HINSBERG METHOD

Separation of amines

When the mixture contains salts of primary, Secondary and tertiary amines along with the quaternary salt, it is first distilled with KOH solution. the mixture of the three amines distils over the quaternary salt does not react with KOH and being non-volatile is left behind.

Amine salts also react in this way.

The distillate contains the mixture of primary, secondary and tertiary amines. it may be separated by this method.

Hinsberg method :-

This involves the treatment of the mixture with benzene sulphonyl chloride (Hinsberg reagent).

The primary amine gives N-alkyl benzene sulphonamide this forms salt with NaOH, which is soluble in water.

The secondary amine gives N, N-dialkyl benzene sulphonamide. This does not form salt with NaOH (no acidic hydrogen) and is insoluble in alkali solution.

The tertiary amine doesn't react.

The resulting alkaline solution is distilled when the tertiary amine posses over and the remaining mixture is filtered. The filtrate on acidification gives the sulfonamide of the primary amine with the solid residue is the sulfonamide of the secondary amine. The two sulphonamides thus isolated are hydrolysed with concentrated HCl and distilled over NaOH to yield the respective amines

Benzene sulphonyl chloride has been replaced by P-toluene sulphonyl chloride, since the substituted sulfonamides thus formed are stable solids which can be easily re-crystallised.

Puvvukonvict................