Amines are reactive in nature, mainly due to difference in electronegativity between Nitrogen and Hydrogen and, due to lone pair of electrons on Nitrogen. Amines behaves like nucleophiles and as good Lewis bases and there are various reactions to support this. Different degree of amines differ in their reactivity due to steric hindrance and electronic effects. Aromatic amines are less basic due to +R effect, hence have higher \(pK_b\) value than the aliphatic amines. Basic strength of amines also depend on stability of corresponding conjugate acid in aqueous medium.
Identify A:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → N-(4-methylphenyl)benzamide
The amine is p-toluidine (4-methylaniline) and the reagent is benzoyl chloride in 10% aqueous NaOH. Amines react with benzoyl chloride by nucleophilic substitution at the acyl carbon (benzoylation): the lone pair on nitrogen attacks the C=O carbon, \( \ce{Cl^{-}} \) leaves, and the H on nitrogen is lost as HCl, which the NaOH removes (Schotten–Baumann conditions).
\( \ce{CH3C6H4NH2} \) + \( \ce{C6H5COCl} \) → \( \ce{CH3C6H4NH-CO-C6H5} \) + HCl
So A is the amide \( \ce{CH3-C6H4-NH-CO-C6H5} \), drawn in Option (1).
Why the other options are incorrect
Option (2) — Incorrect. It puts a –COCl group on the ring of p-toluidine. Benzoyl chloride acylates the –\( \ce{NH2} \) group; it does not substitute the ring.
Option (3) — Incorrect. It shows a –COOH group on the ring of p-toluidine; no carboxylation of the ring takes place in this reaction.
Option (4) — Incorrect. It is the secondary amine \( \ce{CH3C6H4-NH-CH2-C6H5} \), which has a \( \ce{CH2} \) in place of C=O; an acyl chloride gives an amide, not an amine.
NCERT (2026-27 edition):
Acylation – “… Amines also react with benzoyl chloride (C6H5COCl). This reaction is known as benzoylation.”
\( \underset{\text{Methanamine}}{\ce{CH3NH2}} + \underset{\text{Benzoyl chloride}}{\ce{C6H5COCl}} \rightarrow \underset{\text{N-Methylbenzamide}}{\ce{CH3NHCOC6H5}} + \ce{HCl} \)