Epoxide yield determination of oils and fatty acid methyl esters using 1H NMR

Article abstract of DOI:10.1007/s11746-004-0989-1

Product mixtures of epoxidized fatty compounds can be analyzed by using ¹H NMR. Conversion of double bonds and selectivities to different products can easily be calculated. Moreover, if diunsaturated substrates are used in epoxidation reactions, yields to mono- and diepoxidized products can be determined. The effectiveness of this method is proven by comparing some NMR results with those found by GC analysis.

Full text of DOI:10.1007/s11746-004-0989-1

Epoxide Yield Determination of Oils and Fatty Acid
Methyl Esters Using 1H NMR
Hans A.J. Aerts and Pierre A. Jacobs*
Centre for Surface Chemistry and Catalysis, K.U. Leuven, 3001 Heverlee, Belgium
ABSTRACT: Product mixtures of epoxidized fatty compounds
can be analyzed by using 1H NMR. Conversion of double bonds
and selectivities to different products can easily be calculated.
Moreover, if diunsaturated substrates are used in epoxidation re-
actions, yields to mono- and diepoxidized products can be deter-
mined. The effectiveness of this method is proven by comparing
some NMR results with those found by GC analysis.
EXPERIMENTAL PROCEDURES
Materials. Methyl oleate (99%+) and methyl linoleate (99%)
were purchased from MP Biochemicals (Asse, Belgium) and
used as received. High-oleic sunflower oil (SUN) and safflower
oil (SAF) containing 90% trioleate and 80% trilinoleate, re-
spectively, were both received from N.V. Oleon (Oelegem, Bel-
gium). CDCl3 (1% trimethylsilyl), CHCl3, 3-chloroperbenzoic
acid (mCPBA), and MgSO4 (anhydrous) were purchased from
Acros (Geel, Belgium).
Paper no. J10770 in JAOCS 81, 841–846 (September 2004).
KEY WORDS: Epoxidized fatty acids, epoxidized oils, 1H NMR.
1
Analysis using H NMR. Small amounts of substrate and
product mixtures were dissolved in 0.5 mL of CDCl3. 1H NMR
spectra were recorded on a 300 MHz Bruker Avance NMR
spectrometer with a magnetic field of 7.05 T. Only eight scans
were needed to obtain a clear spectrum.
The high environmental burden caused by the use of nonre-
newable petrochemical-based feedstock for the chemical in-
dustry has led to the search for vegetable oil-based alternatives.
In this perspective, as in petrochemical reactions, fatty epox-
ides are very important because they can be used as intermedi-
ates for the production of a variety of chemicals. Up to now,
most of these reaction mixtures have been analyzed by using a
combination of iodine value and oxirane oxygen content (1–3).
This method, however, is labor-intensive and not suitable if
many samples have to be analyzed. Although GC also can be
used, this method can only be applied directly to FA or their
alkyl esters. If fats or oils are used as substrates, transesterifica-
tion is necessary, which makes the analysis time-consuming (4)
and less accurate.
Nowadays, as NMR apparatus is becoming standard equip-
ment in the chemical laboratory, it is realistic to think future
measurements will routinely be carried out this way. The use
of 1H NMR to determine transesterification yields (5) and the
composition of vegetable oils (6) has already been reported.
Although work has been done identifying oxirane functional
groups within FA chains (7), no efforts have been reported
using this method for quantitative analysis.
Analysis using GC. Small amounts of epoxidized alkyl es-
ters were dissolved in CHCl3. GC was performed on a Hewlett-
Packard model 6890 gas chromatograph (N2 carrier gas)
equipped with an FID. A polar BPX 70 column (0.32 mm i.d.
× 60 m) from SGE (Melbourne, Australia) was used with the
following temperature program: 180°C (0 min), 2.5°C/min to
240°C, 240°C (20 min).
Epoxidation using mCPBA. Fatty compound (2 mmol) is
dissolved in 5 or 10 mL of CHCl3. Stoichiometric amounts of
mCPBA are added. The reaction mixture is stirred at room tem-
perature for about 20 min, after which water is added to remove
the mCPBA. The organic layer is separated, dried with MgSO4,
and evaporated under reduced pressure.
RESULTS AND DISCUSSION
Epoxides of methyl oleate, SUN, methyl linoleate, and SAF are
prepared using mCPBA as described in the Experimental Pro-
cedures section. They are all analyzed using 1H NMR; spectra
of the different substrates and products are given in Figures 1
to 4. It is important to see the analogy between the spectra of
the vegetable oils and their methyl esters; differences are due
to the ester function. The assignments of the chemical shifts of
important protons for glycerides and methyl esters (substrates
and products) are summarized in Schemes 1 and 2.
Reaction yields can be determined by evaluating the inte-
gration values of both the appearing and disappearing signals.
To illustrate this feature, oxidation of methyl oleate with
mCPBA is monitored over time by 1H NMR, as shown in Fig-
ure 5. One can clearly see a decrease of the peak area at 2.01
Here, we report our findings on the use of 1H NMR to quan-
tify the yield of fatty epoxides formed in different oxidation re-
actions directly. A variety of substrates such as methyl oleate,
methyl linoleate, high-oleic sunflower oil, and safflower oil are
oxidized and analyzed using 1H NMR. Different products are
easily identified and quantified with little workup. To show the
reliability of the method, comparison is made between GC and
1H NMR and the reproducibility of the method is verified.
*To whom correspondence should be addressed at Centre for Surface Chem-
istry and Catalysis, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium.
E-mail: Pierre.Jacobs@agr.kuleuven.ac.be
Copyright © 2004 by AOCS Press
841
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842
H.A.J. AERTS AND P.A. JACOBS
FIG. 1. 1H NMR spectrum of methyl oleate (lower) and epoxidized methyl oleate (upper).
FIG. 2. 1H NMR spectrum of high-oleic sunflower oil (SUN) (lower) and epoxidized SUN
(upper).
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EPOXIDE YIELD DETERMINATION OF OILS AND FAME USING 1H NMR
843
FIG. 3. 1H NMR spectrum of methyl linoleate (lower) and epoxidized methyl linoleate (upper).
FIG. 4. 1H NMR spectrum of safflower oil (SAF) (lower) and epoxidized SAF (upper).
JAOCS, Vol. 81, no. 9 (2004)

844
H.A.J. AERTS AND P.A. JACOBS
FIG. 5. Oxidation of methyl oleate over time monitored by 1H NMR.
ppm, from the –CH2–CH=CH–CH2– protons, whereas new termine the reaction conversion of double bonds of the methyl
signals are arising at 1.50 (–CH2–CHOCH–CH2–) and 2.90 esters as well as of fats and oils:
ppm (–CHOCH–).
Only the most relevant signals at 2.01 (m) and 2.90 (m) ppm




(N ⋅ A / N
⋅ A ) − (N ⋅ A / N
⋅ A )
2.01 S,t
S
2,0
2.01 S,0
S
2,t
for oleic and at 2.01 (–CH2–CH=CH–CH2–CH=CH–CH2–, m),
2.90 (m), and 3.10 (m) ppm (both oxirane protons) for linoleic
species are used for integration, with both using the signal at
0.88 ppm (–CH3, t) as internal standard because it is unaltered
during reaction. The signal at 2.3 ppm (–CH2–COOR) also can
be used for purposes of an internal standard; the same results
are obtained.
[1]
X (%) =100⋅
N ⋅ A / N ⋅ A
2.01 S,0




S
2,0
As for determination of conversion, the same procedure is
applied for oleic- and linoleic-based species. Reaction conver-
sions, denoted as X, of the double bond(s), at time t, can be de-
termined by using the peak intensity at 2.01 ppm (A2,t) as no
interference from other signals occurs. Because the peak area
at 0.88 ppm (AS,t) remains unaffected by the reaction, it can be
taken as the internal standard. Equation 1 has been used to de-
SCHEME 1
SCHEME 2
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EPOXIDE YIELD DETERMINATION OF OILS AND FAME USING 1H NMR
845
TABLE 1
Analysis of Epoxidation Reaction Mixturesa Using 1H NMR and GC
Amount
oxidant
(mmol)
1H NMR
GC
Substrate
Oxidant
SMO (%)
SDO (%)
X (%)
SMO (%)
SDO (%)
X (%)
Methyl oleate
Methyl oleate
Methyl linoleate
Methyl linoleate
mCPBA
mCPBA
mCPBA
mCPBA
1
2
1
2
96
100
72
—
—
28
95
42
99
53
100
100
84
—
—
16
93
46
100
51
0
100
0
99
aConditions: 1 (or 2 mmol) substrate + stoichiometric amount of oxidant 3-chloroperbenzoic acid (mCPBA), in 5 mL of
CHCl3, were reacted at 293 K for 20 min. SMO, selectivity to monoepoxide; SDO, selectivity to diepoxide; X, conversion of
double bonds.
where A2,0 and A2,t are the intensities of the signals at 2.01 ppm
in the substrate and in the product spectrum and AS,0 and AS,t










(1⋅ A
(1⋅ A
/ N ⋅ A ) − (1⋅ A
/ N ⋅ A )
2.9,t
2,9
S,t
3.1,t 3.1 S,t
S
(%) =100⋅
are the intensities of the resonance peaks of the internal stan-
dard in the substrate and the product spectrum. NS represents
the amount of protons of the internal standard, whereas N2,01
stands for the amount of protons of the signal at 2.01 ppm
(N2.01 = 4).
[3]
[4]
MO
/ N ⋅ A ) + (1⋅ A / N ⋅ A )
∑
2.9 S,t z,t z S,t
2.9,t
z
SDO (%) = 100 − SMO (%)
With respect to selectivity, only one epoxide product can be
formed from oleic species, whereas for linoleic species mono- where Az,t is the signal intensity of by-product peaks, AS,t is the
and diepoxides are formed. Reaction selectivities S for oleic signal intensity of the internal standard, and N is the number of
species at time t can be calculated by using the signal intensi- protons of the functional group (N2.9 = 2; N3.1 = 2). As in the
ties of the peaks at 2.9 ppm (–CHOCH–) and other possible case of oleic base species, the equation can be simplified be-
peaks from by-products taking into account the amount of hy- cause of the absence of by-products.
drogen atoms. Equation 2 can be used to determine selectivi-
ties for the epoxide:
When results obtained by GC and 1H NMR are compared
for the epoxidation of methyl oleate and methyl linoleate, as
shown in Table 1, similar values for conversion and selectiv-
ity are found, which proves the reliability of this method. The
[2] discrepancy between GC and NMR results for methyl
linoleate (Table 1, entry 3) is due to the difference in sensitiv-
ity factors, which we were unable to determine. Because of










1⋅ A
/ N ⋅ A
2.9 S,t
2.9,t
S
(%) =100⋅
Epox
A
/ N ⋅ A ) +
A
/ N ⋅ A
∑
2.9,t
2.9
S,t
z,t z S,t
z
where A2.9,t and AS,t are the intensities of the peaks at 2.9 and the importance of reproducibility, five samples of epoxidized
0.88 ppm (internal standard) and Az,t are the intensities of the by- SUN and SAF were taken at the exact moment and analyzed
products peaks. N2.9 and Nz are the amounts of protons for which by using 1H NMR. In Table 2, for each group of samples the
a peak stands (e.g., N2.9 = 2). Since we observed none during mean value is determined, as is the SD. Only small margins
our reaction, the by-products term drops out in Equation 2.
of error were found. No reproducibility tests were performed
Reaction selectivities for linoleic species are calculated on GC.
from signals at 2.9 and 3.1 ppm. Because the signal intensity at
2.9 ppm (A2.9,t) is due to the protons of the mono- and diepox-
ACKNOWLEDGMENT
ide and the intensity of the peak at 3.1 ppm (A3.1,t) only to those
of the diepoxide, selectivities to these partially and fully oxi-
dized species can be calculated using Equations 3 and 4:
Sponsorship of the research by N.V. Oleon (Belgium) is acknow-
ledged.
TABLE 2
Reproducibility of Resultsa Using 1H NMR
Amount mCPBA
treaction
(min)
Substrate
(mmol)
µ (SMO
)
σ2 (SMO
)
µ (SDO
)
σ2 (SDO
)
µ (X)
σ2 (X)
SUN
SUN
SAF
3
3
6
8
12
10
94.14
94.62
63.20
0.21
0.22
0.16
5.86
5.35
36.80
0.21
0.17
0.16
54.50
51.30
57.75
0.25
0.26
0.33
aFive samples are taken at each time and analyzed by 1H NMR. Conditions include 2 mmol substrate, 10 mL CHCl3, mCPBA
(70%), 293 K. µ, average; σ2, SD; SUN, high-oleic sunflower oil; SAF, safflower oil; for other abbreviations see Table 1.
JAOCS, Vol. 81, no. 9 (2004)

846
H.A.J. AERTS AND P.A. JACOBS
5. Gelbard, G., O. Brès, R.M. Vargas, F. Vielfaure, and U.F.
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[Received December 18, 2003; accepted August 6, 2004]
JAOCS, Vol. 81, no. 9 (2004)