Nitrogen containing organic compound basic in nature when added to benzenesulphonyl chloride produces a compound which is soluble in potassium hydroxide. Suggest the nature of organic compound.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Primary amine.
Benzenesulphonyl chloride (\( \ce{C6H5SO2Cl} \)), called Hinsberg’s reagent, is used to tell primary, secondary and tertiary amines apart. Only a primary amine gives a sulphonamide that still has one H on nitrogen. The strongly electron-withdrawing sulphonyl group makes this hydrogen acidic, so the product dissolves in KOH as its potassium salt:
\( \displaystyle \ce{C6H5SO2Cl + H2N-R -> C6H5SO2NH-R + HCl} \)
\( \displaystyle \ce{C6H5SO2NH-R + KOH -> C6H5SO2NK-R + H2O} \)
The sulphonamide of a secondary amine has no H on nitrogen and does not dissolve in alkali, and a tertiary amine does not react at all. So the compound is a primary amine.
Why the other options are incorrect
Option (2) Secondary amine. — Incorrect. Its sulphonamide has no acidic N–H hydrogen, so it does not dissolve in KOH.
Option (3) Tertiary amine. — Incorrect. It has no hydrogen on nitrogen and does not react with benzenesulphonyl chloride at all.
Option (4) Quaternary ammonium salt. — Incorrect. Its nitrogen has no lone pair and no hydrogen, so it is not basic and cannot form a sulphonamide.
NCERT (2026-27 edition):
Reaction with Arylsulphonyl Chloride
