Question

tertiary amines do not give hinsberg test why​

Answer 1

Why don’t tertiary amines react with Hinsberg reagents?

In the future, I'm going to use my computer, so I can answer pictorially. But for now, it will have to be text.

The Hinsberg Reagent is benzenesulfonyl chloride. You could write this as PhSO2Cl, where Ph = phenyl = the benzene ring to which something is attached.

It is an electrophile. (“Moderately reactive,” in the grand scheme of organic reactions.) Nucleophiles (Nu-H or Nu-) react with the electropositive S atom, displacing chloride ion (Cl-) and forming a new Nu-S bond.

So why don't tertiary amines react with PhSO2Cl?

The answer is that, on the timescale of a qualitative analytical test, the reaction is just too slow for product to form. There is a simple reason for this (and at least one complicated one that you don't need to worry about).

For a given heteroatom, the anionic form is always more nucleophilic than the neutral form. This is because the anion has much greater electron density around the heteroatom, and electron density is one of the important determinants of nucleophilic character. Primary and secondary amine can be deprotonated, to a very small but useful extent under the test conditions. The anionic nitrogen reacts quickly with PhSO2Cl. Tertiary amines can not be deprotonated, and can only be neutral nucleophiles. They are much, much slower to react, and so nothing happens on the timescale of the test.

(Note: Thermodynamically, the reaction is accessible. If you heat a tertiary amine with PhSO2Cl in an inert organic solvent, you will get the quaternized ammonium salt. But those conditions are very different from the Hinsberg Test.)