Synthesis of an amine-oleate derivative using an ionic liquid catalyst

Article abstract of DOI:10.1021/jf901401s

A facile (and environmentally friendly) reaction between epoxidized methyl oleate and aniline to produce an oleate-aniline adduct, without the formation of fatty amide, was discovered. This reaction was carried out neat, with a catalytic amount of an ionic liquid. No solvent was used, no byproducts were produced, and the ionic liquid could be recovered and recycled. The reaction products were fully characterized by NMR and GC-MS. 2009 American Chemical Society.

Full text of DOI:10.1021/jf901401s

8136 J. Agric. Food Chem. 2009, 57, 8136–8141
DOI:10.1021/jf901401s
Synthesis of an Amine-Oleate Derivative Using an Ionic Liquid
Catalyst
#
A
TANU
B
ISWAS,*,† BRAJENDRA K. SHARMA
,
‡,§ KENNETH M. DOLL,‡ SEVIM Z. ERHAN
^,X
,
†
J
ULIOUS L. WILLETT, AND H. N. CHENG
†Plant Polymer Research and ‡Food and Industrial Oil Units, National Center for Agricultural Utilization
Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Stret,
Peoria, Illinois 61604, §Department of Chemical Engineering, Pennsylvania State University, University
Park, Pennsylvania 16802, #Eastern Regional Research Center, Agricultural Research Service, U.S.
Department of Agriculture, Mermaid Lane, Wyndmoor, Pennsylvania 19038, and ^Ashland Hercules
Water Technologies, 500 Hercules Road, Wilmington, Delaware 19808. X Present address: Southern
Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 1100
Robert E. Lee Boulevard, New Orleans, Louisiana 70124.
A facile (and environmentally friendly) reaction between epoxidized methyl oleate and aniline to
produce an oleate-aniline adduct, without the formation of fatty amide, was discovered. This
reaction was carried out neat, with a catalytic amount of an ionic liquid. No solvent was used, no
byproducts were produced, and the ionic liquid could be recovered and recycled. The reaction
products were fully characterized by NMR and GC-MS.
KEYWORDS: Epoxidized methyl oleate; aniline; branched oleochemical; lubrication fluid
INTRODUCTION
properties because of the aromatic and the amine functionalities.
Through this reaction, it is also easy to incorporate additional
functional groups on the aromatic ring to produce a family of
structures relatedto methyl oleate. Caution is advised in the choice
of the aryl amine. Whereas some aryl amines are used as drugs
(e.g., sulfamethoxazole and procainamide) and as sunscreens
(e.g., p-aminobenzoic acid and its esters), some arylamines
(including aniline) are considered to be hazardous or toxic.
Oleic acid is the major component of triacylglycerol in olive oil,
and it is also a significant part of other vegetable oils. It is
considered to be a healthy material, and many “high-oleic” oils
are known (1). It is also known to have medicinal uses; for
example, it has a hypotensive effect (2a) and may hinder the
progression of adrenoleukodystrophy (ALD), a fatal disease that
affects the brain and adrenal glands (2b,2c). Its potassium salt and
other derivatives are known as low-risk pesticides for agricul-
ture (3). As an industrial product, oleic acid and its methyl ester
are important oleochemicals used for the development of novel
substances. In addition to food, oleic acid and its derivatives are
used in many commercial applications, for example, detergents
and soaps (4-6), lubricants (7-11), cosmetics (12-15), and
emulsifying agents (16-18).
For some time we (11, 19-22), and others (7, 23-26), have
been exploring new reaction pathways using natural materials.
Because of its use in food, medicine, and agriculture, we are
interested in oleic acid and its possible derivatives. We have
developed a straightforward and environmentally friendly reac-
tion to functionalize methyl oleate with a model aryl amine
moiety (Scheme 1). This reaction was carried out neat, with a
catalytic amount of an ionic liquid and without solvents or
formation of byproducts. In previous work with fatty acid esters
and amines, a common side reaction is the formation of fatty
amides (24). In this new reaction, amides are not formed.
Time studies and mechanistic implications were investigated in
this work. It may be useful to note that this reaction proceeds most
easily for aryl amines. The resulting product may have interesting
EXPERIMENTAL PROCEDURES
Materials. Methyl oleate (Tech 70%), hydrogen peroxide (ACS
reagent, 30% Solution), formic acid (96%, ACS reagent), hexanes
(>95%, HPLC grade), and aniline (99.5% reagent grade) from Sigma-
Aldrich, St. Louis, MO; methyl oleate (>99%) from Nu-Chek Prep,
Elysian, MN; 1-methylimidazole (99%) from Acros; tetrafluoroboric acid
(48% min w/w aqueous solution) from Alfa Aesar; and NaCl (ACS
reagent) and NaHCO3 (ACS reagent) fromFisher, Fair Lawn, NJ, wereall
used as received.
Epoxidized methyl oleate (methyl 9,10-epoxy stearate; EMO) has been
previously used in our laboratory to make a variety of different oleo-
chemicals (21, 27, 28). The same synthesis was used here, which was
adapted from that of Wool et al. (29) and originally based on Swern
epoxidation (30, 31).
Instrumentation. GC-MS was performed on an Agilent (Santa Clara,
CA) 7890A gas chromatograph equipped with a 7683B series injector and a
5975 C mass detector. The instrument programs and data acquisition were
handled by a Windows XP equipped HP-Compaq DC7700 computer with
a 3.39 GHz Pentium D processor using Agilent MSD Enhanced Chemsta-
tion version E01.00.237. The GC column was 30 m  0.25 mm in dimen-
sions with a film thickness 0.25 μm HP-5MS (Agilent). A helium flow rate of
∼0.3 mL min-1, an injection volume of 0.1 μL, and a 50:1 split ratio were
used. The temperatures were as follows: inlet, 220 ꢀC; detector, 220 ꢀC;
auxiliary transfer line, 250 ꢀC; MSD, 150 ꢀC. The initial temperature of
*Corresponding author (e-mail Atanu.biswas@ars.usda.gov).
pubs.acs.org/JAFC
Published on Web 08/31/2009
© 2009 American Chemical Society

Article
J. Agric. Food Chem., Vol. 57, No. 18, 2009 8137
Scheme 1. Reaction of EMO with Aniline Catalyzed by 1-Methylimidazoline Catalysta
a Two isomers of the ring-opened product were observed, whereas a potential byproduct, a fatty amide, was not found.
Figure 1. 1H NMR spectrum of methyl oleate-aniline product.
150 ꢀC was held for 2 min and then ramped to 280 ꢀC at 15 ꢀC min-1, at
which it was held for 20 min. The detector was run in the EI mode and set to
scan for m/z ratios from 50 to 500 Da.
was stirred for an additional period of 2 h. Water was removed under
vacuum to give the product as a colorless liquid, which solidified on
cooling.
NMR was performed on a Bruker (Boston, MA) Avance 500 NMR
spectrometer operating at 500 MHz for 1H and 125 MHz for 13C. Bruker
Icon NMR software was used on a HP x1100 Pentium 4 workstation.
Peaks were referenced to sodium 3-trimethylsilylpropionate-2,2,3,3-d4
(TSP) at 0.0000 ppm. Simulations of 13C NMR spectra were performed
by ACD/Laboratories 6.00 ACD/CNMR predictor software, running on
a Gateway Pentium 4 CPU with a 2.53 GHz processor.
Aniline, 0.93 g (10 mmol) was added to an 8 dram (30 mL) glass vial
containing 1.56 g (5 mmol) of epoxy methyl oleate and 0.0125 g of the ionic
liquid, 1-methylimidazolium tetrafluoroborate (32). The mixture was
stirred with a U-shaped stirring bar at room temperature for 5 min. It
was allowed to stand for another 5 min so that the layers were separated
before taking the zero time aliquot from the top layer. The mixture was
covered with a septum and placed in a Reacti-therm reactor set at 105 ꢀC.
Samples were withdrawn after 1, 2, 4, 6, 8, 24, and 48 h.
After the final sample had been withdrawn, the remaining mixture was
transferred to a 125 mL separatory funnel with 30 mL of ethyl acetate,
which was washed three times with 50 mL of water. The water layer was
discarded, the water wash was repeated twice, and a wash with a saturated
Reactions. 1-Methylimidazolium tetrafluoroborate (32) was prepared
by taking 1-methylimidazole (61.5 g, 0.75 mol) in a three-neck flask with a
stirrer and cooled to 0 ꢀC. Then tetrafluoroboric acid (0.75 mol, 40%
solution in water) was added slowly over a period of 30 min with stirring
and cooling to maintain the temperature at 0-5 ꢀC. The reaction mixture

8138 J. Agric. Food Chem., Vol. 57, No. 18, 2009
Biswas et al.
Figure 2. 13C NMR spectrum of methyl oleate-aniline product.
Figure 3. 13C-1H HSQC plot for methyl oleate-aniline product.
solution of sodium chloride was performed. The ethyl acetate layer was
transferred to a 100 mL beaker; excess sodium sulfate was added and then
filtered. The filtrate was collected in a round-bottom flask, from which
ethyl acetate was evaporated under vacuumusing a rotary evaporator. The
flask was placed in a vacuum oven at 50 ꢀC overnight. When larger
amounts of ionic liquid were used, the water washes were collected and
combined in a round-bottom flask. Water was evaporated under vacuum
using a rotary evaporator. The ionic liquid recovered in the flask was kept
in a vacuum oven at 50 ꢀC overnight to evaporate the residual water.
RESULTS AND DISCUSSION
In the reaction sequence, we first start with methyl oleate and
epoxidize it to form the epoxidized methyl oleate (EMO).
Epoxidation is a standard procedure and can be done readily
via hydrogen peroxide and formic acid catalyst. The EMO is then
reacted with aniline in the presence of an ionic liquid, 1-methyl-
imidazolium tetrafluoroborate (Scheme 1). We discovered that
although the ionic liquid is essential for the reaction, only a

Article
J. Agric. Food Chem., Vol. 57, No. 18, 2009 8139
Table 1. Assignments of 1H and 13C Spectra of Methyl Oleate-Aniline Adduct
chemical shift of carbon or proton no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
OMe
methyl oleate (O)
1H
2.30
1.62
1.30 1.30 1.30 1.30
29.0 29.0 29.0 29.6
2.00
5.34 5.34 2.00
129.7 129.9 27.1
1.30
1.30 1.30 1.30 1.30 1.30 0.88 3.66
29.3 29.5 29.3 31.9 22.6 14.0 51.2
13C
174.1 34.0
24.9
27.1
29.6
O-epoxide-aniline adduct (A)
2.31
1H
1.62
1.29 1.29 1.29 1.30
1.50
1.53?
3.60
3.27 1.50
1.62
1.38? 1.29 1.29 1.29 1.29 1.29 0.89 3.67
1.46
13C
174.3 34.06a 24.89 29.5 29.5 29.5 25.98b 34.11d 73.42 58.23 32.50c 26.18b 29.5 29.5 29.5 31.86 22.65 14.1 51.3
O-epoxide-aniline adduct (B)
2.31
1H
1.62
1.29 1.29 1.29 1.38? 1.50
1.46 1.62
3.27
3.60 1.50
1.53?
1.30
1.29 1.29 1.29 1.29 1.29 0.89 3.67
13C
174.3 34.03a 24.84 29.5 29.5 29.5 26.08b 32.47c 58.23 73.39 34.05d 25.87b 29.5 29.5 29.5 31.81 22.63 14.1 51.3
a Assignments may be reversed. b Assignments may be reversed. c Assignments may be reversed. d Assignments may be reversed.
catalytic amount is needed, even loadings as low as 0.5% by
weight of the reaction mixture (0.0125 g in 2.5 g of reaction
mixture) is enough to form product.
The reaction is straightforward. The reactants are added
together, without solvents, and heated to 60-100 ꢀC for several
hours. A time study has been conducted under various reaction
conditions and progress monitored by taking reaction aliquots,
which are analyzed by GC-MS. (It is important to do the washing
procedure to samples, as any residual catalyst will cause damage
to the GC column.) The product has been fully characterized by
1H and 13C NMR and GC-MS.
Structural Characterization. The 1H and 13C NMR spectra of
the reaction products are given in Figures 1 and 2, respectively.
The spectra are relatively complex with many peaks. This is
because we have two regioisomers present, corresponding to the
attack of aniline on either position 9 or position 10 of the epoxide
(Scheme 1).
Despite the large number of distinctive carbons and proton
present, we are able to achieve almost complete assignments
through a combination of empirical shift rules (33), chemical
shifts of analogous compounds (34-36), and two-dimensional
NMR. For future reference, the 1H-13C HSQC plot is given in
Figure 3. The assignments are summarized in Table 1.
Figure 4. Two potential structures that correspond to the observed
molecular weights in the EI MS of the products. The molecular formulas
of C15N24N and C16H24O2N have monoisotopic masses of 218.19 and
262.18, which correspond to the observed m/z peak in the spectra.
aniline ring carbons at 147.6 ppm (carbon attached to N), 113.5
ppm (ortho carbons), 117.2 ppm (para carbon), and 129.6 ppm
(meta carbons) also confirm this observation. If the fatty amide
had formed, these ring carbons would have appeared at 138.4
ppm (carbon attached to N), 121.6 ppm (ortho carbons), 124.4
ppm (para carbon), and 129.0 ppm (meta carbons). Similarly, the
methoxy group is also intact (at 51.4 ppm), consistent with
Scheme 1.
Additional evidence that the assigned product is correct has
been shown by the MS detector on the GC. Although the mole-
cular ion is not seen, as is expected for EI, the two largest peaks
have m/z of 218.3 and 262.3 Da. These fragments can be assigned
to the structures (Figure 4) of probable fragments of the proposed
products, which have monoisotopic masses of 218.19 and 262.18
Da, respectively.
In the 1H NMR, the assignment of the aniline moiety is
straightforward from coupling patterns and intensities: ortho, para,
and meta in decreasing shielding. Protons at the positions 9 and
10 can also be easily assigned because the methine attached to
oxygen is more downfield than the methine attached to nitrogen. As
for the other protons, we have the benefit of having the assignments
of the methyl oleate-aza-dicarboxylate ester (34, 35). The use of the
2D HSQC data then completes the assignments. Note that protons
at position 11 in product A (and position 8 in product B) show up as
doublets due to asymmetry at position 10 in product A (and position
9 in product B) as a result of aniline addition.
In the 13C NMR, the assignments reasonably follow the
empirical shift rules (33). It is of interest that at 125 MHz, the
two products A and B give distinctly different peaks for all
carbons, except for C-18, and carbons from aniline, methoxy,
and ester. Because the pairs ofpeaks are often very closely located,
it is not always possible to positively differentiate the A and B
products in each pair. Some reversal in assignments may be likely
as indicated in the footnote of Table 1. It is of interest that product
A is slightly more preponderant than product B. If this assump-
tion is wrong, then some of the assignments need to be reversed.
Note also that in the 13C spectra, there is only the ester peak at
174 ppm. No fatty amide peak is observed. The positions of
The study on the effects of different variables on the rate of
production of products provided several interesting trends. These
trends demonstrate the importance of temperature, catalyst con-
centration, and the molar ratio of EMO/aniline in this reaction.
Effect of Temperature. This novel reaction displays strong
temperature dependence (Figure 5). The reactions were all con-
ducted using 2.5 g of catalyst and a 1:2 EMO/aniline molar ratio.
It is clear that the reaction rate increases at higher temperatures.
At 2 h, the reaction run at 90 ꢀC had nearly twice the amount of
products (90%) as that performed at 60 ꢀC (53%). Because the
reaction conducted at 105 ꢀC was complete in <2 h, reaction
aliquots had to be taken more frequently to monitor the progress

8140 J. Agric. Food Chem., Vol. 57, No. 18, 2009
Biswas et al.
Figure 7. Observed production at varied EMO/aniline ratios at 105 ꢀC with
a 2.5 g catalyst loading. At a 1:1 molar ratio, the reaction is slower, but at
ratios with excess aniline, the reaction is faster.
Figure 5. Observed production at various temperatures with a 2.5 g
catalyst loading and a 1:2 EMO/aniline molar ratio. The reaction rate is
considerably faster at 105 ꢀC than at lower temperatures.
Figure 8. Observed loss of EMO in a reaction with no aniline present at
105 ꢀC with 2.5 g of catalyst. The material is initially stable but, after an
induction period, rapidly reacts.
Figure 6. Observed production at various catalyst loadings at 105 ꢀC with
a 1:2 EMO/aniline molar ratio. The reaction proceeds quickly at catalyst
loadings of 0.125 g (4.8% by weight of reaction mixture) or higher.
product was formed without aniline. At 1 equiv of aniline, the
products did form, but at a fairly slow rate. Nonetheless, the
reaction achieved completion in 6 h. With 2 equiv of aniline,
the reaction proceeded much more quickly, achieving near
completion in an hour. Further excess of aniline had little
additional effect.
In the experiment in which no aniline was used, we also
monitored the loss of starting material, EMO. From this plot
(Figure 8), it seems that initially the catalyst alone did not cause
significant decomposition of the EMO, but after a long induction
period, EMO loss became rapid. However, the product of this
reaction was not observed by GC-MS, and the reaction was not
studied further.
of the reaction. We have used this temperature in subsequent
studies of catalyst and reactant ratio experiments.
Effect of Catalyst Concentration. We observed the effect of
catalyst concentration by monitoring the initial 2-3 h of a series
of reactions, conducted at 105 ꢀC at a 1:2 EMO/aniline molar
ratio, with different amounts of added catalyst (Figure 6). As
expected, there is no product observed in the reaction without the
catalyst. However, even 0.0125 g of catalyst (0.5% by weight of
reaction mixture) is enough to cause considerable product for-
mation. At an amount of catalyst of 0.125 g (5% by weight) or
greater, the reaction nears completion in only 1 h.
Effect of EMO/Aniline Ratio. A final series of experiments,
with differing molar ratios of EMO/aniline was performed at
105 ꢀC with a 2.5 g catalyst loading (Figure 7). As expected, no
In summary, we report a straightforward and environmentally
friendly reaction involving epoxidized methyl oleate and aniline.

Article
J. Agric. Food Chem., Vol. 57, No. 18, 2009 8141
The advantages of this reaction are that it is easily performed,
gives good yield, and requires only a small amount of ionic liquid.
Furthermore, the ionic liquid can be recovered and recycled. The
reaction is a good method to introduce an aromatic amine onto
the methyl oleate structure.
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Received for review April 28, 2009. Revised manuscript received July 21,
2009. Accepted July 29, 2009. The use of trade, firm, or corporation names
in this publication is for the information and convenience of the reader.
Such use does not constitute an official endorsement or approval by the U.S.
Department of Agriculture or the Agricultural Research Service of any
product or service to the exclusion of others that may be suitable.