Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions

Article abstract of DOI:10.1016/j.tet.2014.07.091

Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under organic solvent-free conditions was demonstrated by the MWW-type titanosilicate zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good selectivities at ambient temperature using 1.0-1.2 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at least five cycles, and the only byproduct is water. Sulfides were directly oxidized to give sulfones in high yields by 2.5 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions.

Full text of DOI:10.1016/j.tet.2014.07.091

Accepted Manuscript
Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with
MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions
Yoshihiro Kon, Dr. Toshiyuki Yokoi, Masato Yoshioka, Shinji Tanaka, Yumiko
Uesaka, Takehisa Mochizuki, Kazuhiko Sato, Takashi Tatsumi
PII:
S0040-4020(14)01134-X
10.1016/j.tet.2014.07.091
TET 25885
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 14 April 2014
Revised Date: 24 July 2014
Accepted Date: 25 July 2014
Please cite this article as: Kon Y, Yokoi T, Yoshioka M, Tanaka S, Uesaka Y, Mochizuki T, Sato K,
Tatsumi T, Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with MWW-type
titanosilicate zeolite catalyst under organic solvent-free conditions, Tetrahedron (2014), doi: 10.1016/
j.tet.2014.07.091.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with
MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions
1
)
2)
2)
1)
Yoshihiro Kon , Toshiyuki Yokoi , Masato Yoshioka , Shinji Tanaka , Yumiko
1
)
1)
1)*
2)*
Uesaka , Takehisa Mochizuki , Kazuhiko Sato , Takashi Tatsumi
1

ACCEPTED MANUSCRIPT
Title
Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with
MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions
Authors
1
)
2)
2)
1)
Yoshihiro Kon , Toshiyuki Yokoi , Masato Yoshioka , Shinji Tanaka , Yumiko
1
)
1)
1)*
2)*
Uesaka , Takehisa Mochizuki , Kazuhiko Sato , Takashi Tatsumi
Affiliation
1
) National Institute of Advanced Industrial Science and Technology (AIST), Central5
Higashi 1-1-1, Tsukuba 305-8565, Japan
2
) Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
∗
∗
Corresponding author. Tel.: +81-29-861-4511; fax: +81-29-861-4511; e-mail: k.sato@aist.go.jp
Corresponding author. Tel.: +81-45-924-5238; fax: +81-45-924-5282; e-mail: ttatsumi@cat.res.titech.ac.jp
2

ACCEPTED MANUSCRIPT
Contact address:
Dr. Yoshihiro Kon
National Institute of Advanced Industrial Science and Technology (AIST)
Address: Central 5 Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan.
Fax: +81-29-861-4511
Tel: +81-29-861-4425
E-mail:y-kon@aist.go.jp
3

ACCEPTED MANUSCRIPT
Abstract
Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under
organic solvent-free conditions was demonstrated by the MWW-type titanosilicate
zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good
selectivities at ambient temperature using 1.0-1.2 equivalent of hydrogen peroxide with
the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an
interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good
chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at
least five cycles, and the only byproduct is water. Sulfides were directly oxidized to
give sulfones in high yields by 2.5 equivalent of hydrogen peroxide with the
MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions.
Keywords
oxidation; green chemistry; hydrogen peroxide; titanosilicate zeolite catalyst; sulfide
4

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1
. Introduction
The selective oxidation of sulfides to sulfoxides or sulfones is a useful transformation in
1
organic chemistry. Sulfoxides and sulfones are known as valuable intermediates or
1a,c, 2
building blocks of pharmaceuticals such as antifungal and antihypertensive agents.
And many kinds of oxidants such as nitric acid, organic peroxides, and heavy metal
oxidants have been employed as effective oxidants to form sulfoxides and/or sulfones in
1
high yields. Among various kinds of oxidants, hydrogen peroxide (H O ) is one of the
2
2
3
most straightforward, clean, and versatile oxidant from both an environmental and
economic perspective because H O has a high content of active oxygen and its
2
2
4
byproduct is water.
There are numerous methods for oxidation of sulfides using aqueous H O as an
2
2
1
,5-14
oxidant.
And it is well known that sulfides are oxidized to generate sulfoxides and
sulfones by H O at elevated temperature and/or with a long reaction time without a
2
2
5
metal catalyst. However, highly selective oxidation of sulfides under mild reaction
conditions is achieved by the application of optimized catalysts and/or reaction
6
-10
6
systems.
For example, application of a micro-reactor, an acid- or substrate-catalyzed
7
reaction, and homogeneous catalysts are well known as effective converting
8
-10
methods.
These reactions, however, require large amounts of hazardous organic
5

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solvent and/or high temperature. When a homogeneous catalyst is used, it is also
difficult to separate and reuse it after the reaction. On the other hand, solid catalysts are
11-18
more easily removed and reused after the reaction.
The use of titanosilicate zeolite
catalysts such as TS-1 and Ti-MWW as a solid catalyst is one of the simplest and most
effective choices for achieving high-yield syntheses of various sulfoxides and sulfones.
There are several reports on the synthesis of sulfoxides and sulfones by titanosilicate
12, 13
zeolite catalysts in the presence of H O .
However, the reactions require large
2
2
amounts of organic solvents such as haloalkanes, alcohols, and MeCN. The removal of
organic solvents in these oxidation processes would be required to create
environmentally friendly chemical processes. Recently, we reported on effective
methods of the synthesis using an interlayer expanded titanosilicate zeolite with the
MWW-type structure catalyst (Ti-IEZ-MWW) to give bulky diphenyl sulfoxide under
14
organic solvent-free reaction conditions. A high-yield synthesis of sulfoxide was
achieved by optimization of the zeolite structure to overcome the disadvantage of
organic solvent-free conditions.
We report herein a detailed study on high-yield syntheses of various sulfoxides using
1
.0-1.2 equivalent of 30-35% H O aqueous solution with well-designed titanosilicate
2 2
zeolite catalysts including Ti-MWW and Ti-IEZ-MWW under organic solvent-free
6

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conditions. An effective oxidation of sulfides to give sulfones by 2.5 equivalent of 35%
H O aqueous solution with the MWW-type titanosilicate zeolite catalyst was also
2
2
shown.
7

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2
. Results and Discussion
.1. H O oxidation of sulfides to sulfoxides using titanosilicate zeolite catalysts
2
2
2
Three types of titanosilicate zeolite catalysts (TS-1, Ti-MWW, and Ti-IEZ-MWW)
were prepared to construct an optimized oxidation system. TS-1 was employed as a
standard titanosilicate zeolite catalyst having an MFI-type structure with
1
5
three-dimensional 10-membered-ring (3D 10-MR) pores. Ti-MWW was prepared as
an MWW-type structure which had 12-MR with a system of independent 10-MR
1
6
channels. Ti-IEZ-MWW was prepared as an interlayer-expanded MWW zeolite by the
silylation of the layered precursor of the MWW-type titanosilicate (Ti-MWW(P)) with
17
diethoxydimethylsilane (DEDMS) under acidic conditions followed by calcination.
The atomic ratio of Si/Ti in titanosilicate zeolite catalyst was estimated by ICP analysis;
the ratios were 72, 57, and 86 for TS-1, Ti-MWW, and Ti-IEZ-MWW, respectively
(Table 1). BET (Brunauer-Emmett-Teller) surface area in titanosilicate zeolite catalyst
was calculated from the amount of absorbed N on the surface; the values were 471, 499,
2
and 521 for TS-1, Ti-MWW, and Ti-IEZ-MWW, respectively (Table 1).
Thioanisole was selected as a screening substrate to estimate the catalytic activities of
titanosilicate zeolite catalysts. The reaction was conducted with 30-35% H O (1.0-1.2
2
2
equivalent to thioanisole) and titanosilicate zeolite catalyst (10 mg) in open air at 25 °C
8

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for 2 h with vigorous stirring, and the results are summarized in Table 1.
Table 1. The oxidation of thioanisole with TS-1, Ti-MWW, and Ti-IEZ-MWW catalysts
a
using aqueous H O2
2
O
S
H O aq.
2
2
S
catalyst (10 mg)
2
5 °C, 2 h
b
d
f
Entry
Catalyst
Si /Ti ratio
BET
surface
area
Conv.
Yield (%)
sulfoxide
Selectivity TON
d
e
c
(%)
sulfone
(%)
1
2
3
4
None
-
-
19
18
53
89
70
94
0
95
82
89
89
94
-
TS-1
72
57
471
499
521
521
65
8
230
310
370
490
Ti-MWW
>99
79
10
6
Ti-IEZ-MWW 86
Ti-IEZ-MWW 86
g
5
>99
6
a
Reaction conditions: thioanisole (1.0 mmol), 30% H O (1.0 mmol), titanosilicate
2
2
zeolite catalyst (10 mg), 25 °C, 1000 rpm, 2 h.
b
The atomic ratio of Si/Ti in titanosilicate zeolite catalyst was estimated by ICP
analysis.
c
The BET surface area in titanosilicate zeolite catalyst was calculated from the amount
of adsorbed N on the surface.
2
d
Yield and conversion on the basis of thioanisole, determined by GC analysis with
biphenyl as an internal standard.
e
Yield/conversion x 100
f
moles of product per a mole of Ti atom
g
Reaction conditions: thioanisole (1.0 mmol), 35% H O (1.2 mmol), pretreated
2
2
Ti-IEZ-MWW (10 mg), 25 °C, 1000 rpm, 2 h.
It is well known that the thioanisole is easily oxidized to give methyl phenyl sulfoxide
5
, 7b, 9l
without a catalyst at higher temperatures and/or longer reaction times.
The reaction
9

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at lower temperature (25 °C) without organic solvent reaction conditions for 2 h resulted
in lower levels of sulfoxidation (18% yield, Table 1, entry 1). TS-1 is known as a
common titanosilicate zeolite catalyst that showed a good reactivity for H O oxidation
2
2
1
2, 13
of sulfides by an optimized organic solvent.
However, TS-1 did not show a high
activity under organic solvent-free conditions; it gave methyl phenyl sulfoxide in 53%
yield with methyl phenyl sulfone in 8% yield (Table 1, entry 2). Ti-MWW showed high
activity levels even under organic solvent-free conditions; it catalyzed the sulfoxidation
of thioanisole to give the corresponding sulfoxide in high yield (89%, Table 1, entry 3).
Ti-MWW having a 10-MR interlayer pore has proved to be much more active than TS-1
18
in the epoxidation of linear alkenes with H O . Ti-IEZ-MWW catalyst also showed
2
2
high activity to give methyl phenyl sulfoxide in 70% yield with 89% selectivity (Table 1,
entry 4). The optimization of the amount of H O about the reaction using
2
2
Ti-IEZ-MWW was carried out. The yields of methyl phenyl sulfoxide using 1.0 eq. of
3
0% H O , 1.2 eq. of 30% H O , 1.0 eq. of 35% H O , and 1.2 eq. of 35% H O were
2 2 2 2 2 2 2 2
7
0% (Table 1, entry 4), 86%, 79%, and 91%, respectively. In addition, calcination of
Ti-IEZ-MWW at 550 °C for 5 h just before the reaction improved the activity of
Ti-IEZ-MWW toward the oxidation of thioanisole using 1.2 eq. of 35% H O
2
2
(conversion, >99%; yields, 94%; selectivity, 94%; Table 1, entry 5). On the other hand,
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the same treatment had almost no effect on the reactions using TS-1 and Ti-MWW
catalysts. Although Ti-IEZ-MWW seems to show the high activity derived from 12-MR
interlayer pore in addition to MWW-type structure, it also tends to adsorb water and/or
organic compounds and to diminish the activity. Calcination of Ti-IEZ-MWW just
before the reaction and the use of 1.2 eq. of 35%H O aq. would be effective for
2
2
recovering the original activity of Ti-IEZ-MWW. The turnover numbers (TONs) in TS-1,
Ti-MWW, Ti-IEZ-MWW, and Ti-IEZ-MWW (calcined) were found to be 230, 310, 370,
and 490, respectively. The calculated turn over frequencies (TOFs) in Ti-MWW and
Ti-IEZ-MWW at the oxidation of thioanisole were on the same levels (1900 and 2000
-1
h for Ti-MWW and Ti-IEZ-MWW, respectively).
Thioanisole was converted to the corresponding sulfoxide in high yield with good
selectivity in the presence of the Ti-IEZ-MWW catalyst. On the other hand, small
amounts of sulfone (6% yield) were observed. This trend was also observed by the XSO
1
9
experiment (Figure 1). The X value reflected the extent of oxidation at the SO site in
SO
thianthrene 5-oxide (SSO). The oxidation of SSO using the Ti-IEZ-MWW catalyst was
carried out at 40 °C for 18 hours. And the generated oxidized products were detected by
NMR analysis. The yields of products were as follows; 1.1% yield for thianthrene
5
,5-dioxide (SSO ), 54.2% yield for thianthrene 5,10-dioxide (cis- and trans-mixture,
2
11

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SOSO), 6.7% yield for thianthrene 5,5,10-trioxide (SOSO ). The X
value of
2
SO
Ti-IEZ-MWW was calculated to be 0.11. This XSO value was in a similar range to those
*
of Ti-beta (0.07 and 0.19), which has the BEA-type structure with three-dimensional
1
9d
1
2 MR pores.
Figure 1. Oxidation of thianthrene 5-oxide (SSO) by Ti-IEZ-MWW catalyst
Competitive experiments using a 1:1 mixture of thioanisole and para substituted
thioanisole showed the Hammett linear free-energy relationship;
= -0.41 (Table 2 and Figure 2). The negative value suggests the electrophilic nature
of Ti active species generated in Ti-IEZ-MWW. This tendency is consistent with
σ+ correlated well with
ρ
ρ
9a, 20
previously reported sulfide oxidation with H O .
2
2
a
Table 2. Competitive oxidation of para substituted thioanisoles
12

ACCEPTED MANUSCRIPT
b
b
Entry
para substituents(X)
Conv. of para X(%)
Conv. of H (%)
1
2
3
4
Me
Cl
7.60
7.29
5.46
-
6.03
8.60
2.73
-
OMe
H
a
Reaction was run using a 1:1 mixture of thioanisole and para substituted thioanisole
2.0 mmol), 35% H O aq. (1.4 mmol), and Ti-IEZ-MWW (10 mg) at 25 ˚C for 5 min.
(
2
2
b
Determined by GC analysis.
p-OMe
0.3
0.2
0.1
0
p-Me
-0.405
=
2
p-H
p-Cl
(
r = 0.99)
-0.1
-
1 -0.8 -0.6 -0.4 -0.2 0 0.2
+
Figure 2. Hammett plots for the competitive oxidation of thioanisole and para
2
substituted thioanisole. Slope = -0.41 (r = 0.99).
The application of TS-1−, Ti-MWW−, and Ti-IEZ-MWW−catalyzed H O oxidation
2
2
to various sulfides is shown in Table 3. In the case of the TS-1 catalyst, methyl
-methylphenyl, 4-chlorophenyl methyl, and 4-bromophenyl methyl sulfoxides were
given in 21%, 14%, and 14% yields, respectively (Table 3, entries 2-4). Ti-MWW and
4
13

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Ti-IEZ-MWW catalysts gave methyl para substituted phenyl sulfoxides in high yields
(76-93% for Ti-MWW and 75-92% for Ti-IEZ-MWW; Table 3, entries 2-4). These
results showed that Ti-MWW, which has a 10-MR interlayer pore, is much more active
than TS-1 for the sulfoxidation of para substituted thioanisoles under organic
solvent-free conditions. The reaction of 2-methyl sulfanyl pyridine, which includes a
nitrogen atom as well as a sulfur atom as a reactive site, gave the corresponding
sulfoxide in moderate to good yields using TS-1, Ti-MWW, and Ti-IEZ-MWW
catalysts (62% yield for TS-1, 79% yield for Ti-MWW, and 79% yield for
Ti-IEZ-MWW, respectively; Table 3, entry 5). In these reactions, N-oxide of 2-methyl
sulfanyl pyridine was not observed. Chemoselectivity of this catalytic system was also
checked by the reactions of allyl phenyl sulfide and 2-phenylthioethanol. Allyl phenyl
sulfide and 2-phenylthioethanol were oxidized by Ti-IEZ-MWW to give the
corresponding sulfoxides in 72% and 95% yields, respectively (Table 3, entries 6 and
7
). In these oxidations, epoxidation nor carbonyl compounds were not observed.
The significance of Ti-IEZ-MWW was exerted in the case of sulfides having bulky
2
1
substituents such as diphenyl sulfide. Oxidation of diphenyl sulfide gave the
corresponding sulfoxide in good yield by the Ti-IEZ-MWW catalyst (50% yield; Table
3
, entry 8). In contrast, the reactions of diphenyl sulfide using the TS-1 or Ti-MWW
14

ACCEPTED MANUSCRIPT
catalyst gave the corresponding sulfoxide in low yields (8% and 29% yields for TS-1
and Ti-MWW, respectively; Table 3, entry 8). The calculated TOFs were 15 for
Ti-MWW and 41 for Ti-IEZ-MWW. Ti-IEZ-MWW showed a higher catalytic activity
for sulfoxidation of diphenyl sulfide than did Ti-MWW. The BET surface area of the
titanosilicate zeolite catalysts was almost within the same range, and thus the reactivity
of the catalysts showed a direct correlation with the relative ease with which sulfides
1
3b
contact to the Ti active sites of the zeolites similar to the case of Ti-beta. Although the
potential advantages of the MWW-type materials are expected from their supercages
and side pockets, access to the supercages is seriously restricted by the openings of the
elliptical 10-MR pores. Because Ti-IEZ-MWW has a 12-MR interlayer pore, bulkier
aryl sulfides can access the Ti active site of Ti-IEZ-MWW. TS-1 and Ti-MWW do not
have a 12-MR interlayer pore, and it is hard for bulkier aryl sulfides to come into
contact with the Ti active sites of TS-1 and Ti-MWW. Similar results were observed
from the reactions of the dialkyl sulfides. Di-n-butyl sulfide was sulfoxidized effectively
to give di-n-butyl sulfoxide in this order: Ti-MWW (80% yield) > Ti-IEZ-MWW (62%
yield) > TS-1 (27% yield). Ti-MWW and Ti-IEZ-MWW showed a higher activity than
TS-1. The activities of titanosilicate zeolite catalysts for the sulfoxidation of di-n-octyl
sulfide were directly linked to their interlayer pore size: Ti-IEZ-MWW (29% yield) >
15

ACCEPTED MANUSCRIPT
Ti-MWW (12% yield) > TS-1 (7% yield). Elongation of the interlayer would also be
effective for the sulfoxidation of bulky alkyl sulfides (Table 3, entries 9 and 10).
In the reaction of diphenyl sulfide using the Ti-IEZ-MWW catalyst, the removal of the
catalyst in the middle of the reaction stopped the sulfoxidation. Ti in the filtrate of
diphenyl sulfide oxidation was not detected by ICP analysis. These results clearly
showed that the sulfoxidation was catalyzed at the Ti active sites on solid Ti-IEZ-MWW.
The Ti-IEZ-MWW catalyst could easily be reused in the next reaction. In the
sulfoxidation of thioanisole, no decrease in yields was detected after five cycles to give
the corresponding sulfoxide in 85-94% yields (Table 4). The Ti-IEZ-MWW catalyst was
removed from the product after the reaction, washed by water and acetone, and then
calcinated at 550 °C for 5 h for use in the next reaction.
Table 3. The oxidation of various sulfides to sulfoxides with TS-1, Ti-MWW, and
a
Ti-IEZ-MWW catalysts using aqueous H O
2
2
Entry
1
Substrate
Product
Conv.
Yield
Selectivity
b
b
c
(%)
(%)
(%)
d
d
d
19
18
95
e
e
f
e
6
>
>
5
53
82
f
h
f
99
99
89 (85)
89
g
g
h
g
94 (83)
94
16

ACCEPTED MANUSCRIPT
d
e
f
d
d
e
f
2
3
4
5
6
7
8
9
1
10
8
80
78
93
92
e
2
9
>
7
21
88
f
5
g
g
i
i
i
j
j
j
i
g
99
92 (84)
d
d
d
d
d
1
1
9
9
1
1
8
9
1
>99
e
f
e
e
6
8
14
88
f
f
93
95
g
g
g
7
87 (82)
90
d
d
1
>99
S
e
f
e
e
8
4
8
14
78
Br
f
f
76
90
g
d
e
f
g
g
75 (77)
77
d
12
12
>99
e
e
6
8
8
2
3
8
9
8
2
62
91
f
f
79
96
g
g
g
2
79 (84)
96
d
d
d
1
50
e
e
e
2
67
f
f
f
6
0
72
84
g
d
e
f
g
g
72 (84)
80
d
d
e
f
85
85
>99
>99
>99
>99
e
8
9
9
5
7
5
85
f
97
g
d
e
f
g
g
95 (84)
k
d
d
11
5
45
e
e
1
3
6
6
6
4
8
50
f
f
29
81
g
d
e
f
g
g
50 (47)
78
l
d
d
26
25
96
e
e
3
9
9
6
8
1
3
2
6
27
84
f
f
80
83
g
g
i
g
0
82 (79)
91
l
d
d
d
f
0
6
>99
e
e
e
7
88
f
f
2
0
12
>99
g
g
j
g
29 (32)
97
a
Reaction conditions: for no-catalyst, TS-1, and Ti-MWW: sulfide (1.0 mmol), 30%
H O (1.0 mmol), catalyst (10 mg), 25 °C, 1000 rpm, 2 h, unless otherwise stated; for
2
2
Ti-IEZ-MWW: sulfide (1.0 mmol), 35% H O (1.2 mmol), Ti-IEZ-MWW (10 mg),
2
2
2
5 °C, 1000 rpm, 2 h, unless otherwise stated.
b
Yield and conversion on the basis of sulfide, determined by GC analysis with biphenyl
17

ACCEPTED MANUSCRIPT
or n-decane as an internal standard.
c
Yield/conversion x 100.
d
e
no catalyst.
using TS-1 catalyst.
f
using Ti-MWW catalyst.
g
h
i
using Ti-IEZ-MWW catalyst.
isolated yield (10 mmol scale).
isolated yield (3 mmol scale).
j
1
mixture of sulfoxide and sulfone was obtained, the yield was calculated by H NMR (3
mmol scale).
k
4
0 °C, 1000 rpm, 18 h.
l
2
5 °C, 1000 rpm, 4 h.
Table 4. Oxidation of thioanisole to methyl phenyl sulfoxide with Ti-IEZ-MWW
a
catalyst using 35% aqueous H O , and recycling of catalyst
2
2
Number of reuses
1
2
3
4
5
Yield of methyl phenyl sulfoxide
85
90
91
89
94
b
(%)
a
Substrate: catalyst ratio (wt%); thioanisole: Ti-IEZ-MWW = 1 : 0.08, 35% H O (1.2
2
2
eq.) was used. 25 °C, 1000 rpm, 2 h.
b
Yield on the basis of thioanisole, determined by GC analysis with biphenyl as an
internal standard.
18

ACCEPTED MANUSCRIPT
2
.2.
H O oxidation of sulfides to sulfones using titanosilicate zeolite catalyst
2
2
Oxidation of sulfides to sulfones was attempted using 2.5 eq. of 35% H O aq. with
2
2
Ti-zeolite catalyst at 50 °C for 3 h (Table 5). Thioanisole was oxidized under
catalyst-free conditions to give methyl phenyl sulfoxide in 92% yield, although the
desired sulfone was generated only in 8% yield (Table 5, entry 1). TS-1 catalyst gave
sulfone in 55% yield, while Ti-MWW and Ti-IEZ-MWW catalysts gave methyl phenyl
sulfone quantitatively (Table 5, entry 1). Thioanisole derivatives such as 4-methyl,
4
-chloro, and 4-bromo thioanisole were effectively catalyzed by Ti-IEZ-MWW to give
the corresponding sulfones in high yields (87%, 97%, and 94%, respectively; Table 5,
entries 2-4). TS-1 and Ti-MWW catalyzed the oxidation of para substituted thioanisoles,
producing the corresponding sulfones in 28-35% and 76-94% yields, respectively (Table
5
, entries 2-4). Nitrogen-containing sulfide was effectively oxidized to give methyl
pyridyl sulfone in 67%, 58%, and 78% yields for TS-1, Ti-MWW, and Ti-IEZ-MWW
catalysts, respectively (Table 5, entry 5). Allyl phenyl sulfide was oxidized to give allyl
phenyl sulfone in 62% and 61% yields for Ti-MWW and Ti-IEZ-MWW catalysts,
respectively (Table 5, entry 6). The reaction of 2-phenylthioethanol using Ti-MWW and
Ti-IEZ-MWW gave 2-phenylsulfonylethanol in moderate yields (48% and 55% yields,
respectively, Table 5, entries 6 and 7). Diphenyl sulfone was not observed (0% yields)
19

ACCEPTED MANUSCRIPT
and diphenyl sulfoxide was the only product from the oxidation using 2.5 eq. of 35%
H O aq. with TS-1, Ti-MWW, and Ti-IEZ-MWW catalysts at 50 °C for 18 h under
2
2
organic solvent-free conditions because the generated sulfoxide is solid and not to make
sufficient contact with H O aq. and titanosilicate zeolite catalyst. The oxidation of
2
2
diphenyl sulfide under catalyst-free conditions or with TS-1 and Ti-MWW catalysts
gave no sulfone under toluene solution (Table 5, entry 8). Ti-IEZ-MWW showed an
activity for diphenyl sulfide, producing the corresponding sulfone in 38% yield with
9
3% selectivity under toluene solution (Table 5, entry 8). The larger interlayer pore size
of Ti-IEZ-MWW compared to those of TS-1 and Ti-MWW would be effective to
proceed the oxidation of bulky sulfides. Oxidation of alkyl sulfides such as di-n-butyl
sulfide and di-n-octyl sulfide also led to the production of their sulfones in good yields
(65-88% yields) by Ti-MWW or Ti-IEZ-MWW (Table 5, entries 9 and 10). On the other
hand, di-n-butyl and di-n-octyl sulfoxides were mainly given in the case of using TS-1
or catalyst-free conditions (63-97% yields), and the corresponding sulfones were
formed in low yields (8-35% yields; Table 5, entries 9 and 10).
Table 5. The oxidation of various sulfides to sulfones with TS-1, Ti-MWW, and
a
Ti-IEZ-MWW catalysts using 35% aqueous H O
2
2
20

ACCEPTED MANUSCRIPT
b
Entry
1
Substrate
Product
Conv.
Yield (%)
Sulfoxide
Selectivity
b
c
(%)
Sulfone
(%)
d
e
f
d
d
d
>99
92
8
8
e
e
e
>
>
>
99
99
44
55
55
f
f
f
0
>99
>99
g
g
g
h
g
99
0
>99 (99)
>99
d
d
d
d
2
3
4
5
6
7
99
91
8
8
e
e
e
e
9
>
>
9
64
35
35
f
f
f
f
99
24
76
76
g
g
g
h
g
99
13
87 (83)
87
d
d
d
d
98
95
3
3
e
e
e
e
9
>
>
8
70
28
29
f
f
f
f
99
12
88
88
g
g
g
h
g
99
3
97 (84)
97
d
d
d
d
95
94
0
0
S
e
e
e
e
9
>
>
9
70
29
29
Br
f
f
f
f
99
5
94
94
g
g
g
h
g
99
5
94 (92)
94
d
d
d
d
99
79
2
2
e
f
e
e
e
>
>
>
99
25
67
67
f
f
f
99
31
58
58
g
g
g
h
g
99
13
78 (85)
78
d
d
d
d
99
82
9
9
e
e
e
e
9
>
>
8
68
18
18
f
f
f
f
99
99
27
62
62
g
d
e
f
g
g
h
g
27
61 (61)
62
d
d
d
>99
96
3
3
e
e
e
>
>
>
99
99
99
51
48
48
f
f
f
51
48
48
g
g
g
h
g
44
55 (50)
55
i
d
e
f
d
d
d
8
0
2
3
4
0
0
0
O O
S
e
e
e
2
0
0
f
f
f
3
0
0
g
d
e
g
g
h
g
1
2
38 (23)
93
j
d
d
d
9
98
90
8
8
e
e
e
9
>
>
8
63
35
36
f
f
f
f
99
99
35
65
65
g
g
g
h
g
12
88 (88)
88
21

ACCEPTED MANUSCRIPT
j
d
d
e
f
d
d
1
0
>99
97
75
17
30
3
3
e
e
f
e
f
9
9
25
83
25
83
70
f
>
>
99
99
g
g
g
h
g
70 (37)
a
Reaction conditions: sulfide (1.0 mmol), 35% H O (2.5 mmol), Ti zeolite catalyst (10
2
2
mg), 50 °C, 1000 rpm, 3 h, unless otherwise stated.
b
Yield and conversion on the basis of sulfide, determined by GC analysis with biphenyl
as an internal standard.
c
Yield/conversion x 100
d
no catalyst
e
using TS-1 catalyst
f
using Ti-MWW catalyst
g
using Ti-IEZ-MWW catalyst
h
isolated yield (3 mmol scale)
i
Reaction under toluene solution, 18 h
j
Reaction for 4 h
2
.3.
The reaction mechanism about the H O oxidation of sulfide by
2 2
titanosilicate zeolite catalyst
The reaction mechanisms underlying oxidation of sulfides catalyzed by titanosilicate
1
2-14
zeolite have been investigated.
The reaction of the titanosilicate zeolite catalyst with
H O gives ≡Ti-OOH active species with desorption of silanol. In the presence of water,
2
2
the coordination of an H O molecule to the ≡Ti-OOH active species forms a cyclic
2
1
2-14
structure. On the basis of previous reports,
the XSO experiment, and Hammett plots,
the reaction mechanism was determined as follows (Figure 3). The nucleophilic attack
22

ACCEPTED MANUSCRIPT
of the sulfur atom to an oxygen atom of the ≡Ti-OOH active site leads to sulfoxide
formation. Deoxygenated ≡Ti-OH was stabilized by the coordination with water and
reoxidized by the next H O to reproduce ≡Ti-OOH active species. The formation of
2
2
sulfone is also explained by this mechanism; that is, the nucleophilic attack of the sulfur
atom of sulfoxide is a key step. Sulfoxides are generated in good selectivity at 25 °C
because the nucleophilic attack by sulfide is far superior to that by sulfoxide. The
reactivity can be linked to the topology of the titanosilicate zeolite catalysts due to the
relative ease of accessibility of the nucleophilic S atom on the sulfide to the O atom on
the ≡Ti-OOH active site.
Figure 3. Plausible mechanism for the oxidation of sulfides to sulfoxides and
sulfones.
23

ACCEPTED MANUSCRIPT
3
. Conclusions
Sulfides were oxidized to sulfoxides and sulfones using H O aqueous solution with
2
2
titanosilicate zeolite catalysts. This reaction can be considered a green sustainable
process using the titanosilicate zeolite catalyst in the presence of H O under organic
2
2
solvent-free conditions. Thioanisoles were effectively oxidized by titanosilicate zeolite
having an MWW structure to produce the corresponding sulfoxides in good yields with
good selectivities. Interlayer-expanded MWW-type titanosilicate (Ti-IEZ-MWW)
zeolite was applicable to the oxidation to give sulfoxides and sulfones with bulky
structures, such as diphenyl sulfide. The Ti-IEZ-MWW catalyst can be reused to
produce thioanisole oxidation in good yields for at least five cycles.
24

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4
. Experimental section
.1. General
4
Gas chromatographic (GC) analyses were performed on a Shimadzu GC-2014 using an
1
13
INERT CAP column (0.25 mm x 30 m, GL Sciences Inc.). H NMR (400 MHz) and C
NMR (100 MHz) spectra were recorded on a JEOL ECX-400P spectrometer at 298 K.
Chemical shifts (δ) are in parts per million relative to tetramethylsilane at 0.00 ppm for
1
13
H and relative to residual CHCl at 77.0 ppm for C unless otherwise noted. UV-vis.
3
diffuse reflectance spectra were recorded on a JASCO V-650DS spectrometer. The
diffuse reflectance spectra were converted into the absorption spectra by using the
Kubelka-Munk function. Elemental analyses of the samples (Si/Ti ratio) were
performed on a Shimadzu ICPE-9000 inductively coupled plasma-atomic emission
spectrometer (ICP-AES). N adsorption-desorption measurements were conducted at 77
2
K on a Quantachrome Autosorb-1 to obtain information on the micro- and
meso-porosities. The BET surface area was calculated from the adsorption data in the
relative pressure ranging from 0.04 to 0.2. Prior to each adsorption measurement, the
sample was evacuated at 200 ºC for 6 h.
4
.2.
Materials
Methyl phenyl sulfone, methyl phenyl sulfoxide, di-n-butyl sulfone, di-n-butyl
25

ACCEPTED MANUSCRIPT
sulfoxide, di-n-butyl sulfide, di-n-octyl sulfone, di-n-octyl sulfoxide, di-n-octyl sulfide,
4
4
4
-bromophenyl methyl sulfone, 4-bromothioanisole, 4-chlorophenyl methyl sulfone,
-methylthiotoluene, methyl 4-methylphenyl sulfone, diphenyl sulfone, diphenyl sulfide,
-methoxyphenyl methyl sulfide, 2-methylthiopyridine, thianthrene, decane, biphenyl,
diphenyl sulfoxide, Allyl phenyl sulfide, allyl phenyl sulfone and 2-phenylthioethanol
were obtained from Tokyo Chemical Industry Co., Ltd. Thioanisole, 4-chlorothioanisole,
methanol, 2-phenylsulfonyl ethanol, H SO , ethanol, dichloromethane and CDCl were
2
4
3
obtained from Wako Pure Chemical Industries, Ltd. Thirty-five-percent aqueous
hydrogen peroxide was obtained from Kanto Chemical Co., Inc. Methyl 4-methylphenyl
sulfoxide was obtained from Sigma-Aldrich Corporation. Toluene was obtained from
Junsei Chemical Co., Ltd. 4-Chlorophenyl methyl sulfoxide, 4-bromophenyl methyl
sulfoxide, methyl 2-pyridyl sulfoxide, methyl 2-pyridyl sulfone, allyl
phenyl
sulfoxide and 2-phenylsulfinyl ethanol were generated according to the procedure
9
j,22,24,26,27
described in the literature.
TS-1, Ti-MWW, and Ti-IEZ-MWW were
1
5, 16, 21
generated according to the procedure described in the literature.
were used as received.
All materials
4
.3.
Preparation of titanosilicate zeolite catalysts
Titanosilicate zeolites including TS-1, Ti-MWW, and Ti-IEZ-MWW were prepared and
26

ACCEPTED MANUSCRIPT
used as oxidation catalysts. Si(OEt) (TEOS) and Ti(OBu-n) (TBOT) were used as
4
4
silica and Ti sources, respectively. The layered precursor of the MWW titanosilicate,
1
6
Ti-MWW(P), was hydrothermally synthesized by a previously reported procedure.
16
Ti-MWW was obtained by the calcination of Ti-MWW(P). Ti-IEZ-MWW was
21
prepared by a silylation of Ti-MWW(P) with DEDMS under acidic conditions. To
prepare TS-1, a mother gel containing TEOS, TBOT, (n-Pr) NOH (TPAOH), H O aq.,
4
2
2
1
5
and water was prepared based on the procedure reported and hydrothermally treated.
After the hydrothermal treatment, the obtained precipitate was centrifuged, washed
thoroughly with propanol, and dried at 100 ºC overnight. Acid treatment was conducted
to remove extra-framework Ti species; the as-synthesized sample was treated with an
acid solution (liquid-to-solid ratio, 50 ml/g) under a stirring condition at room
temperature. After the treatment, the sample was filtered, washed with deionized water,
and calcined at 550 ºC.
The Ti environment in the titanosilicates was evaluated by the UV-vis spectroscopy
2
-
technique. The band at around 220 nm, resulting from the charge transfer from O to
4
+
Ti , is attributed to the tetrahedrally-coordinated Ti species (framework Ti), and the
60 and 330 nm bands are assigned to the octahedrally-coordinated Ti species
extra-framework Ti) and the anatase-like phase, respectively. The UV-vis spectra
2
(
27

ACCEPTED MANUSCRIPT
indicated that all titanosilicates mainly have tetrahedrally coordinated Ti species, which
are the active species for oxidation with H O . The atomic ratio of Si/Ti in titanosilicate
2
2
zeolite was estimated by ICP analysis; the ratios were 72, 57, and 86 for TS-1, Ti-MWW,
and Ti-IEZ-MWW, respectively. The BET surface area in titanosilicate zeolite was
calculated from the amount of adsorbed N on the surface; the values were 471, 499,
2
and 521 for TS-1, Ti-MWW, and Ti-IEZ-MWW, respectively.
4
.4.
Procedure for the oxidation of thioanisole to give methyl phenyl sulfoxide
A test tube equipped with a magnetic stirring bar was charged with thioanisole (126.5
mg, 1.0 mmol), aqueous 35% H O (121 mg, 1.20 mmol), and Ti-IEZ-MWW (9.9 mg).
2
2
The mixture was stirred at 25 ˚C for 2 h. The conversion and yield were determined by
GC analysis of the toluene solution with biphenyl as an internal standard. The yield of
methyl phenyl sulfoxide was 94%, conversion of thioanisole was >99%, selectivity
(
yield/conversion) was 94%, and the yield of methyl phenyl sulfone was 6%.
.5. Calculation of XSO value
4
A test tube equipped with a magnetic stirring bar was charged with SSO (50.0 mg, 0.2
mmol), aqueous 35% H O (25.6 mg, 0.18 mmol), and Ti-IEZ-MWW (20 mg). The
2
2
mixture was stirred at 40 ˚C for 18 h under CDCl solution (3 ml). After the reaction,
3
n-decane (13.7 mg, 0.096 mmol) was added to the extracted CDCl solution as an
3
28

ACCEPTED MANUSCRIPT
1
1
internal standard and H NMR was measured. H NMR signals in the area between
δ
1
7
.70 – 8.25 were assigned as follows in comparison with the H NMR data of SSO,
9
l, 25
SSO , SOSO, and SOSO which were previously reported
and the products of the
2
2
oxidation were analyzed quantitatively; SOSO2
2H), cis-, trans-SOSO and SOSO2 8.04 – 8.20 (4H), SSO2
yields of SOSO, SSO , and SOSO were calculated in 54.2%, 1.1%, and 6.7%,
δ
7.70 – 7.82 (4H), SSO
δ 7.90 – 7.97
(
δ
δ
8.20 – 8.25 (4H). The
2
2
respectively. The XSO value was calculated according to: XSO = (nucleophilic oxidation)
/
(total oxidation) = (SSO + SOSO ) / (SSO + SOSO + 2SOSO ), where X = (1.1 +
2 2 2 2 SO
6
4
.7) / (1.1 + 54.2 + 2 x 6.7) = ca 0.11.
.6. Hammett plots using para substituted thioanisoles
A test tube equipped with a magnetic stirring bar and a reflux condenser was charged
with 1.0 mmol of para substituted thioanisole, 1.0 mmol of thioanisole, 1.4 mmol of
aqueous 35% H O , and 10 mg of Ti-IEZ-MWW. After the mixture was vigorously
2
2
stirred at 25 ˚C for 5 min, and Ti-IEZ-MWW was then separated by filtration. The
disappearance of the substrates was monitored by GC analysis with an internal standard,
biphenyl. The initial relative rates (log(k /k )) thus determined were 0.301 (OMe),
X
H
0
.100 (Me), 0 (H), and -0.0718 (Cl), respectively.
4
.7. Gram-scale oxidation of thioanisole using Ti-IEZ-MWW catalyst (as a
29