Reactions of amines: alkylation, acylation, carbylamine, nitrous acid and the Hinsberg test sheet5-mark answer frameWhat is the Hinsberg test? Explain how it distinguishes primary, secondary and tertiary amines, with equations. Also write the carbylamine test.
How to lay out the answer. Follow the frame, then write it in your own words.
- 1 · Name the reagent. Benzenesulphonyl chloride, C₆H₅SO₂Cl (Hinsberg's reagent).
- 2 · Primary amine. C₆H₅SO₂Cl + C₂H₅NH₂ → C₆H₅SO₂NHC₂H₅ + HCl. The N-H is acidic, so the sulphonamide dissolves in alkali.
- 3 · Secondary amine. C₆H₅SO₂Cl + (C₂H₅)₂NH → C₆H₅SO₂N(C₂H₅)₂ + HCl. No N-H, so it is insoluble in alkali.
- 4 · Tertiary amine. No H on N, so no reaction.
- 5 · Carbylamine test. RNH₂ + CHCl₃ + 3KOH (alcoholic), heat → RNC + 3KCl + 3H₂O: foul smell of isocyanide, for 1° amines only.
- 6 · Close in one line. So the Hinsberg test sorts all three classes, and the carbylamine test confirms a primary amine.
Scoring tip: For each class, write what the examiner can see: dissolves in alkali, does not dissolve, or no reaction.
