WolffKishner

The Wolff-Kishner reduction, also known as the Wolff–Kishner reduction or Kishner reduction, is a classical organic transformation that converts aldehydes and ketones into alkanes. It uses hydrazine as the nucleophile to form a hydrazone, followed by base-promoted decomposition that eliminates nitrogen to afford the hydrocarbon.

Mechanism: a carbonyl compound reacts with hydrazine to form a hydrazone. In the presence of base, successive deprotonations generate a diazene intermediate, and extrusion of nitrogen gas yields the corresponding alkane, completing the reduction.

Conditions and scope: typical reagents are hydrazine hydrate and potassium hydroxide in a high-boiling solvent such as ethylene glycol or diethylene glycol; heating in a sealed vessel at about 180–200 C for several hours. The method reduces both aliphatic and aromatic carbonyls; aldehydes reduce rapidly, while ketones may be slower, especially hindered ones. The reaction is relatively selective for carbonyl reduction, but the harsh basic/high-temperature conditions can affect acid-sensitive materials and some other functional groups.

History and usage: named after Ludwig Wolff and Isaak Kishner, the method was developed in the early 20th century and has since been a standard option for deoxygenation of carbonyl groups when other mild reductions are unsuitable. It is complementary to the Clemmensen reduction, which uses acidic media to achieve carbonyl-to-alkane conversion.