Recyclable, green and efficient epoxidation of olefins in water with hydrogen peroxide catalyzed by polyoxometalate nanocapsule

Article abstract of DOI:10.1016/j.catcom.2016.02.007

A practical method for the selective epoxidation of alkenes was discovered using H_xPMo₁₂O₄₀ <> H₄Mo₇₂Fe₃₀(CH₃COO)₁₅O₂₅₄ as a catalyst in the presence of H₂O₂ as a green oxidant. However, the simple catalyst system involving polyoxometalates and H₂O₂ exercised the most successful system in obtaining high to excellent yields of epoxide products for different alkenes, including aromatic and aliphatic alkenes at room temperature in water. The effectiveness of this catalyst is evidenced by 99% selectivity to epoxide and 97-99% efficiency of H₂O₂ utilization. The stability of PMo > Mo₇₂Fe₃₀ under a catalytic reaction has been confirmed by XRD, FT-IR and Raman spectroscopies.

Full text of DOI:10.1016/j.catcom.2016.02.007

Recyclable, green and efficient epoxidation of olefins in water with hydrogen
peroxide catalyzed by polyoxometalate nanocapsule
Reza Fareghi-Alamdari, Shahrbanou Moradpour Hafshejani, Hamid Taghiyar,
Bahram Yadollahi, Mostafa Riahi Farsani
PII:
DOI:
Reference:
S1566-7367(16)30054-1
doi: 10.1016/j.catcom.2016.02.007
CATCOM 4588
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
24 September 2015
5 February 2016
6 February 2016
Please cite this article as: Reza Fareghi-Alamdari, Shahrbanou Moradpour Hafshejani,
Hamid Taghiyar, Bahram Yadollahi, Mostafa Riahi Farsani, Recyclable, green and effi-
cient epoxidation of olefins in water with hydrogen peroxide catalyzed by polyoxometalate
nanocapsule, Catalysis Communications (2016), doi: 10.1016/j.catcom.2016.02.007
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

ACCEPTED MANUSCRIPT
Recyclable, Green and Efficient Epoxidation of Olefins in Water with Hydrogen Peroxide
Catalyzed by Polyoxometalate Nanocapsule
Reza Fareghi-Alamdaria, Shahrbanou Moradpour Hafshejani b, c, Hamid Taghiyard, Bahram
Yadollahid, Mostafa Riahi Farsani*c
a College of Chemistry and Chemical Engineering, Malek-Ashtar University of Technology,
Tehran, Iran
b Chemical Nanoscience Laboratory, School of Chemistry, Bedson Building, Newcastle
University, Newcastle upon Tyne, NE1 7RU, UK
c Department of Chemistry, Faculty of Sciences, Shahrekord Branch, Shahrekord, Iran
d Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
∗ Corresponding author telephone: +98 9133831017
E-mails: Riahim91@gmail.com, Riahim91@yahoo.com
1

ACCEPTED MANUSCRIPT
Abstract
A practical method for the selective epoxidation of alkenes was discovered using
HxPMo12O40⊂H4Mo72Fe30(CH3COO)15O254 as a catalyst in the presence of H2O2 as a green
oxidant. However, the simple catalyst system involving polyoxometalates and H2O2 exercised
the most successful system in obtaining high to excellent yields of epoxide products for different
alkenes, including aromatic and aliphatic alkenes at room temperature in water. The
effectiveness of this catalyst is evidenced by 99% selectivity to epoxide and 97-99% efficiency
of H2O2 utilization. The stability of PMo⊂Mo72Fe30 under a catalytic reaction has been
confirmed by XRD, FT-IR and Raman spectroscopies.
Keywords: Keplerate Polyoxometalates, Catalysis, Epoxidation, Hydrogen Peroxide, Alkenes
2

ACCEPTED MANUSCRIPT
1. Introduction
In recent years, the epoxidation of alkenes has achieved a remarkable level of popularity from
both scientific and industrial researchers. Epoxides play an extremely important role as
intermediates and building blocks in organic synthesis [1]. Different epoxides have been widely
used in paints, epoxy resins, surfactants, and intermediates such as glycols, glycol ethers,
alkanolamines and polymers. For example, annually 4.5 million and 70,000 tons of propylene
and butene oxides are produced, respectively [2].
Divergent compounds such as organometallic and inorganic metal oxides have been employed as
catalysts for alkene epoxidations utilizing various oxidants, for instance, oxygen, ozone and
hydrogen peroxide or organic peroxides [3]. In particular, a hydrogen peroxide-based catalytic
epoxidation has received considerable attention because hydrogen peroxide is generally safe in
storage and operation. In addition, it is not only a cheap, mild and environmentally benign
reagent generating only harmless water as a by-product, but also it has high and effective oxygen
content [4].
These advantages have accelerated the progress of substantial procedures for the epoxidation of
olefins with aqueous hydrogen peroxide and various catalyst systems such as manganese and
cobalt complexes [5], porphyrin [6], salen systems [7], FeCl3·6H2O [8], titanosilicates [9]
methyltrioxorhenium [10], tungsten compounds [11] and manganese complexes [12].
In many of these systems, the efficiency of H2O2 usage and their selectivity to epoxides are low.
The types of usable olefins are confined, requiring efficiency or high reaction temperatures,
which sometimes reduce selectivity to epoxide. Moreover, a major problem in many catalytic
systems is to perform such a process in non-toxic solvents, particularly in aqueous media.
3

ACCEPTED MANUSCRIPT
Polyoxometalates (POMs) are a large family of anionic metal−oxygen clusters with structural
diversity, showing many applications in analytical chemistry, medicinal chemistry,
electrochemistry, photochemistry, and catalyst chemistry [13].
POMs have shown to be efficient Brønsted acid catalysts and highly selective oxidation catalysts
due to both their stability to oxidation and compatibility with diverse oxygen sources [14].
Müller et al. synthesized new giant molecular spheres with the general formula of
[(pentagon)12(linker)30] or [Mo(Mo)5]12(Linker)30] and because of their structural features, so-
called Keplerates, they could be generated in variable sizes by linking the fundamental
2-
pentagonal {(Mo)Mo5} building block with different linkers such as HCOO-, CH3COO-, SO4
,
FeIII(H2O)}3+, etc [15-17].
Furthermore, Müller synthesized a marvelous structure of polyoxometalates containing a core–
shell hybrid made of Keggin-type heteropolyoxomolybdates encapsulated into {Mo72Fe30}-type
Keplerates and HxPMo12O40⊂H4Mo72Fe30(CH3COO)15O254(abbreviation = PMo⊂Mo72Fe30)[18].
The unique structures and topologies of Keplerates have gained a remarkable consideration in
solid state chemistry [19, 20]. Izarova et al. discovered the catalytic efficiency of keplerate
polyoxometalates for the selective oxidation of sulfides [21]. However, the catalytic activity of
these compounds in the oxidation of organic compounds really lags behind [22].
The use of PMo⊂Mo72Fe30 as highly efficient catalysts in the selective oxidation of alkenes to
epoxide has not been previously reported. As a continuous improvement, the present work
reports a simple, recyclable and green method for the selective oxidation of a series of alkenes
using 30% aqueous hydrogen peroxide as an oxidant and PMo⊂Mo72Fe30 as a catalyst to the
corresponding epoxides in excellent selectivity and yield under mild reaction conditions.
4

ACCEPTED MANUSCRIPT
2. General methods and materials:
MoVI72FeIII30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91].150H2O {Mo72Fe30}
and PMo⊂ Mo72Fe30 were prepared according to the literature methods (see supporting
information) [18]. All common laboratory chemicals were of reagent grade quality acquired from
commercial resources and used without further purification. The techniques and methods applied
for the synthesis of Keplerate POMs, as well as the typical procedure used for the oxidation of
alkenes have been compiled into the supporting information.
3. Results and discussion
In this work, cyclooctene was selected as a model of the substrate for initial catalytic tests.
Epoxidation under mixture conditions using Mo72Fe30 did not form any cyclooctenoxide with an
appropriate yield. Similarly, the use of H3PMo12O40 represented the conversion of cyclooctene to
produce the corresponding epoxide in a low yield (Table 1, entry 2). Using PMo⊂ Mo72Fe30 as a
catalyst for the oxidation of cyclooctene gave rise to the conversion of cyclooctene into
cyclooctene oxide with a desirable yield only after 3 h.
a
Table1. Epoxidation of cyclooctene with Mo72Fe30, H3PMo12O40 and PMo⊂Mo72Fe30
Entry Catalyst
Time(h)
Yield b (%)
1
2
3
Mo72Fe30
5
5
3
6
H3PMo12O40
PMo⊂ Mo72Fe30
18
99
a Reaction conditions: catalyst (2.5µmol), substrate (5 mmol), 30% H2O2 (2 mmol), water (5 mL), 25 ºC. b
Yield (%) is calculated as products (mmol) per initial H2O2 (mmol)×100
5

ACCEPTED MANUSCRIPT
After this, the effect of different parameters such as oxidant and catalyst amounts, solvent type
and temperature in the catalytic performance of PMo⊂Mo72Fe30 in the epoxidation of
cyclooctene were studied. Initially, the epoxidation reaction was performed using
PMo⊂Mo72Fe30 as a catalyst and cyclooctene or cyclohexene as a standard substrate in various
solvents and different amounts of oxidant or catalyst at room temperatures (Figure1, 2 and table
1 in the supporting information).
Figure 1. Influence of the catalyst µmol ratio on the oxidation of cyclooctene
Reaction conditions: catalyst (0-10 µmol), substrate (5 mmol), 30% H2O2 (2 mmol), water (5 mL), 25 ºC ,
3h. Yields were determined by gas chromatography using an internal standard technique.
6

ACCEPTED MANUSCRIPT
Figure 2. Influence of the Cyclooctene/H2O2 ratio on the oxidation of cyclooctene
Reaction conditions: catalyst (2.5µmol), substrate (5 mmol), 30% H2O2 (0.2-10 mmol), water (5 mL), 25
ºC, 3h. Yields were determined by gas chromatography using an internal standard technique.
After the optimization of reaction conditions for the model reaction in hand, the selective
epoxidation of several alkenes was studied (Scheme 1).
Scheme 1. Green epoxidation of different alkenes in optimized reaction conditions
Under optimum experimental conditions, various alkenes were subjected to the oxidation method
using 5 mmol of alkenes, 2 mmol of H2O2 and 2.5 µmol of catalysts at 25 °C in water (Table 2).
It is generally assumed that the oxidation of terminal alkenes is difficult owing to the presence of
an electron-deficient double bond. Importantly, the relevant catalytic networks were equally
7

ACCEPTED MANUSCRIPT
effective in the epoxidation of terminal alkenes (Table 2). Various cyclic alkenes such as
cyclohexene, 1-methyl-cyclohexene, 1-phenyl cyclohexene and cyclooctene were epoxidized
with high yields (entries 1-4). The applied method resulted in a styrene (entry 5) of 90% yield
within 5 h. Bulky cyclic olefins (norbornene) were epoxidized with 97% yield (entry 6).
However, the poor reactivity of 1, 1, 2- trisubstituted and those of E-olefins (entries 3, 4) were
identified, demonstrating the steric hindrance around the active site of the catalyst.
The present method led to an excellent chemoselectivity. Different alkenes containing hydroxyl
groups were converted into the corresponding epoxy alcohols with high selectivity and only
obtained small amounts of aldehydes and ketone (entries 12, 13). Terminal alkenes such as
propylene, 1-butene, 1-hexene, and 1-octene could be transformed into the corresponding
epoxide with high conversion and selectivity. PMo⊂Mo72Fe30 oxidized propylene (94%), 1-
butene (91%), 1-hexene (89%), and 1-octene (87%) easily. The reaction mechanism of alkenes’
epoxidation over polyoxometalates using H2O2 as an oxidant has been extensively investigated
by several groups (see supporting information).
Table 2. The selective epoxidation of various substrates with aqueous H2O2 catalyzed by
a
PMo⊂Mo72Fe30
Entry
Substrate
Time(h)
Yield (%)b
H2O2 efficiency (%)c
3
3.5
5
99
98
87
99
99
99
1
2
3
8

ACCEPTED MANUSCRIPT
Ph
5
5
83
90
99
99
4
5d
6
7
97
94
98
6
7e
97
97
8e
9
7
7
7
91
89
87
97
99
10
4
92
11
OH
12f
13f
5
60
75
97
98
4.5
OH
a Reaction conditions: catalyst (2.5µmol), substrate (5 mmol), 30% H2O2 (2 mmol), water (5 mL), 25 ºC.
bYields were determined by gas chromatography using an internal standard technique (Yield (%) is
calculated as products (mmol) per initial H2O2 (mmol)×100).
cEox(H2O2 efficiency) = [products (mol)/consumed H2O2 (mol)] × 100.
The remained H2O2 after reaction completion was estimated by potential difference titration of Ce3+/Ce4+
[0.1 M aqueous Ce(NH4)4(SO4)4.2H2O].
d Benzaldehyde (select. 8%) was formed.
e Propylene (6 atm), 1-butene (3 atm) and 1,3-butadiene (2.5 atm).
f Cyclohexenone (select. 10%) and 3-methyl-2-buten-1-ol (select. 19%) were formed as a by-product.
To show the ability and efficiency of PMo⊂Mo72Fe30 in the epoxidation of alkenes compared to
other polyoxometalates, the results of the cyclooctene epoxidation in the presence of other
polyoxometalates were examined (Table 3). Rezaeifard reported the epoxidation of different
9

ACCEPTED MANUSCRIPT
alkenes catalyzed by (NH4)42[MoVI72MoV60O372(CH3COO)30(H2O)72] (abbreviation= Mo132) in
various reaction conditions [22]. Furthermore, the epoxidation reaction was performed using
ethanol as a solvent and as a result epoxide products with yields of 90-94% and excellent
chemoselectivities were generated (entry 1). In this work, it was reported that the epoxidation
procedure presented an excellent chemoselectivity. Kholdeeva described that PW12O40/MIL-101
as a true heterogeneous catalyst can be recycled several times without loss of activity and
selectivity with the retention of both POM and MIL-101 structures [23]. Moreover, it was
revealed that PW12O40/MIL-101 material indicates similar catalytic activity in H2O2-based alkene
epoxidation reaction compared to the activity of the corresponding homogeneous PW12, while
the catalytic activity of PW12O40/MIL-101 material is significantly higher than the activity of the
n-
known supported PW4 catalyst. Zhou applied Mo8O26 as a catalyst for the olefin epoxidation
using hydrogen peroxide (H2O2) as an oxidant in CH3CN(entry 4) [24]. These catalysts are not
only self-separating, but also brought about excellent catalytic reactivities, which are a great
advantage for the catalyst recycling. Leng et al. synthesized POM-based ionic hybrids which
proved to be highly efficient heterogeneous catalysts for the epoxidation of alkenes with H2O2
(entry 5) [25]. In addition, Mizuno and co-workers identified [γ-SiW10O34]4– presenting a high
catalytic performance for the epoxidation of different olefins with a hydrogen peroxide oxidant
(entry 6) [26]. In these catalytic systems, the epoxidation proceeded with ≥99% selectivity to
epoxide formation, high efficiency of H2O2 utilization (≥99%), high stereospecificity and the
straightforward recovery of the catalyst [26].
Sharma and Patel have carried out the epoxidation of styrene catalyzed by 12-
molybdophosphoric acid and hydrous zirconia under organic solvent-free conditions with H2O2
as an oxidant. Conversion and selectivity toward the epoxide were 85% and 70%, respectively
10

ACCEPTED MANUSCRIPT
(entry 7) [27]. Jalilian et al. reported the catalytic activity of three Keplerate polyoxometalates
and Mo72M30 (M = V, Cr, Fe) in the epoxidation of various alkenes [28]. It was demonstrated
that among the three Keplerate POM catalysts, in the epoxidation of different alkenes under the
same reaction conditions, Mo72Cr30 exercised a higher catalytic activity than the other two
(entries 8-10). In this work, Mo72Fe30 lacks a catalytic activity for the epoxidation reaction. As a
result, the catalyst “PMo⊂Mo72Fe30” gave rise to an excellent catalytic activity for the
epoxidation of alkenes compared to other polyoxometalates. In addition, the epoxidation of
different alkenes was conducted in mild reaction conditions with green oxidants and solvents
(entry 11). The future aim of this work is to explore the factors affecting the low catalytic
activity of Mo72Fe30 and the high catalytic performance of PMo⊂Mo72Fe30 in the oxidation
reaction.
Table 3. Catalytic activity of various catalysts for the epoxidation of cyclooctene with H2O2
Entry
Catalyst
Mo132
Conversion (%)
Ref
21
1
2
90-94
76
22
PW12O40/MIL-101
PW12
3
4
78
99
95
100
85
97
86
7
22
n-
Mo8O26
24
5
MimAM(H)-PW
25
4-
6
γ-SiW10O34
26
7
ZPM
Mo72Cr30
27
8
28
9
Mo72V30
28
28
10
11
Mo72Fe30
99
Present work
PMo⊂Mo72Fe30
11

ACCEPTED MANUSCRIPT
Due to the importance of the catalyst specific features such as stability and reusability in the
catalyst evaluation, these features of the PMo⊂Mo72Fe30 were also investigated. After the
completion of the catalytic epoxidation of cyclooctene with PMo⊂Mo72Fe30 as a catalyst, ethyl
acetate was added to the reaction mixture as a safe solvent for isolating hydrophobic organic
products. Then, an aqueous solution of the catalyst was reused directly for the next run of the
oxidation reactions without further purification. The easy recovery combined with the inherent
stability of the PMo⊂Mo72Fe30 permits the catalyst to be reused over 5 times in the epoxidation
of cyclooctene with a negligible decrease in the catalyst activity after 5 runs (see supporting
information). The IR and Raman spectra and XRD pattern of the recycled compound
“PMo⊂Mo72Fe30” illustrated a slight change after many recoveries, indicating a desirable
stability of the catalyst (see supporting information).
4. Conclusion
Polyoxometalate nanocapsule was employed as catalysts for the selective epoxidation of various
alkenes using hydrogen peroxide as the oxidant in water. The polyoxometalate nanocapsule
showed a high catalytic performance for the epoxidation of different olefins with a hydrogen
peroxide at room temperature in water. The catalyst can be reused for at least 5 runs without
significant loss of activity. These systems demonstrated a straightforward and safe procedure and
established that the high reusability of the catalysts is environmentally benign.
Acknowledgements
12

ACCEPTED MANUSCRIPT
The authors of this study acknowledge gratefully both the help of Prof. Achim Müller and Prof.
Hartmut Bögge from Bielefeld University and the support of the research council of Shahrekord
University.
13

ACCEPTED MANUSCRIPT
References
1. Cancino. P.; Paredes-García. V.; Aguirre.P.; Spodine. E. Catal. Sci. Technol. 4(2014)2599–
2607.
2. Xia. Q. H.; Ge. Q. H.; Ye. C.P.; Liu. Z. M.; Su. K. X. Chem. Rev. 105(2005)1603−1662.
3. Huber. S.; Cokoja. M.; Kühn. F. E. J. Organomet. Chem. 751(2014)25–32.
4. Lane. B. S.; Burgess. K. Chem. Rev. 103(2003) 2457–2473.
5. Leadbeater, N. E.; Marco, M. Chem. Rev. 102(2002) 3217−3274.
6. Sharma, V. B.; Jain, S. L.; Sain, B. Tetrahedron Lett. 44(2003) 383−386.
7. Koya, S.; Nishioka, Y.; Mizoguchi, H.; Uchida, T.; Katsuki, T. Angew. Chem., Int. Ed.
51(2012) 8243−8246.
8. Schroder. K.; Enthaler. S.; Join. B.; Junge. K.; Beller. M. Adv. Synth. Catal. 352(2010)1771–
1778.
9. Notari. B. Adv. Catal. 41(1996)253-334.
10. Romao. C. C.; Kuhn. F. E.; Herrmann. W. A. Chem. Rev. 97(1997) 3197-3246.
11. Venturello. C.; Alneri. E.; Ricci. M. J. Org. Chem. 48(1983) 3831-3833.
12. Devos. D. E.;Meinershagen. J. L.; Bein. T. Angew. Chem. Int. Ed. Engl. 35(1996)2211-2213.
13. Kikukawa. Y.; Yamaguchi. K.; Mizuno. N. Angew. Chem. Int. Ed. 49(2010) 6096–6100.
14. Barats, D.; Neumann, R. Adv. Synth. Catal. 352(2010) 293−298.
15. Müller. A.; Kögerler. P.; Kuhlmann. C. Chem. Commun. 1999, 1347-1358.
16. Müller. A.; Kögerler. P.; Bögge. H. Structure and Bonding, Berlin, 96(2000)203-236
17. Cronin. L, In Comprehensive Coordination Chemistry II, Vol. 7 (Eds.: J. A McCleverty, T. J.
Meyer), Elsevier, Amsterdam, 2004, pp. 1- 56.
14

ACCEPTED MANUSCRIPT
18. Müller. A.; Das. S. K.; Bögge. H.; Schmidtmann. M.; Kögerler. P.; Trautwein. A. X.;
Schünemann. V.; Krickemeyer. E.; Preetz. W. Angew. Chem. Int. Ed. 39(2000) 3413–3417.
19. Müller. A.; Todea. A.M.; Slageren. J. V.; Dressel. M.; Bogge. H.; Schmidtmann. M.; Luban.
M.; Engelhardt. L.; Rusu. M. Angew. Chem., Int. Ed. 44(2005) 3857-3861.
20. Zhang, L.; Xiong, T.; Zhou, Y.; Zhang, L. Chem. Asian J. 5(2010)1984−1987.
21. Izarova. N. V.; Kholdeeva. O. A.; Sokolov. M. N.; Fedin. V. P. Russ. Chem. B. Int. Ed.,
58(2009) 134-137
22. Rezaeifard. A.; Haddad. R.; Jafarpour. M.; Hakimi. M. ACS Sustain. Chem. Eng.
2(2014)942-950.
23. Maksimchuk. N.V.; Kovalenko. K. A.; Arzumanov. S. S.; Chesalov. Y. A.; Melgunov. M.
S.; Stepanov . A. G.; Fedin .V. P.; Kholdeeva. O. A. Inorg. Chem. 49(2010) 2920-2930.
24. Zhou. M.; Liu. M.; Huang. L.; Zhang. J.; Wang. J.; Li. X.; Kühn. F. E.; Zang. S. Green
Chem. 17(2015)1186-1193.
25. Leng. Y.; Wang. J.; Zhu. D.; Zhang. M.; Zhao. P.; Long. Z.; Huang. J. Green Chem.
13(2011)1636–1639.
26. Kamata. K.; Yonehara. K.; Sumida. Y.; Yamaguchi. K.; Hikichi. S.; Mizuno. N. Science.
300(2003) 964-966.
27. Sharma. P.; Patel. A. Appl. Surf. Sci. 255(2009)7635–7641.
28. Jalilian. F.; Yadollahi. B.; Farsani. M. R.; Tangestaninejad. S.; Rudbari. H. A.; Habibi. R.;
RSC Adv. 5(2015) 70424-70428.
15

ACCEPTED MANUSCRIPT
Graphical abstract
16

ACCEPTED MANUSCRIPT
Highlights
PMo⊂ Mo72Fe30 showed a high catalytic activity for the epoxidation of various alkenes with
H2O2.
For different alkenes, 99% selectivity to epoxide and 97-99% efficiency of H2O2 were observed.
PMo⊂ Mo72Fe30 exercised an excellent catalytic activity, stability and reusability.
17