CHEM 162 Lab 6: Synthesis of Aspirin —
Complete Solution Lab Report and Explanation.
Section 1: Title & Purpose
Title: Lab 6: Synthesis of Acetylsalicylic Acid (Aspirin) via Fischer Esterification
Purpose: To synthesize aspirin from salicylic acid and acetic anhydride using acid catalysis, and
to assess product purity through ferric chloride testing and melting point determination.
Section 2: Introduction & Background
Balanced Chemical Equation:
Reaction Mechanism (Fischer Esterification): The phenolic –OH group of salicylic acid acts as a
nucleophile, attacking the carbonyl carbon of acetic anhydride in the presence of the H₃PO₄ acid
catalyst. The acid catalyst protonates the carbonyl oxygen of the acetic anhydride, making the
carbonyl carbon more electrophilic and thus more susceptible to nucleophilic attack by the
phenolic oxygen of salicylic acid. This nucleophilic acyl substitution results in the formation of an
ester linkage (the acetyl group) and acetic acid as a byproduct.
Role of Phosphoric Acid (H₃PO₄) Catalyst: It protonates the carbonyl oxygen of acetic
anhydride, increasing the electrophilicity of the carbonyl carbon and accelerating the
nucleophilic attack by salicylic acid. Phosphoric acid is used instead of a stronger acid like
sulfuric acid because it is less likely to cause charring or side reactions with the aromatic ring.
Purpose of Recrystallization: To dissolve the crude aspirin in hot ethanol-water, then allow slow
cooling to selectively crystallize pure aspirin while leaving impurities (unreacted salicylic acid
and acetic anhydride byproducts) in the supernatant solution. This purification technique
exploits differences in solubility between the desired product and impurities.
Section 3: Materials & Safety
Complete Glassware List:
• 125 mL Erlenmeyer flask
• 250 mL beaker (water bath)
, • Graduated cylinder
• Buchner funnel
• Filter flask
• Vacuum tubing
• Watch glass or weighing paper
Specific Chemical Reagents with Concentrations:
• Salicylic acid (solid)
• Acetic anhydride (liquid, 99%)
• Phosphoric acid (85%, catalyst)
• Ethanol (95%)
• Distilled water
• 1% ferric chloride (FeCl₃) test solution
Safety and Hazard Information:
• Salicylic acid: Skin/eye irritant. Avoid direct contact.
• Acetic anhydride: Flammable, corrosive, lachrymator (causes tearing); causes severe
burns. Handle only in a fume hood.
• Phosphoric acid (85%): Corrosive. Causes severe skin and eye burns.
• General Precautions: Use fume hood during reaction; wear nitrile gloves and safety
goggles throughout the experiment. Avoid inhaling vapors from acetic anhydride.
Section 4: Procedure
Step 1: Synthesis Weigh approximately 2.0 g of salicylic acid into a 125 mL Erlenmeyer flask.
Add 5.0 mL of acetic anhydride, followed by 5 drops of 85% H₃PO₄ catalyst. Swirl to mix. Heat
the flask in a 70–80°C water bath for 15–20 minutes with occasional swirling.
Step 2: Crystallization Remove flask from water bath. Carefully add 5 mL of cold distilled water
dropwise to decompose excess acetic anhydride (exothermic reaction). Then add 30 mL of cold
water. Cool the flask in an ice bath for 10–15 minutes until crystals fully form.
Complete Solution Lab Report and Explanation.
Section 1: Title & Purpose
Title: Lab 6: Synthesis of Acetylsalicylic Acid (Aspirin) via Fischer Esterification
Purpose: To synthesize aspirin from salicylic acid and acetic anhydride using acid catalysis, and
to assess product purity through ferric chloride testing and melting point determination.
Section 2: Introduction & Background
Balanced Chemical Equation:
Reaction Mechanism (Fischer Esterification): The phenolic –OH group of salicylic acid acts as a
nucleophile, attacking the carbonyl carbon of acetic anhydride in the presence of the H₃PO₄ acid
catalyst. The acid catalyst protonates the carbonyl oxygen of the acetic anhydride, making the
carbonyl carbon more electrophilic and thus more susceptible to nucleophilic attack by the
phenolic oxygen of salicylic acid. This nucleophilic acyl substitution results in the formation of an
ester linkage (the acetyl group) and acetic acid as a byproduct.
Role of Phosphoric Acid (H₃PO₄) Catalyst: It protonates the carbonyl oxygen of acetic
anhydride, increasing the electrophilicity of the carbonyl carbon and accelerating the
nucleophilic attack by salicylic acid. Phosphoric acid is used instead of a stronger acid like
sulfuric acid because it is less likely to cause charring or side reactions with the aromatic ring.
Purpose of Recrystallization: To dissolve the crude aspirin in hot ethanol-water, then allow slow
cooling to selectively crystallize pure aspirin while leaving impurities (unreacted salicylic acid
and acetic anhydride byproducts) in the supernatant solution. This purification technique
exploits differences in solubility between the desired product and impurities.
Section 3: Materials & Safety
Complete Glassware List:
• 125 mL Erlenmeyer flask
• 250 mL beaker (water bath)
, • Graduated cylinder
• Buchner funnel
• Filter flask
• Vacuum tubing
• Watch glass or weighing paper
Specific Chemical Reagents with Concentrations:
• Salicylic acid (solid)
• Acetic anhydride (liquid, 99%)
• Phosphoric acid (85%, catalyst)
• Ethanol (95%)
• Distilled water
• 1% ferric chloride (FeCl₃) test solution
Safety and Hazard Information:
• Salicylic acid: Skin/eye irritant. Avoid direct contact.
• Acetic anhydride: Flammable, corrosive, lachrymator (causes tearing); causes severe
burns. Handle only in a fume hood.
• Phosphoric acid (85%): Corrosive. Causes severe skin and eye burns.
• General Precautions: Use fume hood during reaction; wear nitrile gloves and safety
goggles throughout the experiment. Avoid inhaling vapors from acetic anhydride.
Section 4: Procedure
Step 1: Synthesis Weigh approximately 2.0 g of salicylic acid into a 125 mL Erlenmeyer flask.
Add 5.0 mL of acetic anhydride, followed by 5 drops of 85% H₃PO₄ catalyst. Swirl to mix. Heat
the flask in a 70–80°C water bath for 15–20 minutes with occasional swirling.
Step 2: Crystallization Remove flask from water bath. Carefully add 5 mL of cold distilled water
dropwise to decompose excess acetic anhydride (exothermic reaction). Then add 30 mL of cold
water. Cool the flask in an ice bath for 10–15 minutes until crystals fully form.
