A novel catalytic system poly(1-vinyl-3-dodecylimidazolium tribromide)/TBN for the oxidation of sulfides to sulfoxides with air as oxidant

Article abstract of DOI:10.1016/j.tetlet.2018.07.001

A novel and recoverable polymeric ionic liquid, poly(1-vinyl-3-dodecylimidazolium tribromide) (Poly[VDIM]Br₃), was successfully prepared and fully characterized. And a highly efficient metal-free catalytic system Poly[VDIM]Br₃/tert-butyl nitrite was developed for the oxidation of sulfides. With air as oxidant, we have successfully achieved 19 kinds of sulfides selectively and efficiently oxidized to corresponding sulfoxides using this catalytic system at room temperature.

Full text of DOI:10.1016/j.tetlet.2018.07.001

Accepted Manuscript
A novel catalytic system poly(1-vinyl-3-dodecylimidazolium tribromide)/TBN
for the oxidation of sulfides to sulfoxides with air as oxidant
Hua Zhang, Linlin Qi
PII:
S0040-4039(18)30853-0
https://doi.org/10.1016/j.tetlet.2018.07.001
TETL 50110
DOI:
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
26 May 2018
25 June 2018
2 July 2018
Please cite this article as: Zhang, H., Qi, L., A novel catalytic system poly(1-vinyl-3-dodecylimidazolium
tribromide)/TBN for the oxidation of sulfides to sulfoxides with air as oxidant, Tetrahedron Letters (2018), doi:
https://doi.org/10.1016/j.tetlet.2018.07.001
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A novel catalytic system poly(1-vinyl-3-
dodecylimidazolium tribromide)/TBN for the
oxidation of sulfides to sulfoxides with air as
oxidant
Hua Zhang*, Linlin Qi

1
Tetrahedron Letters
journal homepage: www.els evier.com
A novel catalytic system poly(1-vinyl-3-dodecylimidazolium tribromide)/TBN for the
oxidation of sulfides to sulfoxides with air as oxidant
Hua Zhang∗, Linlin Qi
State Key Laboratory of Fine Chemicals, Dalian University of Technology, No. 2 Linggong Road, 116024 Dalian, Liaoning Province, China
ARTICLE INFO
ABSTRACT
Article history:
Received
A novel and recoverable polymeric ionic liquid, poly(1-vinyl-3-dodecylimidazolium tribromide)
(Poly[VDIM]Br3), was successfully prepared and fully characterized. And a highly efficient
metal-free catalytic system Poly[VDIM]Br3/tert-butyl nitrite was developed for the oxidation of
sulfides. With air as oxidant, we have successfully achieved 19 kinds of sulfides selectively and
efficiently oxidized to corresponding sulfoxides using this catalytic system at room temperature.
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Sulfoxide
Sulfide
Aerobic oxidation
Poly ionic liquid
Introduction
properties of the ILs, such as superior ionic conductivity, strong
solubilizing ability and excellent chemical and electrical stability,
Selective oxidation of sulfides to sulfoxides is a significant
and challenging organic reaction,1 because the sulfoxide is a kind
of important organic synthesis intermediate,2 which is
extensively utilized in medicine, pesticide,3 heavy metal
extraction,4 oil desulphurization, organic synthesis5 and other
industries.6,7 Therefore, a great deal of methods have been issued
for the oxidation of sulfides to sulfoxides.8-10 In recent years, as
the oxidant, molecular oxygen has been more and more
popular,11 on account of its many outstanding advantages such as
environmentally friendly, low cost and by-product as water.
Nonetheless, the catalyst was needed to activate molecular
oxygen for the oxidation of sulfides. There have been many
reports that a dual component catalytic system consisted of
bromine-containing and NOX-containing reagents could
successfully achieve the oxidation of sulfides to sulfoxides,12-14
but most of them suffered from the troublesome drawback―the
use of transition metal or acid, which may not environmentally
friendly. Consequently, we sought to design a new kind of dual
component catalytic system free from the drawback.
but also present intrinsic polymer features and enhanced
mechanical stability and durability.17 Possessing these unique
characteristics, PILs are promising candidates for different
technological fields, such as materials,18 catalysts,19
biotechnology,20 and surface science.21 Furthermore, the Br3--
containing regents which are more stable and benign than Br2
have been extensively utilized, including phosphorus tribromide22
and benzyltrimethylammonium tribromide.23 There were a few
reports that the Br3-containing regents were utilized to oxidize
the sulfides,24,25 but they were used as oxidant, which were not as
green as molecular oxygen as the oxidant. In addition, the
catalytic mechanism of Br/NOX systems have been extensively
accepted,26 and tert-butyl nitrite (TBN) as a good substitute for
NOX has been reported.27 And our group have reported related
articles of the oxidation of sulfides.28,29 Accordingly, we designed
-
Br3 -containing
a
kind
of
PIL―poly(1-vinyl-3-
dodecylimidazolium tribromide) (Scheme 1), it was not only an
eligible substitute for Br2 but also recoverable.
As we know, ionic liquids (ILs) are green and recyclable
reagents and have attracted tremendous research interest.15,16
Utilized as monomers, ILs have been frequently employed in the
synthesis of polymeric ionic liquids (PILs) over the past few
years. And the PILs are described as a novel class of materials
combining the unique properties of ILs and the specificities of
polymers. As compared to ILs, PILs not only inherit the eminent
———
Scheme 1. Synthesis of the Poly[VDIM]Br3
∗Corresponding author. Tel./fax: +86 0411 849 86205.
E-mail address: zhanghua@dlut.edu.cn (H. Zhang).

2
Tetrahedron Letters
methyl phenyl sulfide as a typical example were screened. The
results are summarized in Table 1. As is evident in Table 1, the
oxidation reaction proceeds more rapidly in acetonitrile.
Table 1. Aerobic oxidation of methyl phenyl sulfide to
methyl phenyl sulfoxide by Poly[VDIM]Br3/TBN as the
catalyst in different solventsa
Entry
Solvent
Time(h)
Yield(%)b
The oxidation of sulfides to sulfoxides
1
2
3
4
5
6
7
Acetonitrile
2
2
2
2
2
2
2
>99
3
With the optimized conditions in hand, we report on the
chemoselective oxidation of a variety of aliphatic and aromatic
Dichloromethane
Acetone
sulfides
to
their
corresponding
sulfoxides
by
<1
16
4
Poly[VDIM]Br3/TBN catalytic system in presence of water in
acetonitrile at room temperature with air as oxidant. The results
are shown in Table 2.
Ethyl acetate
Tetrahydrofuran
n-Heptane
17
36
With this oxidation system, a variety of sulfides were
successfully converted to sulfoxides with high conversion rate
and it exhibited excellent catalytic efficiency. As was evident in
Table 2, there existed obvious difference between the reaction
time of different sulfides. Aromatic compounds sulfides with
electron-withdrawing groups took more time than those with
electron-donating groups. With regard to methyl phenyl sulfide
which was aromatic compound, while its benzene ring was
connected with the electron-withdrawing groups (-CO-,-X,-NO2),
like entries 5-14, the larger the groups, the time of the reaction
may be longer. In addition, the reaction could also be excellently
finished when with the electron-donating groups (entries 2-4, 15,
16). Besides, sulfides (entries 12, 14) that were not completely
dissolved in acetonitrile probably attributed to considerable
molecular volume could also be selectively oxidized to
corresponding sulfoxides. With respect to aliphatic compounds
Acetonitrile/H2O=1:1c
aReaction conditions: methyl phenyl sulfide 10 mmol, Poly[VDIM]Br3 (0.5
mmol, 0.25 g) , TBN 0.5 mmol, H2O 1 mL, solvent 20 mL, 25 °C.
bDetermined by GC Agilent 6890N and GC-MS.
cVolume ratio.
Herein, we report a novel and efficient catalytic system-
Poly[VDIM]Br3/TBN for selective oxidation of sulfides to
corresponding sulfoxides under mild and metal-free conditions
with air as oxidant (Table 2).
Results and Discussion
Optimization of the reaction solvents
In order to find an appropriate solvent for the oxidation of
sulfides to sulfoxides, different solvents for the oxidation of
Table 2. Oxidation of sulfides to corresponding sulfoxidesa
Entry
1
R1
R2
t/h
2.5
2.5
2.5
2.5
3.0
2.5
6.0
5.0
13
5.5
6.5
8
Conv.(%)b
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>78
>99
>93
Sel.(%)b
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>94
>91
>99
>99
>99
Yield(%)c
97
Ph-
CH3
2
4-CH3C6H4-
4-CH3OC6H4-
2-CH3OC6H4-
4-FC6H4-
CH3
96
3
CH3
96
4
CH3
96
5
CH3
95
6
4-ClC6H4-
2-ClC6H4-
2-BrC6H4-
4-NO2C6H4-
4-HCOC6H4-
4-CH3COC6H4-
4-PhCOC6H4-
4-CH3COOC6H4-
4-PhCOOC6H4-
Ph-
CH3
96
7
CH3
96
8
CH3
97
9
CH3
96
10
11
12
13
14
15
16
17
18
19
CH3
95
CH3
96
CH3
96
CH3
8
97
CH3
8
97
CH3CH2-
HOCH2CH2-
2.5
5
92
Ph-
88
-(CH2)4-
5
71
CH3CH2CH2CH2-
CH3CH2CH2CH2-
CH3
5
94
CH3(CH2)11
-
5
89
aReaction conditions: sulfides (10 mmol), Poly[VDIM]Br3 (0.5 mmol, 0.25 g), TBN (0.5 mmol), H2O (0.5 mL), CH3CN (20 mL), air, 25 °C.
bDetermined by GC Agilent 6890N and GC-MS.
cIsolated yield.

3
R1R2S=O + 2H+
CH2), 2853 (-CH2), 1466 (-CH2/-CH3), 1377 (-CH3) and 722
H2O
cm-1 (-CH2-) were assigned to the long carbon side chain. After
[VTIM]Br through polymerization (curve b), the intensity of the
peaks at 1642, 960 and 915 cm-1 were too weak to be observed
which indicated the unsaturated carbon-carbon double bond had
disappeared. After Poly[VDIM]Br reacting with Br2 (curve c),
the intensity of the peaks at 825, 739 and 648 cm-1 were
2H+
R1R2S+-Br
NO2
NO
2Br-
-
remarkably enhanced. The existence of the Br3 was proved by
Raman spectra.
Br2
R1R2S
0.5 O2
H2O
The Raman spectra of Poly[VDIM]Br and Poly[VDIM]Br3
were presented in Fig. 2. It was evident that there was no
distinctive characteristic peaks in the Raman spectra of
Poly[VDIM]Br (curve a). As compared to it, the Poly[VDIM]Br3
clearly showed two characteristic peaks at 163 and 210 cm-1
(curve b), in agreement with previous report.30 The harmonic
vibrational frequency of Br2 was about 325 cm-1. As was obvious
in the curve b, there was no peak at 325 cm-1, indicating that
there was no free bromine in the Poly[VDIM]Br3. Therefore, the
collective evidence strongly suggests that the formation of the
Poly[VDIM]Br3 through the FT-IR and Raman spectra.
Br2
Poly[VTIM]Br3
TBN
Poly[VTIM]Br
+
2NO2
TBN - BuO
ONOOH
t
O2
t
- BuO
Scheme 2. Mechanism of the oxidation of sulfides
sulfides (entries 17-19), the oxidation reaction could also achieve
with high selectivity and efficiency.
Mechanism
Thermal stabilities of Poly[VDIM]Br and Poly[VDIM]Br3
were investigated by TG analysis in Fig. 3. The decomposition
temperature of the Poly[VDIM]Br (curve a) was about 275 °C,
A plausible mechanism for this novel and metal-free catalytic
oxidation process can be described by the dual cycle shown in
Scheme 2. Firstly, the lone pair electrons on sulfur atom in
sulfide are attacked by Br+ which is derived from Br2 in the
Poly[VDIM]Br3 and generate the intermediate product 1. Then
the intermediate product hydrolyzes and the corresponding
sulfoxide is obtained. What needs to be particularly stated is that
H2O provides the oxygen atom and accelerate the formation of
sulfoxide. In addition, the Br− is continuously reoxidized to Br2
by NO2, which is the key for a catalytic amount of Br2 to oxidize
sulfide substrates, the NO2 is reduced to NO and H+ is turned to
H2O simultaneously. The NO is easily released from TBN as an
efficient NO equivalent and NO can easily be oxidized to NO2 by
O2 in the air. The coupling of the two cycles form a novel and
efficient aerobic sulfide oxidation system.
indicating
a nice thermal stability. The weight loss of
Poly[VDIM]Br was nearly 63.7% in the temperature range 275-
335 °C, which was attributed to the decomposition of C-C bonds
including carbon backbone in the main and side chain. There was
nearly no mass loss after 335 °C, which was mostly due to the
strong electrostatic interaction between the polymeric cation and
the Br-anion. In contrast, the decomposition temperature of
Poly[VDIM]Br3 (curve b) was about 189 °C and 275 °C,
respectively. And they had similar shape of curves after 275 °C,
indicating that there probably existed the same substance when
temperature up to 275 °C. By the synthetic step, Poly[VDIM]Br3
was synthesized by Poly[VDIM]Br and Br2. Therefore, what
could be deduced was that Br2 was firstly released and
Poly[VDIM]Br3 was decomposed into Poly[VDIM]Br at about
189 °C. In addition, it was certain that Poly[VDIM]Br and Br2
were not simply physically adsorbed and Poly[VDIM]Br3 was
really synthesized. And this observation confirmed the rationality
of the chemical structure of Poly[VDIM]Br3 shown in Scheme 1.
After the oxidation reaction was terminated, the solid
Poly[VDIM]Br generated from the Poly[VDIM]Br3 could be
conveniently isolated by filtration, with the further washing with
acetonitrile for three times and vacuum drying at 45 °C for 6 h,
and the fresh Poly[VDIM]Br3 could be uncomplicatedly prepared
through it reacting with bromine again according to the
preparation steps, which made the whole catalytic reaction more
green and thoroughly met the requirements of green chemistry.
With respect to green and sustainable chemistry, it was
undeniable that the Poly[VDIM]Br3/TBN catalytic system was
more attractive, because it not only possessed high selectivity and
efficiency for the oxidation of sulfides to sulfoxides without
using any metal and acid at room temperature but also hardly
generated potentially deleterious byproduct like sulfones. In
-
addition, as an ideal regent, the Br3 in the Poly[VDIM]Br3 was an
exceedingly stable state relative to Br2, and Poly[VDIM]Br was
still a good “carrier” for the Br2.
Characterization of Poly[VDIM]Br3
The FT-IR spectra of [VDIM]Br, Poly[VDIM]Br and
Poly[VDIM]Br3 were illustrated in Fig. 1. The [VTIM]Br (curve
a) exhibited several characteristic peaks. The peaks at 3092 (C-
H), 1642 (C=C), 960 (C-H) and 915 cm-1 (C-H) showed the
existence of the -HC=CH2 of imidazole side chain, and those at
3144 (C-H), 1551 (C=N), 1466 (C=C) and 1172 cm-1 (C-N)
showed the existence of the imidazole ring. The peaks at 816,
769, and 625 cm-1 were derived from in-plane and out-of-plane
rings C–H bending for imidazole. Moreover, the bands at 2922 (-
Figure 1. FT-IR spectra of (a) [VTIM]Br, (b) Poly[VDIM]Br
and (c) Poly[VDIM]Br3

4
Tetrahedron
Supplementary Material
Supplementary data (1H NMR, 13CNMR spectra of all
compounds) associated with this article.
References
1. Dai, W.; Shang, S.; Lv, Y.; Li, G.; Li, C.; Gao, S. ACS Catal.
2017, 7, 4890-4895.
2. Singh, M.; Yadav, A. K.; Yadav, L. D. S.; Singh, R. K. P.
Tetrahedron Lett. 2018, 59, 450-453.
3. Zhang, Q.; Shi, H.; Gao, B.; Tian, M.; Hua, X.; Wang, M. Sci.
Total Environ. 2016, 542, 845-853.
4. Wang, S.; Shi, D.; Yang, R.; Xu, Y.; Guo, H.; Yang, X. Can. J.
Chem. Eng. 2015, 93, 1787-1792.
5. Wang, H.; Sun, S.; Cheng, J. Tetrahedron Lett. 2017, 58, 3875-
3878.
6. Yang, J.; Wang, L.; Lv, Y.; Li, N.; An, Y.; Gao, S. Tetrahedron
Lett. 2018, 59, 156-159.
Figure 2. Raman spectra of (a) Poly[VDIM]Br and (b)
Poly[VDIM]Br3
7. Achilli, C.; Ciana, A.; Minetti, G. Tetrahedron Lett. 2017, 58,
4781-4782.
8. Rajkumar, C.; Thirumalraj, B.; Chen, S. ACS Appl. Mater.
Interfaces 2017, 9, 31794-31805.
9. Mojarrad, A. G.; Zakavi, S. Catal. Sci. Technol. 2018, 8, 768-781.
10. Ren, C.; Fang, R.; Yu, X.; Wang, S. Tetrahedron Lett. 2018, 59,
982-986.
11. Zhou, X.; Ji, H. Catal. Commun. 2014, 53, 29-32.
12. Ghorbani-choghamarani, A.; Sardari, S. Chin. J. Catal. 2010, 31,
1347-1350.
13. Zolfigol, M.; Amani, K.; Ghorbanichoghamarani, A.; Hajjami, M.;
Ayazinasrabadi, R.; Jafari, S. Catal. Commun. 2008, 9, 1739-
1744.
14. Goudarziafshar, H.; Ghorbani-Choghamarani, A.; Nikoorazm, M.
Chin. J. Chem. 2009, 27, 1801-1804.
15. Weilhard, A.; Victor, M. I. Q. ACS Catal. 2018, 8, 1628-1634.
16. Dziedzic, R. M.; Sarah, M. A. W. ACS Appl. Mater. Interfaces
2018, 10, 6825-6830.
17. Lu, Y.; Yu, G.; Wang, W.; Ren, Q.; Li, B.; Zhu, S.
Macromolecules, 2015, 48, 915-924.
18. Chen, S.; Lin, X.; Zhai, Z. Polym. Chem. 2018.
19. Zhang, Y.; Chen, B.; Zhang, Y. Green Chem. 2018, 20, 1594-
1601.
Figure 3. TG curves of (a) Poly[VDIM]Br and (b)
Poly[VDIM]Br3
20. Bacon, S. L.; Ross, R. J.; Daugulis, A. J.; Parent, J. S. Green
Chem. 2017, 19, 5203-5213.
21. Zhou, X.; Zhou, Y.; Nie, J.; Ji, Z.; Xu, J.; Zhang, X.; Du, B. ACS
Appl. Mater. Interfaces, 2014, 6, 4498-4513.
22. Abdelbagi, M. E. M.; Mondal, S.; van Smaalen, S.; Alt, H. G.
Polyhedron, 2018, 144, 176-186.
Conclusion
In summary, a novel and recoverable PIL-Poly[VDIM]Br3 was
successfully prepared and fully characterized through TGA , FT-
IR and Raman spectra. The Poly[VDIM]Br3/TBN catalytic
system equipped with high selectivity and efficiency was
developed for the aerobic oxidation of 19 kinds of sulfides at
room temperature. More importantly, the Poly[VDIM]Br3 was
readily prepared from green solvent ionic liquid, easily isolated
from reaction mixture and renewable, which met the
requirements of green chemistry.
23. Kusampally, U.; Pagadala, R.; Kamatala, C. R. Tetrahedron Lett.
2017, 58, 3316-3318.
24. Ghorbani-Choghamarani, A.; Abbasi, M. Chin. Chem. Lett. 2011,
22, 114-118.
25. Ghorbani-Choghamarani, A.; Azadi, G.; Tahmasbi, B.;
Hadizadeh-Hafshejani, M.; Abdi, Z. Phosphorus, Sulfur Silicon
Relat. Elem. 2014, 189, 433 - 439.
26. Luo, Z.; Geletii, Y. V.; Hillesheim, D. A.; Wang, Y.; Hill, C. L.
ACS Catal. 2011, 1, 1364-1370.
27. Liang, Y.; Li, X.; Wang, X.; Yan, Y.; Feng, P.; Jiao, N. ACS
Catal. 2015, 5, 1956-1963.
Acknowledgments
28. Zhang, H.; Wang, G. Tetrahedron Lett. 2014, 55, 56-58.
29. Zhang, H.; Chen, C.; Liu, R.; Xu, Q.; Zhao, W. Molecules, 2009,
15, 83-92.
The research was supported by Program for Changjiang
Scholars and Innovative Research Team in University
(IRT0711).
30. Sun, Z.; Moore, K. B.; Hill, J. G.; Peterson, K. A.; Schaefer, H. F.;
Hoffmann, R. J. Phys. Chem. B, 2018, 122, 3339-3353.

Highlights
1. The catalytic system exhibits high selectivity for the oxidation of sulfides to
sulfoxides.
2. Excellent yield of sulfoxide was obtained with air as oxidant under mild conditions.
3. The polymeric ionic liquid can be easily isolated and recoverable after the
completion of the oxidation reaction.