Back to Concepts
ChemistryMediumClass 12
Clemmensen & Wolff-Kishner Reduction
Aldehydes, Ketones & Carboxylic Acids
17
JEE Qs
8%
Hard
40
min
Always analyze the entire molecule for other acid-sensitive or base-sensitive functional groups before choosing between Clemmensen and Wolff-Kishner reduction.
🧮 Key Formulas
R-CHO/R-CO-R' + Zn(Hg)/conc. HCl --> R-CH3/R-CH2-R' (Clemmensen Reduction)
R-CHO/R-CO-R' + H2N-NH2, KOH/Ethylene Glycol, heat --> R-CH3/R-CH2-R' (Wolff-Kishner Reduction)
✅ Key Points for JEE
- 1Both Clemmensen and Wolff-Kishner reductions convert the carbonyl group (C=O) of aldehydes and ketones completely into a methylene group (-CH2-).
- 2Clemmensen reduction proceeds under strongly acidic conditions (Zn(Hg) in concentrated HCl) and is suitable for compounds stable to acids but sensitive to bases.
- 3Wolff-Kishner reduction proceeds under strongly basic conditions (hydrazine, KOH in ethylene glycol, heat) and is suitable for compounds stable to bases but sensitive to acids.
- 4The choice between the two methods is dictated by the presence of other acid-sensitive or base-sensitive functional groups within the molecule.
- 5Common side reactions to watch for include rearrangements, dehydration (acidic conditions), or epimerization (basic conditions) if other reactive groups are present.
⚠️ Common Mistakes
- ✕Applying Clemmensen reduction to substrates containing acid-sensitive groups (e.g., alcohols, esters, acetals, or cyclopropane rings which may undergo rearrangement).
- ✕Applying Wolff-Kishner reduction to substrates containing base-sensitive groups (e.g., esters or amides which may hydrolyze, or compounds undergoing aldol condensation).
- ✕Incorrectly assuming the carbonyl group is reduced to an alcohol (-CHOH-) instead of a methylene group (-CH2-).
NCERT Chapters
- Class 12 Chemistry Part 2 Ch 12: Aldehydes, Ketones and Carboxylic Acids