[ravendyg]

Everywhere I've seen it, the reaction is shown like

+ H⁺ = C₆H₆ + HSO₃⁺

But in case of high dilution in water the acid will be deprotonated (it is a strong one). Will the reaction

C₆H₅SO₃^- + H⁺ = C₆H₆ + SO₃

take place?

[Hunter2]

I never have seen this HSO₃⁺. Existing do HSO₃^-

Benzene sulfonic acid is very stable in water, also the second reaction wouldn't take place.

[ravendyg]

I never have seen this HSO₃⁺. Existing do HSO₃^-

Benzene sulfonic acid is very stable in water, also the second reaction wouldn't take place.

At high T sulfonation is reversible

Bruckner, Reinhard - Organic Mechanisms Reactions Stereochemist

As I understand it, in diluted H₂SO₄ there should be no hydrogen in the sulfonic groups. And also how would it proceed if we deal with sodium benzene sulfonate?

[Hunter2]

Here you have an naphthalen system with some more substituents, in some circumstance as here shown this reaction takes place in concentrated sulfuric acid.

In Benzene sulfonic acid  not much will happen.

see synthesis of it : http://en.wikipedia.org/wiki/Benzenesulfonic_acid

[ravendyg]

Here you have an naphthalen system with some more substituents, in some circumstance as here shown this reaction takes place in concentrated sulfuric acid.

Fine. Let's assume that this is naphthalene sulfonic acid in diluted sulfuric acid and sodium salt of this acid (just have not got a reference at hand, but in some textbooks they give example of desulfonation using bezene sulfonic acid; it does not matter much).

The acid is deprotonated (or there is an anion in solution in case of salt). What is the mechanism of desulfonation?