See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The reaction converts an aryl ketone (acetophenone derivative, Ar-CO-CH3) into the corresponding alkyl group (Ar-CH2-CH3). This is a carbonyl-to-methylene reduction, i.e., C=O → CH2, which requires a deoxygenative reduction rather than a simple reduction to alcohol. Step 1 - Identify the transformation: The C=O of the acetyl group is fully reduced to CH2, giving an ethyl group. This rules out NaBH4 and LiAlH4, which reduce ketones to secondary alcohols (C=O → CHOH), not to CH2. Step 2 - Consider the sensitive functional group: The molecule contains a quaternary ammonium salt (-N+(CH3)3). This group is sensitive to strongly basic conditions. Wolf-Kishner reduction requires strongly basic conditions (KOH, ethylene glycol, heat) along with hydrazine. Under these strongly basic conditions, the quaternary ammonium salt could undergo Hofmann elimination or other decomposition, making Wolf-Kishner unsuitable. Step 3 - Clemmensen reduction: Clemmensen reduction uses zinc amalgam (Zn/Hg) with concentrated HCl (acidic conditions). Under acidic conditions, the quaternary ammonium group (-N+(CH3)3) is stable and will not be affected. The ketone is selectively and completely reduced to the methylene (CH2) group. This converts Ar-CO-CH3 to Ar-CH2-CH3 without disturbing the -CH2-CH2-N+(CH3)3 group. Step 4 - Why other options fail: - (a) Wolf-Kishner: Strongly basic conditions would destroy/react with the quaternary ammonium salt. - (c) LiAlH4: Reduces ketone to alcohol, not to CH2; gives Ar-CH(OH)-CH3, not Ar-CH2-CH3. - (d) NaBH4: Also only reduces to alcohol; gives Ar-CH(OH)-CH3, not Ar-CH2-CH3. Therefore, the correct answer is B.