Amphiphilic dipyridinium-phosphotungstate as an efficient and recyclable catalyst for triphasic fatty ester epoxidation and oxidative cleavage with hydrogen peroxide

Article abstract of DOI:10.1039/c7gc00298j

A novel amphiphilic dipyridinium peroxophosphotungstate ion pair was developed as a selective and recyclable catalyst for the triphasic epoxidation of fatty acids and esters with hydrogen peroxide. The synthesis of the catalyst was studied extensively by solid and liquid phase ³¹P nuclear magnetic resonance (NMR). The oxidation of vegetable oils is of prime importance for the production of lubricants, plasticizers, polymer stabilizers and other olefinic compounds. Based on the oxidizing activity of peroxophosphotungstates, we designed a lipophilic phase transfer agent that renders the active complex insoluble in the reaction media, without having to support it on a matrix. This affords a catalyst combining the activity of homogeneous catalysts and the recyclability of heterogeneous systems. We show that this catalyst is able to fully epoxidize methyl oleate with excellent selectivity, with a turnover frequency of 149 at 60 °C, and can be easily recycled, to reach a record turn over number of 1868. A larger scale experiment on 13 grams and a scope including linoleic and ricinoleic acids were also demonstrated. The catalyst also shows excellent activity and selectivity for the oxidative cleavage of methyl oleate and the oxidation of small olefins.

Full text of DOI:10.1039/c7gc00298j

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. de la Garza, K.
De Oliveira Vigier, G. Chatel and A. H. Moores, Green Chem., 2017, DOI: 10.1039/C7GC00298J.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 8
View Article Online
DOI: 10.1039/C7GC00298J
Journal Name
ARTICLE
Amphiphilic dipyridinium-phosphotungstate as efficient and
recyclable catalyst for triphasic fatty-ester epoxidation and
oxidative cleavage with hydrogen peroxide
Received 00th January 20xx,
Accepted 00th January 20xx
a
b
c
a
DOI: 10.1039/x0xx00000x
Luis Carlos de la Garza, Karine De Oliveira Vigier, Gregory Chatel, Audrey Moores *
www.rsc.org/
A novel amphiphilic dipyridinium peroxo-phoshotungstate ion pair was developed as a selective and recyclable catalyst for
the triphasic epoxidation of fatty acids and esters with hydrogen peroxide. The synthesis of the catalyst was studied
3
1
extensively by solid and liquid phase P nuclear magnetic resonance (NMR). The oxidation of vegetable oils is of prime
importance for the production of lubricants, plasticizers, polymer stabilizers and other olefinic compounds. Based on the
oxidizing activity of peroxophosphotungstates, we designed a lipophilic phase transfer agent that renders the active
complex insoluble in the reaction media, without having to support it on a matrix. This affords a catalyst combining the
activity of homogeneous catalysts and the recyclability of heterogeneous systems. We show that this catalyst is able to
fully epoxidize methyl oleate with excellent selectivity, with a turnover frequency of 149 at 60 °C, and can be easily
recycled, to reach a record turn over number of 1868. A larger scale experiment on 13 grams and a scope including linoleic
and ricinoleic acids were also demonstrated. The catalyst also shows excellent activity and selectivity for the oxidative
cleavage of methyl oleate and the oxidation of small olefins.
While these reagents are cheap, they are used homogeneously
and are corrosive and toxic, requiring special equipment and
safety measures. The oxidation with peroxyacids is also highly
Introduction
Biomass valorization constitutes a key instrument in the effort
to mitigate global warming and its multiple environmental and
economical consequences. Research in this area opens
opportunities to address challenges such as the exploitation of
non-edible resources and agricultural waste and transitioning
-1 4
exothermic (ΔH = 230 kJ.mol ), which makes temperature
control difficult at industrial scales and imposes a slow
addition of hydrogen peroxide and catalyst with long cooling
4
times to avoid a runaway reaction. The addition of a strong
1
mineral acid as co-catalyst also limits selectivity, since lowering
out of fossil resources. Among biomass sources, vegetable oils
the pH promoted the epoxide’s ring-opening reaction via
5
hydrolysis.
are the most important renewable raw material used in the
2
chemical industry. Vegetable oils consist of triglycerides with
In
search
for
more
sustainable
approaches,
long lipophilic carbon chains, most of which feature one or
several double bonds, depending on the oil source. These
unsaturations can be oxidized to fabricate added-value
products, such as epoxides, diols or carboxylic acids. Oxidized
oil products are precursors for a variety of functional
compounds such as lubricants, plasticizers, polymer stabilizers
peroxophosphotungstate catalysts were initially found to be
active for the epoxidation of double bonds with hydrogen
6
, 7
peroxide by Venturello et al.
and triggered important
research effort thereafter. To overcome the immiscibility of
the oxidant (aqueous hydrogen peroxide) with the substrate (a
3
fatty
acid,
ester
or
triglceride),
[W(O)(O
the
active
and other olefinic compounds.
3
-
peroxophosphotungstate species (PO
4
2
)
2
]
4
)
trianion
The most common industrial procedure to epoxidize oils is
to use peroxyacids produced in situ from formic acid or acetic
acid in the presence of hydrogen peroxide and sulfuric acid.
can be coupled with cationic phase transfer agents. This
system prevents overheating hazards and efficiently affords
epoxidized double bonds with higher selectivity and lower
toxicity than peroxyacids. The oxidation method using
peroxophosphotungstate species was further developed by
Ishii et al. where they showed it can also be used to fully
cleave double bonds into carboxylic acids and that
phosphotungstic acid can be used as a convenient precursor to
8
the active species. However, this system is currently not
economically viable compared to peroxyacids, because the
catalyst is homogeneously dispersed and thus unrecoverable.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 8
View Article Online
DOI: 10.1039/C7GC00298J
ARTICLE
Journal Name
Research has thus shifted towards creating recyclable catalysts finally for the fully oxidative cleavage of methyl oleate.
that can be both cost-effective and efficient.
Recyclability of the system was also successfully tested.
Results and Discussion
Optimization of the Catalyst Synthesis
Our aim in this study was to design a cationic transfer agent
3
-
able to form a complex with the active PPW , while being
insoluble in both the aqueous and the oil phase to achieve
recovery. It should nonetheless retain enough hydrophilic
interactions to regenerate the active peroxophosphotungstate
species with hydrogen peroxide, enough lipophilic affinity to
react with the substrate and cause limited leaching of the
catalyst by ionic dissociation. Commercial ammonium and
pyridinium surfactants are water soluble, and the catalytic
complexes obtained using those phase transfer agents are thus
homogeneous in the reaction mixture and not recyclable.
Conversely, excessively lipophilic polymers have been found to
fully deactivate the catalyst by preventing catalyst
2
+
3-
Scheme 1: Synthetic procedure to access [DP
3 2
] [PPW ] catalyst.
In past reports, the phase transfer agent was engineered
9
so that the catalyst can be extracted, or precipitated, either
1
0
by cooling the medium, or designing the catalyst to
become insoluble once the hydrogen peroxide has been
1
1, 12
consumed.
Cationic supports have been shown to make
the catalytic complex heterogeneous, such as polymers
3
1
14
derived from ionic liquids, functionalized silica, or even
magnetic iron oxide nanoparticles coated with either
1
cationic polymers or functionalized silica.
5
16, 17
Another
13
regeneration in the aqueous phase. Indeed such supports
common method is to immobilize the neutral complex of
peroxophosphotungstate and phase transfer agent into a
1
solid matrix, such as mesoporous silica, amphiphilic
typically rearrange to expose only their hydrophobic alkyl
chains. We decided to use dicationic or tricationic surfactants,
to optimize ion pairing with the catalyst. We initially explored
the triammonium based on pentamethyldiethylenetriamine to
match the charge of the phosphotungstate, but the resulting
complex was very unstable and degraded quickly. After testing
several diamines and dipyridines, we settled on using 4,4’-
trimethylenedipyridine. Notably, it was found during its
synthesis to be stable at least up to 120 °C and insoluble in
water below 80 °C. A similar type of pyridinium was already
proven to be very stable for supporting phosphotungstates by
8
1
9
copolymers
grafted
onto
silica,
metal-organic
2
frameworks, or metallic supports.
0
21
However, all the heterogeneous catalysts show reaction
rates at least an order of magnitude lower than the best
homogeneous counterparts (see Table S1). While direct
comparisons are often not possible to make due to widely
different conditions such as substrate scope, catalyst loading,
temperature and solvent, it is still clear that heterogeneous
systems are significantly less active. In order to be
economically viable as a replacement of peroxyacids, both
activity and recyclability need to be optimized.
22
Yamada et al. Sufficient lipophilicity was introduced by C14
carbon chains functionalization. Wu et al. showed that by
increasing the length of the carbon chain on an
alkylimidazolium, the activity towards the epoxidation of
cyclohexene of the phosphotungstate-paired catalyst
Herein we report a novel catalytic system, using a
+
dipyridinium dication (DP ) as phase transfer agent paired
2
3
-
with peroxophosphotungstate trianion (PPW ), active for the
oxidation of vegetable oils with hydrogen peroxide that
bridges the gap between the homogeneous and
11
increased. The synthesis of the dicationic phase transfer
agent required only one step from commercially available
3-
substrates, followed by an ion exchange with PPW , produced
2
+
3-
heterogeneous systems. Our catalyst ([DP
3 2
] [PPW ] ) allows
in situ by mixing phosphotungstic acid with excess hydrogen
the reaction to function in a triphasic system –composed of an
organic phase (the substrate), an aqueous phase (the oxidant)
and a solid phase (the catalysts) – and shows reaction rates
similar to reported homogeneous catalysts, while being easy
to recycle through simple filtration and easy to synthesize from
commercial reagents. The synthetic conditions for this well-
defined complex were studied and characterization was
peroxide (scheme 1).
[
DP2+][Br-]2
[DP2+]3[PW12O403-]2
[DP2+] [PW O243-]2
H3PW12O40
Inactive (white)
Active (white)
- HBr
8
H O
2
2
[DP2+][Br ]2
-
+
3-
3
H + PW O
4 24
3
4
-
HBr
+
8 H2WO4
6 H O
3
1
performed by P magic angle spinning nuclear magnetic
1
2
2
3
1
resonance ( P MAS NMR) as well as scanning electron
microscopy (SEM). Leaching during catalytic experiments was
very limited as established by inductively coupled plasma mass
spectrometry (ICP-MS) and a hot filtration test proved
[
DP2+][Br-]2
HBr
DP2+= C14H29 NC H C H C H N C14H29
+
2-
[DP2+][WO62-]
Inactive (orange)
1
6H + 8WO
6
+ 16 H2O
-
5
4
3
6
5 4
heterogeneous mechanism. Excellent results in terms of Scheme 2: Sequential oxidation of phosphotungstic acid by hydrogen peroxide and
2
+
potential pairing with the amphiphilic dipyridinium (DP ). Stoichiometry is not
activity and selectivity were obtained for the epoxidation of
methyl oleate, linoleic and ricinoleic acids, the oxidation of
small alkenes to either the corresponding epoxide or diol and
provided on the right end side of the scheme for clarity.
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 8
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC00298J
Journal Name
ARTICLE
1
1, 23
The oxidation of phosphotungstic acid into its activated directly performing the ion exchange with H
3
PW12
O
40
,
or
peroxide prior to the ion exchange with 4,4’- even mixing the surfactant and the phosphotungstate with the
2
trimethylenedipyridinium bromide was found to be crucial to substrates in situ, this scheme did not work in our hands
4
2
obtaining an active catalyst. Although several reports in the using [DP ] as the phase transfer agent.
+
literature showed that active catalysts can be obtained by
Table 1: Optimisation of catalyst synthetic conditions
a
Catalyst synthetic conditions
Methyl Oleate epoxidation conditions and results
+2
Entry
H
2
O
2
/
DP
/
Solvent
Catalyst Loading
Time
(h)
4
Conversion
Epoxide
Selectivity
58%
TON
TOF
-
1
H
3
PW12
O
40
H
3
PW12
3:2
3:2
3:2
3:2
3:2
5:1
1:2
1:2
1:2
O
40
(mol%)
1.1
(h )
22
b
1
2
3
4
30:1
30:1
H
2
O
99%
97%
98%
95%
71%
24%
88%
89%
98%
89
88
CHCl
3
1.1
4
58%
22
30:1
MeOH
MeOH
MeOH
MeOH
MeOH
1.1
4
84%
88
22
200:1
200:1
200:1
200:1
200:1
200:1
1.1
4
99%
85
22
c
5
1.1
2
73%
64
32
6
7
8
9
1.1
2
96%
22
11
0.22
0.22
0.22
4
99%
400
404
447
100
101
149
H
2
O*
4
95%
MeCN
3
96%
a
b
c
Conditions for the epoxidation of methyl oleate: 500 mg of methyl oleate (1 eq.), 222 μL of H
O needed to be heated above 80 °C to dissolve the dipyridinium bromide.
0 mg of H WO were added to the epoxidation of methyl oleate
2 2
O 30% (1.32 eq.). Heated to 60 °C. No solvent.
H
2
5
2
4
Both the synthesis of the active phosphotungstate catalytic between 0 and 1, indicative of the presence of the strong acid
2
5
species and the ion-pairing with phase transfer constitute a
complex sequence of chemical equilibria and reactions of epoxides, which is bound to adversely affect selectivity.
Scheme 2). It is generally accepted that the active species in Co-precipitation of tungstic acid could be prevented
) , as described by entirely by adding a large excess of hydrogen peroxide (200:1)
2 6
H WO . It is known that mineral acids catalyze the hydrolysis
(
3
-
3-
4 2 2 4
the reaction is PPW , i.e. (PO [W(O)(O ) ]
6
Venturello et al. This species is obtained by the complete to the phosphotungstic acid prior to the addition of the phase
oxidation of phosphotungstic acid with hydrogen peroxide. It transfer agent (Table 1, entries 4 to 9). This causes full
2
-
precipitates out of the aqueous phase when paired with a oxidation of the by-product into WO
6
during catalyst
is an anion, it can also partially bind
4
), as a by-product which can be to the phase transfer agent and co precipitate with the desired
2
-
lipophilic transfer agent. However, this oxidation reaction also synthesis. Yet, since WO
affords tungstic acid (H WO
6
2
difficult to separate from the final product because they co- catalyst. While this does not form adverse acid species,
precipitate together under these conditions. Interestingly, it is affecting catalyst selectivity, it does reduce its activity. Control
also known that H
yield H WO , a strong acid which fully dissociates in water, and
can pair with the cationic phase transfer agent.
In order to optimize production of the active catalyst, Separation of [DP ][WO
2 4 2 2
WO can be further oxidized by H O to experiments showed that directly using tungstic acid to form
2
+
2-
2
6
6
[DP ][WO ] yields an orange product that is inactive towards
the epoxidation of methyl oleate (see supporting information).
2
+
2- 2+
] from [DP ]
3-
6
3 2
[PPW ] was resolved
2
+
3-
[DP ]
3 2
[PPW ] , we explored several parameters: the ratio of by careful solvent selection as explained below. In further
hydrogen peroxide to phosphotungstic acid, the ratio of tests, a ratio of 200 for H
2
O
2
/ H
3
PW12O40 was selected. Next
+2
dipyridinium to phosphotungstic acid, and the solvent used for the impact of DP / H
3
PW12
O
40 ratio on catalytic performance
synthesis. The catalysts obtained were evaluated for their was studied, using catalyst color as an indication of purity (see
activity in the epoxidation of methyl oleate using H
oxidant at 60 °C with no solvent (table 1).
2
O
2
as supporting information).
The ratio of 3 to 2 was first tested as the “natural” choice
2
+
3-
2 2 3 2
Catalysts prepared with 30 eq. of H O (Table 1, entries 1 to afford [DP ] [PPW ] as catalyst. When tested for
to 3) were tested for the epoxidation of methyl oleate and epoxidation of methyl oleate, this catalyst afforded excellent
afforded good conversions. However, poor epoxide selectivity conversion and selectivity of 95% and 99% respectively (Table
was observed when using catalysts that were prepared in 1, entry 4). Addition of H
water or chloroform. We reasoned that the expected release conditions confirmed its adverse effect on both fronts (Table 1,
of H WO under these conditions and its co-precipitation with entry 5). When excess of the transfer agent was added (Table
the catalyst affected negatively the catalytic performances. 1, entry 6), the conversion dropped to 24%, likely because the
Indeed, under catalytic epoxidation conditions where H is transfer agent could precipitate a large amount of the inactive
in large excess compared to the catalyst (60 °C, 1.1mol% WO
catalyst loading, 1.32 eq. of H ), H WO readily oxidizes into Interestingly, when using an excess of phosphotungstic acid
WO . This hypothesis was consistent with a measured pH starting material (DP / H
2 4
WO to the catalyst under these
2
4
2 2
O
2
-
6
by-product, thus contaminating the catalyst.
2
O
2
2
4
+
2
H
2
6
3
PW12
O40 ratio = 1:2, Table 1, entry
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 8
View Article Online
DOI: 10.1039/C7GC00298J
ARTICLE
Journal Name
3
), the catalytic activity was greatly enhanced and the catalyst compounds in the 0-5 ppm region by P MAS NMR (see Fig
1
7
loading could be reduced 5 fold, down from 1.1 mol% to 0.22 S2). These results are in agreement with reports by
mol%. Under these conditions, excellent conversions and Kozhevnikov et al. that showed activity towards the
selectivity were obtained. Finally, methanol, water and epoxidation of oleic acid with a mixture of phosphotungstate
3
1
acetonitrile solvents were screened and acetonitrile was found intermediates, as ascribed by P NMR, suggesting that the
2
5
to be the best system with 98% conversion and 96% selectivity Venturello anion may not be the only active species.
after 3 hours at 60 °C (Table 1, entries 7-9). Under the latter The morphology of the catalyst was studied by SEM. The
conditions, TON and TOF could be greatly enhanced to 447 and catalyst arranges itself in the shape of rectangular prisms with
-1
1
49 h respectively. Our experiments suggest that acetonitrile varying length between 2 and 50 μm, as well as width and
2-
2
helps wash away the inactive, orange [DP ][WO
+
6
] by height roughly between 0.5 and 5 μm. Some amorphous
solubilizing this species. The effect of the solvent was studied regions could also be observed, which is consistent with the
31
3
1
with both liquid P NMR (Fig. S1) prior to the ion exchange,
1
P MAS NMR study, revealing the fact the catalysts are
3
and solid P MAS NMR (Fig. S2) on the precipitated catalyst. present as a mixture of closely related compounds (see Fig.
The analysis showed that acetonitrile was the best solvent to S3).
promote the formation of highly peroxidized species, which is
consistent with the higher activity observed.
Catalytic results
With an optimized catalyst synthesis in hand, we turned to
Characterization of the catalyst
catalytic reaction optimization. Epoxidation of methyl oleate
was tested under neat conditions and with solvents (Table 2).
In all cases but with methanol, the reaction took place in a
triphasic mixture of solid catalyst and two immiscible liquid
phases: the aqueous phase containing hydrogen peroxide, and
the organic phase containing methyl oleate. By design, the
[DP2+]3[PPW3-]2 catalyst possesses amphiphilic properties,
with lipophilic long chains on the cation, combined to the
hydrophilic properties of the peroxophosphotungstate moiety.
Under neat conditions, good conversion (84%) with perfect
selectivity was obtained at room temperature with 1 mol% of
catalyst loading, while a fivefold loading reduction gave an
excellent result of 98% conversion with 96% selectivity at 60°C
(entries 1 and 2). Overall, we observed that selectivity was
perfect until 90% conversion, at which point, traces of the
corresponding diols, hydroxyketones, aldehydes and carboxylic
acids could be observed and selectivity dropped. Selectivity
continued to drop if the reaction was left running past full
conversion, as epoxides can slowly hydrolyse under these
conditions.
3
1
2+
3-
40
2+
3-
Fig. 1: P MAS NMR spectra of a) [DP
]
3
[PW12O
2 3 2
] , b) [DP ] [PPW ] using
conditions from Table 1 entry 9.
Since the catalyst was designed to be heterogeneous, it
could not be dissolved in any common solvents for traditional
3
1
analysis and characterization was performed by P MAS NMR. Table 2: Epoxidation of methyl oleate
As
a standard for comparison, the inactive species
2
DP ] [PW O ]2 was synthesized by simple ion exchange. It
+
3-
DP2+] [PPW ]
3-
[
O
[
3
2
3
12 40
O
O
O
O
1
.32 Eq. H O2
presented a chemical shift of -16.6 ppm, which is very similar
to the chemical shift of phosphotungstic acid in water, -15.2
3
ppm (Fig. 1a). The P MAS NMR spectrum of [DP ] [PPW ]2
2
7
7
Solvent
7
7
1
2+
3-
3
synthesized under the conditions of Table 1, entry 9, reveals
two peaks at 3.5 ppm and 1.5 ppm (Fig. 1b). The chemical shift
3
of PW O species has been reported in the region between 0
-
4
24
and 1 ppm and is known to change when using different
2
cationic surfactants. Also, Duncan et al. had shown that by
6
varying amounts of H O , peaks in the region -15 to 5 ppm
2
2
3
could be observed by P NMR, attributed to fully or partially
1
3
24 , but no formal
-
peroxidized species en route to PW
4
O
2
characterization was reported. This led us to believe that the
6
3
-
4
peaks observed for our catalyst belong to either PW O24 or
highly peroxidized intermediates. However, despite exploring
several reaction conditions and solvents, precipitated
2
+
3-
[
3 2
DP ] [PPW ] always presented itself as a mixture of several
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 8
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC00298J
Journal Name
ARTICLE
Entry
Catalyst
Loading
Solvent
(1 mL)
Time Temp
Conversion
Selectivity
(h)
(°C)
2
+
3-
(mol%)
Scheme 3: Oxidation of alkenes with 0.22 mol% of [DP ] [PPW ] as catalyst at 60 °C
3
2
1
2
3
4
5
6
7
1
neat
neat
4
3
3
3
3
3
3
2
3
21
60
60
60
60
60
60
60
60
84%
98%
70%
64%
96%
91%
87%
93%
2%
100%
96%
2 2
with no solvent. Conditions used for ricinoleic acid: 1h, 1.32 eq. H O . Linoleic acid: 2h,
2
2 2 2 2
.2 eq. H O . Cyclohexene, cyclooctene and styrene: 3h, 1.32 eq. H O .
0.22
0.22
0.22
0.22
0.22
0.22
0.22
0.22
Heptane
EtOAc
MeOH
MeCN
100%
100%
68%
Cyclohexene, cyclooctene and styrene were also tested to
verify if the catalyst, designed for large lipophilic substrates,
would also epoxidize small alkenes effectively. Cyclooctene, in
particular, is a commonly used substrate for epoxidation in the
98%
CHCl
3
100%
98%
a
11, 13-16, 19-21, 23, 24, 27
8
neat
neat
literature of phosphotungstate catalysts.
b
9
100%
The conversion and selectivity for the epoxidation of
cyclooctene were in fact better than those obtained for methyl
oleate, as shown in Scheme 3. 1,2-epoxycyclooctene was
Conditions for the epoxidation of methyl oleate: 500 mg of methyl oleate (1 eq.),
22 μL of H 30% (1.32 eq.). Time and catalyst loading varied depending on
2
2 2
O
activity observed.
obtained with full selectivity and 99% conversion in 3 h at 60
-1
C with 0.22 mol% of catalyst, which gives a TOF of 150 h . To
a
Scaled up to 13.2 g of methyl oleate (1 eq.), 5.9 mL of of H
2
O
2
30% (1.32 eq.)
°
and 200 mg of catalyst (0.0022 eq.)
the best of our knowledge, this is the highest reported TOF for
heterogeneous tungsten catalysts. Cyclohexene afforded full
selectivity towards the diol instead of the epoxide, since 1,2-
epoxycyclohexene quickly hydrolysed in the presence of
b
2+
3-
3 40 2
Control test using [DP ] [PW12O ] as catalyst.
Using a solvent affected both conversion and selectivity.
Lipophilic solvents (heptane, EtOAc and CHCl , entries 3-5)
3
gave lower conversions likely because greater dilution in the
oil limited the catalysis rate. Acetonitrile mixed with the
aqueous phase (entry 6) and gave results more similar to neat
conditions with 91% conversion and 98% selectivity. Among
the solvents tested, methanol was the only one able to
dissolve both the aqueous and the organic phases into a single
phase, thus allowing good mass transfer to reach 96%
conversion. However, this solvent also facilitated the
hydrolysis of the epoxide to form the diol, which reduces
2+
3-
[DP ] [PPW ]2, even at room temperature. Styrene was found
3
to be too reactive for this catalyst, leading to a complex
mixture of aldehydes, carboxylic acids and styrene glycol.
A hot filtration test was carried out with methyl oleate as
substrate to confirm the heterogeneous nature of the catalyst.
In a standard epoxidation method, the solution was filtered
after 30 minutes of reaction at 60 °C, which showed 40.6%
yield by GC-MS. The filtrate was stirred at 60 °C for 12 hours
with an additional 1.32 Eq. of H O and a virtually unchanged
2
2
2
+
3-
selectivity to 68% (entry 7). The catalyst [DP ] [PPW ]2 was
3
yield of 42.4% was then measured. These results confirm that
also tested on a larger scale, showing excellent conversion of
2+
DP ] [PPW ]2 operates as a heterogeneous catalyst.
3-
[
3
9
3% and full selectivity upon epoxidizing 13 grams of methyl
Recycling tests were performed by diluting the mixture at
oleate (entry 8). A control experiment using the precursor
the end of the reaction with ethyl acetate, centrifuging and
removing both aqueous and organic supernatants with a
pipette. The addition of organic solvent was necessary to
remove the product due to the high viscosity of the epoxidized
methyl oleate at room temperature. The solid catalyst
remained in the flask and was dried with air for 1 minute
before reuse. When using 1mol% catalyst loading, the catalyst
performed very well over 5 cycles, with conversions ranging
from 98.6 to 100 % and selectivity remaining stable (Fig. 2),
thus affording a recyclable system. When employing the
optimized loading of 0.22mol%, a decrease in catalytic activity
was observed after three cycles (See supporting information,
table S2). Pushing to 5 cycles under these conditions allowed
achieving a record cumulated turnover number (TON) of 1868.
The highest number of turnovers to date for Venturello-type
2
DP ] [PW O ]2 showed almost no activity (entry 9),
+
3-
[
3 12 40
revealing the importance to pre-peroxidize the catalyst prior to
cation exchange (scheme 2).
In an effort to expand the scope of the reaction, the
epoxidation of two fatty acids, linoleic acid and ricinoleic acid,
2
was tested with [DP ] [PPW ]2 and proceeded with good
+
3-
3
conversions and selectivities (Scheme 3).
2
8
catalyst was reported by Khlebnikova et al. , with a value of
9
40 turnovers for a homogeneous catalysis loaded at
.01mol%. The highest number of recycling cycles to date was
0
1
0
reported by Chen et al. where 17 cycles at 3% catalyst
loading amounted to 560 turnovers.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 8
View Article Online
DOI: 10.1039/C7GC00298J
ARTICLE
Journal Name
We have produced an active heterogeneous catalyst for
the oxidation of olefins and vegetable oils, which is selective,
recyclable and easy to synthesize. This phosphotungsten
catalyst was rendered insoluble by tuning the lipophilicity and
charge of the counter-cation, instead of supporting it to a solid
structure. We optimized the synthetic conditions to access the
3
1
catalyst and used liquid and solid state P MAS NMR to
support our findings. The resulting catalyst has shown
excellent activity and selectivity for the epoxidation of methyl
oleate, linoleic acid, ricinoleic acid and cyclooctene. It afforded
cleanly diols with other small alkenes. At last, changing the
conditions gave access to excellent yields for the full oxidative
cleavage of methyl oleate. It was also recyclable by simple
centrifugation, at least 5 times. Very limited leaching was
measured, while a large-scale experiment of 13 mg was
successfully performed. In short, we have discovered a new
counter anion providing excellent activity, selectivity,
recyclability and versatility in alkene and unsaturated oil
oxidation.
Fig. 2: Conversion (blue, left bars) and selectivity (red, right bars) towards methyl 9,10-
epoxystereate obtained as a function of cycle number for the epoxidation of methyl
2+
3-
oleate with recycled [DP
3 2
] [PPW ] catalyst. Catalytic conditions: 1h, 60 °C, 1mol%
catalyst loading.
In order to study the stability of the catalyst, a leaching
study was conducted. After filtering the solid catalyst, the
aqueous filtrate from the 13 gram scale experiment was
analysed by ICP-MS (using conditions of Table 2, entry 8). A
limited leaching of 2.8% was measured. The product was
recovered without contamination from the organic phase.
2
6
Previous reports by Duncan et al. on quaternary Experimental section
ammonium paired peroxophosphotungstates investigated
degradation of the Venturello catalyst. In their case, it was
All chemicals used were analytical grade except otherwise
reported that the catalyst degraded after approximately 500
3-
noted. Chemicals were all bought from Sigma Aldrich and used
as received. Phosphotungstic acid hydrate water content was
1
determined by thermogravimetric analysis (TGA). H-NMR
2
+
turnovers. Here [DP
3 2
] [PPW ] starts to deactivate noticeably
after 1300 turnovers (see Table S2). Additional experiments
2
+
3-
were performed by preheating [DP
3 2
] [PPW ] for 24 hours
spectra were measured with a 500 MHz Bruker AVIIIHD
with methyl oleate at 60 °C before adding hydrogen peroxide,
in order to exclude thermal degradation. The epoxide yield and
selectivity were unchanged compared to the fresh batch of
catalyst.
2 3
spectrometer at ambient temperature in D O, MeOD or CDCl
31
using TMS as internal reference. P MAS NMR spectra were
measured in a 400 MHz Varian VNMRS in 4 mm zirconia rotors
4 2 4
spinning at 13 kHz at 25 °C using (NH ) HPO as reference.
Homogeneous Venturello-type catalysts have also been
reported to cleave double bonds of fatty acids/esters and
small organic molecules in order to form the corresponding
Tungsten leaching was measured using a Thermo Scientific
iCAP Q ICP-MS. Water content of phosphotungstic acid hydrate
2
was determined with a TGA Q500 instrument under N at a
8, 28, 29
carboxylic acids,
but no heterogeneous systems had
rate of 10 °C/min. GC-MS spectra were measured using an
Agilent 7890A gas chromatography connected to an Agilent
proven successful for this reaction on the fatty molecules. The
cleavage requires higher temperatures to promote the
hydrolysis of the epoxide and a longer reaction time (Scheme
5
975C MS instrument with triple-axis detector. The column
used is an HP-5MS UI (length: 30m, diameter 0.25 mm, film of
.25μm). SEM analysis was performed with a FEI Inspect F-50
2
+
3-
4
). Since [DP ] [PPW ]2 showed comparable activity for the
3
0
epoxidation of methyl oleate to homogeneous systems, we
tested the oxidative cleavage as well. Catalyst loading had to
be increased to 0.5 mol% to support the four oxidation steps
FE-SEM.
Synthesis of 4,4’-(trimethylene)bis(1-tetradecylpyridinium)
2
9
involved in the cleavage. The catalyst successfully cleaved
methyl oleate into its two corresponding carboxylic acids with
a yield of 89% at 90°C for 24 hours. The reaction afforded no
side product, and no sign of transesterification or
saponification was observed.
dibromide C41
H
72
N
2
Br
,4’-Trimethylenedipyridinium (3.9652 g, 20 mmol, 1 eq.) and
-bromotetradecane (16.6368 g, 60 mmol, 3 eq.) were
2
4
1
dissolved in 1-butanol (40 mL) and stirred at 120 °C for 48 h.
The product was precipitated by diluting in ethyl acetate, then
filtered and washed with pentane. The solid was then
recrystallized in water, filtered and washed with acetone.
1
1.5482 g of a white solid was recovered (77% yield). H NMR
1
(
500 MHz, CDCl
3
) δ (ppm) = 0.89 (t, 6H, CH
3
), 1.25 (m, 44H,
),
2+
3-
Scheme 4: Cleavage of methyl oleate with [DP
3 2
] [PPW ] as catalyst.
CH
2
), 2.00 (m, 4H, CH ), 2.33 (q, 2H, CH ), 3.12 (t, 4H, Pyr-CH
2
2
2
+
+
), 8.18 (d, 4H, CH), 9.02 (d, 4H, N -CH). m/z =
4
.76 (4H, N -CH
96.28560
2
2
Conclusion
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC00298J
Journal Name
ARTICLE
(CREATE) in Green Chemistry and McGill University for their
72 2 3 4 24 2
Synthesis of catalyst (C41H N ) (PW O )
financial support. We are grateful to Robin Stein for her
3
1
invaluable help performing P MAS NMR and Oleotek for
hosting and introducing LB to oleochemistry at their facility in
Thetford-Mines.
Phosphotungstic acid hydrate (H
3
PW
.80 mmol, 2 eq.) is dissolved in 15.9 mL H
00 eq.) and stirred at room temperature for 10 minutes, then
4
O
24●16H
2
O) (2.496 g,
0
2
2 2
O 30% (159 mmol,
the solution is diluted with 15 mL of acetonitrile. A solution of
,4’-(trimethylene)bis(1-tetradecylpyridinium) dibromide (300
4
References
mg, 0.40 mmol, 1 eq.) in 50 mL of acetonitrile is slowly added
drop by drop to the first solution, during which the product
precipitates in solution. The mixture is stirred for 2 h at room
temperature. The solid is filtered and washed with 20 mL of
water and then 20 mL of acetonitrile. 465 mg recovered (86%
1
2
3
4
.
.
.
.
C. O. Tuck, E. Perez, I. T. Horvath, R. A. Sheldon and M.
Poliakoff, Science, 2012, 337, 695-699.
M. A. R. Meier, J. O. Metzger and U. S. Schubert, Chem.
Soc. Rev., 2007, 36, 1788-1802.
S. Tayde, M. Patnaik, S. L. Bhagt and V. C. Renge, Int. J.
Adv. Res. Technol., 2011, 2, 491-501.
E. Santacesaria, R. Tesser, M. Di Serio, R. Turco, V. Russo
and D. Verde, Chem. Eng. J., 2011, 173, 198-209.
A. Campanella and M. A. Baltanas, Lat. Am. Appl. Res.,
3
1
4 2 4
yield). P MAS NMR (400 MHz, 13 kHz spinning, (NH )H PO as
chemical shift reference at 0 ppm) δ (ppm) = 3.47 (s), 1.51 (s).
Catalytic epoxidation of methyl oleate
5.
2
005, 35, 211-216.
Methyl oleate (500 mg, 1.69 mmol,
1
eq.),
30%
6
7
8
9
.
.
.
.
C. Venturello, R. Daloisio, J. C. J. Bart and M. Ricci, J. Mol.
Catal., 1985, 32, 107-110.
C. Venturello and R. Daloisio, J. Org. Chem., 1988, 53,
41 72 2 3 4 24 2 2 2
(C H N ) (PW O ) (7.6 mg, 0.0037 mmol) and H O
(222 μL, 2.23 mmol, 1.32 eq.) were added to a 20 mL flask and
heated to 60 °C under vigorous stirring for 3 h. After the
reaction, the mixture was filtered to remove the catalyst. The
1
organic phase was analyzed by GC-MS and H NMR.
1
553-1557.
Y. Ishii, K. Yamawaki, T. Ura, H. Yamada, T. Yoshida and M.
Ogawa, J. Org. Chem., 1988, 53, 3587-3593.
L. Plault, A. Hauseler, S. Nlate, D. Astruc, J. Ruiz, S. Gatard
and R. Neumann, Angew. Chem. Int. Ed., 2004, 43, 2924-
Catalyst recycling method
2
928.
Methyl oleate (500 mg, 1.69 mmol,
(PW (34.4 mg, 0.0168 mmol, 0.01 eq.) and
30% (222 μL, 2.23 mmol, 1.32 eq.) were added to a 20 mL
1
eq.),
1
1
0.
1.
J. Z. Chen, L. Hua, W. W. Zhu, R. Zhang, L. Guo, C. Chen, H.
M. Gan, B. N. Song and Z. S. Hou, Catal. Commun., 2014,
4
J. H. Wu, P. P. Jiang, Y. Leng, Y. Y. Ye and X. J. Qin, Chinese
J. Catal., 2013, 34, 2236-2244.
(
C
41
H
72
N
2
)
3
4 24 2
O )
2 2
H O
7, 18-21.
flask and heated to 60 °C under vigorous stirring for 2 h. After
the reaction, the mixture was diluted with 10 mL of ethyl
acetate and centrifuged at 8000 rpm for 20 minutes. Then 12.
both the organic and aqueous supernatants were removed
with a pipette. The organic phase was filtered using a filter 13.
Y. Chen, R. Tan, W. Zheng, Y. Zhang, G. Zhao and D. Yin,
Catal. Sci. Technol., 2014, 4, 4084-4092.
Y. Leng, J. Wu, P. Jiang and J. Wang, Catal. Sci. Technol.,
2
014, 4, 1293.
paper and analyzed by GC-MS. The solid remaining in the flask
1
1
4.
5.
K. Yamaguchi, C. Yoshida, S. Uchida and N. Mizuno, J. Am.
Chem. Soc., 2005, 127, 530-531.
Y. Leng, J. Zhao, P. Jiang and J. Wang, ACS Appl. Mater.
Interfaces, 2014, 6, 5947-5954.
was dried with air for 1 minute, then reused.
Catalytic cleavage of methyl oleate
Methyl oleate (500 mg, 1.69 mmol,
1
eq.), 16.
Y. X. Qiao, H. Li, L. Hua, L. Orzechowski, K. Yan, B. Feng, Z.
Y. Pan, N. Theyssen, W. Leitner and Z. S. Hou,
ChemPlusChem, 2012, 77, 1128-1138.
(C
41
H
72
N
2
)
3
4 24 2
(PW O ) (17.2 mg, 0.0084 mmol, 0.005 eq.) and
2 2
H O 30% (1.01 mL, 10.12 mmol, 6 eq.) were added to a 20 mL
1
1
1
2
7.
8.
9.
0.
X. X. Zheng, L. Zhang, J. Y. Li, S. Z. Luo and J. P. Cheng,
Chem. Commun., 2011, 47, 12325-12327.
E. Poli, R. De Sousa, F. Jerome, Y. Pouilloux and J.-M.
Clacens, Catal. Sci. Technol., 2012, 2, 910-914.
R. Neumann and M. Cohen, Angew. Chem. Int. Ed., 1997,
flask and heated to 90 °C under vigorous stirring for 24 h. After
the reaction, the organic phase was diluted with 10 mL of ethyl
acetate and filtered to remove the catalyst. The aqueous
phase was saturated with NaCl and the product was extracted
three times with 10 mL ethyl acetate, dried with MgSO
4
and
3
6, 1738-1740.
filtered. The organic phase was analyzed by GC-MS.
N. V. Maksimchuk, K. A. Kovalenko, S. S. Arzumanov, Y. A.
Chesalov, M. S. Melgunov, A. G. Stepanov, V. P. Fedin and
O. A. Kholdeeva, Inorg. Chem., 2010, 49, 2920-2930.
K. Kamata, K. Yonehara, Y. Sumida, K. Hirata, S. Nojima
and N. Mizuno, Angew. Chem. Int. Ed., 2011, 50, 12062-
Acknowledgements
2
1.
We thank the France-Canada Research Fund, Natural Science
and Engineering Research Council of Canada (NSERC)
Discovery Grant program, the Canada Foundation for
Innovation (CFI), the Canada Research Chairs (CRC), the Fonds
de Recherche du Québec – Nature et Technologies (FRQNT)
Equipe program, the Centre for Green Chemistry and Catalysis
1
2066.
Y. M. A. Yamada, H. Q. Guo and Y. Uozumi, Org. Lett.,
007, 9, 1501-1504.
Y. Ding, W. Zhao, H. Hua and B. Ma, Green Chem., 2008,
0, 910.
G. Grigoropoulou, J. H. Clark and J. A. Elings, Green Chem.,
003, 5, 1-7.
2
2
2
2.
3.
4.
2
1
(CGCC), NSERC-Collaborative Research and Training Experience
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 8 of 8
View Article Online
DOI: 10.1039/C7GC00298J
ARTICLE
Journal Name
2
2
2
2
2
5.
6.
7.
8.
9.
I. V. Kozhevnikov, G. P. Mulder, M. C. Steverink-de Zoete
and M. G. Oostwal, J. Mol. Catal. A, 1998, 134, 223-228.
D. C. Duncan, R. C. Chambers, E. Hecht and C. L. Hill, J.
Am. Chem. Soc., 1995, 117, 681-691.
M. V. Vasylyev, D. Astruc and R. Neumann, Adv. Synth.
Catal., 2005, 347, 39-44.
T. B. Khlebnikova, Z. P. Pai, L. A. Fedoseeva and Y. V.
Mattsat, React. Kinet. Catal. Lett., 2009, 98, 9-17.
K. Sato, M. Aoki and R. Noyori, Science, 1998, 281, 1646-
1
647.
Graphical abstract
8
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins