Hinsberg’s reagent (C₆H₅SO₂Cl) forms monoalkyl sulphonamide with 1^o amines which is soluble in KOH. With 2^o amines it gives dialkyl sulphonamide which is insoluble in KOH and with 3^o amines there is no reaction.

In mustard oil test, 1^o amines on action of CS₂ and HgCl₂ give alkyl isothiocyanate having mustard oil smell. 2^o amines react with CS₂ but not with HgCl₂ while 3^o amines give no reaction. However, this test is not able to distinguish 2^o and 3^o amines.