Synthesis and investigation of antioxidant properties of alkylated hydroxybenzyl dodecyl sulfides

Article abstract of DOI:10.1134/S0965544106040116

Various alkyl-substituted hydroxybenzyl dodecyl sulfides were synthesized, and a comparative study of their antiradical activity in the model reaction of initiated styrene oxidation and the overall inhibiting activity in the thermal autooxidation of white

Full text of DOI:10.1134/S0965544106040116

ISSN 0965-5441, Petroleum Chemistry, 2006, Vol. 46, No. 4, pp. 283–288. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.E. Prosenko, O.I. Dyubchenko, E.I. Terakh, A.F. Markov, E.A. Gorokh, M.A. Boiko, 2006, published in Neftekhimiya, 2006, Vol. 46, No. 4, pp. 310–315.
Synthesis and Investigation of Antioxidant Properties
of Alkylated Hydroxybenzyl Dodecyl Sulfides
A. E. Prosenko, O. I. Dyubchenko, E. I. Terakh, A. F. Markov, E. A. Gorokh, and M. A. Boiko
Research Institute of Antioxidant Chemistry, Novosibirsk State Pedagogical Institute,
Vilyuiskaya ul. 28, Novosibirsk, 630126 Russia
e-mail: chemistry@ngs.ru
Received November 2, 2005
Abstract—Various alkyl-substituted hydroxybenzyl dodecyl sulfides were synthesized, and a comparative
study of their antiradical activity in the model reaction of initiated styrene oxidation and the overall inhibiting
activity in the thermal autooxidation of white mineral oil was carried out.
DOI: 10.1134/S0965544106040116
Hydroxybenzyl thio derivatives are high-perfor-
CH2SC12H25
mance antioxidants capable of preventing the oxida-
tive degradation of different organic materials such as
HO
R
,
polyolefins, rubbers, lubricating oils, and fuels [1–6]
and, thus, improve their performance characteristics
and prolong the service life. Of this type of antioxi-
dant, 2,6-di-tert-butylphenol derivatives are of the
greatest practical importance; this is the reason why
most earlier studies have concerned the inhibiting
activity and mechanism of antioxidant action of these
compounds [7–10]. However, there has been no sys-
tematic investigation of the antioxidant activity of
2,6-dialkylsubstituted derivatives that differ in the
structure of ortho-substituents; neither have the activ-
ities of isomeric ortho- and para-hydroxybenzyl thio
derivatives been compared.
Structure 2
(VI-VII)
where 1 R1 = R2 = tert-Bu (I); R1 = R2 = Me (II); R1 =
R2 = cyclo-ë6ç11 (III); R1 = Me, R2 = tert-Bu (IV); and
R1 = Me, R2 = cyclo-ë6ç11 (V) in structure 1 and
R = tert-Bu (VI) or Me (VII) in structure 2.
EXPERIMENTAL
In connection with this, we attempted in the
present work to synthesize hydroxybenzyl dodecyl
sulfides (I−VII) of the specified structure by reacting
dodecyl mercaptan with corresponding N,N-dimethyl-
hydroxybenzylamines obtained earlier [11]. We also
investigated their antiradical activity in model reac-
tion of initiated styrene oxidation and the overall
inhibiting activity in the thermal autooxidation of
white oil.
Dodecyl (3,5-di-tert-butyl-4-hydroxybenzyl) sulfide
(I). A mixture containing 7.0 g (26.60 mmol) of
N,N-dimethyl-(3,5-di-tert-butyl-4-hydroxybenzyl)amine
and 5.0 g (24.20 mmol) of dodecyl mercaptan in 30 ml
of Ó-xylene was refluxed for 16 h in an argon atmo-
sphere, then cooled and diluted with hydrochloric
acid. The organic extract was washed with water and
dried over Na2SO4. The solvent was evaporated and
the residue was distilled in vacuum. The yield of sul-
fide I was 6.5 g (64%), bp 211–214°C (1 mmHg).
R1
Sulfides II–VII were obtained in a similar way and
were purified by vacuum distillation or chromato-
graphically on silica gel using a 25 : 1 hexane–ether
solvent blend.
HO
CH2SC12H25
R2
Proton NMR spectra of the synthesized com-
pounds were recorded on a Bruker DRX500 spec-
trometer at an operating frequency of 500.13 MHz in
Structure 1
(I-V)
283

284
PROSENKO et al.
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SYNTHESIS AND INVESTIGATION OF ANTIOXIDANT PROPERTIES
285
[O2] × 103, mol/l
VO , ml
2
8
7
6
5
2
1
1
2
3
4
3
4
[O ]/[RH]
2
25
20
15
10
5
0.0008
0.0004
0
tanβ
4
3
2
1
0
0
0
0.2 0.4 0.6 0.8 1.0 1.2
–ln(1 – t/t)
20 40 60 80 100 120 140 160 180
t, min
Fig. 1. Rate curves for oxidation of white oil in the presence
of (1) sulfide I, (2) ionol, (3) SO-3, and (4) sulfide IV.
0
0
5
10 15 20 25 30 35 40 45
CDCl3 with TMS as an internal standard. Melting
points were determined with a PTP device.
t, min
Fig. 2. Oxygen uptake rate curves in the initiated oxidation
of styrene at 50°C in the presence of 0.3 mmol/l of sulfides
(1) I and (2) II and their linear transforms 3 and 4, respec-
tively.
The physicochemical properties of synthesized
compounds are listed in Table 1. Searching in the STN
International net showed that compounds II, III, V,
and VII are new, as they have not been described pre-
viously.
chains terminated by one phenoxy group of the inhibi-
tor molecule is 2 [11]:
2[PhOH]0
The inhibiting activity of sulfides II–VII was stud-
ied in the model reactions of azobisisobutyronitrile
(AIBN, Acros Organics, 98%)-initiated oxidation of
styrene (chemically pure grade) in chlorobenzene
(chemically pure, 99%) at 50°C and thermal autooxi-
dation of white mineral oil (KPKhFO “Takhimfarm-
preparaty”, Kazan; a density of 0.86, a pour point of
at most –5°C) at 180°C; the results were compared
with the action of 2,6-di-tert-butyl-4-methylphenol
(ionol) (Acros Organics), 2,4,6-trimethylphenol
(TMP) (Lancaster), as well as bis(3,5-di-tert-butyl-4-
hydroxybenzyl) sulfide (TB-3) and bis[3-(3,5-di-tert-
butyl-hydroxyphenyl)propyl] sulfide (SO-3) prepared
as described in [12, 13]. Styrene and chlorobenzene
were distilled prior to use.
-------------------------
wi =
,
τ
where [PhOH]0 is the initial ionol concentration and τ
is the induction period. The determined value of wi was
(2.7–4.0) × 10–7 l mol–1 s–1.
The oxidation of white oil was carried out in a gas-
ometric unit similar to the one described in [14], at an
oxygen pressure of 1 atm. The total sample volume was
5 ml, and the antioxidant concentration was 1.75 µmol
per 1 g of oil. On the basis of the obtained data, kinetic
curves were further constructed (Fig. 1), which were
used to determine the induction period as the intersec-
tion point of two tangents to a kinetic curve correspond-
ing to the initial and final rates of oxidation of the oil.
The rate of styrene oxidation was determined by
measuring oxygen uptake with a highly sensitive cap-
illary volumeter. The induction period was deter-
mined as a crossing point of two tangents to a kinetic
curve, whose slopes are 0.5 and 0.75 of the slope of
the straight line for the uninhibited reaction [14].
RESULTS AND DISCUSSION
It was found that the initial portions of kinetic
curves for oxygen uptake in styrene oxidation are lin-
earized well in the coordinates of the following equa-
tion (1) for all of the test compounds:
The initiation rate wi was determined by the
method of inhibitors in terms of the length of the
induction period of styrene oxidation in the presence
of ionol and TMP for which stoichiometric inhibition
factor f defined as the average number of oxidation
k2
----
∆[O2]
[RH]
t
τ
⎛
⎞
-------------- = – ln 1 – -- ,
(1)
⎝
⎠
k7
where ∆[O2] is the amount of absorbed oxygen divided
by the sample volume, k7 and k2 are the rate constants
PETROLEUM CHEMISTRY Vol. 46 No. 4 2006

286
PROSENKO et al.
Table 2. Antioxidant properties of hydroxybenzyl dodecyl
The obedience to Eq. (1) suggests that the inhibition
of styrene oxidation follows the conventional scheme
[14] and the rate constant k7 for the reaction of inhibi-
tors with styrene peroxide radicals can be determined
by means of this equation.
sulfides
Compound
k7 × 104, mol–1s–1
τ, min
I
3.0 0.4
11.2 1.3
14.5 3.5
13.5 2.5
10.0 1.0
10.0 1.0
11.0 1.0
2.6 0.4
2.4 0.4
2.6 0.6
17.4 2.3
–
17
305
257
172
284
80
48
16
72
43
43
7
2
Figure 2 depicts oxygen consumption rate curves
for compounds II and III and their transformations in
the variables of Eq. (1). The k2/k7 ratio was determined
from the slope of the transforms (tan β). According to
published data [15], the rate constant k2 in the given
model system is 107.7 l mol–1 s–1; hence, k7 =
107.7/tan β. Table 2 presents the values of k7 for the test
antioxidants; the values are given with the mean-square
deviation.
II
5
8
7
8
7
5
2
5
3
5
2
2
III
IV
V
VI
VII
TB-3
SO-3
Ionol
TMP
BDS
Control
From the data presented in Table 2, it follows that all
test compounds exhibit a marked reactivity towards sty-
rene peroxide radicals; their mean values of the rate con-
stant k7 vary in the range (2.4–17.4) × 104 l mol−1 s−1. The
rate constants k7 for sulfur-containing alkylphe-
nols−sulfides I and II, TB-3, and SO-3—are practically
the same as those for the corresponding monofunctional
antioxidants ionol and TMP. Of the test para-substi-
tuted derivatives, compounds with di-tert-butyl ortho-
substituents have values of the rate constant k7 3.3–7.3
times lower than their less hindered analogues, phenols
with dimethyl, dicyclohexyl, methyl-tert-butyl, and
methylcyclohexyl ortho-substitution, in agreement
with the known literature data [10]. In addition, these
di-tert-butylphenols display a lower antiradical activity
in comparison with ortho-benzyl substituted sulfides
VI and VII.
–
7
Table 3. Synergistic effect of mixed compositions of alky-
lphenols and benzyl dodecyl sulfides in oxidation of white oil
[BDS], [PhOH] : [BDS]
Phenol*
τ, min ∆τsyn, min
µmol/g
mole ratio
0.00
0.88
1.75
3.50
4.38
5.25
0.00
0.88
1.75
2.63
3.50
1 : 0
43
50
–
1 : 0.5
1 : 1
0
The overall inhibiting activity of sulfides I–VII in
comparison with reference antioxidants was evaluated
as their ability to retard the oxidation of white oil. The
results of the investigation show that all synthesized
sulfides increase the stability of white oil against oxida-
tion (Table 2); however, different compounds demon-
strate different inhibiting effects.
50
0
11
24
149
–
Ionol
1 : 2
61
1 : 2.5
1 : 3
74
199
43
1 : 0
Among the synthesized compounds, sulfides II–V
display the highest antioxidant activity and are superior
to ionol and TMP, as well as to sulfur-containing alky-
lphenols SO-3 and TB-3, in their inhibiting effect. The
lowest inhibiting activity was demonstrated by sulfide
I, which significantly weaker retards the oxidation of
white oil in comparison with other synthesized com-
pounds. Note that TB-3, the symmetric analogue of sul-
fide I, also exhibits a low antioxidant activity compara-
ble with that of this sulfide.
1 : 0.5
1 : 1
50
0
TMP
50
0
1 : 1.5
1 : 2
209
308
159
258
* [PhOH] = 1.75 µmol/g.
We associate the high antioxidant activity of sulfides
II–VI first with the bifunctional mechanism of their
antioxidant action and, second, with an intramolecular
synergistic effect. These compounds can exhibit a
bifunctional activity due to combination of the antirad-
of the reaction of peroxide radicals with antioxidant
molecules and the oxidation substrate, respectively; τ is
the induction period; t is the time; and [RH] is the sub-
strate concentration in the sample.
PETROLEUM CHEMISTRY Vol. 46 No. 4 2006

SYNTHESIS AND INVESTIGATION OF ANTIOXIDANT PROPERTIES
287
ical activity of the phenolic OH group, which inacti-
In the case of sulfide I and its symmetric analogue
vates peroxide radicals (Table 2), with the antiperoxide TB-3, the synergistic effect was undetectable. On the
activity of the sulfur-containing moiety capable of act- contrary, the total inhibiting effect in the presence of
ing as a destroyer of peroxide compounds. The exist- ionol and BDS was 3.0 times that exhibited by sulfide I
ence of the intramolecular synergistic effect is due to and TB-3. It is known [17] that antioxidant mixtures
the specific features of the molecular structure of the can exhibit not only synergism but also antagonism;
inhibitors, which enhance their antioxidant activity.
thus, sulfide I and TB-3 seem to display intramolecular
antagonism under the given conditions. The reasons
behind this phenomenon are unclear; however, the
appearance of intramolecular antagonism may be asso-
ciated, e.g., with the formation during oxidation of ther-
mally unstable products that act as a source of free rad-
icals taking part in the propagation of oxidation chains.
The evidence that sulfides II–VI are bifunctional
inhibitors stems from the fact that they are superior to
monofunctional antioxidants in their total inhibiting
activity. Since monofunctional antioxidants can retard
the oxidation process only as a result of interaction with
peroxide radicals, the higher antioxidant activity of sul-
fides II–VI may be attributed only to the additional
antioxidant activity of the sulfide moiety.
From the data obtained by studying the antioxidant
activity of mixed compositions of alkylphenols with
BDS, it follows that the extent of intermolecular syner-
gistic effect depends not only on the BDS concentration
but also on the structure of the phenolic component. For
example, the compositions containing TMP as a phe-
nolic component exhibit a higher inhibiting activity
than compositions on the basis of ionol. This finding
suggests that the degree of intramolecular synergism
may differ for compounds with different structures of
the phenol moiety. It is obviously for this reason that
sulfides II–VII display different inhibiting activities.
To reveal the existence of the intramolecular syner-
gistic effect, as well as to explain the considerable dif-
ference in the activity between the most effective inhib-
itor dimethyl substituted sulfide II and di-tert-butyl
substituted sulfide I having an extremely low antioxi-
dant activity, we studied the inhibiting activity of the
compositions of alkylphenols (using ionol and TMP as
an example) with admixed benzyl dodecyl sulfide
(BDS).
The obtained data showed the absence of synergy
for the compositions with phenol to sulfide molar ratios
of 1 : 0.5 and 1 : 1 (Table 3). The intermolecular syner-
gistic effect in the case of joint use of alkylphenols and
BDS has been revealed at a higher amount of the sulfide
component in the mixture and is evaluated by the quan-
tity ∆τsyn:
In general, the results of the investigation show that
hydroxybenzyl dodecyl sulfides synthesized in this
work exhibit a distinct antiradical activity toward sty-
rene peroxide radicals, as well as a high inhibiting
effect in the thermal autooxidation of white mineral oil.
Owing to the bifunctional mechanism of antioxidant
action and the presence of the intramolecular synergis-
tic effect, some sulfides are superior in their inhibiting
activity to the well-known antioxidants ionol and TMP,
as well as to sulfur-containing alkylphenols SO-3 and
TB-3. Among these compounds, dimethyl and methyl
cyclohexyl substituted sulfides display the highest anti-
oxidant activity, inhibiting the oxidation processes
4.0−19.0 times more effectively than the reference anti-
oxidants.
∆τsyn = τPhOH + BDS – (τBDS + τPhOH
)
where τBDS and τPhOH are the induction periods in the
oxidation of white oil in the presence of BDS and alky-
lphenols as individual compounds, respectively, and
τ
PhOH + BDS is the induction period of white oil oxidation
in the presence of mixed alkylphenol–BDS composi-
tions.
The lack of synergistic effect for alkylphenol com-
positions with BDS at component molar ratios of 1 : 0.5
and 1 : 1 is obviously due to the fact that the added
amount of BDS is insufficient to inactivate the peroxide
compounds formed during the oxidation of oil. An
increase in the BDS concentration results in a more
complete inactivation of the peroxides, thus creating
conditions for the appearance of the synergistic effect.
REFERENCES
1. Yu. Masai and T. Kiyotsukuri, Sen’i Gakkaishi 47, 37
(1991).
2. H. Meier, H. Kuenzi, G. Knobloch, et al., Phosphorus
Sulfur Silicon Relat. Elem. 153–154, 275 (1999).
3. S. B. Bilalov, F. D. Alieva, and B. R. Gasanov, Zh. Org.
Khim. 23, 1508 (1987).
In contrast to the mix composition TMP and BDS
(1 : 1 by mole), the value of the induction period is 6.0
times the sum of induction periods of the individual
antioxidants TMP and BDS in the presence of dimethyl
substituted sulfide II. Such a high value is indicative of
a strong synergistic effect of sulfide II, which is
intramolecular in nature.
4. O. Ajiboye and G. Scott, Polym. Degrad. Stab. 4, 397
(1982).
5. J. Wollensak, R. Meltsner, and R. Oak, US Patent
No. 3553270 (1971).
6. F. Yu. Rachinskii, G. F. Bol’shakov, and Yu. A. Bruk, in
Chemistry of Organic Sulfur Compounds in Petroleum
PETROLEUM CHEMISTRY Vol. 46 No. 4 2006

288
PROSENKO et al.
and Petroleum Products (Khimiya, Moscow, 1968), 13. A. E. Prosenko, E. I. Terakh, E. A. Gorokh, et al., Zh.
Vol. 8, p. 654.
Prikl. Khim. (St. Petersburg) 76, 256 (2003).
7. G. Scott and R. Suharto, Eur. Polym. J. 20, 139 (1984).
8. L. Jirackova and G. Pospisil, Eur. Polym. J. 9, 71 (1973).
14. V. F. Tsepalov, in Study of Synthetic and Natural Anti-
oxidants in Vivo and in Vitro (Nauka, Moscow, 1992),
p. 16.
9. V. F. Tsepalov, A. A. Kharitonova, G. P. Gladyshev, and
N. M. Emanuel, Kinet. Katal. 18, 1261 (1977).
15. N. N. Pozdeeva, I. K. Yakushchenko, A. L. Aleksandrov,
and V. T. Denisov, Kinet. Katal. 32, 1302 (1991).
10. N. N. Kalibabchuk, Ya. A. Gurvich, A. E. Grinberg,
et al., Zh. Org. Khim. 7, 339 (1971).
16. V. A. Roginskii, Phenolic Antioxidants: Reactivity and
Performance (Nauka, Moscow, 1988) [in Russian].
17. Yu. A. Shlyapnikov, S. G. Kiryushkin, and A. P. Mar’in,
Antioxidant Stabilization of Polymers (Khimiya, Mos-
cow, 1986) [in Russian].
11. O. I. Dyubchenko, V. V. Nikulina, E. I. Terakh, et al.,
Neftekhimiya 45, 359 (2005) [Pet. Chem. 45, 330
(2005)].
12. F. O’Shea, US Patent No. 3272869 (1966).
PETROLEUM CHEMISTRY Vol. 46 No. 4 2006