(a) Name the starting material used in the industrial preparation of phenol.
(b) Write complete reaction for the bromination of phenol in aqueous and non-aqueous medium.
(c) Explain why Lewis acid is not required in bromination of phenol ?

Explanation

(a) The starting material used in the industrial preparation of phenol is cumene.

(b) Phenols when treated with bromine water gives polyhalogen derivatives in which all the hydrogen atoms present at ortho and para positions with respect to -OH group are replaced by bromine atoms.

However, in non-aqueous medium such as `CS_(2), C Cl_(4), CHCl_(3)`, moobromophenoles are obtained.

In aqueous solution, phenol ionises to form phenoxide ion. This ion activates the benzene ring to a very large extent and hence the substitution of halogen takes place at all three positions.
On te other hand, in non-aqueous solution ionisation of phenol is greatly suppressed. Therefore, ring is activated slightly and hence monosubstitution occur.
(c) Lewis acid is an electron deficient molecule. In bromination molecule to form `Br^(+)` ion (electrophilic). So, Lewis acid is not required in the brominatio of phenol.
Mechanism of bromination of phenol