Editing Cumene process

{{Short description|Industrial process}}
[[File:Propylene+C6H6.svg|344px|thumb|right|First stage of Hock process: alkylation of benzene with propylene.]]
[[File:Hockpart2.svg|thumb|344px|right|Second stage of Hock process: [[autoxidation]] of cumene.]]

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),<ref>{{Cite web|url=http://izgudrojumi.lza.lv/izg_en.php?id=54|title=Latvian|access-date=2011-02-27|archive-date=2016-03-03|archive-url=https://web.archive.org/web/20160303201522/http://izgudrojumi.lza.lv/izg_en.php?id=54|url-status=dead}}</ref> and independently by Heinrich Hock in 1944.<ref>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 {{doi|10.1002/cber.19440770321}}</ref><ref>''Concise Encyclopedia Chemistry'' (1993) Mary Eagleso</ref>

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.<ref>{{cite web | title=Phenol Market Size, Share, Analysis & Forecast, 2035 – ChemAnalyst | website=ChemAnalyst | url=https://www.chemanalyst.com/industry-report/phenol-market-184 | access-date=2024-04-09}}</ref> In order for this process to be economical, there must also be demand for the [[acetone]] by-product as well as the [[phenol]].<ref name=Plotkin2006>{{Cite web |url=http://www.chemistry.org/portal/a/c/s/1/feature_pro.html?id=c373e908e6e847ac8f6a17245d830100 |title=Direct Routes to Phenol |access-date=2006-12-26 |archive-url=https://web.archive.org/web/20070409042033/http://www.chemistry.org/portal/a/c/s/1/feature_pro.html?id=c373e908e6e847ac8f6a17245d830100 |archive-date=2007-04-09 |url-status=dead }}</ref>


==Steps of the process==
Cumene is formed in the gas-phase [[Friedel–Crafts reaction#With alkenes|Friedel–Crafts alkylation]] of benzene by propene. Benzene and propene are compressed together to a pressure of 30 [[Atmospheric pressure|standard atmospheres]] at 250&nbsp;°C in presence of a [[catalyst|catalytic]] [[Lewis acid]]. [[Phosphoric acid]] is often favored over [[aluminium]] [[halide]]s. Cumene is oxidized in air, which removes the tertiary [[benzyl]]ic hydrogen from cumene and hence forms a cumene [[radical (chemistry)|radical]]:
::[[Image:Cumene-radical-formation-2D-skeletal V2.svg|300px]]
The cumene radical then [[chemical bond|bonds]] with an oxygen molecule to give cumene [[peroxide]] radical, which in turn forms [[cumene hydroperoxide]] (C<sub>6</sub>H<sub>5</sub>C(CH<sub>3</sub>)<sub>2</sub>O<sub>2</sub>H) 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 [[Atmosphere (unit)|atm]] is used to ensure that the unstable peroxide is kept in liquid state.
::[[Image:Cumene-peroxide-radical-formation-2D-skeletal.svg|300px]]
::[[Image:Cumene-hydroperoxide-formation-2D-skeletal.svg|450px]]
Cumene hydroperoxide undergoes a [[rearrangement reaction]] in an [[acid]]ic 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 (chemistry)|resonance]] stabilized tertiary [[carbocation]]. The concerted mechanism of this step is similar to the mechanisms of the [[Baeyer–Villiger oxidation]]<ref>{{cite book|last=Streitwieser|first=A|author2=Heathcock, C.H.|others=Kosower, E.M.|title=Introduction to Organic Chemistry|publisher=MacMillan|location=New York|year=1992|edition=4th|pages=[https://archive.org/details/introductiontoor00stre_0/page/1018 1018]|chapter=30|isbn=0-02-418170-6|chapter-url=https://archive.org/details/introductiontoor00stre_0/page/1018}}</ref> and [[Criegee rearrangement]] reactions, and also the oxidation step of the [[Hydroboration–oxidation reaction#Hydroboration–oxidation|hydroboration–oxidation]] process.<ref>{{cite book|last=K.P.C.|first=Vollhardt|author2=N.E. Schore|authorlink2=Neil E. Schore|title=Organic Chemistry: Structure and Function|publisher=Freeman|location=New York|year=2003|edition=4th|chapter-url=https://archive.org/details/organicchemistry00voll_0/page/988 |page=988|chapter=22|isbn=0-7167-4374-4}}</ref>
In 2009, an acidified [[bentonite]] clay was proven to be a more economical catalyst than [[sulfuric acid]] as the acid medium.
::[[Image:Cumene-process-phenyl-migration-2D-skeletal V2.svg|450px]]

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.

::[[Image:Cumene-process-final-steps-2D-skeletal.svg|600px]]

==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 [[nylon]]s.<ref name="acs phenol">{{cite web |url=https://www.acs.org/content/acs/en/pressroom/cutting-edge-chemistry/what-s-new-in-phenol-production-.html |title=What's New in Phenol Production? |last=Plotkin |first=Jeffrey S. |publisher=American Chemical Society |date=2016-03-21 |access-date=2018-01-02 |archive-url=https://web.archive.org/web/20191027122212/https://www.acs.org/content/acs/en/pressroom/cutting-edge-chemistry/what-s-new-in-phenol-production-.html |archive-date=2019-10-27 |url-status=dead }}</ref>

Starting with the alkylation of benzene with mixture of [[1-Butene|1]] and [[2-Butene|2-butenes]], the cumene process produces phenol and [[butanone]]s.<ref name=Plotkin2006/>

===Alternatives to phenol production===
*[[Hydroquinone]] is prepared by dialkylation of benzene with propene to give [[Diisopropylbenzenes|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:<ref>Gerhard Franz, Roger A. Sheldon "Oxidation" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, 2000 {{doi|10.1002/14356007.a18_261}}</ref>
*:<chem>C6H4(CHMe2)2 + 2 1/2 O2 -> C6H4O2 + 2 OCMe2 + H2O</chem>
*[[Resorcinol]] is analogously prepared by converting [[1,3-Diisopropylbenzene]] into the bis(hydroperoxide), which fragments to resorcinol and acetone.<ref>{{Ullmann |title=Resorcinol|author1=K. W. Schmiedel |author2=D. Decker |doi=10.1002/14356007.a23_111.pub2|year=2012}}</ref>
*[[2-Naphthol]] can also be produced by a method analogous to the cumene process.<ref name=Ullmann2005>Gerald Booth "Naphthalene Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a17_009}}.</ref>
*[[3-Chlorophenol]], which does not arise by chlorination of phenol, can be produced by cumene process beginning with the alkylation of chlorobenzene with propylene.<ref>{{Ullmann|author1=François Muller |author2=Liliane Caillard |title=Chlorophenols |year=2011 |doi=10.1002/14356007.a07_001.pub2}}</ref>
*[[Cresol]]s are produced from isopropyltoluene.<ref name=Patai>{{cite book |title=Syntheses and Uses of Hydroperoxides and Dialkylperoxides |editor1-first=Saul |editor1-last=Patai |author=Roger A. Sheldon |chapter=Synthesis and uses of alkyl hydroperoxides and dialkyl peroxides |year=1983 |publisher=John Wiley & Sons |doi=10.1002/9780470771730.ch6 |series=PATAI'S Chemistry of Functional Groups|pages=161–200 |isbn=978-0-471-10218-2 }}</ref>

===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.<ref name=Ullmann>{{Ullmann |author=Papa, A. J. |title=Propanols |doi=10.1002/14356007.a22_173}}</ref>
[[Mitsui & Co.]] developed additional step(s) to [[hydrogenation|hydrogenating]] acetone and dehydrating the [[isopropanol]] product to propene, which is recycled as a starting reactant.<ref name=Plotkin2006/>

===Byproducts===

Byproducts of the cumene process to produce phenol and acetone are [[acetophenone]] and [[alpha-methylstyrene]].

==See also==
* [[Bisphenol A]]
* [[Dow process (phenol)]]
* [[Friedel Crafts alkylation]]
* [[Baeyer–Villiger oxidation]]
* [[Raschig–Hooker process]] (also produces phenol)

==References==
{{Reflist}}

==External links==
* [http://www.essentialchemicalindustry.org/chemicals/phenol.html Phenol -- The essential chemical industry online]

{{commons category|Cumene process}}

[[Category:Chemical processes]]
[[Category:Soviet inventions]]