Synthesis and evaluation of a series of α-hydroxy ethers derived from isopropyl oleate

Article abstract of DOI:10.1007/s11746-006-5053-7

Several fatty derivatives with bulky moieties were prepared by treatment of epoxidized isopropyl oleate with a number of alcohols in the presence of sulfuric acid catalyst to provide a series of α-hydroxy ethers in good yield. The materials were analyzed for cold flow performance through cloud point and pour point determinations. The most promising α-hydroxy ether produced in this study, with respect to both low temperature behavior and economic criteria, was isopropyl 9(10)-(2-ethylhexoxy)-10(9)-hydroxystearate, which has a cloud point of -23°C and pour point of-24°C. Copyright

Full text of DOI:10.1007/s11746-006-5053-7

πSynthesis and Evaluation of a Series of α-Hydroxy
Ethers Derived from Isopropyl Oleate
Bryan R. Moser* and Sevim Z. Erhan
Food and Industrial Oil Research, USDA, ARS, National Center for Agricultural Utilization Research, Peoria, Illinois 61604
ABSTRACT: Several fatty derivatives with bulky moieties were lization onset (TCO) temperature (17). Recent work demon-
prepared by treatment of epoxidized isopropyl oleate with a num- strated that isopropyl soyate (IPS) has similar emissions behav-
ber of alcohols in the presence of sulfuric acid catalyst to provide
a series of α-hydroxy ethers in good yield. The materials were an-
alyzed for cold flow performance through cloud point and pour
point determinations. The most promising α-hydroxy ether pro-
than 11°C lower than for MS (Table 1). With these studies in
duced in this study, with respect to both low temperature behav-
mind, we set out to produce an isopropyl fatty ester that con-
ior and economic criteria, was isopropyl 9(10)-(2-ethylhexoxy)-
ior to MS, superior low-temperature performance, and slightly
increased viscosity (18). Earlier work (19) showed the CP of
IPS to be –9°C (vs. about –2°C for MS) and TCO to be more
tains a branching moiety along the alkyl backbone as a poten-
tial CFI additive for BD fuel.
1
0(9)-hydroxystearate, which has a cloud point of –23°C and
pour point of –24°C.
Nucleophilic addition to an oxirane moiety to provide a wide
range of products is a well-established process and will not be
Paper no. J11424 in JAOCS 83, 959–963 (November 2006).
KEY WORDS: Biodiesel, cloud point, α-hydroxy ethers, isopro- reviewed here; however, the interested reader is directed else-
pyl esters, pour point.
where (20). Careful selection of the appropriate reagents will in-
troduce branching into the oxirane system. Such an approach
was undertaken in this study (Fig. 1) in which a variety of alco-
Biodiesel, defined as the monoalkyl esters of FA derived from hols in the presence of sulfuric acid catalyst was added to an oxi-
vegetable oil or animal fat, is an attractive alternative to con- rane moiety to afford a series of α-hydroxy ethers (21,22). The
ventional diesel fuel (CDF) for combustion in diesel engines. introduction of branching to the fatty epoxide may impart lower
Biodiesel (BD) has a number of fuel properties that are compa- CP and PP by affecting macrocrystalline formation at low tem-
rable with No. 2 diesel fuel (D2), including viscosity, gross heat peratures. Applied to FA esters, such materials could prove use-
of combustion, and cetane number (1–4). Blends of BD with ful as biodegradable CFI additives for BD fuel and potentially as
ultra low-sulfur D2 (ULSD2) show improved lubricity charac- lubricants in diverse applications such as hydraulic fluids, metal-
teristics over that of unblended ULSD2 (5) and reduced ex- working fluids, crankcase oils, drilling fluids, two-cycle engine
haust emissions, which include particulate matter, hydrocar- oils, wear-resistant fluids, and greases (23).
bons, sulfur dioxide, carbon monoxide, and smoke (1,4,6–11).
However, in most cases the use of BD results in an increase in
MATERIALS AND METHODS
NO emissions over that of CDF (7,8,12,13). Furthermore, an-
x
other challenge facing BD in North America is the issue of rel- Materials. Formic acid (88%) was obtained from Fisher Scien-
atively poor low-temperature performance, which may limit its tific (Pittsburgh, PA) and used without further purification. All
use during winter months (14). For example, methyl soyate other chemicals and reagents were obtained from Aldrich
(MS: BD derived from transesterification of soybean oil) has a Chemical (Milwaukee, WI) and used without further purifica-
cloud point (CP) of approximately –2°C compared with –16°C tion. Technical-grade oleic acid was found to contain, by
for D2 (15). Several approaches for improving the low-temper- GC–MS analysis, ~10% linoleic acid and a trace amount (<1%)
ature behavior of BD are under development, such as blending of other fatty materials, such as stearic acid.
with CDF, transesterification with long- or branched-chain al-
cohols, crystallization fractionation, treatment with already
TABLE 1
commercialized cold-flow improver (CFI) additives developed Crystallization Onset Temperature (TCO, °C), CP (°C), PP (°C), and
2
for CDF, and the use of synthetic CFI additives novel to BD Kinematic Viscosity (υ; mm /s @ 40°C) of Methyl and Isopropyl
a
Esters of Soybean Oil Compared with No. 2 Diesel Fuel
fuel (16).
Crystallization of any substance requires the arrangement of Material
TCOb
CPb
PPb
υc
molecules in an orderly pattern. Introduction of branching into MS
a linear, long-chain ester generally disrupts intermolecular as- IPS
5.2
–6.0
–11.9
–2
–9
–17
–3
–12
–24
4.5926
5.2649
2.8911
D2
sociations at low temperatures, which may reduce the crystal-
aCP, cloud point; PP, pour point; D2, no. 2 diesel fuel; MS, methyl soyate;
IPS, isopropyl soyate.
From Reference 19.
b
*
1
To whom correspondence should be addressed at USDA, ARS, NCAUR,
815 N University St., Peoria, IL 61604. E-mail: moserbr@ncaur.usda.gov
c
From Reference 18.
Copyright © 2006 by AOCS Press
959
JAOCS, Vol. 83, no. 11 (2006)

9
60
B.R. MOSER AND S.Z. ERHAN
1
isopropyl linoleate. No further purification was performed. H
NMR: δ 5.36 (2H, vinyl), 5.02 (COOCH(CH ) ), 2.27 (2H, α
3
2
to ester), 2.02 (4H, α to vinyl), 1.62 (2H, β to ester), ~1.3 (20H,
fatty backbone), 1.25 and 1.23 (6H, methyl protons of head
1
3
group), 0.89 (3H, protons on terminal carbon); C NMR: δ
73.43 (carbonyl C of ester), 129.97 and 129.74 (vinyl), 67.30
COOCH(CH ) ), 34.71 (α to carbonyl), 33.86 and 32.26 (α to
1
(
3
2
–
1
vinyl group), 14.11 (terminal C). FTIR: 2923 and 2853 cm
sharp CH str), 1733 (sharp carbonyl str), 1667 (olefin str),
(
2
1
466 (CH bend vib), 1374 (CH sym bend vib), 1249, 1179,
2 3
and 1108 (ester C–O str), 965 (vinyl C–H out-of-plane bend),
+
7
23 (CH rocking vib). MS (EI): m/z 324 (M ), 281 (M – iPr-
2
H).
Epoxidation of IPO. To a stirred solution of IPO (2, 10.0 g,
7.7 mmol) and formic acid (88%, 5.0 mL, 117 mmol) cooled
in an ice bath (4°C) was added slowly H O (30% in H O, 8.0
2
2
2
2
mL, 78 mmol). The reaction was then allowed to proceed at rt
with vigorous stirring (800+ rpm) until GC–MS analysis indi-
cated that 2 had been consumed (14–16 h). After the reaction
was transferred to a separatory funnel, the lower aqueous phase
was removed, and hexanes (20 mL) was added to the upper oily
phase. The organic phase was then washed with NaHCO (sat.
3
aq., 2 × 5 mL) and brine (2 × 5 mL), dried (MgSO ), filtered,
4
concentrated in vacuo, and placed for 6 h under vacuum to pro-
vide epoxidized isopropyl oleate (EIPO, 3) as a clear oil (9.36
g, 99% overall yield). GC–MS analysis indicated the presence
of ~5% isopropyl 9,10-dihydroxystearate in the sample as well.
FIG. 1. Synthesis of α-hydroxy ethers from oleic acid.
1
Esterification of oleic acid. To a solution of oleic acid (1,
00.0 g, 319 mmol) in 2-propanol (150.0 mL) in a single-neck
No further purification was performed. H NMR: δ 4.99
1
(
COOCH(CH ) ), 2.87 (2H, epoxy), 2.24 (2H, α to ester), 1.60
3 2
round-bottomed flask equipped with a magnetic stir bar was
added at room temperature (rt) H SO (conc., 0.90 mL, 5.2
(2H, β to ester), 1.48 (4H, α to epoxide), ~1.3 (20H, fatty back-
2
4
bone), 1.22 and 1.20 (6H, methyl protons of head group), 0.85
13
mol%), which was heated at reflux with stirring for 4 h. After
cooling to rt, the solvent was removed in vacuo using a rotary
evaporator and the resultant oil dissolved in hexanes (100 mL).
(
3H, protons on terminal C); C NMR: δ 173.32 (carbonyl C
of ester), 67.29 (COOCH(CH ) ), 57.21 and 57.17 (epoxide),
3
2
3
4.64 (α to ester head group), 31.83 and 31.04 (α to epoxide),
–1
After washing with NaHCO (sat. aq., 2 × 10 mL) and brine (2
3
14.07 (terminal C). FTIR: 2923 and 2853 cm (sharp CH str),
2
×
10 mL), the organic phase was dried (MgSO ), filtered, con-
4
1733 (sharp carbonyl str), 1466 (CH bend vib), 1374 (CH
2
3
centrated in vacuo, and placed under vacuum for 6 h to afford
isopropyl oleate (IPO, 2) as a clear oil (101.3 g, 98% overall
yield). GC–MS analysis indicated the product contained ~5%
sym bend vib), 1249, 1179, and 1108 (ester C–O str), 723 (CH2
rocking vib), 1145 (ether C–O–C sym str), 896 (C–C asym ring
str), 824 (“12 micron band;” Ref. 24) and a small peak at 3500
TABLE 2
Reaction Time (h), Yield (% ), CP (°C), and PP (°C) of α-Hydroxy Ethers Derived
from Epoxidized Isopropyl Oleate
R
Ether
Reaction
time
a
CPb
PPb
% Yield
Ethyl, 4
24
72
3, ∆
72
144
96
168
216
240
240
84
81
82
84
84
85
82
84
85
84
–2
–5
–5
–21
–21
–11
–23
–23
–23
–23
–8
–11
–12
–22
–23
–14
–23
–23
–24
–24
Propyl, 5
Isopropyl, 6
Butyl, 7
Isobutyl, 8
2
-Methoxyethyl, 9
Hexyl, 10
Octyl, 11
2
-Ethylhexyl, 12
Decyl, 13
a
Reactions are performed at room temperature unless otherwise noted; ∆ denotes reflux.
Means (n = 3), SD ±2°C.
b
JAOCS, Vol. 83, no. 11 (2006)

α-HYDROXY ETHERS FROM ISOPROPYL OLEATE
961
FIG. 2. FT-IR spectra of isopropyl oleate (IPO) (2), epoxidized IPO (EIPO) (3), and isopropyl
–
1
9
(10)-ethoxy-10(9)-hydroxystearate (4). Note: absorbance at about 2400 cm on 3 and 4 is
due to CO2.
(
(
(
OH stretch) indicative 9,10-dihydroxy by-product in small reaction time and percent yield information for 4–13. See Fig-
~5%) quantity. MS (EI): m/z 340 (M ), 323 (M – 16 – H), 264 ures 2 and 3 for FTIR and H NMR data of ethyl ether 4. All
+
1
M – iPr – 16 – H).
Ring-opening of epoxide. To a stirred solution of 1.0 M
other ethers (5–13) are similar to 4.
Characterization. H and 13C NMR spectra were recorded
1
EIPO (3, 1.0 g, 2.79 mmol) in an alcohol (2.8 mL) was added using a Bruker AV-500 spectrometer (Rheinstetten, Germany)
H SO (conc., 10.0 mol%) and stirring continued at rt until operating at a frequency of 500.13 and 125.77 MHz, respec-
2
4
GC–MS analysis indicated that 3 was consumed (24 to 240 h). tively, using a 5-mm broadband inverse Z-gradient probe in
Hexanes (5 mL) was then added, and the solution was washed CDCl (Cambridge Isotope Laboratories, Andover, MA) as
3
with NaHCO (sat. aq., 1 × 0.5 mL) and brine (2 × 1 mL), dried solvent. FTIR spectra were recorded on a Thermo Nicolet
3
(
MgSO ), filtered, concentrated in vacuo, and placed for 6 h Nexus 470 FTIR system (Madison, WI) with a Smart ARK ac-
4
under vacuum to yield α-hydroxy ethers 4–13. See Table 2 for cessory containing a 45 ZeSe trough in a scanning range of
1
FIG. 3. H NMR Spectrum of isopropyl 9-ethoxy-10-hydroxystearate in CDCl .
3
JAOCS, Vol. 83, no. 11 (2006)

9
62
B.R. MOSER AND S.Z. ERHAN
rt. At elevated temperatures (40°C to reflux temperature of al-
6
50–4000 cm–1 for 32 scans at a spectral resolution of 4 cm–1.
Reactions were monitored by GC–MS every 8 or 24 h using
cohol), ring opening with secondary alcohols would proceed
quickly (3–4 h), but unwanted transesterification would again
occur. Of course, in the case of 2-propanol, transesterification
is irrelevant because 3 is already an isopropyl ester. Further-
more, branched primary alcohols (such as isobutanol and 2-eth-
ylhexanol) react more slowly than their linear counterparts (1-
butanol and 1-octanol, respectively). For instance, reaction of
a Hewlett-Packard (Loveland, CO) 5870 series II GC system
equipped with a 6890 series injector and a 5970 Series MSD in
EI mode. A Supelco SPB-35 (30 m × 320 mm) column was
used with a helium flow rate of 0.9 mL/min. The temperature
program started at 150°C and increased to 290°C at 10°C/min,
which was followed by a hold time of 10 min. The inlet and de-
tector temperatures were set to 250 and 280°C, respectively.
The injection volume was 1 mL with a split ratio of 70:1.
Low-temperature performance. CP and PP determinations
were made in agreement with ASTM D 5773 (25) and ASTM
D 5949 (26) using a Phase Technology Analyzer Model PSA-
1
-butanol with 3 to provide 7 (Table 2) was complete in 72 h;
however, isobutanol afforded 8 in a comparatively sluggish 144
h. Additionally, as the chain length of the alcohol reagent was
increased, a corresponding decrease in reactivity (increase in
reaction time) was observed. For example, 10 was formed from
1
-hexanol in 168 h, which is of course significantly slower than
the aforementioned butyl ether (7) produced from 1-butanol
72 h). Lastly, no effort was made to distinguish the regiochem-
7
0S (Phase Technology, Richmond, British Columbia,
Canada). Each sample was run in triplicate, and an average
value is reported. CP and PP data are rounded to the nearest
whole degree.
(
istry (9-alkoxy-10-hydroxystearate vs. the equally likely 10-
alkoxy-9-hydroxystearate regioisomer) of the α-hydroxy ethers
formed (4–13), nor their stereochemistry (R or S at carbons 9
and 10), which is chiefly due to both the chromatographic
means required for such an analysis and more importantly, the
economics involved at potentially larger scales. If such adducts
are to be eventually used as commercial CFI additives for BD
fuel, then production costs relating to synthetic complexity and
purification requirements are of paramount importance. There-
fore, the α-hydroxy ethers prepared in this study (4–13) were
tested without further purification.
RESULTS AND DISCUSSION
Synthesis. An earlier synthesis of α-hydroxy ethers (22) de-
scribes treatment of epoxidized oleic acid with an alcohol and
acid catalyst to yield products analogous to 4–13. However, in
the earlier study the ether moiety (R′, see Fig. 1) and the ester
head group (R) are identical (R = R′ = Me, Et, Pr), which is un-
avoidable with the synthetic scheme employed by Gast and col-
leagues (22). The current work describes the synthesis of a se-
ries of novel α-hydroxy ethers where R ≠ R′, thereby impart-
ing much greater synthetic flexibility for the production of a
large number of ether derivatives with the same head group.
Unfortunately, no mention of the low-temperature performance
Low-temperature behavior. The α-hydroxy ethers (4–13)
described above were screened for low-temperature behavior
through determination of both CP and PP. EIPO (3), the pre-
cursor for the synthesis of 4–13, was found to have a CP of
–
6°C and PP of –7°C, which is an improvement over MS but
(
CP or PP) of the α-hydroxy ethers produced in the earlier
not as good as IPS (Table 1). Among the ethers, ethyl ether 4
was the only derivative discovered to be less resistant to low
temperatures than 3 (Table 2). The three-carbon ethers, propyl
study is made. Such an analysis would have made for an inter-
esting comparison with the compounds produced in this study.
After the straightforward Fischer esterification (27) of oleic
acid (1) to IPO (2), a modified epoxidation protocol (28) origi-
nally developed by Swern (29) was used to provide EIPO (3).
The reaction was monitored by GC–MS analysis and termi-
nated when >95% of 2 was consumed (14–15 h). Further analy-
sis by GC–MS of the final product indicated the presence of a
small amount (~5%) of isopropyl 9,10-dihydroxystearate,
demonstrating the importance of monitoring the reaction
closely to avoid unwanted over-reaction.
(
5) and isopropyl (6), were comparable to 3 whereas the re-
maining ethers of longer chain length (7–13) were found to be
far superior to 3. For instance, decyl ether 13 has a CP of –23°C
and a PP of –24°C. Not surprisingly, as the chain length of the
alcohol increases, a corresponding improvement in low-tem-
perature behavior is observed. This is due to the greater ability
of the longer-chain ethers to disrupt macrocrystalline forma-
tion more effectively at reduced temperatures. Another obser-
vation of note is the positive effect of branching within the al-
cohol reagent on the low-temperature performance of the re-
sultant α-hydroxy ether. For instance, butyl ether 7 has CP and
PP values of –21 and –22°C, respectively, whereas isobutyl
ether 8 has slightly improved values of –21 and —23°C, re-
Following a protocol set forth by Aggarwal et al. (21) and
Gast et al. (22), ring opening of the oxirane moiety to afford a
series of α-hydroxy ethers (Fig. 1) was accomplished by treat-
ment of a 1.0 M solution of 3 with a number of alcohols in the
presence of acid catalyst (H SO ). The series of reactions was
2
4
spectively. A similar trend was also observed for both the C (5
monitored by GC–MS until 3 was consumed to afford α-hy-
droxy ethers 4–13 (Table 2) in moderate yield (81–85%).
A number of observations were made regarding the reactiv-
ity of alcohols with 3. For instance, the use of methanol as
reagent resulted in transesterification to provide methyl 9(10)-
methoxy-10(9)-hydroxystearate at rt (already reported in Ref.
3
and 6) and C ethers [octyl (11) and 2-ethylhexyl (12)]. Fur-
8
thermore, a dramatic improvement in the cold flow properties
of α-hydroxy ethers is observed when the ether group contains
4
or more carbons (7,8,10–13) vs. ethers with 3 or fewer car-
bons (4–6,9). In conclusion, from both a cold flow performance
and economic standpoint, 2-ethylhexyl ether 12 is the most de-
sirable derivative because 2-ethylhexanol is the cheapest of the
2
2) and none of the desired isopropyl ester. Conversely, sec-
ondary alcohols (2-propanol and 2-butanol) were unreactive at
JAOCS, Vol. 83, no. 11 (2006)

α-HYDROXY ETHERS FROM ISOPROPYL OLEATE
963
C and above alcohols used in this study. Thus, future work will
gines (Paper No. 930936), Society of Automotive Engineers,
Warrendale, PA, 1993, pp. 211–223.
4
entail evaluating 12 and other promising α-hydroxy ethers at
additive levels in MS. Lastly, additional physical property ex-
amination (such as thermal and oxidative stability, viscosity,
1
1. Mittelbach, M., P. Tritthart, and H. Junek, Diesel Fuel Derived
from Vegetable Oils, II: Emission Tests Using Rape Oil Methyl
Ester, Energy Agric. 4:207–215 (1985).
lubricity, surfactant behavior, etc.) may provide interesting in- 12. Chang, D.Y.Z., J.H. Van Gerpen, I. Lee, L.A. Johnson, E.G.
sight into the utility of these derivatives.
Hammond, and S.J. Marley, Fuel Properties and Emissions of
Soybean Oil Esters as Diesel Fuel, J. Am. Oil Chem. Soc.
7
3:1549–1555 (1996).
ACKNOWLEDGMENTS
13. Ali, Y., and M.A. Hanna, Alternative Diesel Fuels from Veg-
etable Oils, Bioresource Technol. 50:153–163 (1994).
The authors gratefully acknowledge Dr. Karl Vermillion for collec-
tion of the NMR spectra.
1
4. Dunn, R.O., Thermal Analysis of Alternative Diesel Fuels from
Vegetable Oils, J. Am. Oil Chem. Soc. 76:109–115 (1999).
5. Dunn, R.O., and M.O. Bagby, Low-Temperature Properties of
Triglyceride-Based Diesel Fuels: Transesterified Methyl Esters
and Petroleum Middle Distillate/Ester Blends, J. Am. Oil Chem.
Soc. 72:895–904 (1995).
1
REFERENCES
1
. Masjuki, H.J., A.M. Zaki, and S.M. Sapuan, Methyl Ester of
Palm Oil as an Alternative Diesel Fuel, in Fuels for Automotive
and Industrial Diesel Engines: Proceedings of the 2nd Institute
of Mechanical Engineering Seminar, Institute of Mechanical
Engineering, London, 1993, pp. 129–137.
1
6. Knothe, G., J. Van Gerpen, and J., Krahl (eds.), The Biodiesel
Handbook, AOCS Press, Champaign, IL, 2005.
1
7. Hernqvist, L., Crystal Structures of Fats and Fatty Acids, in
Crystallization and Polymorphism of Fats and Fatty Acids,
edited by N. Garti and K. Sato, Marcel Dekker, Inc., New York,
2
3
4
5
. Peterson, C.L., R.A. Korus, P.G. Mora, and J.P. Madsen, Fumi-
gation with Propane and Transesterification Effects on Injector
Coking with Vegetable Oils, Trans. ASAE 30:28–35 (1987).
. Schwab, A.W., M.O. Bagby, and B. Freedman, Preparation and
Properties of Diesel Fuels from Vegetable Oils, Fuel
1
988, p. 130.
1
8. Wang, P.S., M.E. Tat, and J.H. Van Gerpen, The Production of
Fatty Acid Isopropyl Esters and Their Use as a Diesel Engine
Fuel, J. Am. Oil Chem. Soc. 82:845–849 (2005).
1
9. Lee, I., L.A. Johnson, and E. Hammond, Use of Branched-Chain
Esters to Reduce the Crystallization Temperature of Biodiesel,
J. Am. Oil Chem. Soc. 72:1155–1160 (1995).
6
6:1372–1378 (1987).
. Clark, S.J., L. Wagner, M.D. Schrock, and P.G. Piennaar,
Methyl and Ethyl Soybean Esters as Renewable Fuels for Diesel
Engines, J. Am. Oil Chem. Soc. 61:1632–1638 (1984).
. Van Gerpen, J.H., S. Soylu, and M.E. Tat, Evaluation of the Lu-
bricity of Soybean Oil-Based Additives in Diesel Fuel, Proceed-
ings, Annual International Meeting of the ASAE, American So-
ciety of Agricultural Engineers, St. Joseph, MI, 1996, paper no.
2
2
0. Taylor, S.K., Reactions of Epoxides with Ester, Ketone, and
Amide Enolates, Tetrahedron 56:1149–1163 (2000).
1. Aggarwal, V.K., I. Bae, and H.Y. Lee, Application of Sulfur
Ylide Mediated Epoxidations in the Asymmetric Synthesis of β-
Hydroxy-δ-lactones. Synthesis of a Mevinic Acid Analogue and
(+)-Prelactone B, Tetrahedron 60:9725–9733 (2004).
9
96134.
2
2
2
2
2. Gast, L.E., C.B. Croston, W.J. Schneider, and H.M. Teeter, Syn-
thetic Lubricants from Polyhydroxystearic Acids, Ind. Eng.
Chem. 46:2205–2208 (1954).
3. Sharma, B.K., A. Adhvaryu, Z. Liu, and S.Z. Erhan, Chemical
Modification of Vegetable Oils for Lubricant Applications, J.
Am. Oil Chem. Soc. 83:129–136 (2006).
4. Silverstein, R.M., and F.X. Webster, Spectrometric Identifica-
tion of Organic Compounds, 6th Edition, John Wiley & Sons,
New York, 1998, p. 92.
5. ATSM D 5773, Standard Test Method for Cloud Point of Petro-
leum Products (Constant Cooling Rate Method), in Annual Book
of ASTM Standards, American Society for Testing and Materi-
als, Philadelphia, PA, Vol. 05.03, 2003.
6
7
. Sheehan, J., V. Camobreco, J. Duffield, M. Graboski, and H.
Shapouri, in Final Report, Life Cycle Inventory of Biodiesel and
Petroleum Diesel for Use in an Urban Bus, NREL-SR-580-
2
1
4089, National Renewable Energy Laboratory, Golden, CO,
998, pp. 206–261.
. Knothe, G., R.O. Dunn, and M.O. Bagby, Biodiesel: The Use of
Vegetable Oils and Their Derivatives as Alternative Diesel
Fuels, in Fuels and Chemicals from Biomass, American Chemi-
cal Society Symposium Series No. 666, edited by B.C. Saha and
J. Woodward, American Chemical Society, Washington, DC,
1
997, pp. 172–208.
8
. Krahl, J., A. Munack, M. Bahadir, L. Schumacher, and N. Elser,
Survey About Biodiesel Exhaust Emissions and Their Environ-
mental Benefits, in Proceedings, Third Liquid Fuel Conference:
Liquid Fuel and Industrial Products from Renewable Resources,
edited by J.S. Cundiff, E.E. Gavett, C. Hansen, C. Peterson,
M.A. Sanderson, H. Shapouri, and D.L. VanDyne, American
Society of Agricultural Engineers, St. Joseph, MI, 1996, pp.
2
6. ASTM D 5949, Standard Test Method for Pour Point of Petro-
leum Products (Automatic Pressure Pulsing Method), in Annual
Book of ASTM Standards, American Society for Testing and
Materials, Philadelphia, PA, Vol. 05.03, 2003.
2
7. Fischer, E., and A. Speier, Ber. Dtsch. Chem. Ges. 28:3252–
3
255 (1895).
1
36–148.
2
8. Doll, K.M., and S.Z. Erhan, Synthesis of Carbonated Fatty
Methyl Esters Using Supercritical Carbon Dioxide, J. Agric.
Food Chem. 53:9608–9614 (2005).
9
. Krahl, J., J. Bunger, H.–E. Jeberien, K. Prieger, C. Schutt, A.
Munack, and M. Bahadir, Analysis of Biodiesel Exhaust Emis-
sions and Determination of Environmental and Health Effects,
in Ibid., pp. 149–165.
2
9. Findley, T.W., D. Swern, and J.T. Scanlan, Epoxidation of Un-
saturated Fatty Materials with Peracetic Acid in Glacial Acetic
Acid Solution, J. Am. Chem. Soc. 67:412–414 (1945).
1
0. Scholl, K.W., and S.C. Sorenson, Combustion of Soybean Oil
Methyl Ester in a Direct Injection Diesel Engine, in Society of
Automotive Engineers Special Publication SP-958: New Devel-
opments in Alternative Fuels and Gasolines for SI and CI En-
[Received June 15, 2006; accepted August 16, 2006]
JAOCS, Vol. 83, no. 11 (2006)