Hydrolysis of Esters
Esters are hydrolysed water and the process is accelerated by dilute mineral acids (HCL or H2SO4) or alkalies.
Ethyl acetate + water gives Acetic acid + Ethyl alcohol (in the presence of dilute mineral acid)
Ethyl acetate + Sodium hydroxide (alkali) Sodium acetate + Ethyl alcohol
Acidic hydrolysis is reversible.
Alkaline hydrolysis is irreversible because resonance stabilized carboxylate (acetate ion is formed and it has very little tendency to react with an alcohol.
Hydrolysis of esters by alkalies is known as saponification. Saponification leads to the formation of soaps. It is a very rapid reaction as alkali acts as catalyst and also as a reactant.
Mechanism of alkaline hydrolysis of esters.
Step I. the nucleophile, OH ¯ ion from the alkali attacks the carboxyl carbon to form an intermediate
Step II the intermediate, then loses a molecule of ethoxide ion to form acetic acid .
Step III. Ethoxide ion then removes a proton from acetic acid and thus acetate ion is formed.
Step IV. This acetate ion combines with Na+ to form Sodium acetate.