Copper mediated epoxidation of high oleic natural oils with a cumene-O2 system

Article abstract of DOI:10.1016/j.catcom.2015.02.008

The epoxidation of methyl oleate or high oleic FAMEs from different vegetable oils was carried out in a one-pot reaction over supported copper catalysts by using cumene as oxygen carrier. Cumene firstly reacts with O₂ generating cumene hydroperoxide, that by reaction with methyl oleate forms the epoxide. By using 8% Cu catalysts supported on alumina or on a polymer yields up to 87% could be obtained in a single pot at 100 °C.

Full text of DOI:10.1016/j.catcom.2015.02.008

Catalysis Communications 64 (2015) 80–85
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Copper mediated epoxidation of high oleic natural oils with a
cumene–O2 system
a
a
b
Nicola Scotti a, Nicoletta Ravasio a, , Rinaldo Psaro , Claudio Evangelisti , Sylwia Dworakowska ,
⁎
Dariusz Bogdal b, Federica Zaccheria a
a
CNR Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milan, Italy
b
Department of Biotechnology and Physical Chemistry, Faculty of Chemical Engineering and Technology, Cracow University of Technology, Warszawska 24, 31-155 Cracow, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The epoxidation of methyl oleate or high oleic FAMEs from different vegetable oils was carried out in a one-
pot reaction over supported copper catalysts by using cumene as oxygen carrier. Cumene firstly reacts with
O2 generating cumene hydroperoxide, that by reaction with methyl oleate forms the epoxide. By using 8%
Cu catalysts supported on alumina or on a polymer yields up to 87% could be obtained in a single pot at
100 °C.
Received 15 December 2014
Received in revised form 4 February 2015
Accepted 5 February 2015
Available online 7 February 2015
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Natural oil epoxidation
Cu catalysts
Cumyl hydroperoxide
Oxygen activation
1. Introduction
to eliminate the excess of acid and to lower the excess of hydrogen
peroxide [2].
The growing demand for sustainable and biodegradable products,
coupled with restrictions on the use of existing ones, are increasing
the importance of oleochemicals in various segments of the chemical
industry, notably polymers, lubricants and surfactants. The global
oleochemicals market was estimated at 14 million tonnes in 2013 and
it is expected to grow at 6%/year over the next five years to reach
18 million tonnes in 2018 [1].
This is strongly fostering innovation in this area, particularly as
far as greener processes are concerned. One of the oleochemical
industry processes requiring a more environmentally friendly
approach is epoxidation. This reaction can lead to very important in-
termediates for large-scale application such as stabilizers and plasti-
cizers in polymers, additives in lubricants, building blocks in plastics
and in polyurethane foams but also as precursors of a wide series of
high added-value compounds. However, the synthesis of epoxidized
vegetable oils still relies on the use of in situ generated peracids. The
reaction is highly exothermic and is normally performed in several
steps, since too high temperature peaks cause the degradation of
the formed oxirane ring. Moreover, a neutralization step is necessary
Grafted Ti mesoporous silica materials were found to be very ac-
tive catalysts for the selective epoxidation of C18 unsaturated fatty
acid methyl esters with tert-butyl-hydroperoxide (TBHP) as oxidant
under acid-free conditions [3] while Nb containing ones showed
good activity and selectivity in the presence of aqueous hydrogen
peroxide [4]. However, also Ti on silica catalysts are active in the
presence of hydrogen peroxide [5,6] and as long as the oxidant is
added dropwise yields up to 91% can be obtained in the epoxidation
of methyl oleate [7].
Although the Ti and Nb based systems are very good alternatives to
the peracid based reaction they still rely on the use of organic hydroper-
oxides or concentrated hydrogen peroxide solutions. A catalytic system
able to in situ generate the active oxidant species would be very inter-
esting from the safety point of view in order to avoid storage and han-
dling of hazardous hydroperoxides.
Some of us recently reported on the epoxidation of olefins by using a
CuO/Al2O3 catalyst and cumene in the presence of O2. According to our
protocol, as in the Sumitomo process for propylene oxide production, O2
and cumene first react together to give cumyl hydroperoxide which is
the active epoxidation species. Yield in epoxide as high as 95% in the
case of activated substrates such as β-methylstyrene could be obtained
in very short times [8].
Here we wish to report that a similar approach can be conveniently
used in the epoxidation of fatty acid methyl esters, thus paving the way
⁎
Corresponding author.
E-mail address: n.ravasio@istm.cnr.it (N. Ravasio).
http://dx.doi.org/10.1016/j.catcom.2015.02.008
1566-7367/© 2015 Elsevier B.V. All rights reserved.

N. Scotti et al. / Catalysis Communications 64 (2015) 80–85
81
to the epoxidation of these strategic intermediates under more sustain-
able conditions.
20 min hold). Conversion was calculated by using the following
mol MO reacted
equation: C ð%Þ ¼ Starting mol MO ꢀ 100, while selectivity was calculated
mol MO reacted
as C ð%Þ ¼ Starting mol MO ꢀ 100:
X-ray powder diffraction patterns were recorded within the range of
10° to 70° 2θ, with a step of 0.02° 2θ and counting time 1 or 4 s/step
on Philips PW-3020 powder diffractometer Ni-filtered Cu Kα radiation.
The peak of CuO (111) at 2θ = 35.5° was used for line-broadening
determinations.
2. Experimental
CuO/γ-Al2O3 and CuO/PVPy (PVPy = polyvinylpyridine) catalysts,
with an 8% metal loading, were prepared by chemisorption–hydrolysis
[9]. The support (γ-Al2O3 or PVPy, 10 g) was added to a [Cu(NH3)4]2+
solution obtained by the addition of NH4OH to a Cu(NO3)2·H2O
water solution (4 g in 20 ml) until pH 9. After 20 min under stirring,
the slurry, held in an ice bath at 0 °C, was slowly diluted in order to
allow hydrolysis of the copper complex and deposition of the finely
dispersed product to occur. The solid was separated by filtration,
washed with 0.5 l of water, dried in oven overnight at 120 °C. Finally,
CuO/Al2O3 was calcined in static in air at 350 °C for 4 h, while CuO/
PVPy was not treated at high temperature, in order to preserve the
polymer.
Copper leaching was measured after a sulfonitric digestion of a
sample of 100 mg of the reaction mixture, after catalyst filtration at
the end of the reaction.
3. Results and discussion
CuO/γ-Al2O3 catalyst shows very high catalytic performances in the
epoxidation of methyl oleate (MO). The one-pot transformation, as
represented in Scheme 1, starts with the copper catalyst promoted
oxidation of cumene into cumyl hydroperoxide by oxygen. The oxidant
species thus formed allows the epoxidation of the substrate again medi-
ated by CuO/Al2O3.
By using 20 ml of cumene and 10 mmol of MO (3 g) after 6 h we ob-
tained a conversion of 87%, but selectivity was only 63%. On the other
hand, by using toluene as co-solvent, selectivity raised to 81% in 6 h,
likely due to the decrease in oxidant species concentration. A further
decrease in cumene and solvent amount (5 ml of cumene + 5 ml of tol-
uene) led to a little worsening in the performances (conv. = 80%, sel. =
75%, t = 6 h), while optimum results were obtained by lowering the
amount of substrate (Table 1, entry 4).
A mixture of cis and trans isomers is obtained, thus suggesting
that a radical mechanism is involved [10]. We already reported [8]
that the first step of the reaction, namely cumene oxidation, follows
a radical pathway: both cumyl-hydroperoxide (CHP) and cumene
hydroperoxide radical are supposed to be the epoxidating species.
Therefore, assuming a pathway similar to the one reported by
Köckritz at al. for the epoxidation of MO in the presence of alde-
hyde/azobisisobutyronitrile, the hydroperoxide radical should be re-
sponsible for the formation of trans-epoxystearate, while only cis
isomer derives from CHP [11].
Metal loadings were determined by ICP-OES (ICAP6300 Duo
purchased from Thermo Fisher Scientific) and an external calibration
methodology, after microwave digestion of fresh and used catalysts in
HNO3.
High-resolution transmission electron microscopy (HRTEM) analy-
sis of CuO/PVPy was operated at 200 kV with a LIBRA 200FE analytical
transmission electron microscope, equipped with FEG source and pur-
chased from Zeiss. Samples were deposited on holey carbon-coated
grids from alcohol suspensions. Samples, in the form of powders, were
ultrasonically dispersed in isopropyl alcohol, and a drop of the suspen-
sion was deposited on a holey carbon film grid (300 mesh). Histograms
of the metal particle size distribution for the Cu samples were obtained
by counting at least 300 particles onto different high resolution micro-
graphs; the mean particle diameter (dm) was calculated by using the
formula dm = Σdini / Σni where ni was the number of particles of diam-
eter di.
Reactions were performed at 100 °C and under stirring (1250 rpm)
in a 50 ml glass flask provided of a condenser, operating at atmospheric
pressure, without the use of radical initiators, by bubbling molecular
oxygen (30–35 ml/min), in the presence of cumene as both solvent
and reactant, and eventually a co-solvent (cumene + co-solvent =
20 ml, olefin 10 or 5 mmol, catalyst 250 mg). All the products
were analyzed by GC–MS HP-5890 series, equipped with HP5 (5%
phenyl)-methyl-polysiloxane capillary column, length 30 m (initial
temperature = 60 °C and 3 min hold, then 15 °C/min to 280 °C and
The reaction of methyl elaidate (the trans isomer) is very much
slower, the difference in activity being comparable with that
observed in the presence of Ti grafted on non-porous, non-ordered
silica and tert-butyl hydroperoxide [10]. The better reactivity of
Scheme 1. One-pot epoxidation of MO over bifunctional CuO/Al2O3, through in-situ formation of CHP by reaction between cumene and O2.

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N. Scotti et al. / Catalysis Communications 64 (2015) 80–85
Table 1
One-pot epoxidation of MO on CuO/Al2O3.a
Entry
MO
Solvent (ml)
Time (h)
Conv. (%)
Sel. (%)
1
2
10 mmol, cis
10 mmol, cis
CUM = 20
CUM = 10
HEP = 10
CUM = 10
TOL = 10
CUM = 10
TOL = 10
CUM = 10
TOL = 10
CUM = 10
TOL = 10
6
6
87
77
63
70
3
10 mmol, cis
5 mmol, cis
5 mmol, trans
5 mmol, cis
6
6
9
8
84
98
36
99
81
86
71
88
4
5
6b
a
T = 100 °C, O2 = 30–35 ml/min, cat. = 250 mg, CUM = cumene, TOL = toluene, HEP = heptane.
CuO/PVPy as the catalyst.
b
oleate is ascribable to steric effects, since the approach to the catalyst
surface for cis C_C bonds is much less hindered than for trans C_C
bonds.
amorphous polyvinylpyridine phase making very difficult to discrimi-
nate individual crystalline particles in order to measure them. Images
at higher magnifications (see as example Fig. 2C–F) pointed out the
presence of crystalline CuO nanoparticles with irregular shape with lat-
tice planes extended to the whole nanoparticle and an amorphous
phase bonded to their surface. Copper nanoparticles are present with
a size distribution ranging from 3 to 18 nm and an average diameter
close to 9 nm (Fig. 3). The particles appeared to be well dispersed and
covered by an amorphous phase which can be ascribed to the PVPy
resin. Lattice fringe analysis of the Cu nanoparticles exhibits spots in
the FT pattern at 2.5 Å in agreement with the (002) lattice spacing of
Cu(II) oxide [15]. This evidence shows that on PVPy big CuO aggregates
survive exposure to the electron beam thus showing to be hardly
reducible.
The presence of CuO on the alumina surface is also witnessed by XRD
(Fig. S2) and TEM that put in light the presence of CuO particles with an
average 4 nm diameters [8]. The CuO/Al2O3 catalyst already showed to
be resistant to reduction, particularly in the liquid phase [16]. This sug-
gests that for the epoxidation reaction bigger, less easily reducible CuO
aggregates are required instead of small ones giving very easily well
formed, three-dimensional Cu crystallites as in the case of hydrogena-
tion reactions. Thus, CuO/SiO2, very easily reducible to very small,
three-dimensional cuboctahedral particles [17] is the most performant
hydrogenation system but does not show any activity in epoxidation
[8]. Work is in progress to better characterize, through FT IR spectrosco-
py of adsorbed CO, the morphology of CuO particles on alumina and
PVP, as it was already shown that bidimensional particles are the most
effective ones in the oxidative polymerization of 2,6-dimethyl-phenol
[18].
As far as the support effect is concerned, a copper catalyst prepared
by using a polymer, namely polyvinylpyridine (PVPy), showed good
catalytic activity (Table 1, entry 6) and selectivity slightly higher than
CuO/Al2O3, as shown by conversion and selectivity profiles reported in
Fig. 1a–b.
Cu catalysts supported on polymers are used in organic synthesis but
they are usually prepared by anchoring Cu salts or Cu complexes
[12–14] this is a rare example of a polymer supported CuO catalyst pre-
pared by chemisorption. The presence of CuO is well evident in XRD
spectra (Fig. S1) from which a particle size of 11 nm 3 can be estimat-
ed. Transmission electron micrographs and particle size distribution of
the CuO/PVPy system are reported in Fig. 2. TEM images at low magni-
fication (see Fig. 2A and B) showed CuO particles held together by the
Comparison of these results with those reported in the literature
puts in light the originality and the effectiveness of the Cu promoted
epoxidation. Thus, the epoxidation of methyl oleate with O2 has been
reported only in the presence of an aldehyde and a radical initiator
[19]. Yields up to 99% without the need of a metal catalyst but a high
pressure of O2 in organic solvents was used. The use of TBHP as an oxi-
dant gave 75% yield at 70 °C in the presence of Co oxides [20], while Ti
grafted catalysts gave yields up to 91% at 90 °C for long reaction times
[10,21–24].
Only hydrogen peroxide as an oxidant allowed one to obtain
yield higher than 85%. Thus, Ti grafted on a mesoporous silica
(MCM41) gave N91% yield at 85 °C due to high conversion and se-
lectivity [7]. Methyl esters epoxidation has been recently reported
also over immobilized peroxometalates and peroxophosphotungstate
[25,26], one-dimensional MoO/bipyridinedicarboxylate hybrid [27]
and also over metal complexes based on Ru and Mo [28,29] always
in the presence of TBHP or H2O2 obtaining yields and reaction times
(3–24 h) comparable to those reported in the present paper.
Following our continuous interest in developing chemical processes
relevant to the biorefinery scenario, we applied this epoxidation method
Fig. 1. Conversion and selectivity profiles of MO epoxidation: a) CuO/Al2O3, see Table 1,
entry 4; b) CuO/PVPy, see Table 1, entry 6.

N. Scotti et al. / Catalysis Communications 64 (2015) 80–85
83
Fig. 2. HRTEM of CuO/PVPy at different magnification.
to methylester mixtures obtained from natural oils. In particular we test-
ed high-oleic sunflower oil fatty acid methyl-esters (FAMEs) and “stabi-
lized” rapeseed and soybean oil FAMEs. We already reported on a
versatile protocol for the selective hydrogenation of many polyunsatu-
rated oils [30–32]. This method, useful not only to improve the oxidative
stability but also to standardize the composition of very different oils
in order to have in hand a raw material with uniform chemical
composition, relies on the use of a supported Cu catalyst under mild hy-
drogenation conditions. The catalyst is selective for the hydrogenation of
polyenes to monoenes thus granting not only an improved stability to-
wards oxidation, but also to preserve acceptable cold properties as the
stearic acid content keeps unchanged during the process. In the
particular case of rapeseed and soybean oil methylester hydrogenation,
very high amount of monounsaturated component can be obtained
(Table 2).
The epoxidation reaction proceeded with very high conversion
and selectivity on all the natural mixtures, over both CuO/PVPy and
CuO/γ-Al2O3 although results confirmed the higher activity of the γ-
alumina supported catalyst (Table 3). It is interesting to note that
performances of bioproducts derived from vegetable oils strongly
depend on their unsaturation level. In particular, the quality of
polyol esters to be used for casting and coating compositions is
very much improved when very high oleic, low stearic vegetable
oils are used as starting materials. Some of us recently reported on
the higher quality of polyurethane foams obtained from hydrogenat-
ed rapeseed oil with respect to the analogs obtained from rapeseed

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N. Scotti et al. / Catalysis Communications 64 (2015) 80–85
Acknowledgments
Regione Lombardia is acknowledged for funding through the project
SusChem Lombardia. COST Action TD 1203 (EUBis) is acknowledged for
STSM to Sylwia Dworakowska.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.02.008.
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Table 2
Starting composition (mol%) of stabilized FAMEs.
FAME
C16:0
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4.2
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Table 3
One-pot epoxidation of MO and natural derived FAMEs.
Substrate
Cat.
Time (h)
Conv. (%)
Sel. (%)
Sunflower highly oleic
CuO/Al2O3
CuO/PVPy
CuO/Al2O3
CuO/PVPy
CuO/Al2O3
CuO/PVPy
6
7
6
9
7
9
99
96
98
81
95
99
78
89
79
80
79
82
Stabilized soybean
Stabilized rapeseed
T = 100 °C, O2 = 30–35 ml/min, olefin = 5 mmol, cat. = 250 mg, CUM = 10 ml,
toluene = 10 ml.

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