Organic chemistry (Amines)
An organic compound (A) with the molecular formula C8H9NO when treated with bromine in aqueous solution of sodium hydroxide gives a new compound (B) having the molecular formula C7H9N. The compound (B) on heating with chloroform and ethanolic potassium hydroxide forms a compound (C) having foul-smelling. Further, the compound (B) gives an alkali soluble sulphonamide on reacting with benzenesulfonyl chloride.
Moreover, a thermally unstable compound (D) is obtained when the compound (B) reacts with sodium nitrite in concentrated hydrochloric acid at very low temperature. Further, the compound (D) on heating with water yields a compound which gives colour with neutral ferric chloride solution.
Answer the following questions on the basis of this passage.
The name of the test that yields an alkali-soluble sulfonamide upon heating with compound B is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Hinsberg's Test
From the passage, B (\( \ce{C7H9N} \)) is formed from an amide by the Hofmann bromamide reaction, so it is a primary amine. Its diazonium salt gives a phenol, so it is an aromatic amine, a toluidine (\( \ce{CH3C6H4NH2} \)):
\( \displaystyle \ce{CH3C6H4CONH2 + Br2 + 4NaOH -> CH3C6H4NH2 + Na2CO3 + 2NaBr + 2H2O} \)
Hinsberg’s test uses benzenesulphonyl chloride (\( \ce{C6H5SO2Cl} \), Hinsberg’s reagent) to tell primary, secondary and tertiary amines apart:
Primary amine: gives an N-substituted sulphonamide, which is soluble in alkali.
Secondary amine: gives an N,N-disubstituted sulphonamide with no H on nitrogen, which is insoluble in alkali.
Tertiary amine: has no H on nitrogen and does not react.
\( \displaystyle \ce{C6H5SO2Cl + H2NC6H4CH3 -> C6H5SO2NHC6H4CH3 + HCl} \)
So the test that gives an alkali-soluble sulphonamide with B is Hinsberg’s test.
Why the other options are incorrect
Option (1) Carbylamine Test — Incorrect. It uses \( \ce{CHCl3} \) and alcoholic KOH and gives a foul-smelling isocyanide, not a sulphonamide.
\( \displaystyle \ce{RNH2 + CHCl3 + 3KOH} \xrightarrow{\Delta} \ce{RNC + 3KCl + 3H2O} \)
Option (2) Isocyanide Test — Incorrect. This is another name for the carbylamine test.
Option (3) Gabriel Phthalimide Test — Incorrect. Gabriel phthalimide synthesis is a method of preparing primary aliphatic amines, not a test; it cannot even make aromatic amines.
NCERT (2026-27 edition):
Reaction with Arylsulphonyl Chloride
