Azide derivatives of soybean oil and fatty esters

Article abstract of DOI:10.1021/jf800123t

An environmentally friendly water-based pathway to form the azide derivatives of soybean oil and fatty esters is reported. This entails first the formation of epoxides and then the azidization of the epoxides. The azidization reaction is carried out at high yields in water with only a small amount of an ionic liquid as a catalyst. The distribution of azide and alcohol functionalities on the fatty acid moiety is approximately random. This reaction has been applied to methyl oleate, methyl linoleate, soybean oil, and methyl soyate. The resulting structures have been studied by NMR.

Full text of DOI:10.1021/jf800123t

J. Agric. Food Chem. 2008, 56, 5611–5616 5611
Azide Derivatives of Soybean Oil and Fatty Esters
ATANU BISWAS,*,† BRAJENDRA K. SHARMA,‡,§ J. L. WILLETT,†
ATANU ADVARYU,# S. Z. ERHAN,‡ AND H. N. CHENG*,⊥
Plant Polymers Research Unit and Food and Industrial Oil Research Unit, National Center for
Agricultural Utilization Research, Agricultural Research Services, U.S. Department of Agriculture,
1815 North University Street, Peoria, Illinois 61604; Department of Chemical Engineering,
Pennsylvania State University, University Park, Pennsylvania 16802; Caterpillar Inc., Peoria, Illinois
61656; and Hercules Incorporated Research Center, 500 Hercules Road, Wilmington, Delaware 19808
An environmentally friendly water-based pathway to form the azide derivatives of soybean oil and
fatty esters is reported. This entails first the formation of epoxides and then the azidization of the
epoxides. The azidization reaction is carried out at high yields in water with only a small amount of
an ionic liquid as a catalyst. The distribution of azide and alcohol functionalities on the fatty acid
moiety is approximately random. This reaction has been applied to methyl oleate, methyl linoleate,
soybean oil, and methyl soyate. The resulting structures have been studied by NMR.
KEYWORDS: Soybean oil; azide; NMR; ionic liquid; epoxides
INTRODUCTION
In this work, we report the azidization of soybean oil and fatty
esters using an environmentally friendly synthetic pathway.
Recently there have been a lot of research activities on azides.
The azide functionality is useful as an intermediate in organic
synthesis (e.g., Tamiflu) (1). It is also a good synthon for click
reactions (2–4). In addition, azide is known to be thermally and
photochemically labile. It can be readily converted to other
functional groups, for example, to amines via reduction (5–8).
The azide is often produced via the chloroalkyl group using
the sodium azide reaction (9, 10). An alternative is to lithiate
the substrate and react it with a suitable azide under anhydrous
conditions to replace most of the lithium with the azide (11, 12).
Although many organic and polymeric substrates have been
azidized, as far as we know, the azidization of fatty acids, esters,
and vegetable oils has not been previously reported.
Vegetable oils and fatty acids are abundant natural materials.
There is much interest in the literature in the reactions of these
materials to produce cost-effective derivatives (13). Some
examples are epoxidized oil (14, 15), soybean oil methyl ester
(methyl soyate) (16, 17), maleated products (18, 19), derivatives
of vegetable oils and fatty esters with diethyl azidodicarboxy-
late (20, 21), soybean oil polymers (22–24), and others (25, 26).
A goal of our work is to develop alternative methods for the
introduction of nitrogen-containing derivatives to vegetable oil
and fatty acids. Earlier we have explored some selected
derivatives of soybean oil and fatty esters (20, 21, 27, 28). Many
of these derivatives have interesting structures and properties.
MATERIALS AND METHODS
Materials. Epoxidized soybean oil (Atofina, VIKOFLEX 7170, 4.2
oxirane moieties per triglyceride), methyl oleate (Sigma-Aldrich, St.
Louis, MO, tech 70%; Nu Check Prep, Elsyian, MN, >99%), methyl
linoleate (Nu Check Prep, >99%), methyl epoxy soyate (Arkema,
Philadelphia, PA, 5.6% oxirane content), hydrogen peroxide (Sigma-
Aldrich, ACS reagent, 30% solution), formic acid (Sigma-Aldrich, 96%,
ACS reagent), hexanes (Sigma-Aldrich, >95%, HPLC grade), NaCl
(Fisher, Fair Lawn, NJ, ACS reagent), and NaHCO3 (Fisher, ACS
reagent) were all used as received. All other materials were acquired
from Sigma-Aldrich.
Epoxidation Reaction. The epoxidation of the unsaturated methyl
esters of soybean oil has been performed as described elsewhere (29–33)
The epoxidation of methyl oleate, methyl linoleate, and methyl
linolenate resulted in fully epoxidized methyl oleate (EMO; methyl-
9,10-oxirane octadecanoate), epoxidized methyl linoleate (EMLO;
methyl-9,10:12,13-dioxirane octadecanoate), and epoxidized methyl
linolenate (EMLEN; methyl- 9,10:12,13:15,16-trioxirane octade-
canoate), respectively.
An epoxidation reaction was performed using hydrogen peroxide
and formic acid catalyst. The reaction was followed directly by GC, to
ensure complete conversion yet limit the productions of various
polyhydroxy compounds. Purification was achieved using a separatory
funnel. Extraction of the material with hexanes was also possible in
the EMO and EMLO syntheses, which improved yields to 97 and 95%,
respectively. The yield in the EMLEN case was 85%. Details on these
syntheses are available elsewhere (29–32).
Azidization Reaction. To a 50 mL round-bottom flask containing
10 mL of water were added 10 g (44 mmol) of ionic liquid (IL)
1-methyl imidazolium tetrafluoroborate (34) and 5 g of epoxidized
soybean oil (5.6 mmol) or 4.7 g of epoxy methyl linoleate (15 mmol).
Sodium azide (1.9 g, 30 mmol) in water (5 mL) was added to the
reaction mixture, and it was stirred using a stirring bar and heated at
* Corresponding author (e-mail Atanu.Biswas@ars.usda.gov).
† Plant Polymers Research Unit, U.S. Department of Agriculture.
‡ Food and Industrial Oil Research Unit, U.S. Department of
Agriculture.
§ Pennsylvania State University.
# Caterpillar Inc.
⊥ Hercules Inc. Research Center.
10.1021/jf800123t CCC: $40.75  2008 American Chemical Society
Published on Web 06/18/2008

5612 J. Agric. Food Chem., Vol. 56, No. 14, 2008
Biswas et al.
Table 1. Reaction of Epoxidized Methyl Oleate with NaN3a
Scheme 1. Epoxidation of Methyl Oleate To Form Epoxidized Methyl
Oleate
unreacted
epoxide azidohydrin
temperature
reaction
sample
methyl oleate derivative derivative
(°C)
time (days)
(%)
(%)
(%)
1
2
3
65
65
65
2
5
12
14
14
14
54
25
0
32
63
85
a Quantitation of unreacted methyl oleate and its epoxide and azidohydrin
derivatives comes from 13C NMR.
65 °C for a few hours to a few days. The pH of the aqueous layer was
6.5. The mixture was cooled to room temperature and transferred to a
125 mL separatory funnel. It was then extracted with 30 mL of ethyl
acetate twice. The ethyl acetate extracts were combined, washed
successively with water and saturated sodium chloride solution, dried
with magnesium sulfate, filtered, and evaporated in a rotatory evaporator
to give the product as an oil in a very quantitative yield.
1
NMR Spectroscopy. All H and 13C NMR spectra were recorded
quantitatively with a Bruker ARX-500 spectrometer (Bruker, Rhein-
stetten, Germany) at a frequency of 500 MHz (1H) and 125 MHz (13C)
and a 5 mm dual probe. The sample solutions were prepared in
deuterochloroform (CDCl3, 99.8% D, Cambridge Isotope Laboratories,
Inc., Andover, MA). Standard operating conditions were used.
RESULTS AND DISCUSSION
To incorporate the azide functionality to the fatty acid moiety,
we need a suitable reaction sequence. A facile route is to convert
the olefin on the fatty acid moiety into the 1,2-epoxide and then
convert the epoxide to the azide. The first reaction (olefins to
epoxides) is well-known; in fact, epoxidized soybean oil is
commercially available. In this work, we carry out this reaction
via formic acid and hydrogen peroxide. The example of methyl
oleate is shown in Scheme 1.
Figure 2. 13C NMR spectra (50-76 ppm) of unreacted epoxidized methyl
oleate (lower trace) and samples of its reaction with sodium azide (as
shown in Table 1).
Table 2. Reaction of Epoxidized Methyl Linoleate with NaN3a
unreacted
epoxide azidohydrin
temperature
reaction
sample
methyl linoleate derivative derivative
(°C)
time (days)
(%)
(%)
(%)
The next step is to react the epoxide with sodium azide to
form azidohydrin (ꢀ-azido alcohol). Whereas such a reaction
is known to occur under different experimental conditions (35–37),
we prefer to use mainly water as an environmentally friendlier
medium. Unfortunately, the reaction barely proceeds in pure
water. Taking a cue from Yadav et al. (38), we discovered that
a small amount of an ionic liquid (IL) can catalyze this reaction
in water.
4
5
6
7
65
65
65
65
1
3
6
15
2
2
2
2
78
18
0
20
80
98
98
0
a Quantitation of unreacted methyl linoleate and its epoxide and azidohydrin
derivatives comes from 13C NMR.
As an example, two reactions are carried out, one with water
only and one with water and ionic liquid. The 13C NMR
spectrum of the reaction of epoxidized soybean oil and sodium
azide in water and an ionic liquid is given in Figure 1, upper
trace (2.1 g of 1-methylimidazolium tetrafluoroborate; ESBO
1.0 g, 1.1 mmol; NaN3 0.653 g, 10 mmol; 2 mL of DI water;
at 65 °C for 3 days). In this case, the ionic liquid is
1-methylimidazolium tetrafluoroborate. It is clear from the
spectrum that all of the epoxides (which resonate at 54 and 57
ppm) have been reacted. In contrast, the 13C NMR spectrum of
the corresponding reaction of epoxidized soybean oil and sodium
azide in water in the absence of an ionic liquid is given in Figure
1, lower trace (ESBO 1.038 g, 1.1 mmol; NaN3 0.781 g, 12
mmol; 4 mL of DI water; at 65 °C for 3 days). The epoxide
signals are mostly intact.
The reaction was carried out at lower temperature also, but
the reaction was slower and took longer to complete. At 75 °C,
no rate increase benefit was observed in the reaction; therefore,
a reaction temperature of 65 °C was used in this study. To better
Figure 1. 13C NMR spectra (50-76 ppm) of the products of epoxidized
SBO and sodium azide in water and in ionic liquid.

Modified Soybean Oil
J. Agric. Food Chem., Vol. 56, No. 14, 2008 5613
Figure 5. 1H NMR spectra of unreacted and reacted epoxidized soybean
oil.
Figure 3. 13C NMR spectra (50-76 ppm) of unreacted epoxidized methyl
linoleate (lower trace) and samples of its reaction with sodium azide (as
shown in Table 2).
a
Table 3. Reaction of Epoxidized Soybean Oil (1.1 mmol) with NaN3
unreacted epoxide azidohydrin
temperature reaction
NaN3
sample
olefins derivative derivative
(°C)
time (days) (mmol)
(%)
(%)
(%)
8
9
10
65
65
65
1
2
2
6
8
10
2
2
2
48
10
0
50
88
98
a Quantitation of unreacted olefins and their epoxide and azidohydrin derivatives
comes from 13C NMR.
Figure 4. 13C NMR spectra (50-76 ppm) of unreacted epoxidized SBO
(lower trace) and samples of its reaction with sodium azide (as shown in
Table 3).
understand the reaction mechanism and to fully interpret the
NMR spectra, we first studied the same reaction with methyl
oleate and methyl linoleate.
Reaction with Methyl Oleate. Because the oleate moiety
has only one olefin, this represents a simple case of azidization
reaction (Scheme 2). Several examples of reactions involving
epoxidized methyl oleate and sodium azide in the presence of
water and an ionic liquid are shown in Table 1.
The reaction is complete in 12 days under the reaction
conditions described. The 13C NMR spectra are straightforward
(Figure 2). The epoxide peaks are found at 57.18 and 57.23
ppm. In the product, the carbinol peak is found at 73.47 and
73.53 ppm, and the carbon bearing the azide resonates at 67.09
and 67.16 ppm. Two peaks are observed for the oleate olefinic
carbons at ca. 129.4 ppm; this is known in the literature and
has been explained via electric field effect (39, 40) or σ-inductive
model (41–43)
Figure 6. 13C NMR spectra (50-76 ppm) of unreacted epoxidized methyl
soyate (lower trace) and samples of its reaction with sodium azide (as
shown in Table 4).
and the ionic liquid 1-methylimidazolium tetrafluoroborate. A
small aliquot was pulled from the reaction vessel at different
times and analyzed by 13C NMR. The samples are summarized
in Table 2.
The reaction is complete in 6 days under similar reaction
conditions. The 13C NMR spectra are, however, much more
complex (Figure 3). The spectrum of the starting epoxide is
already complex: there are two clusters of peaks found at around
54.3 and 56.8 ppm, with a total of eight resolvable resonances.
Gunstone (44) has previously made tentative assignments and
shown that these are due to two diastereomers, where one is
Reaction with Methyl Linoleate. The linoleic acid moiety
has two olefins, which add one additional degree of complexity.
A reaction was carried out between epoxidized methyl linoleate
and sodium azide at 65 °C at pH 6.5 in the presence of water

5614 J. Agric. Food Chem., Vol. 56, No. 14, 2008
Table 4. Reaction of Epoxidized Methyl Soyate with NaN3a
Biswas et al.
shifts for the three structures. For OH in the tertiary structure,
R ) 48.0, ꢀ ) 10.1, γ ) -3.2, δ ) 0.8. For the azide, we use
two amines in sequence; approximately R ) 38.8, ꢀ ) 7.8, γ
) -2.7, δ ) 0.3. The 1,2-disubstitution correction factor used
is -13.0 ppm. The calculated shifts are shown above under each
structure. Thus, in the 13C NMR spectrum, the four groups of
peaks can be assigned to these three structures: group 1
(72.8-75.0 ppm), one carbon from structure I and two carbons
from structure III; group 2 (70.0-72.8 ppm), one carbon from
structure I and two carbons from structure II; group 3 (66.0-68.0
ppm), one carbon from structure I and two carbons from
structure II; group 4 (62.0-65.0 ppm), one carbon from structure
I and two carbons from structure III.
unreacted
olefins
(%)
epoxide
derivative
(%)
azidohydrin
derivative
(%)
temperature
reaction
sample
(°C)
time (days)
11
12
13
14
65
65
65
65
1
3
6
15
<1
<1
<1
<1
80
10
0
20
90
100
100
0
a Quantitation of olefins and their epoxide and azidohydrin derivatives comes
from 13C NMR.
Scheme 2. Reaction of Epoxidized Methyl Oleate To Form the Corre-
sponding Azidohydrin
Of course, this group assignment ignores the fine structures
observed within each group. These are due to diastereomerism
arising from each structure. [The situation is analogous to
polymer NMR, where stereoisomers and regioisomers are
found (46, 47).] Additional (minor) splitting can occur due to
electric field effect, just as in the case of methyl oleate. From
quantitative integration, the spectral areas for groups 1-4 are
roughly equal. Thus, there is no regiospecificity; the azidohydrin
formation is random. The epoxide ring has approximately the
same environment on both sides; thus, the effect of regioselec-
tivity on product distribution was not observed. The epoxides
in linoleate appeared to react equally at 65 °C.
It may be noted that in addition to the main peaks in the
NMR spectra, there are many small peaks as well. These are
due to side reactions, particularly cyclic products.
produced in larger amounts than the other. With azide reaction,
many more peaks start to show up in the region of 63-75 ppm
(Figure 3, day 1). When the reaction is complete, about 30-40
resolvable peaks can be found (Figures 3, days 6 and 15).
Because of the large number of peaks and diastereoisomerism,
a detailed peak-by-peak assignment is not possible. However,
we are able to carry out a group assignment. If we observe the
peaks in the 63-75 ppm region, the peaks fall roughly into
four groups: group 1 at 72.8-75.0 ppm, group 2 at 70.0-72.8
ppm, group 3 at 66.0-68.0 ppm, and group 4 at 62.0-65.0
ppm. If we look at possible azidohydrin structures that can result
from azidization of epoxide, three structures are possible:
Reaction with Soybean Oil (SBO). With a better knowledge
of the NMR spectra of epoxidized methyl linoleate/sodium azide
reaction, we are ready to tackle the epoxidized soybean oil/
sodium azide reaction. SBO contains mostly triacylglycerols
with a mixture of fatty acids moieties (typically 51% linoleic
acid, 25% oleic acid, 10% palmitic acid, 7% linolenic acid, and
5% stearic acid). Palmitic and stearic acids will not undergo
epoxidation reaction. The only added complication comes from
linolenic acid moiety. The structures from epoxidized linolenic/
sodium azide are expected to be more complex because of the
many more diastereomers possible. However, because linolenic
acid is present at only 7%, we can ignore it as a first
approximation. Thus, we can treat the 13C NMR spectrum of
ESBO/sodium azide approximately as the sum of the epoxidized
(oleic + linoleic)/sodium azide spectra.
Some examples of ESBO/sodium azide reaction are shown
in Table 3. As before, the reactions were conducted at 65 °C.
The amount of sodium azide was varied and was found to have
a noticeable effect on the rate of reaction.
Two peaks stand out that are different from linoleate and
oleate (at 62.0 and 68.9 ppm). These are due to the glycerol
moiety, which is absent in the fatty esters. Other than these
glycerol peaks, the 13C NMR spectra in the 60-75 ppm region
We can use the empirical additive shift rules (45) and carry
out an approximate calculation of the expected 13C chemical
Scheme 3. Reaction of Epoxidized Soybean Oil with Sodium Azide To Form Azide Derivativea
a The placement of azide and alcohol along the fatty acid moieties is approximately random.

Modified Soybean Oil
J. Agric. Food Chem., Vol. 56, No. 14, 2008 5615
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can be organized into four groups, as in the linoleate case. In
addition, the oleate carbons contribute to the scheme. The oleate
carbinol is found in the peaks in group 1, and the oleate carbon
directly bonded to azide is found among the peaks in group 3.
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decreases from 100 to 0% (Figure 4). Relative to the spectra of
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1
Examples of the H NMR spectra of epoxidized soybean oil
and soybean oil azidohydrin are given in Figure 5. After azide
reaction, the epoxide peaks at ca. 3.0 ppm disappear, and the
azidohydrin peaks appear as a complex pattern at around
3.4-4.0 ppm.
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the sequence of two reactions (epoxidation and azidization).
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tive. The placement of azide and alcohol along the fatty acid
moiety is approximately random. The reaction is shown in
Scheme 3.
Reaction with Methyl Soyate. A popular derivative of
soybean oil is methyl soyate (methyl ester of soybean oil). This
is being used as a “biodiesel” for fuel applications and as a
useful industrial solvent for grease removal. It is of interest to
see if the azidization reactions can be applied to this material.
Epoxidation of methyl soyate is straightforward. The 13C
NMR spectrum shows that the reaction is essentially quantita-
tive, with no residual olefin left (spectra not shown). The epoxide
region (53-58 ppm) (Figure 6, lower trace) is rather similar
to that of soybean oil.
The sodium azide reaction was carried out with epoxidized
methyl soyate at 65 °C in the presence of water and the ionic
liquid. A small aliquot was pulled from the reaction vessel at
different times and analyzed by 13C NMR. The samples are
summarized in Table 4.
In this case, the azidization is complete in 6 days under similar
reaction conditions. Interestingly, the 13C NMR spectra are also
similar, except for the absence of the glycerol peaks at 62.0
and 68.9 ppm. Again, the assignments can be based on four
groups of reacted linoleate peaks and the reacted oleate peaks
in groups 1 and 3.
In this work we have devised a water-based reaction for the
azidization of epoxides in fatty esters and soybean oil. Only a
small amount of an ionic liquid is needed to achieve high yields.
The placement of azide and alcohol functionalities is ap-
proximately random. This reaction has been applied not only
to methyl oleate, methyl linoleate, and soybean oil but also to
methyl soyate (biodiesel). The structures have been confirmed
by detailed NMR studies.
ACKNOWLEDGMENT
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S. Z.; Cheng, H. N. Novel modified soybean oil containing
hydrazino-ester: synthesis and characterization. Green Chem.
2007, 9 (1), 85–89.
We thank Janet Berfield for expert technical assistance.
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Received for review January 14, 2008. Revised manuscript received
March 24, 2008. Accepted April 16, 2008. Names are necessary to report
factually on available data; however, the USDA neither guarantees nor
warrants the standard of the product, and the use of the name by the
USDA implies no approval of the product to the exclusion of others
that may also be suitable.
JF800123T