This process converts two relatively cheap starting materials, benzene and propylene, into two more valuable ones, phenol and acetone. Other reactants required are oxygen from air and small amounts of a radical initiator. Most of the worldwide production of phenol and acetone is now based on this method.
The overall chemical process is summarised below.
Benzene and propylene are compressed together to a pressure of 30 standard atmospheres at 250 °C (482° F) in presence of a catalytic Lewis acid. Phosphoric acid is often favored over aluminum halides. Cumene is formed in the gas-phase Friedel-Crafts alkylation of benzene by propylene:
It then bonds with an oxygen molecule to give cumene hydroperoxide radical, which in turn forms cumene hydroperoxide (C6H5C(CH3)2-O-O-H) by abstracting benzylic hydrogen from another cumene molecule. This latter cumene converts into cumene radical and feeds back into subsequent chain formations of cumene hydroperoxides. A pressure of 5 atm is used to ensure that the unstable peroxide is kept in liquid state.
Cumene hydroperoxide is then hydrolysed in an acidic medium to give phenol and acetone. Loss of a water molecule from the hydroperoxide leaves an electron-deficient oxygen. Migration of the phenyl to the oxygen leads to a more stable resonance hybridized structure of tertiary benzylic radical, which in turn produce acetone and phenol after an attachment of a water molecule and rearrangement. Research suggests the loss of water molecule and phenyl migration may take place simultaneously, in other words the step of the mechanism is concerted.
The products are extracted by distillation.
- Chemical synthesis
- Dow process
- Friedel Crafts alkylation
- Baeyer-Villiger oxidation
- Concerted reaction
- Raschig process (also produces phenol)