Question

What are carboxylic acids? How is it prepared from isopropyl benzene?

Answer 1

Hint: Carbolic acid is an aromatic compound. It consists of an aromatic ring to which a hydroxyl group is attached. To obtain it from isopropyl benzene, we need to carry out oxidation in the air followed by the addition of dilute acid.

Complete step by step solution: We know carbolic acid by the common name phenol. Phenol is an organic compound and it contains an aromatic ring. It is a volatile compound and in appearance, It is a white crystalline looking solid.
The general formula of phenol is ${{C}_{6}}{{H}_{5}}OH$. It contains a phenol group to which a hydroxyl group is bonded. It is mildly acidic and concentrated phenol can cause serious chemical burns so it needs to be handled with care.
Now let us discuss how it is prepared from isopropyl benzene. We also know isopropyl benzene by the name cumene.
Cumene is prepared by Friedel-Crafts alkylation of benzene by propylene. Cumene is oxidised in the air which leads to the formation of cumene radical by the removal of tertiary benzylic hydrogen.

This radical then reacts with an oxygen molecule which leads to the formation of cumene hydroperoxide. Cumene hydroperoxide is formed by extracting hydrogen from another molecule of cumene which leads to the formation of cumene radical and hence the chain reaction continues.

Then cumene hydroperoxide is hydrolysed in an acidic medium to give us acetone and phenol. The terminal hydroperoxy hydrogen atom is protonated first and the phenyl group migrates from benzyl cation to the adjacent oxygen and a water molecule is lost which forms a stable carbocation. This step is concerted.

The carbocation is attacked by water and a proton is transferred from the hydroxyl group to the ether group and phenol i.e. carbolic acid and acetone is formed.

Therefore, we can understand from the above discussion that carbolic acid is phenol and it is obtained from isopropyl benzene by oxidation and then treating the solution with dilute acid and this is the required answer.

Note: Carbolic acid is of great use commercially. Industrially, it is used for the synthesis of plastic. Medically it is widely used as an antiseptic and is also used as a preservative in vaccines. It is a component of paint remover and its derivatives are used in cosmetic industries. We should not confuse carbolic acid with carbonic acid. Carbonic acid is a chemical compound and its formula is ${{H}_{2}}C{{O}_{3}}$.