Dehydration Reaction Definition in Chemistry

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.

A dehydration reaction is the same as a dehydration synthesis. A dehydration reaction 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-CH_2-CHOH-R → R-CH=CH-R + H₂O)
• Conversion of amides to nitriles (RCONH₂ → R-CN + H₂O)
• Dienol benzene rearrangement
• the reaction of sucrose with concentrated sulfuric acid (a popular chemistry demonstration)