The Hinsberg reagent is

Solution

Chemistry ma’am · 3 steps

Hinsberg reagent is benzenesulphonyl chloride: look for the -SO₂Cl group on the ring.

1. What the reagent is. The Hinsberg reagent is benzenesulphonyl chloride, C₆H₅SO₂Cl. That is structure (a): a benzene ring joined to sulphur, with two S=O bonds and one S-Cl bond.
2. How it works. Primary and secondary amines have an N-H bond, so they attack the sulphur and push out Cl⁻. This forms a sulphonamide. A tertiary amine has no N-H and does not react.

   Amine	Product with C₆H₅SO₂Cl	In aqueous KOH
   Primary, RNH₂	C₆H₅SO₂NHR	dissolves: the N–H left on N is acidic
   Secondary, R₂NH	C₆H₅SO₂NR₂	insoluble: no N–H left
   Tertiary, R₃N	no reaction	no sulphonamide forms

3. So. The Hinsberg reagent is benzenesulphonyl chloride, option (a).

The idea to keep. Hinsberg test uses C₆H₅SO₂Cl to tell 1°, 2° and 3° amines apart: 1° gives a sulphonamide soluble in alkali, 2° gives an insoluble one, 3° does not react.

Answer from the NTA final answer key. Solution by PrepWiser.