Editing Dehydration reaction (section)

==Dehydration reactions in organic chemistry resulting in unsaturated bonds==

===Nitrile formation===
Nitriles are often prepared by dehydration of primary amides.
:RC(O)NH<sub>2</sub>  →   RCN  + H<sub>2</sub>O

===Ketene formation===
[[Ethenone|Ketene]] is produced by heating [[acetic acid]] and trapping the product:<ref>{{Ullmann |doi=10.1002/14356007.a15_063|title=Ketenes|year=2001|last1=Miller|first1=Raimund|last2=Abaecherli|first2=Claudio|last3=Said|first3=Adel|last4=Jackson|first4=Barry|isbn=3527306730}}</ref>
:CH<sub>3</sub>CO<sub>2</sub>H  →   CH<sub>2</sub>=C=O  + H<sub>2</sub>O

===Alkene formation===
Alkenes can be made from alcohols by dehydration.  This conversion, among others, is used in converting biomass to liquid fuels.<ref>{{Cite journal |last1=Besson |first1=Michèle |last2=Gallezot |first2=Pierre |last3=Pinel |first3=Catherine |date=2014-02-12 |title=Conversion of Biomass into Chemicals over Metal Catalysts |url=https://pubs.acs.org/doi/10.1021/cr4002269 |journal=Chemical Reviews |language=en |volume=114 |issue=3 |pages=1827–1870 |doi=10.1021/cr4002269 |pmid=24083630 |issn=0009-2665|url-access=subscription }}</ref>  The conversion of ethanol to [[ethylene]] is a fundamental example:<ref>{{cite book |first1=Heinz |last1=Zimmermann |first2=Roland |last2=Walz |chapter=Ethylene |title=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley-VCH |location=Weinheim |year=2008 |doi=10.1002/14356007.a10_045.pub3|isbn=978-3527306732}}</ref><ref>{{Cite journal |last1=Zhang |first1=Minhua |last2=Yu |first2=Yingzhe |date=2013-07-17 |title=Dehydration of Ethanol to Ethylene |url=https://pubs.acs.org/doi/10.1021/ie401157c |journal=Industrial & Engineering Chemistry Research |language=en |volume=52 |issue=28 |pages=9505–9514 |doi=10.1021/ie401157c |issn=0888-5885|url-access=subscription }}</ref>
:&nbsp;&nbsp; CH<sub>3</sub>CH<sub>2</sub>OH → H<sub>2</sub>C=CH<sub>2</sub> + H<sub>2</sub>O
The reaction is accelerated by [[acid catalyst]]s such as [[sulfuric acid]] and certain [[zeolite]]s.
These reactions often proceed via [[carbocation]] intermediates as shown for the dehydration of [[cyclohexanol]].<ref>{{cite journal |doi=10.15227/orgsyn.005.0033|title=Cyclohexene|journal=Organic Syntheses|year=1925|volume=5|page=33|author=G. H. Coleman, H. F. Johnstone}}</ref>
:[[File:Cyclohexensynthese1.svg|class=skin-invert-image|350px]]
:[[File:Cyclohexensynthese2.svg|class=skin-invert-image|440px]]

Some alcohols are prone to dehydration.  3-Hydroxylcarbonyls, called [[aldol]]s, release water upon standing at room temperature:
:RC(O)CH<sub>2</sub>CH(OH)R'  →  RC(O)CH=CHR'  +  H<sub>2</sub>O

The reaction is induced by dehydrating reagents.  For example, 2-methyl-cyclohexan-1-ol dehydrates to 1-methylcyclohexene in the presence of [[Martin's sulfurane]], which reacts irreversibly with water.<ref>{{cite journal | title = Dehydration of 2-Methyl-1-cyclohexanol: New Findings from a Popular Undergraduate Laboratory Experiment | author1 = J. Brent Friesen | author2 = Robert Schretzman | journal = [[J. Chem. Educ.]] | year = 2011 | volume = 88 | issue = 8 | pages = 1141–1147 | doi = 10.1021/ed900049b| bibcode = 2011JChEd..88.1141F }}</ref><ref>{{cite journal|first1=Brian A.|last1= Roden|title=Diphenylbis(1,1,1,3,3,3-hexafluoro-2-phenyl-2-propoxy)sulfurane|year=2001|journal=Encyclopedia of Reagents for Organic Synthesis|doi=10.1002/047084289X.rd409|isbn= 0471936235}}</ref>

Double dehydration is illustrated by the conversion of [[glycerol]] to [[acrolein]]:<ref>{{OrgSynth | year = 1926|title = Acrolein | author1 = H. Adkins | authorlink1 = Homer Burton Adkins | author2 = W. H. Hartung | doi = 10.15227/orgsyn.006.0001 | volume = 6| page = 1}}</ref><ref>{{Cite journal |last1=Katryniok |first1=Benjamin |last2=Paul |first2=Sébastien |last3=Bellière-Baca |first3=Virginie |last4=Rey |first4=Patrick |last5=Dumeignil |first5=Franck |date=2010 |title=Glycerol dehydration to acrolein in the context of new uses of glycerol |url=http://xlink.rsc.org/?DOI=c0gc00307g |journal=Green Chemistry |language=en |volume=12 |issue=12 |pages=2079 |doi=10.1039/c0gc00307g |issn=1463-9262|url-access=subscription }}</ref>
:[[File:EliminationReactionGlycerol2Acrolein2.svg|class=skin-invert-image|elimination reaction glycerol to acrolein|alt=Elimination reaction of glycerol to acrolein]]