Clemmensen's Reduction

Clemmensen Reduction

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. The first example below shows a common application of this reduction, the conversion of a Friedel-Crafts acylation product to an alkyl side-chain. The second example illustrates the lability of functional substituents alpha to the carbonyl group. Substituents such as hydroxyl, alkoxyl & halogens are reduced first, the resulting unsubstituted aldehyde or ketone is then reduced to the parent hydrocarbon.

   

    Mechanism