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Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved. |
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Answer» Solution :Primary, secondary and tertiary amines can be distinguished by the following tests : 1. Nitrous acid test : Primary aliphatic aminesreact with `HNO_(2)` at 273-278 K to form alcohol with brisk effervescence of `N_(2)`. Primary aromatic amines react with `HNO_(2)` at 273 - 278 K to form arenediazonium salt which give coupling reaction with alkaline b-naphthol to forming orange or red ppt. Aliphatic and aromatic secondary amines react with `HNO_(2)` to form N-nitrosoamine which are OILY yellow compounds. On warming with a crystal of phenol and a few drops of conc. `H_(2)SO_(4)`, they form a green solution which turns blue on adding NaOH and then red on dilution. This test is called Liebermann nitroso reaction. Aliphatic tertiary amines form nitrite salts with `HNO_(2)` while aromatic tertiary amines undergo electrophilic substitution to form green coloured p-nitrosoamines. 2. Hinsberg test : In this test, the amine is shaken with benzene sulphonyl chloride (Hinsberg REAGENT) in the presence of excess of aqueous KOH solution. Primary amine GIVES a clear solution which on acidification gives an insoluble N-alkylbenzene sulphonamide according to the following reaction :  Tertiary amine does not react due to absence of hydrogen attached to nitrogen. Therefore, it remains insoluble in alkaline solution but dissolves on acidification to give a clear solution. 
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