Question

How are arenediazonium salts formed when it comes to benzene reactions? What kinds of reactions can it undergo?

Answer 1

Azo compounds contain nitrogen, and "onium salt" implies it is positively charged (like ammonium). When we talk about diazonium salts, we are probably referring to arenediazonium salts.

Essentially an arenediazonium salt is a benzene ring with an `""^((+))"N"-="N"` group on it.

We would get it by reacting aniline with `"NaNO"_2` in `"HCl"(aq)` at about `0^@ "C"`.

1. Nitration
2. Reduction catalyzed by palladium over carbon
3. Reaction with nitrous acid in situ

These can react in various ways, and you can achieve stereochemical control. i.e. you can achieve specifically para products if you manage to find a para-disubstituted benzene that contains the `"NH"_2` group on it to start with, or meta if you need to, etc., with better yields of that specific isomer.

Here are a few example reactions (Organic Chemistry, Bruice, pp. 684-686):

The three copper-catalyzed reactions (the ones with `"CuBr"`, `"CuCl"`, and `"CuCN"`) are Sandmeyer reactions. The `"KI"` reaction is known as the Schiemann reaction.

In each of these cases, `"N"_2` gas will leave the solution.