Dehydration reaction

<h2 id="dehydration-reactions-in-organic-chemistry">Dehydration reactions in organic chemistry</h2>
<h3>Esterification</h3>
<p>The classic example of a dehydration reaction is the <a href="/facts/Fischer_esterification/a8XgmLgl">Fischer esterification</a>, which involves treating a carboxylic acid with an alcohol to give an ester
</p>
RCO2H + R′OH ⇌ RCO2R′ + H2O
<p>Often such reactions require the presence of a dehydrating agent, i.e. a substance that reacts with water.
</p>
<h3>Etherification</h3>
<p>Two <a href="/facts/Monosaccharide/yzs2d6Eq">monosaccharides</a>, such as <a href="/facts/Glucose/oUSkoLCD">glucose</a> and <a href="/facts/Fructose/pEqWJC2N">fructose</a>, can be joined together (to form <a href="/facts/Saccharose/7y1ke94L">saccharose</a>) using dehydration synthesis. The new molecule, consisting of two monosaccharides, is called a <a href="/facts/Disaccharide/9dnUQggw">disaccharide</a>.
</p>
<h3>Nitrile formation</h3>
<p>Nitriles are often prepared by dehydration of primary amides.
</p>
RC(O)NH2  →   RCN  + H2O
<h3>Ketene formation</h3>
<p><a href="/facts/Ethenone/4Xos5qsc">Ketene</a> is produced by heating <a href="/facts/Acetic_acid/uyBKA2Pd">acetic acid</a> and trapping the product:<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a>
</p>
CH3CO2H  →   CH2=C=O  + H2O
<h3>Alkene formation</h3>
<p>Alkenes can be made from alcohols by dehydration.  This conversion, among others, is used in converting biomass to liquid fuels.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>  The conversion of ethanol to <a href="/facts/Ethylene/QMNBYLYn">ethylene</a> is a fundamental example:<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
   CH3CH2OH → H2C=CH2 + H2O
<p>The reaction is accelerated by <a href="/facts/Acid_catalyst/JkJ7LkT6">acid catalysts</a> such as <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a> and certain <a href="/facts/Zeolite/SNrXy4v2">zeolites</a>.
These reactions often proceed via <a href="/facts/Carbocation/vIggUxTh">carbocation</a> intermediates as shown for the dehydration of <a href="/facts/Cyclohexanol/kHdlHrys">cyclohexanol</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>

<p>Some alcohols are prone to dehydration.  3-Hydroxylcarbonyls, called <a href="/facts/Aldol/6vSSzInq">aldols</a>, release water upon standing at room temperature:
</p>
RC(O)CH2CH(OH)R'  →  RC(O)CH=CHR'  +  H2O
<p>The reaction is induced by dehydrating reagents.  For example, 2-methyl-cyclohexan-1-ol dehydrates to 1-methylcyclohexene in the presence of <a href="/facts/Martin%27s_sulfurane/4wqotmjU">Martin's sulfurane</a>, which reacts irreversibly with water.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a>
</p><p>Double dehydration is illustrated by the conversion of <a href="/facts/Glycerol/sRQ6NBQQ">glycerol</a> to <a href="/facts/Acrolein/1gdt9D3f">acrolein</a>:<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a><a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
</p>

<h2 id="dehydration-reactions-in-inorganic-chemistry">Dehydration reactions in inorganic chemistry</h2>
<p>The formation of the <a href="/facts/Pyrophosphate/L9FPEkhF">pyrophosphate</a> bond is an important dehydration relevant to bioenergetics.
</p><p>Various construction materials are produced by dehydration. <a href="/facts/Plaster_of_Paris/GG73HRD7">Plaster of Paris</a> is produced by dehydration of <a href="/facts/Gypsum/MItYU70n">gypsum</a> in a kiln:<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>
</p>

CaSO
            
              4
            
            
              
            
          
          ⋅
          2
          
          
            H
            
              2
            
            
              
            
          
          O
          +

{\displaystyle {\ce {CaSO4.2H2O +{}}}}
  
 <i>heat</i> 
  
    
      
        
          ⟶
        
      
    
    {\displaystyle {\ce {->}}}
  
 
  
    
      
        
          
            CaSO
            
              4
            
            
              
            
          
          ⋅
          
            
              1
              2
            
          
          
            H
            
              2
            
            
              
            
          
          O
          +
          1
          
          
            
              1
              2
            
          
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {CaSO4.1/2H2O + 1 1/2H2O}}}
  
 <i>(released as steam).</i>
<p>The resulting dry powder is ready to be mixed with water to form a stiff but workable paste that hardens.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Hydration_reaction/T1Vb2u1d">Hydration reaction</a></li>
<li><a href="/facts/Condensation_reaction/wMG0F6La">Condensation reaction</a></li>
<li><a href="/facts/Hydrolysis/JTvwIHPs">Hydrolysis</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Miller, Raimund; Abaecherli, Claudio; Said, Adel; Jackson, Barry (2001). "Ketenes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_063. ISBN 3527306730. <a href="3527306730" target="_blank">3527306730</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Besson, Michèle; Gallezot, Pierre; Pinel, Catherine (2014-02-12). "Conversion of Biomass into Chemicals over Metal Catalysts". Chemical Reviews. 114 (3): 1827–1870. doi:10.1021/cr4002269. ISSN 0009-2665. PMID 24083630. <a href="https://pubs.acs.org/doi/10.1021/cr4002269" target="_blank">https://pubs.acs.org/doi/10.1021/cr4002269</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Zimmermann, Heinz; Walz, Roland (2008). "Ethylene". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_045.pub3. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Zhang, Minhua; Yu, Yingzhe (2013-07-17). "Dehydration of Ethanol to Ethylene". Industrial & Engineering Chemistry Research. 52 (28): 9505–9514. doi:10.1021/ie401157c. ISSN 0888-5885. <a href="https://pubs.acs.org/doi/10.1021/ie401157c" target="_blank">https://pubs.acs.org/doi/10.1021/ie401157c</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>G. H. Coleman, H. F. Johnstone (1925). "Cyclohexene". Organic Syntheses. 5: 33. doi:10.15227/orgsyn.005.0033. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>J. Brent Friesen; Robert Schretzman (2011). "Dehydration of 2-Methyl-1-cyclohexanol: New Findings from a Popular Undergraduate Laboratory Experiment". J. Chem. Educ. 88 (8): 1141–1147. Bibcode:2011JChEd..88.1141F. doi:10.1021/ed900049b. <a href="/wiki/J._Chem._Educ." target="_blank">/wiki/J._Chem._Educ.</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Roden, Brian A. (2001). "Diphenylbis(1,1,1,3,3,3-hexafluoro-2-phenyl-2-propoxy)sulfurane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rd409. ISBN 0471936235. <a href="0471936235" target="_blank">0471936235</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>H. Adkins; W. H. Hartung (1926). "Acrolein". Organic Syntheses. 6: 1. doi:10.15227/orgsyn.006.0001. <a href="/wiki/Homer_Burton_Adkins" target="_blank">/wiki/Homer_Burton_Adkins</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Katryniok, Benjamin; Paul, Sébastien; Bellière-Baca, Virginie; Rey, Patrick; Dumeignil, Franck (2010). "Glycerol dehydration to acrolein in the context of new uses of glycerol". Green Chemistry. 12 (12): 2079. doi:10.1039/c0gc00307g. ISSN 1463-9262. <a href="http://xlink.rsc.org/?DOI=c0gc00307g" target="_blank">http://xlink.rsc.org/?DOI=c0gc00307g</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
<li id="fn:10"><p>Franz Wirsching "Calcium Sulfate" in Ullmann's Encyclopedia of Industrial Chemistry, 2012 Wiley-VCH, Weinheim. doi:10.1002/14356007.a04_555 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li>
<li id="fn:11"><p>Staff. "CaSO4, ½ H2O". LaFargePrestia. Archived from the original on November 20, 2008. Retrieved 27 November 2008. <a href="https://web.archive.org/web/20081120163316/http://www.lafargeprestia.com/caso4___h2o.html" target="_blank">https://web.archive.org/web/20081120163316/http://www.lafargeprestia.com/caso4___h2o.html</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li>
</ol>

Dehydration reaction open-in-new

Dehydration reaction