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Hydration is a term used in science, especially organic chemistry . The term hydration is not sharply delimited from “ hydration ” and “ hydrolysis ”. Hydration is a chemical reaction in which water molecules are added to a substrate by breaking an (H – O) bond . The term should not be confused with hydration, i.e. the attachment of water to ions or in the crystal lattice ( crystal water ), and hydrogenation , which means the addition of hydrogen to a substrate.

Acid-catalyzed addition of water to the C = C double bond of cyclohexene (left) yields cyclohexanol.

Addition of water to a C = C double bond (reaction)

This reaction is usually carried out in a strongly acidic aqueous solution. While the non-water component is broken down into two components during hydrolysis , it remains as one molecule during hydration.

The general formula of the reaction is:

As an example, the reaction of cyclohexene to cyclohexanol, with sulfuric acid as a catalyst .

In laboratory practice, this reaction often produces unwanted by-products. An alternative is oxymercuration , which is no longer up-to-date for toxicological reasons .

Water accumulates on the C = O double bond of chloral (left, trichloroacetaldehyde) with the formation of chloral hydrate (right). The equilibrium is on the side of the chloral hydrate.

Addition of water to a C = O double bond (reaction)

By absorbing water, chloral forms a stable geminal diol , chloral hydrate . This is one of the few compounds that contradicts the Erlenmeyer rule . Formaldehyde forms analogous formaldehyde hydrate with water. The equilibrium is 99.9% on the side of the formaldehyde hydrate.

See also

Individual evidence

  1. Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , p. 1780.
  2. ^ Albert Gossauer: Structure and Reactivity of Biomolecules , Helvetica Chimica Acta, Zurich 2006, p. 108, ISBN 978-3-906390-29-1 .
  3. Joachim Buddrus: Fundamentals of Organic Chemistry , 4th edition, de Gruyter Verlag, Berlin, 2011, p. 484, ISBN 978-3-11-024894-4 .
  4. Joachim Buddrus: Fundamentals of Organic Chemistry , 4th edition, de Gruyter Verlag, Berlin, 2011, p. 483, ISBN 978-3-11-024894-4 .