18.24 : Benzene to Phenol via Cumene: Hock Process

The Hock process converts benzene to phenol via cumene and cumene hydroperoxide.

The first step involves the Friedel–Crafts alkylation of benzene with propene to generate cumene.

In this step, propene reacts with phosphoric acid to form the isopropyl cation that adds to the benzene ring to form cumene.

After this, cumene undergoes a radical chain reaction where a radical initiator abstracts the benzylic hydrogen atom, providing a tertiary benzylic radical. 

In the chain propagation step that follows, the benzylic radical reacts with an oxygen diradical to generate the cumene hydroperoxide radical. A subsequent reaction with another cumene molecule forms cumene hydroperoxide while simultaneously regenerating the benzylic radical.

Next, cumene hydroperoxide is protonated at the terminal oxygen to give the oxonium ion.

Hydrolytic rearrangement of the ion involving migration of the phenyl ring to oxygen, along with the simultaneous loss of water produces a carbocation.

The subsequent addition of water, a rearrangement through proton shift followed by deprotonation generates the phenol, along with the co-product—acetone.