Sulfonylation of Arenes to give sulfonic acids

by James

Description: Treatment of an aromatic molecule such as benzene with sulfur trioxide and a strong acid leads to formation of sulfonic acids.
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{ 9 comments… read them below or add one }

T.R.Prajapati April 29, 2012 at 9:56 am

i want to prepare sulfonic acid at small scale give us details.


james April 29, 2012 at 1:00 pm

You should hire a consultant.


Polina Porotsky February 12, 2015 at 4:52 pm

Does sulfonation activate the ring for future electrophilic aromatic substitutions?


James February 12, 2015 at 4:56 pm

No, SO3H is an electron withdrawing group so it actually deactivates the ring. Hope this helps! James


Polina Porotsky February 13, 2015 at 6:09 pm

Wonderful. Thank you. Electron withdrawing due to the electronegative oxygens, and the fact that the Pi orbitals are not the same size? Would it be useful as an instigator for addition-elimination nucleophilic aromatic substitution? (the same way that NO2 is?)


Taylore Bonn March 15, 2015 at 2:50 am

Why does benzene pie attack the S? It already has 6 bonds?


James March 17, 2015 at 10:57 pm

It’s not easy to do – but it happens. It’s much more difficult to perform this reaction on benzene than on an ordinary alkene. It’s usually important to heat this reaction.


Harry Paul July 9, 2015 at 9:59 pm

Since HSO4- is the conjugate base of a strong acid, how does it strong enough of a base to eliminate the proton (Step 3) to reform the aromatic benzene? I have seen a similar but different mechanism for this reaction that avoids this problem by initially having the pi bond attack SO3 rather than SO3H, resulting in an anion, at which point water acts as a base deprotonating to reform the aromatic system. This water is now a hydronium ion which is used to protonate the SO3- to become SO3H. How do I know which of these two mechanisms is correct?


James July 22, 2015 at 10:28 pm

The proton in question is extremely acidic as its conjugate base is quite stable (it’s aromatic).

If neutral water is present, then yes, neutral water would likely act as the base here.

Protonation of SO3 to give SO3H+ accelerates the reaction considerably. The rate limiting step is not deprotonation, but attack of the benzene ring on sulfur.


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