Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 6607–6609
A novel method for sulfonation of aromatic rings with silica
sulfuric acid
c
a
c
Abdol R. Hajipour,a,b, Bi Bi F. Mirjalili, Amin Zarei, Leila Khazdooz
*
and A. E. Ruohob
aPharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
bDepartment of Pharmacology, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706-1532, USA
cDepartment of Chemistry, College of Science, Yazd University, Yazd, Iran
Received 3 June 2004; revised 2 July 2004; accepted 6 July 2004
Available online 23 July 2004
Abstract—Direct and chemoselective sulfonation of aromatic compounds with silica sulfuric acid in 1,2-dichloeoethane or under
solvent-free conditions.
ꢀ 2004 Elsevier Ltd. All rights reserved.
The sulfonation of aromatic compounds are very impor-
tant and many aromatic hydrocarbons have been sulfo-
nated.1,2 The common methods for synthesis of sulfonic
acids are employing oxidation of a thiol or a thioether
with ether,3 sulfonation of Grignard and lithium rea-
gents,4 nucleophilic aromatic substitution with sodium
sulfite,5 sulfonation of aromatic compounds with con-
centrated sulfuric acid,6 sulfonation with sulfur tri-
oxide–dioxane complex,7 trifluro acetic acid–sulfuric
acid,8 and sulfur trioxide in dichloromethane.9
O
S
SiO2
O
OH
O
I
for conversion of a variety of aromatic compounds in
1,2-dichloroethane or in excess of substrate without
using any solvent to the corresponding sulfonic acids
(Scheme 1). In sulfonation of aromatic compounds,
the sulfonic acids are often in equilibrium with sulfones
as a byproducts. However, at lower temperatures the
equilibrium is very slow and is favorable for the forma-
tion of corresponding sulfonic acids.11 In this method
since silica sulfuric acid is used for sulfonation at mod-
erate temperature and also as silica sulfuric acid is
bulky, therefore this reagent reacts with high selectivity
and the reverse reaction is low and the sulfones are not
produced at all. We tried the reaction of silica sulfuric
acid in excess of a variety of aromatic compounds with-
out using any solvent at 80ꢁC (Table 1). In comparison
to reaction in 1,2-dichloroethane at 80ꢁC, the yield of
the reaction in excess of substrate is higher; this
may be due to the high concentration of substrate in
the later method. Another noteworthy point of this
In continuation of our studies on the application of solid
acids we found that silica gel reacts with chlorosulfonic
acid to give silica sulfuric acid (I). It is interesting to note
that the reaction is easy, clean and without any needed
work-up procedure because HCl gas is evolved from
the reaction vessel immediately. We also found that sil-
ica sulfuric acid (I) is an excellent candidate for sulfuric
acid replacement in organic reactions without any limi-
tations such as destruction of acid sensitive functional
groups.10 To determine the stability of this reagent, we
kept 1g of the reagent at 200ꢁC for 8h and discovered
that the reagent did not lose any weight or activity.
We wish here to report a mild and efficient method for
synthesis of arylsulfonic acids with silica sulfuric acid
80 ˚C
Keywords: Sulfonation; Silica sulfuric acid; Aromatic compound;
Sulfonic acid.
ArSO3H + SIO2-OH
ArH + SIO2O-SO3H
30 min
*
Corresponding author. Tel.: +98-113913262; fax: +98-112350;
Scheme 1.
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.07.023