Fast catalytic epoxidation with H2O2 and [γ-SiW10O36(PhPO)2]4- in ionic liquids under microwave irradiation

Article abstract of DOI:10.1021/jo7016923

(Figure Presented) Olefin epoxidation by [γ-SiW₁₀O ₃₆(PhPO)₂]^4- and H₂O₂ occurs in hydrophobic ionic liquids (ILs), with yields and selectivity up to >99%. The catalytic IL phase is recyclable. Under MW irradiation the reaction occurs with up to 200 turnovers per minute. Simultaneous cooling is instrumental for quantitative H₂O₂ conversion.

Full text of DOI:10.1021/jo7016923

[γ-SiW10O34(H2O)2]4 (1), the phenyl phosphonate derivative
-
3
Fast Catalytic Epoxidation with H2O2 and
γ-SiW10O36(PhPO)2] in Ionic Liquids under
4
-
7
4
-
[γ-SiW O (PhPO) ] (2) displays an improved thermal
1
0
36
2
[
stability, higher turnover frequency (TOF), and a remarkably
wide substrate scope, under microwave (MW)-assisted pro-
cesses, in CH3CN. Further innovation toward environmental
sustainability should also consider the replacement of hazardous
volatile organic solvents (VOCs) by alternative reaction media,
Microwave Irradiation
5
†
,†
†
Serena Berardi, Marcella Bonchio,* Mauro Carraro,
,‡
†
†
Valeria Conte,* Andrea Sartorel, and Gianfranco Scorrano
8
,9
10
ITM-CNR and Department of Chemical Sciences, UniVersity of
PadoVa, Via Marzolo 1, 35131 PadoVa, Italy, and Department
of Chemical Sciences and Technologies, UniVersity of Rome
ranging from fluorinated phases to supercritical CO2 and
1
1,12
13
ionic liquids (ILs),
or a combination of these.
ILs media have been successfully used for metal-catalyzed
oxidations with peroxides,
“
Tor Vergata”, Via della Ricerca Scientifica, 00133 Rome, Italy
14-16
therefore the IL embedding of
catalytically active polyanions, by a straightforward metathesis
strategy, is expected to yield tailored functional phases.17 In
such perspective, we report herein the combined use of 2 and
ILs for catalytic epoxidation with H O (Scheme 1). Our results
marcella.bonchio@unipd.it; Valeria.conte@uniroma2.it
ReceiVed August 2, 2007
2
2
include the following: (i) the screening of ILs to optimize
catalytic efficiency and recycling, (ii) catalyst speciation and
recovery in the IL environment, and (iii) the advantageous use
18
of MW, which are readily absorbed by the ionic catalytic phase
(
IL+POM), to promote unprecedented turnover frequencies
-
1 5,19
(TOF > 200 min ).
A powerful tool for more sustainable
organic synthesis and catalysis is the miniaturization of chemical
processes, through microreactor technology, coupled with the
continuous flow processing of the reaction mixture. This aspect
also has been addressed herein (vide infra).
]4- and H
2 2 2
Olefin epoxidation by [γ-SiW10O36(PhPO) O
Catalytic tests have been initially performed with cis-
cyclooctene, as model substrate, in both hydrophilic and
hydrophobic ILs containing the 1-butyl-3-methylimidazolium
occurs in hydrophobic ionic liquids (ILs), with yields and
selectivity up to >99%. The catalytic IL phase is recyclable.
Under MW irradiation the reaction occurs with up to 200
turnovers per minute. Simultaneous cooling is instrumental
+
-
-
cation, [bmim ], and different anions [BF4 ], [CF3SO3 ],
-
-
20
[
PF6 ], and [(CF3SO2)2N ] (Scheme 1).
2 2
for quantitative H O conversion.
(
5) Carraro, M.; Sandei, L.; Sartorel, A.; Scorrano, G.; Bonchio, M. Org.
Lett. 2006, 8, 3671-3674.
6) Bonchio, M.; Carraro, M.; Scorrano, G.; Bagno, A. AdV. Synth. Catal.
2004, 346, 648-654.
7) (a) Mayer, C. R.; Thouvenot, R. J. Chem. Soc., Dalton Trans. 1998,
7
6
(
The design of catalyst packages with better performance, in
terms of yields, selectivities, recycling, and use of alternative
solvents, is a priority task within sustainable catalysis. In
particular, catalytic epoxidation with hydrogen peroxide (H2O2)
retains a major interest. This is related to the key role of epoxides
as industrial intermediates and to the use of the peroxide with
the highest “atom efficiency” (47% of active oxygen), yielding
(
-13. (b) Mayer, C. R.; Herson, P.; Thouvenot, R. Inorg. Chem. 1999, 38,
152-6158.
(8) (a) Horvath, I. T. Acc. Chem. Res. 1998, 31, 641-650. (b) De Wolf,
E.; Van Koten, G.; Deelman, B. J. Chem. Soc. ReV. 1999, 28, 37-41.
(9) Carraro, M.; Gardan, M.; Scorrano, G.; Drioli, E.; Fontananova, E.;
Bonchio, M. Chem. Commun. 2006, 4533-4535.
(10) (a) Jessop, P. G.; Ikariya, T.; Noyori, R. Chem. ReV. 1999, 99, 475-
494. (b) Leitner, W. Acc. Chem. Res. 2002, 35, 746-756.
1
H2O as byproduct. From the catalyst side, robust polyoxo-
(11) (a) Dyson, P. J.; Geldbach, T. J. Metal Catalysed Reactions in Ionic
metalates (POMs) can promote the epoxidation of internal and
terminal double bonds with outstanding catalytic performance
and selectivity >99%.2 Moreover, the use of hybrid poly-
oxotungstates has been recently proposed as a catalyst up-
Liquids; Springer: Dordrecht, The Netherlands 2005. (b) Wasserscheid,
P.; Welton, T. Ionic Liquids in Synthesis; Wiley-VCH: Weinheim, Germany,
2003.
-4
(
12) (a) Welton, T. Chem. ReV. 1999, 99, 2071-2084. (b) Wasserscheid,
P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3773-3789. (c) Sheldon,
5
,6
grade. When compared to the nonfunctionalized precursor
R. A. Chem. Commun. 2001, 2399-2407.
(13) Dzyuba, S. V.; Bartsch, R. A. Angew. Chem., Int. Ed. 2003, 42,
†
University of Padova.
University of Rome “Tor Vergata”.
148-150.
‡
(14) Muzart, J. AdV. Synth. Catal. 2005, 348, 275-295 and references
(
1) Sheldon, R. A. Pure Appl. Chem. 2000, 72, 1233-1246.
cited therein.
(2) (a) Adam, W.; Alsters, P. L.; Neumann, R.; Saha-M o¨ ller, C. R.;
(15) Conte, V.; Floris, B.; Galloni, P.; Silvagni, A. Pure Appl. Chem.
2005, 77, 1575-1581.
(16) Conte, V.; Floris, B.; Galloni, P.; Silvagni, A. AdV. Synth. Catal.
2005, 347, 1341-1344.
(17) Miao, W.; Chan, T. H. Acc. Chem. Res. 2006, 39, 897-908.
(18) (a) Roberts, B. A.; Strauss, C. R. Acc. Chem. Res. 2005, 38, 653-
661. (b) Larhed, M.; Moberg, C.; Hallberg, A. Acc. Chem. Res. 2002, 35,
717-727.
(19) Bonchio, M.; Carraro, M.; Kortz, U.; Scorrano, G. AdV. Synth. Catal.
2005, 347, 1909-1912.
(20) To avoid irreproducible results often obtained with commercial ILs
of unknown purity, the solvents were synthesized and purified following
the procedure indicated in the Supporting Information.
Sloboda-Rozner, D.; Zhang, R. J. Org. Chem. 2003, 68, 1721-1728. (b)
Sloboda-Rozner, D.; Alsters, P. L.; Neumann, R. J. Am. Chem. Soc. 2003,
1
25, 5280-5281. (c) Sloboda-Rozner, D.; Witte, P.; Alsters, P. L.;
Neumann, R. AdV. Synth. Catal. 2004, 346, 339-345.
3) (a) Mizuno, N.; Kamata, K.; Yonehara, K.; Sumida, Y. Science 2003,
(
3
00, 964-966. (b) Mizuno, N.; Yamaguchi, K.; Kamata, K. Coord. Chem.
ReV. 2005, 249, 1944-1956. (c) Kamata, K.; Nakagawa, Y.; Yamaguchi,
K.; Mizuno, N. J. Catal. 2004, 224, 224-228. (d) Kamata, K.; Kotani, M.;
Yamaguchi, K.; Hikichi, S.; Mizuno, N. Chem. Eur. J. 2007, 13, 639-
6
48.
(
4) Sartorel, A.; Carraro, M.; Bagno, A.; Scorrano, G.; Bonchio, M.
Angew. Chem., Int. Ed. 2007, 46, 3255-3258.
10.1021/jo7016923 CCC: $37.00 © 2007 American Chemical Society
8
954
J. Org. Chem. 2007, 72, 8954-8957
Published on Web 10/17/2007

SCHEME 1. Catalytic Epoxidation of cis-Cyclooctene by 2
with H in ILs
TABLE 1. Catalytic Epoxidation of cis-Cyclooctene by 2 with
Aqueous H2O2 in ILs at 50 °Ca
2 2
O
H2O,b time,
epoxide
yield, % min
TOF,d
c
-1
entry
IL
%
min
+
-
1
2
3
4
5
6
7
[bmim ][BF4 ]
23
23
23
11
45
23
11
11
22
11
300
240
180
90
90
120
45
1
62
81
>99
>99
17
0.6
+
-
[bmim ][CF3SO3 ]
0.7
0.8
3.5
0.1
1.2
5.7
210
100
6.3
+
-
[bmim ][PF6 ]
+
-
[bmim ][(CF3SO2)2N ]
92
>99
>99
94
e
8
e,f
9
2
2
g
1
0
10
a
Reactions performed in the presence of a layered hydrocarbon phase,
cis-cyclooctene (3.0 mmol); H2O2 (0.60 mmol), provided by aqueous
solutions with concentrations in the range 7-24 M; 2 (4.80 µmol); 200 µL
b
of IL. Total amount of water (v/v %) introduced and formed during
The catalytic phase is prepared by dissolving 2 in the
appropriate IL, which thereby acts as a solvating/immobilization
medium for the hybrid organic-inorganic polyelectrolyte.
Indeed, combined UV-vis, FT-IR, and 31P NMR evidence
indicates that both the polyoxotungstate framework and the
organic surface domain of 2 are preserved within the IL
environment (see the Supporting Information). Such spectro-
scopic data have been conveniently used to assess the catalyst
stability under turnover regime and to rule out its washing off
by extraction procedures during reaction sampling and/or
recycling.
turnovers. c Calculated with respect to H2O2. d Turnover frequency calcu-
lated as epoxide (mol)/2 (mol) per minute, and determined at <60%
conversion. e MW irradiation at W ) 10 W, under stirring and simultaneous
) 80 °C. f Entry 8 recharged
cooling with compressed air at 40 psi; T
bulk
with H2O2 (0.60 mmol). g Microflow reaction at 0.017 mL/min (see the
Supporting Information).
The reaction setup has been designed to foster the continuous
feeding of the IL-immobilized catalyst, through a neat-
hydrocarbon phase layered in the system. The hydrocarbon
reservoir provides a stationary concentration of the olefin within
the IL catalytic phase, thus fostering maximum rates at substrate-
2
1
saturation conditions. Quantitative GC analysis, performed
under turnover conditions, indicates that the limiting olefin
amount in the IL-phase is 1.5 M. Epoxidation occurs upon
addition of aqueous H2O2 under vigorous stirring. Both the
supply of the peroxidic reagent and its evolution under catalysis
result in H2O accumulation in the system, which varies in the
range 11-45% calculated with respect to the IL medium (Table
FIGURE 1. Kinetics of cis-cyclooctene epoxidation by 2 with aqueous
H O in hydrophobic ILs, at 50 °C.
2 2
22
the impact of water addition/accumulation on the epoxidation
kinetics and on the resulting turnover frequency (TOF) (Table
1 and Figure 1). Faster epoxidation profiles are obtained by
+
1
). The optimization of the catalytic performance has been
evaluated in selected ILs with increasing hydrophobicity (Table
). According to the water content determined after high vacuum
drying at 70 °C for 4-30 h, IL hydrophobicity is reported to
using the more concentrated H O in hydrophobic [bmim ]-
2
2
-
+
-
[(CF SO ) N ] and [bmim ][PF ] (b and 9 in Figure 1),
3
2 2
6
1
yielding respectively a maximum TOF of 5.7 and 3.5 turnovers
2
4
per minute (entries 7and 4 in Table 1). Addition of more
+
-
+
-
+
-
increase in the order [bmim ][BF4 ] ≈ [bmim ][CF3SO3 ] <
bmim ][PF6 ] < [bmim ][(CF3SO2)2N ].
Inspection of data in Table 1 reveals that selective epoxidation
2 2 6
diluted H O solutions in [bmim ][PF ] results in a remarkable
+
-
+
- 23
[
abatement of the oxidation rate with TOF values decreasing
below unity ([ and 2 in Figure 1 and entries 3 and 5 in Table
1).
and quantitative conversion of H2O2 (epoxide yields up to
+
>
99%) is achieved in the hydrophobic ILs, namely [bmim ]-
The delivery of water is expected to impact the mass-transfer
processes within the substrate/ILs/water multiphase system.
Moreover, the reactivity of POMs is known to be driven by
protonation equilibria and ion-pair association, which can be
strongly affected by the medium composition under turnover
-
+
-
[
PF6 ] and [bmim ][(CF3SO2)2N ]. Instead, slower to sluggish
+
-
reactions occur in the hydrophilic media, [bmim ][CF3SO3 ]
+
-
and [bmim ][BF4 ]. The extent of water content in ILs is an
often-overlooked parameter for the optimization of the catalytic
protocol. This instance has been further addressed by evaluating
4
,25
regime.
Consequently, a direct, on-site, recharge with ad-
ditional portions of aqueous H2O2 fails to restore the pristine
catalytic efficiency, leading to lower TOF values (recharge of
(
21) Under stoichiometric conditions (olefin ) 40 µmol, H2O2 ) 40
+ -
-1
µmol, 2 ) 0.32 µmol, in 200 µL of [bmim ][(CF3SO2)2N ] at T ) 50 °C)
slower reaction rates were generally observed, leading to cyclooctene
epoxide (99%) after 18 h and to 1,2-epoxyoctane (51%) after 66 h (compare
with data in Table 2).
reactions 2, 3, and 6 in Table 1, TOF < 0.5 min ) and overall
26
epoxide yields <60%.
(
24) Under the particular condition explored, anydrous H2O2 in the form
of urea complex (UHP) was not fully soluble in the IL-phase.
25) Protonation equilibria and the extent of ion-pair association are
known to influence POMs reactivity and their physical-chemical properties.
a) Musaev, D. G.; Morokuma, K.; Geletii, Y. V.; Hill, C. L. Inorg. Chem.
004, 43, 7702-7708. (b) Grigoriev, V. A.; Cheng, D.; Hill, C. L.;
Weinstock, I. A. J. Am. Chem. Soc. 2001, 123, 5292-5307.
(
22) Aqueous H2O2 is soluble in all hydrophilic ILs, while a highly
dispersed emulsion is formed within hydrophobic ILs.
23) (a) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H.
(
(
D.; Broker, G. A.; Rogers, R. D. Green Chem. 2001, 3, 156-154. (b)
Kanakubo, M.; Hiejima, Y.; Minami, K.; Aizawa, T.; Nanjo, H. Chem.
Commun. 2006, 1828-1830.
(
2
J. Org. Chem, Vol. 72, No. 23, 2007 8955

Nevertheless, a good recycling performance has been obtained
after extraction of the spent catalytic phase (IL+POM) with
hexane and water followed by vacuum anhydrification over
P2O5. With this treatment the epoxide is recovered with
quantitative yield, in at least four consecutive runs (total TON
TABLE 2. Catalytic Epoxidation by 2 with Aqueous H2O2 in
+
-
a
[
bmim ][(CF3SO2)2N ] at 50 °C and under MW Irradiation
(
Results in Parentheses)b
c
entry
olefin
time, h
epoxide yield, %
1
2
3
4
5
6
7
cyclohexene
E-2-octene
1-octene
4 (0.25)
15 (0.75)
40 (3)
>99
>99
)
500). FT-IR and quantitative UV-vis analysis of the
75 (54)
85 (99)
77 (97)
89 (99)
89 (44)
recovered catalytic phase confirm that both the POM structure
and its loading are preserved upon extraction and recycling (see
the Supporting Information). As a corollary, cis-cyclooctene
epoxidation by the nonhybrid precursor (1) has been screened
1-hexene
40 (2)
Z-2-hexene
E-2-hexene
Z-stilbene
15 (0.5)
15 (1)
d
15 (0.5 )
+
-
+
-
+
-
in[bmim ][PF6 ],[bmim ][(CF3SO2)2N ],and[bmim ][CF3SO3 ].
In these reactions, the epoxide is obtained only in moderate
yields (44-74%), while the exhausted catalyst precipitates out
of the solution. FT-IR analysis indicates a major structural
rearrangement of the lacunary POM. Therefore, further
optimization of the reaction protocol and of the substrate scope
has been performed only with 2, which exhibits a superior
a
In all reactions: olefin (0.20 mmol), H2O2 (40 µmol) provided by 24
+
-
M aqueous solution; 2 (0.32 µmol); 200 µL of [bmim ][(CF3SO2)2N ]; T
50 °C. b Reactions performed in the presence of a layered hydrocarbon
phase (2.0 mmol); H2O2 (40 µmol), provided by 24 M aqueous solution; 2
)
+
-
(
3.2 µmol); 200 µL of [bmim ][(CF3SO2)2N ]. MW irradiation at 5 W,
27
under stirring and simultaneous cooling; Tbulk ) 57-65 °C (see the
Supporting Information for details). c Calculated with respect to H O . MW
d
2
2
irradiation at 4 W; Tbulk ) 58-73 °C.
5
stability. A noteworthy implementation of the system has been
5,8,19
achieved under MW irradiation (entries 8 and 9 in Table 1).
Indeed, the polyelectrolytic nature of the catalytic phase
POM+IL) guarantees negligible vapor pressure, as well as fast
The substrate scope is addressed in Table 2, including the
MW-assisted optimized protocol (results in parentheses).31 In
these reactions the amount of water is maintained below 1%,
to prevent the epoxide conversion to diol and to its over-
oxidation products.
(
and selective MW-induced heating by ionic conduction mech-
anism, even at low power (4-10 W). In our study, continuous
MW irradiation has been applied with simultaneous cooling
The epoxidation of both internal and terminal olefins was
shown to proceed with up to 99% yield and selectivity. A further
point concerns the steric constrains of stereospecific oxygen
transfer to Z- and E-alkenes. Competitive epoxidation of
diastereomeric 2-hexenes shows a reactivity ratio Z/E of 6 (at
50 °C) and 5 (under MW irradiation) at conversion of H2O2
<30%. Such Z preference is similar to that reported for other
(Tbulk < 80 °C). Here, the reaction vessel is cooled from the
outside by compressed air or by a cooling fluid, allowing a
higher level of microwave power to be directly administered to
2
8
the reaction mixture, while preventing bulk overheating. Due
to the fast and efficient response of ILs to MW induced dielectric
heating, a careful optimization of both the supplied MW power
and the cooling flow is crucial to promote selective epoxidation
versus the unproductive decomposition of H2O2. Under the
conditions explored, quantitative epoxidation occurs in 1 min,
incrementing the TOF value by ca. 35 times (entries 7 and 8 in
Table 1).29 Considering the experimental setup, the epoxide
productivity amounts to ca. 7500 mol/h per mol of catalyst.
Moreover, the in situ recharge with H2O2 provides a second
epoxidation run with a reduced, but still remarkable TOF of
5
,32
tungstate-based catalysts.
In conclusion, the combined use of POMs, ionic liquids and
MW irradiation represents an innovative strategy for the
immobilization, recycling, and activation of the catalytic phase
within a solvent-free reaction setup. Further experiments will
be aimed at optimizing the reaction performance and its water-
tolerance with the use of tailor-made, water-proof, IL phases
which might be instrumental for catalytic oxidation with H2O2.
-1
1
00 min (entries 8 and 9 in Table 1). The fast turnover regime
achieved under MW irradiation is amenable to flow type
operations and microfluidic technology, responding to process
Experimental Section
Caution: The uncontrolled heating of large amount of peroxides
must be avoided. Care must be taken to avoid possible explosion.
The synthesis of ILs used in this work was performed in a two-
step procedure by quaternization of the alkyl-substituted imidazole
with an alkyl-bromide followed by metathesis exchange with a
30
intensification issues. In this respect, the application of
microreactors for multiphase systems is expected to provide a
high surface-to-volume ratio, short diffusion distances, improved
mass transfer, fast and efficient heat dissipation, and control.
This latter aspect is of particular importance dealing with the
potentially harmful peroxide run-over. Interestingly, epoxidation
performed in a PTFE microchannel tube (300 µm × 400 mm)
under flow conditions occurs with similar TOFs (entries 7 and
3
3-35
1
suitable anion.
The resulting ILs were characterized by H
NMR, 13C NMR, and FT-IR and their identity was confirmed by
comparison with literature data.3
6,37
Microwave experiments were performed with use of a monomode
microwave apparatus operating at 2.45 GHz with continuous
1
0 in Table 1).
(
31) Under MW irradiation, Tbulk depends both on the substrate nature
(
26) At long reaction time, H2O2 decomposition becomes a competing
and on its concentration. With less reactive substrates, at high temperature,
decomposition of H2O2 competes with catalytic epoxidation, so both the
presence of a layered substrate phase and a higher catalyst loading are
instrumental for higher epoxide yields.
process.
(
27) Evolution of 1 to dimeric complexes has been reported to occur in
nonaqueous environment. Yoshida, A.; Yoshimura, M.; Uehara, K.; Hikichi,
S.; Mizuno, N. Angew. Chem., Int. Ed. 2006, 45, 1956-1960.
(32) Goto, Y.; Kamata, K.; Yamaguchi, K.; Uehara, K.; Hikichi, S.;
Mizuno, N. Inorg. Chem. 2006, 45, 2347-2356 and references cited therein.
(33) Owens, G. S.; Abu-Omar, M. M. J. Mol. Catal. A: Chem. 2002,
187, 215-225.
(
28) Hosseini, M.; Stiasni, N.; Barbieri, V.; Kappe, C. O. J. Org. Chem.
2
007, 72, 1417-1424.
29) In the absence of simultaneous cooling, the yield of epoxide was
negligible.
(
(34) Bonh oˆ te, P.; Dias, A. P.; Papageorgiou, N.; Kalyanasundaram, K.;
Gr a¨ tzel, M. Inorg. Chem. 1996, 35, 1168-1178.
(
30) (a) Ahmed, B.; Barrow, D.; Wirth, T. AdV. Synth. Catal. 2006, 348,
1
043-1048 and references cited therein. (b) Glasnov, T. N.; Kappe, C. O.
(35) Seddon, K. R.; Stark, A.; Torres, M. J. Pure Appl. Chem. 2000, 72,
2275-2287.
(36) Suarez, P. A. Z.; Dullius, J. E. L.; Einloft, S.; De Souza, R. F.;
Dupont, J. Polyhedron 1996, 15, 1217-1219.
Macromol. Rapid Commun. 2007, 28, 395-410. (c) Mason, B. P.; Price,
K. E.; Steinbacher, J. L.; Bogdan, A. R.; McQuade, D. T. Chem. ReV. 2007,
1
07, 2300-2318.
8
956 J. Org. Chem., Vol. 72, No. 23, 2007

irradiation power. (Bu
4
N)
4
[γ-SiW10
O
34(H
2
2
O)
2
] (1)3a and the hybrid
2 5
over P O at 70 °C for 4 h, and then recycled in three more
] (2)7 were prepared fol-
,38
consecutive runs with no loss of catalytic activity. Microwave
experiments were performed with continuous irradiation power at
10 W, under simultaneous cooling (Tbulk < 80 °C).
complex (Bu N) K[γ-SiW10
4
3
O
36(PhPO)
lowing literature procedures. They were characterized by FT-IR
and 1 W NMR and their identities were confirmed by comparison
83
with literature data. Solution characterization of 2 in CH
3
CN and
N ] was also performed by UV-vis, ESI-
31
General Procedure for Catalytic Epoxidation of Internal and
+
-
in [bmim ][(CF
3
SO
2
)
2
+
-
Terminal Alkenes by 2 with H
2 2 3 2 2
O in [bmim ][(CF SO ) N ] at
1
MS, H NMR, and P NMR.
5
0 °C. The catalyst (0.32 µmol) was dissolved under sonication in
1
: FT-IR (KBr, 1200 < ν < 600, cm-1) 998, 958, 920, 902,
2 2
the IL (200 µL). The alkene (0.2 mmol) and H O (40 µmol, 24 M
aqueous solution) were added and the mixture was stirred vigorously
1
8
77, 783, 745, 691. H NMR (300 MHz, DMSO-d
6
) δ 7.26 (2H,
s), 6.61 (2H, s), 3.19 (32H, m), 1.56 (32H, m), 1.32 (32H, m),
in a oil bath at 50 °C. At the end of the reaction the mixture was
diluted in CH Cl containing dodecane as internal standard and
2 2
monitored by quantitative GC analysis.
83
0
.91 (48H, m); 1 W NMR (16.67 MHz, DMSO/DMSO-d
6
) δ -94.7
(
2W), -98.1 (2W), -115.6 (2W), -118.1 (2W), -193.8 (2W).
+
-
2
: UV-vis ([bmim ][(CF SO ) N ]) λ 244 nm (log ꢀ244 ) 4.56);
3 2 2
General Procedure for Catalytic Epoxidation of Internal and
-
1
FT-IR (KBr, 1200 < ν < 600, cm ): 1196, 1137, 1049, 1008,
9
CN/H O) m/z 896.9, [HSiW10O36(PhPO) ] ; H NMR (300 MHz,
2 2
+
-
2 2 3 2 2
Terminal Alkenes by 2 with H O in [bmim ][(CF SO ) N ]
3
70, 943, 911, 884, 834, 796, 785, 752, 699; ESI-MS (-) (CH -
under MW Irradiation. The catalyst (3.2 µmol) was dissolved
3- 1
under sonication in the IL (200 µL). The alkene (2.0 mmol) and
CD
3
CN) δ 7.95-7.88 (m, 4H), 7.55-7.49 (m, 6H), 3.11 (m, 24H),
2 2
H O (40 µmol, 24 M aqueous solution) were added. The reaction
31
1
1
.61 (m, 24H), 1.37 (m, 24H), 0.97 (t, J ) 7.3 Hz, 36H); P{ H}
vessel was placed in the single-mode cavity of the instrument and
31 1
NMR (121.5 MHz, CD CN) δ 14.9; P{ H} NMR (121.5 MHz,
[
3
irradiated with power at 4 or 5 W, thus reaching a Tbulk ) 57-
+
-
183
bmim ][(CF
CD CN) δ -106.6 (2W), -114.4 (4W), -154.9 (4W, d, J ) 10.9
Hz).
2
Catalytic Epoxidation of cis-Cyclooctene by 2 with H O in
3 2 2 3
SO ) N ]) δ 15.7; W NMR (16.67 MHz, CH CN/
65 °C, under simultaneous cooling by a stream of compressed air
3
(
pressure ) 60 psi). At the end of the reaction, the mixture was
diluted in CH Cl containing dodecane as internal standard and
2
2
2
monitored by quantitative GC analysis.
ILs. The catalyst (4.8 µmol) was dissolved in the IL phase (200
µL) upon sonication. cis-Cyclooctene (3.0 mmol) was added and
the biphasic system was placed in a oil bath at 50 °C. H
O
2 2
(0.60
Acknowledgment. Financial support from CNR, MIUR
(FIRB CAMERE-RBNE03JCR5), and ESF COST D29, D40
actions is gratefully acknowledged.
mmol, 7-24 M aqueous solution) was added under vigorous
stirring. The reaction was sampled by quantitative GC analysis after
dilution in CH
the Ph P quencher. The catalytic phase was extracted with hexane
5 × 0.5 mL), washed with H O (0.5 mL), dried under vacuum
2 2
Cl containing dodecane, as internal standard, and
3
Supporting Information Available: Additional experimental
procedures and spectral and chromatographic data. This material
is available free of charge via the Internet at http://pubs.acs.org.
(
2
(
37) Farmer, V.; Welton, T. Green Chem. 2002, 4, 97-102.
(
38) Canny, J.; T e´ z e´ , A.; Thouvenot, R.; Herv e´ , G. Inorg. Chem. 1986,
2
5, 2114-2119.
JO7016923
J. Org. Chem, Vol. 72, No. 23, 2007 8957