Structural Analysis of Partial and Total Esters of Glycerol Undecenoate and Diglycerol Undecenoate

Article abstract of DOI:10.1007/s11746-015-2725-1

The direct esterification reaction between glycerol and undecylenic acid or between diglycerol and undecylenic acid generates all the possible types of glycerol or diglycerol esters. Purification by silica gel chromatography resulted in the isolation of each of these types of ester in a pure form. The molecular structures of the compounds isolated were characterized and identified by mass spectrometry, ¹H NMR, ¹³C NMR and DEPT-135. We then studied the composition of esters of undecylenic acid formed with glycerol or diglycerol as a function of their reaction conditions, which constitute a highly complex system. We purified undecylenic acid esters from each polyol family to allow the structural identification of each ester of glycerol and each ester of diglycerol with undecylenic acid. We found that the polarity of these non-ionic amphiphilic esters directly affected their affinity for organic and inorganic solvents and that these esters behaved very differently from anionic amphiphilic molecules, such as undecylenic acid.

Full text of DOI:10.1007/s11746-015-2725-1

J Am Oil Chem Soc (2015) 92:1567–1577
DOI 10.1007/s11746-015-2725-1
ORIGINAL PAPER
Structural Analysis of Partial and Total Esters of Glycerol
Undecenoate and Diglycerol Undecenoate
Gildas Nyame Mendendy Boussambe1,2 · Romain Valentin1,2 · Zéphirin Mouloungui1,2
Received: 9 April 2015 / Revised: 4 September 2015 / Accepted: 11 September 2015 / Published online: 1 October 2015
©
AOCS 2015
Abstract The direct esterification reaction between glyc-
erol and undecylenic acid or between diglycerol and unde-
cylenic acid generates all the possible types of glycerol or
diglycerol esters. Purification by silica gel chromatography
resulted in the isolation of each of these types of ester in a
pure form. The molecular structures of the compounds iso-
lated were characterized and identified by mass spectrom-
etry, H NMR, C NMR and DEPT-135. We then stud-
ied the composition of esters of undecylenic acid formed
with glycerol or diglycerol as a function of their reaction
conditions, which constitute a highly complex system. We
purified undecylenic acid esters from each polyol family
to allow the structural identification of each ester of glyc-
erol and each ester of diglycerol with undecylenic acid. We
found that the polarity of these non-ionic amphiphilic esters
directly affected their affinity for organic and inorganic sol-
vents and that these esters behaved very differently from
anionic amphiphilic molecules, such as undecylenic acid.
Introduction
Esters of glycerol and diglycerol are amphiphilic molecules
widely used in industry. Glycerol monoesters (GMs) are
used as emulsifiers in the food, pharmaceutical and cos-
metic industries [1–3]. Glycerol diesters (GDs) play an
important role in the lipid domain, because oils containing
80 % GDs are now available on the American and Japanese
markets [4]. Diglycerol ester use is rapidly increasing: they
are present in mixtures of polyglycerol esters, and they
have been shown to reduce tension at the water–air inter-
face [5, 6]. They are used as foaming agents [7, 8] and as
coalescence agents [9].
Such esters may be produced by the esterification of
fatty acids with either glycerol or diglycerol. Glycerol
esters can also be produced by the glycerolysis or partial
hydrolysis of plant oils. There are also other more selec-
tive pathways, such as the condensation of glycidol with
an existing fatty acid [10], but they are not exploited in
industry.
1
13
Keywords Glycerol undecenoate esters · Diglycerol
undecenoate esters · Structural analysis · Direct
esterification · NMR spectroscopy · Mass spectroscopy
In this study, we used undecylenic acid as an acyl donor
for the synthesis of partial esters of glycerol and diglycerol.
Undecylenic acid is obtained from castor oil by pyrolysis
of either the crude oil or the ricinoleic acid methyl esters
[
11]. This acid is potentially useful, because it has two
functional groups: a carboxyl group that can be esterified,
and a terminal reactive alkene group.
Electronic supplementary material The online version of this
article (doi:10.1007/s11746-015-2725-1) contains supplementary
material, which is available to authorized users.
Partial esters of undecylenic acid, such as glycerol mon-
oundecenoate and glycerol diundecenoate, have been stud-
ied. Pace et al. [12] and Cauvel et al. [13] studied partial
esters of glycerol and described the synthesis and struc-
tural characterization of the α-monoglyceride, without tak-
ing into account the presence of the β regioisomer. Berger
and Schnelder [14] proposed a method for enriching the
*
Romain Valentin
romain.valentin@ensiacet.fr
1
Université de Toulouse, INPT-ENSIACET, LCA (Laboratoire
de Chimie Agro-Industrielle), 4 Allée Emile Monso,
3
1030 Toulouse, France
2
INRA, UMR 1010 CAI, 31030 Toulouse, France
1
3

1
568
J Am Oil Chem Soc (2015) 92:1567–1577
preparation in the α-monoglyceride; however, this study
did not consider other glycerides. Chidambaram et al. [15]
produced a stoichiometric mixture of the α and β regioiso-
mers of glycerol monoundecenoate from acetal.
<1 % β,β′-diglycerol and <0.2 % cyclic isomers) was
obtained from Solvay Chemicals, and undecylenic acid
(99 %) was obtained from Acros Organic. Dodecylbenzene
sulfonic acid (DBSA; ≥95 %) was obtained from Sigma-
Aldrich. HPLC-quality solvents (cyclohexane, ethyl ace-
tate, chlorofom and methanol) were obtained from Aldrich.
Kumar et al. [6], in their studies of diglycerol esters,
described the synthesis of diglycerol monoundecenoate
by esterification, followed by silica column chromatogra-
phy purification. The structural analysis did not differenti-
ate between the regioisomers. Brito et al. [16] synthesized
diglycerol tetraundecenoate, with the aim of studying its
lubrication properties. The structure of this molecule was
Synthesis of Esters of Glycerol and of Diglycerol
with Undecylenic Acid
The synthesis of these compounds was adapted from the
procedure developed by Eychenne and Mouloungui [26].
The reactions were carried out in a 250-mL batch reactor
loaded with 80 g of reaction medium and equipped with
a Dean–Stark receiver and a refrigerant, with mechanical
stirring at 500 rpm. The reactor was loaded with unde-
cylenic acid and glycerol (molar ratio of 2:1) or with unde-
cylenic acid and diglycerol (molar ratio of 3:1). DBSA was
used as the catalyst (molar ratio of 0.125 with respect to
undecylenic acid). The reaction was carried out for 3 h, at
a temperature of 120 °C. The reaction medium was cooled
and washed with saturated NaCl solution (4 × 100 mL),
until a neutral pH was reached, to eliminate the DBSA
and any residual glycerol or diglycerol. The molar compo-
sition of the glycerol esters reaction medium was 26.6 %
glycerol monoundecenoate (GMU), 25.3 % glycerol diun-
decenoate (GDU), 4.2 % glycerol triundecenoate (GTU)
and 43.9 % of residual undecylenic acid (UA). The molar
composition of the diglycerol esters reaction medium was
15.2 % diglycerol monoundecenoate (DGMU), 27.6 %
diglycerol diundecenoate (DGDU), 30.9 % diglycerol tri-
undecenoate (DGTU), 5.2 % diglycerol tetraundecenoate
(DGTeU) and 21.1 % of residual UA. Gas chromatogra-
phy analyses are detailed in the supporting information.
Esters of α,β-diglycerol, β,β′-diglycerol and cyclic glycerol
were not identified by gas chromatography or by thin-layer
chromatography.
1
13
confirmed by H and C NMR and by mass spectrometry.
Work characterizing and determining the properties of
these glycerol and diglycerol esters should always include
steps for the separation or purification of the various con-
stituents of the reaction mixtures. Molecular distillation
methods have been developed [17–19], and they yield purer
ester fractions. However, they generally require the use
of high temperatures (240–300 °C) for the distillation of
esters with high boiling points, such as the glycerol diesters
synthesized from sunflower oil, which has a high oleic acid
content (87.6 % oleic acid) [19]. In such situations, there is
a high risk of modifying the composition of partial esters
through acyl transfer.
Temperature appears to be an important parameter
and, at relatively low temperatures (23 °C), close to room
temperature, acyl group migration is extremely limited
[
20–22]. Rapid purification methods at room temperature
should make it possible to obtain samples of glycerides
without the purification method causing isomerization.
One possible approach involves the use of recrystallization
methods for purification. However, these methods are diffi-
cult to implement when the glycerides present have similar
crystallization temperatures, as is the case for partial esters
of glycerol and partial esters of diglycerol [23, 24]. Separa-
tion by silica gel chromatography is widely used in organic
chemistry and is the method that best preserves the struc-
ture of glycerol esters [6, 25].
Here, we report a study of the composition of esters of
undecylenic acid formed with glycerol or diglycerol, based
on their reaction conditions, which constitute a highly com-
plex system. We purified undecylenic acid esters from each
polyol family to allow the structural identification of each
ester of glycerol and each ester of diglycerol with unde-
cylenic acid.
Thin‑layer chromatography (TLC) analyses
The analyses were carried out on plates (5 × 5 cm) coated
with silica gel 60 F . The glycerol esters were separated
2
54
by elution with a 60:40 (v/v) mixture of cyclohexane and
ethyl acetate. The diglycerol esters were separated by elu-
tion with a 3:97 (v/v) mixture of methanol and chloro-
form. Esters of glycerol or diglycerol do not absorb in the
visible spectrum and have very low levels of absorption
for UV light (Fig. 1, supporting information). We were
therefore unable to use UV lamps designed for TLC sig-
nal detection at 254 or 365 nm. GMU and DGMU absorb
at wavelengths of 223 and 220 nm, respectively. We there-
fore used potassium permanganate detection methods on
the TLC plates.
Materials and Methods
Materials
Glycerol (98 %) was obtained from Sigma-Aldrich, lin-
ear diglycerol (84 % α,α′-diglycerol, 14 % α,β-diglycerol,
1
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J Am Oil Chem Soc (2015) 92:1567–1577
1569
Column Gel Chromatography
both electron donors and hydrogen bond acceptors. Unde-
cylenic acid has a relatively low LogP value, similar to that
of GMU and DGMU. It has a high retardation factor. It is
retarded by the silica gel slightly less strongly than GDU or
DGTU, whereas it would be expected to be retained much
more strongly because it contains both an OH group capa-
ble of donating and accepting electrons for hydrogen bond-
ing and a carbonyl group capable of acting as an electron
acceptor for hydrogen bonding. Undecylenic acid would be
expected to form dimers in organic solvents [27–29]. Such
associations between molecules would decrease the capac-
ity of undecylenic acid to interact with the silica stationary
phase, which would therefore “see” only the lipophilic part
We used 19.6-cm-long, 8.5-cm-wide cylindrical Pyrex
glass chromatography columns, which we filled with 500 g
of silica (60 µm, 60–100 mesh) in the eluent, which was
cyclohexane for glycerol esters and chloroform for diglyc-
erol esters. We placed 130 g of Fontainebleau sand on the
top of each silica gel column.
Purification of Glycerol Esters
From a 30-g sample, we isolated GTU (R = 0.86) and
f
then UA (R = 0.66), with 1.5 L of cyclohexane. GDU
f
(
R = 0.52) was purified with 3 L of a 15:85 (v/v) mixture
of the undecylenic acid, accounting for the high R value.
f
f
of ethyl acetate and cyclohexane. Finally, GMU (R = 0.14)
f
was recovered by elution in 2 L of a 40:60 (v/v) mixture of
ethyl acetate and cyclohexane.
Esters of Glycerol and Undecylenic Acid
The direct esterification reaction between glycerol and
undecylenic acid catalyzed by DBSA can generate three
different esters: glycerol mono-, di- and triundecenoate
(Table 1). Glycerol has three OH groups, which accept acyl
groups during esterification reactions with undecylenic
acid. For each group of partial esters of glycerol, two
regioisomers are possible: glycerol α-monoundecenoate
(α-GMU) and glycerol β-monoundecenoate (β-GMU)
for monoglycerides, glycerol α,β-diundecenoate (α,β-
GDU) and glycerol α,α′-diundecenoate (α,α′-GDU) for
the diglycerides. The expected overall ester was glycerol
α,β,α′-triundecenoate (α,β,α′-GTU).
Purification of Diglycerol Esters
Thirty grams of reaction mixture was used. DGTeU
(
R = 0.89), DGTU (R = 0.52) and UA (R = 0.47)
f
f
f
were purified by elution with 3 L of chloroform. DGDU
(
R = 0.10) and DGMU (R = 0) were recoved by elution
f
f
with a 2:98 (v/v) mixture of methanol and chloroform.
Mass Spectrometry
We used a Waters GCT Premier high-resolution mass spec-
trometer. The samples were dissolved in chloroform. DCI
CH ionization techniques were used, with direct introduc-
tion and GC/MS coupling, to the determination of exact
masses.
Determination of the Chemical Structures of Esters
of Glycerol and Undecylenic Acid, in Ascending Order
of Polarity
4
NMR
Glycerol Triundecenoate (GTU) The mass spectrum for
the compound corresponding to this retardation factor is
presented in Fig. 1a. The peak at m/z 590.45 corresponds to
NMR spectra were recorded on a Fourier 300 (300 MHz)
spectrometer (Bruker, Karlsruhe, Germany). The acquisi-
tion temperature was set to 300 K. The samples were dis-
+
the parent ion of α,β,α′-GTU with the formula [C H O ] .
3
6
62
6
+
The m/z 407.32 peak corresponds to [C H O ] , charac-
2
5
43
4
solved in deuterated chloroform (CDCl ). Chemical shifts
teristic of the loss of an undecylenic acid fragment with the
3
+ +
formula [C H O ] . The m/z 241.18 peak [C H O ]
11 19 2 14 25 3
were determined with tetramethylsilane at 0 ppm (TMS) as
1
13
the reference. Standard sequences were used for the H,
C
corresponds to the loss of two undecylenic acid fragments
+
and DEPT-135 NMR spectra.
with the formula [C H O ] . The m/z 166.14 peak corre-
1
1
19
2
+
sponds to a fragment with the formula [C H O] .
1
1
19
1
H NMR analysis of this sample (Fig. 1b, Table 2)
Results and Discussion
revealed chemical shifts between 4.08 and 4.19 ppm and
between 4.24 and 4.34 ppm, corresponding to the four
hydrogens in the α and α′ positions of glycerol. The heav-
ily deshielded multiplet between 5.21 and 5.31 ppm cor-
All the components separated by TLC were identified. The
retardation factors of glycerol esters and diglycerol esters
vary linearly with LogP (Table 1, and Supporting informa-
tion Figs. 2 and 3). Molecules having more free OH groups
are most strongly retarded by the silica stationary phase by
binding to the silanols of the silica. The OH groups act as
responds to the H hydrogen. The chemical shifts between
β
0.95 and 1.46 ppm correspond to the hydrogens car-
ried by carbons 4–8 of undecylenic acid. Between 1.53
and 1.70 ppm the chemical shifts correspond to the H3
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J Am Oil Chem Soc (2015) 92:1567–1577
Table 1 Molecular structures of the esters of glycerol and diglycerol with undecylenic acid
GMU
f
Mw = 258.35 g.mol
ΟΗ
α-GMU
R = 0.14
-1
R =
O
ΟΗ
10
8
6
4
2
R
β
α
α'
1
11
β-GMU
α'1
9
7
5
3
OH
O
R
O
β1
α1
OH
GDU
f
Mw = 424.61 g.mol
GTU
f
Mw = 590.87 g.mol
α,α’-GDU
OH
R = 0.52
R = 0.86
α,β,α’-GTU
-
1
-1
O
R
O
R
O
β
R
α
α'
R
α,β-GDU
O
O
O
β
R
R
α
α'
O
R
OH
β1
α1
α'1
DGMU
f
Mw = 332.43 g.mol
DGDU
f
Mw = 498.69 g.mol
α,α’-DGDU
ΟΗ
OH
α-DGMU
R = 0
R = 0.10
-
1
-1
O
Ο
O
ΟΗ
OH
R
β
β'
R
α
γ
γ '
α'
O
Ο
OH
HO
α,β-DGDU
R
β
β'
α
γ
γ '
α'
R
O
α3
β,β’-DGDU
OH
R
O
β3
β-DGMU
O
O
OH
γ3
R
β1
β'1
α1
γ1
γ '1
α'1
ΟΗ
OH
O
γ '3
O
Ο
O
α,β’
R
-DGDU
R
β
β'
R
OH
O
R
O
β'3
α
γ
γ '
α'
O
O
OH
α'3
R
β2
β'2
α2
γ 2
γ'2
α'2
HO
DGTU
f
Mw = 664.95 g.mol
DGTeU
f
Mw = 833.21 g.mol
α,β,α’-DGTU
α,β,β’,α’-DGTeU
R = 0.52
R = 0.89
R
O
-
1
-1
OH
R
O
R
O
O
O
O
R
β
β'
R
α
γ
γ '
α'
O
O
O
R
β
β'
R
α
γ
γ '
α'
α,β,β’-DGTU
R
O
R
O
O
O
OH
R
β1
β'1
α1
γ1
γ '1
α'1
GMU glycerol monoundecenoate, GDU glycerol diundecenoate, GTU glycerol triundecenoate, DGMU diglycerol monoundecenoate, DGDU
diglycerol diundecenoate, DGTU diglycerol triundecenoate, DGTeU diglycerol tetraundecenoate, R TLC retardation factor, Mw molecular
f
weight
hydrogen, between 1.97 and 2.09 ppm to H and between
H , respectively. These characteristics of undecylenic
9
10
2
4
.24 and 2.37 ppm to the H hydrogen. Those between
.88 and 5.04 ppm and between 5.72 and 5.89 ppm cor-
acid were common for all glycerol esters and will not be
discussed in the further sections. These findings are char-
acteristic of triglycerides [30, 31], such as α,β,α′-GTU in
particular.
2
respond to the hydrogens carried by the ethylenic carbon
residues at the end of the undecylenic acid chain, H11 and
1
3

J Am Oil Chem Soc (2015) 92:1567–1577
1571
Fig. 1 a Mass spectrum of
a
1
GTU, b H NMR spectrum of
GTU, and c 13C NMR and
13
C
DEPT-135 spectra of GTU
b
c
The 13C NMR spectrum of GTU (Fig. 1c, Table 3) con-
tains the chemical shift at 62.25 ppm that is characteristic
of the α and α′ carbons of glycerol. The shift at 69.04 ppm
is characteristic of the β carbon. This was confirmed by the
DEPT-135 analysis, in which the α and α′ carbons give a
positive signal, whereas the β carbon gives a negative sig-
nal. The chemical shifts characteristic of the carbons of
the undecylenic acid, e.g. at 114.13 and at 139.19 ppm
which are characteristic of the ethylenic carbon residues
C11 and C , are common for all glycerol esters. They are
10
1
3

1
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J Am Oil Chem Soc (2015) 92:1567–1577
Table 2 1H NMR chemical shifts of glycerol and diglycerol esters of
Table 3 13C NMR chemical shifts of glycerol and diglycerol esters
undecylenic acid
of undecylenic acid
Molecules
GTU
Chemical shifts (ppm) Hydrogens
Molecules
GTU
Chemical shifts (ppm) Carbons
4.08–4.19
α
62.25
69.04
65.02
68.37
61.70
62.16
72.26
70.48
65.52
63.70
62.98
69.70
69.90
69.98
72.55
69.93
68.88
62.42
65.24
68.77
69.06
72.25
72.25
70.66
68.77
64.71
64.82
63.63
72.80
173.13–174.68
α, α′
β
4
5
.24–4.34
.21–5.31
α′
β
GDU
α, α′
β
GDU
GMU
4.00–4.35
α, β, α′
5
3
.04–5.12
.69–3.75
β1
α1
α′1
β1
α′
α′1
4.07–4.27
α
3
3
3
.54–3.75
.87–3.98
.80–3.85
α′
GMU
β
β
α1, α′
α
DGTeU
3.45–3.80
γ, γ′
DGTeU
DGTU
α, α′
γ,γ′
β, β′
γ
4
5
.00–4.40
.10–5.25
α, α′
β, β′
DGTU
DGDU
3.21–4.46
.12–5.25
3.43–3.86
α, γ, γ′, β′, α′
5
β
γ′
β, β′
α, α′
β1
β2, β2′
α
β
3
5
5
.95–4.25
.14–5.28
.35–5.45
β′
α
α′
DGMU
4.12–4.24
DGDU
DGMU
α, α′
β, β′
γ, γ′
α
4
3
3
3
.06–4.12
.97–4.06
.73–3.89
.45–3.72
β
β′
α′
γ, γ′
2
β
Common shifts of unde-
cylenic chain
2.24–2.37
β′
1
0
1
5
4
.53–1.70
.95–1.46
.97–2.09
.72–5.89
.88–5.04
3
γ
4–8
9
γ′
α′
10
11
β1
1
Common shifts of undecylenic
chain
2
1
4.84–34.27
2–9
10
11
GMU glycerol monoundecenoate, GDU glycerol diundecenoate,
GTU glycerol triundecenoate, DGMU diglycerol monoundecenoate,
DGDU diglycerol diundecenoate, DGTU diglycerol triundecenoate,
DGteU diglycerol tetratundecenoate
39.13–139-50
114.13–114.50
GMU glycerol monoundecenoate, GDU glycerol diundecenoate,
GTU glycerol triundecenoate, DGMU diglycerol monoundecenoate,
DGDU diglycerol diundecenoate, DGTU diglycerol triundecenoate,
DGteU diglycerol tetratundecenoate
reported in the Table 3 and will not be discussed further.
This analysis is consistent with a triglyceride [32], such as
α,β,α′-GTU.
crude formula of GDU is clearly identified, but nevertheless
does not differentiate between the α,α′-GDU and α,β-GDU
isomers.
Glycerol Diundecenoates (GDU) The mass spectrum of
this component (Table 4) contained a peak at m/z 424.32,
with the formula C H O , corresponding to the exact
1H NMR is a technique that is very suitable for the iden-
tification and quantification of regioisomers of diacylg-
lycerol [19]. On the spectrum shown at the top of Table 4,
the multiplet between 4.0 and 4.35 ppm corresponds to the
five H , H and H hydrogens of the glycerol of α,α′-GDU
2
5
44
5
molecular mass of α,α′-GDU or α,β-GDU. The fragment at
m/z 407.32 resulted from the loss of a water molecule from
GDU. The fragment at m/z 241.18 corresponds to the loss
+
of an undecylenic fragment with the formula [C H O ]
1
1
19
2
α
α′
β
and reveals the presence of an ionized fragment of glycerol
(Table 2). The chemical shifts between 5.04 and 5.12 ppm
correspond to the Hβ1 hydrogen of the α,β-GDU isomer.
+
monoundecenoate with the crude formula [C H O ] . The
1
4
25
3
1
3

J Am Oil Chem Soc (2015) 92:1567–1577
1573
Table 4 Mass spectra and H, 13C and DEPT-135 NMR spectra of the esters of glycerol undecenoate and diglycerol undecenoate
1
Mass spectra
1H NMR spectra
13C NMR and 13C DEPT-135 spectra
m/z
= 407.32
-
2
H O
m/z
= 241.18
O
O
O
O
77 76 75 74 73 72 71 70 69 p6 p8 m 67 66 65 64 63 62 61 60 59
OH
m/z
= 424.32
GDU
6
.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
190
170
150
130
110
ppm
90 80 70 60 50 40 30 20 10
0
ppm
m/z
=
407.32
m/z = 227.16
m/z
=
241.18
-
H
2
O
O
+2H et - 2H2O
75
74
73
72
71
70
69
68
6
7
p
p
6
m
6
65
64
63
62
61
60
59
58
57
O
OH
OH
+H
m/z
= 259.19
GMU
DGTeU
6
.0
5.4
4.8
4.2
3.6
ppm
3.0
2.4
1.8
1.2
180 170 160 150 140 130 120 110 100 90
ppm
80
70
60
50
40
30
20
m/z
=
407.32
7
0.5
69.5
68.5
67.5
66.5 ppm 65.5
64.5
63.5
62.5
61.5
m/z
=
241.18
O
O
m/z
=
647.49
O
O
O
O
O
O
O
m/z
=
831.63
180
170
160
150
140
130
120
110
100 ppm 90
80
70
60
50
40
30
20
10
6.0
5.4
4.8
4.2
3.6
3.0
2.4
1.8
1.2
ppm
m/z 315.22
m/z 241.18
O
O
O
O
O
O
OH
73.0
71.5
70.0
68.5
ppm
67.0
65.5
64.0
62.5
m/z 481.35
O
m/z 407.34
-
2
H O
m/z 648.49
DGTU
DGDU
6.0
5.5
5.0
4.5
4.0
3.5
ppm
3.0
2.5
2.0
1.5
1.0
170
160
150
140
130
120
110
100
90
ppm
80
70
60
50
40
30
20
10
m/z = 315.22
m/z = 241.18
-
2
H O
7
3.5
72.5
71.5
70.5
69.5
pp m6 8.5
67.5
66.5
65.5
64.5
-
2
H O
m/z = 481.1
6.0
5.5
5.0
4.5
4.0
3.5
ppm
3.0
2.5
2.0
1.5
1.0
170 160 150 140 130 120 110 100
90
ppm
80
70
60
50
40
30
20
10
m/z 131.07
m/z 241.18
73.0
71.5
70.0
68.5 ppm 67.0
66.0
64.5
63.0
DGMU
m/z 315.22
6
.0
5.5
5.0
4.5
4.0
3.5
ppm
3.0
2.5
2.0
1.5
1.0
170 160 150 140 130 120 110 100
90
80
70
60
50
40
30
20
f1 (ppm)
GMU glycerol monoundecenoate, GDU glycerol diundecenoate, DGMU diglycerol monoundecenoate, DGDU diglycerol diundecenoate, DGTU
diglycerol triundecenoate, DGTeU diglycerol tetraundecenoate
1
3

1
574
J Am Oil Chem Soc (2015) 92:1567–1577
The doublet between 3.69 and 3.75 ppm corresponds to
the two Hα′1 hydrogens characteristic of the presence of the
α,β-GDU regioisomer. These findings are consistent with
those of Hatzakis et al. [33]. It was thus possible to show
that there was 82 % α,α′-GDU and 18 % α,β-GDU in the
at 70.48 ppm. The chemical shifts characteristic of unde-
cylenic chain were found. This spectrum confirms the
structure of α-GMU. It was not possible to detect the shifts
characteristic of β-GMU because of the limited sensitivity
of the apparatus used.
GDU sample of R 0.52.
f
1
3
On the C NMR spectrum (Tables 3, 4), the chemical
shifts corresponding to the undecylenic chains of GDU
were found. On DEPT-135 analysis, the chemical shifts of
Esters of Diglycerol and Undecylenic Acid The esterifica-
tion reaction between undecylenic acid and linear diglycerol
can generate four types of diglycerol: mono-, di-, tri- and
tetraesters of diglycerol (Table 1). Several isomers of these
types of linear diglycerol ester are likely to be present: (1)
α-DGMU and β-DGMU for diglycerol monoesters; (2)
four isomers of diglycerol diundecenoate: α,α′-DGDU, α,β-
DGDU, β,β′-DGDU and α,β′-DGDU; (3) two types of diglyc-
erol triundecenoates: α,β,α′-DGTU and α,β,β′-DGTU and (4)
α,β,α′,β′-DGTeU. It is important to detect the presence of each
regioisomer and to determine their relative proportions in the
reaction mixture reliably, particularly as not all the molecular
structures of these molecules have been published. We used
silica gel chromatography for purification, with TLC as an elu-
tion control. Spectroscopic methods were used to determine
the structures associated with the retardation factors and the
proportions of the various regioisomers identified.
C and C at 65.02 ppm, C at 61.70 and Cα1′ at 62.16 ppm
α
α′
α1
gave positive signals. This confirms the presence of the two
regioisomers, α,α′-GDU and α,β-GDU, consistent with the
attributions of chemical shifts published for other diacylg-
lycerols [33].
Glycerol Monoundecenoates (GMU) The mass spec-
trometry analysis for this sample (Table 4) showed that the
peak at m/z 259.19 corresponded to the molecular mass of
+
the ionized molecule [C H O ] , and the crude formula
1
4
27
4
C H O of α-GMU and β-GMU. The peak at m/z 241.18
1
4
26
4
+
[C H O ] ) corresponds to the loss of a molecule of
14 25 3
(
water from GMU. The peak at m/z 185.15 corresponds to a
+
molecule with the crude formula of [C H O ] . The loss
1
1
21
2
of a molecule of water from this molecule gives rise to the
Qualitative analysis of the reaction mixture by TLC
revealed the presence of various molecules with differ-
ent R values, from the least to the most polar: R = 0.89,
+
peak at 167.14, with a crude formula of [C H O] . The
1
1
19
peak at m/z 149.13 corresponds to the loss of a molecule of
f
f
+
+
water from [C H O] , yielding [C H ] .
0.61, 0.47, 0.10, 0. The component with an R of 0.47 is
1
1
19
11 17
f
1
H NMR analysis (Tables 2, 4) showed that the chemi-
cal shifts between 3.87 and 3.98 ppm corresponded to
the hydrogens in positions H , H and H of glycerol.
undecylenic acid. It was identified by comparison with a
standard.
α
α′1
1
H hydrogens display a chemical shift between 4.07 and
Determination of Chemical Structures on the Basis
of Increasing Polarity of Esters of Diglycerol
and Undecylenic Acid
α
4
.27 ppm. These hydrogens are more deshielded than the
H hydrogen (3.87–3.98 ppm). The two H hydrogens of
β
α′
α-GMU yield a multiplet between 3.54 and 3.75 ppm. Fol-
lowing esterification of the hydroxyl site in the α position
Diglycerol Tetraundecenoate (DGTeU) The mass spec-
of glycerol, the two H hydrogens become more deshielded
trum for the molecule with an R of 0.89 is presented in
α
f
than the Hα′ hydrogens and they have a higher chemical
shift (4.07 and 4.27 ppm). This difference in chemical shift
Table 4. The fragment with m/z 831.63 has a molecular
mass corresponding to that of ionized diglycerol tetraun-
decenoate. The fragment at m/z 649.49 corresponds to the
loss of an undecylenic fragment. The m/z 407.32 fragment
corresponds to the loss of half the diglycerol tetraunde-
cenoate molecule. The fragment at m/z 241.18 corresponds
to an ionized fragment of glycerol monoundecenoate. The
presence of these various fragments identifies the molecule
obtained as diglycerol tetraundecenoate.
between H and H is due to the ester group, which is elec-
α
α′
tron withdrawing. These results thus confirm the presence
of the α-GMU regioisomer.
We can also see the doublet between 3.80 and 3.85 ppm
corresponding to the four Hα1 and Hα′1 hydrogens of
β-GMU. This finding is consistent with those of Compton
et al. [20, 34] for other monoglycerides, making it possible
to quantify the relative proportions of the two regioisomers,
α-GMU and β-GMU. We found that β-GMU accounted
for 7.64 %, and that α-GMU accounted for 92.34 % of the
1
On the H NMR spectrum (Tables 2, 4), the structure
of DGTeU is identified by the presence of hydrogens Hγ
and H , specific to the carbons carrying the ether group of
γ′
sample with R 0.14.
On the C NMR spectrum (Table 4), the chemical shifts
at 70.62, 65.52 and 63.70 ppm correspond to C , C and
diglycerol, for which a multiplet is observed between 3.45
f
1
3
and 3.80 ppm. The H and H hydrogens are identified by
α α′
the presence of a multiplet between 4.00 and 4.40 ppm.
The chemical shifts between 5.10 and 5.25 ppm correspond
α
β
C , respectively (Table 3). Analysis by DEPT-135 confirms
α
the identification of C at 63.48 ppm, Cα′ at 65.52 and Cβ
to the H and H hydrogens.
α
β β′
1
3

J Am Oil Chem Soc (2015) 92:1567–1577
1575
On the 13C NMR spectrum (Tables 3, 4), the DEPT-135
ing of the glycerol and the undecylenic chain. On the basis
of these fragments, this molecule was identified as DGDU.
experiment distinguishes between CH and CH . The chem-
2
1
ical shift at 62.98 ppm is characteristic of C and C . The
The H NMR analysis (Tables 2, 4) shows the two mul-
α
α′
shift at 69.70 ppm is characteristic of C and C , and that
tiplets between 3.43 and 3.86 ppm and between 3.95 and
4.25 ppm corresponding to the two types of hydrogens
on the diglycerol head. The least deshielded hydrogens,
γ
γ′
at 69.90 ppm is characteristic of C and C . This profile
β
β′
corresponds exactly to the three types of carbon present in
diglycerol tetraundecenoate. We thus find all the character-
istic carbons of the undecylenic chain. No discussion of the
attribution of the diglycerol carbons in diglycerol tetraun-
decenoate has ever been published. Only the carbonyl
group carbons of the ester, at 173.16 ppm, and those of the
terminal double bond have been identified [16].
between 3.43 and 3.86 ppm, correspond to the H and H
β
β′
hydrogens, and the most deshielded hydrogens, between
3.95 and 4.25 ppm, correspond to the four H and H
α
α′
hydrogens.
The peaks between 5.14 and 5.28 ppm and between 5.35
and 5.45 ppm are two multiplets that correspond to hydro-
gen Hβ1 of α,β-DGDU, and hydrogens Hβ2 and Hβ′2 of β,β′-
DGDU, respectively.
Diglycerol Triundecenoate (DGTU) Diglycerol triunde-
cenoate has a molecular mass of 664.952 g/mol. The loss
of a water molecule thus yields a fragment at m/z 648.494
The regioisomer composition of the isolated mixture
of diglycerol diesters can be calculated on the basis of the
integration of the characteristic peaks for each diglycerol
ester: 73.8 % α,α′-DGDU, 22.8 % α,β-DGDU and 3.4 %
β,β′-DGDU. The α,β′-DGDU form was not detected.
(
Table 4). The fragment at m/z 481.350 results from the loss
of an undecylenic chain. This fragment was also observed
on the mass spectrum of DGDU. The peak at m/z 407.34
corresponds to the loss of a glycerol monoester fragment.
The fragments at m/z 315.217 and 241.180 correspond to
the loss of two undecylenic chains from diglycerol triunde-
cenoate and the loss of a glycerol monoester fragment and
an undecylenic chain, respectively. The presence of these
fragments indicates that the molecule isolated is diglycerol
triundecenoate.
1
3
On the C NMR spectrum shown in Table 4, there are
six peaks corresponding to the six carbons of diglycerol
(Table 3). These peaks are grouped in twos, at 68.77 ppm
for the C and C carbons, and 69.06 ppm (C16 and C13),
α
α′
corresponding to the two CH carbons carrying the second-
ary hydroxyl groups of diglycerol. The peak at 72.25 ppm
corresponds to the C and C carbons; this peak shows
γ
γ′
On the 1H NMR spectrum (Table 4), the multiplet
between 3.21 and 4.46 ppm corresponds to the nine hydro-
gens of diglycerol: the H , H , H , H and H hydrogens
that the esterification of diglycerol with undecylenic acid
occurs via the primary hydroxyl groups in positions α and
α′. This analysis confirms that the molecule isolated is the
symmetric molecule α,α′-DGDU. The DEPT-135 analysis
confirmed the presence of the α,β-DGDU and β,β′-DGDU
α
γ
γ′
β′
α′
(
Table 2). The Hβ hydrogen characteristic of DGTU is
deshielded and visible between 5.12 and 5.25 ppm. It yields
a multiplet. We observed none of the hydrogens character-
istic of the α,β,β′-diglycerol triundecenoate isomer.
regioisomers, because the C , C , C and C yielded a pos-
α
α′
γ
γ′
itive signal, corresponding to CH groups. The C and C
2
β
β′
1
3
On the C NMR spectrum for this sample (Table 4) the
carbons gave a negative signal, corresponding to CH. We
did not detect the carbons corresponding to the α,β′-DGDU
form.
carbons carrying the ether group, C and C , are visible
γ
γ′
at 69.98 and 72.55 ppm. The strong deshielding of the Cγ′
carbon results from its close proximity to the CH carbon
carrying the OH group. The C close to the CH of the ester-
Diglycerol Monoundecylenate (DGMU) Table 4 shows
the mass spectrum for this sample. The fragment at m/z
315.21 corresponds to the loss of a water molecule from
DGMU, during its ionization. The peak at m/z 241.18 cor-
responds to the loss of a glycerol fragment from α-DGMU
and β-DGMU. The peak at m/z 149.08 results from the loss
of the diglycerol fragment, and the peak at m/z 131.07 cor-
responds to the loss of a water molecule from this fragment,
during its ionization.
γ
ified C is more shielded. The chemical shifts (Table 4) of
β
the C and C carbons can be seen at 69.93 and 68.88 ppm,
β
β′
respectively. The esterified Cα and Cα′ carbons display
shifts at 62.42 and 65.24 ppm. We can also see the carbons
of undecylenic chain. This spectrum is characteristic of
α,β,α′-DGTU. No chemical shift indicative of the presence
of the α,β,β′-DGTU was detected.
1
Diglycerol Diundecylenate (DGDU) The characteriza-
tion of this sample by mass spectrometry (Table 4) revealed
the presence of a fragment at m/z 481.1 corresponding to
the loss of a molecule of water from DGDU. The fragment
at m/z 315.22 corresponds to the loss of an undecylenic
fragment from the symmetric diester. The fragment at m/z
On the H NMR spectrum of Table 4, the multiplet
between 3.45 and 4.25 ppm corresponds to the hydrogens
characteristic of the linear diglycerol head of α-DGMU
(Table 2). The peak between 4.12 and 4.24 ppm corre-
sponds to the H hydrogens. The peaks between 4.06 and
α
4.12 ppm, and between 3.97 and 4.06 ppm correspond to
2
41.18 corresponds to the loss of a part of DGDU consist-
the H and H hydrogens. The chemical shift between 3.73
β β′
1
3

1
576
J Am Oil Chem Soc (2015) 92:1567–1577
and 3.89 ppm is attributed to the Hα′ hydrogens, and the
multiplet between 3.45 and 3.72 ppm corresponds to the
4. Wang Y, Zhao M, Song K, Wang L, Han X, Tang S, Wang Y
(
2010) Separation of diacylglycerols from enzymatically hydro-
lyzed soybean oil by molecular distillation. Sep Purif Technol
75:114–120
four H and H hydrogens. The complexity of the multiplet
γ
γ′
between 3.4 and 4.3 ppm suggests that the β-DGMU regio-
isomer may be present, although its characteristic shifts are
not visible. Additional analyses are required to confirm or
exclude this hypothesis.
5. Holstborg J, Pedersen BV, Krog N, Olesen SK (1999) Physical
properties of diglycerol esters in relation to rheology and stabil-
ity of protein-stabilised emulsions. Colloids Surf B 12:383–390
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.
Kumar TN, Sastry YSR, Lakshminarayana G (1989) Preparation
and surfactant properties of diglycerol esters of fatty acids. J Am
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On the 13C NMR spectrum (Table 4), the presence of
the α-DGMU form was confirmed by the chemical shift
7. Shrestha LK, Shrestha RG, Solans C, Aramaki K (2007) Effect
of water on foaming properties of diglycerol fatty acid ester-oil
systems. Langmuir 23:6918–6926
at 72.25 ppm, corresponding to the C carbon bearing the
α
esterified hydroxyl group of the diglycerol (Table 3). The
8
.
Kunieda H, Shrestha LK, Acharya DP, Kato H, Takase Y, Gutié-
rrez JM (2007) Super-stable nonaqueous foams in diglycerol
fatty acid esters-non polar oil systems. J Disper Sci Technol
chemical shift at 70.66 ppm corresponds to the C carbon,
β
and that at 68.77 ppm corresponds to C . The C and C
β′
γ
γ′
2
8:133–142
carbons give rise to shifts at 64.71 and 64.82 ppm. Finally,
the Cα′ carbon bearing the primary hydroxyl group yields
9
.
Matsumiya K, Nakanishi K, Matsumura Y (2014) Destabiliza-
tion of protein-based emulsions by diglycerol esters of fatty
acids—The importance of chain length similarity between dis-
persed oil molecules and fatty acid residues of the emulsifier.
Food Hydrocoll 25:773–780
a shift at 63.63 ppm. The C , C , C , C and C carbons
α′
γ
γ′
β′
α
gave positive signals on DEPT-135 analysis; they corre-
spond to the CH groups of α-MUG. The chemical shift at
2
1
0. Mouloungui Z, Rakotondrazafy V, Valentin R, Zebib B (2009)
Synthesis of glycerol 1-monooleate by condensation of oleic
acid with glycidol catalyzed by anion-exchange resin in aqueous
organic polymorphic system. Ind Eng Chem Res 48:6949–6956
1. Van der Steen M, Stevens CV (2009) Undecylenic acid: a valu-
able and physiologically active renewable building block from
castor oil. Chem Sus Chem 2:692–713
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Cunin F (2010) Grafting of monoglyceride molecules for the
design of hydrophilic and stable porous silicon surfaces. New J
Chem 34:29–33
7
2.82 ppm corresponds to CH –OH, confirming the pres-
2
1
ence of β-DGMU, as suggested by the H NMR spectrum.
1
1
Conclusion
The direct, non-selective esterification reaction between
glycerol and undecylenic acid or between diglycerol and
undecylenic acid generates all the possible positional iso-
mers of glycerol or diglycerol esters. Isolation of the iso-
mers in high purity was achieved by silica gel chromatog-
raphy. The molecular structures of the isolated compounds
1
1
3. Cauvel A, Renard G, Brunel D (1997) Monoglyceride synthesis
by heterogeneous catalysis using MCM-41 type silicas function-
alized with amino groups. J Org Chem 62:749–751
4. Berger M, Schnelder M (1992) Enzymatic esterification of glyc-
erol II. Lipase-catalyzed synthesis of regioisomerically pure
1
were characterized and identified by mass spectrometry, H
1
(3)-rac-monoacylglycerols. J Am Oil Chem Soc 69:961–965
1
3
NMR, C NMR and DEPT-135. The polarity of these non-
ionic amphiphilic esters directly affected their affinity for
organic and inorganic solvents and were found to behave
very differently from carboxylic acid amphiphilic mol-
ecules, such as undecylenic acid.
15. Chidambaram N, Bhat S, Chandrasekaran S (1992) A highly
selective methodology for the direct conversion of acetals to
esters. J Org Chem 57:5013–5015
1
6. Brito DHA, Cavalcante IM, Rocha NRC, Maier ME, Lima APD,
Schanz MTGF, Ricardo NMPS (2014) Synthesis and characteri-
zation of diglycerol tetraundecylenate as potential biolubricant.
In: Abstract of the IX Congresso Brasileiro de Análise Térmica E
Calorimetria, Serra Negra, SP, Brasil, 2–12 November 2014
Acknowledgments The authors would like to thank the French
government and the Midi-Pyrenees Region for their financial support
through the Fond Unique Interministériel (FUI) and OSEO.
17. Fregolente LV, Fregolente PBL, Chicuta AM, Batistella CB,
Maciel Filho R, Wolf-Maciel MR (2007) Effect of operating
conditions on the concentration of monoglycerides using molec-
ular distillation. Chem Eng Res Des 85:1524–1528
Compliance with Ethical Standards
1
8. Szelag H, Zwierzykowski W (1983) The application of molecu-
lar distillation to obtain high concentration of monoglycerides.
Eur J Lipid Sci Technol 85:443–446
Conflict of interest The authors declare no conflict of interest.
1
9. Compton DL, Laszlo JA, Eller FJ, Taylor SL (2008) Purifica-
tion of 1,2-diacylglycerols from vegetable oils: comparison of
molecular distillation and liquid CO2 extraction. Ind Crop Prod
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