Methods of Preparation of carboxylic acids

Methods of Preparation of carboxylic acids

Some important methods for the preparation of carboxylic acids are as follows :

1. From Primary alcohols and aldehydes

Primary alcohols and aldehydes can easily be oxidised to the corresponding carboxylic acids with oxidising agents such as potassium permanganate (in acidic or alkaline medium), potassium dichromate (in acidic medium)

Example

2. Hydrolysis of Nitriles

Nitriles yield carboxylic acids when subjected to hydrolysis with an acid or alkali.

Example

3. Acidic hydrolysis of esters

Esters on hydrolysis with dilute mineral acids yield corresponding carboxylic acid

Example

4. From Grignard reagent

Grignard reagent reacts with carbon di oxide (dry ice) to form salts of carboxylic acid which in turn give corresponding carboxylic acid after acidification with mineral acid.

Example

Formic acid cannot be prepared by Grignard reagent since the acid contains only one carbon atom

5. Hydrolysis of acylhalides and anhydrides

a) Acid chlorides when hydrolysed with water give Carboxylic acids.

Example

b) Acid anhydride when hydrolysed with water give corresponding carboxylic acids.

6. Oxidation of alkyl benzenes

Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzene with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to –COOH group irrespective of the length of the side chain.

Example

Evaluate yourself

1) What happens when n-propyl benzene is oxidised using H⁺ / KMnO₄?

2) How will you prepare benzoic acid using Grignard reagent.