Clemmensen reduction

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Clemmensen reduction
Named after Erik Christian Clemmensen
Reaction type Organic redox reaction
Organic Chemistry Portal clemmensen-reduction
RSC ontology ID RXNO:0000038

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.

However, the reaction is not suitable for substances sensitive to acids. Also, -COOH group can't be reduced by this method. (-COOH group can be reduced by treating it with soda lime and then heating).


  1. ^ Clemmensen, E. (1913). "Reduktion von Ketonen und Aldehyden zu den entsprechenden Kohlenwasserstoffen unter Anwendung von amalgamiertem Zink und Salzsäure". Chemische Berichte 46: 1837–1843. 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: 51–63. 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: 681–687. 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]