Read the following passage and answer questions
Greater is the stability of the substituted ammonium cation, stronger should be the corresponding amine as a base. Thus, the order of basicity of aliphatic amines should be : primary > secondary > tertiary, which is opposite to the inductive effect based order. Secondly, when the alkyl group is small, like –CH3 group, there is no steric hinderance to H-bonding. In case the alkyl group is bigger than –CH3 group, there will be steric hinderance to H-bonding. Therefore, the change of nature of the alkyl group, e.g., from –CH3 to –C2H5 results in change of the order of basic strength. Thus, there is a subtle interplay of the inductive effect, solvation effect and steric hinderance of the alkyl group which decides the basic strength of alkyl amines in the aqueous medium.
Hinsberg’s reagent is :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Benzenesulphonyl chloride
Hinsberg’s reagent is benzenesulphonyl chloride, \( \ce{C6H5SO2Cl} \). It is used to distinguish primary, secondary and tertiary amines:
Primary amine: gives an N-alkylbenzenesulphonamide, which still has an acidic N–H and so dissolves in alkali.
\( \displaystyle \ce{C6H5SO2Cl + H2N-R -> C6H5SO2NHR + HCl} \)
Secondary amine: gives an N,N-dialkylbenzenesulphonamide with no N–H, which is insoluble in alkali.
\( \displaystyle \ce{C6H5SO2Cl + HNR2 -> C6H5SO2NR2 + HCl} \)
Tertiary amine: has no N–H and does not react.
NCERT (2026-27 edition):
Reaction with Arylsulphonyl Chloride – “Benzenesulphonyl chloride (C6H5SO2Cl), which is also known as Hinsberg’s reagent, reacts with primary and secondary amines to form sulphonamides.”
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 21-05 S1 | 19-07 S1 | – | – |