Separation Of Amine Mixtures

Question

A mixture of primary, secondary, and tertiary amines is separated using the Hinsberg reagent followed by treatment with alkali; which class is recovered unchanged after simple filtration and acidification steps?

RankGuru · Accepted Answer

The Hinsberg method separates a mixture of amines on the basis of their reactivity toward benzenesulphonyl chloride. A primary amine forms a sulphonamide bearing an acidic N–H, which dissolves in alkali as its salt and is later regenerated by acidification. A secondary amine forms a sulphonamide with no N–H, which remains an insoluble solid and is recovered separately. A tertiary amine has no N–H to react with the reagent, so it does not form any sulphonamide; it stays as the free amine and can simply be filtered or extracted unchanged, then collected directly. Therefore the tertiary amine is recovered without having undergone any reaction. The primary amine option is wrong because it must first be derivatised and then hydrolysed back, so it is not recovered unchanged in one step. The secondary amine likewise forms a sulphonamide that must be hydrolysed to regenerate the amine. The claim that none can be recovered contradicts the entire purpose of the separation. This classification-based separation is the standard NCERT and JEE Main application of the Hinsberg reagent. As a plausibility check, the tertiary amine's lack of any N–H explains why it alone emerges chemically untouched.

Separation Of Amine Mixtures

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