This article is about chemical reactions resulting in the loss of water from a molecule. For the removal of water from solvents and reagents, see 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 reactions. 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, -OH2+.
In organic synthesis, there are many examples of dehydration reactions:
Some dehydration reactions can be mechanistically complex, for instance the reaction of a sugar with concentrated sulphuric acid (experiment with video) to form carbon involves formation of carbon carbon bonds.[1]
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.)
^ Margaret Jevnik Gentles, Jane B. Moss, Hershel L. Herzog, and E. B. Hershberg (1958). "The Dienol-Benzene Rearrangement. Some Chemistry of 1,4-Androstadiene-3,17-dione". J. Am. Chem. Soc.80 (14): 3702 - 3705. doi:10.1021/ja01547a058.
