Full text of DOI:10.1002/bkcs.11390

Note
DOI: 10.1002/bkcs.11390
BULLETIN OF THE
Y. M. Kho et al.
KOREAN CHEMICAL SOCIETY
The Use of Dual Catalysts to Obtain High Selectivity for di-Styrenated
Phenol in the Reaction between Styrene and Phenol
‡
‡
§
Yong Min Kho,† Eun Ju Shin,†, Hogeun Ahn, Minchul Chung, Sunghun Jung, and
*
Wonbong Kwak§
†Department of Chemistry, Sunchon National University, Jeonnam, 57922, Republic of Korea.
*E-mail: ejs@scnu.ac.kr
‡Department of Chemical Engineering, Sunchon National University, Jeonnam, 57922, Republic of Korea
§SFC. Co., Ltd., Jeonnam, 59610, Republic of Korea
Received November 27, 2017, Accepted January 4, 2018, Published online January 31, 2018
Keywords: Styrene, Phenol, Styrenated phenol, Catalyst
Sterically hindered phenols effectively inhibit free-radical
processes and are widely used as antioxidants for the stabi-
lization of polymers, rubbers, foods, fuels, and oils.1–3
When the sterically hindered phenol reacts with the peroxy
radical, the O─H bond of the phenol is cleaved to form the
phenoxy radical.2 The phenoxy radicals formed by O─H
bond cleavage are stabilized by the presence of ortho-bulky
substituents to the O─H group in the hindered phenols.
Styrenated phenols belong to a class of sterically hindered
phenols.4–6 Styrenated phenols are widely used as antioxi-
dants for rubber, and as an intermediate in the production of
nonionic surfactants (ethoxylates). Commercially used
styrenated phenol is a mixture, which is made up of three
main components of mono-, di-, and tri-styrenated phenols,
as shown in Scheme 1. Mono-styrenated phenols (MSP) are
composed of o-mono-styrenated phenols (o-MSP) and
p-mono-styrenated phenols (p-MSP). Di-styrenated phenols
(DSP) are composed of o,o-di-styrenated phenols (o,o-DSP)
and o,p-di-styrenated phenols (o,p-DSP). Tri-styrenated
phenol (TSP) is only one compound, o,o,p-tri-styrenated
phenol (o,o,p-TSP).
Styrenated phenols have different characteristics depend-
ing on the proportion of each components.1 Relative
amounts of each component differ depending on the use of
the substance. Styrenated phenols used as an antioxidant
have typically DSP and TSP of 43%, with the MSP of
11%. Styrenated phenols used to make surfactants have a
typical TSP component content of 70%, with DSP of 23%
and MSP of 2%.1–6
Styrenated phenols are prepared by the hydroarylation
reaction of styrene with phenol in the presence of
catalyst.7–9 Hydroarylation of styrene by the introduction of
styrene into an aromatic C─H bond of ortho- or para-
position to phenol OH group provides a mixture of styre-
nated phenols, as shown in Scheme 1.
The presence of ortho-bulky substituents screens effi-
ciently the hydroxy group in substituted phenols and
enhances the stability of the phenoxy radicals. The size and
number of ortho-substituents to hydroxy group have a great
influence on the inhibitory activity of sterically hindered
phenol antioxidants. Because both TSP and o,o-DSP have
two bulky ortho-substituents, TSP is also expected to act as
the effective antioxidant. However, TSP with high viscosity
has the disadvantage of poor physical properties. Therefore,
2,6-di-substituted phenol with two bulky methylbenzyl sub-
stituents in the ortho-position with the unsubstituted para-
position is shown to be the most effective and the most
popular antioxidant.1
Therefore, the lower the MSP content and the higher the
o,o-DSP content in the mixture of styrenated phenols, the
higher the antioxidant effect.
However, although many studies of the synthesis of
styrenated phenol have been focused to the selective prepa-
ration of MSP,10–22 little research has been conducted to
prepare obtain high selectivity for the formation of o,o-
DSP. In addition, although many efficient catalysts are
reported, using two catalysts at a time has been very rarely
reported.23
In this paper, we have investigated the hydroarylation
reaction of styrene with phenol to find the optimal mixed
catalyst to get high o,o-DSP content and low MSP content.
Hydroarylation reactions of styrene with phenol using
various single catalysts, such as inorganic acids, organic
acids, Lewis acids, and metal salt catalysts, have been
reported previously.24 The mixture of phenol and styrene
was stirred for 6 h at 120ꢀC with no solvent, using phenol/
styrene/ catalyst mole ratio of 1/2/0.1, using various cata-
lysts (CH3CO2H, CF3CO2H, CH3SO3H, p-toluenesulfonic
acid, HCl, H2SO4, AlCl3, AuCl3, BF3, CuBr, CuBr2, CuCl,
CuCl2, FeCl3, Fe(OAc)2, FeSO4, InCl3, TiCl4, ZnCl2,
Zn(OAC)2). Among 20 catalysts used, good results in both
high conversion of phenol and high DSP selectivity are
obtained with six catalysts of AuCl3, FeCl3, InCl3, H2SO4,
Among these styrenated phenols, o,o-DSP with two
bulky ortho-substituents is expected to exhibit remarkable
light stabilizing effect.1,2,9
Bull. Korean Chem. Soc. 2018, Vol. 39, 405–407
© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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BULLETIN OF THE
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KOREAN CHEMICAL SOCIETY
Table 2. Hydroarylation of styrene with phenol employing the
mixed catalysts of two metal halides (AuCl3, FeCl3, or InCl3).a
Entry
Cat. A
Cat. B
Yield,b %
Selectivity,c %
1
2
3
a
AuCl3
AuCl3
FeCl3
FeCl3
InCl3
InCl3
100
99
100
33:23:16:28
30:26:17:27
46:20:13:21
Reaction conditions: phenol 1 equiv, styrene 2 equiv, catalyst A
0.05 equiv, catalyst B 0.05 equiv, 120ꢀC, 6 h, no solvent.
Yield of styrenated phenols determined by GC analysis.
Selectivity: MSP/o,o-DSP/o,p-DSP/TSP by GC analysis.
b
c
Scheme 1. Hydroarylation reactions of styrene with phenol.
Table 4 shows the hydroarylation of styrene with phenol
CH3SO3H (MSA), and p-toluenesulfonic acid (p-TSA) cat-
employing the mixed catalysts of FeCl3 and MSA at vari-
ous reaction temperatures. The mixture of phenol and sty-
rene was stirred for 6 h at various temperature with no
solvent, using phenol/styrene/FeCl3/MSA mole ratio of 1/2/
0.05/0.05. Using the mixed catalysts of FeCl3/MSA, the
o,o-DSP selectivity increases and MSP content decreases as
the reaction temperature increases in the range of 25 to
120ꢀC. With raising the temperature to 140ꢀC, the o,o-DSP
selectivity is high, but the yield decreases. The highest o,o-
DSP selectivity and 100% yield are obtained at reaction
temperature of 120ꢀC.
Table 5 shows the hydroarylation of styrene with phenol
employing the mixed catalysts of FeCl3 and MSA with var-
ious catalyst amount. The mixture of phenol and styrene
was stirred for 6 h at 120ꢀC with no solvent. Using phenol/
styrene/FeCl3/MSA mole ratio of 1/2/0.05/0.05, the highest
o,o-DSP selectivity and highest yield are obtained.
alysts and are summarized in Table 1.
In order to find the optimal catalyst to get high o,o-DSP
and low MSP, the hydroarylation reaction of styrene with
phenol has been conducted employing the mixed catalysts
of metal halide (AuCl3, FeCl3, or InCl3). The mixture of
phenol and styrene was stirred for 6 h at 120ꢀC with no sol-
vent, using phenol/styrene/metal halide catalyst A/metal
halide catalyst B mole ratio of 1/2/0.05/0.05. As shown in
Table 2, the desired results of high o,o-DSP and low MSP
are not obtained with the mixed catalysts of two metal
halides. The results with the mixed catalysts are worse than
with single catalysts.
The hydroarylation reaction of styrene with phenol has
been carried out employing the mixed catalysts of metal
halide (AuCl3, FeCl3, or InCl3) and protic acid (H2SO4,
MSA, or p-TSA) to search for the optimal catalyst to get
high o,o-DSP and low MSP. The mixture of phenol and
styrene was stirred for 6 h at 120ꢀC with no solvent, using
phenol/styrene/metal halide catalyst A/protic acid catalyst B
mole ratio of 1/2/0.05/0.05. As shown in Table 3, best
results of high o,o-DSP and low MSP are obtained using
the mixed catalysts of FeCl3/MSA, in which yield is 100%
and MCP/o,o-DSP/o,p-DSP/TSP selectivity is 9/37/11/43.
This result with the mixed catalyst of FeCl3/MSA is better
than with single catalysts. FeCl3 and MSA are both inex-
pensive and relatively nontoxic. Mixture of two inexpen-
sive catalysts provides best results for high o,o-DSP and
low MSP.
In summary, the optimal catalyst to get high o,o-DSP
and low MSP (MSP/o,o-DSP/o,p-DSP/TSP = 9/48/43) is
the mixed catalysts of FeCl3 and MSA, in the hydroaryla-
tion reaction of styrene with phenol for 6 h at 120ꢀC with
Table 3. Hydroarylation of styrene with phenol employing the
mixed catalysts of metal halide (AuCl3, FeCl3, or InCl3) and
protic acid (H2SO4, MSA, or p-TSA).a
Entry
Cat. A
Cat. B
Yield,b %
Selectivity,c %
1
2
3
4
5
6
7
8
AuCl3
AuCl3
AuCl3
AuCl3
FeCl3
FeCl3
FeCl3
FeCl3
InCl3
InCl3
InCl3
InCl3
—
100
100
100
100
100
100
100
100
98
28:25:17:30
13:26:16:45
30:27:16:27
12:26:16:46
38:26:17:19
15:28:14:43
9:37:11:43
20:30:14:36
20:32:33:15
46:23:10:21
45:21:10:24
44:20:11:25
H2SO4
MSA
p-TSA
—
Table 1. Hydroarylation reaction of styrene with phenol using
various catalysts.a
Entry
Catalyst
Yield,b %
Selectivity,c %
H2SO4
MSA
p-TSA
—
1
2
3
4
5
6
a
H2SO4
MSA
p-TSA
AuCl3
FeCl3
InCl3
100
100
100
100
100
98
16:26:17:41
16:25:19:40
10:27:15:48
28:25:17:30
38:26:17:19
20:32:33:15
9
10
11
12
a
H2SO4
MSA
p-TSA
100
100
100
Reaction conditions: phenol 1 equiv, styrene 2 equiv, catalyst 0.1
equiv, 120ꢀC, 6 h, no solvent.
Yield of styrenated phenols determined by GC analysis.
Selectivity: MSP/o,o-DSP/o,p-DSP/TSP by GC analysis.
Reaction conditions: phenol 1 equiv, styrene 2 equiv, catalyst A
0.05 equiv, catalyst B 0.05 equiv, 120ꢀC, 6 h, no solvent.
Yield of styrenated phenols determined by GC analysis.
Selectivity: MSP/o,o-DSP/o,p-DSP/TSP by GC analysis.
b
c
b
c
Bull. Korean Chem. Soc. 2018, Vol. 39, 405–407
© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
406

BULLETIN OF THE
Note
KOREAN CHEMICAL SOCIETY
Table 4. Hydroarylation of styrene with phenol employing the
Innovation and Creativity through the Ministry of Educa-
tion (South Korea) and the National Research Foundation
of Korea (NRF-2014H1C1A1066844)
mixed catalysts of FeCl3 and MSA with various temperature.a
Entry
Temp, oC
Yield,b %
Selectivity,c %
1
2
3
4
5
a
140
120
100
80
96
100
100
100
80
10:36:9:45
9:37:11:43
13:32:10:45
30:31:12:27
32:30:12:26
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General. Commercial grade reagents were used without
further purification. Solvents were dried and freshly dis-
tilled. GC analyses were performed on an Agilent 7890A
GC combined with GERSTEL MPS (MultiPurpose Sam-
pler) using HP-5 capillary column (Palo Alto, CA, USA).
General Procedure for the Hydroarylation Reaction of
Styrene with Phenol. To a stirred solution of phenol
(1 equiv), catalyst A (0.05 equiv) and catalyst B (0.05
equiv), styrene (2 equiv) was added drop wise. The reaction
mixture was stirred at 120ꢀC for 6 h. After cooling to room
temperature, water was added to the reaction mixture. The
solution was filtered through silica gel and extracted with
Et2O (three times). The combined organic layer was
washed with brine and dried over MgSO4. After removal of
the solvents under reduced pressure, a sample was drawn
for GC analysis.
Acknowledgments. This work was supported by the
Human Resource Training Program for Regional
24. V. Kim, E. J. Shin, H. Ahn, M. Chung, S. Jung,
W. Kwak, Lett. Org. Chem. 2018, 15, 139.
Bull. Korean Chem. Soc. 2018, Vol. 39, 405–407
© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
407