walengar@southwestern.edu - 7-2-2005 at 09:12
In preparing sulfanilamide from a nitro-benzene derivative, the first step is often the preparation of the chlorosulfonic acid derivative. Does anyone
know or have a reasonable guess as to why the product is chlorosulfonic acid instead of the SO3 product? Why does the Cl- come off the adduct
intermediate in some syntheses and the OH- come off in others?
Nicodem - 7-2-2005 at 10:07
The electron withdrawing character of Cl makes the Cl-SO2+ electrophyle more reactive than HO-SO2+ (which is in equilibrium with "SO3 + H+"
anyway). The other possible reason is, that it is much harder to imagine a formation of this later electrophyle from ClSO3H where HCl should
eliminate, while the formation of the former is simply the reslut of self protonation and H2O elimination.
I just assume it is because of this that you get the Ar-SO2Cl instead of Ar-SO3H. Not like I read this anywhere.
alchemie - 23-2-2005 at 12:13
Actually the Aromatic sulphonic acid, Ar-SO<sub>2</sub>OH, is an intermediate in the reaction. It gets Chlorinated by the excess
Chlorosulphonic acid to give the final product, Ar-SO<sub>2</sub>Cl.
According to the reaction conditions it is possible to get one or the other.
Resonance frequency - 24-10-2011 at 01:19
Hello, The CORRECT EXPLANATION IS
It requires two moles of chlorosulfonic acid per mole of aromatic moiety for chlorsulfonation purpose.
The first mole of chlorosulfonic acid reacts with aromatic moiety to give aromatic sulfonic acid --- Ar-H + Cl-SO3H--------> Ar-SO3H + HCl the
second mole of chlorosulfonic acid reacts with thus formed aromatic sulfonic acid to give chlorsulphonated product(aromatic sulfanilyl
chloride)--Ar-SO3H + Cl-SO3H-------> Ar-SO2Cl + H2SO4.
You can get the details in "chlorosulphonic acid: a versatile reagent"By Richard James William Cremlyn, Royal Society of Chemistry (Great Britain) ON
PAGE NUMBERS 04 & 12.The book preview is available on GOOGLE BOOKS the mentioned page numbers are also available in free preview.