Question

When propanone is treated with $Zn/Hg$ and Conc. HCl, propane is formed. This reaction is known as ________.

• A. Wolf-Kishner reaction
• B. Clemmensen reduction
• C. Hoffman reaction
• D. Kolbe's reaction
• E. Cannizzaro reaction

Hint:

Clemmensen = Acidic ($HCl$); Wolf-Kishner = Basic ($KOH$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
This question asks for the name of a specific organic reaction that converts a ketone (propanone) into an alkane (propane) using a particular set of reagents. This is a reduction of a carbonyl group.
Step 2: Detailed Explanation
1. Analyze the Transformation:
- Starting Material: Propanone (CH\(_3\)COCH\(_3\)), a ketone. - Reagents: Zinc amalgam (Zn/Hg) and concentrated hydrochloric acid (conc. HCl). - Product: Propane (CH\(_3\)CH\(_2\)CH\(_3\)), an alkane. The reaction involves the complete reduction of the carbonyl group (C=O) to a methylene group (-CH\(_2\)-). 2. Identify the Named Reaction from the Options:
- (A) Wolff-Kishner reaction: This also reduces ketones/aldehydes to alkanes but uses hydrazine (\(N_2H_4\)) and a strong base (like KOH) under heating. The conditions are basic. - (B) Clemmensen reaction: This reaction specifically uses zinc amalgam (Zn/Hg) and concentrated HCl to reduce ketones or aldehydes to alkanes. The conditions are strongly acidic. This perfectly matches the reaction described in the question. - (C) Hofmann reaction: This refers to several reactions, but the most common is the Hofmann degradation of amides to amines with one less carbon atom. It does not reduce ketones. - (D) Kolbe's reaction: This refers to the synthesis of salicylic acid from phenol, CO\(_2\), and base, or the Kolbe electrolysis of carboxylate salts to form alkanes. Neither matches. - (E) Cannizzaro reaction: This is a disproportionation reaction of aldehydes without \(\alpha\)-hydrogens in the presence of a strong base. It does not produce alkanes from ketones.
Step 4: Final Answer
The described reaction is the Clemmensen reaction.