Separation Of A Mixture Of Amines

Treating a mixture of 3 amines with Hinsbergs reagent (benzene sulfonyl chloride) and finally treating the product formed with NaOH can separate the 3 class of amines.

Primary amine:

RNH + C₆H₅SO₂Cl → C₆H₅– SO2 – NH – R + HCl

(N-alkyl benzene sulfonamides)

(Dissolves in NaOH due to acidic H-attached to Nitrogen)

Secondary amine

Tertiary amine

Tertiary amines do not react with Hinsberg’s reagent.

After reacting with NaOH the aqueous layer and the second layer [Secondary and Tertiary) can be separated by ether. Aqueous layer Hydrolysed with conc. HCl gives primary amine. The ether layer is distilled and tertiary amine is distilled over. Residue hydrolysed with conc. HCl to recover secondary amine.

Hofmann’s Method

The mixture of amines is treated with diethyloxalate, which forms a solid oxamide with primary amine, a liquid oxime ester with secondary amine. The tertiary amine does not react.