Clemmensen reduction

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Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid.[1][2][3] This reaction is named after Erik Christian Clemmensen, a Danish chemist.[4]

The Clemmensen reduction

The Clemmensen reduction is particularly effective at reducing aryl-alkyl ketones,[5][6] such as those formed in a Friedel-Crafts acylation. With aliphatic or cyclic ketones, zinc metal reduction is much more effective.[7]

The substrate must be unreactive to the strongly acidic conditions of the Clemmensen reduction. Acid sensitive substrates should be reacted in the Wolff-Kishner reduction, which utilizes strongly basic conditions; a further, milder method is the Mozingo reduction. The oxygen atom is lost in the form of one molecule of water.


  1. ^ Clemmensen, E. (1913). "Reduktion von Ketonen und Aldehyden zu den entsprechenden Kohlenwasserstoffen unter Anwendung von amalgamiertem Zink und Salzsäure". Chemische Berichte 46: 1837. doi:10.1002/cber.19130460292. 
  2. ^ Clemmensen, E. (1914). "Über eine allgemeine Methode zur Reduktion der Carbonylgruppe in Aldehyden und Ketonen zur Methylengruppe". Chemische Berichte 47: 51. doi:10.1002/cber.19140470108. 
  3. ^ Clemmensen, E. (1914). "Über eine allgemeine Methode zur Reduktion der Carbonylgruppe in Aldehyden und Ketonen zur Methylengruppe. (III. Mitteilung.)". Chemische Berichte 47: 681. doi:10.1002/cber.191404701107. 
  4. ^ Biographies of Chemists, accessed 6 Feb 2007
  5. ^ "γ-Phenylbutyric acid". Org. Synth. 2: 499. 1943. ; Vol. 15, p.64 (1935)
  6. ^ "Creosol". Org. Synth. 4: 203. 1963. ; Vol. 33, p.17 (1953).
  7. ^ "Modified Clemmensen Reduction: Cholestane". Org. Synth. 6: 289. 1988. ; Vol. 53, p.86 (1973).


  • Martin, E. L. (1942). Org. React. 1: 155.  Missing or empty |title= (help)
  • Buchanan, J. G. St. C.; Woodgate, P. D. (1969). "The Clemmensen reduction of difunctional ketones". Quart. Rev. 23: 522. doi:10.1039/QR9692300522. 
  • Vedejs, E. (1975). Org. React. 22: 40.  Missing or empty |title= (help)
  • Yamamura, S.; Nishiyama, S. (1991). Comp. Org. Syn. 8: 309–313.  Missing or empty |title= (help)

See also[edit]