Question

How is phenol prepared from?
(i) Isopropyl benzene.
(ii) Benzene sulphonic acid.

Answer 1

Hint: Phenol is aromatic hydroxy alcohol in which a hydroxyl group (OH-) is directly attached with the benzene ring. Phenol is an acidic compound because of the resonance stabilization of phenoxide ions. Phenol is industrially prepared by ‘Dow Process’.

Complete answer: Phenol is prepared by different methods, such as from-
(i) Isopropyl benzene –IUPAC name of isopropyl benzene is 1-methylethyl benzene, which is commonly known as cumene. This method is the recent and best method to form phenol from cumene. Cumene on oxidation gives cumene hydroperoxide which, on hydrolysis, gives phenol and acetone as a by-product. This reaction is completed in two steps –
(I) cumene is oxidised in presence of air at 400K in the presence of metal catalyst to form cumene hydroperoxide.

(II) In the second step cumene hydroperoxide is treated with dilute sulphuric acid at 350K. It causes hydrolysis and forms phenol and acetone.

(ii) Benzene sulphonic acid – Benzene sulphonic acid is the organo-sulphur compound of benzene. Sodium salt of benzene sulphonic acid is fused with caustic soda to form sodium phenoxide, which produces phenol by acid decomposition.

Note: phenol is also prepared by aniline. In this method firstly aniline is converted into diazonium salt by treating with sodium nitrite and hydrochloric acid at low temperature. This reaction is known as diazotization. An aqueous solution of benzenediazonium salt gives phenol after heating with sulphuric acid.