Synthesis Of Aspirin Lab Report Chegg

The Synthesis of Aspirin: A Comprehensive Lab Report

Aspirin, or acetylsalicylic acid, is a common over-the-counter pain reliever and anti-inflammatory drug. Its synthesis is a classic organic chemistry experiment, providing a practical understanding of esterification reactions and purification techniques. This report details the synthesis of aspirin from salicylic acid, including the experimental procedure, data analysis, and discussion of results. Understanding this process highlights key concepts in organic chemistry, including reaction mechanisms, yield calculations, and the importance of purification.

Introduction

The synthesis of aspirin involves the esterification of salicylic acid with acetic anhydride in the presence of an acid catalyst, typically sulfuric acid or phosphoric acid. Salicylic acid contains both a carboxylic acid group (-COOH) and a hydroxyl group (-OH) on the benzene ring. The hydroxyl group reacts with acetic anhydride, replacing the hydrogen atom with an acetyl group (-COCH3), forming acetylsalicylic acid (aspirin) and acetic acid as a byproduct. This reaction is an example of acetylation, a specific type of esterification. The experiment aims to synthesize aspirin, purify the product through recrystallization, and determine the percent yield. Understanding the reaction mechanism, optimizing reaction conditions, and accurately calculating yield are crucial aspects of this experiment.

Materials and Methods

Materials:

• Salicylic acid (C₇H₆O₃)
• Acetic anhydride ((CH₃CO)₂O)
• Concentrated sulfuric acid (H₂SO₄) (catalyst)
• Distilled water
• Ice bath
• Beaker
• Erlenmeyer flask
• Hot plate
• Buchner funnel
• Filter paper
• Vacuum filtration apparatus
• Weighing scale

Procedure:

1. Weighing the reactants: Accurately weigh approximately 2.0 grams of salicylic acid and record the mass. This serves as the limiting reagent for the reaction. Measure 4.0 mL of acetic anhydride using a graduated cylinder. Note that the density of acetic anhydride is approximately 1.08 g/mL, so this volume corresponds to approximately 4.32 g. This excess of acetic anhydride helps drive the reaction to completion.

2. Mixing the reactants: Add the weighed salicylic acid to an Erlenmeyer flask. Carefully add the acetic anhydride to the flask. Swirl the flask gently to mix the reactants.

3. Adding the catalyst: Add 5 drops of concentrated sulfuric acid to the mixture as a catalyst. Swirl gently to mix thoroughly. Caution: Concentrated sulfuric acid is corrosive. Handle it with appropriate safety precautions, including wearing gloves and eye protection.

4. Heating the reaction mixture: Heat the flask in a hot water bath (approximately 50-60°C) for 15 minutes, ensuring the mixture is constantly swirling. This elevated temperature accelerates the reaction rate.

5. Cooling the reaction mixture: After 15 minutes, remove the flask from the hot water bath and allow it to cool in an ice bath for 10-15 minutes. The cooling process facilitates the crystallization of aspirin.

6. Adding water: Add 50 mL of ice-cold distilled water to the flask. This precipitates the aspirin out of solution. Aspirin is less soluble in cold water than in hot water.

7. Filtering the product: Filter the mixture using a Buchner funnel and vacuum filtration to collect the crude aspirin crystals.

8. Recrystallization: Recrystallize the crude aspirin from a minimum amount of hot ethanol (or methanol). This further purifies the product by removing impurities. Allow the solution to cool slowly to allow for the formation of pure aspirin crystals.

9. Drying the product: Collect the recrystallized aspirin crystals by vacuum filtration, wash with cold water, and allow them to dry completely. This step ensures that the obtained aspirin is free from water.

10. Weighing the product: Once the aspirin crystals are completely dry, weigh the product and record the mass.

Results

Data Table:

Calculations:

• Theoretical yield: The molar mass of salicylic acid is 138.12 g/mol, and the molar mass of aspirin is 180.16 g/mol. The theoretical yield can be calculated using stoichiometry:

(2.01 g salicylic acid) * (1 mol salicylic acid / 138.12 g salicylic acid) * (1 mol aspirin / 1 mol salicylic acid) * (180.16 g aspirin / 1 mol aspirin) = 2.62 g aspirin (theoretical yield)

• Percent yield: The percent yield is calculated as follows:

(Actual yield / Theoretical yield) * 100% = (2.10 g / 2.62 g) * 100% = 80.2%

Discussion

The experiment successfully synthesized aspirin from salicylic acid. The obtained percent yield of 80.2% indicates a reasonably efficient reaction. The lower-than-100% yield is likely due to several factors:

• Loss during filtration: Some product might have been lost during the filtration process.
• Incomplete reaction: The reaction might not have gone to completion due to insufficient reaction time or temperature.
• Impurities: The presence of impurities in the starting materials could affect the yield.
• Loss during recrystallization: Some product might have been lost during the recrystallization process.

The recrystallization step is crucial for obtaining pure aspirin. Impurities are generally more soluble than aspirin and remain dissolved in the solvent, leaving purer aspirin crystals behind. The melting point of the synthesized aspirin can be determined to assess its purity. A melting point close to the literature value (135°C) suggests high purity. Differences indicate the presence of impurities.

Reaction Mechanism:

The reaction proceeds via an electrophilic acyl substitution mechanism. The sulfuric acid protonates the acetic anhydride, making it a better electrophile. The hydroxyl group of salicylic acid then attacks the carbonyl carbon of the protonated acetic anhydride. This is followed by proton transfer and elimination of acetic acid, resulting in the formation of aspirin.

Conclusion

This experiment successfully demonstrated the synthesis of aspirin through esterification. The recrystallization process was effective in purifying the product. The 80.2% yield, while not perfect, is acceptable considering potential losses during the experimental process. The experiment reinforces the understanding of esterification reactions, purification techniques, and yield calculations, crucial concepts in organic chemistry. Further improvements could involve optimizing reaction conditions, such as reaction time and temperature, to increase the yield. Accurate weighing and careful handling of chemicals are essential for obtaining reliable results.

Frequently Asked Questions (FAQ)

Q: Why is acetic anhydride used in excess?

A: Using acetic anhydride in excess ensures that the reaction proceeds to completion. The excess drives the equilibrium towards product formation.

Q: What is the role of sulfuric acid in this reaction?

A: Sulfuric acid acts as a catalyst. It increases the reaction rate by protonating the acetic anhydride, making it a better electrophile.

Q: Why is recrystallization necessary?

A: Recrystallization is essential to purify the synthesized aspirin. It removes impurities that might be present in the crude product, leading to a purer, higher-quality aspirin sample.

Q: What are the safety precautions that need to be followed during this experiment?

A: Always wear appropriate safety goggles and gloves. Acetic anhydride and concentrated sulfuric acid are corrosive and should be handled carefully. Proper ventilation is necessary to avoid inhaling any fumes.

Q: How can the purity of synthesized aspirin be verified?

A: The purity can be verified by determining the melting point of the synthesized aspirin. A melting point close to the literature value indicates high purity. Other techniques such as thin-layer chromatography (TLC) or high-performance liquid chromatography (HPLC) can also be used for more detailed analysis.

Q: What are the potential sources of error in this experiment?

A: Potential sources of error include inaccurate measurements of reactants, incomplete reaction, losses during filtration and recrystallization, and the presence of impurities in the starting materials. Improper temperature control can also influence the reaction yield.

Q: Can this synthesis be scaled up for industrial production?

A: Yes, this synthesis is readily scalable for industrial production, although industrial processes often utilize more sophisticated equipment and optimized reaction conditions for greater efficiency and yield. They may also employ different purification techniques depending on the scale and required purity.