Dehydration reaction 1566642 222594199 2008-06-30T04:32:17Z Thijs!bot 1392310 robot Adding: [[id:Reaksi dehidrasi]] {{otheruses4|chemical reactions resulting in the loss of water from a molecule|the removal of water from solvents and reagents|desiccation}} In [[chemistry]], a '''dehydration reaction''' is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of [[elimination reaction]]s. Because the hydroxyl group (-OH) is a poor leaving group, having an [[Brønsted acid]] catalyst often helps by protonating the hydroxyl group to give the better leaving group, -OH<sub>2</sub><sup>+</sup>. In [[organic synthesis]], there are many examples of dehydration reactions: *Conversion of [[alcohol]]s to [[ether]]s ::2 R-OH → R-O-R + H<sub>2</sub>O *Conversion of alcohols to [[alkene]]s ::R-CH<sub>2</sub>-CHOH-R → R-CH=CH-R + H<sub>2</sub>O *Conversion of [[carboxylic acid]]s to [[acid anhydride]]s ::2 RCO<sub>2</sub>H → (RCO)<sub>2</sub>O + H<sub>2</sub>O *Conversion of [[amide]]s to [[nitrile]]s ::RCONH<sub>2</sub> → R-CN + H<sub>2</sub>O * in this [[rearrangement reaction]] called the '''dienol benzene rearrangement''' <ref>{{cite journal | title = The Dienol-Benzene Rearrangement. Some Chemistry of 1,4-Androstadiene-3,17-dione | author = Margaret Jevnik Gentles, Jane B. Moss, Hershel L. Herzog, and E. B. Hershberg | journal = [[J. Am. Chem. Soc.]] | year = 1958 | volume = 80 | issue = 14 | pages = 3702–3705 | doi = 10.1021/ja01547a058}}</ref>: :[[Image:Dienol benzene rearrangement.png|400px|Dienol benzene rearrangement]] Some dehydration reactions can be mechanistically complex, for instance the reaction of a sugar with concentrated sulphuric acid [http://www.madphysics.com/exp/dehydrating_sugar_with_acid.htm (experiment with video)] to form carbon involves formation of carbon carbon bonds.[http://www.exo.net/~pauld/activities/astronomy/transitvenus/sugarsulfuricacid.htm] *Sugar (sucrose) is dehydrated[http://chemlearn.chem.indiana.edu/demos/16-1%20The%20Dehydration%20of%20Sugar%20by%20Sulfuric%20Acid.htm]: :C<sub>12</sub>H<sub>22</sub>O<sub>11</sub> + 98% Sulfuric acid → 12 C <sub>(graphitic foam)</sub> + 11 H<sub>2</sub>O <sub>steam</sub> + Sulfuric acid/water mixture The reaction is driven by the strongly exothermic reaction sulfuric acid has with water. (Beware that this reaction produces dangerous sulfuric-acid containing steam, and should only be performed in a fume-hood or well ventilated area.) Common dehydrating agents; concentrated [[sulfuric acid]], concentrated [[phosphoric acid]], hot [[aluminium oxide]], hot ceramic. ==See also== *[[Hydration reaction]] ==References== {{reflist}} [[Category:Elimination reactions]] [[de:Dehydrierung]] [[et:Dehüdraatimine]] [[es:Reacción de deshidratación]] [[id:Reaksi dehidrasi]] [[nl:Dehydratie (chemie)]] [[ja:脱水反応]] [[pt:Desidratação (química)]] [[ru:Дегидратация]] [[tr:Dehidrasyon]] [[zh:失水反应]]