Epoxidation of soybean oil using a homogeneous catalytic system based on a molybdenum (VI) complex

Article abstract of DOI:10.1016/j.apcata.2010.06.038

The ability of bis(acetyl-acetonato)dioxo-molybdenum (VI) [MoO ₂(acac)₂] to catalyse the epoxidation of soybean oil in the presence of tert-butyl hydroperoxide as oxidizing agent has been investigated. The influence of reaction time and temperature in the course of the epoxidation reaction was evaluated by quantitative ¹H NMR. When epoxidation was carried out in refluxing toluene at 110 °C for 2 h, a 70.1% conversion of substrate was obtained, producing 54.1% epoxidation with a selectivity of 77.2%. The ¹H NMR spectroscopic method selected for the purpose of this work allowed a simple and rapid evaluation of the mono- and diepoxides obtained following the epoxidation of soybean oil.

Full text of DOI:10.1016/j.apcata.2010.06.038

Applied Catalysis A: General 384 (2010) 213–219
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Epoxidation of soybean oil using a homogeneous catalytic system based on a
molybdenum (VI) complex
Maritana Farias , Márcia Martinelli , Diana Pagliocchi Bottegab
a,∗
b
a
Curso de Química, Instituto Federal de Educa c¸ ão, Ciência e Tecnologia Sul-rio-grandense, Campus Pelotas, Pra c¸ a Vinte de Setembro, 455, 96015-360 Pelotas, RS, Brazil
Departamento de Química Inorgânica, Universidade Federal do Rio Grande do Sul, Avenida Bento Gon c¸ alves, 9500, 91501-970 Porto Alegre, RS, Brazil
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The ability of bis(acetyl-acetonato)dioxo-molybdenum (VI) [MoO (acac) ] to catalyse the epoxidation of
soybean oil in the presence of tert-butyl hydroperoxide as oxidizing agent has been investigated. The
2
2
Received 1 February 2010
Received in revised form 14 June 2010
Accepted 19 June 2010
influence of reaction time and temperature in the course of the epoxidation reaction was evaluated by
1
◦
quantitative H NMR. When epoxidation was carried out in refluxing toluene at 110 C for 2 h, a 70.1%
Available online 25 June 2010
conversion of substrate was obtained, producing 54.1% epoxidation with a selectivity of 77.2%. The 1
H
NMR spectroscopic method selected for the purpose of this work allowed a simple and rapid evaluation
of the mono- and diepoxides obtained following the epoxidation of soybean oil.
Keywords:
Molybdenum (VI) acetylacetonate complex
Epoxidation
©
2010 Elsevier B.V. All rights reserved.
Homogeneous catalysis
Soybean oil
1
H NMR
1
. Introduction
less effective catalysts for olefin epoxidations than organorhenium
oxides [24,25]. However from an economic and environmental per-
spective, the use of simple, affordable and commercially available
molybdenum compounds in such a capacity would offer significant
advantages [26].
The epoxidation of vegetable oils is commercially important
since the epoxides produced from these renewable raw mate-
rials present numerous applications, including the formation of
polyurethane foams (via oxirane ring opening to generate poly-
ols) [1–3], synthetic detergents [4,5], coatings [6–9] and lubricants
Alongside the peracids, various alternative oxidizing agents may
be employed in epoxidation reactions. In this regard, hydrogen
peroxide and organic peroxides, such as tert-butyl hydroperoxide
(TBHP), have the capacity to epoxidize olefins in the presence of
metallic catalysts. Indeed, the properties of Mo (VI) complex cata-
lysts are closely associated with the capacity of the metal to react
with peroxides to form peroxomolybdenum complexes [27,28]. In
[
10–13]. Within the concept of “Green Chemistry”, the production
of biodegradable lubricants from epoxidized vegetable oils is of
particular interest considering the undesirable impact on the envi-
ronment associated with the use of mineral oil-based lubricants.
The epoxidation processes most commonly employed in indus-
try utilize peracids as oxidizing agents together with strong mineral
acids as catalyst. Such methods, however, present a number of dis-
advantages in that they are not selective, cause corrosion of the
equipment and generate considerable amounts of residue [14]. In
contrast, the use of transition metal complexes as catalyst elim-
inates many of these problems and also provides a reaction that
is very selective. Although various types of metallic catalysts are
able to promote epoxidation reactions, complexes of Mo (VI) prob-
ably represent the best catalysts for olefin epoxidation and a vast
literature is available in this specific area [15–19]. In epoxida-
tions with homogeneous systems, rhenium catalysts in particular
give excellent results [20–23]. Oxomolybdenum compounds are
◦
its highest oxidation state (d ), Mo (VI) is a Lewis acid and hence
possesses a low redox potential and is thus labile to the substitution
of ligands. Complexes of transition metals in high oxidation states
facilitate the heterolysis of hydrogen peroxide and alkyl perox-
ides forming, with the latter, transition metal–alkyl hydroperoxide
complexes (Scheme 1). Complexes formed with alkyl hydroperox-
ides are, from a synthetic point of view, more useful than those
produced with hydrogen peroxide because of their superior sol-
ubility in non-polar solvents [15,29–31]. The application of alkyl
hydroperoxides as epoxidation agents offers a number of advan-
tages since the compounds are easy to obtain, give high yields and
selectivities, and may be used in diluted form thus reducing the ele-
ment of risk during epoxidation. Additionally, opening of epoxide
rings by hydroperoxides during the epoxidation reaction is mini-
mal and, in any case, gives rise to by-products that may be reduced
to commercially valuable alcohols [32].
∗ Corresponding author. Tel.: +55 51 33086305; fax: +55 51 33087304.
E-mail address: maritana@pelotas.ifsul.edu.br (M. Farias).
0
926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.06.038

2
14
M. Farias et al. / Applied Catalysis A: General 384 (2010) 213–219
Soybean oil represents an excellent model system for the inves-
tigation of epoxidation processes since more than 80% of its content
is composed of unsaturated long-chain fatty acids, with approx-
imately 52% linoleic acid, 26% oleic acid and 8% linolenic acid
[
33]. The double bonds present in these acids can be transformed
through the use of oxidizing agents and appropriate catalysts into
oxirane groups, thus transforming the original oil into a more reac-
tive substrate.
Scheme 1. Mechanism of epoxidation of an olefin by reaction with hydroperoxide
in the presence of a transition metal catalyst.
Gas chromatography (GC) is commonly used to analyse the
epoxidation products obtained from vegetable oils. In this method,
the epoxidized vegetable oil must be derivatised, typically by trans-
formation into its alkyl ester, a step that is time consuming, uses
large amounts of reagent [34] and presents the possibility of open-
ing the oxirane ring as a result of the action of the derivatising
agents [35]. In contrast, methods based on quantitative proton
toluene and the concentration of the resulting solution was
determined by 1H NMR spectroscopy. Quantofix® Peroxide 100
test strips (Sigma) were used for the semi-quantitative deter-
mination of peroxide. Oleic acid (analytical grade) was obtained
from Synth. A sample of degummed soybean oil, donated by
Oleoplan-RS-Brazil, was employed as substrate for the epoxidation
reactions.
1
nuclear magnetic resonance ( H NMR) spectroscopy do not neces-
sitate derivatisation of the analyte, require only small amounts of
reagent and, compared with GC, are rapid with respect to both sam-
ple preparation and collection of data. Application of 1H NMR in
the determination of the yield of transesterification [36] and of
the composition of unsaturated fatty acids in vegetable oils [37]
has already been reported. Additionally, 1H NMR, C NMR and
GC–mass spectrometry have been employed in monitoring the
catalytic epoxidation of methyl linoleate using transition metal
complexes as catalysts [38]. Aerts and Jacobs [34] used 1H NMR
method to determine the yields of epoxidized oils and methyl esters
of fatty acids, and showed that the results obtained for the epoxi-
dation of methyl oleate and methyl linoleate were similar to those
given by GC analysis with respect to the percentage conversion
of double bonds and the selectivities for mono- and diepoxides.
The same authors also evaluated the reproducibility of the results
2.2. Acquisition of NMR spectra
A Varian Inova 300 MHz spectrometer was employed to mea-
1
sure the H NMR spectra of samples (60 mg) dissolved in deuterated
13
chloroform (0.6 mL) containing TMS as internal standard. The mean
values of the relaxation times (T1) of the hydrogens involved in
the quantitative determinations were ≤2.0 s. The spectrometric
parameters employed were: 7.5 ␮s pulse width corresponding to
◦
a flip angle of 71.1 , relaxation delay of 10 s; acquisition time
of 2.049 s for 65,536 points, and spectral width of 4807.7 Hz.
For each spectrum, 32 transients were accumulated in 6 min
49 s.
2.3. GC–MS analysis
1
obtained by H NMR for the selectivities for mono- and diepox-
ide produced in oil samples and found only small margins of error
The reaction products were detected in an DB-wax capillary col-
2
(
approximately 0.2 in ꢀ ) in all cases. NMR techniques have also
umn (30 m × 0.25 mm × 0.25 ␮m) using a Shimadzu QP-2010 gas
chromatograph coupled with a mass spectrometer with 70 eV E.I
detector and MS WILEY7.LIB library. The injection volume was 1 ␮L
been used to characterise the products of epoxidation of castor
oil and derivatives with the catalytic system [VO(acac) ]/TBHP
2
[
39], epoxidation of soybean oil by the methyltrioxorhenium-
◦
split of 1:20. The oven temperature was programmed from 50 C
CH Cl /H O catalytic biphasic system [20], and the monoepoxides
2
2
2
2
◦
◦
◦
◦
at 20 C/min to 200 C (5 min), at 5 C/min to 230 C (20 min). The
products were derivatised in agreement with the Rothenbacher
method [35] as follows: for transesterification, 5 mL of sodium
methoxide solution (6% in methanol) were added in 100 mg of the
sample and shaken vigorously for 90 s. Extraction was performed
by the addition of 10 mL of n-hexane and 10 mL of disodium hydro-
gen citrate (15% in water), and the organic phase was used for GC
analysis.
obtained from methyl esters of linoleic acid [40].
Considering the foregoing facts, in the present study, the ability
of bis(acetyl-acetonato)dioxo-molybdenum (VI) [MoO (acac) ] to
2
2
catalyse the epoxidation of soybean oil using toluene as solvent
and TBHP as oxidizing agent has been investigated. Quantitative
analysis of the hydrogen resonances in the NMR spectra of soybean
oil and of the epoxidized oils was performed in order to determine
the average molar mass, the number of double bonds in the oil,
the conversion of substrate, the percentage of epoxidation and the
selectivity of the catalytic system. The data obtained by NMR were
also compared with the ones produced by GC–MS spectrometry.
The effects of reaction time and temperature on the formation of
products were investigated. Additional experiments with oleic acid
were also carried out.
2
.4. Epoxidation reaction
Soybean oil (1 g; 1.1 mmol; equivalent to 4.1 mmol of double
bonds) in toluene (2 mL) was placed in a 50 mL round bot-
tomed flask connected to a reflux condenser. MoO (acac)2 (13 mg;
2
4
1 ␮mol; equivalent to 1% of double bonds present in the oil) and
anhydrous TBHP (1.4 mL; 4.1 mmol; equivalent to the double bonds
present in the oil) were added and the mixture was maintained
under vigorous stirring at temperatures and periods of time stated
in Table 1. At the end of the required reaction time, the flask was
placed into an ice bath, sodium bisulphite solution (15%, w/v) was
added slowly and the consumption of peroxide monitored using
Quantofix Peroxide 100 test strips. The organic phase was sep-
arated, dried over anhydrous sodium sulphate, filtered and the
solvent removed using a rotary evaporator. The remaining cata-
lyst was separated by transferring the reaction product to a silica
gel column, which was subsequently eluted with chloroform. All
reactions were carried out in triplicate and their catalytic activities
were obtained by 1H NMR, 5% of incertitude [20,41].
2
. Experimental
2.1. Materials
Chloroform (analytical grade) and deuterated chloroform con-
taining 1% tetramethylsilane (TMS) were obtained from Merck,
whilst toluene, methanol and n-hexane were acquired from
Ecibra and used as supplied. Sodium bisulphite, sodium methox-
ide, disodium hydrogen citrate (Vetec) and anhydrous sodium
sulphate (F. Maia) were purchased in analytical grade, and
MoO (acac) was supplied by Aldrich. In order to obtain anhy-
2
2
drous TBHP, a 70% aqueous solution (Merck) was extracted with

M. Farias et al. / Applied Catalysis A: General 384 (2010) 213–219
215
Table 1
Epoxidation of soybean oil at 80 C using the catalytic system MoO2(acac)2/TBHP,a determined by 1H NMR spectroscopy.
◦
Reaction time (h)
Conversion (%)
Epoxidation (%)
Selectivity (%)
TONb
TOFc (h−1
)
2
4
8
6
4
49.7 ± 1.0
54.8 ± 1.1
63.0 ± 1.0
94.1 ± 0.4
94.1 ± 0.9
16.3 ± 0.4
17.6 ± 0.5
23.6 ± 0.5
39.4 ± 1.1
39.0 ± 0.6
32.8
32.1
37.5
41.9
41.4
4.6
4.9
6.6
11.0
11.0
2.3
1.2
0.8
0.7
0.5
1
2
a
Reactions were carried out with toluene as solvent and molar ratio of anhydrous TBHP:number of double bonds in the oil:catalyst of 100:100:1. The results were calculated
1
by H NMR, 5% of incertitude.
b
TON: total turnover number, moles of epoxide formed per mole of catalyst.
c
−1
TOF: turnover frequency which is calculated by the expression [epoxide]/[catalyst] × time (h ).
2.5. Quantitative NMR analysis
soybean oil (ND equal to 3.58 mol) was determined from:
i
A − NF
The mean molecular weight (M) of the original soybean oil
equal to 872.63 g mol ) was calculated from its H NMR spectrum
Fig. 1) according to [42]:
NDi =
(3)
2
NF
−1
1
(
(
Eqs. (4)–(6) were then applied in order to calculate the further
parameters of the reactions studied:
ꢀ
ꢁ
M = 1
5.034G
+
14.026(C + D + E + F + H)
ND − ND
i
f
Conversion (%) =
× 100
(4)
(5)
(6)
3NF
2NF
ND
i
+ 2
6.016(A − NF)
+ 173.1
(1)
ꢂ
ꢃ
(I + J)/2
2
NF
Epoxidation (%) =
× 100
NF · ND
i
where NF is the normalisation factor (the relative peak area of one
hydrogen) calculated from the area of the signal associated with
the four hydrogens of the methylene groups of the glycerol moiety
ꢀ
ꢁ
Epoxidation (%)
Conversion (%)
Selectivity (%) =
× 100
(
B in Fig. 1) by the expression:
where ND is the number of double bonds that remain unreacted,
f
obtained by substitution into Eq. (3) of the appropriate peak areas
in the spectrum of the epoxidized oil. I and J are the peak areas
associated with the hydrogens of the epoxide groups and occur
at chemical shifts of 2.9 (monoepoxide) and 3.1 (diepoxide) ppm,
respectively (Scheme 2) [34].
NF = B
(2)
4
These hydrogens were selected because they exhibited the lowest
relaxation times compared with other triglyceride hydrogens and
their signals did not interfere with any others in the spectrum [42].
In Eq. (1) C, D, E, F and H are the peak areas associated with the
methylene hydrogens (14.026 g) of the triglyceride, G is the peak
area of the methyl hydrogens (15.034 g) of the triglyceride, and A is
the peak area of the olefinic hydrogens (26.016 g) plus the peak area
of the methine hydrogen of the glycerol moiety, which all appear in
the same region. Finally, the value 173.1 represents the molecular
weight of the triglyceride fragment depicted in Fig. 2.
3. Results and discussion
In preliminary experiments, appropriate conditions for the
epoxidation of soybean oil using the MoO (acac) /TBHP catalytic
2
2
system were evaluated, with particular emphasis given to the
effects of employing an aqueous solution or anhydrous TBHP
as oxidizing agent. Tests using TBHP in solution gave lower
percentage of epoxide than anhydrous TBHP and after 2 h of
reaction, large amounts of hydroxilated products were found.
Since the best results were obtained by using anhydrous TBHP,
the study reported herein employed the oxidizing agent in this
form. The temperature conditions were also investigated. At tem-
In order to determine the values of conversion, epoxidation and
selectivity, the number of double bonds (ND) present in the original
◦
peratures below 80 C, epoxidation products were not observed.
◦
◦
Therefore, the reactions were carried out at 80 C and at 110 C,
which is the temperature of toluene reflux. Temperatures above
◦
1
10 C were not considered because epoxy ring opening could
occur.
The main experimental conditions can be seen from Table 1,
◦
when soybean epoxidation was carried out at 80 C, the values
for conversion, epoxidation and selectivity of reaction increased
with time. The results shown are the average of triplicates. It can
Fig. 1. 1H NMR spectrum of the original soybean oil sample represented by a triglyc-
eride of linoleic acid (R1 and R2 are alkyl groups).
Fig. 2. Triglyceride fragment of molecular weight 173.1 specified in Eq. (1).

2
16
M. Farias et al. / Applied Catalysis A: General 384 (2010) 213–219
Scheme 2. Principal chemical shifts (ppm) of hydrogens influenced by double bonds
and/or epoxide groups in (a) methyl linoleate; (b) methyl linoleate diepoxide; and
(
c and d) methyl linoleate monoepoxide (R = Me).
Adapted from [34].
be observed that the results show no difference when referred to
the elapsed time from 16 to 24 h of ongoing reactions and that
1
6 h reaction time gives the most satisfactory marks in this series
1
◦
Fig. 3. H NMR spectra of soybean oil showing: (a) oil epoxidized at 80 C for 8 h;
of experiments. Throughout the catalytic procedure, it was also
observed that there was no color change during the reaction, being
observed by the persistent yellow color of the catalyst [43]. This
possibly indicates that the catalyst does not decompose into Mo(V)
species during the reaction [44]. On the characterization of the
reaction products after 8 h of reaction at 80 C, the formation of
monoepoxide products could be verified from the appearance of a
hydrogen signal related to the formation of the epoxide group at
2
(b) oil epoxidized at 80 ◦C for 16 h; (c) oil epoxidized at 110 ◦C for 2 h: (R and R2 are
alkyl groups).
1
of reaction, the presence of diepoxides could also be detected as
evidenced by the hydrogen signals of the epoxide groups at both
2.9 and 3.1 ppm (Fig. 3b). Table 2, which gives the results for reac-
tions carried out under conditions of toluene reflux (110 C), shows
that conversion increased slightly with reaction time, but epoxi-
◦
◦
1
.9 ppm in the H NMR spectrum (Fig. 3a). However, following 16 h
Table 2
Epoxidation of soybean oil at 110 C using the catalytic system MoO2(acac)2/TBHP,a determined by 1H NMR spectroscopy.
◦
Reaction time (h)
Conversion (%)
Epoxidation (%)
Selectivity (%)
TONb
TOFc (h−1
)
2
4
8
6
4
70.1 ± 0.9
69.3 ± 1.1
77.6 ± 0.5
79.3 ± 0.6
83.2 ± 1.3
54.1 ± 0.9
53.1 ± 0.8
49.7 ± 0.7
43.7 ± 0.5
40.9 ± 0.7
77.2
76.6
64.0
55.1
49.2
15.0
14.8
13.9
12.2
11.4
7.5
3.7
1.7
0.8
0.5
1
2
a
Reactions were carried out with toluene as solvent and molar ratio of anhydrous TBHP:number of double bonds in the oil:catalyst of 100:100:1. The results were calculated
1
by H NMR, 5% of incertitude.
b
TON: total turnover number, moles of epoxide formed per mole of catalyst.
c
−1
TOF: turnover frequency which is calculated by the expression [epoxide]/[catalyst] × time (h ).

M. Farias et al. / Applied Catalysis A: General 384 (2010) 213–219
217
Fig. 4. Total ion chromatogram of the methyl esters of epoxidized soybean oil with
◦
the catalytic system [MoO2(acac)2]/TBHP, 110 C, 2 h.
Scheme 3. Proposed mechanism for the epoxidation of olefins by the catalytic sys-
tem MoO2(acac)2/TBHP. Adapted from [15].
dation and selectivity diminished. However, with the increase in
◦
temperature from 80 to 110 C, with only 2 h of reaction, the con-
version reached 70% and there was a significant gain in the amount
of epoxidized product and selectivity. The turnover numbers in
Table 2 were higher than the ones in Table 1, indicating increased
activity of the catalyst at this temperature. Color change that could
be related to the decomposition of the catalyst was not observed,
Fig. 5. Mass spectrum fragmentation of epoxidized methyl oleate obtained from
Fig. 4, under the catalytic system [MoO2(acac)2]/TBHP, 110 C, 2 h.
◦
◦
even under drastic conditions of 110 C, although TON started to
significant reduction in the catalytic activity as the reaction time
elapses.
decline for longer reaction times. Comparing Mo catalysts for epoxi-
dation reactions of other substrates, our catalytic system has similar
activity and stability [44,45] or lower [17,46]. As far as we could
investigate, data for epoxidation reactions using molybdenum cat-
alytic systems and unsaturated fatty acids [18] as substrates have
not been reported so far. However, values of TON and TOF for the
catalytic epoxidation of a mixture of methyl oleate and methyl
linoleate in ionic liquids, using the Mo (VI) complex as catalyst [47],
are higher than those found in this work. The characterization of the
In the present study, the catalytic activity of MoO (acac)2 in
2
the epoxidation of soybean oil using TBHP was compared with
the epoxidation of oleic acid using anhydrous cumene hydroperox-
ide (CHP) and chlorobenzene as solvent [18]. Oleic acid subjected
◦
to epoxidation for 140 min at 80 C underwent 48.4% conversion
with a selectivity of 50.3%. In our system involving soybean oil and
◦
MoO (acac) /TBHP, conversion after 120 min at 80 C was 49.7%
2
2
◦
1
with a selectivity of 32.8% (Table 1), whereas at 110 C the con-
version was 70.1% with a selectivity of 77.2% (Table 2). At 110 C
reaction products by H NMR revealed that after only 2 h of reac-
◦
◦
tion at 110 C, the formation of diepoxides had already occurred
the results obtained by using the system described in this paper
(
Fig. 3c), and similar diepoxide formation was observed under sev-
◦
were superior to those available in the literature at 80 C [18],
eral other conditions. Evidence of the generation of hydroxylated
products, formed by the opening of the oxirane ring, can also be
◦
while at 80 C the results were similar to those reported previ-
1
ously.
observed in the 3.4–4.0 ppm region of the H NMR spectrum shown
For further comparison, our system was used for the epoxida-
tion of oleic acid. As can be seen from Table 3, the results obtained
by using our system were again superior to those available in the
in Fig. 3c. Perhaps these products are likely to decrease the activity
of the catalyst.
The formation of cis epoxides, under all the conditions stud-
ied, was confirmed from the observed hydrogen chemical shift
literature with MoO (acac) /CHP and chlorobenzene as solvent
2
2
[
18].
The total ion chromatogram (TIC) of the epoxidation products
(
2.9 ppm) associated with the epoxide. This shift is characteristic
of authentic cis epoxide, whilst the epoxide hydrogens of trans
epoxide resonate at 2.63 ppm [38]. The present findings indicate
that the cis configuration, present in the majority of the unsat-
urated fatty acids of vegetable oils [48], is maintained in the
corresponding epoxides. Indeed, the trans configuration is rarely
found in natural products such as vegetable oils, and great care
must be taken in representing the molecular structure of such com-
pounds.
obtained for best reaction condition for epoxidation of soybean
◦
oil, at 110 C and 2 h, can be seen in Fig. 4. Peaks until 15 min
corresponded to the saturated and unsaturated fatty esters from
the unreacted soybean oils and peaks around 20–22 min corre-
sponded to epoxidation products. The signal of the precursor ion
with a mass to charge ratio (m/z) of 155 amu, which evidences
the formation of the epoxidized methyl oleate [50] is shown at
Fig. 5 with its fragmentations (Scheme 4). However, the electron
impact ionization (EI) detector produces a strong high sensitiv-
ity fragment and at (m/z) 155, which points to epoxidized methyl
oleate, it is little selective because the fragment does not include
the other product expected from the NMR data obtained, epox-
idized methyl linoleate (m/z 344). Chemical ionization (CI) with
ammonia is supposed to be more suitable for such characterization
It is proposed that the mechanism (Scheme 3) of epoxidation
of olefins, using the catalytic system MoO (acac) /TBHP, occurs
2
2
via formation of a catalytic species A, by the reaction of the com-
plex MoO (acac) with TBHP. Subsequently, the species A transfers
2
2
an oxygen to the olefin generating the species B. The tert-butyl
alcohol formed during the course of the reaction acts as a com-
petitive inhibitor of TBHP attack, since this by-product can also
coordinate to the molybdenum center [49]. This could lead to a
[
51,52].

2
18
M. Farias et al. / Applied Catalysis A: General 384 (2010) 213–219
Table 3
Epoxidation of oleic acid using the catalytic system MoO2(acac)2/TBHP , determined by 1H NMR spectroscopy.
a
◦
TONb
TOFc (h−1
)
Reaction temperature ( C)
Conversion (%)
Epoxidation (%)
Selectivity (%)
8
10
0
67.2 ± 0.6
62.5 ± 0.9
40.6 ± 0.6
42.2 ± 0.9
60.3
67.9
40.6
42.2
20.3
21.1
1
a
Reactions were carried out with toluene as solvent, 2 h and molar ratio of anhydrous TBHP:oleic acid:catalyst of 100:100:1. The results were calculated by 1H NMR, 5%
of incertitude.
b
TON: total turnover number, moles of epoxide formed per mole of catalyst.
TOF: turnover frequency which is calculated by the expression [epoxide]/[catalyst] × time (h ).
c
−1
Scheme 4. Fragmentations of epoxidized methyl oleate.
4
. Conclusions
[6] T. Tsujimoto, H. Uyama, S. Kobayashi, Macromol. Rapid Commun. 24 (2003)
11–714.
7
[
[
7] Z. Zong, J. He, M.D. Soucek, Prog. Org. Coat. 53 (2005) 83–90.
8] M.A. de Luca, M. Martinelli, M.M. Jacobi, P.L. Becker, M.F. Ferrão, J. Am. Oil Chem.
Soc. 83 (2006) 147–151.
The results obtained demonstrate the catalytic potential of the
system MoO (acac) /TBHP in the epoxidation of soybean oil. This
2
2
[
9] M.A. de Luca, M. Martinelli, C.C.T. Barbieri, Prog. Org. Coat. 65 (2009) 375–380.
catalytic system shows great promise and may substitute for clas-
sical methods of epoxidation, particularly since it offers lower
environmental impact with a minimization of residues. Under the
conditions tested, the best results obtained for conversion, epoxi-
[
[
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5
dation and selectivity occurred when the reaction was carried out at
[
◦
1
10 C for 2 h. For vegetable oils that are composed predominantly
of triglycerides, the positions of unsaturation within the fatty acids
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double bonds of short chain alkenes.
[
[
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