Aldehydes and Ketones to Alkanes: Wolff–Kishner Reduction

Wolff–Kishner reduction transforms a carbonyl group into a methylene group through deoxygenation by replacing the oxygen atom with two hydrogen atoms.

The reaction is carried out at elevated temperatures, using a strong base and hydrazine.

The reduction mechanism has two parts: Formation of hydrazone and elimination of nitrogen.

The first part involves a multi-step condensation reaction between hydrazine and the carbonyl compound to form a hydrazone.

In the second part, the base removes an N–H proton to generate the hydrazone anion, which resonance stabilizes to give a negative charge on the carbon atom.

This deprotonation step is not easy and requires heat, necessitating the use of high-boiling solvents.

The anion is reprotonated by water, followed by a second deprotonation of nitrogen, which drives the reaction forward by eliminating nitrogen gas and generating a carbanion.

A final reprotonation on the carbanion gives an alkane.