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A dehydration reaction (sometimes called 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, –OH2+.
Common dehydrating agents used in organic synthesis include concentrated sulfuric acid, concentrated phosphoric acid, phosphorus pentoxide, hot aluminium oxide, zinc oxide, ceramic, molecular sieves, organic acid anhydrides, etc.
Important dehydration reactions
- Synthesis of esters (Fisher esterification)
- Preparation of symmetrical or cyclical ethers
- Conversion of alcohols to alkenes
- Conversion of carboxylic acids to acid anhydrides
- Dehydration of sugars to carbon