Definition of Dehydration Reaction

A dehydration reaction involves the loss of a water molecule from a reacting molecule.
A dehydration reaction involves the loss of a water molecule from a reacting molecule. Toshiro Shimada, Getty Images

Dehydration Reaction Definition

A dehydration reaction is a chemical reaction between two compounds where one of the products is water. For example, two monomers may react where a hydrogen (H) from one monomer binds to a hydroxyl group (OH) from the other monomer to form a dimer and a water molecule (H2O). The hydroxyl group is a poor leaving group, so Bronsted acid catalysts may be used to help to protonate the hydroxyl to form -OH2+.

The reverse reaction, where water combines with hydroxyl groups, is termed hydrolysis or a hydration reaction.

Chemicals commonly used as dehydrating agents include concentrated phosphoric acid, concentrated sulfuric acid, hot ceramic and hot aluminum oxide.

Also Known As: A dehydration reaction is the same as a dehydration synthesis. A dehydration reactions may also be known as a condensation reaction, but more properly, a dehydration reaction is a specific type of condensation reaction.

Dehydration Reaction Examples

Reactions that produce acid anhydrides are dehydration reactions. For example: acetic acid (CH3COOH) forms acetic anhydride ((CH3CO)2O) and water by the dehydration reaction

2 CH3COOH → (CH3CO)2O + H2O

Dehydration reactions are also involved in the production of many polymers.

Other examples include:

  • Conversion of alcohols to ethers (2 R-OH → R-O-R + H2O)
  • Conversion of alcohols to alkenes (R-CH2-CHOH-R → R-CH=CH-R + H2O)
  • Conversion of amides to nitriles (RCONH2 → R-CN + H2O)
  • Dienol benzene rearrangement
  • reaction of sucrose with concentrated sulfuric acid (a popular chemistry demonstration)
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Helmenstine, Anne Marie, Ph.D. "Definition of Dehydration Reaction." ThoughtCo, Mar. 10, 2018, thoughtco.com/definition-of-dehydration-reaction-605001. Helmenstine, Anne Marie, Ph.D. (2018, March 10). Definition of Dehydration Reaction. Retrieved from https://www.thoughtco.com/definition-of-dehydration-reaction-605001 Helmenstine, Anne Marie, Ph.D. "Definition of Dehydration Reaction." ThoughtCo. https://www.thoughtco.com/definition-of-dehydration-reaction-605001 (accessed May 25, 2018).