Chemistry Preparation of Phenols

Topics Covered :

● Preparation of Phenols
● From Haloarenes
● From Benzenesulphonic Acid
● From Diazonium Salts
● From Cumene

Preparation of Phenols :

`=>` Phenol, also known as carbolic acid, was first isolated in the early nineteenth century from coal tar.

`=>` Nowadays, phenol is commercially produced synthetically.

`=>` In the laboratory, phenols are prepared from benzene derivatives by any of the following methods :

From haloarenes :

Chlorobenzene is fused with `color{red}(NaOH)` at `623K` and `320` atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced.

From benzenesulphonic acid :

`=>` Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.

From diazonium salts :

`=>` A diazonium salt is formed by treating an aromatic primary amine with nitrous acid `color{red}(NaNO_2 + HCl)` at 273-278 K.

`=>` Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids.

From cumene :

`=>` Phenol is manufactured from the hydrocarbon, cumene.

`=>` Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide.

`=>` It is converted to phenol and acetone by treating it with dilute acid.

`=>` Acetone, a by-product of this reaction, is also obtained in large quantities by this method.