An aromatic compound (A) on treatment with aqueous ammonia and heating forms compound (B) which on heating with Br2 and KOH forms a compound (C) of molecular formula C6H7N.
Identify (A) from the given data.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Benzoic acid
A compound that gives an amide when heated with ammonia is a carboxylic acid.
Working back from (C): \( \ce{C6H7N} \) is aniline, \( \ce{C6H5NH2} \) (6 C, 5 + 2 = 7 H, 1 N). It is formed when an amide is heated with \( \ce{Br2} \) and \( \ce{KOH} \) (Hoffmann bromamide degradation), which gives an amine with one carbon atom less than the amide. So (B) is benzamide, \( \ce{C6H5CONH2} \), and (A) is the acid with the same seven carbon atoms, benzoic acid. The full sequence is:
\( \displaystyle \ce{C6H5COOH + NH3 <=> C6H5COONH4} \)
\( \displaystyle \ce{C6H5COONH4} \xrightarrow[-\ce{H2O}]{\text{heat}} \ce{C6H5CONH2} \)
\( \displaystyle \ce{C6H5CONH2 + Br2 + 4KOH -> C6H5NH2 + K2CO3 + 2KBr + 2H2O} \)
So (A) is benzoic acid, \( \ce{C6H5COOH} \).
Why the other options are incorrect
Option (1) Benzaldehyde — Incorrect. Benzaldehyde, \( \ce{C6H5CHO} \), has a \( \ce{-CHO} \) group but no carboxyl group (\( \ce{-COOH} \)). It cannot form an ammonium salt with ammonia, so heating it with ammonia does not give an amide.
Option (3) Acetophenone — Incorrect. Acetophenone, \( \ce{C6H5COCH3} \), is an aromatic ketone, not an acid. It has no \( \ce{-OH} \) on its carbonyl carbon to be replaced by \( \ce{-NH2} \), so it gives no amide with ammonia.
NCERT (2026-27 edition):
Reactions Involving Cleavage of C–OH Bond
Preparation of Amines
