Efficient and selective hydrogen peroxide-mediated oxidation of sulfides in batch and segmented and continuous flow using a peroxometalate-based polymer immobilised ionic liquid phase catalyst

Article abstract of DOI:10.1039/c4gc01770f

The peroxometalate-based polymer immobilized ionic liquid phase catalyst [PO₄{WO(O₂)₂}₄]@PIILP has been prepared by anion exchange of ring opening metathesis-derived pyrrolidinium-decorated norbornene/cyclooctene copolymer and shown to be a remarkably efficient system for the selective oxidation of sulfides under mild conditions. A cartridge packed with a mixture of [PO₄{WO(O₂)₂}₄]@PIILP and silica operated as a segmented or continuous flow process and gave good conversions and high selectivity for either sulfoxide (92% in methanol at 96% conversion for a residence time of 4 min) or sulfone (96% in acetonitrile at 96% conversion for a residence time of 15 min). The immobilized catalyst remained active for 8 h under continuous flow operation with a stable activity/selectivity profile that allowed 6.5 g of reactant to be processed (TON = 46 428) while a single catalyst cartridge could be used for the consecutive oxidation of multiple substrates giving activity-selectivity profiles that matched those obtained with fresh catalyst.

Full text of DOI:10.1039/c4gc01770f

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ARTICLE
Efficient and Selective Hydrogen Peroxide-Mediated
Oxidation of Sulfides in Batch and Segmented and
Continuous Flow using a Peroxometalate-Based
Polymer Immobilised Ionic Liquid Phase Catalyst
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
S. Doherty,*a J. G. Knight,a M. A. Carroll,a J. R. Ellison,a S. J. Hobson,a S.
Stevens,a C. Hardacre*b and P. Goodrichb
DOI: 10.1039/x0xx00000x
www.rsc.org/
The
peroxometalate-based
polymer
immobilized
ionic
liquid
phase
catalyst
[PO4{WO(O2)2}4]@PIILP has been prepared by an anion exchange of ring opening metathesis-
derived pyrrolidinium-decorated norbornene/cyclooctene copolymer and shown to be a
remarkably efficient system for the selective oxidation of sulfides under mild conditions. A
cartridge packed with a mixture of [PO4{WO(O2)2}4]@PIILP and silica operated as a
segmented or continuous flow process and gave good conversions and high selectivity for
either sulfoxide (92% in methanol at 96% conversion for a residence time of 4 min) or sulfone
(96% in acetonitrile at 96% conversion for a residence time of 15 min). The immobilized
catalyst remained active for
8 h under continuous flow operation with a stable
activity/selectivity profile that allowed 6.5 g of reactant to be processed (TON = 46,428) while
a single catalyst cartridge could be used for the consecutive oxidation of multiple substrates
giving activity-selectivity profiles that matched those obtained with fresh catalyst.
well as transition metal catalysts based on iron,14 manganese,15
vanadium,16 titanium,17 ruthenium,18 molybdenum,19 tungsten,20
Introduction
The selective oxidation of sulfides is a challenging and
technologically important process as sulfoxides and sulfones
are versatile intermediates used in the synthesis of fine
chemicals, bioactive compounds, agrochemicals,1 as chiral
auxiliaries2 and most recently as ligands for transition metal
asymmetric catalysis.3 Moreover, sulfide oxidation is also the
basis for the catalytic oxidative desulfurisation of crude oil in
which sulfur compounds are removed by selective extraction of
their sulfones into a polar solvent under much milder conditions
than typically required for classical industrial catalytic
hydrodesulfurization.4 Sulfoxidations have traditionally
employed either strong oxidants, (e.g. nitric acid or KMnO4)
which suffer numerous drawbacks such as low yields, extreme
reaction conditions and poor E-factors,5 or reagents such as m-
chloroperbenzoic acid,6 UHP,7 NaClO,8 NaIO4,9 oxone10 and
dimethyldioxirane11 which are expensive, must be used in
excess, generate stoichiometric amounts of by-product and
involve protocols that require long reaction times, high
temperatures and complicated handling procedures. Since
hydrogen peroxide is economical, more environmentally benign
and relatively atom efficient it is considered the oxidant of
choice and as such numerous organocatalysts,12 enzymes13 as
and zinc21 have been developed for this process. In this regard,
an efficient catalyst must be highly selective for either sulfone
or sulfoxide, inexpensive, easy to prepare and handle, operate
under mild conditions across a wide range of substrates and
functionality, have long term stability and be easy to recover
and recycle. While several of these criteria have been
successfully realized there is still a demand to identify and
develop alternative systems to address remaining drawbacks
such as long reaction times, protracted and tedious isolation and
catalyst recovery protocols and leaching of the active
components under liquid-liquid biphasic conditions while also
being suitable for use in a continuous flow process.22
To this end, oxidation catalysts have been immobilized on the
surface of porous supports or polymers to improve separation
and recovery as well as recycling but such systems often suffer
from slow reaction rates as well as leaching.23 Ionic liquids
(ILs) are a fascinating class of solvent that have been widely
embraced by the catalysis community as a method for
immobilization of catalysts under homogeneous, liquid-liquid
biphasic and liquid-solid (SILP) biphasic conditions.24 Recent
relevant examples include an efficient protocol for the
oxidation of sulfides to sulfones catalyzed by V2O5 in
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Journal Name
[C12mim][HSO4],25 highly selective sulfoxidation of sulfides to catalyst for sulfide oxidation and to undertake preliminary
sulfoxides catalysed by the bifunctional IL combination optimization studies and recycle experiments.
[SO3HC3py][TiF6]/[C4py][BF4],26
a
selective catalyst-free
oxidation of sulfides to sulfoxides that is faster in ionic liquid
than conventional solvents,27 and, most recently, heterogeneous
selective oxidation of sulfides catalysed by ionic liquid–based
polyoxometalates28 or tungstate-based poly(ionic)liquid
entrapped magnetic nanoparticles.29 While good conversions
and high selectivities have been obtained In IL media,
surprisingly few recycle studies have been reported.
Our initial catalyst evaluation, comparison and optimization
focused on thioanisole as the benchmark substrate as this
oxidation has recently been catalysed by peroxometalate-based
systems immobilized on the surface of ionic liquid modified
Taking SILP catalysis as a lead, we have been exploring the
concept of Polymer Immobilized Ionic Liquid Phase (PIILP)
catalysis30 whereby an ionic liquid is immobilized in the form
of a cation-decorated co-polymer. This is an intriguing concept
with a great deal of design potential as it aims to combine the
favourable properties of ILs with the advantages of a solid
support. Such a catalytic process will minimize the amount of
ionic liquid in much the same manner as a SILP system,
eliminate undesired leaching of ionic liquid, and facilitate
catalyst recovery and recycling while also being ideally suited
to liquid and gas phase continuous flow processing. Thus, we
reasoned that the use of a well-behaved living polymerization
should enable surface properties, the ionic microenvironment
and porosity of the polymer to be modified in a rational and
systematic manner and thereby catalyst-surface interactions,
substrate accessibility and efficiency to be optimized and new
activity-selectivity relationships to be established. Our initial
foray in this area demonstrated that peroxophosphotungstate
[PO4{WO(O2)2}4]3- immobilized on a ROMP-derived cation-
decorated polymer ([PO4{WO(O2)2}4]@PIILP) is an efficient
catalyst for H2O2-mediated epoxidations.30a Herein, we report
that the same system catalyses the oxidation of sulfides under
mild conditions, both in batch and in a continuous flow process
with short residence times and that high selectivity for
sulfoxide and sulfone can be obtained in segmented and
continuous flow using methanol and acetonitrile, respectively,
as the mobile phase. Moreover, continuous flow operation can
be maintained over 8 h with only a minor reduction in
performance and the same resin can also be used consecutively
with different substrates to give yields and selectivities that
match those obtained when a fresh batch of catalyst is used for
each substrate.
silica,23b,c ionic liquid-based polyoxometalates salts,28
a
temperature responsive phase transfer catalyst based on a
Keggin-type lacunary anions20b as well as tungstate ions
embedded in mesochannels of SBA-1523a and poly(ionic) liquid
entrapped magnetic nanoparticles.29 A series of batch reactions
were first conducted to explore the effect of the H2O2:substrate
mole ratio on conversion and selectivity in acetonitrile and
methanol, details of which are presented in Table 1.
Table 1 Oxidation of thioanisole as a function of hydrogen peroxide mole
ratio using [PO4{WO(O2)2}4]@PIILP (2
) as catalyst.a
Solvent
H2O2
equiv
1.0
2.0
2.5
3.0
5.0
2.5
2.5
1.0
2.0
2.5
3.0
5.0
2.5
2.5
2.5
2.5
2.5
2.5
Convb
%
%
sulfoxide
sulfoxideb sulfoneb selectivityb,c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
MeCN
MeCN
MeCN
MeCN
MeCN
MeCNd
MeCNe
MeOH
MeOH
MeOH
MeOH
MeOH
MeOHd
MeOHe
EtOH
54
68
88
100
100
100
2.2
70
90
95
100
100
100
0
52
65
74
80
53
5
2
3
96
96
84
80
53
5
14
20
47
95
-
0
2
4
5
15
7
-
14
0
0
-
-
70
88
91
95
85
93
-
71
52
21
56
100
98
96
95
85
93
-
84
100
100
78
85
32
21
72
i-PrOH
EGe
PCf
16
Results and discussion
a
Reaction conditions: 0.5 mol% 2, 1 mmol substrate, 1.0-3.0 mmol 35%
H2O2, 3 mL solvent, 20 °C, 15 minutes.b Determined by 1H NMR
spectroscopy. sulfoxide selectivity = [%sulfoxide/%sulfoxide+%sulfone] ×
100%. Reactions conducted under the same conditions using 0.5 mol%
[nBu4]3[PO4{WO(O2)2}4] as catalyst. Reaction conducted without catalyst
Catalyst synthesis, batch and recycle studies
c
Peroxometalate-based PIILP [PO4{WO(O2)2}4]@PIILP (
was prepared by stoichiometric exchange of the bromide anions
in pyrrolidinium-based ROMP-derived polymer
[PO4{WO(O2)2}4]3- (Scheme 1)30a and the resulting amorphous
white solid that precipitated was characterized by
2)
d
e
1
with using 0.5 mol% 1. f EG = ethylene glycol. g PC = propylene carbonate.
a
High sulfoxide selectivity (96%) and moderate to good
conversions were obtained in acetonitrile using a 0.5 mol%
combination of solid state P-31 NMR spectroscopy, ICP-OES
(tungsten content), nitrogen sorption analysis, TEM and
TGA/DSC. A series of catalytic reactions was first conducted
loading of
2 to catalyse the oxidation of thioanisole at room
temperature for 15 min with H2O2:S mole ratios of either one or
two while selectivity dropped to 80% when the peroxide to
under batch conditions to evaluate the efficiency of
2 as a
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substrate ratio reached three, albeit at complete conversion methanol. Both solvents will be promising candidates to
(Entries 1-4). In contrast, a parallel series of reactions develop greener processes and, in this regard, studies are
conducted in methanol showed that sulfoxide selectivity currently underway to improve selectivity. Although reactions
remained high even at a H2O2:S mole ratio of three (Entries 8- conducted in isopropanol and ethylene glycol gave sulfoxide as
11). In this regard, the solvent has been previously been the sole product a marked improvement in conversion will be
reported to have a dramatic effect on the selectivity of sulfide required if these solvents are to be considered as viable
oxidation with protic solvents such as methanol and ethanol replacements for methanol.
favouring formation of sulfoxide which in some cases was
Encouraged by the efficacy of 2 for the selective oxidation of
obtained as the exclusive product at short reaction times; this thioanisole, catalyst testing was extended to a range of sulfides,
has been attributed to the high hydrogen bonding capacity of full details of which are summarized in Table 2. Gratifyingly,
these solvents.23d,31 for example, high sulfoxide and sulfone high conversions were obtained across the range of substrates
selectivity has been obtained with relatively low loadings of examined and in each case selectivity for sulfoxide was higher
Merrifield
resin
supported
peroxomolybdenun(VI) in methanol than in acetonitrile ranging from 89–98% in the
compounds23g and polymer-immobilised peroxotungstates23d former compared with 58-98% in the latter. Oxidation of
under mild conditions while peroxotungstates immobilised on allylphenyl sulfide and homoallylphenyl sulfide occurred with
multilayer ionic liquid brushes-modified silica23c or ionic liquid complete chemoselectivity for sulfoxide and sulfone with no
modified silica23a and Keggin heteropolycompounds19f required evidence for epoxidation of the double bond, presumably due to
elevated temperatures, higher catalyst loading and/or markedly the mild conditions and short reaction times.19b,20c,23a-d The
longer reaction times to reach comparable conversions. The moderate
conversion
obtained
for
the
data in Table 1 also shows that high sulfoxide selectivity is [PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of DBT at
retained at high conversion for reactions conducted in methanol room temperature in acetonitrile is entirely consistent with the
(Entries 10-11) whereas selectivity appears to drop with proposed electrophilic pathway, the lower nucleophilicity of
increasing conversion in acetonitrile (Entries 3-4) and that this substrate and previous reports that the rate of oxidation
sulfoxide selectivity decreases much more dramatically in increases
with
increasing
nucleophilicity
of
the
acetonitrile compared with methanol as the hydrogen peroxide sulfide.20b,23d,31c,32 As expected, the same oxidation occurred
ratio increases (Entries 5 and 12). In stark contrast, under the more rapidly at higher temperatures such that a conversion of
same reaction conditions the [nBu4]3[PO4{WO(O2)2}4]- 95% was obtained after 15 min at 65 °C, albeit at the expense
catalysed sulfoxidation of thioanisole with 2.5 equivalents of of sulfoxide selectivity as the sulfone was obtained as the major
H2O2 in acetonitrile resulted in quantitative conversion to afford product in 81% selectivity. Unfortunately, it was not possible to
sulfone as the major product in 95% selectivity (Entry 6), obtain reliable data for the sulfoxidation of dibenzothiophene in
whereas the corresponding reaction in methanol gave sulfoxide methanol, possibly due to its low solubility in this solvent.
as the major product in 93% selectivity (Entry 13), again with
As sulfones are a useful class of compound, the conversion-
complete consumption of sulfide. Even though heterogenisation selectivity profile was also monitored as a function of time and
of [PO4{WO(O2)2}4]3- in the form of [PO4{WO(O2)2}4]@PIILP temperatures in methanol and acetonitrile using a catalyst
results in an inversion of selectivity to favour sulfoxide, high loading of 0.5 mol% and a peroxide to substrate ratio of 5 with
yields of sulfone have been obtained with
at a higher reaction temperature (vide infra). The efficiency of
2
using excess H2O2 the aim of identifying optimum conditions for the formation of
methyl phenyl sulfone. Not surprisingly, selectivity for sulfone
2
enabled the catalyst loading to be reduced to 0.025 mol% and increased with increasing temperature and reached a maximum
under otherwise identical conditions the oxidation of at 45 °C for a reaction time of 15 min, irrespective of the
thioanisole using 2.5 equivalents of H2O2 in acetonitrile reached solvent, however, the data in Figure 1a also highlights the
74% conversion with a sulfoxide selectivity of 96% after 2 h at disparate solvent dependent selectivity as reactions conducted
25 °C, which corresponds to a total TON of 2,960 mole in acetonitrile consistently gave a higher selectivity for sulfone,
sulfoxide per mole cat-1 and a TOF of 1,480 mole sulfoxide per under comparable conditions. This solvent dependent
mole cat-1 h-1. This TOF compares favourably with those of selectivity is also evident in Figure 1b which shows the
1470 h-1 and 1235 h-1 reported for a Merrifield resin supported selectivity as a function of time at 45 °C; in acetonitrile sulfone
dioxomonoperoxomolybdenun(VI)23g
and
a
polymer- is obtained as the exclusive product after only 30 min whereas
immobilised peroxotungstate,23d respectively. Control reactions in methanol a reaction time of 60 min is required to obtain
for the oxidation of thioanisole conducted in methanol and sulfone with 100% selectivity. High selectivity for methyl
acetonitrile in the absence of the tungstate catalyst but with 0.5 phenyl sulfone has previously been reported for the oxidation of
mol% polymer immobilized ionic liquid
of H2O2 gave 0% and 2.2% conversion, respectively, which moreover, conditions were similar to those identified above.28
confirmed the active role of the catalyst (Entries 7 and 14). A Under optimum conditions 0.025 mol% of catalysed the
1 and 2.5 equivalents thioanisole in methanol catalysed by [C4mim]3[PMo12O40] and,
2
survey of the influence of solvent on conversion and selectivity oxidation of thioanisole in acetonitrile at 45 °C to give a total
revealed that reactions conducted in ethanol and propylene turnover number of 3,960 mole sulfone per mole cat-1, albeit
carbonate gave high conversions and good sulfoxide selectivity after 6 h.
(Entries 15 and 18), albeit slightly lower than that obtained in
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Table 2 Selective oxidation of sulphides to sulfoxides with hydrogen peroxide catalysed by [PO4{WO(O2)2}4]@PIILP.a
Substrate
Solvent
% Conversionb
% sulfoxideb
% sulfoneb
sulfoxide
TONd
selectivityb,c
MeCN
MeOH
88
95
74
91
14
4
84
96
704
760
MeCN
MeOH
92
92
74
86
18
6
80
93
736
736
MeCN
MeOH
98e
99
64e
97
34e
2
65
98
784
792
MeCN
MeOH
89
56
78
53
11
3
88
95
712
448
MeCN
MeCNf
24
95
21
18
3
77
88
19
192
760
MeCN
MeOH
98
62
58
56
40
6
58
90
792
456
MeCN
MeOH
99
92
75
90
24
2
76
98
792
736
MeCNg
59
99
58
77
1
22
98
78
472
792
MeOHg
a
b
Reaction conditions: 0.5 mol% 2, 1 mmol substrate, 2.5 mmol 35% H2O2, 3 mL MeCN, room temperature, 15 minutes. Determined by 1H NMR
spectroscopy. c sulfoxide selectivity = [%sulfoxide/%sulfoixde+%sulfone] × 100%. d TOF = moles sulfide consumed per mole catalyst per hour. e Determined
by 13C NMR spectroscopy. f Reaction conducted at 65 °C. g Reactions conducted in deuteriated solvent for 2 minutes and monitored by NMR spectroscopy.
The favourable formation of sulfone when the sulfoxidation
was conducted in acetonitrile is consistent with previous
reports23d and having identified optimum conditions for the (a)
100
formation of sulfone catalyst testing was extended to include a
selection of aryl alkyl sulfides, details of which are summarized
80
60
in Table 3. Under these conditions, a 0.5 mol% loading of
2
40
20
0
catalysed the sulfoxidation to give complete conversion after 15
min with high selectivity for the corresponding sulfone (77–
100%) with the exception of dibenzothiophene which only
reached 68% conversion and 51% selectivity for its sulfone;
however, for all other substrates tested complete conversion to
sulfone was achieved when the reaction time was extended to
60 min. Even though the TOF of 280 h-1 obtained for the
sulfoxidation of dibenzothiophene under these conditions is
lower than that for the other substrates examined the data in
Table 2 shows that high TOFs and high sulfone selectivity can
be obtained at 65 °C; the TOF of 760 h-1 is a marked
improvement on that obtained with the temperature responsive
phase transfer system [(C18H37)2(CH3)2N]7[PW11O39] (248 h-1 at
60 °C),20b polymer immobilised peroxotungstates (9 h-1 at 78
°C),23d V2O5/[C12mim][HSO4] (ca. 4 h-1 at 45 °C)25 and
Merrifield resin supported peroxomolybdenum(VI) compounds
(7.2 h-1 at 78 °C).23g Even at 45 °C the sulfoxidation of allyl
and homoallylphenyl sulfone occurred with complete
chemoselectivity to the sulfoxide and sulfone with no evidence
for epoxidation of the double bond.
MeCN
MeOH
15
25
35
45
temp (oC)
(b)
Figure 1 Influence of reaction conditions on the selectivity for methyl phenyl
sulfone for the oxidation of thioanisole with H2O2 using 0.5 mol%
100
80
60
40
20
MeCN
MeOH
0
0
10
20
30
40
time (min)
50
60
70
[PO4{WO(O2)2}4]@PIILP. Influence of (a) temperature at a reaction time of 15 min
(b) reaction time at 45 °C. Reaction conditions: 0.5 mol% catalyst, 1 mmol
substrate, 5 mmol 35% H2O2, 3 mL solvent. All reactions reached 100%
conversion under these conditions.
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ICP-OES (i.e. < 1 ppm), confirming that the peroxotungstate
was efficiently retained by the polymer immobilized ionic
liquid and potentially suitable for application in a continuous
flow process (vide infra). Moreover, analysis of catalyst
recovered after the 6th run gave a tungsten content of 25.84%
which is close to that of unused catalyst, again a strong
indication that leaching was negligible. In a direct comparative
study, [nBu4N]3[PO4{WO(O2)2}4], immobilised on Geduran®
Si60 (43-60 m) by wet impregnation (6.5 wt%), was shown to
be an efficient catalyst for the sulfoxidation of thioanisole in
methanol and a 0.5 mol% loading gave 99% conversion and
97% selectivity for phenyl methyl sulfoxide after 15 min at
room temperature. However, the system recycled very poorly as
evidenced by a dramatic drop in conversion to 44% after the
first run and a subsequent drop to only 14% for the third run,
although the selectivity remained constant at 97% across the
three runs (Table 4). ICP-OES analysis of the combined
aqueous and organic phases collected after work-up and
analysis of the first run revealed that 23% of the tungsten had
been removed or extracted, a strong indication that the drop in
conversion was due to efficient leaching of the active tungstate
from the SILP based catalyst demonstrating the advantage of
the PILP methodology. The IR spectrum of 2 contains
characteristic bands at 1079 cm-1 (P-O), 957 cm-1 (W=O),
Table 3 Selective oxidation of sulphides to sulfones with hydrogen peroxide
catalysed by [PO4{WO(O2)2}4]@PIILP.a
Substrate
Convb
100
%
%
sulfone
TOFd
688
sulfoxideb sulfoneb selectivityb,c
14
0
86
100
98e
77
86
100
99e
77
100
99e
800
792
616
1e
33
100
68
33
3
35
97
51
97
280
776
100
100
4
96
96
768
a
Reaction conditions: 0.5 mol% 2, 1 mmol substrate, 5 mmol 35% H2O2, 3
mL MeCN, 45 °C, 15 minutes. Determined by 1H NMR spectroscopy.
Sulfone selectivity = [%sulfone/%sulfone+%sulfoxide] × 100%. TOF =
mole sulfone generated per mole catalyst per hour. e Determined by 13C NMR
spectroscopy.
b
c
d
585 cm-1
 sym(W-O2) which are
asym(W-O2) and 531 cm-1
entirely consistent with those for related supported
peroxometalates reported in the literature.33 Catalyst recovered
after the 6th run was found to contain IR bands similar to that
Reasoning that the polymer immobilized ionic liquid
should efficiently retain the peroxometalate, catalyst recycle
experiments on the sulfoxidation of thioanisole were
undertaken to assess the robustness and longevity of the
catalyst and the potential for incorporation into a continuous
flow process. Methanol was identified as the solvent of choice
for the initial recycle experiments on the basis that conditions
for the selective oxidation to sulfoxide and sulfone had already
been identified (vide supra). The catalyst was recovered in an
operationally straightforward filtration, washed with methanol,
dried and reused directly without being replenished or
reconditioned. A comparative study of the conversion and
sulfoxide selectivity for the [PO4{WO(O2)2}4]@PIILP-
catalyzed sulfoxidation of thioanisole in methanol as a function
of time across two runs is presented in Figure 2a. The data
clearly shows that selectivity reduces gradually from 99% to
90% with increasing conversion and that the conversion and
selectivity-time profiles for the two runs map closely to each
other. For comparison, a parallel recycle experiment in
acetonitrile revealed a much more dramatic drop in selectivity,
from 98% to 54%, as a function of conversion/time than the
corresponding reaction in methanol (Figure 2b). Thus,
methanol was chosen for a more extensive recycle study which
showed that [PO4{WO(O2)2}4]@PIILP recycled efficiently
across six runs with only a minor reduction in conversion and
no significant change in selectivity (Table 4).
for
2 with no evidence for oxidation of the benzylic group to
the corresponding benzoyl pyrrolidinium cation strongly
suggesting that the catalyst remains intact; a comparison of
these IR spectra are provided in the supporting information
(Figure S19). A benchmark oxidation of thioanisole in the
presence of ethylbenzene also confirmed that benzylic
oxidation did not occur under these mild conditions and short
reaction times.
Table
4 Comparative recycle studies for the sulfoxidation of
thioanisole in methanol catalysed by [PO4{WO(O2)2}4]@PIILP and
[NBu4]3[PO4{WO(O2)2}4]/SiO2.a
Run
[PO4{WO(O2)2}4]@PIIP
[NBu4]3[PO4{WO(O2)2}4]/SiO2
Conversion
Sulfoxide
selectivityb,c
Conversionb
Sulfoxide
selectivityb,c
b
1
2
3
4
5
6
88
87
88
86
86
84
92
92
92
91
90
88
99
44
14
97
97
96
Analysis of the solvent after filtration and recovery of the
catalyst from the first two runs of the recycle experiment
revealed that the tungsten content was too low to be detected by
a Reaction conditions: 0.5 mol% 2, 1 mmol substrate, 2.5 mmol 35% H2O2, 3
b
mL MeOH, 30 °C, 20 minutes. Determined by 1H NMR spectroscopy.
c Sulfoxide selectivity = [%sulfoxide/%sulfone+%sulfoxide] × 100%
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Journal Name
(a)
100
80
60
40
20
0
Conversion run1
Conversion run 2
Selectivity run 1
Selectivity run 2
0
5
10
15
20
Figure 3 Schematic representation of the set-up for segmented and continuous
flow sulfoxidations catalysed by [PO4{WO(O2)2}4]@PIILP ( ).
Time / min
2
(b)
100
Using the optimized batch conditions as a lead, we first
explored the effect of residence time, temperature and the
amount of hydrogen peroxide on selectivity and conversion for
the sulfoxidation of thioanisole in acetonitrile and methanol.
Preliminary studies examined the effect of temperature on the
conversion and selectivity profile at a fixed flow rate of 1.1 mL
min-1, corresponding to a residence time (Rt) of 4 min, and in
acetonitrile conversions increased smoothly from 44% at 20 °C
to 100% above 45 °C while sulfoxide selectivity decreased
across this temperature range from 88% to 21% (Figure 4a). For
comparison, the corresponding conversion-selectivity profile
obtained using methanol as the mobile phase revealed that
conversions increased steadily from 24% at 20 °C to 88% at 50
°C while sulfoxide selectivity remained high and decreased
only slightly from 100% to 90% within this temperature range
(Figure 4b); a similar solvent dependent selectivity profile was
obtained in batch wherein the sulfoxide selectivity obtained at
high conversion in acetonitrile was lower than that in methanol
under the same conditions. Taking both studies into account, a
reaction temperature of 30 °C gave the optimum
balance/compromise between conversion and sulfoxide
selectivity and as such this temperature was chosen to examine
a range of substrates (vide infra). A corresponding study to
explore the influence of residence time on the conversion-
selectivity profile at 30 ºC with acetonitrile as the mobile phase
revealed that conversions increased gradually with increasing
residence time from 21% for a residence time of 0.5 min to
90% when this was increased to 4 min and that high selectivity
for sulfoxide was maintained across this range of retention
times; however, selectivity decreased quite dramatically at
longer residence times such that sulfone was obtained as the
major product in 96% selectivity after 15 min (Figure 4c). For
comparison, the conversion–selectivity profile in methanol was
qualitatively similar although interestingly the optimum balance
of conversion and sulfoxide selectivity of 96% and 92%,
respectively, obtained at a residence time of 5 min was a
significant improvement on that in acetonitrile while the
selectivity for sulfone only reached 63% for a residence time of
15 min; this is markedly lower than the 96% obtained under the
same conditions in acetonitrile (Figure 4d). Thus, the data in
Figure 4 clearly shows that high selectivity for either sulfoxide
or sulfone can be obtained under continuous flow processing
through a judicious choice of solvent, residence time and
temperature.
50
0
Conversion run 1
Conversion run 2
Selectivity run 1
Selectivity run 2
0
5
10
15
20
Time / min
Figure 2 (a) Conversion and sulfoxide selectivity profiles as a function of time for
a recycle [PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of thioanisole in (a)
methanol at room temperature (b) acetonitrile at room temperature, using 0.5
mol% 2 and a substrate:H2O2 ratio 1:2.5.
Segmented and Continuous Flow Processing
The short reaction times and mild conditions required for
[PO4{WO(O2)2}4]@PIILP catalysed oxidations and the
recyclability of the system prompted us to explore the potential
applications of this system in a continuous flow protocol and to
establish how residence time, substrate/peroxide mole ratio and
temperature influence selectivity. The flow set-up for
sulfoxidation of thioanisole is shown in Figure 3 and is based
on a Uniqsis FlowSyn reactor. Preliminary evaluation and
optimization studies were conducted using segmented flow in
which either methanol or acetonitrile solutions of sulfide (0.2
M) and 30% hydrogen peroxide (0.6 M) are simultaneously
pumped through a cartridge reactor packed with 2.0 g of silica
(Geduran® Si60 43-60 m) mixed with 0.1
g
of
[PO4{WO(O2)2}4]@PIILP with precise control of the flow
rates; the residence times were calculated based on these flow
rates and methanol was used as the transport solvent. The
exiting product stream was collected in triplicate as 2 mL
aliquots, subjected to an aqueous work-up and analysed by
1
either H or 13C NMR spectroscopy to determine conversion
and selectivity.
6 | J. Name., 2012, 00, 1-3
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ARTICLE
effectively. This may also be the reason why methanol has a
reduced overall rate compared with acetonitrile. The possible
effect of the additional water content on the conversion-
selectivity profiles arising from the increasing mole ratio of
aqueous hydrogen peroxide was also investigated by doping
experiments based on three equivalents of hydrogen peroxide
with the corresponding amount of water that would be present
with six equivalents of peroxide; the associated conversion-
selectivity profiles as a function of residence time are provided
in the Supporting Information (Figures S23-S24). Interestingly,
for reactions conducted in acetonitrile the first oxidation is
more rapid in the water-doped system while the second
oxidation appears to be slightly slower. In contrast, the profile
for the water-doped methanol system maps more closely, across
the range of retention times, to the data for the undoped system
with three mole equivalents of hydrogen peroxide. The slight
increase in rate for the water doped-acetonitrile system
compared with methanol may be due to interaction of the water
with the catalyst-support surface facilitating access of the
substrate to the catalyst, possibly through a network of
hydrogen bonds. High selectivity for sulfoxide was retained
when the water content was increased further by generating the
segmented flow with equal volumes of aqueous hydrogen
peroxide and methanolic thioanisole. Under these conditions
the combination of 93% sulfoxide selectivity and 92%
conversion at a flow rate of 0.88 mL min-1 (Rt = 5 min) was a
marked improvement on that obtained by varying the hydrogen
peroxide concentration; the associated conversion-selectivity
profile as a function of residence time is presented in the
Supporting Information (Figure S25). A comparison with the
corresponding batch reaction in 1:1 methanol/water revealed a
further potential benefit of continuous flow as 0.5 mol%
catalyst gave a conversion of only 22% in batch after 15 min,
albeit with high sulfoxide selectivity (91%); such a poor
conversion may well be due to agglomeration of the catalyst.
av sulfide
av sulfone
av sulfoxide
av sulfide
av sulfone
av sulfoxide
(a)
(b)
100
80
60
40
20
0
100
80
60
40
20
0
20 25 30 35 40 45 50
20 25 30 35 40 45 50
Temp/ (oC)
Temp/ (oC)
av sulfide
av sulfone
av sulfoxide
(c)
(d)
100
80
60
40
20
0
av sulfide
av sulfone
av sulfoxide
100
80
60
40
20
0
0.5
1
2
3
4
5
10 15
0.5
1
2
3
Rt
4
5
10 15
Rt
F
igure 4 Conversion-selectivity profile as a function of temperature for the
continuous flow [PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of thioanisole in
(a) acetonitrile (b) methanol for a residence time of 4 min. Conversion-selectivity
profile as a function of residence time (Rt) for the [PO4{WO(O2)2}4]@PIILP-
catalysed sulfoxidation of thioanisole in (c) acetonitrile (d) methanol at 30 °C.
Reaction conditions: 0.1 g catalyst/2.0 g silica, 3 equiv. 35% H2O2, solvent,
residence time 0.5-15 min or temperature 20-50 ºC.
A survey of the influence of the amount of H2O2 on
conversion and selectivity as a function of residence time for
the oxidation of thioanisole revealed a disparate solvent
dependent behaviour. In the case of acetonitrile, a strong
dependence on the rate was observed up to 12 equivalents of
H2O2. For both 12 and 20 equivalents similar profiles with
respect to Rt were observed. In comparison a much weaker
dependence on [H2O2] was observed in methanol and Table 5 Estimated rate constants for the formation of methyl phenyl
sulfoxide (ka) and methyl phenyl sulfone (kb) in acetonitrile and methanol a
.
approximately zero order behaviour was found. Details of the
composition-time profile and analysis are provided in the
supporting information (Figures S9-S22). Approximate rate
constants for the formation of methyl phenyl sulfoxide (ka) and
methyl phenyl sulfone (kb) in acetonitrile and methanol were
extracted by fitting the concentration-time profile for the
consumption of sulfide and the formation of product using
pseudo steady state analysis. As 2.5 equivalents of H2O2 are
consumed during the reaction the rate constants derived were
only calculated for the reaction with 20 equivalents of H2O2.
Table 5 compares the effects of the solvent on the two rates
assuming a first order dependence on the substrate and
sulfoxide. Interestingly, the solvent has a much less significant
effect on the second oxidation compared with the first. The
strong dependence on peroxide concentration in acetonitrile
may reflect a reduced solubility of the substrate compared with
methanol which blocks the surface sites on the catalyst and/or
hydrogen bonding between H2O2 and the substrate impeding
access to the catalyst. In contrast, the increased H-bonding
capacity of methanol could result in a greater degree of
solvation of the substrate which would reduce the coverage of
MeCN
MeOH
Entry
1
H2O2
20
ka
2.68
kb
0.17
ka
0.55
kb
0.11
a
Data obtained using 0.2 M solution of thioanisole and a 4.0 M solution of
H2O2 with flow rates between 0.293 mL min-1 and 8.8 mL min-1 at 30 °C.
In addition to the obvious advantages associated with
continuous flow operation such as simple product catalyst
separation and ease of scale-up due to the linear increase in
TON with time, our preliminary studies revealed that high
selectivity for sulfoxide or sulfone can also be obtained by
changing the solvent and residence time. For example, a
sulfoxide selectivity of 98% at 83% conversion was obtained
for the sulfoxidation of thioanisole at a residence time of 4 min
under segmented flow in methanol, which is a marked
improvement on the corresponding selectivity of 89% at 75%
conversion in acetonitrile under otherwise identical conditions.
For comparison, the corresponding sulfoxidation conducted in
substrate at the catalyst and thereby allow peroxide to bind methanol under batch conditions gave 96% conversion but with
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slightly lower selectivity of 95%. In contrast, complete
conversion and a sulfone selectivity of 96% was obtained in
acetonitrile by extending the residence time to 15 min; this is
significantly higher than the 62% selectivity obtained either
under segmented flow in methanol or under batch conditions in
both solvents (Table 1). With the optimized conditions in hand
the substrate range was extended to establish the scope and
efficiency of this system. As for thioanisole, the selectivity for
sulfoxide obtained in methanol at any given residence time was
higher than that in acetonitrile for each substrate studied and in
the majority of cases the optimum compromise between
conversion and selectivity appeared to peak at a flow rate of 1.1
mL min-1 (Rt = 4 min) with the exception of 4-nitrothioanisole
which required a slightly longer residence time. Under these
conditions sulfoxide selectivities as high as 90% were obtained
with reasonable to good conversions (61-93%). While sulfone
selectivity increased with increasing residence time and reached
75-89% at complete conversion, the optimum selectivity was
solvent dependent. Full details of the conversion-selectivity
monitored over 8 h and the resulting time-performance profile
(Figure 5a) revealed a slight decrease in activity with time, as
evidenced by the decrease in conversion from 89% to 79%,
with a parallel decrease in sulfone formation from 29% to 16%
while the concentration of sulfoxide remained constant.
Reasoning that these changes may be due to either deactivation
or leaching of the catalyst and/or decomposition of peroxide the
experiment was repeated and the reservoir replenished with
fresh hydrogen peroxide after 4 h. The resulting system showed
a marked improvement in the activity/selectivity profile as the
concentration of sulfide, sulfoxide and sulfone remained
constant and stable (Figure 5b), indicating that the change in
performance with time is unlikely to be due to leaching and
more likely associated with the efficacy of catalyst activation
and/or decomposition of hydrogen peroxide. In this regard,
ICP-OES analysis of aliquots collected every hour revealed that
4.3% of the tungsten leached from [PO4{WO(O2)2}4]@PIILP
over an 8 h period. Interestingly, the corresponding scale-up
study in methanol showed a much more dramatic variation in
the activity/selectivity profile which was manifested by a
marked reduction in conversion from 85% to just 55% after 8h
accompanied by a concomitant reduction in formation of
profile as
a
function of residence time for the
[PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of each
sulfide in methanol and acetonitrile are reproduced in the
Supporting Information (Figures S7-S8 and S26-S32) and a
summary of the optimum selectivity and conditions is given in sulfoxide from 77% to 53% and a minor reduction in sulfone
Table 6.
(Figure 5c). Although stability, as measured by the absolute
change in conversion and selectivity, improved noticeably after
replenishing the peroxide a gradual decrease in conversion was
paralleled by a decrease in the amount of sulfoxide (Figure 5d).
The contrasting behaviour of this system may be due, at least in
part, to catalyst leaching as ICP-OES analysis of samples
collected every hour indicated that 21% of the tungsten leached
over an 8 h run. A comparative set of life-time studies was also
Table 6 Summary of the optimum sulfide and sulfone selectivity for the
segmented flow [PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of
selected aryl sulfides.a
Substrate
Rt
solvent
%
Convb
83
sulfoxide
sulfone
selectivityb,c selectivityb,d
4
15
MeOH
MeCN
98
-
-
96
100
conducted
using
a
cartridge
packed
with
4
15
MeOH
MeCN
93
100
90
-
-
79
[nBu4N]3[PO4{WO(O2)2}4]/SiO2 in order to assess the
effectiveness and influence of the PIILP-based approach. Under
4
15
MeOH
MeCN
61
100
90
-
-
75
the same flow conditions
a
cartridge packed with
[nBu4N]3[PO4{WO(O2)2}4]/SiO2 was more active than its
polymer immobilized ionic liquid-based counterpart for the
oxidation of an acetonitrile solution of thioanisole, as judged by
the quantitative conversion of sulfide during the first 3 hours of
operation. However, in addition to a minor but steady increase
in the amount of unreacted sulfide after 3 h there was a smooth
and significant change in the sulfoxide selectivity from 60% to
90% over the same time (Figure 5e); the tungsten leaching of
7% over the 8 h run is higher than that determined for the
[PO4{WO(O2)2}4]@PIILP/SiO2 system under the same
4
15
MeOH
MeCN
80
100
89
-
-
89
-
15
MeOH
MeCN
-
76
-
-
-
76
a Reaction conditions: 0.1 g 2/2.0 g silica, 3 equivalents 35% H2O2, solvent,
residence time 0.5-15 min, 30 °C. b Determined by H NMR spectroscopy.
1
c
d
Sulfoxide selectivity
Sulfone selectivity = [%sulfone/%sulfone+%sulfoxide] × 100%.
= [%sulfoxide/%sulfone+%sulfoxide] × 100%.
conditions.
The
corresponding
comparison
with
[nBu4N]3[PO4{WO(O2)2}4]/SiO2 and methanol as the mobile
phase resulted in a rapid and dramatic drop in activity such that
the system was essentially inactive after the first hour (Figure
5f); in this case ICP analysis of the methanol collected over the
first 60 min contained 14.9 ppm tungsten, which corresponds to
21% leaching after only 1 h thereby accounting for the dramatic
loss in activity.
Encouraged by the recyclability of
2 in batch and the
conversion-selectivity profile obtained under segmented flow
conditions, comparative scale-up continuous flow studies were
conducted in methanol and acetonitrile using a mixture of
[NBu4]3[PO4{WO(O2)2}4] and silica as the benchmark to assess
the robustness, longevity and relative merits of the PIILP-based
system. The efficiency of [PO4{WO(O2)2}4]@PIILP for the
catalytic oxidation of thioanisole under continuous flow
conditions (1.1 mL min-1, 30 °C, Rt = 4 min) in acetonitrile was
8 | J. Name., 2012, 00, 1-3
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ARTICLE
sulfide sulfoxide sulfone
(b)
100
80
60
40
20
0
(b)
100
sulfide
sulfoxide
sulfone
(a)
(a)
100
80
60
40
20
0
av sulfide av sulfoxide av sulfone
av sulfide av sulfoxide av sulfone
100
80
60
40
20
0
80
60
40
20
0
0
1
2
3
4*
5
6
7
8
0
1
2
3
4
5
6
7
8
5
15
5
15
5
15
5
15
5
15
5
15
time (hour)
time (hour)
nitrothioanisole DBT
thioanisole
nitrothioanisole
Rt
thioanisole
DBT
Rt
(c)
100
80
60
40
20
0
sulfide
sulfoxide
sulfone
(d)
sulfide sulfoxide sulfone
Figure 6 (a) Conversion-selectivity profile at residence times of 5 and 15 min for
the continuous flow [PO4{WO(O2)2}4]@PIILP-catalysed consecutive sulfoxidation
of three different substrates (i) thioanisole, (ii) 4-nitrothioanisole and (iii)
dibenzothiophene with the same catalyst cartridge. (b) Conversion-selectivity
100
80
60
40
20
0
profile at residence times of
5 and 15 min for the continuous flow
[PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation using a fresh catalyst cartridge for
each substrate. Reaction conditions: 0.1 g catalyst/2.0 g silica, 3 equiv. 35% H2O2,
MeCN, 30 °C, residence times 5 and 15 min.
0
1
2
3
4
5
6
7
8
0
1
2
3
4*
5
6
7
8
time (hour)
time (hour
Conclusions
(e)
(f)
sulfide
sulfoxide
sulfone
sulfide sulfoxide sulfone
100
80
60
40
20
0
100
A peroxophosphotungstate-based pyrrolidinium-decorated
polymer immobilized ionic liquid ([PO4{WO(O2)2}4]@PIILP)
catalyses the oxidation of sulfides with remarkable efficacy
under mild conditions and in short reaction times using
hydrogen peroxide as oxidant. High selectivity for sulfoxide
can be obtained at room temperature in methanol while the
sulfone can be obtained in acetonitrile at higher temperature
with an excess hydrogen peroxide. The catalyst could be
recovered in a straightforward filtration procedure with no
evidence for leaching and recycle studies gave good
conversions and a stable selectivity profile over several runs. A
segmented flow process based on a catalyst cartridge packed
with a mixture of [PO4{WO(O2)2}4]@PIILP and silica gave
good conversions and high selectivity for sulfoxide in methanol
at short residence times while sulfone was obtained with high
selectivity in acetonitrile at longer residence times. The catalyst
is remarkably robust and ideally suited for scale-up and could
be operated under continuous flow conditions for 8 h with a
stable activity-selectivity profile, allowing 6.5 g of material to
be processed (TON = 46,428). A single cartridge was also used
for the consecutive oxidation of three different substrates and
resulting conversion and selectivity profiles closely matched
those obtained with fresh catalyst. Future studies are underway
to develop robust adaptable multifunctional support materials
based on polymer immobilized ionic liquids and to this end we
are currently (i) introducing functionality onto the polymer
chain and modifying hydrophilicity to explore what factors
influence catalyst performance in order to identify an optimum
catalyst-support combination to improve the selectivity profile,
stability and recyclability, (ii) exploring whether phase
separated polymers can be used for catalyst isolation, (iii)
extending the concept of PIILP catalysis to a wider range of
80
60
40
20
0
0
1
2
3
4*
5
6
7
8
0
1
2
3
4*
5
6
7
8
time (hour)
time (hour)
F
igure 5 Conversion-selectivity profile as a function of time for an 8 h continuous
flow [PO4{WO(O2)2}4]@PIILP-catalysed sulfoxidation of thioanisole at 30 °C with a
residence time of 4 min in (a) acetonitrile, (b) acetonitrile with the H2O2 reservoir
replenished after 4 h (*), (c) methanol, (d) methanol with the H2O2 reservoir
replenished after 4 h (*). Conversion-selectivity profile as a function of time for
an
8
h
continuous
flow
sulfoxidation
of
thioanisole
using
[nBu4N]3[PO4{WO(O2)2}4] as catalyst at 30 °C with a residence time of 4 min in (e)
acetonitrile and (f) methanol.
The
promising
long
term
stability
of
[PO4{WO(O2)2}4]@PIILP for the continuous flow oxidation of
thioanisole in acetonitrile provided the driver to examine
whether the same resin-packed column could be used
consecutively for the oxidation of several different substrates.
In a proof of principle exercise, a column packed with
[PO4{WO(O2)2}4]@PIILP and silica was operated under
continuous flow (1.1 mL min-1, 30 °C, Rt = 4 min, MeCN) for
the sequential oxidation of thioanisole, 4-nitrothioanisole and
dibenzothiophene. Gratifyingly the conversion-selectivity
profile for residence times of 5 and 15 min for the substrates
run sequentially closely matched that obtained for the oxidation
of each substrate conducted with fresh catalyst under the same
conditions (Figure 6a-b), provided the cartridge was purged
with methanol between different substrates.
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transformations as well as the stabilization of nanoparticles and An oven-dried Schlenk flask was allowed to cool to room
(iv) developing peroxometalate@PIILP systems for the temperature and charged sequentially with sulfide (3.0 mmol),
oxidative desulfurization of crude oil in batch and under polymer immobilised catalyst
2 (0.039 g, 0.015 mmol) or
continuous flow as well as the capture and removal/scavenging [nBu4N]3[PO4{WO(O2)2}4]/SiO2 (100 mg, 6.5 wt% W) and
of toxic/odorous sulfur compounds.
solvent (9 mL). The reaction was initiated by addition of 35%
H2O2 (0.72 mL, 7.5 mmol) and the resulting mixture allowed to
stir at room temperature for 20 min. After this time the solution
was centrifuged (10 min, 12000 rpm), decanted using a pipette
and the remaining catalyst washed with the reaction solvent and
dried prior to reuse under the same conditions. The remaining
solution was subject to the same work-up and analysis as
described above. ICP analysis of a portion of the organic and
aqueous phases between recycles was conducted using a using a
Perkin Elmer Optima 4300DV ICP-OES (Inductively Coupled
Plasma Optical Emission Spectrometer).
Experimental
Synthesis of polymer immobilised peroxophosphotungstate
2
.
A hydrogen peroxide solution (35% w/w, 9.7 mL, 100 mmol)
was added to phosphotungstic acid (1.73 g, 0.6 mmol)
dissolved in a minimum volume of water and stirred at room
temperature for 30 min. After this time, pyridine (0.145 mL, 1.8
mmol) was added followed by a solution of 1 (0.877 g, 1.8
mmol) in the minimum volume of ethanol, which resulted in
the immediate precipitation of an amorphous white solid. The
mixture was cooled to 0 ˚C, filtered through a sintered glass frit
and the precipitate washed with water (2 × 10 mL) and diethyl
ether (3 × 75 mL) and dried under vacuum to afford 6 in 84%
yield. FT-IR (KBr plates, cm-1): ṽ = 1087, 1058, 1028 (P-O),
956 (W=O), 837 (O-O), 585, 535 W(O2)asym,sym: Anal. Calc for
C108H168N3O24PW4: N, 1.58; W, 27.66. Found: N, 1.46; W,
26.31. Loading of tungsten 1.4 mmol g-1.
General Procedure for Catalytic Sulfoxidation Kinetic
Studies
An oven-dried Schlenk flask was allowed to cool to room
temperature and charged sequentially with sulfide (3.0 mmol),
polymer immobilised catalyst
2 (0.039 g, 0.005 mmol) and
solvent (9 mL). The reaction was initiated by addition of 35%
H2O2 (0.72 mL, 7.5 mmol) and the resulting mixture stirred at
room temperature for the 20 min during which time 0.5 mL
aliquots were removed for work-up (as above) and analysis by
1H NMR spectroscopy. After the final aliquot had been
removed the remaining reaction mixture was decanted, the
catalyst washed with diethyl ether, dried and replenished to
account for losses arising from the sampling. The recycle
kinetic experiment was conducted by charging the Schlenk with
fresh sulphide (3.0 mL), solvent (9 mL) and 35% H2O2 (0.72
mL, 7.5 mmol).
Synthesis of [
nBu4N]3[PO4{WO(O2)2}4]/SiO2
A
flame-dried Schlenk flask was charged with
[nBu4N]3[PO4{WO(O2)2}4] (0.094 g, 0.05 mmol) and
dichloromethane (6 mL) and the mixture stirred at room
temperature for 15 min after which time 1.0 g of Geduran® Si60
(43-60 m) was added and stirring continued for a further 2 h.
The dichloromethane was removed under vacuum to afford a
free flowing powder. FT-IR (KBr plates): ṽ = 1087, 1058, 1028
(P-O), 956 (W=O), 837 (O-O), 585, 535 W(O2)asym,sym. The
tungsten loading was confirmed to be 0.19 mmol of W g-1 of
silica by ICP-OES analysis.
General Procedure for Segmented and Continuous Flow
Catalytic Sulfoxidation
Two reservoirs were charged with sulfide (5.0 mmol) dissolved
in the appropriate solvent (25 mL, 0.2 M) and hydrogen
peroxide (1.29 mL, 35%) in the same (25 mL, 0.6 M). A
Uniqsis FlowSyn reactor was used to pump 1 mL of each
reagent at total flow rates that varied between 0.293 mL min-1
and 8.8 mL min-1 through a T-piece mixer to combine the two
streams; in the case of segmented flow an additional reservoir
of carrier solvent was also employed. The reaction stream was
then flowed through a OMNIFIT® glass column reactor
cartridge (10 mm id x 100 mm) packed with 0.1 g of
[PO4{WO(O2)2}4]@PIILP and 2.0 g of SiO2 (Geduran® Si 60)
and mounted in a FlowSyn column heater. The exiting stream
was passed through a back pressure regulator (BPR) and 2 mL
fractions were collected into separate vials followed by a 2 mL
post-collect. Each sample was diluted with dichloromethane (10
mL), washed with water (c.a. 15 mL), the organic extract dried
over MgSO4, the solvent removed under reduced pressure and
the resulting residue analysed by either 1H or 13C NMR
spectroscopy to quantify the composition of starting material
and products.
General Procedure for Catalytic Sulfoxidation in Batch
An oven-dried Schlenk flask was allowed to cool to room
temperature and charged sequentially with sulfide (1.0 mmol),
catalyst (0.013 g, 0.005 mmol) and solvent (3 mL), the reaction
was then activated by the addition of 35% H2O2 (0.24 mL, 2.5
mmol) and allowed to stir at room temperature for 15 min. The
reaction mixture was diluted with dichloromethane (25 mL),
washed with water (ca. 50 mL) and the organic extract dried
over MgSO4 and the solvent removed under reduced pressure.
The resulting residue was analysed by either H or 13C{1H}
1
NMR spectroscopy to quantify the composition of starting
material and products; for each substrate tested an internal
standard of 1,3-dinitrobenzene was initially employed to ensure
mass balance.
General Procedure for Catalytic Sulfoxidation Recycle
Studies
10 | J. Name., 2012, 00, 1-3
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Journal Name
Green Chemistry
ARTICLE
(h) E. Lissner, W. F. de Souza, B. Ferrera and J. Dupont,
Acknowledgements
ChemSusChem, 2009, 2, 962–964.
We gratefully acknowledge Newcastle University for financial
support (J.R.E.). Solid-state 31P NMR spectra were obtained at
the EPSRC UK National Solid-State NMR Service at Durham
and high resolution mass spectra were obtained at the EPSRC
National Mass Spectrometry Service Centre in Swansea.
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Newcastle upon Tyne, NE1 7RU, UK.
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†Electronic Supplementary Information (ESI) available: Synthesis and
characterization of polymer
TGA and DSC curves for
1
, polymer immobilized peroxometalate
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12 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C4GC01770F
Graphical Abstract
Good conversions and high selectivity for sulfide oxidation has been achieved under segmented and continuous flow using a
peroxometalate-based polymer immobilised ionic liquid phase (PIILP) catalyst.
0.5 mol%
[PO4{WO(O2)2}4]@PIILP
SiO2
98% selectivity
MeOH, Rt = 4min
96% selectivity
MeCN, Rt = 15 min

Green Chemistry
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DOI: 10.1039/C4GC01770F
Supporting Information for
Efficient and Selective Hydrogen Peroxide-Mediated Oxidation of Sulfides in Batch and
Segmented and Continuous Flow using a Peroxometalate-Based Polymer Immobilised Ionic
Liquid Phase Catalyst
Simon Doherty, Julian G. Knight, Michael A. Carroll, Jack R. Ellison, Stephen J. Hobson, Shaun Stevens,
Christopher Hardacre and Peter Goodrich
1

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DOI: 10.1039/C4GC01770F
Contents
S7
S8
Experimental: General Comments
Ring opening metathesis polymerisation of 1ꢀbenzylꢀ1ꢀ((2ꢀmethylbicyclo[2.2.1]heptꢀ5ꢀenꢀ2ꢀ
yl)methyl)pyrrolidinꢀ1ꢀium bromide with cisꢀcyclooctene: Synthesis and characterisation of 1.
Figure S1 Differential refractive index (dRI) GPC trace of polymer 1 in DMF (0.6 mL/ min).
Figure S2 TGA and DSC curves for benzylꢀ1ꢀ((2ꢀmethylbicyclo[2.2.1]heptꢀ5ꢀenꢀ2ꢀ
yl)methyl)pyrrolidinꢀ1ꢀium bromideꢀcisꢀcyclooctene copolymer 1
Synthesis of polymer immobilised peroxophosphotungstate 2
S9
S10
S11
S11
S12
S12
S13
S13
S13
S14
S16
S17
Synthesis of [nBu4N]3[PO4{WO(O2)2}4]/SiO2
Figure S3 TEM image of freshly prepared polymerꢀsupported peroxophosphotungstate 2
General Procedure for Catalytic Sulfoxidation in Batch
General Procedure for Catalytic Sulfoxidation Recycle Studies
General Procedure for Catalytic Sulfoxidation Kinetic Studies
General Procedure for Segmented and Continuous Flow Catalytic Sulfoxidation
Characterisation data for Sulfoxides and Sulfones
References
1
Figures S3-S43 H and 13C{1H} NMR spectra and mass spectra for oxidation sulfoxides and
sulfones
S58
S59
Figure S44 FTꢀIR Spectra of (a) fresh [PO4{WO(O2)2}4]@PIILP (2) and (b) catalyst isolated after
the 6th run of a methanol recycle experiment
Figure S45 Conversionꢀselectivity profile as a function of temperature for the continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole in acetonitrile with a residence
time of 4 min
S60
S61
Figure S46 Conversionꢀselectivity profile as a function of temperature for the continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole in methanol with a residence time
of 4 min
Figure S47 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C
2

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S62
S63
Figure S48 Conversionꢀselectivity profile as
a
function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C.
Figure S49 Conversionꢀselectivity profile as function of residence time for the
a
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 2
equivalents of H2O2
S64
S65
S66
S67
S68
S69
S70
S71
Figure S50 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 3
equivalents of H2O2
Figure S51 Conversionꢀselectivity profile as
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 6
equivalents of H2O2
Figure S52 Conversionꢀselectivity profile as
a function of residence time for the
.
a
function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 12
equivalents of H2O2
Figure S53a,b Determination of rate constants for the formation of methyl phenyl sulfoxide (ka) and
methyl phenyl sulfone (kb) in acetonitrile with 12 equivalents of H2O2 by fitting the concentrationꢀ
time profile for the consumption of sulfide and the formation of product.
Figure S54 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 20
equivalents of H2O2
Figure S55a,b Determination of rate constants for the formation of methyl phenyl sulfoxide (ka) and
methyl phenyl sulfone (kb) in acetonitrile with 20 equivalents of H2O2 by fitting the concentrationꢀ
time profile for the consumption of sulfide and the formation of product.
Figure S56 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 2
equivalents of H2O2.
Figure S57 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 3
equivalents of H2O2.
3

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S72
S73
S74
S75
S76
S77
S78
S79
Figure S58 Conversionꢀselectivity profile as
a
function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 6
equivalents of H2O2
Figure S59 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 12
equivalents of H2O2.
Figure S60a,b Determination of rate constants for the formation of methyl phenyl sulfoxide (ka) and
methyl phenyl sulfone (kb) in methanol with 12 equivalents of H2O2 by fitting the concentrationꢀtime
profile for the consumption of sulfide and the formation of product.
Figure S61 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 20
equivalents of H2O2.
Figure S62a,b Determination of rate constants for the formation of methyl phenyl sulfoxide (ka) and
methyl phenyl sulfone (kb) in methanol with 20 equivalents of H2O2 by fitting the concentrationꢀtime
profile for the consumption of sulfide and the formation of product.
Figure S63 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in acetonitrile at 30 °C with 3
equivalents of H2O2 and doped with water.
Figure S64 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanol at 30 °C with 3
equivalents of H2O2 and doped with water.
Figure S65 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of thioanisole in methanolꢀwater (1:1, v/v) at 30
°C with 3 equivalents of H2O2.
S80
S81
Figure S66 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of benzyl phenyl sulfide in acetonitrile at 30 °C.
Figure S67 Conversionꢀselectivity profile as
a function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of benzyl phenyl sulfide in methanol at 30 °C.
4

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S82
S83
S84
Figure S68 Conversionꢀselectivity profile as
a
function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of nitrothioanisole in acetonitrile at 30 °C.
Figure S69 Conversionꢀselectivity profile as function of residence time for the
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of nitrothioanisole in methanol at 30 °C.
Figure S70 Conversionꢀselectivity profile as function of residence time for the
a
a
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of homoallylphenyl sulfide in acetonitrile at 30
°C.
S85
S86
S87
Figure S71 Conversionꢀselectivity profile as
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of homoallylphenyl sulfide in methanol at 30 °C.
Figure S72 Conversionꢀselectivity profile as function of residence time for the
a function of residence time for the
a
[PO4{WO(O2)2}4]@PIILPꢀcatalyzed sulfoxidation of dibenzothiophene in acetonitrile at 30 °C.
Figure S73 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole at 30 °C with a residence time of 4
min in acetonitrile at 30 ºC.
S88
S89
S90
S91
S92
Figure S74 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole at 30 °C with a residence time of 4
min in acetonitrile at 30 ºC, with the H2O2 reservoir replenished after 4 h (*).
Figure S75 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole at 30 °C with a residence time of 4
min in methanol at 30 ºC.
Figure S76 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
[PO4{WO(O2)2}4]@PIILPꢀcatalysed sulfoxidation of thioanisole at 30 °C with a residence time of 4
min in methanol at 30 ºC, with the H2O2 reservoir replenished after 4 h (*).
Figure S77 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
sulfoxidation of thioanisole using [nBu4N]3[PO4{WO(O2)2}4] as catalyst at 30 °C with a residence
time of 4 min in acetonitrile, with the H2O2 reservoir replenished after 4 h (*).
Figure S78 Conversionꢀselectivity profile as a function of time for an 8 h continuous flow
sulfoxidation of thioanisole using [nBu4N]3[PO4{WO(O2)2}4] as catalyst at 30 °C with a residence
time of 4 min in methanol, with the H2O2 reservoir replenished after 4 h (*).
5

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Experimental
General Comments. All reagents were purchased from commercial suppliers and used without further
[NBu4]3[PO4{WO(O2)2}4]1
1ꢀbenzylꢀ1ꢀ((2ꢀmethylbicyclo[2.2.1]heptꢀ5ꢀenꢀ2ꢀ
purification.
and
yl)methyl)pyrrolidinꢀ1ꢀium bromide were prepared as previously described2 and H3[PO4{WO(O2)}4] was
generated in situ immediately prior to use as previously described.3 1H and 13C{1H} spectra were recorded
on JEOL LAMBDAꢀ500 or ECSꢀ400 instruments. Solidꢀstate 31P spectra were recorded at 161.87 MHz
using a Varian VNMRS 400 spectrometer and a 4 mm (rotor o.d.) magicꢀangle spinning probe. They were
obtained using crossꢀpolarization with a 2 s recycle delay, 3 ms contact time, at ambient probe temperature
(~25 °C) and at
a
sample spinꢀrate of 10 kHz. Between 1000 and 3600 repetitions were
accumulated. Spectral referencing was with respect to an external sample of neat tetramethylsilane (carried
out by setting the highꢀfrequency signal from adamantane to 38.5 ppm). Thermogravimetric analysis (TGA)
was performed using a TA TGA Q5000, at a heating rate of 5 °C minꢀ1. All samples were sealed in the
glovebox into aluminium pans. The onset of the weight loss in each thermogram was used as a measure of
the decomposition temperature. TEM images were acquired in bright field using a Tecnai 200 kV F20
Transmission Electron Microscope with a Field Emission Gun. A few drops of sample were pipetted onto an
Agar holey carbon film copper TEM grids and the prepared grid was set aside for ca. 20 min prior to
inserting it into the microscope, in order to allow the solvent to evaporate. Images were taken with a Gatan
CCD digital camera attached to the microscope. Gel permeation chromatography (GPC) was conducted on a
Varian ProStar instrument (Varian Inc.) equipped with a Varian 325 UVꢀvis dual wavelength detector (254
nm), a Dawn Heleos II multiꢀangle laser light scattering detector (Wyatt Technology Corp.), a Viscotek 3580
differential RI detector, and a pair of PL gel 5 ꢁm Mixed D 300 × 7.5 mm columns with guard column
(Polymer Laboratories Inc.) in series. Near monodisperse polystyrene standards (Agilent Technologies) were
used for calibration. Data collection was performed with Galaxie software (Varian Inc.) and chromatograms
analysed with the Cirrus software (Varian Inc.) and Astra software (Wyatt Technology Corp.). Flow
reactions were performed using a Uniqsis FlowSyn Maxi all stainless steel platform with mandrels supplied
by Uniqsis.
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Ring opening metathesis polymerisation of 1-benzyl-1-((2-methylbicyclo[2.2.1]hept-5-en-2-
yl)methyl)pyrrolidin-1-ium bromide with cis-cyclooctene. A flameꢀdried threeꢀneck round bottom flask
under a nitrogen atmosphere was charged with chloroform (80 mL), cisꢀcyclooctene (3.0 mL, 23.0 mmol)
and 1ꢀbenzylꢀ1ꢀ((2ꢀmethylbicyclo[2.2.1]heptꢀ5ꢀenꢀ2ꢀyl)methyl)pyrrolidinꢀ1ꢀium bromide (4.23 g 11.7
mmol). To this was added a solution of [RuCl2(PCy3)2(=CHPh)] (0.571 g, 0.694 mmol) in chloroform (ca.10
mL) and the resulting mixture was heated at 40oC and left to stir for 19 h. Upon completion the reaction was
allowed to cool to room temperature, ethyl vinyl ether (0.69 mL, 7.0 mmol) added and the solution stirred for
an additional hour. The polymer was precipitated by slowly adding the reaction mixture portion wise to
diethyl ether (ca. 600 mL) with vigorous stirring; after stirring for a further 60 minutes the polymer was
isolated by filtration, using a sintered glass frit, washed with diethyl ether and dried to yield 5.2 g of a pale
green solid. A solution of tris(hydroxymethyl)phosphine was prepared by degassing 2ꢀpropanol (90 mL)
with nitrogen for 30 min prior to adding tetrakis(hydroxymethyl)phosphonium chloride (2.6 mL, 18 mmol).
Potassium hydroxide (1.0 g, 18.0 mmol) was added slowly over 15 minutes to the vigorously stirred solution
during which time a white precipitate formed. The mixture was allowed to stir for an additional 10 min and
o
then added to a solution of the polymer in chloroform (ca. 100ꢀ150 mL). After heating at 60 C for 19 h,
NaBr (18.52 g, 180 mmol) was added and the mixture stirred for an additional 3 h at 60 ˚C. The mixture was
then filtered, washed rigorously with distilled water (3 × 50 mL) and the resultant organic layer added
dropwise to diethyl ether (ca. 500 mL) with vigorous stirring. After stirring for a minimum of 60 min the
polymer was allowed to settle, isolated by filtration through a frit, washed with diethyl ether (2 × 50 mL) and
dried under high vacuum to afford 1 as a buff brown solid in 61% yield (4.1 g). Anal. Calc for C36H56NBr: C,
74.20, H, 9.69, N, 2.40. Found: C, 73.82, H, 10.01, N, 2.35 (corresponding to a pyrrolidinium monomer
content of 62.5 mol%, 1.72 mmol gꢀ1); GPC (average over 3 runs): Mw = 9100, Mn = 8600, PDI = 1.06
(Figure S1).
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Figure S1 Differential refractive index (dRI) GPC trace of polymer 1 in DMF (0.6 mL/ min).
1
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
Retention Time / min
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Figure S2 TGA and DSC curves for benzylꢀ1ꢀ((2ꢀmethylbicyclo[2.2.1]heptꢀ5ꢀenꢀ2ꢀyl)methyl)pyrrolidinꢀ1ꢀ
ium bromideꢀcisꢀcyclooctene copolymer 1. The heating rate was 5 ºC minꢀ1.
^ e xo
%
!11T GA 020B
Sample Weight
11TGA020B, 5.8000 mg
100
80
60
40
20
50
100
150
200
250
300
350
400
450
°C
Wg^-1
!11TGA 020B
Heatflow
11TGA020B, 5.8000 mg
-10
-20
-30
50
100
150
200
250
300
350
400
450
°C
TAR e SW 9.1 0
S
L a b: M ETTL ER
o
The heat flow plot (lower trace) of coꢀpolymer 1 clearly shows an exotherm at 100 C which could
correspond to Hoffmann elimination with no loss in mass.
9

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Synthesis of polymer immobilised peroxophosphotungstate 2. A hydrogen peroxide solution (35% w/w,
9.7 mL, 100 mmol) was added to phosphotungstic acid (1.73 g, 0.6 mmol) dissolved in a minimum volume
of water and stirred at room temperature for 30 min. After this time, pyridine (0.145 mL, 1.8 mmol) was
added followed by a solution of 1 (0.877 g, 1.8 mmol) in the minimum volume of ethanol, which resulted in
the immediate precipitation of an amorphous white solid. The mixture was cooled to 0 ˚C, filtered through a
sintered glass frit and the precipitate washed with water (2 × 10 mL) and diethyl ether (3 × 75 mL) and dried
under vacuum to afford 6 in 84% yield. FTꢀIR (KBr plates): ṽ = 1087, 1058, 1028 (PꢀO), 956 (W=O), 837
(OꢀO), 585, 535 W(O2)sym,asym: Anal. Calc for C108H168N3O24PW4: N, 1.58; W, 27.66. Found: N, 1.46; W,
26.31. Loading of tungsten 1.4 mmol gꢀ1.
Synthesis of [nBu4N]3[PO4{WO(O2)2}4]/SiO2
A flame dried Schlenk flask was charged with [nBu4N]3[PO4{WO(O2)2}4] (0.094 g, 0.05 mmol) and
dichloromethane (6 mL) and the mixture stirred at room temperature for 15 min after which time 1.0 g of
Geduran® Si60 (43ꢀ60 µm) was added and stirring continued for a further 2 h. The dichloromethane was
removed under vacuum to afford a free flowing powder. FTꢀIR (KBr plates): ṽ = 1084, 1059, 1028 (PꢀO),
966 (W=O), 845 (OꢀO), 592, 532 W(O2)sym,asym. The tungsten loading was confirmed to be 0.19 mmol of W
gꢀ1 of silica by ICPꢀOES analysis.
10

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Figure S3a TEM image of freshly prepared polymer immobilised peroxophosphotungstate 2
Figure S3b TEM image of polymer supported peroxophosphotungstate 2 recovered after use in catalysis
11

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General Procedure for Catalytic Sulfoxidation in Batch
An ovenꢀdried Schlenk flask was allowed to cool to room temperature and charged sequentially with sulfide
(1.0 mmol), catalyst (0.013 g, 0.005 mmol) and solvent (3 mL), the reaction was then activated by the
addition of 35% H2O2 (0.24 mL, 2.5 mmol) and allowed to stir at room temperature for 15 min. The reaction
mixture was diluted with dichloromethane (25 mL), washed with water (c.a. 50 mL) and the organic extract
dried over MgSO4 and the solvent removed under reduced pressure. The resulting residue was analysed by
1
either H or 13C{1H} NMR spectroscopy to quantify the composition of starting material and products; for
each substrate tested an internal standard of 1,3ꢀdinitrobenzene was initially employed to ensure mass
balance.
General Procedure for Catalytic Sulfoxidation Recycle Studies
An ovenꢀdried Schlenk flask was allowed to cool to room temperature and charged sequentially with sulfide
(3.0 mmol), polymer immobilised catalyst 2 (0.039 g, 0.015 mmol) or [nBu4N]3[PO4{WO(O2)2}4]/SiO2 (100
mg of a 6.5 wt%) and solvent (9 mL). The reaction was initiated by addition of 35% H2O2 (0.72 mL, 7.5
mmol) and the resulting mixture allowed to stir at room temperature for 20 min. After this time the solution
was centrifuged (10 min, 12000 rpm), decanted using a pipette and the remaining catalyst washed
with the reaction solvent and dried prior to reuse under the same conditions. The remaining solution
was subject to the same workꢀup and analysis as described above. ICP analysis of a portion of the
organic and aqueous phases between recycles was conducted using a using a Perkin Elmer Optima 4300DV
ICPꢀOES (Inductively Coupled Plasma Optical Emission Spectrometer).
General Procedure for Catalytic Sulfoxidation Kinetic Studies
An ovenꢀdried Schlenk flask was allowed to cool to room temperature and charged sequentially with sulfide
(3.0 mmol), polymer immobilised catalyst 2 (0.039 g, 0.005 mmol) and solvent (9 mL). The reaction was
initiated by addition of 35% H2O2 (0.72 mL, 7.5 mmol) and the resulting mixture stirred at room temperature
for the 20 min during which time 0.5 mL aliquots were removed for workꢀup (as above) and analysis by 1H
NMR spectroscopy. After the final aliquot had been removed the remaining reaction mixture was decanted,
the catalyst washed with diethyl ether, dried and replenished to account for losses arising from the sampling.
12

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The recycle kinetic experiment was conducted by charging the Schlenk with fresh sulphide (3.0 mL), solvent
(9 mL) and 35% H2O2 (0.72 mL, 7.5 mmol).
General Procedure for Segmented and Continuous Flow Catalytic Sulfoxidation
Two reservoirs were charged with sulfide (5.0 mmol) dissolved in the appropriate solvent (25 mL, 0.2 M)
and hydrogen peroxide (1.29 mL, 35%) in the same (25 mL, 0.6 M). A Uniqsis FlowSyn reactor was used to
pump 1 mL of each reagent at total flow rates that varied between 0.293 mL minꢀ1 and 8.8 mL minꢀ1 (using
the same solvent as stock) through a Tꢀpiece mixer to combine the two streams; in the case of segmented
flow an additional reservoir of carrier solvent was also employed. The reaction stream was then flowed
through a OMNIFIT® glass column reactor cartridge (10 mm id x 100 mm) packed with 0.1 g of
[PO4{WO(O2)2}4]@PIILP and 2.0 g of SiO2 (Geduran® Si 60) and mounted in a FlowSyn column heater. The
exiting stream was passed through a back pressure regulator (BPR) and 2 mL fractions were collected into
separate vials followed by a 2 mL postꢀcollect. Each sample was diluted with dichloromethane (10 mL),
washed with water (c.a. 15 mL), the organic extract dried over MgSO4, the solvent removed under reduced
pressure and the resulting residue analysed by 1H NMR spectroscopy to quantify the composition of starting
material and products.
13

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Characterisation of Sulfoxides and Sulfones
Methyl phenyl sulfoxide.[4] 1H NMR (400 MHz, CDCl3, δ): 7.69ꢀ7.62 (m, 2H), 7.50ꢀ7.41 (m, 2H), 7.36ꢀ7.30
(m, 1H), 2.73 (s, 3H); 13C NMR (100.5 MHz, CDCl3, δ): 145.42, 130.95, 128.63, 123.54, 43.93; LRMS (EI+)
m/z 163 [M+Na]+.
Methyl phenyl sulfone.[4] 1H NMR (400 MHz, CDCl3, δ): 7.95ꢀ7.87 (m, 2H), 7.71ꢀ7.61 (m, 2H), 7.59ꢀ7.52
(m, 1H), 3.02 (s, 3H); 13C NMR (100.5MHz, CDCl3, δ): 137.44, 133.21, 128.54, 126.23, 44.88; LRMS (EI+)
m/z 179 [M+Na]+.
Ethyl phenyl sulfoxide.[4] 1H NMR (400 MHz, CDCl3, δ): 7.84ꢀ7.49 (m, 2H), 7.48ꢀ7.13 (m, 3H), 2.91 (q,
1H,
J = 6.61 Hz), 2.78ꢀ2.69 (q, 1H, J = 6.61 Hz), 1.23 (t, 3H, J
= 6.61 Hz); 13C NMR (100.5 MHz, CDCl3,
δ): 145.69, 131.47, 129.85, 125.42, 47.19, 10.39; LRMS (EI+) m/z 177 [M+Na]+.
Ethyl phenyl sulfone.[4] 1H NMR (400 MHz, CDCl3, δ): 7.99 (m, 2H), 7.59 (m, 3H), 3.09 (q, 2H,
J = 7.11
Hz), 1.30 (t, 3H,
7.34; LRMS (EI+) m/z 193 [M+Na]+.
J
= 7.11 Hz); 13C NMR (100.5MHz, CDCl3, δ): 138.31, 133.47, 128.92, 127.86, 50.28,
Allyl phenyl sulfoxide.[4] 1H NMR (400 MHz, CDCl3, δ): 7.64ꢀ7.60 (m, 2H), 7.39ꢀ7.36 (m, 2H), 7.31ꢀ7.26
(m, 1H), 5.44 (ddt, 1H,
J
= 7.11, 10.22, 17.10 Hz), 5.16 (dq, 1H,
= 7.11, 1.12 Hz); 13C NMR (100.5 MHz, CDCl3, δ): 142.13, 131.24, 129.06,
125.09, 124.71, 117.93, 60.63; LRMS (EI+) m/z 167 [M+Na]+.
J = 1.12, 10.22 Hz), 5.01 (dq, 1H, J = 1.42,
17.10 Hz), 3.43 (dt, 2H,
J
Allyl phenyl sulfone.[4] 1H NMR (400 MHz, CDCl3, δ): 7.95ꢀ7.91 (m, 2H), 7.69ꢀ7.62 (m, 2H), 7.37ꢀ7.44 (m,
1H), 5.63 (ddt, 1H,
J
= 7.19, 10.31, 17.21 Hz), 5.18 (dq, 1H,
= 7.19, 1.22Hz); 13C NMR (100 MHz, CDCl3, δ): 138.27, 133.74, 129.02, 128.88,
124.63, 117.51, 60.67; LRMS (EI+) m/z 189 [M+Na]+.
J = 1.22, 10.31 Hz), 5.02 (dq, 1H, J = 1.48,
17.21Hz), 3.91 (dt, 2H,
J
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Methyl 4-nitrophenyl sulfoxide.[5] 1H NMR (400 MHz, CDCl3, δ): 8.39 (d,
J = 8.0 Hz, 2H), 7.90 (d, J = 7.5
Hz, 2H), 2.85 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 152.4, 150.0, 126.2, 125.8, 43.5; LRMS (EI+) m/z 205
[M+Na]+.
Methyl 4-nitrophenyl sulfone.[6] 1H NMR (400 MHz, CDCl3, δ): 8.43 (d,
J = 8.8 Hz, 2H), 8.16 (d, J = 8.8
Hz, 2H), 3.12 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 150.9, 145.9, 129.0, 124.6, 44.3. LRMS (EI+) m/z 224
[M+Na]+.
Dibenzothiophene sulfoxide.[4] 1H NMR (400M Hz, CDCl3, δ): 7.98ꢀ7.91 (m, 4H), 7.75ꢀ7.71 (m, 2H), 7.59ꢀ
7.52 (m, 2H); 13C NMR (100.5 MHz, CDCl3, δ): 143.33, 132.67, 129.83, 126.37, 124.16, 123.45; LRMS (EI+)
m/z 223 [M+Na]+.
Dibenzothiophene sulfone.[4] 1H NMR (400 MHz, CDCl3, δ): 7.85ꢀ7.77 (m, 4H), 7.66ꢀ7.61 (m, 2H), 7.55ꢀ
7.51 (m, 2H); 13C NMR (100.5 MHz, CDCl3, δ): 137.62, 133.77, 131.53, 130.16, 121.97, 121.54; LRMS (EI+)
m/z 239 [M+Na]+.
Homoallyl phenyl sulfoxide.[7] 1H NMR (300 MHz, CDCl3, δ): 7.75ꢀ7.55 (m, 5H), 6.04ꢀ5.90 (m, 1H), 5.31ꢀ
5.20 (m, 2H), 2.98ꢀ2.83 (m, 2H), 2.73ꢀ268 (m, 1H), 2.50ꢀ2.45 (m, 1H); 13C NMR (100 MHz, CDCl3, δ):
135.4, 130.4, 129.0, 124.1, 117.0, 56.2, 26.3; LRMS (EI+) m/z 203 [M+Na]+.
Homoallyl phenyl sulfone.[8] 1H NMR (400 MHz, CDCl3, δ): 7.89ꢀ7.87 (m, 2 H), 7.65ꢀ7.62 (m, 1H), 7.56ꢀ
7.53 (m, 2 H), 5.73ꢀ5.64 (m, 1 H), 5.04ꢀ4.99 (m, 2 H), 3.15ꢀ3.11 (m, 2 H); 2.46ꢀ2.40 (m, 2H); 13C NMR (100
MHz, CDCl3, δ) 138.9, 133.7, 133.6, 129.2, 128.0, 117.1, 55.3, 26.7; LRMS (EI+) m/z 219 [M+Na]+.
Benzyl phenyl sulfoxide.[4] 1H NMR (400 MHz, CDCl3, δ): 7.55ꢀ7.42 (m, 2H), 7.36ꢀ7.17 (m, 3H), 7.11ꢀ6.63
(m, 5H), 3.98 (s, 2H); 13C NMR (100.5 MHz; CDCl3, δ): 142.59, 130.83, 130.26, 128.87, 128.57, 128.24,
128.15, 124.21, 63.44; LRMS (EI+) m/z 239 [M+Na]+.
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Benzyl phenyl sulfone.[4] 1H NMR (400 MHz, CDCl3, δ): 7.74ꢀ7.65 (m, 2H), 7.41ꢀ7.32 (m, 3H), 7.14ꢀ7.06
(m, 5H), 4.41 (s, 2H); 13C NMR (100.5 MHz; CDCl3, δ): 137.49, 133.44, 130.53, 128.61, 128.47, 128.39,
128.31, 62.53; LRMS (EI+) m/z 255 [M+Na]+.
tert-Butyl methyl sulfoxide.[9] 1H NMR (300 MHz, CDCl3, δ): 2.42 (s, 3H), 1.37 (s, 9H); 13C NMR (100
MHz; CDCl3, δ): 57.80, 36.68, 26.60; LRMS (EI+) m/z 143 [M+Na]+.
tert-Butyl methyl sulfone.[10] 1H NMR (300 MHz, CDCl3, δ): 2.70 (s, 3H), 1.41 (s, 9H); 13C NMR (100
MHz; CDCl3, δ): 50.51, 32.05, 23.25. LRMS (EI+) m/z 137 [M+H]+.
References
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16