18.30: Benzene to Phenol via Cumene: Hock Process
The synthesis of phenol from benzene via cumene and cumene hydroperoxide is called the Hock process. First, a Friedel–Crafts alkylation reaction of benzene with propene gives cumene. Then cumene forms cumene hydroperoxide via a radical chain reaction. In the chain initiation step, the benzylic hydrogen is abstracted to give a benzylic radical. In the chain propagation step, the benzylic radical reacts with an oxygen diradical to form a cumene hydroperoxide radical. The cumene hydroperoxide radical reacts with another cumene molecule to yield cumene hydroperoxide, regenerating the benzylic radical. In the subsequent protonation step, cumene hydroperoxide gives an oxonium ion. Further, a hydrolytic rearrangement migrates the phenyl group to oxygen (with the loss of water) to yield the carbocation. Finally, the addition of water and a subsequent rearrangement involving a proton shift gives phenol as the product.