Dehydration reaction

The dehydration or dehydration means the removal of water as a result of a chemical reaction, ie, an elimination reaction ( elimination ), but also the elimination of water of crystallization or water from aqua complexes.

In contrast, the related term dehydration refers to the chemical elimination of hydrogen.

In the presence of dehydrating agents such as concentrated sulfuric acid, phosphoric acid, or anhydrous zinc chloride, alcohols react in the heat intramolecular dehydration to give the corresponding alkenes. Particularly prone to dehydration and the tertiary alcohols. Industrially, the dehydration of alcohols are carried out catalytically under pressure in the gas phase. However, it has - because of easy availability of alkenes from petrochemical sources - the importance of the dehydration of alcohols to alkenes removed. Rather, alcohols are obtained to a large extent by the hydration of olefins.

It is the preferred direction at which the double bond is formed, the Saytzeff rule - after Alexander Mikhailovich Zaitsev (1841-1910) - Remove. It states that the required hydrogen atom from hydrogen poorest adjacent carbon atom and the highly substituted ( and thus thermodynamically most stable ) alkene is formed.

Alcohols can also react in an intermolecular dehydration. The result of two molecules of ethanol in the technical dehydration in the gas phase at 260 ° C, a molecule of diethyl ether.

Another important example of a dehydration is the formation of acid anhydrides by dehydration of the corresponding acids, for example, the technical production of acetic anhydride from acetic acid or of phthalic acid of phthalic anhydride.