See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Acetanilide is formed by acylation of the amine group of aniline (-NH2) with an acetyl group (CH3CO-), producing PhNHCOCH3. The reagent must be capable of transferring an acetyl group to the amine (i.e., it must be an acylating agent). Step 1: Evaluate option (a) - Acetyl chloride (CH3COCl). Acid chlorides are highly reactive acylating agents. Aniline reacts readily with acetyl chloride to give acetanilide. This works. Step 2: Evaluate option (b) - Acetic anhydride (CH3CO-O-COCH3). Acid anhydrides are well-known acylating agents. Aniline reacts with acetic anhydride to give acetanilide. This works. Step 3: Evaluate option (c) - Acetaldehyde (CH3CHO). Acetaldehyde is an aldehyde, not an acylating agent. Reaction of aniline with acetaldehyde does not yield acetanilide; instead it can form a Schiff base (imine, PhN=CHCH3) via nucleophilic addition-elimination, but no acyl transfer occurs. An aldehyde lacks the leaving group necessary for acylation of the amine to produce an amide. Therefore, acetaldehyde does NOT react with aniline to give acetanilide. Step 4: Evaluate option (d) - Phenyl acetate (PhOCOCH3). Esters of phenol are reactive acylating agents toward amines (aminolysis). Aniline can displace the phenoxy group to give acetanilide. This works. Why option (c) fails: Acetaldehyde (CH3CHO) does not have an acyl leaving group; it undergoes nucleophilic addition with aniline to form an imine (Schiff base), not an amide. The carbonyl carbon in an aldehyde has a hydrogen as the leaving group position, which does not facilitate amide (acetanilide) formation. Therefore, the correct answer is C.