Synthesis and characterization of some long-chain diesters with branched or bulky moieties

Article abstract of DOI:10.1007/s11746-000-0138-x

Several novel fatty diesters with bulky moieties were synthesized by esterification of mono- or bifunctional fatty acids or with mono- or bifunctional alcohols using ρ-toluenesulfonic acid as catalyst. They were characterized by ¹H and ^13<

Full text of DOI:10.1007/s11746-000-0138-x

Synthesis and Characterization of Some Long-Chain Diesters
with Branched or Bulky Moieties
1
2
Gerhard Knothe*, Robert O. Dunn, Michael W. Shockley , and Marvin O. Bagby
ARS, USDA, NCAUR, Peoria, Illinois 61604
ABSTRACT: Several novel fatty diesters with bulky moieties
were synthesized by esterification of mono- or bifunctional fatty
A
acids or with mono- or bifunctional alcohols using p-toluene-
1
sulfonic acid as catalyst. They were characterized by H and sen as the monofunctional alcohol for the present study. So mB e
1
3
C nuclear magnetic resonance as well as positive chemical central diol and diacid moieties were selected that bear struc-
ionization (PCI) mass spectrometry. The PCI mass spectra of the
resulting diol diesters and diacid diesters are discussed and
compared. The compounds were investigated as potential addi-
tives for improving the cold flow properties of vegetable oil es-
ters used as biodiesel.
tural resemblance (e.g., neopentyl glycol and 3,3,-dimethyl
SCHEME 1
glutaric acid). Scheme 1 and Table 1 provide information on
the exact nature of the compounds studied here. The com-
pounds arising from the reaction of monoacids with diols will
be termed diol diesters and those derived from diacids with
monohydric alcohols will be termed diacid diesters in the fol-
lowing text. Besides studying the potential application of these
compounds as additives in vegetable oil-based alternative
diesel fuels, their analytical characterization, especially by
positive chemical ionization (PCI) mass spectrometry (MS)
Paper no. J9343 in JAOCS 77, 865–871 (August 2000).
KEY WORDS: Additives, biodiesel, diacid diesters, diol di-
esters, low-temperature flow properties, mass spectrometry, nu-
clear magnetic resonance.
Long-chain compounds with branched or bulky moieties find
uses in various commercial products. In biodiesel (1,2), an al-
ternative diesel fuel derived from vegetable oils or animal
fats, branched esters such as neat isopropyl or isobutyl esters
have been applied to improve the low-temperature properties
as documented by cloud and pour points (3–5). The use of
branched esters constitutes one of the possible solutions for
improving the low-temperature properties of biodiesel, the
others being dilution with conventional diesel fuel, the use of
various polymeric additives (1,2), and winterization (6–9).
Other compounds with branched or bulky moieties, such as
neopentylglycol diesters, are used commercially in lubricants
13
and C nuclear magnetic resonance (NMR), is reported.
Some other patent syntheses (21,22) of compounds such
as the present ones have been reported. Nonpatent syntheses
include some compounds with neopentylglycol as diol (23),
compounds derived from α,α-dimethylalkanoic acids and
polyols (24), esters from dodecanedioic acid, and mono-alco-
hols (25) as well as the enzymatic synthesis of related wax
esters (26). Besides their synthesis, the mass spectrometric
(
10–15), plasticizers (16,17), cosmetics (18), and even edible TABLE 1
fat replacers (19,20).
Some Compounds Synthesized in the Present Work
The present long-chain compounds were synthesized by p-
toluenesulfonic acid (p-TsOH)-catalyzed esterification of
acids and alcohols in toluene. Either diols were reacted with
acids or diacids were reacted with alcohols (see Scheme 1A
and 1B, respectively). One of the reactants was monofunc-
tional whereas the other was bifunctional. 2-Octanol was cho-
Diol diesters
Entry
Acid
Diol
a
b
c
d
Lauric
Hexanoic
Hexanoic
1,4-Di(hydroxymethyl)cyclohexane
Neopentylglycol
1,4-Di(hydroxymethyl)cyclohexane
1,4-Di(hydroxymethyl)cyclohexane
3,6-Dioxaheptanoic
Diacid diesters
*
1
To whom correspondence should be addressed at USDA, ARS, NCAUR,
815 N. University St., Peoria, IL 61604.
Entry
Diacid
Alcohol
E-mail: knothegh@mail.ncaur.usda.gov
1
e
f
g
3,3-Dimethylglutaric
Suberic
2-Octanol
2-Octanol
1,4-Cyclohexanedicarboxylic 2-Octanol
Present address: Caterpillar, Inc., Tech Center—E, P.O. Box 1875, Peoria,
IL 61656-1875.
2Retired.
Copyright © 2000 by AOCS Press
865
JAOCS, Vol. 77, no. 8 (2000)

866
G. KNOTHE ET AL.
behavior of compounds similar to the present ones was stud- 53.7 –55.6°C).
ied, including esters of neopentyl glycol (27), other esters of
Low-temperature studies. Cloud points (CP) and pour
polyols of neopentane (28–33), the decomposition products points (PP) were determined according to ASTM standard
of neopentylglycol dilaurate (34), and ethane (35,36) and pro- methods D97 (PP) and D2500 (CP) (bath obtained from
panediol (35) diesters.
Koehler Instrument Co., Bohemia, NY).
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
All starting materials were purchased from Aldrich (Milwau- Various moieties were incorporated to give bulky substituents
kee, WI) except 3,6-dioxaheptanoic acid (“oxa” indicating re- or branching in the products (for a listing of compounds syn-
placement of CH by O in the chain), which was obtained thesized here, see Table 1). These kinds of structures may ren-
2
from Hoechst (Frankfurt am Main, Germany). Solvents were der the products useful as additives for improving the low-
supplied by Fisher Scientific (Fair Lawn, NJ) or Aldrich. temperature properties of vegetable oil methyl esters used as
Methyl soyate (biodiesel) was obtained from Ag Environ- alternative diesel fuel (biodiesel). Note that compounds with
mental Products (Lenexa, KS).
cyclohexyl moieties were obtained as cis/trans isomers as
High-performance liquid chromatography (HPLC) equip- shown by NMR and two peaks giving identical mass spectra
ment consisted of a preparative-scale pump (obtained from in GC–MS. No attempt was made to separate the isomers.
1
13
MidAmerica Analytical Instruments, St. Louis, MO), a The products were characterized by H NMR, C NMR, and
Rainin (Varian Chromatography Systems, Walnut Creek, CA) MS. Spectroscopic characterization of the compounds will be
Dynamax 60 Å silica column (41.4 mm i.d.), a Kratos discussed first and then the low-temperature studies.
(
PerkinElmer Corp., Norwalk, CT) Spectroflow 757 ultra-
MS. Generally, electron impact (EI) spectra of the present
violet (UV) absorbance detector, and a Waters (Millipore compounds are somewhat more complex than those obtained
Corp., Milford, MA) R401 differential refractometer detec- by methane PCI. The enhanced complexity is especially no-
tor. The runs were monitored on a chart recorder and a per- ticeable in the region m/z < 100. This is due to fragments re-
sonal computer equipped with Justice (Mountain View, CA) sulting from rearrangements, cyclizations, etc., occurring
HPLC software.
more prominently in the EI spectra. Essential features of
Mass spectra were obtained on a gas chromatography EI–MS of diesters of neopentylglycol, 1,2-ethanediol, and the
GC)–MS system consisting of a Hewlett-Packard (Palo Alto, propanediols have been discussed (27,35,36). Methane PCI
(
CA) 5890 Series II Plus gas chromatograph equipped with a usually yields spectra in which the peaks at higher m/z, which
DB-5MS capillary column (30 m × 0.25 mm i.d.) attached to are strongly related to straightforward features such as chain
a Hewlett-Packard 5989B mass spectrometer operating in lengths of the original molecules, are more intense and the
electron ionization (70 eV) or PCI mode (methane as reagent molecular ion is always present, removing any ambiguities
gas, 230 eV) using methane as reagent gas. All PCI spectra about the molecular weight of the sample.
were background-subtracted. NMR spectra were obtained on
The compounds whose spectra are depicted in Figure 1 and
a Bruker (Rheinstetten, Germany) ARX-400 spectrometer op- discussed as examples contain a neopentylglycol moiety and
1
13
erating at 400 MHz ( H NMR) or 100 MHz ( C NMR). The the diacid congener 3,3-dimethylglutaric acid as well as di(hy-
solvent was CDCl3. droxymethyl)cyclohexane and cyclohexanedicarboxylic acid
General synthetic procedure. All syntheses were carried moieties (entries a, c, d, f, h, and j in Table 1). The EI spectra
out by mixing the starting materials (10 g acid component; will not be discussed in detail because this has been largely
6
0 mol% diol relative to the acid when synthesizing diol accomplished in the literature (27,35,36). The four mass spec-
diesters, 220 mol% alcohol relative to the acid when syn- tra depicted in Figure 1 serve to illustrate the methane PCI
thesizing diacid diesters) in toluene with 10 mol% p-TsOH mass spectral features of the present compounds.
relative to the acid component as catalyst. The reaction ap-
PCI with methane as reagent gas yielded significant dis-
paratus consisted of a flask equipped with a Dean-Stark tinctive peaks at higher masses for the present compounds.
trap and reflux condenser. The reaction mixture was refluxed This coincides with the mass spectral studies on branched di-
for 6 h. Workup consisted of adding 100 mL of saturated Guerbet esters (37), where PCI was found to give distinctive
aqueous NaHCO solution and then extracting with 5 × 50 m/z peaks at higher abundances and at higher mass ranges.
3
mL diethyl ether. The combined organic layers were washed Cleavages yielding the distinctive fragments are shown in
with saturated KCl solution and then dried over MgSO . They Figure 2.
4
were then filtered, the solvent removed on a rotary evapora-
Generally, the methane PCI mass spectra of the diacid di-
tor, and the product placed under vacuum for 2 h at 60°C. esters display more peaks than those of the diol diesters. The
Yields ranged from 70% to nearly quantitative (97%) for spectra of bis-(2-octyl)-3,3-dimethylglutarate (Fig. 1A) and
these reactions. Reaction products were finally purified by bis-(2-octyl)-1,4-cyclohexane dicarboxylate (Fig. 1B) are
HPLC using hexane as solvent except for entry f in Table 1 very similar despite the differences in the nature of the diacid.
for which 1:1 hexane/dioxane was used. The products were The mass spectra of diol diesters (Figs. 1C and 1D), however,
liquids at ambient temperature except entry a in Table 1 (m.p. differ depending on the nature of the diol moiety. Note that
JAOCS, Vol. 77, no. 8 (2000)

LONG-CHAIN DIESTERS
867
FIG. 1. Positive chemical ionization mass spectra of (A) bis-(2-octyl) 3,3-dimethyl glutarate, (B) bis-(2-octyl) 1,4-cyclohexanedicarboxylate, (C)
neopentylglycol bis-hexanoate, and (D) 1,4-cyclohexanedimethanol bis-hexanoate.
the diol moiety in the diol diesters resembles that of the diacid Figure 2B.
moiety in the diacid diesters. Major cleavages for diacid di-
Diacid diesters. The diacid diesters exhibit three major
esters are depicted in Figure 2A and those for diol diesters in clusters of peaks. The first one is due to diacid diesters ex-
JAOCS, Vol. 77, no. 8 (2000)

868
G. KNOTHE ET AL.
resulting from one cleavage B-II in Figure 2B. However, fur-
ther liberation of water gives rise to the base peak at m/z 185.
Direct cleavage A-II in the spectrum in Figure 1C contribut-
ing to m/z 185 cannot be excluded. Thus, successive loss of
hexanoic acid (m/z = 116) would be responsible for the ion
series 301 (protonated molecular ion) → 185 → 69. The dif-
ferences in the spectra depicted in Figures 1C and 1D can
likely be explained by greater stability of the cyclohexyl-con-
taining moiety in the diester causing the spectrum in Figure
1
D. The significantly greater stability of the cyclohexyl-con-
taining fragment is additionally demonstrated by the presence
of m/z 109 as strong/base peak in Figure 1D. This peak corre-
sponds to the fragment depicted in Figure 2C. The loss of
hexanoic acid is again shown in Figure 2D by the ion series
m/z 341 → 225 → 109. The corresponding EI mass spectrum
(
not shown) exhibits m/z 108, which corresponds to further
FIG. 2. Cleavages in methane positive chemical ionization mass spec-
trometry of (A) diacid diesters and (B) diol diesters.
deprotonation of the m/z 109 fragment as the base peak. Both
EI and PCI spectra exhibit m/z 99 (acylium ion from the
monoacid), which corresponds to fragment B-I in Figure 2B.
However, in Figure 1D, m/z 117 corresponding to protonated
hexanoic acid (note adduct formation at m/z 145) is observed.
The intensity of m/z 99 is greater in Figure 1D than in 1C,
leading to the conclusion that liberation of water from m/z 117
contributes significantly here. In Figure 1C, m/z 117 is nearly
completely absent.
+
+
hibiting strong [M + H] and [M − H] (which may corre-
+
spond to [M + H] − H , see Ref. 38) peaks. Straight-chain
fatty acid methyl esters exhibit such behavior (38). Loss of
hydrocarbon moieties at high m/z, for example [M − 15] ,
2
+
leads to peaks such as m/z 381 in Figure 1B and m/z 369 in
Figure 1A.
The distinctive fragments in methane PCI–MS for selected
compounds synthesized in the present work are listed in
Table 2. No detailed further assignments are made in Table 2,
because they correspond to the examples whose patterns are
discussed.
A second cluster of peaks results from one cleavage frag-
ment B-II in Figure 2A to give the monoester monoacid frag-
ment that is protonated leading to m/z 273 in Figure 1A and
m/z 285 in Figure 1B. Liberation of water causes the peaks at
m/z 255 and m/z 267, respectively. Monoester monoacids are
1
+
NMR spectroscopy. Table 2 also contains data for the H
also detected as adducts with C H (peaks at m/z 301 in Fig.
2
5
and 1 C NMR spectra of compounds synthesized. The main
3
1A and m/z 313 in Fig. 1B). Such adduct formations are com-
1
3
features of the C NMR spectra will be discussed here
briefly.
mon in the mass spectra of straight-chain fatty acid methyl
esters with methane as reagent gas due to its low proton affin-
ity (38).
The third cluster of peaks in the methane PCI mass spectra
of the diacid diesters results from both B-II cleavages in Fig-
ure 2A to give the protonated diacid (m/z 161 in Fig. 1A, m/z
In the diol diester derived from neopentyl glycol, the three
C NMR signals of the diol moiety occur at 68.91 (carbons
1
3
attached to the oxygen), 34.54 (quaternary carbon), and 21.70
ppm (methyl carbons). In the diacid diester derived from 3,3-
dimethylglutaric acid, the signal for the carbons attached to
the ester moieties is at 45.68 ppm, that of the quaternary car-
bon is at 32.61 ppm, and that of the methyl groups is at 27.52
ppm. These assignments are confirmed through DEPT (dis-
tortionless enhancement of polarization transfer) NMR ex-
periments, which distinguish carbons with odd and even num-
bers of protons as well as no attached protons.
1
73 in Fig. 1B). In both cases, the liberation of water gives
the peaks at m/z 155 and m/z 143, respectively. Peaks related
to the diacid are the base peak in both spectra (dehydrated
diacid in Fig. 1A, protonated diacid in Fig. 1B). The diacid
+
and its dehydrated derivative both form adducts with C H
2
5
to give the peaks at m/z 171 and 189 in Figure 1A and m/z 183
and 201 in Figure 1B. Note that m/z 171 in Figure 1A could
be explained from a cleavage within the dimethylglutaric acid
moiety but likely arises as discussed because the correspond-
ing peak (at different m/z) is present in Figure 1B.
The diesters with cyclohexyl moieties exist as cis/trans
isomers (as the cyclohexyl-containing starting materials were
already cis/trans isomers). In addition to these samples elut-
1
3
ing during GC–MS investigations as two peaks, C NMR is
also useful for showing the existence of two isomers. The cy-
clohexyl moiety of corresponding diol diester has signals at
Diol diesters. A similar cleavage pattern holds for the diol
diesters, although in these cases fewer peaks are observed
+
(
Figs. 1C and 1D) compared to the diacid diesters. [M + H]
+
3
7.00–37.05 and 34.40–34.45 ppm (C and C tertiary car-
and [M − H] are found in both cases. These peaks are
stronger in Figure 1D, and adduct formation is observed here
also (m/z 369). The peak at m/z 225 in Figure 1D results from
one cleavage A-II in Figure 2B. In Figure 1C, a peak at m/z
1 4
bons of the cyclohexyl moiety) and 28.80 and 25.25–25.30
ppm (C , C , C , and C secondary carbons of the cyclohexyl
2
3
5
6
moiety). These assignments were confirmed again via DEPT
experiments. The cis and trans isomers were not assigned
2
03 for the protonated monoester monoalcohol is observed
JAOCS, Vol. 77, no. 8 (2000)

LONG-CHAIN DIESTERS
869
TABLE 2
Positive Chemical Ionization Mass Spectrometry (PCI—MS) Peaks (methane as reagent gas) and Nuclear Magnetic
Resonance (NMR) Signals of Some of the Compounds Synthesized in the Present Work
Entrya
PCI–MS
1H NMR
13C NMR
a
175 (100%), 157 (90%),
3.97 (d, J = 7.2 Hz), 3.88
(d, J = 6.5 Hz), 2.28 (t,
J = 7.5 Hz), 1.79 (d), 1.60
(t), 1.26 (m), 0.99 (m),
0.86 (t)
163.94, 69.10, 66.90 (5:1
ratio), 37.03, 34.44,
34.33, 31.86, 29.55,
29.43, 29.29, 29.22,
29.13, 28.81, 25.27,
287 (55%), 399 (39%), 203
(20%), 185 (17%), 400
(11%), 269 (10%), 176
(9%), 397 (9%), 285 (8%)
25.00, 22.64, 14.07
+
b
c
301 ([M + 1] , 4%), 203
(
(
3.84 (s), 2.27 (t), 1.58
(quintuplet), 1.29–124
(m), 0.92 (s), 0.85 (t)
173.66, 68.91, 34.54,
34.19, 31.24, 24.60,
22.24, 21.70, 13.83
3%), 186 (11%), 185
100%), 99 (4%)
369 (adduct, 4%), 341
[M + 1] , 65%), 339 ([M − 1] ,
8%), 225 (97%), 109
3.96 (d), 3.86 (d) (14:6
ratio), 2.26 (t), 1.79–1.24
(m), 0.97 (m), 0.86 (t)
173.89, 69.07, 66.88 (3:1
ratio), 37.02, 34.42,
34.26, 31.26, 28.79,
+
+
(
1
(100%), 99 (20%)
25.25, 24.64, 22.25, 13.84
+
d
e
377 ([M + 1] , 32%), 244
(
(
1
4.04 (s), 3.97 (d), 3.87
(d), 3.61(m), 3.48 (m),
3.27 (s)
170.21, 71.61, 70.49,
69.22, 68.27, 67.06,
58.69, 36.64, 34.07,
28.40, 24.89
15%), 243 (100%), 163
adduct, 11%), 135 (60%),
09 (41%), 89 (11%), 59 (5%)
+
385 ([M + 1] , 41%), 383
4.84 (sextuplet), 2.33 (t),
1.52–1.20 (m), 1.15 (d),
1.06 (s), 0.82 (t)
171.42, 70.66, 45.68,
35.89, 32.61, 31.68,
29.05, 27.52 (CH3),
+
+
(
[M − 1] , 15%), 369 ([M − CH ] ,
%), 313 (6%), 301
3
4
(adduct, 10%), 273 (49%),
25.34, 22.50, 19.94, 13.98
2
1
55 (12%), 189 (adduct,
3%), 171 (11%), 161
(46%), 143 (100%)
+
f
399 ([M + 1] , 28%), 397
(
4.86 (m), 2.23 (t, 2H),
1.60–1.20 (m), 1.15 (d, 3H),
0.84 (t, 3H)
173.29, 70.71, 35.92,
34.59, 31.70, 29.06,
28.74, 25.33, 24.85,
+
+
[M − 1] , 10%), 383 ([M − CH ] ,
%), 315 (adduct,
%), 287 (60%), 285 (8%),
69 (9%), 203 (adduct,
2%), 185 (adduct, 13%),
75 (100%), 157 (66%)
3
2
6
2
2
1
22.52, 19.96 (CH ), 14.00
3
+
g
397 ([M + 1] , 35%), 395
(
4
(
2
(
1
4.86 (septuplet), 2.38
(m), 2.20 (m), 1.98 (d),
1.86 (m), 1.65–1.22 (m),
1.15 (2 d), 0.92 (d),
0.86–0.82 (2 t)
173.26, 70.67, 35.87,
34.54, 31.67, 29.02,
28.70, 25.30, 24.81,
22.49, 19.92, 13.97
+
+
[M − 1] , 15%), 381 ([M − CH ] ,
%), 325 (5%), 313
3
adduct, 8%), 285 (53%),
83 (7%), 267 (16%), 201
adduct, 20%), 183 (adduct,
0%), 173 (100%), 155 (63%)
aEntry numbers correspond to Table 1.
specific peaks as the literature values on similar compounds tive molecules co-crystallize onto the surface, functional
39 and references therein) appear to be contradictory. The groups attached to their backbone hinder growth habit by in-
other signals can be assigned to the monoacid or monoalco- terfering with the orderly formation of the layers. Obviously,
hol moieties in agreement with literature data (39,40). nucleation must be initiated prior to activation of these
(
Low-temperature flow properties. Cold-flow improvers for copolymers; thus, these additives are more effective in reduc-
conventional diesel are typically copolymers containing sev- ing PP than CP of diesel fuels. These copolymers, called pour
eral carboxylic functional groups (such as ethylene vinyl ac- point depressants (PPD), are typically most efficient at con-
etate, acrylate, or methacrylate) attached to a paraffin back- centrations at an additive level (ppm).
bone similar in structure and melting point properties to those
An earlier study (7) showed that copolymer PPD for con-
of the fuel component molecules (41,42). In diesel fuels, crys- ventional diesel were also effective in reducing PP of
talline growth occurs when long-chain hydrocarbons continue biodiesel as well as biodiesel/diesel blends. As was the case
to adsorb in structured layers on the solid surface. As addi- for conventional diesel fuel, copolymer PPD did not signifi-
JAOCS, Vol. 77, no. 8 (2000)

870
G. KNOTHE ET AL.
cantly affect CP of biodiesel or blends. This indicates that this compound likely initiated crystallization in the mixture at
mechanisms associated with crystalline growth habit are sim- lower temperatures. Nevertheless, it is feasible that this addi-
ilar for biodiesel; that is, wax crystal growth and agglomera- tive had a significant rate of co-crystallization.
tion in biodiesel occur by formation of structured layers.
It is known that during crystallization of neat methyl
As discussed previously, branched-chain esters such as stearate the molecules align themselves head-to-head in bi-
isopropyl and 2-butyl esters of fats and oils typically have layers with carboxylic headgroups in proximity with each
better low-temperature flow properties than their correspond- other (44). If, in a mixture with methyl soyate, the rate of co-
ing straight-chain isomers. Comparison of neat esters shows crystallization of 1,4-di(hydroxymethyl)cyclohexane bis-lau-
that bulky moieties in the short-chain alkyl group (headgroup) rate molecules was significant, it is likely these molecules
had reduced PP compared to esters with straight-chain head- aligned themselves in the crystal lattice with one or both ester
groups. Thus, crystalline growth habit was hindered by the linkages in proximity to the carboxyl groups of the saturated
presence of the bulky headgroups. In contrast to treatment fatty methyl esters. Such an alignment may limit the effec-
with copolymer PPD such as those discussed above, these es- tiveness of the bulky aliphatic ring moiety with respect to al-
ters themselves had reduced CP values, implying that the tering the ordered alignment of tailgroups within the bilayers.
bulky moieties also interfere with formation of clusters of Subsequent adsorption of saturated fatty methyl esters would
molecules that precede nucleation in bulk liquid solution. occur with the ester tailgroups wrapping themselves about the
However, improvements in CP and PP were directly propor- bulky moiety with little or no alteration in the rate of crystal
tional to the blend level, meaning that a considerable volume growth. These results indicate that future trials should exam-
of esters with branched-chain headgroups must be replaced ine modifying the nature and location of the bulky moiety for
with their branched-chain isomer to achieve significant im- more effective hindering of crystalline growth habit.
provement.
This study examines the hypothesis that compounds with ACKNOWLEDGMENTS
bulky or branched-chain moieties at locations other than the
We thank Dale W. Ehmke, Haifa Khoury, Amanda L. Callison, and
headgroup (that is, within the midst of the structure) might be
effective in hindering nucleation at additive level concentra-
tions. Most of the compounds in Table 1 were structured with
two straight-chain paraffinic or olefinic groups connected by
ester linkages symmetrically about an aliphatic ring or
branched-chain interior structure.
Methyl soyate gave CP = 0°C and PP = −3°C. Compounds
synthesized in this study were evaluated at loadings of 2,000
ppm, a typically heavy concentration relative to treatment
levels in the fuel industry. Compounds tested in this study had
only minor effects (no more than 1°C), if any, on CP or PP
parameters. Increasing loadings to 5,000 or 10,000 ppm
yielded no significant benefits.
The relative ineffectiveness of these additives in decreas-
ing PP suggests that the rates of additive co-crystallization
were relatively low. As discussed previously, additives whose
backbone structure has melting properties similar to those of
crystallizing fuel molecules are most effective in reducing PP.
With one exception, each of the additives in Table 1 had melt-
ing points 10°C or more below the PP of methyl soyate. Thus
it is feasible that the physical properties of the basic molecu-
lar structure (perhaps in part due to the nature of the bulky
moiety itself) of these additives precluded establishment of a
significant rate of co-crystallization following initial forma-
tion of crystal nuclei by saturated fatty methyl ester mole-
cules. The melting point of a straight-chain polymer is largely
a function of chain length and its degree of unsaturation.
Thus, future trials should consider lengthening the chains
and/or reducing the number of double bonds in the tailgroup
structure to facilitate compatible melting properties.
Rebecca (Burke) Zick for excellent technical assistance.
REFERENCES
1
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Vegetable Oils and Their Derivatives as Alternative Diesel
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mass), American Chemical Society, Washington, DC, 1997, pp.
1
72–208.
2
3
4
5
. Dunn, R.O., G. Knothe, and M.O. Bagby, Recent Advances in
the Development of Alternative Diesel Fuel from Vegetable Oils
and Animal Fats, Recent Res. Devel. Oil Chem. 1:31–56 (1997).
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Chain Esters to Reduce the Crystallization Temperature of
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Temperature Properties of Alkyl Esters of Tallow and Grease,
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6
. Lee, I., L.A. Johnson, and E.G. Hammond, Reducing the Crys-
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8
. Dunn, R.O., Effect of Winterization on Fuel Properties of
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9
. Dunn, R.O., M.W. Shockley, and M.O. Bagby, Winterized
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The only additive that did not have a low melting point was
1
,4-cyclohexanedimethanol bis-laurate (MP = 53–56°C).
1
0. Fujii, K., M. Izumi, and M. Nakahara (Sanken Kako Co., Ltd.),
Given that the melting point of methyl stearate is 37.8°C (43),
JAOCS, Vol. 77, no. 8 (2000)

LONG-CHAIN DIESTERS
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(1991).
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Chem. Abstr. 94:174253r.
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2
Pirozhkov, and Y.T. Eidus, Synthesis and Properties of Esters 40. Gunstone, F.D., High Resolution 13C NMR Spectroscopy of
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of Dodecanedioic Acid with Monohydric Alcohols, Okislenie
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[Received August 3, 1999; accepted May 31, 2000]
JAOCS, Vol. 77, no. 8 (2000)