Lesson 4 of 13 · 6 min
Preparing phenols
NCERT §7.4.2
A drum in the store is labelled 'phenol, from the cumene plant'. Nila had assumed phenol came from coal tar, the source in her textbook's history box.
The lesson in notes
In short
Phenol (carbolic acid) was originally obtained from coal tar, early in the nineteenth century. Today most of it is made synthetically.
From haloarenes: chlorobenzene is fused with NaOH at 623 K and 320 atm to give sodium phenoxide, and acidifying the phenoxide gives phenol.
From benzenesulphonic acid: benzene is sulphonated with oleum, the sulphonic acid is heated with molten sodium hydroxide to give sodium phenoxide, and acid then liberates phenol.
From diazonium salts: an aromatic primary amine treated with nitrous acid (NaNO₂ + HCl) at 273–278 K forms a diazonium salt, which is hydrolysed to phenol by warming with water or dilute acid.
From cumene: cumene (isopropylbenzene) is oxidised by air to cumene hydroperoxide, and dilute acid converts this into phenol and acetone.
The cumene route supplies most of the world's phenol, and its second product, acetone, is also sold in large amounts.