Oxidations by the system 'hydrogen peroxide-[Mn2L 2O3]2 + (L = 1,4,7-trimethyl-1,4,7- triazacyclononane)-carboxylic acid': Part 13. Epoxidation of methyl oleate in acetonitrile solution [1]

Article abstract of DOI:10.1016/j.catcom.2012.04.019

Methyl oleate can be efficiently (yield and selectivity attain 100%, turnover number is up to 2000) epoxidized with hydrogen peroxide in acetonitrile solution at 25°C using the combination "[Mn₂L ₂O₃](PF₆)₂ (L = 1,4,7-trimethyl-1,4, 7-triazacyclononane)/oxalic acid" as a catalyst. Kinetic features of the reaction were studied and the conclusion has been made that high-valent oxo-manganese rather than hydroxyl radicals is a crucial oxidizing species in this process.

Full text of DOI:10.1016/j.catcom.2012.04.019

Catalysis Communications 26 (2012) 93–97
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Oxidations by the system ‘hydrogen peroxide–[Mn2L2O3]2+
(L=1,4,7-trimethyl-1,4,7-triazacyclononane)–carboxylic acid’
Part 13. Epoxidation of methyl oleate in acetonitrile solution [1]
b
a
Dalmo Mandelli a, , Yuriy N. Kozlov , Wagner A. Carvalho , Georgiy B. Shul'pin
⁎
b,⁎⁎
a
Center of Natural and Human Sciences, Federal University of ABC (UFABC), Santa Adélia Street, 166, Bangu, Santo André, SP, 09210‐170, Brazil
Semenov Institute of Chemical Physics, Russian Academy of Sciences, Ulitsa Kosygina, dom 4, Moscow 119991, Russia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl oleate can be efficiently (yield and selectivity attain 100%, turnover number is up to 2000) epoxidized
with hydrogen peroxide in acetonitrile solution at 25 °C using the combination “[Mn2L2O3](PF6)2 (L=1,4,7-
trimethyl-1,4,7-triazacyclononane)/oxalic acid” as a catalyst. Kinetic features of the reaction were studied
and the conclusion has been made that high-valent oxo-manganese rather than hydroxyl radicals is a crucial
oxidizing species in this process.
Received 22 February 2012
Received in revised form 3 April 2012
Accepted 12 April 2012
Available online 25 April 2012
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Biodiesel
Epoxidation
Fatty acid methyl esters (FAMEs)
Homogeneous catalysis
Manganese complexes
Renewables
1. Introduction
such practically valuable substances. Catalytic oxygenation of methyl
oleate with hydrogen peroxide is one of the promising routes to the
Modified vegetable oils play an important role in the modern
chemical industry because they can be easily obtained from renew-
able resources [2–4]. Unsaturated vegetable oils (for example, soy-
bean oil contains 23% oleic acid) can be epoxidized [5–7] to various
products that are used as building blocks for the preparation of valu-
able chemical intermediates: reactive diluents for paints and interme-
diates in the production of polyurethane-polyols. Epoxides of fatty
acid methyl esters (FAMEs) play an important role as intermediates
in the production of lubricants, plasticizers in polymers and stabi-
lizers in chlorine-containing resins, and they find applications in the
manufacture of cosmetics, wood impregnation, pharmaceuticals,
and bio-fuel additives. Methyl oleate [methyl (Z)-octadec-9-enoate;
a component of the Queen Retinue Pheromone [8]; compound 2 in
Scheme 1] and methyl epoxystearate (the epoxide obtained from
methyl oleate epoxidation; compound 3 in Scheme 1) are among
important epoxide.
The dinuclear manganese(IV) complex [LMn(O)3MnL](PF6)2 (catalyst
1; L is 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN; see Scheme 1)
as well as some similar compounds [9–11] are known to catalyze oxida-
tions of olefins and phenols. Earlier some of us discovered that compound
1 catalyzes the oxidation of various organic compounds by hydrogen
peroxide much more efficiently if a small amount of a carboxylic acid
is added to the reaction solution [1,12–28]. The ‘1/carboxylic acid/H2O2’
system in acetonitrile solution very efficiently epoxidizes olefins
[14,16–18,24], transforms alcohols into ketones (aldehydes) [14,19,23],
sulfides into sulfoxides [14] and causes the degradation of dye Rhoda-
mine 6G [22]. The reaction with olefins gave rise to the products of
dihydroxylation [16] in addition to the corresponding epoxides. The
combination ‘1/carboxylic acid/H2O2’ oxidizes also inert alkanes in ace-
tonitrile [12–16,20,21] to afford primarily the corresponding alkyl
hydroperoxides which are transformed further into the more stable ke-
tones (aldehydes) and alcohols. Olefins [17], alcohols [19] and alkanes
[17] were oxidized also in the absence of acetonitrile. Olefins and al-
kanes can be oxidized by tert-butyl hydroperoxide [14] or peroxyacetic
acid [12,25] using complex 1 as a catalyst. The reaction with tert-butyl
hydroperoxide is significantly accelerated in the presence of a small
⁎ Corresponding author.
⁎⁎ Corresponding author. Fax: +7 499 1376130.
E-mail addresses: dalmo.mandelli@uol.com.br (D. Mandelli), Shulpin@chph.ras.ru
(G.B. Shul'pin).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.04.019

94
D. Mandelli et al. / Catalysis Communications 26 (2012) 93–97
O
(CH2)7
C
CH3(CH2)7
H
OCH3
Me
Me
H
2
O
N
IV
N
N
IV
Me
H2O2
CH3CN
catalyst 1
N
Mn
Mn
N
Me
oxalic acid (4)
O
O
N
O
Me
Me
(CH2)7
CH3(CH2)7
C
(PF6)2
OCH3
1
3
O
Scheme 1. Epoxidation of methyl oleate (2) catalyzed by complex 1.
amount of a carboxylic acid [14]. Very recently, it was reported that,
similar to our system, alkene epoxidation with H2O2 catalyzed by the
manganese(V) nitrido complex (PPh4)2[Mn(N)(CN)4] is greatly en-
hanced by the presence of just one equivalent of acetic acid [29].
In the present work we report first results on the epoxidation of
methyl oleate (compound 2) to the corresponding epoxide (com-
pound 3) with H2O2 in acetonitrile catalyzed by complex 1 and oxalic
acid (compound 4; see Scheme 1). Oxalic acid is an obligatory compo-
nent of the catalytic system.
The initial epoxidation rate does not depend on the initial concen-
tration of substrate 2 in the interval of its concentrations [2]0 =
0.03÷0.12 M (Fig. 4A). These data allow us to propose the
epoxidation mechanism which does not involve hydroxyl radicals as
oxidizing species. Indeed, if hydroxyl radicals are involved into
the process, the competitive interaction of these radicals with 2
and acetonitrile should give the half of the maximum epoxidation
rate at
kMeCN½MeCNꢀ
≈1:
k2½2ꢀ
2. Results and discussion
However, it is known that the half-effect for the cyclohexane
oxidation with the participation of hydroxyl radicals can be measured
at cyclohexane concentration close to 0.2 M [30]. The rate constant
for the interaction between hydroxyl radicals and 2 should be only
a few times higher than the corresponding constant for the reaction
with cyclohexane. Due to this the half-effect should be attained at
[2]0 >0.02 M. In contrast, the experimental data presented in Fig. 4A
demonstrate that this effect is attained at the 2 concentration which
is much lower than 0.02 M. This conclusion is in a good agreement
with our previous proposal [22,25]. The oxidations catalyzed by man-
ganese complexes are believed to proceed with the participation of a
high-valent oxo-manganese species [31–35]. Fig. 1 demonstrates that
the reaction proceeds with pronounced auto-acceleration. This shape
of the kinetic curves testifies that in the initial period of the reaction a
catalytically active species is generated. This species is apparently a
high-valent oxo-manganese derivative. As it can be expected, abso-
lute concentrations of 3 (in M) obtained after 2 and 10 h depend on
the initial concentration of 2 (Fig. 4B and C, respectively).
The linear dependence of the initial epoxidation rate on the initial
H2O2 concentration was found when concentration of water was
maintained fixed (Fig. 5A). Yield of 3 after 2 h is proportional to
[H2O2]0 (Fig. 5B) and the reaction during 10 h leads to maximum
yield (0.08÷0.10 M) for the interval [H2O2]0 =0.15÷0.25 M
(Fig. 5C). Addition of some water does not dramatically affect the ini-
tial rate (Fig. 6).
We also explored the effect of other acids as co-catalysts in the
epoxidation of methyl linoleate. The results are summarized in
Table 1. It can be seen that oxalic acid is the best co-catalyst for this
process.
We have found that methyl oleate (2) can be easily epoxidized to
3 with aqueous H2O2 in acetonitrile solution under very mild condi-
tions if complex 1 and a small amount of oxalic acid (4) are present.
Examples of the kinetic curves of the reactions carried out under dif-
ferent conditions are presented in Fig. 1. When a very low concentra-
tion of catalyst 1 is used and the [H2O2]0/[2]0 ratio is 2 the initial rate
of the reaction is relatively low and final yield of 3 attains only 63%
(Fig. 1A). However, at higher concentration of 1 (5×10−5 M) and
[H2O2]0/[2]0=5 maximum yield 100% is achieved after only 2 h
(Fig. 1B). Turnover number (TON, moles of 3 per 1 mol of 1) is 2000.
Since a large excess of H2O2 is used in this case some over-oxidation oc-
curs and after 10 h yield of 3 is lower in comparison with that obtained
after 2 h. The optimal conditions for the epoxidation were found at
[1]0=5×10−5 M and [H2O2]0/[2]0=2.25 (Fig. 1C). In this case maxi-
mum yield 100% and TON=2000 were attained after 10 h. The selectiv-
ity is close to 100%.
Fig. 2 demonstrates that the initial epoxidation rate is proportional
to the initial concentration of 1 in the interval 0÷5×10−5 M. It can
be seen in Fig. 3A that the initial rate W0 does not depend on the
concentration of oxalic acid (4) in the interval of its concentration
[4]=0.002÷0.012 M. It is reasonable to assume that the accelerating
effect of the oxalic acid additives is due to the formation of an adduct
between complex 1 and oxalic acid:
1 þ 4⇄adduct equilibrium constant K1
:
Taking into account the fact that there is no effect of 4 additive up
to its concentration [4]=0.002 M allows us to estimate the low limit
for the equilibrium constant:
K1½4ꢀ≫1:
3. Conclusions
Consequently, K1 ≫500 M−1. Yields of 3 after 2 and 10 h (Fig. 1B
and C, respectively) only slightly depend on concentration of added
oxalic acid.
Here we describe a very efficient and green method for the epox-
idation of methyl oleate with aqueous H2O2 in acetonitrile catalyzed
by a manganese complex in obligatory combination with oxalic acid.

D. Mandelli et al. / Catalysis Communications 26 (2012) 93–97
95
0.10
0.08
0.06
0.04
A
2
3
0.02
0
0.05
0.04
0.03
0.02
0.01
0
B
Fig. 2. Dependence of the initial reaction rate W0 in the epoxidation of methyl
oleate (2; initial concentration 0.1 M) with H2O2 (0.2 M) catalyzed by complex 1
in the presence of 4 (0.01 M) on initial concentration of 1. Reaction was at 25 °C
in acetonitrile.
3
QP-2010 Plus, He was carrier gas); in both instruments the column
was BP-20 (SGE; polyethyleneglycol — 30 m×250 μm×0.25 μm). At-
tribution of peaks was made by comparison with chromatograms of
authentic samples and by GC–MS. In the kinetic study of the alkane
2
A
0.10
0.08
0.06
0.04
0.02
0
C
3
2
B
0
2
4
6
8
10
12
Time / h
Fig. 1. Consumption of methyl oleate (curve 2) and accumulation of methyl oleate ep-
oxide (curve 3) in the oxidation of methyl oleate (compound 2) with H2O2 catalyzed
by complex 1 in the presence of oxalic acid (compound 4) at 25 °C in acetonitrile at
different concentrations of the reactants. Graph A: [2]0=0.1 M; [1]0=2×10−5 M;
[4]0 =0.01 M; [H2O2]0=0.2 M; yield of 3 based on 2 was 63% after 10 h; TON=1260.
Graph B: [2]0=0.04 M; [1]0 =5×10−5 M; [4]0 =0.01 M; [H2O2]0 =0.2 M; yield of 3
based on 2 was 100% after 2 h; TON=2000. Graph C: [2]0=0.1 M; [1]0 =5×10−5 M;
C
[4]0 =0.0125 M; [H2O2]0 =0.225 M; yield of
3 based on 2 was 100% after 10 h;
TON=2000.
4. Experimental
The catalyst was prepared as described in [15]. The oxidations of
hydrocarbons in acetonitrile were carried out in air in thermostated
vessels under vigorous stirring. Typically, the reaction started by
the addition of an oxidant to the mixture containing catalyst,
co-catalyst, substrate (“Aldrich”) and solvent. The total volume of
the reaction mixture was 5 mL, and 70% aqueous H2O2 (“Peróxidos
do Brasil”) was used as the oxidant. CAUTION: the combination of
air and H2O2 with organic compounds at elevated temperatures
may be explosive! Samples of the reaction mixture were analyzed
by GC (Agilent 6890, N2 was carrier gas, FID) and GC–MS (Shimadzu
Fig. 3. Dependence of the initial reaction rate (Graph A) and concentration of 3 after 2 h
(Graph B) and 10 h (Graph C) in the epoxidation of methyl oleate (2; initial concentra-
tion 0.1 M) with H2O2 (0.2 M) catalyzed by complex 1 (5×10−5 M) in the presence of
4 on initial concentration of 4. Reaction was at 25 °C in acetonitrile.

96
D. Mandelli et al. / Catalysis Communications 26 (2012) 93–97
A
B
A
B
C
C
Fig. 4. Dependence of the initial reaction rate (Graph A) and concentration of 3 after 2 h
(Graph B) and 10 h (Graph C) in the epoxidation of methyl oleate (2) with H2O2
(0.2 M) catalyzed by complex 1 (5×10−5 M) in the presence of 4 (0.01 M) on initial
concentration of 2. Reaction was at 25 °C in acetonitrile.
Fig. 5. Dependence of the initial reaction rate (Graph A) and concentration of 3 after 2 h
(Graph B) and 10 h (Graph C) in the epoxidation of methyl oleate (2, initial concentra-
tion 0.10 M) with H2O2 catalyzed by complex 1 (5×10−5 M) in the presence of 4
(0.01 M) on initial concentration of H2O2. Concentration of H2O was maintained con-
stant (0.165 M) in all runs. Reaction was at 25 °C in acetonitrile.
oxidation, we measured the concentrations of 2 and 3 after the
treatment with PPh3 because in this case H2O2 and all peroxides
present in the solution are reduced and additional oxidative process-
es do not proceed in the chromatograph. Hence, this method gives the
most precise values of total concentrations of the substrate and
product.
Acknowledgments
This work was supported by the Russian Foundation for Basic
Research (grant No. 12-03-00084-a), the State of São Paulo Research
Foundation (Fundação de Amparo a Pesquisa do Estado de São Paulo,
FAPESP; grant nos. 2005/51579-2, 2006/03996-6), the Brazilian Nation-
al Council on Scientific and Technological Development (Conselho
Nacional de Desenvolvimento Cientifico e Tecnológico, CNPq, Brazil;
grant nos. 300984/2004-9, 478165/2006-4, 305014/2007-2), and the
Fundação para a Ciência e a Tecnologia (FCT), Portugal (project PTDC/
QUI-QUI/119561/2010). The authors thank Miss Danielle C. Silva for
her participation in the experiments. G.B. Shul'pin expresses his grati-
tude to the FAPESP (grant No. 2006/03984-8) and the CNPq (grant
No. 300601/01-8) for the financial support.
Fig. 6. Dependence of the initial reaction rate in the epoxidation of methyl oleate (2,
initial concentration 0.10 M) with H2O2 (0.2 M) catalyzed by complex 1 (5×10−5 M)
in the presence of 4 (0.01 M) on the total concentration of H2O present in the solution.
Reaction was at 25 °C in acetonitrile.

D. Mandelli et al. / Catalysis Communications 26 (2012) 93–97
97
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26 (2002) 1238–1245.
Table 1
Epoxidation of methyl oleate (2) to the epoxide 3 co-catalyzed by various acids.a
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Journal of Molecular Catalysis A: Chemical 222 (2004) 103–119.
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Ferreira, D. Mandelli, Journal of Organometallic Chemistry 690 (2005) 4498–4504.
[18] D. Mandelli, R.A. Steffen, G.B. Shul'pin, Reaction Kinetics and Catalysis Letters 88
(2006) 165–174.
[19] V.A. dos Santos, L.S. Shul'pina, D. Veghini, D. Mandelli, G.B. Shul'pin, Reaction
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[20] G.V. Nizova, G.B. Shul'pin, Tetrahedron 63 (2007) 7997–8001.
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Acid
Concentration
(M)
Yield of 3 (% based on 2) after
1 h
2 h
10 h
None
Oxalic (4)
Acetic
Trifluoroacetic
Nitric
–
0
43
0
0
83
0
1
100
2
0.012
0.010
0.010
0.010
58
2
65
3
70
7
a
Conditions. [2]0 =0.1 M; [1]0 =5×10−5 M; [H2O2]0 =0.21 M; 25 °C; in
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A: Chemical 299 (2009) 77–87.
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(2007) 1315–1331.
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