Primary amine: A primary (1°) amine is an amine that has the following general structural formula.
R= alkyl or aryl group
Secondary amine: A secondary (2°) amine is an amine that has the following general structural formula.
R1 and R2= alkyl or aryl group
Tertiary amine: A tertiary amine is an amine that has the following structure
R1, R2 and R3 are alkyl or aryl groups
Identification of Primary, Secondary and Tertiary amines
Primary, secondary and tertiary amines can be identified by the following test:
Hinsberg’s test: This is an excellent test for the identification of primary, secondary and tertiary amines. In this test, the amine is shaken with benzenesulphonyl chloride ( Hinsberg’s reagent) in the presence of an excess of aqueous KOH solution when
(i) A primary amine gives a clear solution which on acidification gives an N-alkylbenzene sulphonamide which is soluble in alkali.
Due to the presence of strong electron withdrawing sulphonyl group in the sulphonamide, the H-atom attached to nitrogen can be easily released as a proton. So it is acidic and dissolves in alkali.
(ii) A secondary amine reacts with Hinsberg's reagent to give a sulphonamide which is soluble in water.
There is no H-atom attached to the N-atom in the sulphonamide Therefore it is not acidic and soluble in alkali.
(iii) A Tertiary amine does not react with Hinsberg’s reagent at all
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