Clemmensen’s reduction involves the reduction of which compound?

Clemmensen’s reduction is an important organic reaction used to convert ketones (and sometimes aldehydes) into alkanes. The reaction employs a zinc amalgam (Zn-Hg) and concentrated hydrochloric acid (HCl) mixture as the reducing agent. It is named after the Danish chemist Erik Christian Clemmensen, who developed the method in the early 20th century.

The general reaction can be represented as:
R₂C=O + 4[H] → R₂CH₂ + H₂O

Here, a ketone is reduced to an alkane through the removal of the oxygen atom (replaced by hydrogen). The reduction occurs under strongly acidic conditions, making this method suitable for compounds that are stable in acidic environments.

Mechanism (Simplified):

1. 
   

   The ketone carbonyl group interacts with zinc in the presence of acid.

   
   


2. 
   

   A series of electron transfers occurs, leading to the stepwise replacement of oxygen with hydrogen.

   
   


3. 
   

   The final product is a hydrocarbon (alkane).

   
   

Important Features:

• 
  

  Reagent Used: Zinc amalgam (Zn-Hg) + concentrated HCl.

  
  


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  Medium: Acidic.

  
  


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  Applicable To: Ketones and some aldehydes.

  
  


• 
  

  Product Formed: Corresponding alkane.

  
  

Example:
Conversion of acetophenone (a ketone) to ethylbenzene:
C₆H₅COCH₃ → C₆H₅CH₂CH₃

Comparison with Wolff-Kishner Reduction:
While Clemmensen’s reduction is carried out under acidic conditions, the Wolff-Kishner reduction uses basic conditions (hydrazine and KOH). Both achieve the same end — conversion of carbonyl compounds to hydrocarbons — but are chosen based on the compound’s stability toward acid or base.

Applications:

• 
  

  Used in the synthesis of hydrocarbons from carbonyl-containing intermediates.

  
  


• 
  

  Valuable in the Friedel–Crafts acylation–reduction sequence to produce alkylated aromatic compounds.

  
  

Key Facts:

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  Reagent: Zn-Hg + HCl

  
  


• 
  

  Medium: Acidic

  
  


• 
  

  Converts: Ketones → Alkanes

  
  


• 
  

  Invented by: Erik Clemmensen

  
  

✅ Correct Answer: A) Ketone