temperatures and increasing the catalyst concentration may lead to a more complete reaction and a higher yield of pure aspirin.

Conclusion

The experiment successfully synthesized aspirin with a percent yield of approximately 97.5%. The limiting reagent was identified as salicylic acid, and impurities were detected in the final product through the Ferric chloride test. To improve the experiment's results, measures can be taken to prevent a stalled reaction and enhance the catalyst concentration.