Iron-catalyzed selective oxidation of sulfides to sulfoxides with the polyethylene glycol/O2 system

Article abstract of DOI:10.1039/c1gc15821j

Readily available iron compounds were found to be active catalysts for the selective oxidation of sulfide to sulfoxide with molecular oxygen as the oxidant in polyethylene glycol (PEG). As an indispensable component, PEG had a great promotive effect on the reaction. Notably, high conversion (>99%) along with excellent chemo-selectivity of up to 94% could be attained by using Fe(acac)₂ as the catalyst at 100 °C. This methodology was proved to be applicable for the transformation of various aromatic and aliphatic sulfides into the corresponding sulfoxides with high selectivity. PEG is considered to play a crucial role in stablizing the Fe(IV)-oxo species formed in situ which is supposed to be responsible for the sulfide oxidation.

Full text of DOI:10.1039/c1gc15821j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Green Chemistry
Cite this: Green Chem., 2012, 14, 130
www.rsc.org/greenchem
PAPER
Iron-catalyzed selective oxidation of sulfides to sulfoxides with the
polyethylene glycol/O2 system†
Bin Li, An-Hua Liu, Liang-Nian He,* Zhen-Zhen Yang, Jian Gao and Kai-Hong Chen
Received 10th July 2011, Accepted 3rd October 2011
DOI: 10.1039/c1gc15821j
Readily available iron compounds were found to be active catalysts for the selective oxidation of
sulfide to sulfoxide with molecular oxygen as the oxidant in polyethylene glycol (PEG). As an
indispensable component, PEG had a great promotive effect on the reaction. Notably, high
conversion (>99%) along with excellent chemo-selectivity of up to 94% could be attained by using
Fe(acac)2 as the catalyst at 100 ◦C. This methodology was proved to be applicable for the
transformation of various aromatic and aliphatic sulfides into the corresponding sulfoxides with
high selectivity. PEG is considered to play a crucial role in stablizing the Fe(IV)-oxo species
formed in situ which is supposed to be responsible for the sulfide oxidation.
So far, a large number of metal catalysts have been developed
Introduction
for the sulfide oxidation, including V,8 W, 9 Ti,10 Mn,11 Co,3a
Cu,12 and Ag.13 In particular, iron would be an ideal candidate
to be an environmentally benign catalyst because of its easy
availability, low toxicity and low price as well as exceptional
catalytic activity.14 In recent years, significant advances in
sulfide oxidation15 has been accomplished by applying iron cat-
alysts, such as Fe(NO3)3/FeBr3,5a,16 Fe(acac)3/Schiff base,17 and
Fe(Salen)18 oxidative systems. However, those iron-catalyzed
processes would either involve complicated ligands to stabilize
iron reactive species, or need toxic solvents to promote the
reaction. In this aspect, an environmentally benign process
remains in great demand.
With respect to such aspects of innocuous chemistry, sig-
nificant effort has been devoted to the development of sulfide
oxidation in green solvents, such as supercritical carbon dioxide
(scCO2)19 and water.18a While water would probably be the most
desired reaction medium, the inherent hydrophobic nature of the
sulfides often prohibits its aqueous reactivity, and the sensitivity
of many catalysts in hydrous conditions can not be neglected.20
PEG and its derivatives are commonly known to be inexpensive,
thermally stable, and environmentally benign media for chemical
reactions and phase transfer catalysts as well as having an almost
negligible vapor pressure.21 In particular, Neumann found that
PEG-200 could act as an excellent solvent for H5PV2Mo10O40-
catalyzed aerobic oxidation reactions including the oxidation
of sulfides.20 PEG also can be utilized as a support, leading to
recycling of homogeneous catalysts with remarkable synergic
effect.22 An environmentally benign scCO2/PEG biphasic sys-
tem was successfully used in the aerobic oxidation of styrene.23
Recently, we have found that the PEG radicals from its oxidative
degradation24 could be used to induce oxidation of benzylic
alcohols and benzylic C–H bond oxygenation in compressed
Organic sulfoxides have wide applications in the synthesis of
chemically useful and biologically active molecules such as
drugs, flavors, germicides as well as catabolism regulators.1
The common synthetic method for the formation of sulfoxide
is the oxidation of organic sulfides (Scheme 1). However,
a stoichiometric amount of organic or inorganic oxidant is
required in those preparative processes and thus a large amount
of toxic waste would be generated.2 With the increasing environ-
mental and economical concerns in recent years, the procedures
employing hydrogen peroxide3 or molecular oxygen4 as terminal
oxidants would be promising because only water is produced
as the sole by-product. In this aspect, those catalytic processes
involving dioxygen, which is an abundant, inexpensive and
easily available oxidant are particularly attractive. However, few
successful reaction systems have been established.4a,5 Still, toxic
organic solvents such as toluene,4b methanol,6 and acetonitrile7
as well as ligands and/or metal additives would be inevitably
needed to perform the reaction smoothly.
Scheme 1 Oxidation of sulfides.
State Key Laboratory and Institute of Elemento-Organic Chemistry,
Nankai University, Tianjin, 300071, People’s Republic of China.
E-mail: heln@nankai.edu.cn; Fax: +86 22 2350 1493; Tel: +86 22-2350
1493
† Electronic supplementary information (ESI) available: General exper-
imental methods, experimental procedures, characterization products
and copies of the NMR spectra. See DOI: 10.1039/c1gc15821j
130 | Green Chem., 2012, 14, 130–135
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
elevated temperature (100 ◦C) is required for the reaction. When
the temperature was further increased to 120 ◦C, the same result
as that at 100 ◦C was obtained (entry 6 vs. 2, Table 1). It is also
worth mentioning that shortening the reaction time to 2 h gave
rise to selective formation of the sulfoxide product as the main
product in 93% yield rather than the sulfone product (entry 7
vs. 2, Table 1), suggesting that aerobic oxidation could proceed
through an initial oxidation of the sulfide to the sulfoxide, and
further oxidization of the sulfoxide to the sulfone as the reaction
progressed.
Next we screened various iron catalysts, including Fe(acac)3,
FeCl2, FeCl3, FeBr2, FeBr3, Fe(NO3)3·9H2O (entries 8–13, Table
1) with an aim to investigate anion effect on the iron’s catalytic
performance. Fe(acac)3 and Fe(acac)2 gave almost the same
results (entries 7 and 8, Table 1). However, in the case of chloride
or bromide as the anion, neither Fe(III) or Fe(II) can catalyze
the oxidation reaction resulting in only starting material being
recovered (entries 9–12, Table 1). In addition, Fe(NO3)3·9H2O
gave a relatively low yield of sulfoxide as the main product (51%)
compared with Fe(acac)2 (entry 7 vs. 13, Table 1). These results
could suggest that oxygen-donor anions are effective for iron-
catalyzed oxidation of sulfides, presumably because the electron
richness of the iron catalyst is an important factor in stabilizing
the iron species generated in situ to achieve oxygen transfer from
molecular oxygen to the sulfide.26 Fe(acac)2 as a catalyst, proved
effective for the reaction even when the catalyst loading was as
low as 1 mol% (entry 14, Table 1).
This kind of oxygenation reaction was completely suppressed
by adding 10 mol% of TEMPO (2,2,6,6-tetramethyl-piperidine-
1-oxyl) (entry 15, Table 1), which supports the free radical
reaction pathway.25c
Furthermore, to evaluate the role of trace amounts of metal
impurities or contaminants (typically copper oxide in iron
salts),27 Fe(acac)2 with 99.95% purity was employed for this
sulfide oxidation. The results show that almost the same results
were obtained (entry 7 vs. 16, Table 1). On the other hand, Cu(I)
oxide and Cu(II) oxide can not catalyze the reaction, leaving the
thioanisole intact (entries 17–18, Table 1).
Table 1 Aerobic oxidation of thioanisole using commercially available
iron catalysts in PEG-1000a
Entry Cat. (2 mol%)
Time (h) Conv (%)b Yield (%)b
Sulfoxide Sulfone
1
None
12
12
12
12
12
12
2
2
2
2
2
2
2
2
2
2
2
2
0
100
0
0
4
0
4
28
3
93
91
—
—
—
—
51
94
0
0
96
0
0
0
97
7
7
—
—
—
—
0
2
Fe(acac)2
Fe(acac)2
Fe(acac)2
Fe(acac)2
Fe(acac)2
Fe(acac)2
Fe(acac)3
FeCl2
FeCl3
FeBr2
FeBr3
Fe(NO3)3·9H2O
Fe(acac)2
Fe(acac)2
Fe(acac)2
Cu2O
3c
4d
5e
4
28
100
100
98
<1
<1
<1
<1
51
>99
0
6f
7
8
9
10
11
12
13
14g
15h
16i
17
18
6
0
3
0
97
0
0
94
0
0
CuO
0
a All the experiments were carried out with 0.5 mmol (62 mg) of
thioanisole, PEG-1000 (0.3 mmol, 0.3 g), O2 (2 MPa), 100 ◦C,
unless otherwise noted. b Determined by GC using area normalization.
c Without PEG. d Air (balloon). e 80 ◦C. f 120 ◦C. g Fe(acac)2 (1 mol%).
h TEMPO (0.05 mmol) was added. i Fe(acac)2 was purchased from
Sigma–Aldrich with 99.95% purity.
CO2.25 In brief, PEG could effectively immobilize and stabilize
the metal catalysts, and may provide a more active oxidant by
incorporating oxygen into the peroxide species.
Herein, we wish to report an efficient process for the selective
synthesis of sulfoxides through the Fe(acac)2-catalyzed aerobic
oxidation of sulfides with molecular oxygen as an oxidant in
PEG. This approach represents a more environmentally friendly
method for the sulfoxidation with potential economic benefits.
Results and discussion
Thioanisole was chosen as a model substrate for a preliminary
study. The results are summarized in Table 1. The oxidation
was first examined with 0.5 mmol of PEG-1000 (molecular
weight: 1000 Da) and 2.0 MPa of O2 at 100 ◦C for 12 h.
Under such conditions, no oxidation product was detected
and only intact substrate was recovered (entry 1, Table 1),
indicating that PEG/O2 can not initiate the sulfide oxidation.
This is different from oxidation reactions initiated by PEG
radicals in compressed CO2.25c Fortuitously, a catalytic amount
of Fe(acac)2 could remarkably promote the reaction. As a result,
the sulfone product (methylsulfonyl benzene) was obtained in
96% yield, along with 4% yield of the sulfoxide product i.e.
methyl sulfinyl benzene (entry 2, Table 1). Furthermore, the
reaction did not occur in the absence of PEG (entry 3, Table 1).
The experiment using 1 atm of air showed almost inactive under
otherwise identical reaction conditions (entry 4, Table 1). As a
consequence, PEG, molecular oxygen and an iron catalyst are
prerequisites for performing the reaction smoothly.
In order to understand the effect of PEG in the sulfide
oxidation, we further examined the reaction in conventional
organic solvents3a,28 for the sulfide oxidation, including CH3CN,
CH2Cl2, CH3OH, and ethereal solvents like diethyl ether and
dioxane. Notably, ethereal solvents were supposed to facilitate
the formation of the Fe(IV)-oxo species from Fe(II) and O2.26
However, those solvents were proved to be ineffective, leaving
the thioanisole intact (Table S1, see ESI†). Therefore, PEG
might be able to play a crucial role in stabilizing the in situ
formation of the Fe(IV)-oxo oxidative center under the reaction
conditions. Indeed, PEG proved to be indispensable for the
oxidation reaction of thioanisole (entries 1–4, Table 1).
Influence of PEG molecular weight
As an indispensable component, PEG had a great promotive
effect on the reaction outcome. Therefore, the influence of
PEG with different molecular weights on the reaction was
investigated. When the reaction was conducted in PEG-200,
the sulfoxide was attained in merely 2% yield (entry 1, Table
2). However, as the PEG molecular weight increased to 400,
Subsequently, we found that the reaction temperature had a
great influence on the reaction outcome. The reaction gave only
◦
28% conversion at 80 C (entry 5, Table 1), suggesting that an
This journal is
The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 130–135 | 131
©

View Article Online
Table 2 The influence of PEG molecular weight on oxidation of
reaction conditions could be finally set to Fe(acac)2 (1 mmol%),
PEG-1000 (0.3 g), O2 (2 MPa), at 100 ◦C for 2 h.
thioanisolea
Entry
PEG
PO2 (MPa) Conv.b (%)
Yieldb (%)
Sulfoxide
Substrate scope
Sulfone
In order to explore the generality of this procedure, a series
of sulfides were evaluated by performing the reaction under
the given conditions. The results are summarized in Table
4. As expected, the catalyst used with the PEG/O2 system
worked well for various aromatic and aliphatic sulfides, thus
providing easy access to valuable symmetric and asymmetric
sulfoxides. Aromatic substrates 1a–1d gave good to excellent
yields of the sulfoxide product (entries 1–4, Table 4). Whereas, a
strong electron-withdrawing group at the para-position showed
a negative effect on the reaction. In particular, a much longer
reaction time (16 h) was needed for 1e to complete the reaction
(entry 5, Table 4), presumably due to the strong electron-
withdrawing effects of the nitrile group. On the other hand,
the influence of steric hindrance was also found in the case
of 1f (entry 6, Table 4). To our delight, this procedure also
proved applicable to the oxidation of aliphatic sulfides (1g and
1h) (entries 7 and 8, Table 4), giving the corresponding isolated
yield of sulfoxide of 83% and 74%, respectively.
1
2
3
4
5
6
7
200
400
600
1000
2000
6000
20 000
2
2
2
2
2
2
2
2
2
0
8
2
6
3
0
0
73
92
>99
79
61
3
65
90
94
76
61
3
a Reaction conditions: thioanisole (0.5 mmol, 62 mg), Fe(acac)2 (1 mol%,
1.2 mg), PEG (0.3 g, [OCH2CH2] unit 6.82 mmol), 100 ◦C, 2 h.
b Determined by GC using area normalization.
the yield of sulfoxide was dramatically enhanced (entry 2, Table
2). When PEG-1000 was employed, the reaction took 2 h for
completion with 94% yield of sulfoxide together with sulfone
(6%). We assumed that the chain length of PEG-200 was not
sufficient to wrap around the active oxoiron species derived in
situ from Fe(acac)2. PEG-1000 was presumably suitable to wrap
around the active iron complex and thus, could stabilize the
metal intermediate through rounding coordinations. The sulfide
conversion gradually decreased with the PEG molecular weight
increasing from 1000 to 20 000 (entries 4–7, Table 2), being
tentatively ascribed to the increasing mass transport limitation
of gaseous oxygen in highly viscous long chained PEG.25a,29
Proposed mechanism
A detailed mechanism of iron-catalyzed sulfoxidation is not
clear at the present stage. Recently, existence of Fe(IV)-oxo
species has been evidenced as the active oxidizing species in
enzymatic and biomimetic reactions (Scheme 2)30 Furthermore,
mononuclear non-heme Fe(IV)-oxo complexes, generated in situ
during the reaction of Fe(II) complexes with O2, were reported
to be capable of oxidizing PPh3 to Ph3PO.31 We also found
that the PEG radical alone could not initiate the oxidation of
thioanisole (entry 1, Table 1), implying that the iron catalyst
plays an essential role in the sulfoxidation. Effect of TEMPO
also supports the free radical pathway (entry 14, Table 1).
Influence of PEG amounts and O2 pressure
Subsequently, the effects of the amount of PEG and the O2
pressure on the reaction were evaluated. As shown in Table 3,
the conversion was sensitively affected by the amount of PEG.
The suitable molar ratio of thioanisole and PEG-1000 could
be 1.67; namely, the proper PEG amount could be 0.3 g when
0.5 mmol of thioanisole was used. Otherwise, the conversion
would be restrained by altering PEG amount (entries 1–4, Table
3). Obviously, a higher O2 concentration is more favourable for
the oxidation reaction (entry 2, Table 3). While a deficient yield
of sulfoxide was observed under 1 MPa of O2 (entry 5, Table
3), and further reducing the O2 pressure to 1 bar resulted in
only 2% conversion (entry 6, Table 3). As a consequence, the
Scheme 2 Fe(IV)-oxo species observed in non-heme iron proteins and
model complexes.
Based on the understanding of Fe(IV)-oxo species, a mech-
anism for the iron-catalyzed selective oxidation of sulfides to
sulfoxides was proposed as shown in Scheme 3. Firstly, Fe(II) 1
reacts with O2 to form a Fe(III)-superoxo intermediate 2.32 Then
the m-oxo bridged diiron species, Fe(III)–(O)4–Fe(III) 333 could
form to further generate 4, Fe(III)–(O)2–Fe(III)4, after releasing
one molecule of oxygen. Subsequent O–O bond homolysis of
4 results in the generation of the Fe(IV)-oxo species 5 which
are involved in oxygen atom transfer reactions. Simultaneously,
Fe(II) 1 is regenerated and could participate in the next catalytic
cycle. Alternatively, this Fe(IV)-oxo complex 5 could also be
generated through formation of the intermediate 7 from Fe(III)
6 and oxygen. Regeneration of Fe(III) 6 via oxidation of the
formed Fe(II) 1 could complete the catalytic cycle. In this
context, Fe(II) and Fe(III) gave almost the same catalytic activity
(entries 7 and 8, Table 1).
Table 3 The influence of PEG amount and O2 pressure on oxidation
of methyl phenyl sulfidea
PEG-1000
amount (g)
PO2
(MPa)
Conv.b
(%)
Entry
Yieldb (%)
Sulfoxide
Sulfone
1
2
3
4
5
6
0.1
0.3
0.5
1
0.3
0.3
2
2
2
2
1
0.1
2
2
0
6
0
0
0
0
>99
59
11
37
2
94
59
11
37
2
a Reaction conditions: thioanisole (0.5 mmol), Fe(acac)2 (1 mol%,
1.2 mg), 100 ◦C, 2 h. b Determined by GC using area normalization.
132 | Green Chem., 2012, 14, 130–135
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 4 Iron(II)-catalyzed oxidation of various sulfides in PEG-1000a
Entry
Substrate
Time (h)
Conv.b (%)
100
Yieldb (%)
Sulfoxide (2a–2h)
94(89)
Sulfone
6
1
2
2
3
2
2
97
98
91(77)
95(93)
9
3
4
5
6
3
100
98
96(94)
96(94)
97(91)
4
2
2
16
4
>99
7
8
6
3
96
97
90(83)
92(74)
6
5
a All the experiments were carried out with the substrate (0.5 mmol), PEG-1000 (0.3 g), Fe(acac)2 (1 mol%, 1.2 mg), O2 (2 MPa) at 100 ◦C. b Determined
by GC using area normalization and data in parentheses refer to isolated yields.
6 could play the same role in this process as PEG (Table S2, see
ESI†), as depicted in Scheme 4.
Scheme 4 Fe(II) catalyzed aerobic oxidation of sulfide in 18-crown-6.
Accordingly, PEG-1000 like crown ether, could wrap around
Fe(acac)2 containing a more oxygen-donor anions, and subse-
quently create a microenvironment around the iron center that
aids in stabilizing the Fe(IV)-oxo unit.34
Scheme 3 Proposed mechanism.
Conclusions
In summary, we have developed a highly selective sulfoxidation
On the other hand, PEGs are acyclic polyethers that have
flexible polyethylene oxide chains, which render it possible to
have ion-dipole interactions with metal salts.34 It has been
reported that the PEG-1000 matrix could effectively stabilize
and immobilize the catalytically active Pd particles in the aerobic
oxidation of alcohols.35 In this regards, we found that 18-crown-
system with molecular oxygen as the oxidant in PEG, using
cheap and readily available Fe(acac)2 as the catalyst. Meanwhile,
this process has been proven to be applicable for the selective
oxidation of the aromatic and aliphatic sulfides. Notably, PEG-
1000, which can provide an electron-rich environment, could
play a key role in stabilizing the catalytic Fe(IV)-oxo species
This journal is
The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 130–135 | 133
©

View Article Online
formed in situ, thus promoting the oxidation of sulfides to sul-
foxides. Further studies will be aimed at ultimately disclosing the
mechanistic details for this highly chemo-selective sulfoxidation
and extending the PEG/O2/Fe(acac)2 system to other oxidative
transformations.
1-Chloro-4-(methylsulfinyl)benzene 2d. Oxidation of 4-
chlorothioanisole 1d (79 mg, 0.5 mmol) gave chloro-4-
(methylsulfinyl)benzene 2d (82 mg, 94%) as a yellow oil. H
NMR (400 MHz, CDCl3): d 7.60 (d, J = 8.8 Hz, 2H), 7.51 (d,
J = 8.4 Hz, 2H), 2.72 (s, 3H). 13C NMR (100.6 MHz, CDCl3): d
144.23, 137.20, 129.61, 124.93, 44.06. EI-MS: m/z 173.97 (M+,
61%), 159.05 (M+–CH3, 100%).
1
Experimental Section
4-(Methylsulfinyl)benzonitrile
cyanothioanisole 1e (74 mg, 0.5 mmol) gave 4-(methylsulfinyl)-
benzonitrile 2e (78 mg, 94%) as a white solid. H NMR (400
MHz, CDCl3): d 7.83 (d, J = 8.4 Hz, 2H), 7.77 (d, J = 8.4 Hz,
2H), 2.76 (s, 3H). 13C NMR (100.6 MHz, CDCl3): d 151.42,
132.98, 124.28, 117.67, 114.81, 43.78. EI-MS: m/z 165.07 (M+,
96%), 150.06 (M+–CH3, 100%).
2e. Oxidation
of
4-
Materials
1
Sulfides were purchased from Sigma-Aldrich and Aladdin. The
various iron catalysts were purchased from Aladdin with >98%
purity (Cu content was determined to be 0.013% w/w by using
the ICP method).
General procedure for the iron-catalyzed selective oxidation of
sulfide to sulfoxide
Sulfinyldibenzene 2f. Oxidation of diphenyl sulfide 1f (93 mg,
0.5 mmol) gave sulfinyldibenzene 2f (92 mg, 91%) as a white oil.
1H NMR (400 MHz, CDCl3): d 7.64–7.66 (m, 3H), 7.44–7.48 (m,
5H). 13C NMR (100.6 MHz, CDCl3): d 145.57, 131.04, 129.31,
124.76. EI-MS: m/z 202.02 (M+, 100%), 154.19 (M+–S–O, 94%).
A mixture of the substrate (0.5 mmol), PEG-1000 (0.3 mmol)
and Fe(acac)2 (1 mol%, 1.2 mg) was placed in a 25 mL autoclave,
equipped with an inner glass tube. 2 MPa of O2 was then
introduced into the autoclave and heated to 100 ◦C. The mixture
was stirred continuously for the designed reaction time, then the
reactor was placed into ice water and the O2 was released slowly.
After depressurization, the products were then extracted by
diethyl ether (10 mL ¥ 3), and analyzed by a gas chromatograph
(SHIMADZU-2014) equipped with a capillary column (RTX-
17, 30 m ¥ 0.25 mm) using a flame ionization detector. Then
the solvents were distilled off and the products were purified by
silica gel column chromatography (200–300 mesh, 1 : 2 v/v ethyl
acetate : petroleum as eluant). The structure and the purity of
the products were further identified using NMR (BRUKER-
400 MHz), GC–MS (Thermo Finnigan Polaris Q) and GC
by comparing retention times and fragmentation patterns with
those of authentic samples.
1-(Propylsulfinyl)propane 2g. Oxidation of dipropyl sulfide
1g (59 mg, 0.5 mmol) and work up gave 1-(propylsulfinyl)
propane 2g (56 mg, 83%) as a yellow oil. 1H NMR (400 MHz,
CDCl3): d 2.72–2.79 (m, 2H), 2.57–2.65(m, 2H), 1.83 (m, 4H),
1.09 (t, J = 7.4 Hz, 6H). 13C NMR (100.6 MHz, CDCl3): d
54.28, 16.31, 13.42. EI-MS: m/z 135.13 (M+, 17%), 92.03 (M+–
+
CH2CH2CH3, 100), 43.02 (CH3CH2CH2 , 94).
Dimethyl sulfoxide 2h. Oxidation of dimethyl sulfide 1h
(31 mg, 0.5 mmol) and work up gave dimethyl sulfoxide 2h
(29 mg, 74%) as a white oil. 1H NMR (400 MHz, CDCl3): d 2.56
(s, 6H). 13C NMR (100.6 MHz, CDCl3): d 40.79.
Acknowledgements
Synthesis of sulfoxide products
We are grateful to the National Natural Science Foundation of
China (No 20872073), Research Fellowship for International
Young Scientists from NSFC (21150110105), and the Commit-
tee of Science and Technology of Tianjin for financial support.
(Methylsulfinyl)benzene 2a. Oxidation of thioanisole 1a
(62 mg, 0.5 mmol) gave (methylsulfinyl)benzene 2a (62 mg, 89%)
1
as a white oil. H NMR (400 MHz, CDCl3): d 7.52–7.66 (m,
5H), 2.73 (s, 3H). 13C NMR (100.6 MHz, CDCl3): d 145.66,
131.03, 129.35, 123.49, 43.94. EI-MS: m/z 139.98 (M+, 81%),
97.08 (M+–O–CH3–H, 100%).
References
1 (a) P. Metzner and A. Thuillier, Sulfur Reagents in Organic Synthesis,
Academic Press, London, 1994; (b) The chemistry of sulfones,
sulfoxides and cyclic sulfides, ed. S. Patai, Z. Rappoport, C. Stirling,
Wiley, Chichester, 1994.
2 (a) D. H. R. Barton, W. Li and J. A. Smith, Tetrahedron Lett.,
1998, 39, 7055–7058; (b) M. Hirano, S. Yakabe, J. H. Clark and
T. Morimoto, J. Chem. Soc., Perkin Trans. 1, 1996, 2693–2698.
3 (a) M. D. A. Maria, P. Mastrorilli and C. F. Nobile, J. Mol. Catal. A:
Chem., 1996, 108, 57–62; (b) H. Fakhraian and F. Valizadeh, J. Mol.
Catal. A: Chem., 2010, 333, 69–72; (c) J. Fujisaki, K. Matsumoto,
K. Matsumoto and T. Katsuki, J. Am. Chem. Soc., 2011, 133, 56–61;
(d) F. Shi, M. K. Tse, H. M. Kaiser and M. Beller, Adv. Synth. Catal.,
2007, 349, 2425–2430.
4 (a) T. Punniyamurthy, S. Velusamy and J. Iqbal, Chem. Rev., 2005,
105, 2329–2363; (b) I. Klement, H. Liitjens and P. Knochel, Angew.
Chem., Int. Ed. Engl., 1997, 36, 1454–1456; (c) A. M. Khenkin and
R. Neumann, Catal. Lett., 2000, 68, 109–111; (d) H. Tanaka, H.
Nishikawa, T. Uchida and T. Katsuki, J. Am. Chem. Soc., 2010, 132,
12034–12041; (e) H. Zhang, C. Y. Chen, R. H. Liu, Q. Xu and W.
Q. Zhao, Molecules, 2010, 15, 83–92; (f) S. Colonna, N. Gaggero, F.
Montanari, G. Pozzi and S. Quici, Eur. J. Org. Chem., 2001, 181–186.
1-Methyl-4-(methylsulfinyl)benzene 2b. Oxidation of 4-
methythioanisole 1b (69 mg, 0.5 mmol) gave methyl-4-
(methylsulfinyl)benzene 2b (59 mg, 77%) as a white solid. H
1
NMR (400 MHz, CDCl3): d 7.54 (d, J = 8.4 Hz, 2H), 7.33 (d,
J = 8.0 Hz, 2H), 2.71 (s, 3H), 2.42 (s, 3H). 13C NMR (100.6 MHz,
CDCl3): d 142.49, 141.51, 130.03, 123.53, 44.00, 21.39. EI-MS:
m/z 153.98 (M+, 30%), 139.05 (M+–CH3, 71%), 77.01 (C6H5 ,
+
100%).
1-Methoxy-4-(methylsulfinyl)benzene 2c. Oxidation of 4-
methoxythioanisole 1c (77 mg, 0.5 mmol) gave 1-methoxy-4-
(methylsulfinyl)benzene 2c (79 mg, 93%) as a white oil. 1H NMR
(400 MHz, CDCl3): d 7.59 (d, J = 8.8 Hz, 2H), 7.03 (d, J = 8.8 Hz,
2H), 3.85 (s, 3H), 2.70 (s, 3H). 13C NMR (100.6 MHz, CDCl3): d
161.93, 136.61, 125.43, 114.82, 55.51, 44.01. EI-MS: m/z 169.93
(M+, 18%), 155.08 (M+-CH3, 100%).
134 | Green Chem., 2012, 14, 130–135
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
5 (a) S. E. Mart´ın and L. I. Rossi, Tetrahedron Lett., 2001, 42, 7147–
7151; (b) T. Chinnusamy and O. Reiser, ChemSusChem, 2010, 3,
1040–1042.
6 I. Gamba, S. Palavicini, E. Monzani and L. Casella, Chem.–Eur. J.,
2009, 15, 12932–12936.
22 (a) Y. Du, Y. Wu, A. H. Liu and L. N. He, J. Org. Chem., 2008, 73,
4709–4712; (b) Y. Du, J. Q. Wang, J. Y. Chen, F. Cai, J. S. Tian, D. L.
Kong and L. N. He, Tetrahedron Lett., 2006, 47, 1271–1275; (c) X.
Y. Dou, J. Q. Wang, Y. Du, E. Wang and L. N. He, Synlett, 2007, 19,
3058–3062; (d) D. L. Kong, L. N. He and J. Q. Wang, Synlett, 2010,
8, 1276–1280.
7 T. Iwahama, S. Sakaguchi and Y. Ishii, Tetrahedron Lett., 1998, 39,
9059–9062.
23 J. Q. Wang, F. Cai, E. Wang and L. N. He, Green Chem., 2007, 9,
8 For the vanadium-catalyzed oxidation of sulfide, see: (a) C. Bolm
and F. Bienewald, Angew. Chem., Int. Ed. Engl., 1996, 34, 2640–2642;
(b) M. Al-Hashimi, E. Fisset, A. C. Sullivan and J. R. H. Wilson,
Tetrahedron Lett., 2006, 47, 8017–8019; (c) M. R. Maurya, A. K.
Chandrakar and S. Chand, J. Mol. Catal. A: Chem., 2007, 263, 227–
237; (d) I. Khedher, A. Ghorbel, J. M. Fraile and J. A. Mayoral, J.
Mol. Catal. A: Chem., 2006, 255, 92–96; (e) Y. Jeong, S. Choi, Y. D.
Hwang and K. H. Ahn, Tetrahedron Lett., 2004, 45, 9249–9252; (f) J.
Sun, C. Zhu, Z. Dai, M. Yang, Y. Pan and H. Hu, J. Org. Chem.,
2004, 69, 8500–8503; (g) A. M. Khenkin, G. Leitus and R. Neumann,
J. Am. Chem. Soc., 2010, 132, 11446–11448.
9 For wolframium-catalyzed oxidation of sulfide: (a) N. N. Mahamuni,
P. R. Gogate and A. B. Pandit, Ultrason. Sonochem., 2007, 14, 135–
142; (b) B. Karimi, M. Ghoreishi-Nezhad and J. H. Clark, Org. Lett.,
2005, 7, 625–628; (c) K. Sato, M. Hyodo, M. Aoki, X. Q. Zheng
and R. Noyori, Tetrahedron, 2001, 57, 2469–2476; (d) R. Noyori, M.
Aoki and K. Sato, Chem. Commun., 2003, 1977–1986.
882–887.
24 For typical examples on thermal/oxidatvie degradation of PEG, see:
(a) J. Glastrup, Polym. Degrad. Stab., 1996, 52, 217–222; (b) J. R.
Conder, N. A. Fruitwala and M. K. Shingari, J. Chromatogr., A,
1983, 269, 171–178; (c) E. A. Altwicker, Chem. Rev., 1967, 67, 475–
531.
25 (a) J. Q. Wang, L. N. He and C. X. Miao, Green Chem., 2009, 11,
1013–1017; (b) J. Q. Wang and L. N. He, New J. Chem., 2009,
33, 1637–1640; (c) J. Q. Wang, L. N. He, C. X. Miao and J. Gao,
ChemSusChem, 2009, 2, 755–760.
26 S. O. Kim, C. V. Sastri, M. S. Seo, J. Kim and W. Nam, J. Am. Chem.
Soc., 2005, 127, 4178–4179.
27 S. L. Buchwald and C. Bolm, Angew. Chem., Int. Ed., 2009, 48, 5586.
28 (a) P. Veerakumara, Z. Z. Lu, M. Velayudhamb, K. L. Lub and S.
Rajagopala, J. Mol. Catal. A: Chem., 2010, 332, 128–137; (b) H. M.
Shi, C. G. Yu and J. He, J. Catal., 2010, 271, 79–87; (c) E. Baciocchi,
M. F. Gerini and A. Lapi, J. Org. Chem., 2004, 69, 3586–3589.
29 T. Seki, J. D. Grunwaldt and A. Baiker, Chem. Commun., 2007,
3562–3564.
10 J. S. Gao, H. C. Guo, S. Z. Liu and M. Wang, Tetrahedron Lett.,
2007, 48, 8453–8455.
11 (a) F. Hosseinpoor and H. Golchoubian, Tetrahedron Lett., 2006, 47,
5195–5197; (b) J. Brinksma, R. L. Crois, B. L. Feringa, M. I. Donnoli
and C. Rosini, Tetrahedron Lett., 2001, 42, 4049–4052.
30 (a) I. V. Korendovych, S. V. Kryatov and E. V. Rybak-Akimova, Acc.
Chem. Res., 2007, 40, 510–521; (b) M. Costas, M. P. Mehn, M. P.
Jensen and L. Que, Jr., Chem. Rev., 2004, 104, 939–986; (c) L. D. Slep
and F. Neese, Angew. Chem., Int. Ed., 2003, 42, 2942–2945; (d) D.
A. Proshlyakov, T. F. Henshaw, G. R. Monterosso, M. J. Ryle and
R. P. Hausinger, J. Am. Chem. Soc., 2004, 126, 1022–1023; (e) P. J.
Riggs-Gelasco, J. C. Price, R. B. Guyer, J. H. Brehm, E. W. Barr, J.
M. Bollinger, Jr. and C. Krebs, J. Am. Chem. Soc., 2004, 126, 8108–
8109; (f) J. U. Rohde, J. H. In, M. H. Lim, W. W. Brennessel, M. R.
Bukowski, A. Stubna, E. Mu¨nck, W. Nam and L. Que, Jr., Science,
2003, 299, 1037–1039; (g) M. H. Lim, J. U. Rohde, A. Stubna, M.
R. Bukowski, M. Costas, R. Y. N. Ho, E. Mu¨nck, W. Nam and L.
Que, Jr., Proc. Natl. Acad. Sci. U. S. A., 2003, 100, 3665–3670; (h) J.
Kaizer, E. J. Klinker, N. Y. Oh, J. U. Rohde, W. J. Song, A. Stubna, J.
Kim, E. Mu¨nck, W. Nam and L. Que, Jr., J. Am. Chem. Soc., 2004,
126, 472–473.
31 (a) D. H. Chin, G. N. L. Mar and A. L. Balch, J. Am. Chem. Soc.,
1980, 102, 5945–5947; (b) A. L. Balch, Y. W. Chan, R. J. Cheng, G. N.
L. Mar, L. Latos-Grazynski and M. W. Renner, J. Am. Chem. Soc.,
1984, 106, 7779–7785; (c) R. A. Ghiladi, R. M. Kretzer, I. Guzei,
A. L. Rheingold, Y. M. Neuhold, K. R. Hatwell, A. D. Zuberbu¨hler
and K. D. Karlin, Inorg. Chem., 2001, 40, 5754–5767.
32 (a) S. W. Hong, Y. M. Lee, W. Shin, S. Fukuzumi and W. Nam, J. Am.
Chem. Soc., 2009, 131, 13910–13911; (b) Y. M. Lee, S. W. Hong, Y.
Morimoto, W. Shin, S. Fukuzumi and W. Nam, J. Am. Chem. Soc.,
2010, 132, 10668–10670; (c) A. Thibon, J. England, M. Martinho, V.
G. Young, Jr., J. R. Frisch, R. Guillot, J. J. Girerd, E. Mu¨nck, L. Que,
Jr. and F. Banse, Angew. Chem., Int. Ed., 2008, 47, 7064–7067; (d) S.
V. Kryatov, S. Taktak, I. V. Korendovych and E. V. Rybak-Akimova,
Inorg. Chem., 2005, 44, 85–99; (e) M. Martinho, G. Blain and F.
Banse, Dalton Trans., 2010, 39, 1630–1634.
12 R. Das and D. Chakraborty, Tetrahedron Lett., 2010, 51, 6255–6258.
13 R. Das and D. Chakraborty, Synthesis, 2011, 2, 277–280.
14 General reviews: (a) C. Bolm, J. Legros, J. Le Paih and L. Zani,
Chem. Rev., 2004, 104, 6217; (b) “Iron Catalysis in Organic Chemistry:
reactions and applications”, (Ed.: B. Plietker) WILEY-VCH Verlag,
Weinheim, 2008; (c) S. Enthaler, K. Junge and M. Beller, Angew.
Chem., Int. Ed., 2008, 47, 3317; (d) A. Correa, O. Garcia Mancheno
and C. Bolm, Chem. Soc. Rev., 2008, 37, 1108; (e) B. D. Sherry and
A. Fu¨rstner, Acc. Chem. Res., 2008, 41, 1500; (f) W. M. Czaplik,
M. Mayer, J. Cvengros and A. Jacobi von Wangelin, ChemSusChem,
2009, 2, 396; (g) G. Cahiez and S. Marquais, Pure Appl. Chem., 1996,
68, 53; (h) C. L. Sun, B. J. Li and Z. J. Shi, Chem. Rev., 2011, 111,
1293–1314; (i) W. M. Czaplik, M. Mayer, S. Grupe and A. Jacobi
von Wangelin, Pure Appl. Chem., 2010, 82, 1545; (j) K. Junge, K.
Schrder and M. Beller, Chem. Commun., 2011, 47, 4849–4859; (k) R.
H. Morris, Chem. Soc. Rev., 2009, 38, 2282–2291.
15 (a) L. Chen, Y. Yang and D. L. Jiang, J. Am. Chem. Soc., 2010, 132,
9138–9143; (b) C. Duboc-Toia, S. Me´nage, R. Y. N. Ho, L. Que, Jr.,
C. Lambeaux and M. Fontecave, Inorg. Chem., 1999, 38, 1261–1268.
16 C. O. Kinen, L. I. Rossi and R. H. De Rossi, J. Org. Chem., 2009, 74,
7132–7139.
17 (a) J. Legros and C. Bolm, Angew. Chem., Int. Ed., 2004, 43, 4225–
4228; (b) J. Legros and C. Bolm, Chem.–Eur. J., 2005, 11, 1086–1092;
(c) J. Legros and C. Bolm, Angew. Chem., Int. Ed., 2003, 42, 5487–
5489.
18 (a) H. Egami and T. Katsuki, J. Am. Chem. Soc., 2007, 129, 8940–
8941; (b) H. Egami and T. Katsuki, Synlett, 2008, 10, 1543–1546.
19 (a) S. Campestrini and U. Tonellato, J. Mol. Catal. A: Chem., 2000,
164, 263–272; (b) S. K. Karmee, L. Greiner, A. Kraynov, T. E. Mu¨ller,
B. Niemeijer and W. Leitner, Chem. Commun., 2010, 46, 6705–6707;
(c) R. Mello, A. Olmos, A. Alcalde-Aragone´s, A. D´ıaz-Rodr´ıguez,
M. E. G. Nu´n˜ez and G. Asensio, Eur. J. Org. Chem., 2010, 6200–6206;
(d) Q. H. Chen and E. J. Beckman, Green Chem., 2007, 9, 802–808.
20 A. Haimov and R. Neumann, Chem. Commun., 2002, 876–877.
21 (a) J. Chen, S. K. Spear, J. G. Huddleston and R. D. Rogers, Green
Chem., 2005, 7, 64–82; (b) D. J. Heldebrant and P. G. Jessop, J. Am.
Chem. Soc., 2003, 125, 5600–5601; (c) Z. S. Hou, N. Theyssen, A.
Brindmann and W. Leitner, Angew. Chem., 2005, 117, 1370–1373.
33 C. E. MacBeth, A. P. Golombek, V. G. Young, Jr., C. Yang, K.
Kuczera, M. P. Hendrich and A. S. Borovik, Science, 2000, 289,
938–941.
34 (a) S. P. Luo, S. Zhang, Y. F. Wang, A. B. Xia, G. C. Zhang, X. H. Du
and D. Q. Xu, J. Org. Chem., 2010, 75, 1888–1891; (b) G. W. Gokel,
D. M. Goli and R. A. Schuitz, J. Org. Chem., 1983, 48, 2837–2842;
(c) H. K. Frensdorff, J. Am. Chem. Soc., 1971, 93, 600–606.
35 (a) Z. S. Hou, N. Theyssen, A. Brinkmann and W. Leitner, Angew.
Chem., Int. Ed., 2005, 44, 1346–1349; (b) Z. S. Hou, N. Theyssen and
W. Leitner, Green Chem., 2007, 9, 127–132.
This journal is
The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 130–135 | 135
©