Inhibiting effect of phenolic compounds in initiated oxidation of tridecane

Article abstract of DOI:10.1134/S107042721104015X

Initiated oxidation of tridecane in chlorobenzene solution with molecular oxygen in the presence of a series of phenol derivatives was studied by chemiluminescence and gas-volumetric methods. The kinetic parameters of the antiradical and antioxidant activ

Full text of DOI:10.1134/S107042721104015X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 4, pp. 649−654. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.N. Nikolaevskii, V.V. Morenko, O.P. Kniga, T.N. Ivleva, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 4,
pp. 612−617.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Inhibiting Effect of Phenolic Compounds in Initiated
Oxidation of Tridecane
A. N. Nikolaevskii, V. V. Morenko, O. P. Kniga, and T. N. Ivleva
Donetsk National University, Donetsk, Ukraine
Received July 30, 2010
Abstract—Initiated oxidation of tridecane in chlorobenzene solution with molecular oxygen in the presence
of a series of phenol derivatives was studied by chemiluminescence and gas-volumetric methods. The kinetic
parameters of the antiradical and antioxidant activity of the compounds were determined.
DOI: 10.1134/S107042721104015X
Search for environmentally safe inhibitors of
oxidation of polymeric materials contacting with food
remains a topical problem. Unshielded natural phenols
show promise for this purpose. A solution of tridecane
in chlorobenzene can be a primary model system for
choosing antioxidants, which is due to similarity of
the kinetic relationships of free-radical oxidation with
molecular oxygen of long-chain hydrocarbons and
polymers [1] having certain specific features. It should be
primarily noted that the oxidizability parameter k2(2k6)–0.5
for these systems is lower by an order of magnitude
compared to ethylbenzene and cumene, in agreement
with lower susceptibility to oxidation of secondary C–H
bonds of the substrate, compared to tertiary C–H bonds.
As a result, at comparable rates, the oxidation of saturated
C12–C13 compounds occurs with shorter reaction chains
[1, 2]. The oxidation kinetics is affected by isomerization
of peroxy radicals. As a result, the oxidation products
are not only monohydroperoxides, but also appreciable
amounts of bifunctional hydroperoxides (e.g., >20%
with n-decane [3]) and other compounds [4]. The
kinetic relationships of inhibited oxidation of long-chain
hydrocarbons are studied poorly.
chlorobenzene, initiated with azobis(isobutyronitrile)
(AIBN).An important parameter of the inhibited oxidation
in this system is the rate constant of recombination of
tridecane peroxy radicals k6, which was determined using
the oxygen aftereffect method [5] from the expression
–
–
2.3
√I0 + √I
t = ——––– log ————– ,
(1)
––
2√Wi k6
–
–
√I0 – √I
where t is the time (s); Wi is the initiation rate (mol l–1 s–1);
I and I0 in this experiment are the emission intensities at
successive bubbling of the reaction mixture with argon
and molecular oxygen, respectively (mV).
From the data obtained, we plotted the kinetic curves
of chemiluminescence in TD oxidation (Fig. 1a), and from
the slope of the linear dependences (Fig. 1b) we calculated
the rate constant of the recombination of peroxy radicals:
k6 = (1.87 ± 0.04) × 106 l mol–1 s–1 at 353 K.
The chemiluminescence observed in the reaction is the
emission I0 arising in events of recombination of peroxy
radicals in the course of oxidation of organic substances
with molecular oxygen. The main step of the inhibition
process is the reaction of a phenolic antioxidant (PhOH)
with tridecane peroxy radical:
In this study we examined the specific features of the
inhibiting effect of certain natural unshielded phenols
in comparison with synthetic sterically shielded Ionol
and its derivatives in oxidation of tridecane (TD) in
k7
RO· + PhOH –––– ROOH + PhO·.
(2)
→
2
649

650
NIKOLAEVSKII et al.
(a)
I, mV
I, mV
O2 feeding
t, s
Fig. 2. Variation with time t of the emission intensity I in initi-
ated oxidation of tridecane at various concentrations of syringic
acid с. Т = 353 K; [TD] = 0.82, [AIBN] = 3.04 × 10–2 M; the
same for Fig. 3. с, M: (1) 1.5 × 10–3, (2) 5.0 × 10–4, (3) 2.5 ×
10–4, (4) 1.0 × 10–4, and (5) 2.5 × 10–5.
t, s
I, mV
(b)
To obtain this dependence experimentally, a series of
chemiluminescence curves are recorded at various in-
hibitor concentrations. For example, Fig. 2 shows the
chemiluminescence curves in TD oxidation in the pres-
ence of syringic acid. Similar series were obtained with
all the phenolic compounds. Using Eq. (3), we calculated
the inhibition rate constants k7, and from the S-shaped
dependences (Fig. 2) we determined the induction periods
of oxidation τ. With this parameter, using the equation
f = (τWi)/[InH],
(4)
6.0
8.0 t, s
we calculated the stoichiometric coefficients of inhibition
f in tridecane oxidation. The values obtained are given in
Table 1. The constants k7 and coefficients f are relatively
low compared to the other model systems. For example,
in AIBN-initiated oxidation of ethylbenzene at 333 K,
the rate constants of the reactions of phenols with peroxy
radicals are higher by an order of magnitude [6]. In this
study we used the same phenols. According to [7, 8], the
nature of substituent R in peroxy radical does not affect
its reactivity in reaction (2). Most probably, significant
difference in the parameters of the antiradical activity of
phenols in oxidation of various substrates is due to spe-
cific features of oxidation of long-chain hydrocarbons:
competition of reaction (2) and isomerization of tridecane
peroxy radicals (intramolecular chain transfer). Decreased
values of the parameter f may be due to short oxidation
chains (termination on primary radicals). The value of f
calculated for quercetin and Fenozan-23 is higher, which
may be due to the presence of several reaction centers in
molecules of these compounds.
Fig. 1. Variation with time t of the (a) emission intensity I and
(b) logarithm of the chemiluminescence intensity ratio accord-
–
–
–
–
ing to Eq. (1). A = log[(√I0 + √I)/(√I0 – √I)].
Therefore, on introducing an inhibitor the chemilu-
minescence intensity I drastically decreases, and with
an increase in the concentration the inhibiting effect is
enhanced (Fig. 2).
To determine the rate constant k7 of reaction (2), we
used expression [5] relating this constant to the concen-
tration of peroxy radicals and, correspondingly, to the
chemiluminescence intensity:
1/2
[RO2·]0
I0
k7
——— = —– = 1 + 1.1 ——– [InH],
[RO2·]
k W
(3)
I
√
6
i
where [RO2·]0 and [RO2·] are the concentrations of peroxy
radicals in the absence and in the presence of oxidation
inhibitors, and [InH] is the inhibitor concentration.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 4 2011

INHIBITING EFFECT OF PHENOLIC COMPOUNDS
Table 1. Kinetic parameters of oxidation inhibitors
651
Inhibitor
Rutin
Formula
f
k7, l mol–1 s–1
IC50%, M
–
(2.17 ± 0.09) × 102
–
OH
O
HO
OH
C12H21O9
O
OH
O
Vanillic acid
Ferulic acid
–
(4.35 ± 0.10) × 102
(2.13 ± 0.08) × 103
–
HO
COOH
H3CO
0.32
8.5 × 10–5
HO
CH=CH_COOH
H3CO
(H3C)3C
HO
Fenozan-1
Ionol
0.26
0.33
0.20
0.38
(2.24 ± 0.09) × 103
(2.40 ± 0.10) × 103
(3.80 ± 0.13) × 103
(4.18 ± 0.13) × 103
1.4 × 10–4
1.4 × 10–4
1.2 × 10–4
9.0 × 10–5
(CH2)2COOCH3
(H3C)3C
(H3C)3C
HO
CH3
(H3C)3C
H3CO
Syringic acid
Fenozan-28
HO
COOH
H3CO
(H3C)3C
HO
(CH2)2COO(CH2)2
O
(H3C)3C
2
Protocatechuic acid
Gallic acid
0.45
0.30
(7.84 ± 0.14) × 103
(7.84 ± 0.21) × 103
4.0 × 10–5
1.6 × 10–5
HO
HO
HO
HO
HO
COOH
COOH
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652
NIKOLAEVSKII et al.
Table 1 (Contd.)
Inhibitor
Formula
f
k7, l mol–1 s–1
IC50%, M
1.4 × 10–4
Fenozan-23
1.20
(1.03 ± 0.06) × 104
(H3C)3C
HO
(CH2)2COOCH2
C
(H3C)3C
4
Pyrocatechol
Quercetin
0.37
0.70
(1.83 ± 0.08) × 104
(2.32 ± 0.09) × 104
8.0 × 10–6
7.5 × 10–6
OH
OH
OH
O
O
HO
OH
OH
OH
Caffeic acid
Ethyl gallate
0.33
0.30
(2.78 ± 0.10) × 104
(3.54 ± 0.12) × 104
1.2 × 10–5
1.1 × 10–5
HO
CH=CHCOOH
HO
HO
HO
HO
HO
COOC2H5
OH
Hydroquinone
0.37
(5.31 ± 0.13) × 104
6.0 × 0–6
Analysis of the results obtained (Table 1) shows that,
in the examined series, hydroquinone and o-polyphenol
derivatives exhibit the highest antiradical activity toward
tridecane peroxy radicals. On the whole, rigorous correla-
tion of k7 with the energy of the ОН bond in the reaction
center of these phenols is not observed [6].At equal bond
energies, sterically shielded phenols are less effective than
dihydroxybenzene derivatives as inhibitors of tridecane
oxidation, in contrast to ethylbenzene oxidation.
in Table 1 and are well consistent with the values of k7.
In parallel with the chemiluminescence studies in this
system, we evaluated the antioxidant activity of some
phenolic inhibitors in initiated oxidation of tridecane by
the gas-volumetric method and determined the initial
rates of the uninhibited reaction and of the reaction in the
presence of antioxidants (Table 2). The kinetics of oxygen
uptake is shown in Figs. 3a and 3b. The phenols behave
as weak inhibitors which only decrease the reaction rate,
because induction periods of the oxidation in the kinetic
curves are lacking. The curves with saturation (Fig. 3b)
show that the oxidation is inhibited by transformation
products of ethyl gallate and quercetin. With quercetin
and caffeic acid, formation of viscous polymeric products
was observed, which complicated the gas-volumetric
To compare the antiradical acitvities of the com-
pounds, we used the parameter ІС50%, i.e., the inhibitor
concentration at which the chemiluminescence intensity
decreases by a factor of 2. The more active the inhibitor,
the smaller its amount required to decrease the concen-
tration of peroxy radicals. The values of ІС50% are given
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 4 2011

INHIBITING EFFECT OF PHENOLIC COMPOUNDS
653
Table 2. Antioxidant activity of phenolic compounds in initi-
ated oxidation of tridecane. Т = 353 K; [InH] = 5.0 × 10–3,
measurements.
It should also be noted that, to decrease the oxygen
uptake volume by a factor of 2, inhibitor concentrations
exceeding ІС50% by an order of magnitude are required
(Tables 1, 2). This may be due to consumption of phenols
in side reactions, detected in gas-volumetric measure-
ments.
[TD] = 0.82, [AIBN] = 3.04 × 10–2
M
Inhibitor
Quercetin
WО2 × 103, M
WО2/(WО2)0, %
3.69
2.27
2.27
1.77
0.41
30.4
42.9
44.6
66.6
92.7
Ethyl gallate
Ionol
The data we obtained (Table 2) show simlar trends
with the results of chemiluminescence determinations
(Table 1), i.e., the antioxidant acitvity of the compounds
is associated with their capability to react with tridecane
peroxy radicals.
Protocatechuic acid
Caffeic acid
EXPERIMENTAL
an inhibitor, W(O2), to the rate of the uninhibited process,
W(O2)0. To attain the conditions of the kinetic control, the
oxidation was performed at the partial oxygen pressure
of 600 mm Hg with vigorous stirring with a magnetic
stirrer (200–250 rpm).
Chlorobenzene and tridecane were purified by distil-
lation, following standard procedures. The oxidation
experiments were performed at 353 K, tridecane concen-
tration of 0.82 M, and initiator concentration of 3.04 ×
10–4 M; the initiation rate was Wi = 6.6 × 10–7 mol l–1 s–1.
The antiradical activity of phenolic inhibitors was de-
termined with a chemiluminescence installation equipped
with an FEU-38 photoelectron multiplier in the presence
of an emission activator, 9,10-dibromoanthracene, whose
optimal concentration determined in the preliminary
experiments was 8.5 × 10–5 M.
CONCLUSIONS
(1) Kinetic parameters characterizing the reactivity of
a series of phenolic compounds were determined.
(2) Unshielded natural o-polyphenols are more ef-
fective than Ionol and its derivatives as antioxidants in
oxidation of a long-chain hydrocarbon. In this system,
rigorous correlation between the antiradical activity and
the energy of the O–H bond of the reaction center of
phenol was not observed.
The antioxidant activity of the compounds was evalu-
ated by the gas-volumetric method from the oxygen up-
take and was determined from the ratio of the oxidation
rate in the initial step of the reaction in the presence of
(a)
(b)
t, min
t, min
Fig. 3. Kinetic curves of oxygen uptake [O2] in initiated oxidation of tridecane. Inhibitor ([InH] = 5 × 10–3 M): (1) none, (2) Ionol, (3)
protocatechuic acid, (4) caffeic acid, (5) quercetin, and (6) ethyl gallate. (t) Time.
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NIKOLAEVSKII et al.
5. Shlyapintokh, V.Ya., Karpukhin,. O.N., Postnikov, L.M., et
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