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Clemmensen Reduction

The reaction of aldehydes and ketones with zinc amalgam (Zn/Hg alloy) in concentrated hydrochloric acid, which reduces the aldehyde or ketone to a hydrocarbon, is called Clemmensen reduction.

Introduction

This alternative reduction involves heating a carbonyl compound with finely divided, amalgamated zinc in a hydroxylic solvent (often an aqueous mixture) containing a mineral acid such as HCl. The mercury alloyed with the zinc does not participate in the reaction, it serves only to provide a clean active metal surface.  

 

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Example

 

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Possible mechanism

The mechanism of Clemmensen reduction is not fully understood; intermediacy of radicals are implicated. Clemmensen reduction is complementary to Wolff-Kishner reduction, which also converts aldehydes and ketones to hydrocarbons, in that the former is carried out in strongly acidic conditions and the latter in strongly basic conditions.

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Images2/clemsen2.gif

References

  1. Clemmensen, E. Ber. Dtsch. Chem. Ges. 1913, 46, 1837–1843.
  2. Clemmensen, E. Ber. Dtsch. Chem. Ges. 1914, 47, 51–63.
  3. Clemmensen, E. Ber. Dtsch. Chem. Ges. 1914, 47, 681–687.

Contributors

Prof. Steven Farmer (Sonoma State University)

William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook of Organic Chemistry