Synthesis and structural analysis of branched-chain derivatives of methyl oleate

Article abstract of DOI:10.1007/s11746-008-1235-9

As part of a project to develop new value-added industrial applications for cottonseed oil (such as biodiesel, fuel additives, and lubricants), studies were conducted on the synthetic conversion of oleic acid to branched-chain fatty acid esters. In these studies, methyl oleate was brominated in the allylic position and subsequently treated with organocuprate reagents to produce novel branched-chain derivatives (methyl, n-butyl, phenyl). Original reaction conditions afforded only the branched methyl derivatives as major products. Modification of reaction conditions (lower temperature, less organocuprate reagent) afforded predominantly the desired n-butyl and phenyl derivatives and minimized products resulting from attack on the ester functionality. Details of the syntheses, characterization (especially by NMR), and the properties of the products (with emphasis on low-temperature properties) are discussed.

Full text of DOI:10.1007/s11746-008-1235-9

J Am Oil Chem Soc (2008) 85:647–653
DOI 10.1007/s11746-008-1235-9
ORIGINAL PAPER
Synthesis and Structural Analysis of Branched-Chain
Derivatives of Methyl Oleate
Oliver D. Dailey Jr Æ Nicolette T. Prevost Æ
Gary D. Strahan
Received: 30 July 2007 / Revised: 12 March 2008 / Accepted: 13 March 2008 / Published online: 6 May 2008
Ó AOCS 2008
Abstract As part of a project to develop new value-added
industrial applications for cottonseed oil (such as biodiesel,
fuel additives, and lubricants), studies were conducted on
the synthetic conversion of oleic acid to branched-chain
fatty acid esters. In these studies, methyl oleate was bro-
minated in the allylic position and subsequently treated
with organocuprate reagents to produce novel branched-
chain derivatives (methyl, n-butyl, phenyl). Original reac-
tion conditions afforded only the branched methyl
derivatives as major products. Modification of reaction
conditions (lower temperature, less organocuprate reagent)
afforded predominantly the desired n-butyl and phenyl
derivatives and minimized products resulting from attack
on the ester functionality. Details of the syntheses, char-
acterization (especially by NMR), and the properties of the
products (with emphasis on low-temperature properties)
are discussed.
the United States, soybean oil has received the most
interest. However, neat vegetable oils pose a problem
impairing their widespread use as biodiesel in that they
cause engine deposits [1]. In an attempt to overcome this
problem, biodiesel is typically obtained by the conver-
sion of vegetable oils or animal fats to simple monoalkyl
esters of fatty acids. These products, usually methyl or
ethyl esters, can be used as alternative fuels or extenders
in diesel engines. However, the relatively poor low-
temperature properties (freezing in cold climates) of
these biodiesel fuels present an obstacle to their contin-
ued development and commercialization [2, 3]. The
conversion of vegetable oils and animal fats into esters
of branched-chain alcohols, such as isopropyl or 2-butyl,
has resulted in improved low-temperature properties, as
demonstrated by their reduced crystallization onset tem-
peratures [3–5].
Simple monoalkyl esters or modified oils containing
branched-chain fatty acids could have improved or
superior low-temperature properties. Oleic acid and lin-
oleic acid are the most abundant fatty acids of many
vegetable oils, including cottonseed oil. As part of a
project to develop new value-added industrial applica-
tions for cottonseed oil (such as biodiesel, fuel additives,
and lubricants), studies were conducted on the synthetic
conversion of oleic acid to branched-chain fatty acid
esters. In these studies, the model compound methyl
oleate (1) was brominated in the allylic position
(Scheme 1) and subsequently treated with cuprate
reagents to produce branched-chain derivatives. In pre-
viously reported research [6], reaction of the allylic
bromides 2 with lithium dimethylcuprate using condi-
tions (fivefold excess of cuprate reagent, quenching of
the reaction at 0 °C) described in the literature [7, 8]
produced the expected desired products (3, Scheme 1).
Keywords Allylic bromides ꢀ Branched-chain fatty
acids ꢀ DSC ꢀ Low-temperature properties ꢀ NMR ꢀ
Organocuprate reagents
Introduction
The use of vegetable oils as alternative diesel fuels
(biodiesel) has been investigated for over a century. In
O. D. Dailey Jr (&) ꢀ N. T. Prevost
USDA, ARS, Southern Regional Research Center,
1100 Robert E. Lee Blvd, New Orleans, LA 70124, USA
e-mail: Oliver.Dailey@ars.usda.gov
G. D. Strahan
USDA, ARS, Eastern Regional Research Center,
600 E. Mermaid Lane, Wyndmoor, PA 19038, USA
123

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J Am Oil Chem Soc (2008) 85:647–653
OCH3
NBS, benzoyl peroxide
Methyl oleate, 1
or AIBN, CCl4, reflux
O
R'
OCH3
+
2a R' = Br, R" = H
O
R"
2b R' = H, R" = Br
OCH3
+
2c
O
Br
Br
OCH3
2d
O
O
R2CuLi
Et2O
OCH3
2a
3a R = CH3
4a R = nBu
5a R = Ph
R
R
O
R2CuLi
Et2O
OCH3
2b
3b R = CH3
4b R = nBu
5b R = Ph
R
O
R2CuLi
Et2O
OCH3
2c
2d
3c R = CH3
4c R = nBu
5c R = Ph
O
R2CuLi
Et2O
OCH3
3d R = CH3
4d R = nBu
5d R = Ph
R
Scheme 1 Synthetic route to branched-chain derivatives of methyl oleate
However, reaction of the allylic bromides with a fivefold
excess of lithium di-n-butylcuprate and quenching at
-20 °C afforded no expected branched chain derivatives
but primarily products resulting from attack at the ester
functionality (Scheme 2). In this paper, we describe the
modification of reaction conditions (less organocuprate
reagent, lower temperatures) which provide the desired
intact branched-chain derivatives of methyl oleate.
Details of the syntheses, characterization, and properties
of the products are discussed.
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J Am Oil Chem Soc (2008) 85:647–653
649
Scheme 2 Synthesis of the
tertiary alcohols 6. Structures of
two of the four isomeric
nBu
OH
fivefold excess
(nBu)2CuLi
nBu
products are given
2a
Et2O
6a
nBu
quenching at -20 deg C
fivefold excess
(nBu)2CuLi
OH
nBu
2b
Et2O
quenching at -20 deg C
6b
nBu
nBu
Experimental Procedures
indication. However, the percentages should be fairly
realistic since the compounds analyzed are generally clo-
sely related structurally.
Materials
Methyl oleate (99%), N-bromosuccinimide (NBS, 99%),
benzoyl peroxide (97%), n-butyllithium (2.5 M in hex-
anes), t-butyllithium (1.7 M in pentane), phenyllithium
(1.8 M in di-n-butyl ether), silica gel (Merck, grade 9385,
230–400 mesh) and diethyl ether (anhydrous, 99%+, ACS
reagent) were purchased from Aldrich Chemical Company
(Milwaukee, WI, USA). Cuprous iodide (98%) was pur-
chased from Alfa-Aesar (Ward Hill, MA, USA). Calcium
hydride (97%+) was purchased from Fluka (Milwaukee,
WI, USA). Diethyl ether was distilled from calcium
hydride and stored over Type 4A molecular sieves under a
nitrogen atmosphere.
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) was performed
using a TA Instruments (New Castle, DE, USA) DSC Q100
thermal analytical device. For methyl oleate, the experi-
ment consisted of heating the samples (6 mg) from -100
to +40 °C at a rate of 10 °C/min followed by cooling from
+40 to -100 °C at the same rate. The cycle was then
repeated, and the thermal transitions recorded. For the
methyl (3), n-butyl (4), and phenyl derivatives (5) the
temperature range was -125 to +30 °C. The second
cooling scan was used to find the recrystallization tem-
perature, Tc. The second heating scan was used to find the
melting temperature, Tm, and the onset and the midpoint of
the glass transition temperature, Tg. The second run is
considered more reliable, since the first run results in a
more uniform sample.
Gas Chromatography/Mass Spectroscopy
A 1 lL aliquot of the sample was injected into a split/
splitless injector (300 °C) on an Agilent 6890 gas chro-
matograph (Palo Alto, CA, USA). The initial column
pressure was held at 25 psi and a constant flow rate of
1.2 mL/min was maintained through the column using
electronic pressure control (EPC). The oven temperature
was held at 50 °C for 1 min, and then raised at a rate of
3 °C/min to 80 °C; the rate was changed to 10 °C/min and
the oven temperature raised to 340 °C and held for 18 min
for a total run time of 55 min. The GC was equipped with
a 0.25 mm ID 9 30 m capillary column coated with a
0.5 lm film of 5% diphenyl/95% dimethylsiloxane
(DB-5MS, J&W Scientific, Folsom, CA, USA). The
effluent from the column was analyzed by an Agilent 5973
MSD employing electron ionization and operated in scan
mode in the m/z range 40–550. Initial identification of
known compounds was made by comparison with the
seventh edition of the Wiley Mass Spectral Library. Per-
centages of components of crude products based on GC/
MS are not meant to be definitive; they are used only as an
Nuclear Magnetic Resonance Spectroscopy (NMR)
Solution-state NMR spectra were recorded at 9.4 T on a
Varian (Palo Alto, CA, USA) Inova NMR spectrometer,
using a 5 mm broadband probe and operating at 25 °C. The
1H (proton) spectra at 400 MHz had a sweep-width of
6,000 Hz, were acquired with a 90° pulse angle and a 2.5 s
relaxation delay, and were referenced to internal tetra-
methylsilane (TMS). The 13C spectra at 100 MHz had a
sweep-width of 30,000 Hz for 13C, were acquired with a
45° pulse angle and a 2 s relaxation delay, and were ref-
erenced to the CDCl3 peak, 77.05 ppm from TMS. For
compounds 4 and 5, a fully edited distortionless enhance-
ment polarization transfer (DEPT) experiment was run
using the standard flip angles of 45°, 90° and 135°, fol-
lowed by mathematical manipulation to generate the CH,
CH2 and CH3 spectra. Proton signals for all compounds
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J Am Oil Chem Soc (2008) 85:647–653
were assigned by proton spin-decoupling experiments,
in hexanes) to 2.63 g (13.8 mmol) of cuprous iodide stirred
in 50 mL of dry ether for 0.5 h under nitrogen at -40 °C.
The resulting black solution was stirred at -40 °C for
20 min and cooled to -78 °C over 30 min. To the solution
was added 2.91 g (ca. 7.74 mmol) of allylic bromides (2)
in 30 mL of ether. The solution was stirred at -78 °C for
2 h and then the reaction was quenched with 10 mL of
methanol added dropwise. Following work-up, 2.84 g of
crude product was isolated as a colorless liquid (theoretical
yield: 2.73 g).
gradient-enhanced COSY and TOCSY (50 ls mixing
time). All homonuclear 2-D experiments used H spectral
1
widths of 8,000 Hz, and were acquired with 16 transients, a
2 s relaxation time, and either 400 or 512 indirectly
detected points. Gradient-enhanced versions of hetero-
nuclear multiple quantum coherence (HMQC, phase-
insensitive) and heteronuclear multiple bond correlation
experiments (HMBC) (8 Hz) were performed to assign the
1
13C signals. These heteronuclear 2-D experiments had H
spectral widths of 8,000 Hz and 13C spectral widths of
25,000 Hz, and were acquired with 16 directly detected
transients, a 2 s relaxation time, and 300–400 indirectly
detected points.
Flash chromatography (first column: silica gel, 2% ethyl
acetate/petroleum ether eluant; second column: silica gel, 1%
ethyl ether/petroleum ether) [9] provided the analytical sam-
ple(16.0%yield):MS(EI):m/z(%) = 352(53), 321(45), 310
(23), 295 (36), 263 (39), 211 (43), 210 (51), 153 (57), 152 (48).
151 (57), 143 (55), 139 (54), 125 (72), 111 (76), 97 (88),
83 (91), 69 (95), 55 (100), 41 (91); 1H NMR (CDCl3) d 0.87
(t, 3, side-chain CH3), 0.88 (t, 3, terminal CH3), 1.60 (m, 2,
CH2–CH2CO2CH3), 1.62 (m, CH2–CH–nBu), 1.83 (m, 1,
CH2CH=CHCH–nBu), 1.96 (q, 2, CH2CH=CHCH–nBu),
2.31 (t, 2, CH2CO2CH3), 1.0–1.4 (m, 24, remaining 12 CH2),
3.66 (s, 3, OCH3), 5.08 (m, 1, CH2CH=CHCH–nBu), and
5.28 (m, 1, CH2CH=CHCH–nBu); 13C NMR (CDCl3) d,
14.16 (terminal CH3 and branch-chain CH3), 22.72, 22.86,
25.01 (CH2–CH2CO2CH3), 27.13, 27.25, 27.32, 28.72, 28.92,
29.04, 29.09, 29.14, 29.22, 29.31, 29.40, 29.58, 29.61,
29.69, 29.77, 29.84, 31.96, 32.52, 32.58, 32.62, 34.15
(CH2CO2CH3), [35.33, 35.54, 35.59, 35.61] (CH2–CH–nBu),
42.81 (CH2CH=CHCH–nBu), 51.44 (OCH3), [129.78, 129.89,
130.09, 130.14] (CH2CH=CHCH–nBu), [135.02, 135.08,
135.25, 135.33] (CH2CH=CHCH–nBu), [174.34, 174.36]
(C=O).
Allylic Bromination of Methyl Oleate
A solution of methyl oleate (5.26 g, 17.7 mmol), NBS
(3.57 g, 20.1 mmol), and benzoyl peroxide (95.5 mg,
0.41 mmol) in 50 mL of CCl4 was heated at reflux under
nitrogen for 2 h. After cooling, the precipitate was filtered
and the solvent removed in vacuo, giving 6.53 g of allylic
bromides 2 (Scheme 1). This material, owing to its insta-
bility, was used in subsequent reactions without further
purification.
Reaction of Allylic Bromides with Lithium
Dialkylcuprate Reagents
General Procedure
A twofold excess of lithium di-n-butylcuprate, lithium di-t-
butyllithium or lithium diphenylcuprate was prepared at
-40 to -50 °C, the allylic bromides were added at
-78 °C, and the reaction mixture was stirred for 2–3 h.
The reaction was quenched at -78 °C by the dropwise
addition of methanol, with the temperature maintained at
-50 °C or below during the addition. The reaction mixture
was allowed to warm to room temperature overnight. The
precipitate was removed by filtration and the filtrate con-
taining the organic product was dissolved in ethyl ether
(50 mL). The ether solution was washed with saturated
ammonium chloride solution (pH 8) (2 9 50 mL). Com-
bined aqueous layers were extracted with ether (50 mL);
combined ether layers were washed with deionized water
(100 mL) and brine (100 mL) and dried over MgSO4.
Solvent was removed in vacuo and the product was dried to
a constant weight at ca. 1 torr.
Preparation of Phenyl Derivatives 5
A similar procedure was followed for the reaction of the
allylic bromides (1.54 g, 4.10 mmol) with a twofold excess
of lithium diphenylcuprate, affording 1.86 g of crude
product as a pale yellow liquid. Correcting for the presence
of biphenyl, GC/MS analysis indicated that the crude
product consisted of 64.1% 5. Flash chromatography (first
column: silica gel, 3% ethyl acetate/hexanes eluant; second
column: silica gel, 3% ethyl ether/hexanes) afforded the
analytical sample (26.2% yield): MS (EI): m/z (%) = 372
(46), 341 (21), 273 (21), 259 (41), 241 (25), 229 (59), 227
(44), 215 (39), 209 (42), 145 (34), 143 (44), 131 (71), 130
(47), 129 (71), 128 (47), 117 (100), 115 (60), 91(89), 69
1
(37), 55 (52), 43 (52), 41 (55); H NMR (CDCl3) d 0.87
(t, 3, CH3), 1.60 (m, 2, CH2–CH2CO2CH3), 1.64 (m, 2,
CH2CHPh), 1.98 (q, 2, CH2CH=CHCHPh), 2.27 (t, 2,
CH2CO2CH3), 1.0–1.4 (m, 18, remaining 9 CH2), 3.16
(m, 1, CH2CH=CHCHPh), 3.65 (s, 3, OCH3), 5.42 (m, 1,
CH2CH=CHCHPh), 5.52 (m, 1, CH2CH=CHCHPh), 7.15
Preparation of n-Butyl Derivatives 4
Lithium di-n-butylcuprate was prepared in situ by the
addition of 10.8 mL (27.0 mmol) of n-butyllithium (2.5 M
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J Am Oil Chem Soc (2008) 85:647–653
651
(m, p aromatic H), 7.16 (m, 2, o aromatic H) and 7.26 (m, 2, m
aromatic H); 13C NMR (CDCl3) d, 14.34 (CH3), 22.91, 25.17
(CH2–CH2CO2CH3), 27.66, 27.77, 27.85, 28.96, 29.20,
29.31, 29.36, 29.39, 29.44, 29.55, 29.64, 29.68, 29.74, 29.79,
29.83, 32.12, [32.70, 32.76, 32.81] (CH2CH=CHCHPh),
34.33 (CH2CO2CH3), 36.38 (CH2CHPh) 49.12 (CH2CH=
CHCHPh), 51.66 (OCH3), 126.05 (p aromatic C) 127.72
(o aromatic C), 128.54 (m aromatic C), [130.13, 130.25,
130.45, 130.48] (CH2CH=CHCHPh), [134.14, 134.20, 134.37,
134.47] (CH2CH=CHCHPh), [145.88, 145.94, 145.98]
(quaternary phenyl C), 174.54 (C=O).
branched-chain n-butyl derivatives 4. The allylic bromides
2 were added to a solution containing a twofold excess of
lithium di-n-butylcuprate at -78 °C, and the reaction was
quenched at -78 °C. GC/MS analysis of the isolated liquid
showed that the major products (63.2%) had M+ of 352,
corresponding to the expected products 4. The most
abundant secondary products (10.4%) were the tertiary
alcohols 6. Flash chromatography afforded fractions con-
taining 95.0% 4 (GC/MS analysis) as a colorless liquid.
Under the same low-temperature conditions, reaction of
lithium diphenylcuprate with the allylic bromides afforded
a product consisting of 64.1% 5 (Scheme 1) based on GC/
MS analysis. A second component with M+ 372 (2.0%)
was also observed, as well as M+ 296 (3.8 % unreacted
methyl oleate) and M+ 294 (5.9%, dienes). Flash chroma-
tography afforded fractions containing 75.6% 5 as a
colorless liquid. The remaining material exhibited M+ 294
(16.1%) and M+ 372 (8.3%).
Reaction of the allylic bromides (1.560 g, 4.16 mmol)
with a twofold excess of lithium di-t-butylcuprate provided
1.222 g of product. However, GC/MS analysis showed a
complex mixture with no evidence of desired product.
Results and Discussion
The proton NMR spectrum of phenyl derivatives 5 is
shown in Fig. 1 and is consistent with the structure as shown.
Peak assignments are given for structure 5a; analogous
assignments would be made for 5b, 5c, and 5d, taking into
account the configuration about the double bond. Since the
structures of the four isomers are so closely related, the
proton NMR spectra are expected to be indistinguishable.
Peak assignments were accomplished by proton spin-
decoupling experiments and the 2-D experiments, using the
proton NMR spectrum of methyl oleate [14] as a guide. The
signals associated with the olefinic protons were very
complex. However, analysis of a series of spin-decoupling
experiments did allow for a definitive assignment of con-
figuration about the double bond. The signal centered at
5.52 ppm (–CH2CH=CHCHPh–) was determined to be a
doublet of doublets with coupling constants of 15.2 Hz and
The conversion of oleic acid and methyl oleate to saturated
branched-chain derivatives has been reported [10]. In this
paper we report the conversion of methyl oleate to branched-
chain derivatives in which the double bond is retained. The
free-radical allylic bromination of methyl oleate [11] gives
four different isomeric products (Scheme 1). Only two of the
four structures were given in our initial report [6]. Reaction
of the allylic bromides 2 with selected lithium dialkylcuprate
reagents yields the branched-chain derivatives 3–5
(Scheme 1). The four isomeric allylic bromides give rise to
four distinct products (confirmed by 13C NMR spectral
analysis) correspondingly designated a through d. The pro-
posed structural assignments of the products are based upon
nucleophilic attack at the c-carbon via the SN20 mechanism
[12]. Finally, the assignment of the trans configuration to the
products is based on the findings of proton spin-decoupling
experiments.
Lithium dialkylcuprates were selected for the introduc-
tion of branch chains since these reagents are reported to be
unreactive toward esters under the conditions employed.
The ester n-C4H9CO2CH3 was recovered ([85%) when
treated with three equivalents of lithium dimethylcuprate at
18 °C or three equivalents of lithium di-n-butylcuprate at
-10 °C [13]. In previously reported research [6], reaction
of the allylic bromides 2 with lithium dimethylcuprate
using conditions (fivefold excess of cuprate reagent,
quenching of reaction at 0 °C) described in the literature
[7, 8] produced the expected desired products 3. How-
ever, the tertiary alcohols 6 (Scheme 2) were the major
products obtained in the reaction of 2 with lithium di-
n-butylcuprate, and the expected products 4 (Scheme 1)
were not observed.
Fig. 1 Proton NMR spectrum of phenyl derivatives 5. Assignments
of peaks to the corresponding protons are made in the structural
diagram of isomer 5a
Reaction conditions were modified (lower temperature,
less organocuprate reagent) in order to obtain the desired
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J Am Oil Chem Soc (2008) 85:647–653
approximately 7.5 Hz. Analysis of the signal centered at
5.42 ppm (–CH2CH=CHCHPh–) yielded coupling con-
stants of 15.2 Hz and approximately 6.9 Hz. The signal
centered at 1.98 ppm (–CH2CH=CHCHPh–) appears to be a
quartet but actually consists of two overlapping triplets or a
triplet of doublets, with J = 6.9 Hz. The signal centered at
3.16 ppm (–CH2CH=CHCHPh–) also appears to be a
quartet but actually consists of two overlapping triplets, with
J = 7.5 Hz. These splitting patterns are consistent with the
isomeric structures 5a–d, in which 15.2 Hz corresponds to
the coupling of the olefinic protons, and 7.5 and 6.9 Hz are
the couplings of each olefinic proton and adjacent alkyl
proton. The coupling constant of 15.2 Hz for the olefinic
protons is definitive for the trans conformation.
Table 1 DSC properties of branched-chain derivatives of methyl
oleate
Compound(s)
R
Tc (°C)
Tm (°C)
Tg (°C)
-92.8
Methyl oleate 1
H
-45.8, -47.2
-41.8, -79.0
-85.4, -89.4
-19.5
-72.1
-81.6
3
4
5
CH3
n-Bu
Ph
Coupling constant analysis of the olefinic region of the 1H
spectrum of the n-butyl derivatives 4 also yielded J values
that indicated the trans conformation. Upon the analysis of
spin-decoupling experiments, the signal centered at
5.28 ppm (–CH2CH=CHCH–nBu–) was determined to be
four overlapping triplets (triplet of two doublets) and the
signal centered at 5.08 ppm (–CH2CH=CHCH–nBu–) was
determined to be a doublet of two doublets. The coupling
constant between the two olefinic protons was 15.1 Hz,
specifying a trans geometry. The signal centered at
1.96 ppm (–CH2CH=CHCH–nBu–) appears to be a quartet
but actually consists of two overlapping triplets or a triplet of
doublets, with J = 6.8 Hz. The signal centered at 1.83 ppm
(–CH2CH=CHCH–nBu–) was too complex for resolution
but the coupling constant with the adjacent olefinic proton
was determined to be approximately 8.4 Hz.
Fig. 2 DSC thermogram of methyl oleate. The lower scan is the
heating curve. The upper scan is the cooling curve
Analysis of the 13C NMR chemical shifts of the olefinic
carbons of the methyl derivatives 3 and alcohols 6 using
alkene shift parameters [15] had previously led to the
conclusion that these compounds were probably in the cis
conformation [6]. Similar analyses for compounds 4 and 5
would lead to similar conclusions. However, these analyses
of small changes in chemical shifts are based on empirical
generalizations and are therefore inconclusive. Instead, the
coupling constants conclusively indicate that the configu-
ration about the double bond of the branched-chain
derivatives is exclusively trans.
The 13C resonance analysis (DEPT, HMQC and HMBC)
for 4 and 5 allowed for the specific assignments made in the
‘‘Experimental Procedures’’ section. All of the remaining
carbons in the range 20–33 ppm are CH2 and cannot be
unambiguously assigned due to spectral overlap. The DEPT
spectrum analysis confirmed the assignments of all primary,
tertiary, and quaternary non-aromatic carbon atoms.
Fig. 3 DSC thermogram of n-butyl derivatives 4. The lower scan is
the heating curve. The upper scan is the cooling curve
that similar carbons have similar relaxation rates, there are
roughly equal amounts of each of the four isomers.
The results of DSC studies of branched-chain deriva-
tives 3, 4, and 5 are summarized in Table 1. The DSC
thermograms of methyl oleate and methyl derivatives 3
have been reported previously [6] but are included for
comparison of all branched-chain derivatives on the same
basis. Since a different newer instrument was used in these
As was the case with the methyl derivatives 3 and tertiary
alcohols 6, there are two sets of four distinct peaks in the
olefinic region of the 13C NMR spectra of compounds 4 and
5, providing concrete evidence of the presence of the four
isomers of each of the branched-chain derivatives. Assuming
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653
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studies, somewhat different thermograms were obtained. A
commercial sample of methyl oleate was used for com-
parison purposes (Fig. 2). In the DSC thermogram of 3,
there were two Tc maxima (-41.8 and -79.0 °C). The
latter was of the greatest magnitude and was substantially
lower than the Tc of methyl oleate. The Tm was observed at
-72.1 °C. The DSC thermogram of the branched-chain n-
butyl products 4 is shown in Fig. 3. It exhibits pronounced
Tc maxima at -85.4 and -89.4 °C and Tm = -81.6 °C.
The DSC thermogram of the branched-chain phenyl
derivatives 5 (Fig. 4) is best described by the low glass
transition temperature of -92.8 °C.
11. Ucciani E, Naudet M (1963) Sur l’halogenation en position al-
lylique des chaines grasses monoinsatutees. V. Isomerie de place
et de position des chaines mono- et dihalogenees. Bull Soc Chim
Fr 28–32
The significantly lower recrystallization temperature of
branched-chain derivatives (3 and 4) of methyl oleate
provides evidence that simple monoalkyl esters of bran-
ched-chain fatty acids could have improved or superior
low-temperature properties and may prove useful as addi-
tives to biodiesel for use at low temperatures.
12. Anderson RJ, Henrick CA, Siddall JB (1970) Stereoselective
synthesis of olefins. Reactions of dialkylcopper–lithium reagents
with allylic acetates. J Am Chem Soc 92:735–737
13. Posner GH, Whitten CE, McFarland PE (1972) Organocopper
chemistry. Halo-, cyano-, and carbonyl-substituted ketones from
the corresponding acyl chlorides and organocopper reagents. Ibid
94:5106–5108
14. The Lipid Library (2003) 1H-NMR spectroscopy of fatty acids
with non-conjugated double bonds. http://www.lipidlibrary.co.uk/
nmr/1NMRdbs/index.htm. Accessed July 2003
Acknowledgments Thanks to Steven Lloyd (SRRC) for conducting
the GC/MS studies. Mention of a trademark, proprietary product, or
vendor does not constitute a guarantee or warranty of the product by
the US Department of Agriculture and does not imply its approval to
the exclusion of other products or vendors that may also be suitable.
15. Dorman DE, Jautelat M, Roberts JD (1971) Carbon-13 nuclear
magnetic resonance spectroscopy. Quantitative correlations of the
carbonchemicalshiftsofacyclicalkenes.JOrgChem36:2757–2766
123