Synthesis of cyclic sulfites from epoxides and sulfur dioxide with silica-immobilized homogeneous catalysts

Article abstract of DOI:10.1002/cssc.201100492

Quaternary ammonium- and amino-functionalized silica catalysts have been prepared for the selective synthesis of cyclic sulfites from epoxides and sulfur dioxide, demonstrating the effects of immobilizing the homogeneous catalysts on silica. The cycloaddition of sulfur dioxide to various epoxides was conducted under solvent-free conditions at 100 °C. The quaternary ammonium- and amino-functionalized silica catalysts produced cyclic sulfites in high yields (79-96 %) that are comparable to those produced by the homogeneous catalysts. The functionalized silica catalysts could be separated from the product solution by filtration, thereby avoiding the catalytic decomposition of the cyclic sulfite products upon distillation of the product solution. Heterogenization of a homogeneous catalyst by immobilization can, therefore, improve the efficiency of the purification of crude reaction products. Despite a decrease in catalytic activity after each recycling step, the heterogeneous pyridine-functionalized silica catalyst provided high yields after as many as five recycling processes. Immobilized for crimes of pyrolysis: Quaternary ammonium- and amino-functionalized silica catalysts promote the cycloaddition of sulfur dioxide to epoxides to produce cyclic sulfites in high yields (79-96 %) that are comparable to those with the homogeneous catalysts. Separation of the functionalized silica catalyst from the product solution by filtration avoids pyrolysis of the cyclic sulfites during purification by distillation. Copyright

Full text of DOI:10.1002/cssc.201100492

DOI: 10.1002/cssc.201100492
Synthesis of Cyclic Sulfites from Epoxides and Sulfur
Dioxide with Silica-Immobilized Homogeneous Catalysts
Yasumasa Takenaka,*[a] Takahiro Kiyosu,[b] Goro Mori,[b] Jun-Chul Choi,[a] Norihisa Fukaya,[a]
Toshiyasu Sakakura,[a] and Hiroyuki Yasuda*[a]
Quaternary ammonium- and amino-functionalized silica cata-
lysts have been prepared for the selective synthesis of cyclic
sulfites from epoxides and sulfur dioxide, demonstrating the
effects of immobilizing the homogeneous catalysts on silica.
The cycloaddition of sulfur dioxide to various epoxides was
conducted under solvent-free conditions at 1008C. The quater-
nary ammonium- and amino-functionalized silica catalysts pro-
duced cyclic sulfites in high yields (79–96%) that are compara-
ble to those produced by the homogeneous catalysts.
The functionalized silica catalysts could be separated from the
product solution by filtration, thereby avoiding the catalytic
decomposition of the cyclic sulfite products upon distillation
of the product solution. Heterogenization of a homogeneous
catalyst by immobilization can, therefore, improve the efficien-
cy of the purification of crude reaction products. Despite a de-
crease in catalytic activity after each recycling step, the hetero-
geneous pyridine-functionalized silica catalyst provided high
yields after as many as five recycling processes.
Introduction
Organic sulfites are attractive monomers for use in ring-open-
ing polymerization reactions, as solvents, and as electrolyte
additives.[1,2] For instance, small amounts of cyclic sulfites, such
as ethylene sulfite and propylene sulfite, may be added to the
electrolyte of a lithium ion battery to suppress the decomposi-
tion of the electrolyte solvent and/or protect the graphite
anode.[2] Cyclic sulfites are generally synthesized by the stoi-
chiometric reaction of 1,2-diol and thionyl chloride in the pres-
ence of an organic base, such as triethylamine or pyridine.[3,4]
This process, however, produces stoichiometric amounts of the
ammonium or pyridinium salts as waste. Additionally, chlorina-
tion of 1,2-diol by thionyl chloride generates chloride deriva-
tive by-products. Furthermore, chlorine-containing impurities
in cyclic sulfites negatively influence the electrochemical prop-
erties of a battery.[5] Therefore, the development of efficient
synthetic processes that use chlorine-free raw materials is
desired.
Scheme 1. Reaction of epoxide and SO2.
zation onto silica for the cycloaddition of carbon dioxide to ep-
oxides to produce a five-membered cyclic carbonate.[10] This
finding prompted us to investigate the use of silica-immobi-
lized ammonium salts or amine catalysts for the analogous
reaction of epoxides and SO2. Herein, we describe how the im-
The synthesis of cyclic sulfites by the cycloaddition of sulfur
dioxide to epoxides is very attractive from environmental and
economic perspectives because the process does not produce
co-products (100% atom economy) and SO2 is a relatively
cheap resource. Lewis bases,[6] quaternary ammonium salts,[7,8]
and alkali metal salts[7] homogeneously catalyze the reaction of
epoxides and SO2 to form five-membered cyclic sulfites
(Scheme 1). Homogeneous catalysts have disadvantages, how-
ever, related to catalyst separation and recycling. The immobili-
zation of homogeneous catalysts onto a solid support is a
promising strategy to simplify the separation of catalysts from
the products and facilitate catalyst recycling;[9] however, het-
erogenization of homogeneous catalysts often sacrifices cata-
lytic performance, which includes activity and/or selectivity.
We have previously reported that the catalytic activity of
phosphonium salts is enormously enhanced by their immobili-
[a] Dr. Y. Takenaka,+ Dr. J.-C. Choi, Dr. N. Fukaya, Prof. T. Sakakura,
Prof. H. Yasuda
National Institute of Advanced Industrial Science and Technology (AIST)
Tsukuba Central 5, 1-1-1 Higashi
Tsukuba, Ibaraki 305-8565 (Japan)
Fax: (+81)29-861-4559
E-mail: h.yasuda@aist.go.jp
[b] Dr. T. Kiyosu, Dr. G. Mori
Wako Pure Chemical Industries, Ltd.
1633 Matoba, Kawagoe, Saitama 350-1101 (Japan)
[+] Current address:
RIKEN, Biomass Engineering Program
2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)
E-mail: yasumasa.takenaka@riken.jp
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201100492.
194
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ChemSusChem 2012, 5, 194 – 199

Silica-Immobilized Homogeneous Catalysts
mobilization of a homogeneous catalyst onto silica affects the
catalyst performance as well as the recoverability of the cyclic
sulfites from the reaction mixture.
the 13C CP-MAS NMR spectra (Figure S3). These results indicat-
ed that the quaternary ammonium or 2-pyridyl moieties were
cleanly introduced onto the silica surface through SiÀOÀSi
bonds.
The catalytic performance of each organo-functionalized
silica, in terms of promoting the reaction of propylene oxide
with SO2 (1 equiv.), was compared with that of its homoge-
neous counterpart. The quantity of catalyst was adjusted to
0.5 mol% with respect to nitrogen. [Et4N]I, which is a typical
homogeneous catalyst, promoted the reaction at 1008C to
afford the desired propylene sulfite in excellent yield (96%)
within 48 h (Table 2, Entry 1). The reaction of an epoxide with
SO2 also produced poly(alkylene sulfite)[6,7] and a dipolar ionic
compound[6,7,12] (Scheme 1). Under the reaction conditions
used here, five-membered cyclic propylene sulfite was formed
selectively. The by-products were 2-ethyl-4-methyl-1,3-dioxo-
lane (propylene oxide dimer)[13] and a trace amount of poly-
(propylene sulfite).[6,7] Other homogeneous catalysts, which in-
clude [Et4N]Br, [Et4N]Cl, pyridine, and Et3N, also produced pro-
pylene sulfite in high yields (86–95%, Table 2, Entries 2–5).
As described in Entry 1, an attempt to isolate propylene sulfite
by distillation under reduced pressure (10 mmHg, 55–608C) re-
sulted in a low yield (74%). Grobov et al.[8] have also reported
moderate isolated yields (37–58%) for the synthesis of cyclic
alkylene sulfite from epoxides and SO2 catalyzed by quaternary
ammonium salts. The decreased isolated yield was a result of
the decomposition of propylene sulfite, which was promoted
by the catalyst present in the product solution.
Results and Discussion
Quaternary ammonium- or amino-functionalized silica catalysts
were prepared by reacting trialkoxysilane-type coupling re-
agents with mesoporous silica (TMPS-4 and TMPS-7, referred
to as MS1 and MS2, respectively) or amorphous silica (AS).
Table 1 summarizes the compositional and textural data for the
Table 1. Compositional and textural data for the organo-functionalized
silica catalysts.
[b]
[c]
[d]
Catalyst
Organic loading[a]
[wt%] [mmolgÀ1
SBET
Vp
DBJH
]
[m2 gÀ1
]
[cm3 gÀ1
]
[nm]
[EtMe2N]IÀC3H6ÀMS1
0.67
0.48
0.69
0.82
0.84
0.83
0.56
0.47
0.45
946
774
758
853
879
700
867
169
1.35
1.06
1.05
1.16
1.33
1.08
1.26
–
3.3
3.3
3.3
3.3
3.3
4.2
4.2
–
[EtMe2N]BrÀC3H6ÀMS1 0.96
[Me3N]ClÀC3H6ÀMS1
2-Py(C2H4)ÀMS1
1.14
1.17
1.16
0.79
0.66
0.63
Me2NÀC3H6ÀMS1
[EtMe2N]IÀC3H6ÀMS2
2-Py(C2H4)ÀMS2
[EtMe2N]IÀC3H6ÀAS
[a] Determined by performing elemental analysis of nitrogen. [b] BET spe-
cific surface area. [c] Pore volume determined at a relative pressure (P/P0)
of 0.99. [d] Average pore diameter calculated by using the Barrett–
Joyner–Halenda method from the adsorption branch.
Under the same reaction conditions, [EtMe2N]IÀC3H6ÀMS1
(the structure of which was analogous to that of [Et4N]I) afford-
ed propylene sulfite in a yield (93%) comparable to that of
[Et4N]I (Entry 6). In addition, propylene sulfite was isolated in
an excellent yield (96%) by distillation after removal of the het-
organo-functionalized silica catalysts. The organic content,
which was quantified by nitrogen elemental analysis, was
0.45–0.84 mmolgÀ1. The XRD patterns of the organo-function-
alized mesoporous silica catalysts were similar to
those of the parent mesoporous silica materials[11]
and exhibited three peaks, which were assigned to a
Table 2. Reaction of propylene oxide (PO) and SO2 with various catalysts.[a]
2D hexagonal structure (Supporting Information, Fig-
ure S1). This indicated that the immobilization of
quaternary ammonium halides or amines preserved
the mesoporous structure. The nitrogen adsorption–
desorption isotherms of the organo-functionalized
mesoporous silica catalysts showed type IV sorption
curves, which are typical of mesoporous structures
(Figure S2). The introduction of the organic groups
reduced the surface area by 10–30% and narrowed
the average pore diameter of MS1 and MS2.
Entry
Catalyst
Conversion[b]
[%]
Yield PS[b,c]
[%]
Yield PO
dimer[b,d] [%]
1
2
3
4
[Et4N]I
[Et4N]Br
[Et4N]Cl
Pyridine
98
99
99
96 (74)[e]
86
90
98
1
13
10
1
99
The successful functionalization of silica with
quaternary ammonium or amino groups was verified
by using solid-state 13C cross-polarization magic
angle spinning (CP-MAS) NMR spectroscopy of
[EtMe2N]IÀC3H6ÀMS1 and 2-Py(C2H4)ÀMS1. The chemi-
cal shifts observed in the 13C CP-MAS NMR spectra of
[EtMe2N]IÀC3H6ÀMS1 and 2-Py(C2H4)ÀMS1 agree well
with those in the 13C NMR spectra of the correspond-
ing trimethoxysilane coupling reagents in CD2Cl2,
except that the relative intensity of the peak corre-
sponding to the leaving methoxy group decreased in
5
6
7
8
Et3N
99
99
99
93
97
97
>99
98
93
95
4
4
5
3
4
2
3
3
[EtMe2N]IÀC3H6ÀMS1
[EtMe2N]BrÀC3H6ÀMS1
[Me3N]ClÀC3H6ÀMS1
2-Py(C2H4)ÀMS1
Me2N-C3H6ÀMS1
[EtMe2N]IÀC3H6ÀMS2
2-Py(C2H4)ÀMS2
[EtMe2N]IÀC3H6ÀAS
93 (96)[e]
72
72
75
59
9
10
11
12
13
88
87 (83)[e]
76
1
[a] PO (14 mmol), SO2 (14 mmol), catalyst (0.5 mol%), 1008C, 48 h. [b] Determined by
using GC with 1,3,5-trimethylbenzene as an internal standard. [c] Propylene sulfite.
[d] 1,3-Dioxolane derivatives. [e] Isolated yield after distillation.
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195

Y. Takenaka, H. Yasuda, et al.
erogeneous catalyst using a membrane filter. [EtMe2N]BrÀ
C3H6ÀMS1, [Me3N]ClÀC3H6ÀMS1, and 2-Py(C2H4)ÀMS1 also pro-
vided propylene sulfite in somewhat lower yields than the cor-
responding homogeneous catalysts, whereas Me2NÀC3H6ÀMS1
provided a significantly lower yield than Et3N (Entries 7–10).
The [EtMe2N]IÀC3H6- and 2-Py(C2H4)-functionalized silica cata-
lysts were tested to examine the influence of the silica support
on the yield of propylene sulfite. The yield depended slightly
on the type of silica, and each functionalized silica catalyst
gave yields that were comparable or slightly lower than those
of the corresponding homogeneous catalysts. Immobilization
of a homogeneous catalyst onto silica largely increased the
catalytic activity in the cyclic carbonate synthesis.[10] In con-
trast, the catalytic activities towards the analogous cyclic sulfite
synthesis of the quaternary ammonium- or amino-functional-
ized silica catalysts were similar to the activities of their homo-
geneous counterparts.
Figure 1a) shows the time course for the reaction of propyl-
ene oxide and SO2 with homogeneous [Et4N]I. The molecular
weight of poly(propylene sulfite) measured by gel permeation
chromatography (GPC) is also shown in Figure 1a). The reac-
tion proceeded rapidly during the initial stage, and propylene
sulfite was formed in 52% yield within 3 h. Simultaneously,
poly(propylene sulfite), Mw =12500 gmolÀ1, was formed, which
increased the viscosity of the reaction solution. Subsequently,
the amount of propylene sulfite increased slowly as the poly-
mer decomposed (i.e., its molecular weight decreased), and
the propylene sulfite yield reached 96% after 48 h. A similar
trend was observed for the time course of the homogeneous
pyridine catalyst (Figure 1b). The heterogeneous organo-func-
tionalized silica catalysts displayed different reaction profiles.
Figure 1c) shows the time course of the [EtMe2N]IÀC3H6ÀMS1
catalyst. The initial polymer growth was significantly sup-
pressed, and the propylene sulfite concentration increased
gradually. The reaction was almost complete after 48 h, as in
the case of [Et4N]I. The poor material balance during the initial
stages of the reaction may result from the lodging of the poly-
mers in the mesopores and/or their adsorption onto the silica
Figure 1. Time courses for the reaction of propylene oxide and SO2 catalyzed
by a) [Et4N]I, b) pyridine, c) [EtMe2N]IÀC3H6ÀMS1, d) [EtMe2N]IÀC3H6ÀMS2,
e) [EtMe2N]IÀC3H6ÀAS, and f) 2-Py(C2H4)ÀMS2; * represents propylene sul-
fite, * propylene oxide, & 1,3-dioxolane derivatives (propylene oxide
dimer), and & molecular weight of the poly(propylene sulfite).
tive sites were mainly present within the spatially limited
mesopores.[14] Therefore, propylene sulfite may have formed
mainly by Route A and/or the formation and decomposition of
surface. The time courses of the heterogeneous [EtMe2N]IÀ propylene oxide and SO2 oligomers. Even if the major propyl-
C3H6ÀMS2, [EtMe2N]IÀC3H6ÀAS, and 2-PyÀC2H4ÀMS2 catalysts
were similar to those of [EtMe2N]IÀC3H6ÀMS1 (Figures 1d–f).
Two propylene sulfite formation routes are possible for the
cycloaddition of SO2 to propylene oxide: the direct propylene
sulfite formation from propylene oxide and SO2 (Route A), and
propylene sulfite formation by pyrolysis of the copolymers of
propylene oxide and SO2 [poly(propylene sulfite), Route B,
Scheme 2].[8] Propylene sulfite formation in the presence of the
homogeneous [Et4N]I and pyri-
ene sulfite formation route is different in the presence of the
homogeneous and heterogeneous catalysts, the [EtMe2N]IÀ
C3H6ÀMS1 and 2-Py(C2H4)ÀMS2 catalysts efficiently produced
propylene sulfite by the reaction of propylene oxide and SO2,
similar to their homogeneous counterparts.
The cycloaddition of SO2 to various epoxides was investigat-
ed with [EtMe2N]IÀC3H6ÀMS2. The reactions of butylene oxide,
dodecene oxide, and epichlorohydrin with SO2 at 1008C for
dine catalysts likely proceeded
by Route B because polymer
growth was substantial during
the initial period of the reaction.
Polymer growth in the presence
of the quaternary ammonium-
and amino-functionalized meso-
porous silica catalysts was inhib-
ited, probably because the ac- Scheme 2. Possible propylene sulfite formation routes.
196
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ChemSusChem 2012, 5, 194 – 199

Silica-Immobilized Homogeneous Catalysts
96 h gave the corresponding cyclic sulfite in good to high
yields (Table 3, Entries 2–4). The reaction of styrene oxide and
cyclohexene oxide did not form the corresponding cyclic sul-
fite, and many unknown by-products were produced (Entries 5
and 6). In addition to copolymerization with SO2, homopoly-
merization and/or oligomerization, as well as decomposition of
the products, may occur as a result of the high reactivity of
the reactants.
Table 3. Reaction of various epoxides and SO2 catalyzed by [EtMe2N]IÀ
C3H6ÀMS2.[a]
Figure 2. Catalyst recycling experiments for the reaction of propylene oxide
and SO2 catalyzed by a) [EtMe2N]IÀC3H6ÀMS2 and b) 2-Py(C2H4)ÀMS2. Reac-
tion conditions: propylene oxide (14 mmol), SO2 (14 mmol), catalyst
(0.5 mol%), 1008C, 48 h; the reaction times of the fifth and sixth runs in b)
were 96 and 72 h, respectively.
Entry Epoxide
Conversion[b] Yield
[%]
cyclic sulfite[b] 1,3-dioxolane[b,c]
Yield
ed in the complete decomposition of propylene sulfite to pro-
duce many compounds, which included 2-ethyl-4-methyl-1,3-
dioxolane as a major product. 2-Ethyl-4-methyl-1,3-dioxolane
was presumably formed by the association of two propylene
sulfite molecules by SO2 elimination. Berti et al.[15] reported
that pyrolysis of cyclic sulfites at 2008C cleanly produces ole-
fins, ketones, and aldehydes with the evolution of SO2. When
propylene sulfite alone was heated under an argon atmos-
phere at 1008C for 96 h in the absence of [Et4N]I, only 4% pro-
pylene sulfite was found to decompose (Figure 3c). The cata-
lyst in the product solution apparently promoted propylene
sulfite decomposition. In contrast, the functionalized silica cat-
alyst was easily separated by filtration from the reaction solu-
tion, and removal of the catalyst prior to distillation minimized
the decomposition of propylene sulfite. The product solution
[%]
[%]
1
2
3
4
5
6
Propylene oxide >99
Butylene oxide >99
92
85
94
79
0
8
trace
trace
trace
trace
trace
Dodecene oxide
Epichlorohydrin
Styrene oxide
Cyclohexene
oxide
96
89
>99
>99
0
[a] Epoxide (14 mmol), SO2 (14 mmol), catalyst (0.5 mol%), 1008C, 96 h.
[b] Determined by using GC with 1,3,5-trimethylbenzene as an internal
standard. [c] 1,3-Dioxolane derivatives.
The recyclability of the functionalized silica catalysts was ex-
amined. First, we tested the feasibility of recycling [EtMe2N]IÀ collected after 48 h, shown in Figures 1c) and f), was cooled to
C3H6ÀMS2. After the reaction of propylene oxide and SO2 at
1008C for 48 h, the catalyst was separated using a membrane
filter, washed thoroughly with chloroform, and dried under re-
duced pressure at room temperature. The catalyst was reused
in a subsequent run, although the catalytic activity largely de-
creased during the second run (Figure 2a). The iodine content
of [EtMe2N]IÀC3H6ÀMS2 recovered after the second run was
below the detectable limit in iodine elemental analysis.
Next, we performed a recycling experiment using nonionic
2-Py(C2H4)ÀMS2 (Figure 2b). The decrease in the catalytic activ-
ity of 2-Py(C2H4)ÀMS2 with catalyst recycling was smaller com-
pared with that of [EtMe2N]IÀC3H6ÀMS2. However, the propyl-
ene sulfite yield decreased to 50–60% during the second and
third recycling processes. Prolonging the reaction time to 72–
96 h provided propylene sulfite yields that exceeded 50% until
the fifth recycling process.
room temperature, and [EtMe2N]IÀC3H6ÀMS1 or 2-Py(C2H4)À
MS2 was removed by filtration. The filtrate was then heated at
1008C for 48 h. The propylene sulfite yield did not change sig-
nificantly (Figures 3d and e). The propylene sulfite yields after
separating the heterogeneous catalyst from the reaction solu-
In a practical cyclic sulfite synthesis method, the pure cyclic
sulfite product must be separated from the catalyst, and the
crude product must be purified typically by distillation, which
requires heating the product solution. The product solutions
collected after 48 h, shown in Figures 1a) and b), were further
heated at 1008C for 48 h, during which 58 and 43% propylene
sulfite, respectively, was found to decompose (Figures 3a and
b). Heating the solution obtained with [Et4N]I for 120 h result-
Figure 3. Decomposition of propylene sulfite after a) 48 h at 1008C after
48 h reaction of propylene oxide and SO2 catalyzed by [Et4N]I at 1008C,
b) 48 h at 1008C after 48 h reaction of propylene oxide and SO2 catalyzed by
pyridine at 1008C, c) pyrolysis of propylene sulfite under an argon atmos-
phere at 1008C for 96 h, d) 48 h at 1008C after 48 h reaction of propylene
oxide and SO2 catalyzed by [EtMe2N]IÀC3H6ÀMS1 at 1008C followed by re-
moval of the catalyst, and e) 48 h at 1008C after 48 h reaction of propylene
oxide and SO2 catalyzed by 2-Py(C2H4)ÀMS2 at 1008C followed by removal
of the catalyst.
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Y. Takenaka, H. Yasuda, et al.
Plus system equipped with a TC-1 column. GPC was performed
using a Shimadzu GPC system equipped with a refractive index de-
tector RID-10A, and GPC-804c and GPC-802c columns using a poly-
styrene standard.
tion and distilling the filtrate were almost equal to the analyti-
cal yields (Table 2, Entries 6 and 12). These results clearly show
that heterogenization of a homogeneous catalyst by immobili-
zation improved the efficiency of purifying crude reaction
products.
Preparation of N,N-dimethyl-N-ethyl-N-[3-(trimethoxysilyl)-
propyl]ammonium iodide
Conclusions
To a solution of N,N-dimethylaminopropyltrimethoxysilane (20.7 g,
100 mmol) in acetonitrile (100 mL) was added iodoethane (18.7 g,
120 mmol), and the mixture was refluxed with mechanical stirring
for 24 h. Acetonitrile and unreacted iodoethane were then re-
moved under reduced pressure. The product (36.7 g, 100%) was
Quaternary ammonium- and amino-functionalized silica cata-
lysts promoted the cycloaddition of SO2 to epoxides to pro-
duce cyclic sulfites in high yields, which were comparable to
the yields with the corresponding homogeneous catalysts. The
heterogeneous pyridine-functionalized silica catalyst could be
recycled by as many as five times, although the catalytic activi-
ty decreased with each cycle. More importantly, separation of
the functionalized silica catalysts from the product solution by
filtration avoided the catalytic decomposition of cyclic sulfites
upon further heating of the product solution. This suggests
that the immobilization of homogeneous catalysts is highly ef-
fective in increasing the yields of high-purity products that re-
quire purification by distillation.
1
identified by comparing the H and 13C NMR spectra with those of
an authentic sample. N,N-Dimethyl-N-ethyl-N-[3-(trimethoxysilyl)-
propyl]ammonium bromide was prepared by reacting N,N-dime-
thylaminopropyltrimethoxysilane with bromoethane in a similar
manner.
Preparation of quaternary ammonium- and amino-function-
alized silica catalysts
A typical procedure, namely the preparation of the 3-(iodo-N,N-di-
methyl-N-ethylammonium)propyl-functionalized MS1 ([EtMe2N]IÀ
C3H6ÀMS1) catalyst, is as follows: MS1 was dried in vacuum at
1508C for 12 h prior to use. To a suspension of MS1 (3.0 g) in
chloroform (100 mL) was added N,N-dimethyl-N-ethyl-N-[3-(trime-
thoxysilyl)propyl]ammonium iodide (4.4 g, 12 mmol) under an
argon atmosphere, and the mixture was refluxed with mechanical
stirring for 24 h. The resulting solid (3.72 g) was collected by
filtration, washed with chloroform, and dried under vacuum at
1208C for 3 h. The 3-(bromo-N,N-dimethyl-N-ethylammonium)-
propyl-, 3-(chloro-N,N,N-trimethylammonium)propyl-, 2-(2-pyridy-
l)ethyl-, and N,N-dimethylaminopropyl-functionalized silica catalysts
were prepared in a similar manner.
Experimental Section
Propylene oxide, butylene oxide, dodecene oxide, epichlorohydrin,
styrene oxide, cyclohexene oxide, iodoethane, bromoethane, Et3N,
pyridine, acetonitrile, and chloroform were obtained from
Wako Pure Chemical Industries and were used after distillation.
2-(2-Pyridyl)ethyltrimethoxysilane, N,N-dimethylaminopropyltrime-
thoxysilane, trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride,
[Et4N]I, [Et4N]Br, [Et4N]Cl, 2-ethyl-4-methyl-1,3-dioxolane, and 1,3,5-
trimethylbenzene were obtained from Wako Pure Chemical Indus-
tries, Gelest, Atlantic Research Chemicals, and Sigma–Aldrich, and
were used without further purification. Two types of mesoporous
silica with 2D hexagonal structures (TMPS-4 and TMPS-7,[11] referred
to as MS1 and MS2, respectively) were supplied by Taiyo Kagaku.
The specific surface area, pore volume, and average pore diameter
Reaction of epoxides and sulfur dioxide
A typical procedure is as follows: Into a glass pressure vessel
(10 mL) were successively placed a Teflon-coated magnetic stirrer
bar, catalyst (0.5 mol% based on nitrogen), propylene oxide
(0.83 g, 14 mmol), and 1,3,5-trimethyl benzene (86 mg, 0.72 mmol)
as an internal standard for GC analysis. The suspension was cooled
to À608C, and SO2 (0.91 g, 14 mmol) was introduced into the
vessel. The reaction mixture was heated at 1008C with stirring.
After the reaction, the catalyst was separated by filtration, and the
filtrate was analyzed by using GC and GPC to determine the prod-
uct yield and the molecular weight of the polymer, respectively.
were 1036 m2 gÀ1
, , and 3.8 nm for MS1, and
1.35 cm3 gÀ1
1093 m2 gÀ1, 1.60 cm3 gÀ1, and 5.2 nm for MS2, respectively. Amor-
phous silica (Aerosil 200, referred to as AS) was supplied by
Nippon Aerosil. The specific surface area of AS was 208 m2 gÀ1
.
Sulfur dioxide (Sumitomo Seiko, 99.9%) was used without purifica-
tion. Argon (Taiyo Nippon Sanso, 99.9999%) was used after passing
through a Dryclean column (4 A molecular sieve) and a Gasclean
CC-XR column purchased from Nikka Seiko.
Powder XRD data were acquired with a Bruker AXS D8-Advance
X-ray diffractometer using Cu Ka radiation. Nitrogen adsorption–
desorption isotherms were measured at À1968C with a Bel Japan
BELSORP-MAX analyzer after the samples were evacuated at 2008C
for 1 h. Nitrogen and halogen elemental analysis were performed
with a CE Instruments EA1110 elemental analyzer and a Dionex
DX-500 ion chromatograph system equipped with a Mitsubishi
AQF-100 combustion apparatus, respectively. Solid-state 13C CP-
MAS NMR spectra were recorded with a Bruker AVANCE 400WB
spectrometer (100.6 MHz) using a 4 mm CP-MAS probe head.
1H and 13C NMR spectra were recorded with a Jeol LA400WB super-
conducting high-resolution spectrometer (400 MHz for 1H). Gas
chromatography (GC) was performed using a Shimadzu GC-2014
system equipped with a flame ionization detector and a TC-1
column. GC–MS was performed with a Shimadzu GCMS-QP2010
Acknowledgements
This research was financially supported by the “Development of
Microspace and Nanospace Reaction Environment Technology for
Functional Materials” project of the New Energy and Industrial
Technology Development Organization (NEDO), Japan.
Keywords: cycloaddition · immobilization · heterogeneous
catalysis · mesoporous materials · sulfur heterocycles
198
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ChemSusChem 2012, 5, 194 – 199

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Published online on December 1, 2011
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