Acylation of aniline with acetic anhydride gives:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → N-Phenylacetamide
Primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution: an H of the –\( \ce{NH2} \) group is replaced by an acyl group and an amide is formed. This is acylation. With acetic anhydride the acyl group is acetyl (\( \ce{CH3CO} \)–):
\( \ce{C6H5NH2} \) + \( \ce{(CH3CO)2O} \) → \( \ce{C6H5NHCOCH3} \) + \( \ce{CH3COOH} \)
The product \( \ce{C6H5NHCOCH3} \) is acetanilide, IUPAC name N-phenylethanamide, also written N-phenylacetamide: an acetamide with a phenyl group on the nitrogen.
Why the other options are incorrect
Option (1) N-Methylbenzamide — Incorrect. \( \ce{C6H5CONHCH3} \) is formed from methylamine and benzoyl chloride (benzoylation); it contains a benzoyl group, not an acetyl group, and no phenyl on N.
Option (3) N-Ethylethanamide — Incorrect. \( \ce{CH3CONHC2H5} \) is the acetylation product of ethylamine, not of aniline.
Option (4) N-Phenylbenzamide — Incorrect. \( \ce{C6H5CONHC6H5} \) (benzanilide) is formed when aniline reacts with benzoyl chloride, not with acetic anhydride.
NCERT (2026-27 edition):
Acylation – “Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. This reaction is known as acylation. You can consider this reaction as the replacement of hydrogen atom of –NH2 or >N–H group by the acyl group. The products obtained by acylation reaction are known as amides.”
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 14-06 S1 07-06 S3 30-05 S1 | – |