How is chemical interesterification initiated: Nucleophilic substitution or α-proton abstraction?

Article abstract of DOI:10.1007/s11746-004-0903-x

Esters of carboxylic acids including 2-methylhexanoic, 2-methylbutyric, 2,2-dimethyl-4-pentenoic, palmitic, and oleic acids were tested as substrates in methoxide-catalyzed interesterification and transesterification. The aliphatic acid esters participated in the ester-ester interchange upon addition of catalytic sodium methoxide. Their isopropyl esters also produced methyl esters on heating with sodium methoxide. The esters of dimethyl-substituted acids did not participate in the ester-ester interchange. Their isopropyl esters did not react with methoxide to produce methyl esters. However, upon addition of methanol with sodium methoxide, their methyl esters were produced. These results indicate that the first step in interesterification is possibly that methoxide abstracts the α-hydrogen of an ester to form a carbanion. Interesterification is then likely completed via a Claisen condensation mechanism involving the β-keto ester anion as the active intermediate. The β-keto ester anion contains positively charged ketone and acyl carbons that are active sites for nucleophilic attack by anions such as methoxide and glycerinate, which would produce a methyl ester or rearrange acyls randomly. On the other hand, transesterification is a nucleophilic substitution by methoxide at the acyl carbon in the presence of methanol.

Full text of DOI:10.1007/s11746-004-0903-x

How Is Chemical Interesterification Initiated:
Nucleophilic Substitution or α-Proton Abstraction?
Linsen Liu*
The Oklahoma Food and Agricultural Products Center, Oklahoma State University, Stillwater, Oklahoma 74078
ABSTRACT: Esters of carboxylic acids including 2-methylhexa- the art, experimental evidence revealing the identity or struc-
noic, 2-methylbutyric, 2,2-dimethyl-4-pentenoic, palmitic, and ture of the catalytic species is still lacking. Once the real cata-
oleic acids were tested as substrates in methoxide-catalyzed in-
teresterification and transesterification. The aliphatic acid esters
participated in the ester–ester interchange upon addition of cat-
alytic sodium methoxide. Their isopropyl esters also produced
methyl esters on heating with sodium methoxide. The esters of α-
methyl-substituted acids did not participate in the ester–ester in-
terchange. Their isopropyl esters did not react with methoxide to
produce methyl esters. However, upon addition of methanol with
sodium methoxide, their methyl esters were produced. These re-
lyst is formed, the interchange period of the reaction begins.
Acyl groups continue to interchange until thermodynamic
equilibrium is reached and no further net change in the distri-
bution of FA occurs. At this point, the reaction reaches the third
period, completion, which is usually terminated out by quench-
ing with water to destroy the real catalyst.
Two reaction mechanisms have been proposed for inter-
esterification. Weiss et al. (4) suggested that interesterification
sults indicate that the first step in interesterification is possibly that was initiated when methoxide abstracted the α-hydrogen of an
methoxide abstracts the α-hydrogen of an ester to form a carban- ester to form an enolate anion (α-carbanion ester) that then
ion. Interesterification is then likely completed via a Claisen con- formed a β-keto ester via Claisen condensation (5). Interesteri-
densation mechanism involving the β-keto ester anion as the ac-
tive intermediate. The β-keto ester anion contains positively
charged ketone and acyl carbons that are active sites for nucle-
ophilic attack by anions such as methoxide and glycerinate,
which would produce a methyl ester or rearrange acyls randomly.
On the other hand, transesterification is a nucleophilic substitu-
tion by methoxide at the acyl carbon in the presence of methanol.
Paper no. J10726 in JAOCS 81, 331–337 (April 2004).
fication was then understood to occur by repetitive nucleophilic
substitution of β-keto esters by glyceride anions (diglycerinate)
on the ketone carbon or acyl carbon until thermodynamic equi-
librium was reached. This β-keto ester mechanism was sup-
ported by the detection of an IR absorption peak at 6.4 µm
−
1
(
1562.5 cm ) in the oil and water phases of sodium methox-
ide-catalyzed interesterification reactions (4). This evidence
has been challenged because this absorption is also characteris-
KEY WORDS: Carbanion, Claisen condensation, decarboxyla- tic of the ionized carboxyl group of soap that is commonly
tion, enolate, interesterification, β-keto ester anion, laurone, formed as a by-product in sodium methoxide-catalyzed inter-
mechanism, palmitone, transesterification.
esterification (1,6). Coenen (7) proposed that interesterification
was initiated by a direct nucleophilic addition and substitution
of methoxide on the acyl carbon of a glycerol ester to form a
Chemical interesterification rearranges the distribution of FA diglycerinate. Interesterification was achieved by repetitive nu-
in TG. This rearrangement changes the TG composition, and cleophilic substitution of diglycerinate moieties at the acyl car-
therefore the physical properties of the oils, and does not lead bons of TG. So far, no additional experimental research to sup-
to the formation of trans FA.
port either mechanism has been published.
Interesterification can occur without catalysts at very high
In this research, the reaction between sodium methoxide and
temperatures, such as 250°C, or catalytically under milder con- a series of acid esters with and without α-methyl branching was
ditions, such as 60°C. Many compounds have been patented as studied to further elucidate the mechanism of chemical inter-
interesterification catalysts including metal salts, alkali hydrox- esterification.
ide, alkoxide (alkylates), and alkali metals (1–3). Sodium
methoxide is the most commonly used catalyst for chemical in-
teresterification. The reaction is commonly divided into three
EXPERIMENTAL PROCEDURES
periods: induction, interchange, and completion. During the in- Chemicals. Sodium methoxide was purchased from Aldrich
duction period (ranging from seconds to minutes), sodium (Milwaukee, WI) as a 30% solution in methanol and the
methoxide reacts with glycerides to produce an intermediate sodium methoxide powder was prepared by evaporating the
commonly referred to as the “real catalyst” (1); no interchange methanol at about 90°C just prior to use. 2-Methylhexanoic
of acyl groups takes place during this period. Although the ex- acid (99% purity by GC), 2-methylbutyric acid (98%), 2,2-
istence of this real catalyst is not doubted by those skilled in dimethyl-4-pentenoic acid (95%), palmitic acid (99%), and
oleic acid (99%) were purchased from Sigma Chemical Co. (St.
Louis, MO). The acids were converted into methyl and iso-
propyl esters by the following acid-catalyzed esterification.
*
Address correspondence at 3353 Michelson Dr., Irvine, CA 92612.
E-mail: linsen.liu@conagrafoods.com
Copyright © 2004 by AOCS Press
331
JAOCS, Vol. 81, no. 4 (2004)

332
L. LIU
Acid-catalyzed esterification. Methods recommended by
(v) Interesterification and transesterification (methanolysis)
Christie (8) were modified as follows: 100 mg of the acid was of isopropyl 2,2-dimethyl-4-pentenoate. In interesterification,
heated with 6 mL of alcohol (methanol or isopropanol) con- 30 mg of ester was dissolved in 1 mL of hexane and reacted
taining 2% (vol/vol) concentrated sulfuric acid in a sealed vial with 9, 18, and 27 mg of sodium methoxide, respectively.
at around 95°C for an hour. Then 5 mL of hexane and 3 mL of Transesterification was conducted by sequential addition of 30,
a 5% NaCl solution were added and mixed well. After settling, 60, 120, and 240 µL of methanol to the mixture containing 30
the hexane layer was separated and washed three times with 3 mg of ester and 27 mg of sodium methoxide.
mL of 2% (wt/vol) potassium bicarbonate or until the aqueous
layer tested neutral by pH paper. The hexane layer was dried
over molecular sieves and analyzed for purity by GC. The syn-
RESULTS AND DISCUSSION
thesized esters were further purified by washing with alkali to All reactions and analyses were conducted in duplicate. The
remove residual acids. The purified esters were at least 99.7% difference between results was within 7%, and therefore only
pure as analyzed by GC.
one run of each experiment is discussed.
GC (9). The esters were analyzed by a Hewlett-Packard
Yield of acid-catalyzed esterification. Acid-catalyzed esteri-
(
Wilmington, DE) model 5890 gas chromatograph fitted with fication produced acid esters with at least 98% purity for all
an FID and a 15 m × 0.244 mm Alltech (Deerfield, IL) DB-23 acids except 2,2-dimethyl-4-pentenoic acid, which yielded
capillary column. The column was run isothermally at 200°C about 86% ester. After alkali treatment, the residual acids were
for long-chain FA esters (oleate and palmitate) and at 90°C for removed, and all the purified esters were at least 99.7% pure as
the other short-chain esters. The peaks were identified using analyzed by GC.
the pure standards prepared as above and integrated for quan-
tification. The compositions were expressed as the percentage The two reactants were mixed in about 1:1 weight ratio, as con-
of the integrated peak areas. firmed by GC (Table 1). After addition of sodium methoxide
Interesterification of methyl palmitate and isopropyl oleate.
Interesterification. An ester sample of about 30 mg was dis- and heating for 1 min at 60°C, two new esters (isopropyl palmi-
solved in 1 mL of hexane. Sodium methoxide powder was tate and methyl oleate) were formed. The amount of those
added while stirring at about 60°C, and the sample was incu- newly formed esters increased when the dose of sodium
bated for 1 min in screw-capped vials. The vials were then cen- methoxide increased from 1.5 to 3.6 g (0.79 to 5.36% for iso-
trifuged, and 2 µL of hexane supernatant was injected into a propyl palmitate and 1.88 to 14.53% for methyl oleate). More
gas chromatograph for analysis. The amounts of esters used methyl oleate than isopropyl palmitate was produced; there-
were chosen so that the final solutions could be analyzed using fore, methoxide not only catalyzed the interesterification reac-
GC directly without further dilution or concentration. The tion but also participated as a reactant in the reaction. The re-
amount of sodium methoxide used in this research was higher sults confirmed that the experimental conditions were adequate
than that in a neat oil interesterification (0.3–0.5%) to ensure for interesterification.
the initiation of reaction under the diluted hexane solution. The
following reactions were conducted.
Interesterification of methyl 2-methylbutyrate and iso-
propyl oleate. In this reaction, methyl 2-methylbutyrate was
(
i) Interesterification of methyl palmitate and isopropyl used to replace methyl palmitate in reaction with isopropyl
oleate. A 30-mg mixture of equal weights of methyl palmitate oleate. Methyl 2-methylbutyrate contains a methyl branch at
and isopropyl oleate were mixed in 1 mL hexane. Two inter- its α-position and therefore has only one α-hydrogen that is
esterification reactions were conducted, using 1.5 and 3.6 mg not acidic enough for methoxide to abstract (5). The experi-
of sodium methoxide, respectively.
ii) Interesterification of methyl 2-methylbutyrate and iso- interchange or interesterification between methyl 2-methyl-
propyl oleate. Methyl 2-methyl butyrate and isopropyl oleate butyrate and isopropyl oleate because only methyl oleate was
~1:2 w/w ratio) were mixed in 1 mL hexane, and 3.6 mg of produced. The amount of methyl 2-methylbutyrate decreased
sodium methoxide was added. to 23.16% after reaction from the initial 38.58% (39% de-
iii) Interesterification of isopropyl oleate. Isopropyl oleate crease), and the amount of isopropyl oleate increased slightly
30 mg) was dissolved in vials, each containing 1 mL of from 61.42 to 62.06%, which might be caused by evaporation
hexane; 3 and 6 mg of sodium methoxide, respectively, were during heating as methyl 2-methylbutyrate has a low b.p. The
mental results listed in Table 2 show that there was no ester
(
(
(
(
added to the reaction vials.
iv) Interesterification and transesterification (methanoly-
trace amount (0.23%) of isopropyl ester might be formed via
(
sis) using isopropyl 2-methylhexanoate. Interesterification was
conducted by reacting 30 mg of esters in 1 mL of hexane with
TABLE 1
Interesterification of Methyl Palmitate and Isopropyl Oleate
3, 6, 9, and 18 mg of sodium methoxide, respectively. Transes-
NaOCH3
Palmitate (%)
Oleate (%)
terification (methanolysis) was conducted by sequential addi-
tions of 5, 35, and 100 µL of methanol to the reaction mixture
containing 18 mg sodium methoxide. The mixtures were
heated for 1 min at 60°C with stirring after each addition of
methanol and sampled prior to the next addition of methanol.
The hexane layer was analyzed using GC.
a
added (mg)
Methyl
Isopropyl
Methyl
Isopropyl
0
1
3
.0
.5
.6
49.9
—b
—
1.88
14.53
50.1
46.43
34.37
50.89
45.74
0.79
5.36
a
As catalyst.
Not detected.
b
JAOCS, Vol. 81, no. 4 (2004)

THE MECHANISM OF INTERESTERIFICATION AND TRANSESTERIFICATION
333
TABLE 2
Interesterification of Methyl 2-Methylbutyrate and Isopropyl Oleate
TABLE 4
Interesterification of Isopropyl 2-Methylhexanoate
with Sodium Methoxide
NaOCH3
2-Methylbutyrate (%)
Oleate (%)
a
NaOCH3
Isopropyl ester Methyl ester Isopropanol Methanol
added (mg)
Methyl
Isopropyl
Methyl
Isopropyl
—b
0.23
(mg) (µmol)
(%)
(%)
(%)
(%)
0
38.58
23.16
—
13.63
61.42
62.06
3
.6
0
3
6
9
8
0
98.04
99.76
99.48
98.91
98.01
0.00
0.20
0.44
0.94
1.44
0.11
0.02
0.02
0.06
0.13
0.00
0.02
0.06
0.09
0.42
a
0.06
0.11
0.17
0.33
As catalyst.
b
Not detected.
1
transesterification as described below. If interesterification
were indeed initiated by nucleophilic substitution of methox-
ide at the acyl carbon, isopropyl 2-methylbutyrate should also a methyl branch at the α-carbon of its acid moiety. With addition
be produced at a level similar to that of isopropyl palmitate in of up to 18 mg of sodium methoxide (0.33:0.17 molar ratio of
Table 1. It is very unlikely that the 2-isopropylbutyrate was methoxide to ester), only a trace amount of methyl ester
formed and then lost by evaporation because its amount (<1.44%) was formed (Table 4). Thus, an ester having no active
would still be higher than 0.23% at the loss rate of 39%, α-hydrogen did not react with sodium methoxide to form methyl
which was consistent with the results below from the iso- esters, indicating that methoxide was not able to attack the acyl
propyl esters of 2-methylhexanoic and 2,2-dimethyl-4-pen- carbon to carry out a nucleophilic substitution and produce
tenoic acids. Methyl 2-methylbutyrate has an α-methyl methyl 2-methylhexanoate. Further analyses revealed that trace
branch at its α-position and contains only one α-hydrogen. It amounts of methanol existed in the reaction mixture (0.02–
is known that the basicity of sodium methoxide is not suffi- 0.42%), which may account for the trace amounts of methyl ester
cient to abstract the only α-hydrogen of an α-substituted produced through methanolysis as described below. Methanol
ester, and a strong base such as sodium triphenylmethide is can be formed in situ by sodium methoxide with the α-hydrogen
needed (5). Isopropyl oleate contains an α-hydrogen that is of an ester or any compounds containing acidic hydrogen, or it
acidic enough to be abstracted by methoxide, and therefore may be brought in as a impurity along with sodium methoxide.
methyl oleate was produced. Although the isopropylate anion Trace amounts of isopropanol were also formed as the product
is large in size compared with methoxide, isopropyl esters of methanolysis or transesterification.
have been successfully synthesized in high yield by the acid-
To test the effect of methanol on the reaction, methanol was
catalyzed esterification as above including those α-substi- added to the interesterification mixture. Table 5 presents the re-
tuted acids. Lee et al. (10) also reported the syntheses of iso- sults after up to 100 µL of methanol was added to the reaction
propyl esters using the base-catalyzed transesterification. mixture containing 18 mg of sodium methoxide. With addition
Therefore, failure to produce isopropyl 2-methylbutyrate is of methanol, significant amounts of methyl ester (1.87–7.7%)
unlikely to be due to steric hindrance of the isopropylate were produced. The amount of isopropanol also increased in
anion and the α-methyl branch. This is the first experimental the mixture as the result of transesterification. Methanol is a
evidence showing the essential role of the active α-hydrogen polar solvent and can form hydrogen bonds with acyl oxygens,
for interesterification.
which may activate the acyl carbon of isopropyl ester so that
Interesterification of isopropyl oleate. This test was used to the methoxide can attack nucleophilically at the acyl carbon
examine the reaction of an individual ester with sodium and produce the methyl ester. The results also argue against the
methoxide. On heating with sodium methoxide, isopropyl possibility that α-substitution can inhibit methoxide from mak-
oleate reacted with methoxide and produced methyl oleate ing a nucleophilic attack at the acyl carbon of an acid ester by
(Table 3). The amount of methyl oleate was doubled when the steric hindrance.
sodium methoxide was increased from 3 to 6 mg. This result
Interesterification and transesterification (methanolysis) of
shows that an aliphatic acid ester can react with methoxide to isopropyl 2,2-dimethyl-4-pentenoate. 2,2-Dimethyl-4-pen-
produce a methyl ester, although it is not clear if this is the re- tenoate has two methyl branches at its α-position and contains
sult of nucleophilic substitution or α-proton abstraction.
Interesterification and transesterification (methanolysis) double-substituted acid ester were similar to those obtained
using isopropyl 2-methylhexanoate. 2-Methylhexanoate contains
no α-hydrogen. Table 6 shows that results obtained with this
TABLE 5
Transesterification (methanolysis) of Isopropyl 2-Methylhexanoate
TABLE 3
Interesterification of Isopropyl Oleate with Sodium Methoxide
Methanol
Isopropyl ester Methyl ester Isopropanol Methanol
NaOCH3
added (mg)
(µL)
0a
5
35
(%)
(%)
(%)
(%)
Isopropyl ester (%)
Methyl ester (%)
98.01
96.35
94.36
86.46
1.44
1.87
3.65
7.7
0.13
0.21
0.31
0.67
0.42
1.56
1.68
5.17
0
3
6
99.59
94.26
88.32
—a
5.74
11.68
100
a
aNot detected.
The mixture containing 18 mg of NaOCH from Table 4.
3
JAOCS, Vol. 81, no. 4 (2004)

334
L. LIU
TABLE 6
with the single-substituted acid esters. Without added methanol,
Interesterification and Methanolysis of Isopropyl 2,2-Dimethyl-4-
pentenoate
only a trace amount of methyl ester (<0.23%) was formed even
within the presence of 27 mg of sodium methoxide in the reac-
tion mixture. After methanol was added to the reaction mixture
containing 27 mg of sodium methoxide, significant amounts
Isopropyl ester (%)
Methyl ester (%)
NaOCH (mg)
3
0
9
100
100
99.79
99.77
0
0
0.21
0.23
(
1.10–2.66%) of methyl ester were produced, albeit less than
the amount of methyl ester formed with a single-substituted
acid ester (Table 4).
1
2
8
7
Methanol (µL)a
The results presented in the foregoing paragraphs show that
methoxide-catalyzed interesterification is very likely initiated
by α-proton abstraction and that methoxide functions as an al-
kali. Transesterification (methanolysis) is a nucleophilic sub-
stitution reaction in the presence of methanol, and methoxide
functions as a nucleophile.
3
6
0
0
98.9
1.1
98.29
98.07
97.34
1.71
1.93
2.66
1
2
20
40
aMethanol was added to the mixture above that contained 27 mg NaOCH3.
FIG. 1. Formation of methyl ester from isopropyl ester via the β-keto ester anion mechanism.
JAOCS, Vol. 81, no. 4 (2004)

THE MECHANISM OF INTERESTERIFICATION AND TRANSESTERIFICATION
335
FIG. 2. The β-keto ester anion is the acyl donor for the formation of the new TG.
Figure 1 proposes a new interesterification scheme for the for- an acidic α-hydrogen (pK = 9–13) and therefore further reacts
a
mation of methyl ester from isopropyl ester and sodium methox- with sodium isopropylate to form a β-keto isopropyl ester anion
ide via the Claisen condensation mechanism. The first step is to and isopropanol. The β-keto isopropyl ester anion contains three
abstract the α-hydrogen by methoxide and thus form an α-car- negatively charged centers (two oxygens and one carbanion) that
banion, a resonance isomer of an enolate anion that is a strong polarize the keto and acyl carbons into becoming more positively
nucleophilic agent. A β-keto ester is formed when an α-carban- charged, which may activate those centers for a nucleophilic re-
ion is condensed with another isopropyl ester via Claisen con- action by an anion or alcohol. When the methanol formed in the
densation by nucleophilic substitution. A β-keto ester contains first step attacks at the acyl carbon of the β-keto isopropyl ester
JAOCS, Vol. 81, no. 4 (2004)

336
L. LIU
FIG. 3. Formation of laurone by the decarboxylation of β-keto acid.
anion, a β-keto methyl ester anion and isopropanol are formed, CCB. The first step is to abstract the α-hydrogen in AAA by
−
−
resulting in a net transesterification. When the methanol attacks methoxide to form AAA (α-carbon anion TG). AAA then
at the keto carbon, a methyl ester and an enolate (α-carbanion) reacts with triglyceride BBB via a Claisen condensation to form
−
are formed, resulting in a net ester–ester exchange or interesteri- AAAB (β-keto ester TG) and BB (diglycerinate). The latter two
−
fication. The β-keto ester anion contains a conjugated system then exchange a proton to form AAAB (β-keto ester TG anion)
−
that has three resonance isomers and would have an absorption and DG BB. AAAB then reacts with another DG (CC) that is
in the near UV region; this accounts for the reddish-brown color generated through the same mechanism as BB. When the nucleo-
that has been cited as an indicator of interesterification (1) and philic substitution occurs at the keto group, a new hybrid TG
−
that is used for reaction control (11).
(CCB) is formed and AAA is regenerated. When the reaction
Figure 2 shows the suggested scheme for the rearrangement occurs at an acyl group, a new DG (AA) and a new hybrid β-
−
of FA in TG AAA, BBB, and CCC to form a new hybrid TG keto ester TG anion (CCAB ) are produced. Repeated reactions
will lead to randomization of FA among the TG.
This β-keto ester anion mechanism can also explain other
side reactions and by-products produced during interesterifica-
tion. Huyghebaert et al. (12) isolated a series of long-chain ke-
tones such as laurone (C H COC H ) and palmitone
11
23
11 23
(
C H COC H ) from three butter substitutes, and those ke-
15 31 15 31
tones did not exist in natural butters. Figure 3 shows a proposed
mechanism for the formation of laurone from the β-keto ester
containing lauric acid. After interesterification is complete,
water is usually added to ensure the reaction is stopped. Water
quenches the β-keto ester anion into a β-keto ester that is then
hydrolyzed into a β-keto acid. β-Keto acid is not stable and is
easily decarboxylated to produce a ketone upon heating. A car-
bon is lost due to decarboxylation, which results in odd-chain
(
C11 or C ) ketones from lauric and palmitic acids, respec-
15
tively. Other long-chain ketones can be formed similarly. This
decarboxylation is referred to as ketonic cleavage (13).
The β-keto ester can also undergo acid cleavage (13) to form
soap (Fig. 4). Soap is a well-known by-product from interester-
ification and causes a 3–5% neutral oil loss in a typical inter-
esterification. It is commonly believed that soap is formed after
interesterification when water is added. According to this
mechanism, soap can be formed from the β-keto ester anion
with sodium hydroxide during interesterification. Sodium hy-
droxide can be introduced as an impurity in sodium methoxide
and can be formed when sodium methoxide is exposed to mois-
ture. The author has observed that soap is mainly formed during
FIG. 4. Formation of soap during interesterification.
JAOCS, Vol. 81, no. 4 (2004)

THE MECHANISM OF INTERESTERIFICATION AND TRANSESTERIFICATION
337
oil interesterification before water is added, and it can be sepa-
rated by centrifugation. The formation of soap turns the oil
from a clear reddish brown solution into a turbid reddish solu-
tion because soap is less soluble in oil. Similarly, methyl ester
can be produced as another by-product when methanol is
formed from methoxide. Ahibo-Coffy and Prome (14) reported
that glycerol-β-keto ester synthesized using palmitic acid pro-
duced mono- and dipalmitoyl glycerol, palmitone, and mixed
glycerides containing β-keto ester and palmitate upon heating
with alkaline K CO . This is an additional support for the β-
5. Solomons, T.W.G., Organic Chemistry, 3rd edn., John Wiley &
Sons, New York, 1984, pp. 897–902.
. Bellamy, L.J., Infrared Spectra of Complex Molecules, John
Wiley & Sons, New York, 1954, pp. 149–150.
. Coenen, J.W.E., Fractionnement et Interesterification des Corps
Gras dans la Perspective du Marche Mondial des Matières et des
Produits Finis. II. Interesterification, Rev. Fr. Corps Gras
6
7
2
1:403–413 (1974).
8
9
. Christie, W.W., Lipid Analysis, 2nd edn., Pergamon Press, Ox-
ford, United Kingdom, 1982, pp. 52–53.
. Liu, L., and E.G. Hammond, Phenylethyl Esters of Fatty Acids
for the Analytical Resolution of Petroselineate and Oleate, J.
Am. Oil Chem. Soc.72:749–751 (1995).
2
3
keto ester anion mechanism for interesterification.
1
0. Lee, I., L.A. Johnson, and E.G. Hammond, Use of Branched-
Chain Esters to Reduce the Crystallization Temperature of
Biodiesel, J. Am. Oil Chem. Soc. 72:1155–1160 (1995).
1. Liu, L., and D. Lampert, Partial Interesterification of Triacyl-
glycerols, U.S. Patent 6,238,926 (2001).
ACKNOWLEDGMENT
1
1
The author would like to thank Dr. Scott Bloomer, Senior Research
Scientist at Land O’Lakes, for editing.
2. Huyghebaert, A., H. Hendrickx, N. Schamp, and L. DeBuyck,
Occurrence of Ketones in Products Resembling Butter, Fette
Seifen Anstrichm. 72: 289–293 (1970).
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[Received November 5, 2003; accepted March 4, 2004]
JAOCS, Vol. 81, no. 4 (2004)