Clemmensen reduction
Abstract
The Clemmensen reduction is a reaction that converts a ketone or aldehyde into the corresponding alkane using zinc/mercury amalgam in concentrated hydrochloric acid. It is one of the two classical methods for the deoxygenation of carbonyl compounds, complementary to the Wolf-Kishner reduction.
Keywords
Aldehyde, Ketone, Reduction, Alkane
Category
Aldehyde/Ketone
Mechanism
The mechanism of the Clemmensen reduction is not fully established and remains a subject of debate. Among the proposed mechanisms, the most widely accepted to date is described hereafter. First, the carbonyl compound adsorbs onto the zinc surface. Two successive single-electron transfers from zinc reduce the carbonyl to a zinc-bound carbenoid intermediate. Then, the zinc–carbon bond is protonated by HCl, releasing the corresponding alkane.
The amalgamation of zinc with mercury is essential, it poisons the zinc surface toward direct proton reduction (which would give H2 instead of reducing the carbonyl), ensuring that the electrons are delivered selectively to the carbonyl substrate.
