Dehydrogenation
Dehydrogenation is a chemical reaction that involves the removal of hydrogen from a molecule. It is the reverse process of hydrogenation. Dehydrogenation reactions are conducted both on industrial and laboratory scales. Dehydrogenation converts saturated fats to unsaturated fats. Enzymes that catalyze dehydrogenation are called dehydrogenases. Dehydrogenation processes are used extensively to produce styrene in the fine chemicals, oleochemicals, petrochemicals, and detergents industries.
Classes of the reaction
A variety of dehydrogenation processes have been described, especially for organic compounds:
- In typical aromatization, six-membered alicyclic rings, e.g. cyclohexene, can be aromatized in the presence of hydrogenation acceptors. The elements sulphur and selenium promote this process. Quinones, especially 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone are effective.
- Oxidation of alcohols to ketones or aldehydes can be effected by metal catalysts such as copper chromite. In the Oppenauer oxidation, hydrogen is transferred from an alcohol to an aldehyde or ketone to bring about the oxidation.
- Dehydrogenation of amines to nitriles using a variety of reagents, such as Iodine pentafluoride (IF
5). - Dehydrogenation of paraffins and olefins — paraffins such as n-pentane and isopentane can be converted to pentene and isopentene using chromium (III) oxide as a catalyst at 500 °C.
Examples
One of the largest scale dehydrogenation reactions is the production of styrene by dehydrogenation of ethylbenzene. Typical dehydrogenation catalysts are based on iron(III) oxide, promoted by several percent potassium oxide or potassium carbonate.[1]
- C6H5CH2CH3 → C6H5CH=CH2 + H2
Formaldehyde is produced industrially by the catalytic oxidation of methanol, which can also be viewed as a dehydrogenation using O2 as the acceptor. The most common catalysts are silver metal or a mixture of an iron and molybdenum or vanadium oxides. In the commonly used formox process, methanol and oxygen react at ca. 250–400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation:[2]
- 2 CH3OH + O2 → 2 CH2O + 2 H2O
References
- Advanced Organic Chemistry, Jerry March, 1162-1173.
- http://www.firstprincipals.com/DeHydrogenation.htm
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- ↑ Denis H. James William M. Castor, “Styrene” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.
- ↑ Günther Reuss, Walter Disteldorf, Armin Otto Gamer, Albrecht Hilt “Formaldehyde” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_619
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