Synthesis of sodium (+)-(12S,13R)-epoxy-cis-9-octadecenyl sulfonate from vernonia oil

Article abstract of DOI:10.1007/s11746-009-1377-4

A water-soluble, foaming epoxyalkene sulfonate, sodium (+)-(12S,13R)-epoxy- cis-9-octadecenyl sulfonate, was synthesized from vernonia oil (VO) by a series of simple reactions that include transesterification, metal hydride reduction, tosylation, and S

Full text of DOI:10.1007/s11746-009-1377-4

J Am Oil Chem Soc (2009) 86:675–680
DOI 10.1007/s11746-009-1377-4
ORIGINAL PAPER
Synthesis of Sodium (+)-(12S,13R)-Epoxy-cis-9-octadecenyl
Sulfonate from Vernonia Oil
Darryl C. Sutton Æ Nikki S. Johnson Æ
Caswell Hlongwane Æ Folahan O. Ayorinde
Received: 22 October 2008 / Revised: 20 March 2009 / Accepted: 27 March 2009 / Published online: 23 April 2009
Ó AOCS 2009
Abstract A water-soluble, foaming epoxyalkene sulfo-
nate, sodium (?)-(12S,13R)-epoxy-cis-9-octadecenyl sul-
fonate, was synthesized from vernonia oil (VO) by a series of
simple reactions that include transesterification, metal
hydride reduction, tosylation, and SN2 reactions. Conversion
of VO into vernonia oil methyl esters (VOME) using sodium
methoxide was quantitative. Subsequent reduction of VOME
with lithium aluminum hydride yielded (?)-(12S,13R)-
epoxy-cis-9-octadecenol (94%), along with minor amounts of
hexadecenol, octadecenol, cis-9-octadecenol, and cis-9,12-
octadecandienol. The (?)-(12S,13R)-epoxy-cis-9-octadece-
nol, was tosylated with p-toluenesulfonyl chloride to give
(?)-(12S,13R)-epoxy-cis-9-octadecenyl tosylate at 96%
yield. Iodination of the tosylate with sodium iodide and
subsequent SN2 reaction with sodium sulfite afforded (?)
-(12S,13R)-epoxy-cis-9-octadecenyl sulfonate (63% yield).
This study demonstrates the ability to produce an epox-
yalkenyl sulfonate, belonging to a class of anionic surfac-
tants, from VO without destroying the epoxy functionality
in the (?)-(12S,13R)-epoxy-cis-9-octadecenyl moiety of
VO. The critical micelle concentration of the synthesized
sulfonate was also determined.
Introduction
Vernonia oil (VO) is extracted from the seed of the
Vernonia galamensis plant [1]. This plant has been culti-
vated on a semi-commercial scale in Kenya, Zimbabwe,
and parts of Central and South America [1, 2]. The fatty
acid composition of vernonia oil triacylglycerols include
palmitic, stearic, oleic, linoleic, and (?)-(12S,13R)-epoxy-
cis-9-octadecenoic acids [2]. The naturally epoxidized VO
contains about 80% of (?)-(12S,13R)-epoxy-cis-9-octa-
decenoic acid[2] upon hydrolysis, thus potentially providing
unique oleochemicals that could find applications in the
production of new surfactants.
In previous work in our laboratory, we demonstrated the
ability to control the lithium aluminum hydride (LAH)
reduction of the epoxy functionality in VO or vernonia
oil methyl esters (VOME) with the choice of polar
or nonpolar solvents [3]. The use of polar solvents
resulted in the formation of 12(13)-hydroxy-cis-9-octade-
cenol, while nonpolar solvent afforded (?)-(12S,13R)-
epoxy-cis-9-octadecenol.
Fatty alcohols have been studied extensively for their
use as raw materials for the production of surfactants [4, 5].
Ricinoleic acid (12-hydroxy-9-octadecanoic acid), is the
only naturally occurring functionalized, hydroxylated fatty
acid presently used in the oleochemistry industry [6, 7],
and it is the major component of castor bean oil, com-
prising approximately 85–90% of the fatty acids present [6,
8]. Ricinoleyl alcohol is a precursor of anionic surfactants,
[5, 9–12] used in commercial formulations such as cos-
metics, lubricants, de-icers, and in the industrial processing
for paper, plastics and biopolymers [13–15]. Both ricin-
oleic acid and vernolic acid are C-18 molecules with
unsaturation at the 9, 10, and oxygen at the 12 positions of
their aliphatic chain. Studies of a ricinoleic acid-based
Keywords Fatty acids ꢀ MALDI-TOF MS ꢀ Seed oil ꢀ
Sulfonate ꢀ Surfactant ꢀ Triacylglycerol ꢀ Vernonia oil
D. C. Sutton ꢀ N. S. Johnson ꢀ C. Hlongwane ꢀ
F. O. Ayorinde (&)
Department of Chemistry, Howard University,
525 College St. NW, Washington, DC 20059, USA
e-mail: fayorinde@howard.edu
N. S. Johnson
e-mail: johnson_s_nikki@yahoo.com
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J Am Oil Chem Soc (2009) 86:675–680
anionic surfactants show good wetting ability, detersive
power, emulsifying power, and surface tension lowering
ability, but poor to average foaming characteristics and
detersive efficiency [9, 12]. The uniqueness of vernolic
acid is derived from the presence of the epoxy functionality
at the 12, 13, positions, and thus vernolic acid-based sur-
factants would be expected to display some unique sur-
factancy characteristics similar to those from castor-based
surfactants.
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 Aldrich
Chemical Co. (Milwaukee, WI, USA). Matrix solution
(10 mg/mL CHCl3) and analyte solution [2 mg/mL meth-
anol/H2O (4:1)] were mixed (80 lL/20 lL) in 2-mL
Eppendorf microcentrifuge 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.
As part of an ongoing research effort aimed at demon-
strating the potentials of using VO to generate industrial
chemicals [3], this paper reports on the laboratory con-
version of VO to (?)-(12S,13R)-epoxy-cis-9-octadecenyl
sulfonate and the measurement of its critical micelle
concentration.
Conversions of VO to VOME (1) and (?)-(12S,13R)-
Epoxy-cis-9-octadecenol (2)
Previously reported procedures were used without modifi-
cation [3].
Experimental Procedures
Tosylation of (?)-(12S,13R)-Epoxy-cis-9-octadecenol(2)
Reagents
In a 100-mL round-bottom flask equipped with a stirring
bar, was transferred (?)-(12S,13R)-epoxy-cis-9-octadece-
nol (2) (2.4 g, 8.5 mmol), followed by 10 mL of chloro-
form and dried pyridine (1.3 g, 17 mmol). The solution
was cooled in an ice bath (5 °C) for 15 min. To this
solution p-TsCl was added (2.4 g, 13 mmol) at a rate of
approximately 0.2 g every 10 min while stirring. After 3 h
of stirring at 5 °C, 10 mL of water was added, followed by
40 mL of diethyl ether. The ethereal solution was washed
with HCl (10 wt.%, 3 9 40 mL, 5 °C) followed by sodium
bicarbonate, and brine. The resulting solution was stripped
with a rotary evaporator to yield, 3.6 g of a colorless liquid
(96%), consisting of (?)-(12S,13R)-epoxy-cis-9-octadece-
nyl tosylate (3) and trace amount of starting alcohol. MS
(EI) analysis showed the molecular ion for (?)-(12S,13R)-
epoxy-cis-9-octadecenyl tosylate (3) was at m/z 436, and
diagnostic ion at m/z 281 (M-SO2C7H7). A small amount of
the crude 3 was purified for characterization purposes.
About 0.5 g of 3 was column chromatographed on silica
gel column (5% ethyl acetate/n-hexane, 45 g silica gel,
Crude VO was obtained from IXTT Corporation (Culver,
IN). Sodium methoxide, methanol, lithium aluminum
hydride, p-toluenesulfonyl chloride, chloroform, acetone,
isopropyl alcohol, sodium sulfite, sodium sulfate, pyridine,
diethyl ether, hydrochloric acid, sodium iodide, sodium
bicarbonate, sodium chloride, and sodium hydroxide were
purchased from Aldrich Chemicals Co. (Milwaukee, WI).
Instrumentation
Reactions and products were monitored with an Agilent
6890 N gas chromatograph interfaced with an Agilent 5973
inert mass spectrometer. The interface oven was main-
tained 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-1 (30 m,
0.32 mm ID, 0.25 lm film) column (Bellefonte, PA), oven
temperature was programmed from 50 to 300 °C
(20 °C/min), and helium was used as the carrier gas with
head pressure 9.8 psi. The 13C nuclear magnetic resonance
(13C NMR) and proton nuclear magnetic resonance (1H
NMR) spectra were recorded on a Bruker Avance
400 MHz spectrometer with chloroform-d (CDCl3) as
solvent and source of internal standard. The molecular
mass of the sulfonate was determined by matrix-assisted
laser desorption/ionization time-of-flight mass spectrome-
try (MALDI-TOF MS) 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
´
˚
70–230 mesh, 60 A pore size) to yield pure 3 (0.4 g, 80%
based on amount chromatographed). 1H NMR (CDCl3)
d 0.95 (t, 3H, CH3), 1.05–2.00 (m, 22H, 11CH2), 2.10
(q, 2H, CH2CH=CH), 2.50 (s, 3H, Ar CH3), 2.95 (broad,
2H, epoxide CHCH), 4.05 (t, 2H, CH2O), 5.40–5.70 (m,
2H, CH=CH), 7.35–7.80 (AA0BB0, 4H, Ar H); 13C NMR
(CDCl3) d 14.2 (1C, CH3), 21.1 (1C, Ar CH3), 22.2 (1C,
CH3CH2), 26.0–33.0 (11C, CH2), 57.5 and 58.0 (2C, epoxy
CHCH), 71.0 (1C, CH2O), 123.0 and 132.0 (2C, CH=
CH), 128.0, 130.0, 133.0 and 145.0 (5C, Ar carbons);
MALDI-TOF MS, showed molecular ion m/z 459.9
([ROTs ? Na]?).
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J Am Oil Chem Soc (2009) 86:675–680
Iodination of Epoxy Tosylate
677
overnight to yield 1.4 g of sodium (?)-(12S,13R)-epoxy-
cis-9-octadecenyl sulfonate (5) (63% yield). 1H NMR
(CD3OD) d 0.95 (t, 3H, CH3), 1.05–2.00 (m, 22H, 11CH2),
2.10 (q, 2H, CH2CH=CH), 2.80 (t, 2H, CH2SO3Na), 2.95
(broad, 2H, epoxide CHCH), 5.40–5.70 (m, 2H, CH=CH);
13C NMR (CDCl3) d 14.2 (1C, CH3), 24.2 (1C, CH3CH2),
26.0–33.0 (11C, CH2), 57.5 and 58.0 (2C, epoxy CHCH),
53.0 (1C, CH2SO3), 123.0 and 132.0 (2C, CH=CH);
MALDI-TOF MS, showed sodiated molecular ion at m/z
391.3 ([RSO3Na ? Na]?).
In a 100-mL round-bottom flask equipped with a stirring
bar, was added crude (?)-(12S,13R)-epoxy-cis-9-octade-
cenyl tosylate (3) (1.0 g, 2.3 mmol), followed by 60 mL of
acetone. To the resulting solution was added sodium iodide
(0.72 g, 4.8 mmol) with stirring. The flask was then fitted
with a condenser, and the mixture was refluxed with stir-
ring for 4 h. The resulting brownish solution was allowed
to cool to room temperature, after which 40 mL of water
was added to the flask. Acetone was then evaporated on a
steam bath. The aqueous solution was transferred to a 125-
mL separatory funnel. The aqueous solution was extracted
with diethyl ether (3 9 50 mL). The ethereal solution was
washed with water and brine, dried with sodium sulfate,
and stripped with a rotary evaporator to give 0.78 g of a
light-yellow product (87% yield). GC-MS analysis indi-
cated (?)-(12S,13R)-epoxy-1-iodo-cis-9-octadecene (4)
with trace amount of the starting tosylate. MS (EI) data
showed the molecular ion for (?)-(12S,13R)-epoxy-1-iodo-
cis-9-octadecene (4) at m/z 392, and a diagnostic ion at m/z
265 (M-I). A small amount of the crude 4 was purified for
characterization purposes. About 0.50 g of 4 was column
chromatographed on silica gel column (1.0% ethyl acetate/
Critical Micelle Concentration (CMC) Measurement
Determination of the CMC was performed using a Kruss
Processor Tensiometer K12 by the Wilhelmy Plate method
at room temperature. A 1% by weight solution of the
epoxyalkene sulfonate was prepared and added to deionized
water in a glass vessel equipped with a magnetic stirrer of
which automated serial dilutions were prepared ranging
from 6.11 9 10-5–0.016 mol/L for run 1 and 3.06 9 10-5
–0.008 mol/L for run 2.
Results and Discussion
´
˚
n-hexane, 45.0 g silica gel, 70–230 mesh, 60-A pore size)
to give purified 4 (0.33 g, or 63% recovery). 1H NMR
(CDCl3) d 0.95 (t, 3H, CH3), 1.05–2.00 (m, 22H, 11CH2),
2.10 (q, 2H, CH2CH=CH), 2.95 (broad, 2H, epoxide
CHCH), 3.20 (t, 2H, CH2I), 5.40–5.70 (m, 2H, CH=CH);
13C NMR (CDCl3) d 8.0 (1C, CH2I), 14.2 (1C, CH3), 22.2
(1C, CH3CH2), 26.0–33.0 (11C, CH2), 57.5 and 58.0 (2C,
epoxy CHCH), 123.0 and 132.0 (2C, CH=CH).
Synthesis of Epoxidized Linear Alkenyl Sulfonate (5)
The most important property of the synthetic approach was
preservation of the epoxy functionality, which is expected
to have a positive impact on the surfactant properties of the
desired product. Synthesis of the epoxidized alkenyl sul-
fonate 5 from VO required five reaction steps (Scheme 1)
with an overall yield of 48%. Conversion of VO to VOME
(1) was achieved with a base-catalyzed methanolysis
(transesterification) of VO, a method previously published
[3]. The yield of this reaction was 98% (crude product).
Similarly, reduction of VOME (1) to epoxy alcohol 2 was
achieved with a previously published method in a 94%
yield [3].
Sulfonation of Epoxy Iodide
To a 100-mL round-bottom flask equipped with a stirring
bar was added crude (?)-(12S,13R)-epoxy-1-iodo-cis-9-
octadecene (1.9 g, 4.8 mmol), followed by 30 mL of iso-
propyl alcohol (IPA) and 30 mL of deionized water. To the
resulting solution, while stirring, was added sodium sulfite
(0.93 g, 7.4 mmol). The flask was fitted with a condenser
and the mixture was refluxed with stirring for 12 h. The
IPA was then evaporated on a steam bath, and the resulting
aqueous solution was allowed to cool to room temperature.
The aqueous solution was washed with diethyl ether
(3 9 45 mL), followed by hexane (3 9 45 mL) and then
allowed to dry overnight. To the dried product was added
3 mL water with gentle swirling and then cooled (-5 °C).
The supernatant was pulled off with a pipet to remove
unreacted sodium sulfite and sodium iodide by-product,
and the solid was air-dried. The dried product was further
washed with 25 mL of acetone and then vacuum filtered.
The precipitate was then allowed to dry under the hood
Conversion of the primary alcohol to a tosylate (3) was
undertaken in order to create a good leaving group for the
subsequent SN2-type reaction. However, tosylation of the
epoxy alcohol (2) was not as straightforward as expected
owing to the presence of a reactive epoxy functional group,
whose preservation was key in the synthetic strategy. A
number of published synthetic methods were attempted,
including reacting 2 with p-TsCl dissolved in dry pyridine
with the mixture kept at 0 °C [16], treating 2 with sodium
hydride to form an alkoxide and adding p-TsCl to the
resulting solution; and treating 2 with sodium hydroxide
and p-TsCl in pyridine with the mixture at 0 °C [17]. In the
first case, the yield was extremely low, under 20%. Fur-
thermore, the epoxy ring opened to give the hydroxy group.
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J Am Oil Chem Soc (2009) 86:675–680
Scheme 1 Synthetic scheme of sodium (?)-(12S,13R)-epoxy-cis-9-
octadecenyl sulfonate (5) from vernonia oil. 1 is a mixture with
R=CH3(CH2)13CH2–, CH3(CH2)15CH2–, cis-9-C8H17CH=CHC7H14–,
cis,cis-9,12-C5H11CH=CHCH2CH=CHC7H14–, and cis-9-cis-12,13-
C5H11CH(O)CHCH2CH=CHC7H14– as major components. Reagents
and reaction conditions: (1) NaOCH3/MeOH, hexane, rt, 80 min; (2)
LiAlH4, hexane, rt, 2 h; (3) p-TsCl, CHCl3, pyr., 0 °C, 3 h; (4) NaI,
acetone, reflux, 4 h; (5) Na2SO3, IPA, H2O, reflux, 12 h
For the second and third cases, tosylation was not achieved
and the epoxy ring opened forming a hydroxy group, the
the phosphorous tribromide reaction, phosphoric acid,
would have potentially opened the epoxy ring: our previous
studies of the reactivity of the epoxide ring of VO have
indicated that it was susceptible to ring opening under
strong acidic conditions.
1
evidence of which was obtained with both FT-IR and H
NMR: the IR spectrum revealed the presence of a hydroxy
group at 3,350 cm-1 and 1H NMR revealed the disap-
pearance of the epoxy group at 2.9 ppm and the presence
of the hydroxy group at 3.6 ppm.
The nucleophilic substitution of the iodide with a sulfite
was fairly straightforward. It entailed dissolving sodium
sulfite in aqueous isopropyl alcohol and adding 4 while re-
fluxing. The reaction was monitored by the disappearance of
epoxy iodide using GC-MS, which also revealed the for-
mation of minor by-products that were attributed to dehy-
drohalogenation. After 12 h of refluxing, the isopropyl
alcohol was evaporated, and the resulting aqueous solution
was washed with diethyl ether, hexane, and then air-dried
under the hood to yield 5 as a white powder-like solid in order
to remove any unreacted iodide and alkene by-products.
The acetone wash was used to remove any sodium iodide
by-product. MALDI-TOF MS was used to determine the
molecular mass of the sulfonate as shown in Fig. 1 with a
sodiated molecular ion at m/z 391.0 (RSO3Na ? Na). To
further confirm the molecular mass of the (?)-(12S,13R)-
epoxy-cis-9-octadecenyl sulfonate, the MALDI sample was
spiked with 1 lL of a 5-mg KOH/mL methanol solution. The
resulting MALDI-TOF MS (Fig. 2) revealed the disappear-
ance of the sodiated ion at m/z 391.0 (RSO3Na ? Na) in
Fig. 1, and the appearance of an ion at m/z 423.0, corre-
sponding to the formation of potassiated (?)-(12S,13R)-
epoxy-cis-9-octadecenyl sulfonate, (RSO3K ? K), in the
MALDI ion source.
However, when 2 was dissolved in chloroform and
pyridine, cooled to 0 °C, and p-TsCl added over a period
of time with stirring, tosylation was achieved with a 96%
yield. Furthermore, the epoxy ring remained intact. Care
had to be exercised during workup, particularly when
extracting pyridine in the form of the water-soluble
pyridinium chloride. Addition of very concentrated hydro-
chloric acid opened the epoxy ring. However, extraction of
pyridine with 10% aqueous hydrochloric acid (5 °C) was
found to be mild enough to prevent epoxy ring opening.
After obtaining the epoxy tosylate (3), attempts were
made to obtain the epoxy alkenyl sulfonate (5), by treating
3 with sodium sulfite: a more direct way of obtaining a
sulfonate in contrast to substituting the tosylate with a
halogen—bromine or iodine—followed by nucleophilic
substitution of halogen with the sulfonate group. Contrary
to the published methods’ assertion that such a transfor-
mation was achievable [18, 19], when attempted, the
transformation was not achieved. Consequently, we trans-
formed 3 to (?)-(12S,13R)-epoxy-1-iodo-cis-9-octadecene
(4). The choice of iodination over bromination was dictated
by the fact that alkyl iodides give a characteristic peak of
the a-methylene carbon (alpha to iodo) in the 13C NMR
spectrum. Even more direct would have been the conver-
sion 2 to 1-bromo-(?)-(12S,13R)-epoxy-cis-9-octadecene
with phosphorous tribromide. However, one by-product of
To establish the surfactancy of the synthesized epoxy
sulfonate, a preliminary study of the CMC was carried out
using the Wilhelmy Plate method. A plot of Log C[M] as a
function of surface tension was constructed, Fig. 3, and the
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J Am Oil Chem Soc (2009) 86:675–680
679
Fig. 3 Plot of Log C[M] as a function of surface tension for (?)-
(12S,13R)-epoxy-cis-9-octadecenyl sulfonate in which the CMC was
determined to be 0.0010 M
Fig. 1 MALDI-TOF MS of sodiated (?)-(12S,13R)-epoxy-cis-9-
octadecenyl sulfonate represented by the molecular ion at m/z 391
(RSO3Na ? Na) and the molecular ion at m/z 369 is due to charge
transfer
In summary, this study demonstrates the ability to pro-
duce an epoxyalkenyl sulfonate, belonging to a class of
anionic surfactants, from VO without destroying the epoxy
functionality in the (?)-(12S,13R)-epoxy-cis-9-octadece-
nyl moiety of VO. The low critical micelle concentration of
the epoxy sulfonate could lead to unique applications.
Acknowledgments We thank the Howard University Graduate
School and the US Department of Education (GAANN), for their
financial support. Our appreciation also goes to the Colgate Palmolive
Company for the use of their analytical facilities.
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