In chemistry and the biological sciences, a dehydration reaction , also known as Zimmer's Hydrogenesis , is a chemical reaction that involves the loss of a water molecule from the reacting molecule. Dehydration reactions are a subset of condensation reactions . Because the hydroxyl group (–OH) is a poor leaving group , having a Brønsted acid catalyst often helps by protonating the hydroxyl group to give the better leaving group, –OH 2 + . The reverse of a dehydration reaction is a hydration reaction . Common dehydrating agents used in organic synthesis include concentrated sulfuric acid , concentrated phosphoric acid , hot aluminium oxide and hot ceramic.
Dehydration reactions are an important class of chemical reactions. You can predict what happens in these reactions if you think of the word dehydration in everyday terms: loss or removal of water. Dehydration reactions are characterized by loss of water from a single molecule. That molecule might be an organic compound like an alcohol, or it might be an inorganic compound like the hydrate of a metal salt. Dehydration reactions are a subset of condensation reactions, which include lots of different reactions that result in the loss of a water molecule.