Question

Which of the following is a Wolff–Kishner reduction?

• A. ${>C=O + 4[H] →[Zn-Hg/conc.HCl][\Delta] >CH2 + H2O}$
• B. ${-COCl →[H2][Pd-BaSO4] -CHO + HCl}$
• C. ${-C#N + 2[H] →[SnCl2/dil.HCl] -CH=NH.HCl →[H3O^+] -CHO + NH4Cl}$
• D. ${>C=O →[H2N-NH2][-H2O] >C=NNH2 →[KOH/ethylene\ glycol][\Delta] >CH2 + N2}$

Hint:

Wolff–Kishner reduction uses hydrazine and strong base, whereas Clemmensen reduction uses Zn–Hg in acidic medium.

Answer 1

The Correct Option is D

Step 1: Recall the definition of Wolff–Kishner reduction.
Wolff–Kishner reduction is a reaction in which aldehydes or ketones are converted into hydrocarbons using hydrazine $(H_2N\!-\!NH_2)$ and strong base such as KOH in a high-boiling solvent like ethylene glycol, with heating.
Step 2: Analyze the given options.
(A) This is Clemmensen reduction, carried out using Zn–Hg and concentrated HCl.
(B) This represents Rosenmund reduction of acid chlorides to aldehydes.
(C) This is Stephen reduction, where nitriles are reduced to aldehydes.
(D) This reaction shows conversion of carbonyl compound into hydrazone followed by treatment with KOH and heat to give hydrocarbon and nitrogen gas, which is characteristic of Wolff–Kishner reduction.
Step 3: Conclusion.
Option (D) correctly represents Wolff–Kishner reduction.