Question: 88: Which one of the following reaction sequence is incorrect method to prepare phenol?
Answer: Option (3)
Explanation:
In option (1), aniline is first converted into benzene diazonium chloride using \mathrm{NaNO_2} and \mathrm{HCl} at low temperature.
On heating with water, the diazonium salt undergoes hydrolysis to give phenol.
This is a correct method.
In option (2), cumene undergoes air oxidation to form cumene hydroperoxide,
which on acidic hydrolysis gives phenol and acetone.
This is the industrial cumene process and is a correct method.
In option (3), chlorobenzene reacts with sodium hydroxide only under very high temperature and pressure, such as about 623 \ \mathrm{K} and 300 \ \mathrm{atm}.
At STP conditions, chlorobenzene does not react with \mathrm{NaOH} to form phenol.
Hence, this method is incorrect.
In option (4), benzene reacts with oleum to form benzene sulfonic acid.
On fusion with \mathrm{NaOH}, sodium phenoxide is formed,
which on acidification gives phenol. This is a correct laboratory method.
Therefore, the incorrect method to prepare phenol is option (3).