Question:
Which of the following is Clemmensen reduction?
Which of the following is Clemmensen reduction?
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Clemmensen reduction uses amalgamated zinc and concentrated HCl to reduce carbonyl groups (aldehydes or ketones) directly to alkanes. Remember other named reductions like Wolff-Kishner (hydrazine and base), Rosenmund (H$_2$/Pd-BaSO$_4$ for acyl chlorides to aldehydes), and Stephen reduction (SnCl$_2$/HCl for nitriles to aldehydes) for distinguishing them.
Updated On: Apr 28, 2026
- A
- B
- C
- D
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The Correct Option is C
Solution and Explanation
Step 1: Understand Clemmensen reduction.\nClemmensen reduction is a chemical reaction used to reduce carbonyl groups (aldehydes or ketones) to alkanes using amalgamated zinc (Zn-Hg) and concentrated hydrochloric acid (HCl).\n\[\text{R-CO-R'} \xrightarrow{\text{Zn-Hg, Conc. HCl \text{R-CH}_2\text{-R'} + \text{H}_2\text{O}\]\n
Step 2: Evaluate Option A.\n\n\[\text{RCOCl} \xrightarrow{\text{H}_2, \text{Pd} - \text{BaSO}_4} \text{RCHO} + \text{HCl}\]\nThis reaction, the reduction of an acyl chloride to an aldehyde using hydrogen gas over a palladium catalyst poisoned with barium sulfate, is known as Rosenmund reduction.\n\n
Step 3: Evaluate Option B.\n\n\[\text{RCN} \xrightarrow{\text{SnCl}_2, \text{HCl}, \text{H}_2\text{O \text{RCHO} + \text{NH}_4\text{Cl}\]\nThis reaction, the reduction of nitriles to aldehydes using stannous chloride and hydrochloric acid, is known as Stephen reduction.\n\n
Step 4: Evaluate Option C.\n\n\[\text{RCHO} \xrightarrow{\text{Zn-Hg, Conc. HCl \text{RCH}_3 + \text{H}_2\text{O}\]\nThis reaction shows an aldehyde (RCHO) being reduced to an alkane (RCH$_3$) using zinc amalgam and concentrated HCl. This matches the definition of Clemmensen reduction.\n\n
Step 5: Evaluate Option D.\n\n\[\text{R-CO-R'} \xrightarrow{\text{i) H}_2\text{N-NH}_2, \text{ii) KOH/HOCH}_2\text{CH}_2\text{OH \text{RCH}_2\text{R'}\]\nThis reaction, the reduction of a carbonyl group to an alkane using hydrazine and a strong base (like KOH) in a high-boiling solvent, is known as Wolff-Kishner reduction.\n\n
Step 6: Conclude the correct option.\nBased on the analysis, Option C represents the Clemmensen reduction.\n
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