Answer to Question #165385 in Organic Chemistry for Fils Parfait

Question

Give a suitable chemical reaction to distinguish between a primary and a secondary amine.

Answer 1

The mixture of amines is treated with benzene sulphonyl chloride (Hinsberg's reagent) and shaken with an alkali solution.

(1) Primary amine forms alkyl benzenesulfonamide which dissolves in alkali to form sodium or potassium salt of monoalkyl benzene sulphonamide.

$PhSO_2Cl+HNHR\rightarrow PhSO_2NHR\overset{KOH}{\rightarrow}PhSO_2NKR$ (water soluble)

(2) Secondary amine forms alkyl sulphonamide which does not form salt with alkali and hence remains insoluble (solid) in alkali solution.

$PhSO_2Cl+NHR_2\overset{}{\rightarrow}PhSO_2NR_2$ (water insoluble)$\rightarrow$ no action