Vernonia oil: Conversion to a mixture of tertiary amines including N,N-Dimethyl-(12S,13R)-Epoxy-cis-9-Octadecenyl amine

Article abstract of DOI:10.1007/s11746-011-1808-x

Vernonia galamensis is a new potential industrial oilseed crop found in tropical Africa. It is the source of a naturally epoxidized oil called vernonia oil (VO) which is extracted from the seed of the plant. In this study VO was used as the starting material for the synthesis of a mixture of amines, with the major product amine being N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine. VO was transesterified via a base catalyzed methanolysis using sodium methoxide to yield VO methyl esters (VOME). Aminolysis of the VOME with dimethylamine as reagent and solvent under reflux conditions afforded the tertiary amides, with N,N- dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amide as the major product. The mixture was then subjected to metal hydride reduction with lithium aluminum hydride in diethylether under reflux conditions to obtain the desired amine mixture including N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine. Electron impact mass spectrometry was used to characterize the mixture of amines. Additionally, proton NMR, ¹³C NMR, and FTIR were used for characterization of N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine. To further confirm the conversion of VO to the amines, the quaternary ammonium salts were synthesized and characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Full text of DOI:10.1007/s11746-011-1808-x

J Am Oil Chem Soc (2011) 88:1425–1430
DOI 10.1007/s11746-011-1808-x
ORIGINAL PAPER
Vernonia Oil: Conversion to a Mixture of Tertiary Amines
Including N,N-Dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl Amine
•
Nikki S. Johnson Folahan O. Ayorinde
Received: 24 November 2010 / Revised: 10 March 2011 / Accepted: 14 March 2011 / Published online: 27 March 2011
ꢀ AOCS 2011
Abstract Vernonia galamensis is a new potential indus-
trial oilseed crop found in tropical Africa. It is the source of
a naturally epoxidized oil called vernonia oil (VO) which is
extracted from the seed of the plant. In this study VO was
used as the starting material for the synthesis of a mixture of
amines, with the major product amine being N,N-dimethyl-
(12S,13R)-epoxy-cis-9-octadecenyl amine. VO was transe-
sterified via a base catalyzed methanolysis using sodium
methoxide to yield VO methyl esters (VOME). Aminolysis
of the VOME with dimethylamine as reagent and solvent
under reflux conditions afforded the tertiary amides, with
N,N- dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amide
as the major product. The mixture was then subjected to
metal hydride reduction with lithium aluminum hydride in
diethylether under reflux conditions to obtain the desired
amine mixture including N,N-dimethyl-(12S,13R)-epoxy-
cis-9-octadecenyl amine. Electron impact mass spectrom-
etry was used to characterize the mixture of amines.
Additionally, proton NMR, 13C NMR, and FTIR were used
for characterization of N,N-dimethyl-(12S,13R)-epoxy-cis-
9-octadecenyl amine. To further confirm the conversion of
VO to the amines, the quaternary ammonium salts were
synthesized and characterized by matrix-assisted laser
desorption ionization time-of-flight mass spectrometry.
Introduction
Vernonia oil is a naturally epoxidized oil that is extracted
from the seeds (40% oil) of the Vernonia galamensis plant
which is a biorenewable resource that grows wild as weeds
in tropical Africa [1]. The oil is a complex mixture of
triacylglycerols, primarily made up of trivernolin, with the
predominant acid moiety being (?)-(12S,13R)-epoxy-cis-
9-octadecenoic (vernolic) acid. Upon hydrolysis, VO tria-
cylglycerols yield about 72–80% vernolic acid [2, 3]. It is
the epoxy functionality in vernonia oil that makes it unique
in comparison to other vegetable oils such as coconut oil,
palm kernel oil, soybean oil, sunflower oil, etc., of which
none contain the epoxy functionality in the same percent-
age found in vernonia oil. Epoxidized fatty acids and their
derivatives are of great value to industry because they are
used in plastic formulations and polymer blends/coatings
[4]. Currently the production of epoxidized fatty acids and
derivatives is from expensive chemical epoxidation of
vegetable oils such as soybean oil and linseed oil [5, 6].
Fatty amines are important raw materials in the oleo-
chemical industry, and they are intermediates in the pro-
duction of cationic surfactants [7, 8]. Amines have been
synthesized from the amination of alcohols [9] and of alkyl
halides [10] as well as from the reduction of amides [11]
and of nitriles [12]. Further, functionalized amines such as
epoxy fatty amines are useful intermediates in the pro-
duction of industrial products such as polymers [13, 14].
Epoxidized oleochemicals have been successfully utilized
as lubricants, antirust agents, and resins [15–17]. Because
vernonia oil and its derivatives naturally contain both
epoxy and double bond functionalities, oleochemicals
derived from the oil would be of great value to industry.
Here we report a facile synthesis of a tertiary amine
mixture from vernonia oil, with the major product being
Keywords Vernonia oil Á Oilseed Á Epoxy amide Á
Epoxy amine Á MALDI-TOF
N. S. Johnson Á F. O. Ayorinde (&)
Department of Chemistry, Howard University,
525 College St. NW, Washington, DC 20059, USA
e-mail: fayorinde@howard.edu
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N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine.
Amines from this oil are potential intermediates in the
production of unique surfactants. For characterization
purposes we also report the synthesis of a mixture of
quaternary ammonium salts with the predominant salt
being N,N,N-ethyl dimethyl-(12S,13R)-epoxy-cis-9-octa-
decenyl ammonium bromide derived from the aforemen-
tioned tertiary amine mixture.
(10 mg/mL CHCl3) and analyte solution {2 mg/mL H2O}
were mixed (70/30 lL) in 2-mL Eppendorf microcentri-
fuge tubes. After vortexing for 10 s, 1 lL of the sample
solution was deposited on the sample plate and then
allowed to evaporate at room temperature to enable
co-crystallization of matrix and analyte.
Transesterification of VO to VOME (1)
A previously reported procedure by Elhilo et al. [18] was
followed without modification for the conversion to the
methyl esters.
Experimental Procedures
Reagents
Amidation of VOME
Crude VO was acquired from International Exchange of
Trade and Technology Inc. (Culver, IN, USA). Sodium
methoxide in methanol, hexane, dimethylamine, diethyl
ether, lithium aluminum hydride, sodium sulfate, ethanol,
and, bromoethane were purchased from Sigma-Aldrich
Corp. (St. Louis, MO, USA).
To a 50-mL round-bottom flask equipped with a magnetic
stir bar, was added VOME (1) (3.12 g, 10.01 mmol), fol-
lowed by 10 mL of dimethylamine (1 M solution in
methanol), and 2.4 mL of sodium methoxide (25 wt%).
After 2 h of reflux, the reaction mix was quickly trans-
ferred to a 50-mL beaker and placed in an ice bath (0 ꢁC)
for 15 min and then allowed to solidify for 24 h. Next, the
solidified product was carefully washed with 5-mL ethanol.
A pale yellow solid (1.11 g, 34.23%) resulted. GC–MS
data revealed a mixture of palmitamide, oleamide, steara-
mide, and the major product vernolamide (2). The pseudo-
molecular ion for vernolamide (2) was at m/z 324 [M ? H]
with diagnostic ions at m/z 87, 210 [M-113], and 252
[M-71]. IR: 1,631.21 and 1,552.52 cm-1, 842.13 and
Instrumentation
Monitoring of reactions was with an Agilent 6890N gas
chromatograph interfaced with an Agilent 5973 inert mass
spectrometer. The interface oven was maintained at
250 ꢁC, the ionizer temperature setting was at 230 ꢁC,
using electron ionization (EI) with electron energy at
70 eV. High resolution capillary gas chromatography was
conducted with a Supelco fused-silica SPB-5 (15 m,
0.25 mm ID, 0.25 lm film) column (Bellefonte, PA, USA),
oven temperature was programmed from 50 to 300 ꢁC
(20 ꢁC/min), and helium was used as carrier gas with head
pressure 9.8 psi. IR spectra were collected on a Perkin
Elmer Spectrum 100 FTIR spectrometer. The 13C nuclear
magnetic resonance (13C NMR), proton nuclear magnetic
resonance (1H NMR), and DEPT-135 spectra were recor-
ded on a Bruker Avance 400 MHz spectrometer with either
chloroform-d (CDCl3) or deuterium oxide (D2O) as sol-
vent. For characterization purposes the quaternary ammo-
nium salts of the amine mixture were synthesized. The
molecular masses were determined by matrix-assisted laser
desorption/ionization time-of-flight mass spectrometry
(MALDI-TOFMS) using an Applied Biosystems Voyager-
DE STR BioSpectrometry Workstation equipped with a
two-stage acceleration ion source. Positive ion MALDI
spectra (200 summed acquisitions) were acquired in
delayed-extraction (150 ns) and reflector modes. The
acceleration voltage was 20 kV, the grid voltage at 75%,
nitrogen laser (337 nm, 3 ns pulse width), and low mass
gate at m/z 50. The matrix, meso-tetrakis(pentafluorophe-
nyl)porphyrin (F20TPP), was purchased from Sigma-
Aldrich Corp. (St. Louis, MO, USA). Matrix solution
1
821.71 cm-1. H: (MeOD) d 0.84 (t, 3H, CH3), 1.18–1.97
(m, 20H, 10 CH2), 2.17 (t, 2H, CH2C=O), 5.40–5.60 (m,
2H, CH=CH), 2.4 (m, 2H, CH2–CHOCH), 2.95 (broad, 2H,
epoxy, CHCH), 3.21 (s,6H, N(CH3)2); 13C: (D2O) d 13.9
(1C, CH3), 22.0–36.0 (10C, CH2), 37.4 (1C, CH2C=O),
37.8 (1C, CH2CHOCH), 55.8 (2C, N(CH3)2), 56.6 and
57.3 (2C, epoxy CHCH), 123.6 and 132.9 (2C, CH=CH),
174.3 (1C, C=O); DEPT-135: (D2O) d 13.80 (1C,CH3),
22.61–31.66 (10C, CH2), 56.38 and 56.74 (2C, epoxy,
CHCH), 123.57 and 132.68 (2C, CH=CH), 56.2 (2C,
N(CH3)2).
Reductive Amination of Vernonia Oil Amides
To a 100-mL round-bottom flask equipped with a magnetic
stir bar was added the amide mixture containing vernola-
mide (2) (0.513 g, 1.59 mmol), followed by trituration with
20 mL of diethyl ether after which an additional 30 mL of
diethyl ether was added. Then LAH (0.12 g, 3.18 mmol)
was added slowly, and refluxed for 30 min. The reaction
mixture was then allowed to cool to room temperature and
placed in an ice-water bath (0 ꢁC) while 20 mL of water
was added slowly. The solution was vacuum filtered and
the filtrate extracted with two 40-mL portions of diethyl
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1427
ether. The ether layers were combined and dried with
anhydrous sodium sulfate. The ether was evaporated via a
rotary evaporator to reveal a light yellow oil 0.26 g
(52.1%) of the desired product. GC–MS revealed a mixture
of palmitamine, oleamine, stearamine, and major product
vernolamine (3). The molecular ion for vernolamine (3)
1
was at m/z 309 and diagnostic ion of m/z 238 [M-71]. H:
(CDCl3) d 0.91 (t, 3H, CH3), 1.25–1.60 (m, 22, 11CH2),
2.03 (q, 2H, CH2CH=CH), 2.21 (s, 6H, N(CH3)2), 3.63 (t,
2H, CH2N), 2.92 (broad, 2H, epoxy, CHCH), 5.53 (m,
2H,CH=CH); 13C: (CDCl3) d 14.0 (1C, CH3), 22.0-33.0
(11C, CH2), 45.5 (2C, N(CH3)2), 56.6 and 57.2 (2C, epoxy,
CHCH), 59.9 (1C, CH2N), 123.8 and 132.7 (2C, CH=CH).
DEPT-135: (CDCl3) d 14.01 (1C,CH3), 22.60–31.75 (11C,
CH2), 45.49 (2C, N(CH3)2), 56.24 and 57.24 (2C, epoxy,
CHCH), 59.95 (1C, CH2N), 62.95 (1C, CHOCHCH2
CH=CH), 123.82 and 132.68 (2C, CH=CH).
Synthesis of N,N,N-Ethyl-dimethyl-(12S,13R)-epoxy-cis-9-
octadecenyl Ammonium Bromide (Fig. 2)
and Other Quaternary Amines
The amine mixture (0.35 g, 0.001 mol) was refluxed with
bromoethane (5 mL, 0.07 mol) for 28 h in ethanol. The
solvent was then removed via a rotary evaporator. Next,
20 mL of water was added and the aqueous mixture was
extracted with three 15-mL portions of diethyl ether. The
water was evaporated in the hood in 24 h to reveal the
desired quaternary ammonium salts which were confirmed
by MALDI-TOF MS (Fig. 3).
Results and Discussion
The goal and challenge in this synthetic approach was to
preserve the integrity of the double bond and epoxy func-
tionalities of the major products, which are expected to
show good versatility in the epoxy amine product. The first
step in this synthetic approach was the synthesis of VOME
from VO which was adapted from a previous method in our
lab [18]. The desired methyl ester products were achieved
via a based-catalyzed methanolysis in a 98% yield
(Scheme 1).
Scheme 1 Synthetic scheme for the conversion of trivernolin, the
major TG of vernonia oil, to N,N-dimethyl-(12S,13R)-epoxy-cis-9-
octadecenyl amine. Only the major product of each step is shown
methoxide resulted in shorter reaction times and complete
conversion as evidenced by GC–MS monitoring of the
reaction. The GC (Fig. 1) showed a mixture in which all
methyl esters were converted to their corresponding
amides. The optimal molar ratio of ester:dimethyl-
amine:sodium methoxide was 1:1:10. The optimal catalytic
amount of sodium methoxide was 0.1 mol. If less was
used, incomplete conversion resulted. A larger amount of
catalyst showed no distinguishable difference in the yield
observed. It is believed that the addition of sodium
methoxide increases the nucleophilicity of the amine and
From the literature it is known that esters react with
amines to form amides [19–21]. With this knowledge we
chose to react VOME (1) with dimethylamine serving as
reagent and solvent in the presence of sodium methoxide as
catalyst under reflux conditions for 2 h to afford the amide
mixture with major product vernolamide (2) (Scheme 1).
Before arriving at these optimum reaction conditions,
several attempts were made without catalyst, resulting in
long reaction times and incomplete conversion of the
starting methyl esters to amides. Incorporation of sodium
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therefore promotes the attack of the amine on the carbonyl
carbon of the ester. We also investigated reaction time in
which aliquots of the reaction mixture were taken for GC–
MS analysis every 30 min. Longer reflux times did not
show an increase in product yield. The pseudo- molecular
ion peak in MS (Fig. 1) for vernolamide (2) was at m/z 324
(M ? H) with diagnostic peaks at m/z 210 (M-113) and
m/z 87 (McLaferty rearrangement). FTIR data showed an
absorbance at 1,631.21 cm- which was representative of
the carbonyl of an amide. 13C data revealed peaks at 37.4
and 37.8 ppm corresponding to the two methyl carbons
attached to the nitrogen in vernolamide and the disap-
pearance of the peak at 51.38 ppm corresponding to the
methyl group attached to the oxygen in methyl vernolate.
The peaks at 56.6 and 57.3 ppm and 123.6 and 132 ppm
corresponding to the double bond and the epoxy, respec-
tively, still remained, indicating the presence of these
functionalities. No additional peaks were seen correspond-
ing to epoxy ring opening. This was further confirmed with
DEPT-135 NMR.
trying BH3-THF which afforded no positive outcome. The
reduction using BH3-THF as reducing agent was monitored
with GC–MS but after 18 h of reflux only amide starting
material was seen and thus the optimal conditions for this
route of reduction were not explored. LAH as reducing
agent, was employed in a ratio of 1:2 (amide:LAH). Total
conversion of the amides to amines was confirmed by
GC–MS. Analysis of the product by GC–MS showed a
mixture of palmitamine, oleamine, stearamine, and the
predominant amine vernolamine (3) whose molecular ions
were **m/z 269, m/z 295, m/z 297, and m/z 309 respec-
tively. There was also a small amount of epoxy ring
opening product as evidenced by a small peak with
molecular ion at m/z 311. This finding was also confirmed
by MALDI-TOF MS (Fig. 2). FTIR data revealed the
Synthesis of the desired tertiary amines including ver-
nolamine (3) (52.15%), was by the reduction of the
vernonia oil amides synthesized in the previous step with
lithium aluminum hydride with diethyl ether as solvent.
LAH was the second choice of reducing agent after first
Fig. 2 Structure of N,N,N-ethyl-dimethyl-(12S,13R)-epoxy-cis-9-oc-
tadecenyl ammonium bromide synthesized from the amine mixture
containing the major product N,N-dimethyl-(12S,13R)-epoxy-cis-9-
octadecenylamine and ethyl bromide in ethanol under reflux
conditions
Fig. 1 Gas chromatogram of the amide mixture, and mass spectrum of
N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amide (vernola-
mide). The chromatogram shows four peaks corresponding to palmi-
tamide (r.t. 11.86), oleamide (r.t. 12.65), stearamide (r.t. 12.76), and
vernolamide (r.t. 13.42) and an unknown impurity at r.t. 14.24. The
mass spectrum of vernolamide shows a pseudo-molecular ion at
m/z 324 (M ? H) and diagnostic peaks at m/z 210 (M-113) and m/z 87
(McLaferty rearrangement)
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Fig. 3 MALDI-TOF mass spectrum of the mixture of quaternary
ammonium salts which contained palmityl (m/z 298), linoleyl
(m/z 322), oleyl (m/z 324), stearyl (m/z 326) and vernolyl (m/z 338)
along with their corresponding isotopic peaks. The peak corresponding
to m/z 340 is attributed to a small amount of the epoxy ring opening
product
Acknowledgments Colgate Palmolive and the US Department of
Education (GAANN program) for financial support.
disappearance of the amide carbonyl absorbance which
was expected. 13C NMR spectrum showed the appearance
of the methylene carbon attached to the nitrogen at
59.9 ppm and the disappearance of the peak at 174.3 ppm
which was representative of the amide carbonyl. Also still
present were the peaks representing the double bond and
epoxy carbons. DEPT-135 NMR confirmed these findings.
To further confirm the presence of the tertiary amine
products, their quaternary ammonium salts were also syn-
thesized and characterized by MALDI-TOF (Fig. 3).
MALDI revealed a mixture of palmitic, oleic, linoleic,
stearic, and vernolic quaternary salts with the predominant
salt being vernolic, corresponding to peaks at m/z 298,
m/z 322, m/z 324, m/z 326, and m/z 338, respectively, as
well as their isotopic peaks (Fig. 3). The ion at m/z 340 was
attributed to epoxy-ring opening.
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