Dehydration
Dehydrogenation refers to the splitting off of hydrogen from a chemical compound. It is the reverse reaction to hydrogenation . Dehydration takes place both in biochemical processes and in chemical-technical processes.
Types of dehydration
Hydrogen can be split off with the release of molecular hydrogen, but the hydrogen is often transferred to other chemical compounds ( transfer hydrogenation ) or bound by oxidizing acceptors. If a dehydrogenation takes place in the presence of enzymes or metallic or oxidic catalysts , one hydrogen molecule is split off in an elimination reaction . Oxygen - radical , quinones , sulfur or selenium , however, lead to the cleavage of individual hydrogen atoms ( univalent dehydrogenation ).
Enzymatic dehydration
The enzymes that enable dehydration in biochemistry are called dehydrogenases . An important coenzyme of such dehydrogenases is NAD + , which acts as a hydrogen acceptor and is reduced to NADH in the process.
Technical dehydrations
Dehydration is an important reaction in chemical engineering. In most cases, molecular hydrogen is split off from the respective substrates . In order to steer this actually endothermic process in the desired direction, the dehydrogenation is often carried out in the presence of oxygen , which reacts with the split off hydrogen to form water; this makes the overall reaction exothermic .
Examples of technically carried out dehydrations:
- Primary alcohols → aldehydes
- Secondary alcohols → ketones
- Alkanes → alkenes
- Cycloalkanes → aromatics
The latter reaction also takes place on an industrial scale as a partial reaction of catalytic reforming in petroleum refineries .
literature
- The chemistry . Schülerduden, Bibliographisches Institut Mannheim 1984, ISBN 3-411-01367-2 , p. 92
- Heinz M. Hiersig : Lexicon production engineering, process engineering . ISBN 978-3184013738 , p. 150
- Joachim Buddrus: Fundamentals of Organic Chemistry . De Gruyter, 3rd edition 2003, ISBN 978-3-11-014683-7 , pp. 254ff