Sciencemadness Discussion Board - Are hydrogen sulfite esters and sulfonic acids the same thing?

Are hydrogen sulfite esters and sulfonic acids the same thing?

weiming1998 - 4-6-2012 at 02:58

This question has always troubled me.

I know that sulfurous acid has not being observed in aqueous form, but can its esters form?

If they can, wouldn't a hydrogen sulfite ester be the exact same thing as a sulfonic acid? http://en.wikipedia.org/wiki/Sulfonic_acid

And if that is the case, would bubbling SO2 through a mix of water and alcohol, catalyzed by sulfuric acid, make a sulfonic acid/sulfonate ester? It certainly seems to be an extremely convenient way to produce them instead of using SO3 or the oxidation of thiols (which, apart from the fact that the production of them is much more than just bubbling H2S through alcohol, is that when you do make it, the stench would make you stay 1 km away!).

Searching on the internet yielded patents describing some obscure use for H2S, which is totally irrelevant, and even this website (http://www.webreactions.net/search.html) did not help because I cannot draw the structure of the reactants (it won't let me draw sulfur bonded to oxygens). That, or I don't know how to use the program properly.

turd - 4-6-2012 at 03:25

Uh no ... a sulfonic acid is obviously not an ester if you look at the structural formula in the Wikipedia article you posted.

And obviously there are esters of sulfurous acid (alkyl sulfites). It takes about 2 seconds of Googling to find this information.

All in all very incoherent.

woelen - 4-6-2012 at 03:31

No, sulfonic acids are derived from sulphuric acid, not sulphurous acid. They can be regarded as sulphuric acid with one of the OH-groups replaced by something else, such as a methyl group. Similar compounds, when derived from sulphurous acid are the so-called sulfoxides.

Sulphonates are not esters of sulphuric acid in the classical sense, because of the lack of an oxygen atom. Look at the difference between the monomethyl ester of sulphuric acid and methylsulphonic acid:

The methyl ester: CH3-O-S(OH)O2
methylsulfonic acid: CH3-S(OH)O2

In the esters, one can think of combination of an alcohol and an OH-group of the acid:

R-OH + HO-X --> R-O-X + H2O

In the sulfonates, you have true replacement of an OH-group by e.g. a methyl group.

For sulfites there is a similar difference. You have sulfite esters and sulfoxides. The difference is very similar, R-O-S(O)OH vs. R-S(O)(OH). the second (OH) group also can be replaced. An example of such a sulfoxide is dimethylsulfoxide. I'm not sure about the stability of monosubstituted sulfoxides.

After this explanation I think that you can easily imagine now that making sulfonates by simply bubbling SO2 through alcohol or water and alcohol does not work. This process also does not make sulfite esters and it also does not make sulfoxides.
Sulfite esters are possible. They can be prepared by reacting SOCl2 with suitable reagents under the right conditions. Not something for the average home chemist though.

[Edited on 4-6-12 by woelen]

Nicodem - 4-6-2012 at 04:04

Quote: Originally posted by weiming1998

If they can, wouldn't a hydrogen sulfite ester be the exact same thing as a sulfonic acid? http://en.wikipedia.org/wiki/Sulfonic_acid

Alkyl hydrogen sulfites are unstable and not isolable, upon formation immediately decomposing to an alcohol and SO₂. The salts are however stable, for example sodium methyl sulfite and similar. In principle, it should be possible to prepare alkali alkyl sulfites by the reaction of SO₂ with alkali alcoholates in the same alcohol, just like it is done with the isosteric alkali alkyl carbonates, but I'm not interested enough to actually check the literature.

weiming1998 - 4-6-2012 at 04:46

Oh damn.

http://en.wikipedia.org/wiki/Sulfurous_acid
Sulfurous acid is S(OH)2O, while sulfonic acids are S(=O)2–OH. Hydrogen sulfite esters are not the same thing as sulfonic acids. I got sucked into thinking that they are the same by this phrase in the article on sulfonic acids:

"The parent compound (with the organic substituent replaced by hydrogen) is the hypothetical compound sulfurous acid."

Looks like the phrase is wrong and sulfurous acid's stucture is totally different. Sorry about the mess-up. I'll try looking at better sites next time.

turd - 4-6-2012 at 05:01

Quote: Originally posted by weiming1998

"The parent compound (with the organic substituent replaced by hydrogen) is the hypothetical compound sulfurous acid."

Looks like the phrase is wrong and sulfurous acid's stucture is totally different. Sorry about the mess-up. I'll try looking at better sites next time.

The phrase is - from a conceptual point of view - not entirely wrong if you consider the hypophosphorous acid/phosphinic acid tautomerism.

I suggest you sit down and read one of the many educational texts on oxoacids.

weiming1998 - 4-6-2012 at 05:14

Quote: Originally posted by turd

Quote: Originally posted by weiming1998

Yes, you are right. Looking at the Wikipedia article on sulfurous acid again, it does describe an isomer of the hydrosulfite ion, HSO3-, that exists at an equilibrium with another isomer, HOSO2-. That makes them a tautomer.

I think I do need to read some more books.