Azo dye test is not used for the distinction in 1°, 2° and 3° aliphatic amines. The other tests can be easily used to distinguish between 1°, 2° and 3° amines.
Test
Primary amine
Secondary amine
Tertiary amine
i
Hinsberg's reagent test
Forms a sulphonamide soluble in alkali
Forms a sulphonamide insoluble in alkali
No reaction
ii
Carbylamine reaction
Forms a carbylamine with unpleasant smell
No reaction
No reaction
iii
Reaction with nitrous acid
Forms primary alcohol and evolves nitrogen gas with effervescence
Forms nitrosamine which gives Libermann's nitroso amine reaction