Ester Hydrolysis with NaOH

What is an Ester?

Ester is an organic compound emanated from carboxylic acid. At least one hydroxyl group ( -OH) in the ester group is substituted by an -O- alkyl (i.e. alkoxy) group. Esters are pleasant smelling compounds derived from carboxylic acid and alcohol reactions under a dehydrating agent.

What is Hydrolysis?

Hydrolysis refers to the reaction of an organic compound with water, leading to the decomposition of the organic compound. An ester hydrolyses to give alcohol and carboxylic acid or carboxylate salt.

Table of Content

• Ester Hydrolysis
• Ester Hydrolysis with H₂SO₄
• Ester Hydrolysis with NaOH
• Mechanism of ester hydrolysis with NaOH
• Synthesis of Ester
• Frequently Asked Questions – FAQs

Ester Hydrolysis

Ester is an organic compound emanated from carboxylic acid. At least one hydroxyl group ( -OH) in the ester group is substituted by an -O- alkyl (i.e. alkoxy) group. Esters are pleasant smelling compounds derived from carboxylic acid and alcohol reactions under a dehydrating agent.

Hydrolysis of ester or ester hydrolysis is one of the most critical ester reactions. The hydrolysis of ester takes place in an acidic or basic medium. In an acidic medium, ester interacts with the water molecule to give a carboxylic acid and alcohol. In contrast, ester interacts with the water molecule to give a carboxylate salt and alcohol in a basic medium.

Ester Hydrolysis with H₂SO₄

Ester Hydrolysis with H₂SO₄ or acid catalysed ester hydrolysis is the reaction of an ester with water under an acidic medium. It is merely the reverse of the esterification reaction. In it, an ester is heated under reflux with dilute H₂SO₄ to yield carboxylic acid and alcohol. It is a type of reversible reaction.

Ester Hydrolysis with NaOH

Ester Hydrolysis with NaOH or base catalysed ester hydrolysis is the reaction of an ester with water under a basic medium. In it, an ester is heated under reflux with dilute NaOH to yield carboxylate salt and alcohol. It is also known as saponification reaction, i.e. it is used to synthesise soap.

Mechanism of ester hydrolysis with NaOH

Step 1: Attack of Nucleophile

In the first step, the hydroxide ion attacks the electron-deficient carbon centre of the ester. It breaks the C=O π bond of ester and forms a tetrahedral intermediate structure.

Step 2: Elimination of Leaving Group

In the second step, an internal attack of O^– ion takes place, reforming the C=O bond, leading to loss of alkoxide (RO^–) ion.

Step 3: Deprotonation of Carboxylic Acid

In the third step, an acid-base equilibrium is set up between carboxylic acid and alcohol. Alkoxide (RO^–) ion works as a base; it deprotonates the carboxylic acid, thus leading to the formation of alcohol and carboxylate ion.

Synthesis of Ester

An esterification reaction is used to synthesise esters. It is a reaction between an alcohol and a carboxylic acid under an acidic medium. In it, carboxylic acid and alcohol are heated under reflux with dilute H₂SO₄ to yield ester. It is a type of reversible reaction.

RCOOH + R′OH ⇌ RCOOR′ + H₂O

Instead of carboxylic acid, we can also use carboxylic acid derivatives like acyl halide or anhydrides to synthesise ester.

Reaction with Acyl Halide

Reaction with Anhydride