Structure-induced catalysis enhancement of Cu-amino catalysts for rapidly selective oxidation of sulfides in the presence of H2O2

Article abstract of DOI:10.1039/c6ra22393a

With benzyl phenyl sulfide as a model substrate and H₂O₂ as an oxidant, high selectivity toward the desired sulfoxide is obtained when using two Cu^II-amino acid complexes as catalysts, while strong stereospecific obstruction in a 1D helical array of complex 2 enables speedy sulfoxidation with excellent conversion.

Full text of DOI:10.1039/c6ra22393a

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Z. Zhang, X. Yang,
Q. Zhang, L. Wang, M. He, Q. Chen and X. huang, RSC Adv., 2016, DOI: 10.1039/C6RA22393A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 6
View Article Online
DOI: 10.1039/C6RA22393A
RSC Advance
COMMUNICATION
Structure-Induced Catalysis Enhancement of Cu-Amino Catalysts
for Rapidly Selective Oxidation of Sulfides in the Presence of H2O2
Received 00th January 20xx,
Accepted 00th January 20xx
Zhi-Hui Zhang,a Xu-Sheng Yang,a Qing-Qing Zhang,a Liang Wang,a Ming-Yang He,a Qun Chen,*,a and
Xian-Feng Huang*,a
b
DOI: 10.1039/x0xx00000x
www.rsc.org/
With benzyl phenyl sulfide as a model substrate and H2O2 as the was found in the catalytic sulfoxidation reactions due to the
oxidant, high selectivity toward the desired sulfoxide is obtained chiral ligand (L-lac) was not effective for chiral induction in the
for using two CuII-amino acid complexes as the catalysts, while sulfoxidation promoted by the metal ions.16, 18 Meanwhile, the
strong stereospecific obstruction in 1D helical array of complex 2 coordination polymers (CPs) especially 1D CPs have seldom
been involved in catalysis.19,
20
endows a speedy sulfoxidation with excellent conversion.
Very recently, the selective
oxidation of methylphenylsulfide with chiral 1D coordination
polymers of salen manganese metalloligands and lanthanide
Selective oxidation of sulfides to sulfoxides is a very important
reaction deserved much attention for sulfoxides are important
chiral auxiliary in asymmetric synthesis and valuable
pharmaceuticals.1, 2 Avoiding over oxidation of the sulfoxides
to their sulfones is also a significant issue for selective
oxidation of sulfides3. Among them, the use of H2O2 as a
selected oxidant offers many advantages that it is a cheap and
readily available reagent with water as the only by product.4, 5
The oxidation of prochiral sulfides to sulfoxides has been
catalyzed by a range of iron complexes6, titanium complexes7,
and vanadyl complexes8, 9, as well as copper complexes of
Schiff base ligands.10 Most of the metal-based catalysts were
discrete complexes with a combination of Schiff bases ligands
and metal salts.6, 11-15 The enantioselective sulfoxidation has
been studied using catalysts of chiral metal-organic
knots, an excellent conversion 100% and
a
good
chemoselectivity 88% were observed using iodosobenzene as
the oxidant20, which is expensive and leads to complicate by
products and related environment problems.
On the other hand, natural amino acids and their derivatives
are promising candidates to construct numerous interesting
22
coordination architectures21,
and apply in heterogeneous
catalysis and proton conductivity.23, 24 At this stage, Rosseinsky
and co-workers reported an aspartic acid based chiral MOF
with 1,2-bis(4-pyridyl)ethylene (bpe) co-ligand showing 3D
pillared layer structure. The protonated framework by HCl
endorses Brönsted acid catalytic activity for methanolysis of
cis-2,3-epoxybutane, confirming the heterogeneous nature of
the catalytic system25. A serine-based chiral MOF with 2D grid
network was design and synthesized by Wu and co-workers
toward the catalysis performance to 1,2-addition of α,β-
unsaturated ketones and Biginelli reaction24. In the pioneering
work to control the orientation of coordination helices, N-(2-
pyridylmethyl)-aspartic acids (2L-pasp and 2D-pasp) with
differing α-carbon chiralities have been utilized to assemble
with CuII salts into infinite single helices within the
coordination architecture26. However, examples of 1D
coordination polymers based on such pyridine-amino acid
functional reduced Schiff bases have not been documented to
date in the aspect of heterogeneous catalysis.
frameworks (CMOFs)16, 17
.
A porous homochiral MOF, namely [Zn2(bdc)(L-lac)(DMF)]·DMF
(L-lac = L-lactic acid, and H2bdc = 1,4-benzenedicarboxylic acid),
showed a remarkable catalytic activity in the oxidation of
thioethers to sulfoxides by urea hydroperoxide (UHP) or H2O2
for the substrates with small substituents. Even higher
conversion (up to 100%) and chemoselectivity was observed
with 90% H2O2 as the oxidant in a mixed solvent system of
CH2Cl2/CH3CN. Unfortunately, no or little asymmetric induction
Taking all these observations into account, we decided to
reinvestigate the coordination helical chains based on the
complexation of amino acid ligands with copper(II) ions. A
suitable modification to promising salen and salan ligands in
combination with an appropriate copper(II) source may
provide desired results. In this work, two pyridine-amino
reduced Schiff bases copper complexes, namely {[Cu(2L-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2016, 00, 1-5 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 6
View Article Online
DOI: 10.1039/C6RA22393A
COMMUNICATION
Journal Name
pasp)(H2O)]·3.5H2O}n
[
1
, 2L-H2pasp = N-(2-pyridylmethyl)-L- vgly ligand, one acetate anion and one coordinated water
, 3L-vgly = N- molecule as well as two water guests (Fig. 2a). Each CuII cation
aspartic acid], {[Cu(3L-vgly)(OAc)(H2O)]·2H2O}n [
2
(3-pyridylmethyl)-L-valine acid]‡ were synthesized and utilized coordinates to two carboxyl groups (one from 3L-vgly, the
for the selective oxidation of sulfides under green conditions other from acetate), one amine group, one pyridyl group and
using aqueous hydrogen peroxide as the oxidant and alcohol one aqua ligands, adopting a nearly ideal square-pyramidal
as the solvent.
geometry (τ = 0.09). Each 3L-vgly ligand bridges two
The chiral pyridylmethyl-amino acid derivatives were prepared neighboring copper atoms via the pyridyl group and the
by the Schiff base condensation of pyridinecarboxaldehyde carboxylate group to extend into 1D polymeric chains running
with enantiopure amino acid followed by reduction with along the crystallographic b-axis (Fig. 2b). In comparison with
NaBH4, as described elsewhere27. Complexation of reduced complex
Schiff base ligands with copper salts (1: 1 molar ratio) in opposite of the square-pyramids, and the helical pitch
dioxane/water afforded two blue block shape crystals of and [16.263(4) Å] is longer than that of because of 3-positional
, respectively. The products are stable in air and insoluble in pyridyl coordination in . Furthermore, hydrogen-bonding
1, there exists large isopropyl substituents on the
1
1
2
2
water and common organic solvents, and were formulated on between aqua ligand and carboxylate group from 3L-vgly
the basis of X-ray single-crystal diffraction and elemental (O3−H3A···O2) join neighboring helical chains into a 2D
analysis (See ESI for details).
network, which is extended to a 3D supramolecular framework
Compound 1 crystallizes in the orthorhombic space groups by O3−H3B···O5 interactions with lattice water included (Fig.
P21212 and exhibits 1D chiral coordination chains structure. 2c).
The basic coordination unit is [Cu(2L-pasp)(H2O)] with one
copper ion, one 2L-pasp ligand, and one coordinated water
molecule as well as four water guests (Fig. 1a). The CuII center
is coordinated by three O atoms from two carboxylate and one
lattice water, and two N atoms from one amino and one
pyridyl with a square-pyramidal geometry (τ = 0.16)28. Each 2L-
pasp chelates one copper atom through the pyridyl, amino,
and the carboxylate group and further bridges a neighboring
CuII ion through another carboxylate to form a 21 helical chain
with a pitch of 11.249(1) Å along the crystallographic a-axis
(Fig. 1b). The coordination assembly is the same as previously
reported Cu 2L-Pasp complex26, but with reduced number of
lattice water molecules and reduced crystal symmetry. Robust
hydrogen-bonding interactions were found to interlink
adjacent helical chains into a 3D supramolecular network (Fig.
S1).
Fig. 2 (a) The coordination environment of CuII with labeling
of the asymmetric atoms. (b) View of showing the 1D helix.
2
(c) Hydrogen-bonding network with the inclusion of water
guests.
Both complexes are air stable at ambient condition and
thermogravimetric experiments were implemented to
investigate their thermal stabilities. The thermogravimetric (TG)
curves of
1
and
2
(Fig. S2) reveal that the first weight loss of
and 14.1 % for ) from
23.1 and 13.2 (calculated: 22.1 % for
1
2
the room temperature to ca. 135 and 140 °C, respectively,
Fig. 1 Views of 1 showing the coordination environment of
CuII with labeling of the asymmetric atoms (a) and the 1D helix
which can be ascribed to the stepwise release of guest and
coordinated water molecules. There is
(135−190 °C) for the TG curve of indicating the thermal
stability of activated polymeric coordination molecules. In the
case of complex , a similar but shorter plateau (140−160 °C)
a short plateau
(b).
1
Complex
2
crystallizes in monoclinic P21 space group and has a
, but more
2
similar 1D chiral coordination structure as that of
1
as that in
1
also shows remain active structure is intact with
twist. The asymmetric unit contains one copper ion, one 3L-
2 | RSC Adv., 2016, 00, 1-5
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 6
View Article Online
DOI: 10.1039/C6RA22393A
Journal Name
open CuII center. After that, sharp weight losses of
COMMUNICATION
1
and
2
solvent, the oxidation with 30% hydrogen peroxide as the
indicate the decomposition of remain structures with oxidant was studied in a variety of organic solvents such as
comparable trends. methanol, ethanol, acetonitrile, toluene and dichloromethane.
Complex shows modest catalysis performance either in
1
Table 1 Selective oxidation of benzyl phenyl sulfide to the CH3CN or C2H5OH (Table 1, entries 1 and 2), and longer
corresponding sulfoxide with different Cu-based catalysts and reaction time leads to higher conversion of sulfide (Table 1,
various solvent systems.
entry 6). Complex 2 exhibits excellent catalysis performance in
a short time using CH3OH, C2H5OH or CH3CN as the solvent,
respectively (Table 1, entries 3–5). As an environmental
friendly solvent, water was also taken into account (Table 1,
entries 7 and 12). The result indicated that pure water is not
effective solvent for catalysis nevertheless the mixed
H2O/C2H5OH solvents result in good conversion and selectivity.
Interestingly, pure non-polar solvents such as toluene and
dichloromethane cause rather low conversion (entries 10 and
11). While incorporation of ethanol in the non-polar solvents
increases the conversion of benzyl phenyl sulfide in the fast
catalysis procedure (Table 1, entries 13–15).
Entr
y
Conversio
Selectivi TONc
ty (%)b
Solvent
Catalyst
Time (h)
n (%)b
25
24
98
98
99
86
13
18
4
1
CH3CN
1
1
2
2
2
1
2
2
2
2
2
0.5
0.5
0.5
0.5
0.5
8
>99
>99
>99
>99
>99
>99
98
5
2
C2H5OH
CH3CN
5
3
20
20
20
17
3
4
CH3OH
5
C2H5OH
CH3CN
6
7
H2O
6
Table 2 Substrate scope of sulfoxidation.
Conversion
8
THF
6
>99
97
4
Substrate
Product
Selectivity (%)b
TONc
9
EtOAc
6
1
(%)b
10
11
CH2Cl2
6
5
>99
>99
1
Toluene
H2O/C2H5O
H (1:1)
6
1
0
47
46
91
92
9
9
12
13
14
2
2
2
2
1
1
1
99
55
53
98
99
99
20
11
11
CCl4/C2H5O
H (1:1)
THF/C2H5O
H (1:1)
65
78
50
86
80
13
16
10
CH2Cl2/C2H
5OH (1:1)
C2H5OH
15
16
17
1
87
8
99
17
2
Blank
24
24
>99
>99
Cu(NO3)2·
2.5H2O
Cu(OAc)2·
H2O
C2H5OH
C2H5OH
71
14
>99
18
19
24
20
35
>99
>99
4
7
3L-vgly
+
>99
88
>99
99
20
18
C2H5OH
Cu(OAc)2· 24
H2O
Reaction conditions: Sulfide (1.0 mmol), catalyst (5 mol%), solvent (10
mL), 30% H2O2 (3.0 mmol), 30 oC. bConversion (%) and selectivity (%)
were determined by HPLC. cTON, Turn Over Number.
Reaction conditions: Sulfide (1.0 mmol), catalyst 2 (5 mol%), ethanol
(10 mL), 30% H2O2 (3 equiv), 30 oC, 0.5 h. bConversion (%) and
selectivity (%) were determined by HPLC. cTON, Turn Over Number.
The selective oxidation of sulfides to sulfoxides is one of the
most fundamental organic transformations due to the fact that
sulfoxides are important intermediates for various
pharmaceutically active compounds.3 Both two copper
complex catalysts were utilized to react with related sulfides
with 30% H2O2 as the oxidant to test their catalytic capability.
Initially, benzyl phenyl sulfide was chosen as the model
substrate to optimize the reaction conditions. The effects of
different reduced Schiff base catalysts, reaction time and
solvent media were investigated in an attempt to optimize the
sulfoxidation condition. The catalytic performances of copper
complex catalysts are listed in Table 1. To select the proper
Continually, the optimum condition was established as using
catalyst
2 (5 mol%), 30% H2O2 (3.0 mmol) and ethanol (10 mL)
at 30 oC by varying the reaction factors (See ESI, Table S2–5), if
enantioselectivity was not taking into account. With the
proper reaction condition recognized, the substrate scope was
extended to a series of structurally diverse sulfides such as
methylphenyl sulfide, 4-nitrophenylmethyl sulfide, 4-
methoxyphenylmethyl sulfide, dibutyl sulfide, diphenyl sulfide,
and the sulfide intermediate of omeprazole (Table 2). S-
enantiomer of the omeprazole, esomeprazole, is a proton-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-5 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 6
View Article Online
DOI: 10.1039/C6RA22393A
COMMUNICATION
Journal Name
pump inhibitor for the treatment of gastroesophageal reflux
disease, which was successfully synthesized using chemical or
biological oxidations3. Noticeably, it turns out that either small
alkyl or bulky diphenyl group leads to modest conversion for
sulfides (Table 2, entries 1–5). And electron rich thioether
substrates result in lower selectivity. While semirigid groups
with flexible methylene provide decent conversion and
selectivity (entries 6 and 7 in Table 2), which is favorable to the Fig. 4 SEM images of complex
selective synthesis of omeprazole. The better catalysis
2
before and after catalysis.
property of
2
than that of
1 may be ascribed to the inherent
nature of complex
2, suitable supramolecular window (Fig. 2c)
available for the shape selection.
The stability and recyclability of catalyst
2
were confirmed by
presented
XRD and SEM studies (Fig. 3 & 4). It is notable that
2
modest stability in acetonitrile (better than ethanol), being
reused for 4 cycles without significant loss in its activity. A
simple filtration testified the reaction is mainly
a
heterogeneous catalysis with a slight homogeneous way (Fig.
5). Despite the good conversion and chemoselectivity, very low
asymmetric induction was observed in the catalytic
sulfoxidation (around 20%, Table S2–S5). This phenomenon
may be attributed to inadequate steric effect of the chiral
centers. In comparison, recently reported manganese and
lanthanide 1D chiral coordination polymers of a salen ligand20
leads to a better conversion but lower chemoselectivity for the
sulfoxidation of methylphenyl sulfide and 4-nitrophenylmethyl
sulfide. Although the lanthanide complex contains bulk
substituent groups, enantioselectivity is relatively low for the
sulfoxidation (up to 25%).
For the catalysts in this work, the CuII centers adopt similar
square-pyramidal coordination geometry and dissimilar
environments. But each of them has a teminal aqua ligand,
which was assumed to activate equivalent H2O2 oxidant and
avoid over oxidation of sulfide, leading to excellent
Fig. 5 Filtration experiment for complex 2. Conversions and
selectivities are given as a function of time.
In summary, two copper coordination polymers based on
pyridylmethyl amino acids have been synthesized and
structurally characterized. They exhibit dissimilar coordination
environments of the CuII centers but similar 1D helical
coordination assemblies. Their catalytic activity in sulfoxidation
was evaluated. The reaction parameters, such as reaction time
and solvents, were varied to improve the conversion and
selectivity for the benzyl phenyl sulfide. This method
represents the first example of the reduced Schiff amino
complexes catalyzing the sulfoxidation under environmentally
friendly and mild conditions (H2O2 as the oxidant). Both the
two copper complexes exhibit catalytic activity with high
chemoselectivity for all reactions. Nevertheless, complex
2 has
remarkable catalytic activity with size and shape selectivity,
and high conversion in the fast sulfoxidation of thioethers
bearing rigid groups with flexible methylene.
conversion and chemoselectivity. Complex
2 promoted a rapid
catalysis and was favorable to the chemoselective synthesis of
omeprazole. The investigation of enantioselective synthesis of
prochiral sulfoxides is on the way to screen coordination
polymers based on pyridylmethyl amino acids in the oxidation
processes with environmentally friendly oxidants.
We gratefully acknowledge the financial support from the
National Natural Science Foundation of China (21201026 and
21302014), Qing Lan Project and a Project Funded by the
Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD), Jiangsu Key Laboratory of
Advanced Catalytic Materials and Technology (BM2012110).
Notes and references
‡ Crystal data for 1: C20H38Cu2N4O17, Mr = 733.62, orthorhombic,
space group P21212 (no. 18), a = 11.2493(11), b = 16.5313(17), c
= 8.4611(8) Å, V = 1573.5(3) Å3, Z = 2, Dc = 1.548 Mg/m3, Flack
parameter, 0.029(5); µ = 1.429 mm–1, R(int) = 0.0207; goodness-
of-fits on F2 = 1.072; R1 = 0.0219, wR2 = 0.0645. Crystal data for
Fig. 3 XRD patterns of complex 2 before and after catalysis.
2: C13H24CuN2O7, Mr = 383.88, monoclinic, space group P21 (no.
4), a = 7.2507(16), b = 16.263(4), c = 7.3756(16) Å, V = 868.0(3)
4 | RSC Adv., 2016, 00, 1-5
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 6
View Article Online
DOI: 10.1039/C6RA22393A
Journal Name
COMMUNICATION
Å3, Z = 2, Dc = 1.469 Mg/m3, Flack parameter, 0.038(8); µ = 1.293
28. G. A. Senchyk, A. B. Lysenko, H. Krautscheid, E. B. Rusanov,
A. N. Chernega, K. W. Kraemer, S.-X. Liu, S. Decurtins and K.
V. Domasevitch, Inorg. Chem. , 2013, 52, 863-872.
mm–1, R(int) = 0.0173; goodness-of-fits on F2 = 0.844; R1
0.0210, wR2 = 0.0616.
=
1. M. C. Carreno, G. Hernandez-Torres, M. Ribagorda and A.
Urbano, Chem. Commun. , 2009, 6129-6144.
2. G. E. O'Mahony, A. Ford and A. R. Maguire, J. Sulfur Chem. ,
2013, 34, 301-341.
3. E. Wojaczynska and J. Wojaczynski, Chem. Rev. , 2010, 110
,
4303-4356.
4. H. Srour, P. Le Maux, S. Chevance and G. Simonneaux, Coord.
Chem. Rev. , 2013, 257, 3030-3050.
5. G. La Sorella, L. Sperni, G. Strukul and A. Scarso, Adv. Synth.
Catal. , 2016, DOI: 10.1002/adsc.201600430, Ahead of Print.
6. H. Egami and T. Katsuki, J. Am. Chem. Soc. , 2007, 129, 8940-
8941.
7. L. Postigo, M. Ventura, T. Cuenca, G. Jimenez and B. Royo,
Catal. Sci. Technol., 2015, 5, 320-324.
8. C. Drago, L. Caggiano and R. F. W. Jackson, Angew. Chem. Int.
Ed., 2005, 44, 7221-7223.
9. A. Lazar, P. Sharma and A. P. Singh, Microporous Mesoporous
Mater. , 2013, 170, 331-339.
10. G. E. O'Mahony, A. Ford and A. R. Maguire, J. Org. Chem. ,
2012, 77, 3288-3296.
11. P. K. Bera, N. Gupta, S. H. R. Abdi, N. H. Khan, R. I. Kureshy
and H. C. Bajaj, Rsc Adv., 2015, 5, 47732-47739.
12. Z.-Z. Li, S.-Y. Yao, J.-J. Wu and B.-H. Ye, Chem. Commun. ,
2014, 50, 5644-5647.
13. W. Dai, G. Li, L. Wang, B. Chen, S. Shang, Y. Lv and S. Gao, Rsc
Adv., 2014,
4, 46545-46554.
14. P. K. Bera, P. Kumari, S. H. R. Abdi, N.-u. H. Khan, R. I.
Kureshy, P. S. Subramanian and H. C. Bajaj, Rsc Adv., 2014, 4,
61550-61556.
15. P. Kelly, S. E. Lawrence and A. R. Maguire, Synlett, 2007,
1501-1506.
16. D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov, E. P.
Talsi, V. P. Fedin and K. Kim, Angew. Chem. Int. Ed., 2006, 45
,
916-920.
17. W. Xuan, C. Ye, M. Zhang, Z. Chen and Y. Cui, Chem. Sci.,
2013, , 3154-3159.
4
18. A. L. Nuzhdin, D. N. Dybtsev, V. P. Fedin and G. A.
Bukhtiyarova, Dalton Trans. , 2009, 10481-10485.
19. W. L. Leong and J. J. Vittal, Chem. Rev. , 2011, 111, 688-764.
20. M. Yadav, A. Bhunia, S. K. Jana and P. W. Roesky, Inorg.
Chem. , 2016, 55, 2701-2708.
21. X. L. Yang and C. D. Wu, CrystEngComm, 2014, 16, 4907-
4918.
22. E. V. Anokhina, Y. B. Go, Y. Lee, T. Vogt and A. J. Jacobson, J.
Am. Chem. Soc. , 2006, 128, 9957-9962.
23. S. C. Sahoo, T. Kundu and R. Banerjee, J. Am. Chem. Soc. ,
2011, 133, 17950-17958.
24. M. Wang, M.-H. Xie, C.-D. Wu and Y.-G. Wang, Chem.
Commun. , 2009, 2396-2398.
25. M. J. Ingleson, J. P. Barrio, J. Bacsa, C. Dickinson, H. Park and
M. J. Rosseinsky, Chem. Commun., 2008, 1287-1289.
26. S.-P. Wu and C.-H. Lee, CrystEngComm, 2009, 11, 219-222.
27. Q.-Q. Zhang, Z.-H. Zhang, B.-H. Qu, Q. Chen and M.-Y. He,
Inorg. Chim. Acta 2014, 418, 59-65.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-5 | 5
Please do not adjust margins

RSC Advances
Page 6 of 6
View Article Online
DOI: 10.1039/C6RA22393A
A Cu-amino coordination polymer promotes a rapid sulfoxidation of benzyl phenyl sulfide toward the
sulfoxide with high conversion and selectivity.