Which of the following amine do not respond to Hinsberg test?

N,N-Dimethyl aniline

The correct answer is Option (3) → N,N-Dimethyl aniline

Hinsberg reagent is benzenesulfonyl chloride ($C_6H_5SO_2Cl$), a colorless oily compound used in organic chemistry to distinguish between primary, secondary, and tertiary amines. It works by reacting with amines in the presence of alkali to form sulfonamides, which differ in solubility.

Detailed Explanation

Option 1: Aniline

Aniline is a primary amine.

Primary amines react with Hinsberg reagent to form sulphonamide which dissolves in alkali.

Hence it responds to the test.

Option 2: N-Methyl aniline

It is a secondary amine.

Secondary amines react with Hinsberg reagent to form sulphonamide but do not dissolve in alkali.

Hence it also responds to the test.

Option 3: N,N-Dimethyl aniline

It is a tertiary amine.

Tertiary amines do not react with Hinsberg reagent because they lack N-H bond.

Hence they do not respond to the test.

Option 4: o-Toluidine

It is a primary amine.

Thus it reacts with Hinsberg reagent and responds to the test.