The cumene process ( cumene-phenol process, Hock process) is an industrial process for synthesizing phenol and acetone from benzene and propylene. The term stems from cumene (isopropyl benzene), the intermediate material during the process. It was invented by R. Ūdris and P. Sergeyev in 1942 (USSR),[Hock, H. and Lang, S. (1944), Autoxydation von Kohlenwasserstoffen, IX. Mitteil.: Über Peroxyde von Benzol-Derivaten. Berichte der deutschen chemischen Gesellschaft (A and B Series), 77: 257–264 ][ Concise Encyclopedia Chemistry (1993) Mary Eagleso]
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. In 2022, nearly 10.8 million tonnes of phenol was produced by the cumene process.
Steps of the process
Cumene is formed in the gas-phase Friedel–Crafts alkylation of benzene by propene. Benzene and propene are compressed together to a pressure of 30 standard atmospheres at 250 °C in presence of a
catalyst Lewis acid.
Phosphoric acid is often favored over
aluminium . Cumene is oxidized in air, which removes the tertiary
hydrogen from cumene and hence forms a cumene radical:
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The cumene radical then
chemical bond with an oxygen molecule to give cumene
peroxide radical, which in turn forms cumene hydroperoxide (C
6H
5C(CH
3)
2O
2H) by abstracting a 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.
- :
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Cumene hydroperoxide undergoes a rearrangement reaction in an
medium (the
Hock rearrangement) to give
phenol and
acetone. In the first step, the terminal hydroperoxy oxygen atom is protonated. This is followed by a step in which the phenyl group migrates from the benzyl carbon to the adjacent oxygen and a water molecule is lost, producing a resonance stabilized tertiary
carbocation. The concerted mechanism of this step is similar to the mechanisms of the Baeyer–Villiger oxidation
and Criegee rearrangement reactions, and also the oxidation step of the hydroboration–oxidation process.
In 2009, an acidified
bentonite clay was proven to be a more economical catalyst than
sulfuric acid as the acid medium.
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The resulting carbocation is then attacked by water, forming a hemiacetal-like structure. After transfer of a proton from the hydroxy oxygen to the ether oxygen, the ion falls apart into phenol and acetone.
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Related reactions and modifications
Alternatives to acetone co-production
Cyclohexylbenzene can replace isopropylbenzene. Via the Hock rearrangement, cyclohexylbenzene hydroperoxide cleaves to give phenol and
cyclohexanone. Cyclohexanone is an important precursor to some
.
Starting with the alkylation of benzene with mixture of 1 and 2-butenes, the cumene process produces phenol and .[
]
Alternatives to phenol production
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Hydroquinone is prepared by dialkylation of benzene with propene to give 1,4-diisopropylbenzene. This compound reacts with air to afford the bis(hydroperoxide). Analogous to the behavior of cumene hydroperoxide, it rearranges in acid to give acetone and hydroquinone. Oxidation of hydroquinone gives 1,4-benzoquinone:
[Gerhard Franz, Roger A. Sheldon "Oxidation" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000 ]
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:C6H4(CHMe2)2 + 2 1/2 O2 -> C6H4O2 + 2 OCMe2 + H2O
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Resorcinol is analogously prepared by converting 1,3-Diisopropylbenzene into the bis(hydroperoxide), which fragments to resorcinol and acetone.
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2-Naphthol can also be produced by a method analogous to the cumene process.
[Gerald Booth "Naphthalene Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. .]
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3-Chlorophenol, which does not arise by chlorination of phenol, can be produced by cumene process beginning with the alkylation of chlorobenzene with propylene.
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are produced from isopropyltoluene.
Acetone processing
Crude acetone is hydrogenated in the liquid phase over Raney nickel or a mixture of copper and chromium oxide to give isopropyl alcohol. This process is useful, when it is coupled with excess acetone production.[
]
Byproducts
Byproducts of the cumene process to produce phenol and acetone are acetophenone and alpha-methylstyrene.
See also
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Bisphenol A
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Dow process (phenol)
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Friedel Crafts alkylation
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Baeyer–Villiger oxidation
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Raschig–Hooker process (also produces phenol)
External links
