Synthesis and antioxidant activity of alkyl 3-(4-hydroxyaryl)propyl sulfides

Article abstract of DOI:10.1134/S0965544106060119

4-Alkylthiopropylphenols were synthesized from corresponding 2,6-dialkylphenols via the allyl derivative. A comparative study of the antioxidant activity of the prepared compounds was carried out in five model systems. The rate constants for the reactions

Full text of DOI:10.1134/S0965544106060119

ISSN 0965-5441, Petroleum Chemistry, 2006, Vol. 46, No. 6, pp. 442–446. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.E. Prosenko, A.F. Markov, A.S. Khomchenko, M.A. Boiko, E.I. Terakh, N.V. Kandalintseva, 2006, published in Neftekhimiya, 2006, Vol. 46, No. 6,
pp. 471–475.
Synthesis and Antioxidant Activity
of Alkyl 3-(4-Hydroxyaryl)propyl Sulfides
A. E. Prosenko, A. F. Markov, A. S. Khomchenko, M. A. Boiko, E. I. Terakh,
and N. V. Kandalintseva
Research Institute of Antioxidant Chemistry, Novosibirsk State Pedagogical University, Novosibirsk, Russia
e-mail: chemistry@ngs.ru
Received April 3, 2006
Abstract—4-Alkylthiopropylphenols were synthesized from corresponding 2,6-dialkylphenols via the allyl
derivative. A comparative study of the antioxidant activity of the prepared compounds was carried out in five
model systems. The rate constants for the reactions of the test compounds with cumene, styrene, and methyl
oleate peroxide radicals were measured. It was shown that 4-thioalkylphenols with methyl and cyclohexyl
ortho-substituents are powerful inhibitors in the oxidation of mineral oil.
DOI: 10.1134/S0965544106060119
R1
Bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl
sulfide (SO-3) is a high-performance heat stabilizer of
polymer materials [1, 2], mineral oils [3], and edible
fats [3, 4] and exhibits a pronounced protective activ-
ity in vivo in pathological conditions caused by acti-
vation of the peroxide oxidation of lipids [5–7]. We
have found that two groups of structural analogues of
SO-3 possess a higher antioxidant activity (AOA):
bis-(3-(4-hydroxyaryl)propyl sulfides with a sterically
less hindered phenolic OH group [3] and alkyl 3-(3,5-
di-tert-butyl-4-hydroxyphenyl)propyl sulfides with an
equal number of phenolic and sulfide moieties in mole-
cules [8].
HO
S
R2
,
R
(I–VIII)
where R = cyclo-C6H11, R1 = Me, and R2 = Bu (I); R =
R1 = cyclo-C6H11 and R2 = Bu (II) or ë12ç25 (III); R =
R1 = Me and R2 = Bu (IV), ë12ç25 (V), or ë18ç37 (VI);
or R = R1 = tert-Bu and R2 = Bu (VII) or ë12ç25 (VIII).
EXPERIMENTAL
Sulfides I–VI were synthesized from corresponding
2,6-dialkylphenols via intermediate synthesis of allyl
derivatives. Allyl phenyl ethers were prepared in the reac-
tions of methyl- and cyclohexyl-substituted phenols with
3-bromo- or 3-chloropropene, and then the Claisen rear-
rangement was performed with the subsequent free-radi-
cal thiylation initiated by azobisisobutyronitrile (AIBN):
This work was devoted to the synthesis and compar-
ative study of the antioxidant activity of alkyl 3-(4-
hydroxyaryl)propyl sulfides (I–VIII):
R1
R
R1
R1
CH2CHCH2Hal
RSH
t°
(I–VI),
O
HO
HO
AIBN
R
R
(IX–XI)
(XII–XIV)
where Hal = Cl or Br, R = cyclo-C6H11 and R1 = Me (IX,
XII), R = R1 = cyclo-C6H11 (X, XIII), and R = R1 = Me fide VIII was prepared according to a procedure given
(XI, XIV). in [10].
The synthesis of VII was described in [9], and sul-
442

SYNTHESIS AND ANTIOXIDANT ACTIVITY
443
–1
The examples of synthesis of some other sulfides oxidant concentration was (2.5–5.0) × 10–5 mol l . Sty-
are given below.
rene was oxidized at 50°ë, [AIBN] = 0.07–
−1
–1 –1
0.12 mol l , wi – (2.53–4.10) × 10–7 mol l s , an
1-Allyloxy-2-methyl-6-cyclohexylbenzene (IX).
3-Bromopropene-1 (0.53 mol, 46 ml) was added drop-
wise to a mixture of 2-methyl-6-cyclohexylphenol
(0.26 mol, 50 g), NaOH (0.32 mol, 13 g), and DMF
(100 ml) at 40°ë. The mixture was stirred for 2 h,
cooled, and treated with benzene. The extract was
washed with water and dried over Na2SO4, and the sol-
vent was removed by distillation. The residue was dis-
tilled in vacuum. The yield of desired ether IX was
57.5 g (95%).
4-Allyl-2-methyl-6-cyclohexylphenol (XII).Allyl-
oxybenzene IX (15 g, 65 mmol) was heated and held at
200°ë for 2 h and then distilled in vacuum. The yield of
allylphenol XII was 13.95 g (93%).
Butyl 3-(3-methyl-5-cyclohexyl-4-hydroxyphenyl)pro-
pyl sulfide (I). Butanethiol-1 (8.9 g, 85 mmol) was
added dropwise to a mixture of allylphenol XII (13 g,
56 mmol) and AIBN (2.41 g, 14.7 mmol) at 60°C. The
mixture was stirred for 4 h, cooled, and treated with
benzene. The extract was successively washed with
20% an aqueous NaOH solution and water dried with
Na2SO4; then the solvent was distilled off. The residue
was distilled in vacuum. The yield of desired sulfide I
was 7.94 g (44%).
1-Allyloxy-2,6-dialkylbenzenes X and XI, 4-allyl-
2,6-dialkylphenols XIII and XIV, and alkyl 3-(4-
hydroxyaryl)propyl sulfides II–VI were synthesized in
a similar manner.
oxidation chain length of ≥116, and [Ar OH] = 0.27–
–1
0.44 mmol l . Methyl oleate oxidation was carried out
in chlorobenzene (1 : 1 by volume) at 60°C, [AIBN] =
–1
–1 –1
12 mmol l , wi – 5.12 × 10–8 mol l s , an oxidation
–1
chain length of ≥ 56, [ArOH] = 0.3–0.6 mmol l .
White oil was oxidized in a gasometric unit similar to
that described in [12] at 180°C, an oxygen pressure of
1 atm, a sample volume of 5 ml, and [ArOH] =
1.75 µmol per gram of oil (0.875 µmol per 1 g for binu-
clear phenol SO-3). The induction time was determined
as a point of intersection of two tangents to the rate
curve corresponding to the initial and final oxidation
rates for white oil. Lard was oxidized under conditions
of oxygen bubbling at 130°ë with the use of the proce-
dure and the oxidation cell described in [14]. The oxy-
gen flow rate was 1 l/min, the mass of the sample sub-
jected to oxidation was 50 g, [ArOH] = 2.75 µmol/g
(1.375 µmol/g for SO-3). During an experimental run,
~1-g aliquots were taken, and the concentration of per-
oxide compounds was determined by iodometry [15].
The time of lard oxidation to have a peroxide number
of 0.1 (the initial peroxide number was 0.003) was
taken as an induction period.
The composition and the structure of the com-
pounds were confirmed by elemental analysis and spec-
tral data (Table 1). According to the search in the STN
International Database, sulfides I–VI and allyl deriva-
tives IX, X, XII, and XIII are novel compounds, which
have not been described in the literature.
1H NMR spectra of the prepared compounds were
recorded in CDCl3on a Bruker DRX500 spectrometer
operating at a frequency of 500.13 MHz. The melting
points were measured with a PTP device.
RESULTS AND DISCUSSION
Compounds I–VIII contain two antioxidant centers
in their structure. Therefore, their antioxidant activity is
determined by three factors: the antiradical activity
(ARA) of the phenol moiety, the antiperoxide activity
of the sulfide group, and the synergistic effect due to the
presence of both these functions in the antioxidant mol-
ecule. The differences in the structure of ortho-substit-
uents in the series of compounds I–VIII must be
reflected in both the reactivity of the phenolic OH
group and in the total antioxidant activity. Therefore,
the antioxidant properties of the synthesized com-
pounds with respect to model hydrocarbon and lipid
substrates were studied under different oxidation con-
ditions.
White oil (KPKhFO Tatkhimpharmpreparaty, Kazan),
lard (Novosibirsk meat-packing plant), cumene (Acros
Organics), styrene (Russia), and methyl oleate (Acros
Organics) were used as model oxidation substrates.
Cumene, styrene, and methyl oleate were doubly dis-
tilled in vacuum before use. AIBN (Acros Organics) was
used as an initiator. Rate curves were plotted and pro-
cessed with the use of the Origin 6.0 software.
In kinetic studies, the value of k7 was determined by
manometric method [11] with the use of a Warburg
setup or a volumetric system similar to that described in
[12]. The k/k7 ratio was determined from the experi-
mental dependence [O2]/[RH] = – k/k7 ln(1 – t/τ)
(where k is the rate constant of the chain propagation
The antiradical activity of the compounds was
judged from the values of the rate constants of their
reaction (k7) with cumene, styrene, and methyl oleate
peroxyl radicals:
reaction ROO• + Rç
ROOç + R•). The absolute
values of k7 were calculated with the use of the litera-
ture values of k [13]. All measurements were repeated
five to seven times with the mean-square deviations
being less than 20%.
ArOH + ROO•
ArO• + ROOH,
(1)
Cumene oxidation was carried out at 60°C and the as measured in the initiated-oxidation mode. The total
–1
AIBN concentration of 3–6 mmol l , with the initia- antioxidant activity was determined from the duration of
–1 –1
tion rate wi being (0.38–1.44) × 10–7 mol l
s
and the the induction period in the autooxidation of white oil and
oxidation chain lengths being longer than 76. The anti- lard. 2,6-Di-tert-butyl-4-methylphenol (ionol, Acros
PETROLEUM CHEMISTRY Vol. 46 No. 6 2006

444
PROSENKO et al.
Table 1. Characterization of the synthesized compounds
Elemental analysis,
found/calcd, %
Com-
Bp, °C
Yield,
%
Empirical
formula
pound (1–2 mmHg)
Mp, °C
1H NMR, δ, ppm
C
H
S
I
191–192
Tar
44
C20H32OS 0.96 t (3H, CH2Me), 1.31 m (1H, cyclo-
C6H11), 1.46 m (4H, cyclo-C6H11; 2H,
75.06 10.07 10.03
------------ ------------ ------------
74.94 10.06 10.00
CH2Me), 1.60 m (2H, CH2Et), 1.80 m (1H,
cyclo-C6H11), 1.89 m (4H, cyclo-C6H11; 2H,
ArCH2CH2), 2.25 s (3H, ArMe), 2.55 t (4H,
SCH2), 2.64 t (2H, ArCH2), 2.81 m (1H, cyc-
lo-C6H11), 4.70 s (1H, OH), 6.81 d (1H, Harom
J 2 Hz), 6.88 d (1H, Harom, J 2 Hz)
,
II
230
Tar
Tar
64
58
C25H40OS 1.02 t (3H, CH2Me), 1.37 m (2H, cyclo-
C6H11), 1.51 m (8H, cyclo-C6H11; 2H,
77.13 10.33 8.33
------------ ------------ ---------
77.26 10.37 8.25
CH2Me), 1.65 m (2H, CH2Et), 1.86 m (2H,
cyclo-C6H11), 1.94 m (8H, cyclo-C6H11; 2H,
ArCH2CH2), 2.56 m (4H, SCH2), 2.68 t (2H,
ArCH2), 2.80 m (2H, cyclo-C6H11), 4.79 s
(1H, OH), 6.85 s (2H, Harom
)
III
C33H56OS 0.88 t (3H, CH2Me), 1.26 m (16H, (CH2)8Me),
1.37 m (2H, cyclo-C6H11), 1.42 m (8H, cyc-
lo-C6H11; 2H, CH2C9H19), 1.56 m (2H,
78.93 11.07 6.45
------------ ------------ ---------
79.13 11.27 6.40
CH2C10H21), 1.76 m (2H, cyclo-C6H11),
1.85 m (8H, cyclo-C6H11; 2H, ArCH2CH2),
2.50 m (4H, SCH2), 2.61 t (2H, ArCH2),
2.71 m (2H, cyclo-C6H11), 4.64 s (1H, OH),
6.82 s (2H, Harom
)
IV
V
169–170
Tar
46
63
55
C15H24OS 0.91 t (3H, CH2Me), 1.40 m (2H, CH2Me),
1.55 m (2H, CH2Et), 1.85 m (2H,
71.24 9.56 12.87
------------ --------- ------------
71.38 9.60 12.70
ArCH2CH2), 2.22 s (6H, ArMe), 2.51 t (4H,
SCH2), 2.58 t (2H, ArCH2), 4.56 s (1H,
OH), 6.79 s (2H, Harom
)
C23H40OS 0.89 t (3H, CH2Me), 1.26 m (16H,
(CH2)8Me), 1.36 m (2H, CH2C9H19), 1.54 m
(2H, CH2C10H21), 1.80 m (2H, ArCH2CH2),
2.19 s (6H, ArMe), 2.44 m (4H, SCH2), 2.54 t
(2H, ArCH2), 4.30 s (1H, OH), 6.71 s (2H,
75.61 10.92 8.97
------------ ------------ ---------
75.76 11.06 8.79
Harom
)
VI
IX
63
75
95
C29H52OS 0.87 t (3H, CH2Me), 1.26 m (30H,
(CH2)15Me), 1.55 m (2H, CH2C16H33),
1.83 m (2H, ArCH2CH2), 2.21 s (6H,
77.46 11.63 7.29
------------ ------------ ---------
77.59 11.68 7.14
ArMe), 2.48 m (4H, CH2SCH2), 2.56 t (2H,
ArCH2), 4.48 s (1H, OH), 6.78 s (2H, Harom
)
102–106
Tar
C16H22O 1.41 m (1H, cyclo-C6H11), 1.53 m(4H, cyc-
lo-C6H11), 1.89 m (1H, cyclo-C6H11), 1.95 m
(4H, cyclo-C6H11), 2.42 s (3H, ArMe), 3.08 m
(1H, cyclo-C6H11), 4.40 m (2H, OCH2),
83.57 9.64
------------ ---------
83.43 9.63
5.39 m (1H, =CH), 5.78 m (1H, =CH), 6.24 m
(1H, =CH), 7.11 m (2H, Harom), 7.19 m (1H,
Harom
)
X
Tar
96
C21H30O 1.27 m (2H, cyclo-C6H11), 1.40 m (8H, cyclo-
C6H11), 1.75 m (2H, cyclo-C6H11), 1.82 m
(8H, cyclo-C6H11), 2.93 m (2H, cyclo-
C6H11), 4.26 m (2H, OCH2), 5.30 m (1H,
=CH), 5.47 m (1H, =CH),
84.21 9.83
------------ ------------
84.51 10.13
6.14 m (1H, =CH), 7.07 m (3H, Harom
)
PETROLEUM CHEMISTRY Vol. 46 No. 6 2006

SYNTHESIS AND ANTIOXIDANT ACTIVITY
Elemental analysis,
445
Table 1. (Contd.)
Com-
Bp, °C
Yield,
%
Empirical
formula
found/calcd., %
pound (1–2 mmHg)
Mp, °C
1H NMR, δ, ppm
C
H
S
XI
(67–68/2
mmHg [19])
Tar
82
C11H14O 2.40 s (6H, ArMe), 4.40 m (2H, OCH2),
81.40 8.73
------------ ---------
81.44 8.70
5.35 m (1H, =CH), 5.55 m (1H, =CH), 6.19 m
(1H, =CH), 6.98 m (1H, Harom), 7.19 m (1H,
Harom, J 7 Hz)
XII
130–137
185–190
49–51
93
C16H22O 1.28 m (1H, cyclo-C6H11), 1.43 m (4H, cyclo-
C6H11), 1.77 m (1H, cyclo-C6H11),
83.55 9.64
------------ ---------
83.43 9.63
1.86 m (4H, cyclo-C6H11), 2.23 s (3H, ArMe),
2.76 m (1H, cyclo-C6H11), 3.29 d (2H, ArCH2,
J 7 Hz), 4.55 s (1H, OH),
5.04 m (1H, =CH), 5.07 m (1H, =CH),
5.95 m (1H, =CH), 6.80 m (1H, Harom
,
J 2 Hz), 6.86 m (1H, Harom, J 2 Hz)
XIII
XIV
Tar
30
96
97
C21H30O 1.28 m (2H, cyclo-C6H11), 1.43 m(8H, cyclo-
C6H11), 1.77 m (2H, cyclo-C6H11), 1.87 m (8H,
cyclo-C6H11), 2.72 m (2H, cyclo-C6H11),
84.31 9.93
------------ ------------
84.51 10.13
3.31 m (2H, ArCH2), 4.65 s (1H, OH), 5.04 m
(1H, =CH), 5.07 m (1H, =CH), 5.96 m (1H,
=CH), 6.84 s (2H, Harom
)
(90.5–91.4/2–
3 mmHg [19])
C11H14O 2.24 s (6H, ArMe), 3.27 d (2H, ArCH2,
J 7 Hz), 4.43 s (1H, OH), 5.04 m (1H, =CH),
5.07 m (1H, =CH), 5.93 m (1H, =CH), 6.76 s
81.39 8.74
------------ ---------
81.44 8.70
(2H, Harom
)
Table 2. Antioxidant activity of alkyl-3-(4-hydroxyaryl)propyl sulfides and their structural analogs
Induction period (τ), min
white oil, 180°C lard, 130°C
k7 × 10–4, mol–1s–1
Compound
methyl oleate
cumene, 60°C
styrene, 50°C
in chlorobenzene, 60°C
I
II
III
IV
V
VII
VIII
SO-3
Ionol
TMP
DCMP
366 10
233 20
237
100
120
5
5
4
5
3
7
19.4
19.1
19.5
15.0
15.2
2.5
16
15
2.9
4.0
3.8
4.0
3.3
2.5
1.8
2.1
2.6
3.6
4.7
8
90
15.2
18.8
13.7
2.3
416 10
386 20
110
98
119
5
277
126 10
265 13
2.2
2.2
72
43
40
21
5
5
5
5
287
162
80
6
8
5
5
2.2
2.9
2.4
2.8
10.0
12.0
18.0
17.0
108
Organics), 2,4,6-trimethylphenol (TMP, Lancaster), and hindered analogues sulfides VII, VIII, and SO-3. This
2,6-dicyclohexyl-4-methylphenol (DCMP synthesized is consistent with the differences between these com-
according to [16]) were used as reference antioxidants.
pounds in reactivity toward active radicals formed in
the free-radical oxidation of cumene and styrene.
The results obtained (Table 2) indicate that the test
compounds exhibit a significant antioxidant activity in
It is noteworthy that TMP having a higher value of
the model systems used. In their ability to inhibit the k7 than ionol is not superior to the latter in inhibiting
oxidation of white oil, methyl- and cyclohexyl-substi- activity in the autooxidation of white oil. This behavior
tuted sulfides I–V were far superior to their sterically agrees with the well-documented fact that trialkylphe-
PETROLEUM CHEMISTRY Vol. 46 No. 6 2006

446
PROSENKO et al.
ArO• + Rç
ArOç + R•.
(4)
nols can terminate at most two oxidation chains,
regardless of the value of k7, in accordance with the
principle of free valence conservation as a result of con-
secutive reactions (1) and (2) or (1) and (3) [11]:
It is known [11] that the reactivity of phenoxyl rad-
icals in reaction (4) substantially increases when the
hindering effect of ortho-substituents is reduced.
ArO• + ROO•
ArO• + ArO•
+ Molecular products.
Molecular products,
(2)
In general, the results indicate that sulfides I–V syn-
thesized in this work hold promise as antioxidants for
saturated hydrocarbon substrates (mineral oils, poly-
mers).
ArOH
(3)
In the autooxidation of hydrocarbon substrates, the
antioxidant activity of thiaalkylphenols substantially
increases owing to the ability of the sulfide moiety to
reduce hydroperoxides:
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R'–SO–R" + ROOH
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R'–SO2–R" + ROH,
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inhibit the oxidation of lard. 2,6-Di-tert-butylphenols
had close values of k7 in the oxidation of cumene, sty-
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hexyl-substituted compounds were characterized by
lower values of k7 in methyl oleate than in the model
hydrocarbons. Such effects were observed earlier [18].
The decrease in the k7 value in this case is presumably
due to the involvement the hydrogen atom of the phe-
nolic OH group in H-bonding with the ester groups of
the substrate molecules ArOH…OC(OR)R'. The for-
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butylphenols, because its reaction center is sterically
hindered.
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PETROLEUM CHEMISTRY Vol. 46 No. 6 2006