The first catalytic sulfoxidation of saturated. Hydrocarbons with SO2/O2 by a vanadium species [3]

Full text of DOI:10.1021/ja000333w

7390
J. Am. Chem. Soc. 2000, 122, 7390-7391
Table 1. Sulfoxidation of Adamantane (1) by SO2/O2 Catalyzed by
VO(acac)2
The First Catalytic Sulfoxidation of Saturated
Hydrocarbons with SO2/O2 by a Vanadium Species
a
Yasutaka Ishii,* Katsuhisa Matsunaka, and Satoshi Sakaguchi
Department of Applied Chemistry
Faculty of Engineering & High Technology Research Center
Kansai UniVersity, Suita, Osaka 564-8680, Japan
ratio of SO2/O2
(atm/atm)
conv.
(%)
select.
(%)
run
catalyst
VO(acac)2
nothing
VO(acac)2
VO(acac)2
V(acac)3
VOCl3
1
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
0.5/0.5
43
98
ReceiVed January 31, 2000
2
no reaction
no reaction
3b
4c
5
Selective and efficient activation of unreactive C-H bonds in
aliphatic hydrocarbons is particularly difficult and is one of the
major challenges in chemistry.1 In contrast to the liquid phase
sulfoxidation of aromatic hydrocarbons which has been exten-
sively studied, work on the sulfoxidation of saturated hydrocar-
bons to alkylsulfonic acids remains at a less satisfactory level. In
general, alkylsulfonic acids are prepared by the Strecker synthesis
using alkyl halides, preferably alkyl bromides, and an alkali metal
or ammonium sulfides,2 and by the oxidation of thiols with
bromine in the presence of water or hydrogen peroxide combined
with acetic acid.3 Until recently, there have been very few studies
on the sulfoxidation of saturated hydrocarbons, despite their
importance probably because of the difficulty in cleaving the
carbon-hydrogen bond. Thus, photo- and peroxide-initiating
sulfoxidations, which proceed through a radical process, are
usually employed for alkanes such as cyclohexane using a mixture
of SO2 and O2.4a,b Alkanes are known to react with SO2/Cl2
through a radical route under irradiation of light to form the
corresponding sulfonyl chlorides.4c However, the efficiency of
the sulfoxidation by these methods is insufficient to produce
alkylsulfonic acids, and no real progress can be made in the
sulfoxidation of alkanes. Therefore, if alkanes can be sulfoxidated
catalytically by SO2/O2 without irradiation of light or in the
absence of peroxide, such a method has enormous synthetic
potential and provides a very attractive route to alkylsulfonic acids.
However, such sulfoxidation of alkanes via a catalytic process
has not been realized so far. We have recently developed the
oxidation of alkanes to oxygen-containing compounds with
molecular oxygen using N-hydroxyphthalimide which serves as
the radical catalyst.5 In the course of our work, we studied the
sulfoxidation of alkanes using SO2/O2, and found that vanadium
compounds catalyze efficiently the sulfoxidation of alkanes under
mild conditions. In this paper, we wish to report the first catalytic
sulfoxidation of saturated hydrocarbons by SO2/O2 in the presence
of a catalytic amount of a vanadium species such as VO(acac)2
under mild conditions (eq 1).
64
50
39
56
15
37
89
80
54
94
88
81
94
85
88
n.d.
78
64
85
98
27
65
6
7
8
9
10
11
12c
13
14c
VO(C17H35COO)2 0.5/0.5
VOSO4
0.5/0.5
0.5/0.5
0.67/0.33
0.67/0.33
0.67/0.33
0.75/0.25
0.75/0.25
VO(OiPr)3
VO(acac)2
VOCl3
VO(acac)2
VO(acac)2
VO(acac)2
a 1 (2 mmol) was allowed to react under 1 atm of SO2/O2 (∼2 L) in
AcOH (10 mL) in the presence of VO(acac)2 (0.01 mmol). b In the
presence of hydroquinone (1 mol%). c Reaction condition was 25 °C,
24 h. Conversion (%) was based on the molar ratio of 1 consumed to
1 added. Selectivity (%) was based on the molar ratio of 2 formed to
1 reacted.
atm of a 1:1 mixture of SO2 and O2 in the presence of VO(acac)2
(0.5 mol %) in acetic acid at 40 °C for 2 h produced 1-adamantane
sulfonic acid (2) in 98% selectivity at 43% conversion of 1.6 The
X-ray measurement shows that 2 crystallized as the monohydrate
C10H15SO3H‚H2O (2‚H2O) (Figure 1).7
Although the photosulfoxidation of 1 with SO2/O2 in the
presence of H2O2 at 70 °C for 1 h gives 2‚H2O (15%),8 our
sulfoxidation is thought to be the first catalytic method for the
synthesis of 2. Needless to say, no sulfoxidation took place in
the absence of VO(acac)2 (run 2). To reveal the potential of
various metal ions on the present sulfoxidation, 1 was allowed
to react in the presence of a series of first row transition metal
salts, TiO(acac)2, Cr(acac)3, Mn(acac)3, Fe(acac)3, Co(acac)2, Ni-
(OAc)2, and Cu(OAc)2 under these conditions. It is interesting to
note that no sulfoxidation of 1 was induced by these metal salts
other than vanadium ions.9 Thus, various vanadium salts were
examined. Among the vanadium compounds used, VO(acac)2 and
V(acac)3 were found to be good catalysts. Surprisingly, the
sulfoxidation of 1 was promoted by VO(acac)2 even at room
(4) (a) Bjellqvist, B. Acta Chem. Scand. 1973, 27, 3180-3194. (b)
Ferguson, R. R.; Crabtree, R. H. J. Org. Chem. 1991, 56, 5503-5510. (c)
Crabtree, R. H.; Habib, A. ComprehensiVe Organic Synthesis; Trost, B. M.,
Ed.; Pergamon Press: New York, 1991; Vol 7., p 14 and references therein.
(5) Ishii, Y.; Iwahama, T.; Sakaguchi, S.; Nakayama, K.; Nishiyama, Y.
J. Org. Chem. 1996, 61, 4520-4526.
(6) A typical reaction procedure is as follows: A solution (5 mL) of 1 (2
mmol), VO(acac)2 (3 mg) was placed in a pear-shaped flask equipped with a
balloon filled with SO2 (0.5 atm) and O2 (0.5 atm). The mixture was stirred
at 40 °C for 2 h and then extracted with ethyl acetate. The aqueous layer was
concentrated by evaporation, and the solid obtained was recyrystallized
carefully with ethyl acetate.
(7) The compound 1 crystalized in the orthorhombic space group P21/m
with cell dimensions of a ) 8.5046(9) Å, b ) 6.5354(6) Å, and c ) 10.1605-
(7) Å; â ) 10.037(7)°, V ) 545.40(9) Å3, and an occupation of Z ) 2 in cell
unit. Data were collected at 23.0 ( 1 °C on an AFC7R Rigaku diffractometer
(Cu KR radiation), to a maximum 2q ) 120.1°, giving 897 unique reflections;
the structure was solved by direct methods (SIR88) and refined within full
matrix least squares, yielding R ) 0.072, Rw ) 0.141 (GOF ) 9.76) for 887
unique reflections with I > 3.00σ(I). Elemental analysis data are as follows:
Anal. Calcd for C10H18O4S: C, 51.26; H, 7.74. Found: C, 51.11, H, 7.55.
(8) Smith, G. W.; Williams, H. D. J. Org. Chem. 1961, 26, 2207-2212.
(9) A review for the modern synthesis using vanadium species as a catalyst
has been reported: Hirao, T. Chem. ReV. 1997, 97, 2707-2724.
The sulfoxidation of adamantane (1) was chosen as a model
reaction and allowed to react with a mixture of SO2 and O2 under
various reaction conditions (Table 1). The reaction of 1 under 1
(1) (a) Hill, C. L. ActiVation and Fanctionalization of Alkanes; Wiley: New
York, 1989. (b) Davies, J. A.; Watson, P. L.; Liebman, J. F.; Greenberg, A.
SelectiVe Hydrocarbon ActiVation, Principles and Progress; VCH: Weinheim,
1990. (c) Olah, G. A.; Molna´r, A. Hydrocarbon Chemistry; Wiley: New York,
1995. (d) Arndtsen, A. B.; Bergman, G. R.; Mobley, A. T.; Peterson, H. T.
Acc. Chem. Res. 1995, 28, 154-162. (e) Shilov, A. E.; Shul’pin, G. B. Chem.
ReV. 1997, 97, 2879-2932. (f) Dyker, G. Angew. Chem. Int. Ed. 1999, 38,
1698-1712.
(2) (a) Ullmann’s Encyclopedia of Industrial Chemistry; VCH: Weinheim,
1994; Vol. A25, pp 503-506. (b) Beringer, F. M.; Falk, R. A. J. Am. Chem.
Soc. 1959, 81, 2997-3000.
(3) (a) Young, H. A. J. Am. Chem. Soc. 1937, 59, 811-812. (b) Murray,
R. C. J. Chem. Soc. 1933, 739-740.
10.1021/ja000333w CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/14/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7391
Table 2. Sulfoxidation of Various Alkanes by SO2/O2 Catalyzed
by VO(acac)2
Scheme 1. Possible Reaction Path for V-Catalyzed
Sulfoxidation
a
56% conversion. Unfortunately, methane was not reacted at all
under these reaction conditions.11
The sulfoxidation of 1 seems to proceed via the following
reaction steps. The sulfoxidation may be initiated by one-electron
transfer from adamantane 1 to a V(V) species generated in situ
from VO(acac)2 and O2 to form an adamantantyl cation radical
which readily liberates a proton to form an adamantyl radical
[A].12 The resulting [A] is trapped by SO2 and then O2 to generate
an adamantylsulfonylperoxy radical [B] which is eventually
converted into 3 through the well-known reaction path.13 A V(IV)
species is reported to undergo the disproportionation to V(V) and
V(III) in the oxidative polymerization of diphenyl disulfide by
the vanadium ion under dioxygen atmosphere.14 In addition,
R-hydroxycarbonyl compounds are oxidized to R-dicarbonyl
compounds by VOCl3 and VO(acac)2 under an oxygen atmo-
sphere.15 In our reaction system, it is reasonable to assume that
a V(V) species is generated from VO(acac)2 under the influence
of SO2/O2 in the course of the reaction. In fact, adamantane 3
was oxidized to 3,5-dimethyladamantan-1-ol (15) in the presence
of a catalytic amount of VO(acac)2 (0.5 mol %) under a dioxygen
atmosphere. This shows that an adamantyl radical derived from
3 is formed and then oxygenated with O2 to form 15 (Scheme 1
and eq 2).
a The reaction was carried out under the same conditions as run 1 in
Table 1. b Ratio of SO2/O2 was 0.67/0.33 atm. c A mixture of 2-, 3-,
and 4-octane sulfonic acids. Conversion and selectivity were calculated
as the same way as Table 1.
temperature to form 2 in 81% selectivity at 64% conversion after
24 h (run 4). However, when a small amount of hydroquinone
was added to the present reaction system, the reaction did not
take place at all (run 3). These observations strongly suggest that
a radical chain process is involved in the present catalytic
sulfoxidation.
When a 2:1 mixture of SO2 and O2 was employed for the
sulfoxidation of 1, the reaction was performed in high conversion,
but the selectivity to 2 decreased slightly. It is interesting to note
that the same reaction at room temperature produced 2 in almost
complete selectivity (98%) at 54% conversion (run 12). The
sulfoxidation of 1 using a SO2/O2 ) 3/1 ratio at 40 °C resulted
in a considerable amount of undesired byproducts other than 2
(run 13).
In conclusion, we have developed the first catalytic sulfoxi-
dation of alkanes by SO2/O2 under the influence of VO(acac)2
under mild conditions. This method provides a novel approach
to alkylsulfonic acids which have been difficult to prepare so far.
On the basis of these results, several cycloalkanes were allowed
to react using a 1:1 mixture of SO2 and O2 (SO2/O2 ) 0.5/0.5
atm) in the presence of VO(acac)2 (0.5 mol %) under selected
reaction conditions (Table 2). 1,3-Dimethyladamantane (3) and
1-adamantanecarboxylic acid (5) were also subjected to sulfoxi-
dation to form 1,3-dimethyladamantane-5-sulfonic acid (4) and
1-carboxyadamantane-3-sulfonic acid (6), respectively, in high
selectivities. 1-Chloroadamantane (7) was also sulfoxidated by
the present system to give 1-chloroadamantane-3-sulfonic acid
(8) (95%) in slightly lower conversion (56%). Thus, the sulfoxi-
dation using a 2:1 mixture of SO2/O2 gave 8 in high conversion
(82%) and selectivity (91%). Furthermore, cyclohexane (9) and
cyclooctane (11) formed the corresponding sulfonic acids, cy-
clohexanesulfonic acid (10) and cyclooctanesulfonic acid (12),
respectively. Aliphatic hydrocarbon, octane (13), afforded a
mixture of 2-, 3-, and 4-octanesulfonic acids (14)10 in 83% at
Acknowledgment. This work was partly supported by Research for
the Future program JSPS and Grant-in-Aid for Scientific Research (No.
10450337) from Monbusho.
Supporting Information Available: Experimental details for the
general procedure and compound characterization data for all products
as well as Figure 1 (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
JA000333W
(11) The reaction was carried out using 50 mL-Teflon autoclave. Methane
(15 atm) was allowed to react under SO2 (2.5 atm) and O2 (2.5 atm) in the
presence of VO(acac)2 (3 mg) in AcOH (5 mL) at 60 °C for 36 h.
(12) The generation of an alkyl radical by the hydrogen atom abstraction
from an alkane by V(V) ion has been suggested as an alternative possibility
by a reviewer.
(13) Graf, R. Ann. 1952, 578, 50-82.
(14) Yamamoto, K.; Tsuchida, E.; Nishide, H.; Jikei, M.; Oyaizu, K.
Macromolecules 1993, 26, 3432-3437.
(10) The octane sulfonic acids formed were difficult to isolate each isomer,
and were found to consist of about a 1:1:1 regioisomeric mixture of 2, 3, and
4-octane sulfonic acids by the LC and NMR measurements.
(15) Kirihara, M.; Ochiai, Y.; Takizawa, S.; Takahata, H.; Nemoto, H.
Chem. Commun. 1999, 1387-1388.