The Wolff-Kishner reduction uses hydrazine, a base, and a high-boiling solvent to convert an aldehyde or ketone to an alkane. The hydrazine first attacks the ketone or aldehyde, releasing water to form a hydrazone intermediate. Subsequent proton transfer steps result in the release of nitrogen gas and the formation of a carbanion, which abstracts a proton from water to produce the final alkane product.

• The original procedure involves refluxing the carbonyl compound, hydrazine, and excess base in a high-boiling solvent. Water generated during the formation of the hydrazone lowers the temperature, resulting in long reaction times (50 – 100 hours) and the need to use an excess of reagents and solvent. ^[1]
• Reaction times can be shortened to about 3-6 hours if water and excess hydrazine are removed via distillation (once the hydrazone is formed in situ), so that the reaction temperature can rise to about 200°C (called the Huang-Minlon modification). This modification increases yields and allows the use of hydrazine hydrate along with water-soluble bases (KOH or NaOH). ^[1,2]
• Sterically hindered carbonyl compounds require higher reaction temperatures (Barton modification). ^[3,4]
• Esters, lactones, amides, and lactams are hydrolyzed under the reaction conditions. ^[1]
• Potential side reactions include azine formation or the reduction of ketones to alcohols. ^[1]

• Reagents: Hydrazine, Base (Sodium Metal, NaOEt, etc.), High-Boiling Solvent (Ethylene Glycol, Triethylene Glycol, etc.)
• Reactant: Aldehyde or Ketone
• Product: Alkane
• Type of Reaction: Nucleophilic Addition of Hydrazine
• Bond Formation: C-C

Mechanism

Original Paper

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Related Compounds