Theory & Defination :


E.clemmensem a Danish Chemist in 1913 converted an alkane from carbonyl group hence the name Clemmensen Reduction is given.In this reaction a carbonyl compound ( aldehyde or ketone ) converted into their corresponding alkanes using metals and amalgam in concentrated Hydrochloric acid.In short we can say this method of converting carbonyl group to corresponding methylene group is known as Clemmensen reduction.

General Reaction :

<img src="claisen-condensation.jpg" alt="reaction of ester with sodium ethoxide by claisen-condensation mechanism "/>







The Clemmensen Reduction allows the deoxygenation of aldehyde or ketones, to produce the corresponding hydrocarbon.

Mechanism :


The reduction takes place at the surface of the zinc catalyst. In this reaction, alcohols are not postulated as intermediates, because subjection of the corresponding alcohols to these same reaction conditions does not lead to alkanes.
The following proposal mechanism of the Clemmensen Reduction involving steps will be

a.Carbocation is formed in the presence of organic solvent.

b.Carbanion is formed when electrons starts flowing from zinc to carbonyl carbon.

c.Hydrogen gets added to the carbon during protonation.

d.By the similar way, the second hydrogen also gets added to carbon, so that, alkane is formed from      carbonyl compound.



<img src="claisen-condensation.jpg" alt="reaction of ester with sodium ethoxide by claisen-condensation mechanism "/>



Example and Application : 


1) Conversion of Acetophenone to Ethyl benzene


<img src="claisen-condensation.jpg" alt="reaction of ester with sodium ethoxide by claisen-condensation mechanism "/>



2) The attached phenol or methoxt group in unaffected in Clemensen reduction due to Sp2 carbon



<img src="claisen-condensation.jpg" alt="reaction of ester with sodium ethoxide by claisen-condensation mechanism "/>



3) The attached -Cl group gets affected



<img src="claisen-condensation.jpg" alt="reaction of ester with sodium ethoxide by claisen-condensation mechanism "/>


Due to avoidi such side effects as shown in above reaction better to prefer Wolf-Kishner reaction.