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Also known as: Base Hydrolysis of Esters, Ester Saponification
Irreversible base hydrolysis of an ester to give a carboxylate salt and an alcohol. The name comes from soap-making (saponification of fats). Unlike acid hydrolysis, this is irreversible because the carboxylate anion product is very stable.
Hydroxide (OH⁻) attacks the electrophilic carbonyl carbon of the ester, forming a tetrahedral intermediate.
Nucleophilic addition to carbonyl
The tetrahedral intermediate collapses, expelling the alkoxide (R'O⁻) as leaving group to regenerate the C=O.
Alkoxide is the leaving group
Fast proton transfer: alkoxide deprotonates the carboxylic acid to give the carboxylate salt. This step makes the reaction irreversible.
Irreversible — carboxylate is very stable conjugate base
Ethyl acetate
NaOH (aq), reflux
Sodium acetate + Ethanol
Tristearin (animal fat)
NaOH (aq), heat
Sodium stearate (soap) + Glycerol
Fundamental method for ester hydrolysis. Essential in soap production and deprotection of ester protecting groups.