The Fischer esterification uses a catalytic acid to convert a carboxylic acid and alcohol to an ester. Protonation of the carbonyl oxygen activates the carboxylic acid to nucleophilic attack by the alcohol, producing a tetrahedral intermediate with two hydroxyl groups. Ester formation occurs when a proton is transferred to one of the hydroxyl groups, converting it to a good leaving group that is released when the carbonyl group is restored.

• Reagents: Catalytic Acid (HCl or H₂SO₄), Alcohol
• Reactant: Carboxylic Acid, Alcohol
• Product: Ester, Water
• Type of Reaction: Nucleophilic Acyl Substitution

Lab Tips

• Fisher esterification works well for 1° or 2° alcohols. Carboxylate alkylation by halides or sulfonates may be a better method for the preparation of hindered esters. ^[1] Moreover, sterically hindered esters can be prepared from the corresponding acyl chlorides and alcohols in the presence of silver cyanide. ^[2]
• As a reversible reaction, ester formation can be favored when a large excess of alcohol is used as a solvent, which is feasible for simple and relatively inexpensive alcohols such as methanol, ethanol, and propanol. ^[1,3] Irreversible removal of water (azeotropic distillation is one method for this) can also drive ester formation forward.^[1]
• Alternatively, Brönsted acidic ionic liquids can be used as an efficient and reusable catalyst and reaction medium, affording good ester yields. ^[4]
• Note that intramolecular esterification is also possible in some cases. ^[3]

Mechanism

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Related Compounds