(i) Hydrolysis of esters
Oil or fats are glycerides of higher fatty acid and when they undergo hydrolysis soaps are formed in presence of alkali is known as saponification.
Esters do not undergo substitution reaction with halide ions or with carboxylate ions because these nucleophiles are much weaker bases than the RO- leaving group of the ester. Esters react with water to form carboxylic acids and with alcohols to form different esters. A reaction with water is known as hydrolysis, and a reaction with an alcohol is called alcoholysis. The hydrolysis or alcoholysis of an ester is a very slow reaction. Therefore, when these reactions are carried out in the laboratory, they are always catalyzed. Both hydrolysis and alcoholysis of an ester can be catalyzed by acids (H+). The rate of hydrolysis can also be increased by hydroxide ion (HO-), and the rate of alcoholysis can be increased by presence of alkoxide ion.