Question

Which from following reactions converts carbonyl group of aldehydes and ketones to methylene group on treatment with zinc amalgam and concentrated HCl ?

• A. Wolf-Kishner reaction
• B. Stephen reduction
• C. Clemmensen reduction
• D. Rosenmund reduction

Hint:

To avoid confusing the two alkane-forming reductions:
Clemmensen uses Chloric acid (HCl) — Acidic medium.
Wolff-Kishner uses a Base (KOH) — Basic medium.

Answer 1

The Correct Option is C

Step 1: Understand the question.
We need the named reaction that changes a carbonyl group $\text{C=O}$ of aldehydes and ketones into a $\text{CH}_2$ group, using zinc amalgam and concentrated HCl.

Step 2: Focus on the reagent clue.
The reagents given are zinc amalgam (Zn-Hg) and concentrated HCl. This is an acidic set of conditions, so the right name must be tied to acid.

Step 3: Recall the overall change.
The reaction simply pulls off the oxygen and puts two hydrogens in its place: \[ \text{C=O} \longrightarrow \text{CH}_2 \]
Step 4: Rule out the wrong names.
Stephen reduction makes an aldehyde from a nitrile. Rosenmund reduction makes an aldehyde from an acid chloride. Neither fits a full reduction to $\text{CH}_2$.

Step 5: Compare the two full-reduction methods.
Wolff-Kishner also turns $\text{C=O}$ into $\text{CH}_2$, but it uses hydrazine with a strong base (KOH), which is basic, not acidic. The acidic Zn-Hg / HCl route is the Clemmensen reduction.

Step 6: Pick the answer.
Since our reagents are acidic, the answer is the Clemmensen reduction, option (C).
\[ \boxed{\text{Clemmensen reduction}} \]