Clemmensen Reduction

Clemmensen Reduction

Using hydrochloric acid and zinc amalgam, the Clemmensen reaction converts aldehydes or ketones to alkanes. Danish chemist Erik Christian Clemmensen is named after the Clemmensen reduction.



Reduction of aryl-alkyl ketones formed during the Friedel-Crafts acylation is particularly efficient using this reaction. When cyclic ketones or aliphatic compounds and zinc metal are reduced, the reaction is more efficient.
Example,

Mechanism of Clemmensen Reaction

There are two proposed mechanisms for this reaction, but neither is fully understood;

Carbanionic mechanism
Zinc attacks directly and directly on the protonated carbon under carbanionic conditions.

Carbenoid mechanism
Carbenoid mechanisms are radical processes that reduce the happenings on zinc metal surfaces. Reduced materials are formed on zinc metal surface. Alkanes cannot be considered intermediates in this reaction because the corresponding alcohols cannot be subjected to the same conditions.

In order to rationalize the mechanism of the Clemmensen Reduction, zinc carbenoids will be used as intermediaries:



Acidic conditions must not react with the underlying substance. If the Wolff-Kishner reduction is milder than the Mozingo reduction, the acid sensitive base substance reacts with it. Acid sensitive substances do not react in the Wolff-Kishner reduction. Despite its antiquity, the mechanism is obscure due to its heterogeneous nature and the difficulty of studying it. The particular reaction proposed such as the formation of zinc carbenoids and organozinc intermediates has only been studied a few times.

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