FISHERIES AND MARINE SERVICE
Translation Series No.
4335
Autoxidation of unsaturated fatty acid methyl esters.
I. Monoene compounds
By N. Ikeda and K.
Original title:
From:
Tukuzumi
Fuhowashibosan mechiruesteru no jidosanka
(Dai 1 poi.
Yukagaku (J. Jpn Oil Chem. Soc.)
27 (1): 21-25, 1978
Translated by the Translation Bureau (SH/PS)
Multilingual Services Division
Department of the Secretary of State of Canada
Department of Fisheries and the Environment
Fisheries and Marine Service
Technology Branch
Halifax,.N.S.
12 Pages typescript
.
-
r^-^►
DÉPARTMENT OF THE SECRETARY OF STATE
y
SECRÉTARIAT D'ÉTAT
TRANSLATION BUREAU
E,.,^.
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DIVISION
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TRANSLATED FROM - TRADUCTION DE
INTO - EN
English
Japanese
AUTHOR - AUTEUR
Nobuo Ikeda and Kazuo Fukuzumi
TITLE IN ENGLISH - TITRE ANGLAIS
Autoxidation of Unsaturated Fatty Acid Methyl Esters. I.
TITLE IN FOREIGN LANGUAGE ( TRANSLITERATE FOREIGN CHARACTERS)
TITRE EN LANGUE ÉTRANGÉRE ( TRANSCRIRE EN CARACTÉRES ROMAINS)
Fuhowashibosan mechiruesteru no jidosanka '(Dai 1 po)
REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE,FOREIGN CHARACTERS.
REFERENCE EN LANGUE ÉTRANGÉRE (NOM DU LIVRE OU PUBLICATION), AU COMPLET, TRANSCRIRE EN CARACTÉRES ROMAINS.
Yukagaku
REFERENCE IN ENGLISH - RÉFÉRENCE EN ANGLAIS
Journal of Japan Oil ()hem!sts I Society
PAGE NUMBERS IN ORIGINAL
PUBLISHER - ÉDITEUR
DATE OF PUBLICATION
DATE DE PUBLICATION
NUMEROS DES PAGES DANS
L'ORIGINAL
21 - 25
YEAR
ANNEE
PLACE OF PUBLICATION
LIEU DE PUBLICATION
1978
REQUESTING DEPARTMENT
MINISTERE-CLIENT
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DACTYLOGRAPHIÉES
12
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2 4 1978
p.'
Autoxidation of Unsaturated Fatty Acid Meth3A Esters. I.
Monoene Compounds
Nobuo
IKEDA
and Kazuo FUKuzumi
Department of Applied Chemistry, Faculty tof Engineering, Nagoya University
(Furii cho, Chikusa-ku, Nagoya.)
-
Methyl oleate and methyl elaidate were autoxidized in the conditions free from natural antioxidants
and metals. The autoxidation of methyl oleate gave the rate 10.4 times as fast as that found for
methyl elaidate in comparison of the induction period, and 2.2 times in comparison of the rate of the
oxidative weight increase and the hydroperoxide formation rate after the induction period. Results from
analyses of the various autoxidation products from ole,ate and elaidate showed that the autoxidation
products from oleate were formed in a shorter interval of autoxidation in comparison with those from
elaidate, but the amount of the autoxidation products from oleate was similar to that from elaidate if
the autoxidation products were compared at the same autoxidation level (oxidative weight gains). These
results showed that the different rates of the autoxidation between oleate and elaidate resulted from the
different affinity of oxygen molecule with the olefinic double bond of substrates (equations 7 and 8).
LU
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L, Foreword
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12
Many reports have been made on autoxidat ion of various kinds of .
unsaturated fatty acid esters. The autoxidation of methyl oleate and methyl
1)-3) . These studies, however, have not yet
elaidate has also been studied
investigated dynamical data such as autoxidation rates and their relation
with autoxidation mechanisms as seen from autoxidation products. Thus,
differences in autoxidation mechanisms on which dynamical data taken from
autoxidation of unsaturated fatty acid esters are based are still in the
realm of conjecture.
SEC 5-25T (6/76)
21
".
2
Furthermore, in relation to autoxidation of methyl oleate and
methyl elaidate, there have been no studies on the influence which differences in geometrical structure have on autoxidation dynamical data and
autoxidat ion products.
In this study, methyl oleate and methyl elaidate were autoxidized
under fixed conditions free from natural antioxidants and metals.
And
influences on their autoxidation structures and geometrical isomers were
fully investigated from their autoxidation rates and products.
2.
2.1
Experiment
Materials
For use as autoxidation substrate methyl oleate (GLC purity 99.8%)
was prepared from olive oil fatty acids followed by urea-adduct formation
and methyl esterification, and gas chromatography using silicic acid in
n-hexane in order to remove trace amounts of peroxides and pigments.
Methyl elaidate (IR purity 99.9%) was prepared using commercial elaidic
acid, which was crystallized three times in ethanol, then methyl esterified.
It was confirmed by iron chloride (III)-2, 2 1 -bipyridine method 4)
and atomic absorption analysis that these autoxidation substrates were free
of any natural antioxidants or metals.
2.2 Autoxidation
Methyl oleate and methyl elaidate (1.5000-1.5005 g) were added to
beakers (4.1 cm diameter), respectively. They were then autoxidized in an
incubator at 36.5 ± 0.50 0 after trace amounts of volatile matter in the
samples had been removed under 10
-3
mmHg pressure at 30 d 10C for 1 hr.
Weight gains of the samples following autoxidation were measured by the
gravimetric method 5) - 9)
p. 22
3
2.3
Analysis
To investigate the autoxidation mechanism of methyl oleate and
methyl elaidate the following were measured:
IR, UV, NMR and ESR spectra,
peroxide value (POV), molecular weight (MW) and refraction index of samples
at each autoxidation level.
IR spectra were measured using a Shimadzu Co.
IR-27B apparatus and a Japan Spectro Scopic Co. DS-402G apparatus.
The samples were made into solution of carbon tetrachloride and
determined at 0.10 and
9.97 mm NaCl cell. The 9.97 mm cell was measured
-1
at a concentration of 3.98 g/1, which was used for determination of 3520 cm
hydroperoxyl group lo) ' 11) and 3600 cm-1 hydroxyl group 12) .
Absorption based on hydroperoxides when determined at a concentra-1
tion of 66.7 g/1 appeared at 3450 cm
due to intermolecular association.
When determined at a concentration of 3.98 g/1 it appeared at 3520 cm-1
due to intermolecular association decomposition.
The 0.10 mm cell was used for the measurement of isolated trans
double bonds (968 cm-1 ) 13) at a concentration of 66.7 g/l. POV were
14)
measured by iodometric titration
. UV spectra were determined using a
Shimadzu Co. UV-200 type apparatus obtaining a3 -unsaturated carbonyl (223 nm).
NMR spectra were determined in a carbon tetrachloride solution (0.333 g/m1)
with
a high resolving power spectrometer (Japan Electron Optics Laboratory
Co. model JNM-C-6OHL, 60 MHz).
For detection and determination of radicals formed in autoxidation
of samples ESR spectra measurements at 20°C were used (Japan Electron Optics
Lab. Co. model JES-1X).
MW was obtained with a Hitachi Perkin-Elmer model
115 apparatus by measuring depression of vapor pressure of sample solutions
in benzene. Refractive index was measured at 20°C with an Abbe refractometer.
4
Results
3.
covese,
Fig. 1 showeweight gains
in autoxidizing methyl oleate
and methyl elaidate.
50.0
3É,
40.0
■
20.0
Daidaw,
OleMe
60.0
2000
4000
6000
Time (h)
Fig.-1 Weight gain with time in autoxidizing methyl
oleate and methyl elaidate. Conditions : 36.5±
0.5'C ; oil thickness, 1.03 mm.
In changes of weight gains during autoxidation, the time required
to attain 10 mg weight was considered the induction period. After the
induction period, oxidative weight gains increased rapidly.
Table 1 shows the rates of weight gains during and after the
induction period. During the induction period the rate of autoxidation of
methyl oleate was 10.4 times faster than that of methyl elaidate, and after
the induction period 2.0 times faster in the rate of oxidative weight gain.
Maximum values of oxidative weight gain of methyl oleate and methyl elaidate
Table-1 Comparison of induction period
procedure or iodornetric analysis
Weighing procedure
Induction period"
Rate
(h )
Methyl oleate
Methyl Elaidate
390
4040
(mg/I-Q .
1
0.106
0.053
a) Time to gain 10 mg of weight gain or 0.38 X 10 nree,
ra:e, measured by weighing
Iodometric analysis
i
Rate
Induction period"
I (mew kg- l•h-i)
( h .`
3.36
310
i
1.52
3980
I
of peroxide value.
-
5
were roughly equal at 82 mg, which was only about 1/2 the theoretical
weight gain (163 mg) based on the assumption that 1 mol of substrate
absorbs 1 mol of oxygen.
The IR spectra at 0.10 mm cell of each autoxidation sample of
methyl oleate and methyl elaidate showed changes in the following absorp-1
(increases), (2) in hytion bands: (1) In hydroxyl group at 3600 cm
-1
-1
(increases), (3) in aldehyde group at 1725 cm
droperoxyl group at 3450 cm
(5) in the band
(increases), (4) in ketone group at 1715 cm
-1 accompaning polymerization (increases), (6) in the
between 1400-1100 cm
-1
(increase/decrease [respectively]),
isolated trans double bond of 968 cm
-1 (decreases/increases
(7) in the isolated cis double bond of 913 cm
[respectively]).
The maximum value of hydroxyl formation in autoxidation of methyl
oleate and methyl elaidate was 0.60 % (mol/mol sample).
Formation of
aldehyde group was negligible even at maximum autoxidation levels (weight
gains). The NMR spectra of methyl oleate and methyl elaidate autoxidation
samples showed the following changes in each proton signal:
1.91 ppm
(1) 1.96 or
a-methylene (doublet, decrease), (2) 4.07 ppm methene with
hydroperoxyl group (comparatively broad, increase), (3) 5.24 ppm vinylene
(seven lines, decrease).
Fig. 2 shows the decrease of a-methylene proton in NMR spectra
following autoxidation of methyl oleate' and methyl elaidate.
Methyl oleate,
which is relatively easily oxidized, showed a rapid decrease in a-methylene
contents.
However, when
a -methylene contents were plotted against oxida-
tive weight gains instead of time, the changes in a—methylene following
autoxidation were almost same in both autoxidative substrates.
p. 23
6
a. Nlethylene
100.0
80.0
Oleate
Maidate-
100.0
00.0
te
40.0
e
3.00
2.00
)7
lodometric peroxide value
te
Elaidate
•1' 50.0
D
"eeileate
1.00
DP
g
3.00
2.00
Loo
111 Photonsetrie peroxide value
Elaidate \peeClleate
0.00
1
5-D-o-ol-o-b-cro-D-4D-c4-o-rar9±
4.00
Radicals
4.00
Maidate
Fig.-3
°lento
`i
2.00
Peroxide value ( X 10 3meq/kg)
2.00
2000
4000
6000
Time (h)
Relations between- oxidative weight gains
and peroxide values in the autoxidation of
methyl oleate and methyl elaidate, a. a curve
for JR. photometric and iodometric peroxide
values of autoxidized methyl oleate and
methyl elaidate, h. a theoretical curve,
Fig.-2 Change in cr-methylene contents, peroxides
values, and radicals with time in autoxidiz="
log methyl oleate and methyl elaidate.
Fig. 2 shows POV changes obtained by iodometric titration and IR
spectra following autoxidation of methyl oleate and methyl elaidate. POV
changes following autoxidation of samples were similar to those in oxidative weight gains (Fig. 1).
The time required to reach 0.38 x 10
3 meq/kg
POV was considered the induction period. This, together with the formation
rate of hydroperoxide after induction period, is shown in Table 1.
Fig. 3
shows relations between oxidative weight gains and POV in autoxidation
samples.
Tb.. theoretical curve was obtained by assuming that oxygen absorbed by
autoxidation samples (weight gains) forms hydroperoxide quantitatively.
The relationship between weight gains and POV corresponded in both methyl
oleate and methyl elaidate, and with POVs based on iodometric titration
7
and IR spectra measurements (Fig. 3â). Samples corresponded to the
a
a
theoretical curve until oxidized to'66.2 mg weight gain ane2.47 x 10 3 meg/kg
POT.
POV obtained by IR spectra demonstrates that hydroperoxide components
can exist in a state of nonassociation.
Consequently, formation of intra-
molecular hydrogen bonds (difference in IR photometric and iodometric POVs)
was not observed in the autoxidation of either of the substrates.
The
changes in POV of methyl oleate and methyl elaidate were similar to those
following autoxidation of methene proton signal with hydroperoxyl group
at 4.07 ppm NMR spectra.
Fig. 2 shows changes in radical concentrations (e-value 2.0061)
in autoxidizing methyl oleate and methyl elaidate.
Formation of radicals
following autoxidation of substrates increased roughly in a straight line
after the induction period and deviated from the straight line near maximum
radical concentration.
Maximum radical formation rates of methyl oleate
-10
and methyl elaidate were 4.90 and 1.34 x 10
mol/h, respectively. When
the changes in radical concentrations were plotted against oxidative weight
gains instead of time, the changes for methyl oleate and for methyl elaidate
were roughly in agreement with each other.
Fig. 4 shows data on isolated trans double bonds, mean molecular
weights, deig -unsaturated carbonyls (223 nm) and refractive indices following autoxidation of methyl oleate and methyl elaidate.
Isolated trans
double bonds showed an increase in methyl oleate and a decrease in methyl
elaidate.
However, isolated trans double bonds remaining near maximum
oxidative weight gain were greater in methyl elaidate than in methyl oleate.
Data in Fig. 4 demonstrates that when methyl oleate and methyl
elaidate are autoxidized to an oxidative weight gain of over 40 mg,
p. 24
8
polymers and unsaturated carbonyls gradually increase.
, Isolated trans double bond
100r
5: 0
0I e a te
,
370
Molecular weight
Elaidate
350
-Oleate
330
,,
-
310 ,L 96?
25014.00 Fi•-•
Unsaturated
carbonyl
Oleate
Elaidate
J
• Y
2. Où
Refractive index at 20'C
1.4570
Elaidate
1.4550
1.4530
1.4510-,
0
4000
2000
6000
Time (h)
Fig.-4 Change in isolated trans double bond, moler-cular weight, a„8-unsaturated czrbonyl, and
refractive index will time in autoxidizing
methyl oleate and methyl elaidate.
4.
Discussion
The autoxidation mechanism15)/16) of olefins has been generally
proposed as follows:
RH +02 —> R. + •00H
R.
+ 0 —> ROO.
ROO• + RH —> ROOH + R.
ROOH --> RO. + 'OH
RH --> ROH + R. RO.+
Various termination reaction induced by the
ing and disproportionation of free radicals
(1 )
(2)
(3)
(4 )
(5)
couplc;
(6)
9
As apparent in Fig. 3, the fact that the relation between weight
gains and POV agreed with a theoretical curve shows that up until autoxidiz -
ing methyl oleate and methyl elaidate attained 66.2 mg weight gain or
2.47 x 10 3 meek POV, oxygen absorbed in these samples (weight gains) was
used quantitatively in forming hydroperoxide.
Accordingly, chain propagat-
ions based on equations (4) and (5) may be disregarded until the samples
reach the above-mentioned oxidation levels. Moreover, from the facts thatthe
relation between weight gains and POV agreed with the theoretical curve and
that the majority of the radicals in autoxidation under normal oxygen
15)
it is
pressure are not alkyl radicals but rather peroxyl radicals
possible that the chemical species of the radicals (Fig.2) measured in
autoxidizing methyl oleate and methyl elaidate might be peroxyl radicals
based on the equations (1) and (2) up until the samples reach the abovementioned autoxidation levels.
In changes of weight gains (Fig. 1) and POV (Fig. 2) in autoxidiz-
ing methyl oleate and methyl elaidate, weight gains and formation of hydroperoxide at autoxidation levels in the initial induction period were hardly
measurable and increased only a little close to the end point of induction
period.
This shows that autoxidation of methyl oleate and methyl elaidate
accompanied by accumulation of peroxyl radicals increases the rate of
radical chain propagation (equation (3)) and reaches a maximum rate of
chain propagation after the end point of induction period.
The rates of weight gains and hydroperoxide formation (Table 1)
after the autoxidation induction period (when indicated in molar units)
were almost the same, showing 3.27 and 1.63 x 10
-6
mol/h for methyl oleate
and methyl elaidate, respectively. These values demonstrate the full
10
dynamics of equations (1), (2) and (3), and show the maximum chain propagation rates under conditions of this study.
Methyl oleate, because of its short induction period and fast
oxidative weight gain rate (Table 1), was oxidized rather rapidly compared
to methyl elaidate. From analytical results of various autoxidation
products it has also become apparent that methyl oleate produced autoxida,
tion products faster than methyl elaidate did; yet in a comparison at the
same autoxidation level (oxidative weight gains), both autoxidation
substrates produced nearly the same autoxidation products. These results
indicate that autoxidation of methyl oleate and methyl elaidate proceeds
in the same mechanism (hydrogen transfer from
d -methylene groups, shift
of double bond to trans or to ois configuration, formation of hydroperoxides,
oxidative polymarization and decomposition), and gives similar products
at the same autoxidation level in spite of the time differences in formation
of autoxidation products.
No differences in the autoxidation products of both methyl oleate
and methyl elaidate at the same autoxidation level are present: it may be
concluded, therefore, that the difference of their oxidative rates is based
on differences in the geometric structures of these autoxidation substrates.
Under these autoxidation conditions where neither pigments nor
light participate (the addition of p -carotene produced no observable effects),
reacting oxygen is a triplet state electrophilic diradical 17) .
When considering steric hindrance, electron density, and stability
of radicals in autoxidation substrates, hydrogen transfer from e -methylene
groups is superior in methyl elaidate than in methyl oleate, while addition
affinity of oxygen towards double bond is greater in methyl oleate than in
11
methyl elaidate. Consequently, the difference of autoxidation rates between
methyl oleate and methyl elaidate can be based on the difference in the
initial autoxidation reactions shown in equations (7) and (8).
+ 02
(7)
o
0
0
+ RH
R'CH=CHR" + R • + • 00H
(8)
By comparison of differences of induction periods, rates of
oxidative weight gains and hydroperoxide formation, it became apparent that
the rates of autoxidation o
methyl oleate and methyl elaidate are
significantly different. Still, the trans isomer effect which reduces
autoxidation rates was relatively great, when compared with effects observed
in non—conjugated diene
18)
and conjugated diene
19)
This may be because hydrogen readily shifts from
fatty acid methyl esters.
a—methylene or active
methylene groups.
When comparing methyl oleate and methyl elaidate autoxidations to
that of methyl linoleate
18)
the induction period for these monoen compounds
is longer, and their oxidation weight gains, formation rate of hydroperoxide,
maximum weight gains, maximum hydroperoxide formation, amount of radical
formation, and changes in mean molecular weight were all smaller, while
isolated trans double bonds and unsaturated carbonyl formation were greater.
Autoxidation differences of methyl oleate and methyl elaidate
were investigated from their autoxidation rates and products.
The results
obtained here should provide useful information for studies on the autoxidation mechanism of lipids and the effects of antioxidants.
(Received July 27, 1977)
12
References
A
1)
2)
3)
H.B. Knight, C.R. Eddy, D. Swern, J. Am. Oil
Chem. Soc., 28, 188 (1951)
R. Schnner, R. Herzschuh, Fete Seifen An
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J. Sliwiok, W.J. Kowalski, Fette Seifen Anstriz.
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4) V.C. Mehlenbacher, "The Analysis of Fats and Oils",
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5) H.S. Olcott, E. Einset, J. Am. Oil Chem. Soc., 35,
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Co., New York, N.Y. (1966) p. 290
16) L. Bateman, Quart. Rev. (London), 8, 147 (1954)
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Co., New York, N.Y. (1966) p. 293
18)
19)
ittEee,
iit1EI-17-,
27, 26 (1978)
jiifL, 27, 99 (1979)
18) Nobuo Ikeda, Kazuo Fukuzumi t this journal
26 (1978)
19) Nobuo Ikeda, Kazuo Flikuzumi,
33 (1978)
this jouvlal
27 1
27,