Wolff-Kishner Reduction

This article explains about Wolff-Kishner Reduction converts aldehydes and ketones to hydrocarbons under strong base and heat.

• Type: Strong base reduction

Purpose of Wolff-Kishner Reduction:

• Converts aldehydes and ketones to alkanes, like the Clemmensen reduction.
• Basic conditions, so suitable for acid-sensitive compounds.

Reagents:

• Hydrazine (NH₂NH₂)
• Strong base (e.g., KOH)
• Heat
• Often done in high-boiling solvents like ethylene glycol.

Mechanism of Wolff-Kishner Reduction:

• Step 1: Hydrazone Formation

  • Carbonyl compound reacts with hydrazine:
    • R₂C=O  +  H₂NNH₂  →  R₂C=NNH₂  +  H₂O

• Step 2: Deprotonation

  • Under basic conditions, the hydrazone is deprotonated:
    • R₂C=NNH₂  +  OH⁻  →  R₂C=NNH⁻  +  H₂O

• Step 3: Resonance and Rearrangement

  • Electron rearrangement creates a double bond and leaves a good leaving group:
    • R₂C=NNH⁻  →  R₂CH⁻  +  N₂↑

• Step 4: Protonation

  • Final deprotonation/protonation cycle yields the alkane:
    • R₂CH⁻  +  H₂O  →  R₂CH₂  +  OH⁻
  • Nitrogen gas has evolved — this drives the reaction forward (Le Chatelier’s principle).
  • 

Example:

Ph-CO-CH₃  +  NH₂NH₂/KOH  →  Ph-CH₂-CH₃  +  N₂↑

Key Point:

• Neutralizes the carbonyl group fully to CH₂.
• Works where acidic conditions of Clemmensen would fail.

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