Mesoporous aromatic frameworks modified by metal chlorides in phenol alkylation with oct-1-ene

Article abstract of DOI:10.1007/s11172-019-2669-y

Mesoporous polyaromatic frameworks (PAF) based on tetraphenylmethane were synthesized. The PAF/AlCl₃ and PAF/FeCl₃ catalysts were prepared by impregnating the synthesized products with aluminum and iron chlorides, respectively. The r

Full text of DOI:10.1007/s11172-019-2669-y

Russian Chemical Bulletin, International Edition, Vol. 68, No. 11, pp. 2083—2087, November, 2019
2083
Mesoporous aromatic frameworks modified by metal chlorides
in phenol alkylation with oct-1-еne
M. Yu. Talanova, M. Guojun, E. A. Karakhanov, and A. V. Anisimov
Department of Chemistry, M. V. Lomonosov Moscow State University,
Build. 3, 1 Leninskie Gory, 119991 Moscow, Russian Federation.
E-mail: marta_tal@mail.ru
Mesoporous polyaromatic frameworks (PAF) based on tetraphenylmethane were synthesized.
The PAF/AlCl3 and PAF/FeCl3 catalysts were prepared by impregnating the synthesized prod-
ucts with aluminum and iron chlorides, respectively. The resulting materials were characterized
by low-temperature adsorption—desorption of nitrogen, IR spectroscopy, and transmission
electron microscopy. The catalytic activity of PAF/AlCl3 and PAF/FeCl3 was tested in the
phenol alkylation with oct-1-ene. The tests showed that the use of these catalysts gave both
alkylphenols (C-alkylates) and alkyl phenyl ethers (O-alkylates) in the total yields up to 78 and
65% for PAF/AlCl3 and PAF/FeCl3, respectively. The fraction of alkylphenols depends on both
the catalyst amount and reaction temperature.
Key words: nanoporous materials, modified mesoporous aromatic frameworks, Lewis acids,
alkylation, alkenes, alkylphenols, alkyl phenyl ethers.
The Friedel—Crafts alkylation with olefins, alcohols,
and halogen derivatives is the main route to the synthesis
of alkylaromatic compounds. The use of heterogeneous
catalysts of diverse types has presently been acknowledged
as the most efficient and promising method for the prep-
aration of alkylated aromatic compounds. These catalysts
are polymeric sulfonic cation-exchange resins1; meso-
porous structured materials of the МСМ-41, МСМ-48,
and SBA-15 types functionalized by sulfo groups;
metal halides; and ionic liquids.2—7 We have previously
shown that the catalysts based on supports consisting of
carbon atoms only, namely, porous aromatic frameworks
(PAF) modified by sulfo groups can successfully be used
in the alkylation of phenol with alkenes8 and in the
aldol condensation of furfural with carbonyl compounds.9
The purpose of this work is to synthesize the PAF catalysts
with supported Lewis acids, aluminum and iron chloride
salts, and to study the activity of the obtained PAF/AlCl3
and PAF/FeCl3 catalysts in the alkylation of phenol with
oct-1-ene.
Results and Discussion
Synthesis and characterization of the supports and
catalysts. The PAF polymer was synthesized by the cross-
coupling of tetrakis(4-bromophenyl)methane and para-
benzeneboric acid as shown in Scheme 1. The material
was characterized by low-temperature adsorption—de-
sorption of nitrogen and IR spectroscopy. Its more detailed
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2083—2087, November, 2019.
1066-5285/19/6811-2083 © 2019 Springer Science+Business Media, Inc.

2084 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 11, November, 2019
Talanova et al.
Adsorption of N2/cm3 g–1
350
Table 1. Results of analysis of the mesoporous polymers before
and after modification by low-temperature adsorption—desorp-
tion of nitrogen
a
300
250
200
150
2
1
Sample
Ssp
Total pore Average pore Content
/m2 g–1
volume
diameter
/nm
of metal
(wt.%)
/cm3 g–1
PAF
PAF/FeCl3
PAF/AlCl3
584
455
471
0.32
0.18
0.19
4.9
4.0
4.1
—
16.1
15.8
0.2
0.4
0.6
0.8
P/P0
Adsorption of N2/cm3 g–1
b
According to the data of low-temperature adsorp-
tion—desorption of nitrogen (Table 1, Fig. 1, a), the PAF
material has a high specific surface area (584 m2 g–1) and
an average pore diameter of 4.9 nm. The material structure
contains micropores, which is indicated by a sharp nitro-
gen uptake in the low-pressure range (Р/Р0 = 0—0.05).
The hysteresis loop confirms the mesoporous structure of
the material, which is consistent with published data.10,11
The IR spectrum of the PAF material (Fig. 2) exhibits
signals characteristic of aromatic compounds: an intense
band of bending vibrations of C—H bonds at 809 cm–1
and less intense bands with absorption maxima at 1486
and 1600 cm–1 attributed to stretching vibrations of С—С
bonds for para-substituted phenyl fragments.
300
250
200
150
100
2
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 P/P0
Adsorption of N2/cm3 g–1
c
300
250
200
150
100
2
1
The PAF polymer was modified by aluminum and iron
chlorides using the impregnation method. According to
the elemental analysis data, the metal content in the
samples was 15.8 wt.% for PAF/AlCl3 and 16.1 wt.% for
PAF/FeCl3. After the metal salts were introduced into the
PAF material, the obtained catalysts PAF/AlCl3 and PAF/
FeCl3 were studied by low-temperature adsorption—de-
sorption of nitrogen, IR spectroscopy, and TEM.
The mesoporous structures of the polymer materials
PAF/AlCl3 and PAF/FeCl3 remained unchanged after
PAF modification, which is indicated by the shapes of the
nitrogen adsorption—desorption isotherms (Fig. 1, b, c).
Their specific surface areas (see Table 1) as the total vol-
ume and average pore diameter decreased as compared to
0.2
0.4
0.6
0.8
P/P0
Fig. 1. Isotherms of adsorption—desorption of N2 on the meso-
porous materials PAF (а), PAF/AlCl3 (b), and PAF/FeCl3 (c);
1, adsorption and 2, desorption.
characteristics (obtained by transmission electron micro-
scopy (TEM) and 13С NMR spectroscopy) were described
earlier.8,9
3
2
A (arb. units)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
1
4000 3800
Fig. 2. IR spectra of the mesoporous materials PAF (1), PAF/AlCl3 (2), and PAF/FeCl3 (3).
2400 2200 2000 1800 1600 1400 1200 1000 800 600 ν/cm–1

Mesoporous frameworks in phenol alkylation
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 11, November, 2019
2085
C/O
Conversion (%)
80
2.5
2.0
1.5
1.0
0.5
PAF/AlCl3,
conversion
60
40
20
PAF/FeCl3,
conversion
PAF/AlCl3,
C/O
PAF/FeCl3,
C/O
0
5
15
25
35 m/mg
Fig. 4. Alkylation of phenol with oct-1-ene in the presence
of the catalysts PAF/AlCl3 and PAF/FeCl3 (m is the catalyst
mass, C/O is octylphenol/ether). Reaction conditions: octene
0.32 mmol, phenol : octene = 6 : 1, 90 °C, 6 h.
200 nm
mers: oct-2-ene, oct-3-ene, and oct-4-ene. These isomeric
octenes can also enter into the alkylation reaction, the
products of which are isomeric octylphenols and isomeric
octyl phenyl ethers as reported in our earlier studies.8
The influence of the catalyst amount (5—35 mg) on
the conversion of octenes and the distribution of the
products (ratio of the amounts of octyl phenyl ethers and
octylphenols, С/O) are presented in Fig. 4. The maximum
conversions of octenes at 90 °С within 6 h (80% for PAF/
AlCl3 and 64% for PAF/FeCl3) were achieved when using
25 mg of the catalysis in both cases. In these cases, the
yields of the target products (octylphenols, C) were 54%
for PAF/AlCl3 and 38% for PAF/FeCl3. This optimum
amount of the catalyst (25 mg) corresponds to 40 mol.%
of the amount of oct-1-ene taken into the reaction for the
PAF/AlCl3 catalyst and to 20 mol.% for the PAF/FeCl3
catalyst. This amount of the catalyst was used in further
experiments.
An attempt to increase the yield of the alkylation
products by increasing reaction temperature to 120 °С did
not result in a significant increase in the conversion of
octenes (Fig. 5): it was 88 and 67% for PAF/AlCl3 and
PAF/FeCl3, respectively, but the fraction of octylphenols
in the products increased (the С/О ratio became ~2.5 in
both cases). For example, when PAF/AlCl3 was used,
octylphenols were obtained in a yield of 64% with 72%
Fig. 3. TEM image of the PAF/AlCl3 sample.
those of the initial material. It appears that the supported
aluminum and iron salts partially occupy pores of the
framework and block the surface.
The morphology of PAF/AlCl3 and PAF/FeCl3 was
studied using the TEM method. All samples have the
structure of typical porous polymers and consist of globules
100—150 nm in diameter (Fig. 3), which was also observed
for the initial PAF material.
In the IR spectra of the materials PAF/AlCl3 and PAF/
FeCl3 (see Fig. 2), the absorption peak at 1600 cm–1 shifts
to a range of 1580 cm–1 for PAF/FeCl3 and 1570 cm–1
for PAF/AlCl3 and its intensity increases. This possibly
indicates a certain interaction of the π-electron clouds of
the benzene rings with the orbitals of the aluminum and
iron atoms, which is consistent with published data.12
Catalytic experiments. The obtained catalyst was tested
in the alkylation of phenol, and oct-1-ene was chosen as
the substrate (Scheme 2).
The alkylation products contain octyl phenyl ethers
(O-alkylates) and o- and p-substituted monooctylphenols
(C-alkylates). In addition, oct-1-ene undergoes isomeri-
zation under the reaction conditions to form linear iso-
Scheme 2

2086 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 11, November, 2019
Talanova et al.
Table 2. Alkylation of phenol with oct-1-ene with repeatedly using the catalysts PAF/AlCl3 and PAF/FeCl3
Cycle
PAF/AlCl3
Yield
of octylphenols
PAF/FeCl3
Yield Octylphenol/ether
Conversion
of octenes
Octylphenol/ether
(С/О)
Conversion
of octenes of octylphenols
(С/О)
%
%
1
2
3
4
5
78
70
63
26
12
54
42
32
16
—
2.2
1.5
64
59
55
19
15
38
31
21
13
—
1.4
1.1
1.0
0.6
0.3
Only ether
0.2
Only ether
Note. Reaction conditions: octene 0.32 mmol, phenol : octene = 6 : 1, catalyst 25 mg, 90 °C, 6 h.
Table 3. Alkylation of phenol with oct-1-ene using various
catalysts
selectivity, whereas the yield of octylphenols was 46% and
selectivity was 71% when PAF/FeCl3 was used.
The possibility of the repeated use of the catalyst plays
an important role in catalytic processes. After the reaction,
the catalyst was separated by centrifugation followed by
decantation. The repeated alkylation cycles were carried
out on the used portion of the catalyst without additional
loading. As can be seen from Table 2, the total conversion
of octenes in the first three catalytic cycles is significant
(78—55%) and substantially decreases in the subsequent
two cycles. The yield of alkylphenols also decreased sharply
in each subsequent cycle: to 32 and 21% for PAF/AlCl3
and PAF/FeCl3, respectively. Evidently, the catalysts can
be used repeatedly until metal chlorides would be hydro-
lyzed under the action of moisture.
Catalyst
Conversion
Yield
Octylphenol
/ether
of octenes of octylphenols
(С/О)
%
a
AlCl3
99
78
79
64
60
54
38
38
1.5
2.2
0.9
1.4
PAF/AlCl3
b
FeCl3
PAF/FeCl3
Note. Reaction conditions: octene 0.32 mmol, phenol : octene =
= 6 : 1, catalyst 25 mg, 90 °C, 6 h.
a The weight of AlCl3 was 19 mg.
b The weight of FeCl3 was 12 mg.
A comparison of the obtained catalysts with the Lewis
acids (aluminum and iron(III) chlorides) traditionally used
in the alkylation of aromatic compounds showed that the
PAF-based catalysts modified by these chlorides exhibit
somewhat lower activity than that of free AlCl3 and FeCl3
(Table 3): the conversion of octenes is lower (78 and 64%),
the yields of octylphenols is also lower, but the selectivity
to the C-products is higher, namely, 69% for PAF/AlCl3
(60% for free AlCl3) and 59% for PAF/FeCl3 (48% for
free FeCl3).
Thus, polymeric mesoporous organic frameworks
(PAF) based on the tetraphenylmethane core were syn-
thesized. The PAF/AlCl3 and PAF/FeCl3 catalysts were
prepared by the impregnation of the synthesis products.
It is found that the use of 40 mol.% PAF/AlCl3 and
20 mol.% PAF/FeCl3 (with respect to octane taken into
the reaction) in phenyl alkylation with oct-1-ene affords
octylphenols (С-alkylates) and octyl phenyl ethers
(O-alkylated) in the total yields up to 65—80% at 90 °С
within 6 h. The fraction of octylphenols accounts for about
60—70% in the total yield of the reaction products and
increases as temperature increases to 120 °С. The synthe-
sized catalysts based on porous aromatic frameworks with
supported aluminum and iron chlorides are characterized
by somewhat lower activity than Lewis acids, non-sup-
ported metal salts, but alkylphenols are formed with
a higher selectivity in this case.
Conversion (%)
100
C/O
3.0
PAF/AlCl3,
conversion
2.5
2.0
1.5
1.0
0.5
80
60
40
20
PAF/FeCl3,
conversion
PAF/AlCl3,
C/O
PAF/FeCl3,
C/O
0
70
90
100
120 T/°C
Experimental
Fig. 5 Alkylation of phenol with oct-1-ene in the presence of the
catalysts PAF/AlCl3 and PAF/FeCl3 at various temperature (C/O
is octylphenol/ether). Reaction conditions: octene 0.32 mmol,
phenol : octene = 6 : 1, catalyst weight 25 mg, 6 h.
Trityl chloride, isoamyl nitrite, hypophosphorous acid (50%
solution in water), 1,4-phenylenediboric acid, triphenylphos-

Mesoporous frameworks in phenol alkylation
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 11, November, 2019
2087
phine, palladium(II) acetate, phenol, oct-1-ene, iron(III) chloride,
and aluminum chloride (all Aldrich) were used.
Catalytic experiments. The calculated amounts of the catalyst,
phenol, oct-1-ene, and undecane as an internal standard were
placed in a steel autoclave equipped with a magnetic stirrer. The
autoclave was sealed and placed into a thermostat. The reaction
mixture was stirred at certain temperature for specified time.
After cooling, the autoclave was depressurized, ether (1 mL) was
added, and the catalyst was separated by filtration. The mixture
was analyzed using GLC, and the total conversion of octenes,
yields of octylphenols, and the ratio of amounts of octylphenols
and octyl phenyl ethers (C/O) were calculated.
Analysis by GLC was carried out on a Hewlett-Packard
chromatograph (Hewlett-Packard, USA) with a flame-ionization
detector and a temperature programmable capillary column
(30 m) packed with the SE-30 phase and heated from 60 to 230 °С
using helium as a carrier gas and n-undecane as an internal
standard.
The IR spectra of the obtained samples were recorded in
a range of 4000—400 cm–1 on a Nicolet IR-2000 instrument
(Thermo Scientific, USA) by the multiple attenuated total reflec-
tion method using a Multi-reflection HATR attachment contain-
ing the ZnSe crystal (angle 45°) for various wavelength ranges
with a resolution of 4 nm.
References
1. R. Pal, T. Sarkar, S. Khasnobis, ARKIVOC, Rev. Accounts,
2012, 1, 570.
2. R. Ehsan, R. Mohammad, Micropor. Mesopor. Mater., 2017,
249,118.
3. X. Pu, Y. Su, Chem. Eng. Sci., 2018, 184, 200.
4. K. Bahrami, M. M. Khodaei, P. Fattahpour, J. Por. Mater.,
2015, 23, 47.
5. H. Tang, M. Ji, X. Wang, M. He, T. Cai, Chinese J. Catal.,
2010, 31,725.
TEM analysis was conducted with a LEO912 AB OMEGA
microscope (Carl Zeiss, Germany; magnification from 80× to
500000×, image resolution 0.2—0.34 nm). The electron beam
potential was 100 eV. The images were processed and the average
particle size was calculated using the ImageJ program.
The isotherms of adsorption—desorption of nitrogen were
detected at –193 °С (77 K) with a Gemini VII 2390 instrument
(Micromeritics, USA). Prior to measurements, the samples were
degassed at 130 °С for 6 h. The Brunauer—Emmett—Teller (BET)
6. X. Hu, M. L. Foo, G. K. Chuah, S. Jaenicke, J. Catal., 2000,
195, 412.
method was used for the calculation of the surface area (SBET
)
from the adsorption data in the range of relative pressures
Р/Р0 = 0.04—0.2. The total volume and average pore diameter
were determined using the Barrett—Joyner—Halenda model.
Polymer PAF was prepared from brominated tetraphenyl-
methane and benzene-1,4-diboric acid according to previously
described procedures.7,8
7. S. A. Mihailov, N. A. Mamonov, L. M. Kustov, M. N.
Mihailov, Russ. Chem. Bull., 2017, 66, 2066.
8. E. A. Karakhanov, Ma Gotszyun, I. S. Kryazheva, M. Yu.
Talanova, M. V. Terenina, Russ. Chem. Bull., 2017, 66, 39.
9. M. Yu. Talanova, V. A. Yarchak, E. A. Karakhanov, Russ. J.
Appl. Chem., 2019, 92, 857.
10. E. Merino, E. Verde-Sesto, E. M. Maya, A. Corma, M. Igle-
sias, F. Sánchez, Appl. Cat. A, 2014, 469, 206.
11. Y. Yuan, F. Sun, Y. Ren, X. Jing, W. Wang, Y. Ma, Y. Zhao,
G. Zhu, J. Mater. Chem., 2011, 21, 13498.
12. D. Heijnsbergen, T. D. Jaeger, G. Helden, G. Meijer, M. A.
Duncan, Chem. Phys. Lett., 2002, 364, 345.
Catalysts PAF/FeCl3 and PAF/AlCl3. The metal salts were
introduced onto the PAF support by impregnating the support
with solutions of aluminum and iron(III) chlorides in toluene.
The typical procedure includes the dissolution of aluminum or
iron chloride (0.5 g) in toluene (50 mL) at 75—80 °С in a round-
bottom flask preliminarily purged with an argon flow. After the
salt was dissolved, the PAF polymer (0.25 g) was rapidly added
to the obtained solution. The prepared suspension was stirred at
this temperature for 3 h and then at room temperature for 18 h
more. The black powder was filtered off, washed with toluene,
and dried in vacuo at 70 °С for 6 h. The weight fractions of
aluminum and iron in the obtained materials PAF/AlCl3 and
PAF/FeCl3 were 15.8 and 16.1%, respectively.
Received July 3, 2019;
in revised form August 19, 2019;
accepted September 3, 2019
PAF/AlCl3: IR, ν/cm–1: 1580 (C=CAr).
PAF/FeCl3: IR, ν/cm–1: 1570 (C=CAr).