Trifluoromethanesulfonic acid catalyzed preparation of symmetrical diaryl sulfoxides from arenes and thionyl chloride

Article abstract of DOI:10.1055/s-1999-2861

The preparation of symmetrical diaryl sulfoxides from thionyl chloride and arenes catalyzed by trifluoromethanesulfonic acid is described. The reaction is characterized by its mildness, high yields, selectivity, and ease of workup.

Full text of DOI:10.1055/s-1999-2861

LETTER
1397
Trifluoromethanesulfonic Acid Catalyzed Preparation of Symmetrical Diaryl
Sulfoxides from Arenes and Thionyl Chloride1
George A. Olah*, Eric R. Marinez, G. K. Surya Prakash*
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1661
Received 27 June 1999
Abstract: The preparation of symmetrical diaryl sulfoxides from
thionyl chloride and arenes catalyzed by trifluoromethanesulfonic
acid is described. The reaction is characterized by its mildness, high
yields, selectivity, and ease of workup.
Key words: trifloromethanesulfonic acid, thionyl chloride, sulfox-
ide, arenes
Methodology for the direct preparation of sulfoxides is
limited. Usually, the synthesis of sulfoxides is accom-
plished by the oxidation of sulfides, the reduction of sul-
fones, or by the reaction of sulfinic acid esters or
anhydrides with organometallic reagents.2 Laali and
Nagvekar have found that diaryl sulfoxides can be ob-
tained from SO2 and aromatics in Magic Acid (FSO3H/
SbF5) in good yields.3 This represents the reaction of in
situ formed arenesulfinic acid with arenes. However,
Magic Acid is a very corrosive, oxidizing, and difficult to
handle reagent. Recently Tsuchida et al. have obtained di-
aryl sulfoxides from the sodium salt of benzene sulfinate
with trifluoromethanesulfonic acid (triflic acid) in good
yields.4 The direct preparation of diaryl sulfoxides
through the electrophilic activation of thionyl chloride is
practically unexplored. First studied in 1887 by Colby and
McLaughlin,5 the AlCl3 catalyzed reaction produces mod-
erate yields of diaryl sulfoxides with activated aromatics
and produces in addition to the sulfoxide the correspond-
ing sulfonium salt.2 We now report the ready preparation
of symmetrical diaryl sulfoxides from arenes with thionyl
chloride catalyzed by trifluoromethanesulfonic acid in
high yields under mild conditions and high selectivity.
O
TfOH
SOCl2
+
2 ArH
Ar
S
Ar
- 2 HCl
Scheme 1
the aluminum chloride catalyzed arenesulfinylation of
benzene and polymethylbenzenes in nitromethane in
which they concluded that the sulfinylating agent is a
weak electrophile in contrast to that involved in sulfony-
lation.6
As shown in the Table, yields are for isolated products and
are essentially quantitative for activated aromatics, but
drop drastically with deactivated aromatics. a,a,a-Triflu-
orotoluene and nitrobenzene do not react under the reac-
tion conditions. A further feature is that longer reaction
times are needed for less activated aromatics. The reaction
also shows high selectivity in that no sulfonium salts, sul-
fides, and sulfones are observed. Toluene, bromobenzene,
and chlorobenzene gave only para substituted products.
This agrees with Olah and Nishimura’s detailed studies on
In general, Friedel-Crafts methodology requires the use of
excess aromatic in order to minimize further reaction. In
the sulfinylation reaction of benzene with thionyl chlo-
ride, it has been found that CH2Cl2 can be used as an alter-
native solvent. However, the yield went from 92% to 80%
when benzene was replaced with CH2Cl2 as the solvent. In
the reaction of biphenyl which used CH2Cl2 as solvent,
Synlett 1999, No. 9, 1397–1398 ISSN 0936-5214 © Thieme Stuttgart · New York

1398
G. A. Olah et al.
LETTER
when a 1 SOCl2: 4 biphenyl mole ratio was employed, the arylsulfonium salts which are used as photoactive cationic
sulfoxide was produced in 88% yield. However, when a 1 initiators7 and for the photogeneration of protonic acid in
SOCl2: 1 biphenyl mole ratio was used, a polymer resulted the lithographic resist field.8,9
which could not be characterized due to insolubilty in all
solvents investigated.
Acknowledgement
A typical procedure is as follows: To 1.2 mL (16.4 mmol)
thionyl choride is added 40 mL of aromatic in a 100 mL
Schlenk flask under argon. The flask is cooled to 0 °C and
The support of our work by the Loker Hydrocarbon Research Insti-
tute is gratefully acknowledged.
stirred while 6.2 mL (70.6 mmol) of triflic acid is added.
References and Notes
HCl is generated and vented through the stop cock of the
Schlenk flask. After 1 hr, the reaction is allowed to further
stir at room temperature for the indicated time shown in
the Table. The reaction mixture gradually turns to a dark
purple color as the reaction progresses. It is quenched by
pouring into ice and neutralized with NaHCO3. Extraction
with CH2Cl2, drying the organic extract with MgSO4 , fil-
teration followed by rotary evaporation provides a white
solid that is recrystallized. All products are known in the
literature and were characterized by 1H and 13C NMR, IR,
GC-MS in addition to their melting points.
(1) Considered Synthetic Methods and Reactions, Part 203. for
Part 202 see, Buchholz, H.; Prakash, G. K. S.; Deffieux, D.;
Olah, G. A. Angew. Chem. Int. Ed. Engl. submitted.
(2) Drabowicz, J.; Kielbasinski, P.; Mikolajczyk, M. In The
Chemistry of Sulfones and Sulfoxides; Patai, S., Rappoport,
Z., Stirling, C. J. M., Eds.; Wiley: New York, 1988; Chapter 8.
(3) Laali, K. K.; Nagvekar, D. S. J. Org. Chem. 1991, 56, 1867.
(4) Yamamoto, K.; Miyatake, K.; Nishimura, Y.; Tsuchida, E.
Chem. Commun. 1996, 2099.
(5) Colby, C. E.; McLaughlin, C. S. Ber. 1887, 20, 195.
(6) Olah, G. A.; Nishimura, J. J. Org. Chem. 1974, 39, 1203.
(7) Crivello, J. V.; Lam, J. H. W. Macromolecules 1977, 10, 1307.
(8) Miller, R. D.; Renaldo, A. F.; Ito, H. J. Org. Chem. 1988, 53,
5571.
In conclusion, the preparation of symmetrical diaryl sul-
foxides is readily achieved by the electrophilic reaction of
thionyl chloride with aromatics catalyzed by triflic acid.
The reaction is characterized by high yields, high selectiv-
ity and ease of work-up and purification of products. De-
spite that deactivated aromatics do not react under the
reaction conditions, this methodology of diaryl sulfoxides
should provide a convenient route to the preparation of tri-
(9) Uhrich, K. E.; Reichmanis, E.; Heffner, S. A.; Kometani, J.
M.; Nalamasu, O. Chem. Mater. 1994, 6, 287.
Article Identifier:
1437-2096,E;1999,0,09,1397,1398,ftx,en;S02699ST.pdf
Synlett 1999, No. 9, 1397–1398 ISSN 0936-5214 © Thieme Stuttgart · New York