Clemmensen reduction to alkanes

Clemmensen reduction to alkanes Definition:


Addition of zinc amalgam, Zn(Hg) and acid to a ketone results in an alkane. This is called the Clemmensen reduction.



Clemmensen reduction to alkanes Explained:


The Clemmensen reaction can be used to reducing an aryl ketone which is the product of a Friedel-Crafts acylation. It allows the deoxygenation of aldehydes or ketones, to produce the corresponding hydrocarbon. This reaction is only as effective on ketones that are adjacent to the aromatic system. The Clemmensen reduction is complementary to the 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.

Mechanism of the Clemmensen Reduction

In the presence of HCl and zinc amalgam, the carbonyl group is completely reduced and replaced with two hydrogen atoms. Although the mechanism of Clemmensen reduction is not fully understood, that reduction takes place at the surface of the zinc catalyst via a radical intermediate. An addition of acid protonates the ketone, and electrons from the Zn(Hg) are delivered to the carbon. The new hydrogens come from the acid. This is one of the proposed mechanisms: