Fischer Esterification
Fischer Esterification: Acid protonates the carboxylic acid's carbonyl oxygen, making the carbonyl carbon electrophilic enough for the alcohol to attack…
What happens
Acid protonates the carboxylic acid's carbonyl oxygen, making the carbonyl carbon electrophilic enough for the alcohol to attack; after a proton shuffle, water leaves and deprotonation gives the neutral ester.
Reaction summary
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
Reagents and conditions
- Starting material: Acetic acid; Ethanol
- Reagents: H₂SO₄ (catalyst)
- Conditions: H₂SO₄ catalyst, heat
- Products: Ethyl acetate; Water
Mechanism
- Protonation of the carbonyl: H₂SO₄ protonates the carbonyl oxygen of acetic acid, making the carbonyl carbon much more electrophilic.
- Nucleophilic addition of the alcohol: Ethanol's oxygen attacks the activated carbonyl carbon, forming a tetrahedral intermediate.
- Loss of water: After a proton transfer, one of the two hydroxyl groups on the tetrahedral intermediate leaves as water, regenerating a C=O.
- Deprotonation: Loss of a proton from the protonated ester gives the neutral ester and regenerates the acid catalyst.
Common mistakes
- Forgetting the reaction is reversible (an equilibrium), driving it to completion needs excess alcohol or removal of water (e.g. a Dean-Stark trap).
- Confusing this acid-catalyzed addition-elimination mechanism with acyl chloride chemistry, no chloride is involved here at all.
Memory trick
"Fischer = acid + alcohol, acid-catalyzed, reversible", remove water (or use excess alcohol) to push the equilibrium toward the ester.