Dimerization and oligomerization of styrene in the presence of pentasils

Article abstract of DOI:10.1007/s11172-009-0009-3

Styrene is converted to dimers under the action of zeolite ZSM-12 both in the presence and absence of the solvent (chlorobenzene). This transformation is characterized by a high conversion of the monomer (up to 100 wt.%) and selective formation of linear

Full text of DOI:10.1007/s11172-009-0009-3

Russian Chemical Bulletin, International Edition, Vol. 58, No. 1, pp. 59—63, January, 2009
59
Dimerization and oligomerization of styrene in the presence of pentasils*
N. G. Grigor´eva,a R. R. Talipova,a L. F. Korzhova,a A. V. Vosmerikov,b B. I. Kutepov,a and U. M. Dzhemileva
aInstitute of Petrochemistry and Catalysis, Russian Academy of Sciences,
141 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347) 231 2750. Eꢀmail: ink@anrb.ru
bInstitute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences,
3 prosp. Akademicheskii, 634021 Tomsk, Russian Federation.
Fax: +7 (382 2) 49 1457. Eꢀmail: canc@ipc.tsc.ru
Styrene is converted to dimers under the action of zeolite ZSMꢀ12 both in the presence and
absence of the solvent (chlorobenzene). This transformation is characterized by a high converꢀ
sion of the monomer (up to 100 wt.%) and selective formation of linear isomers (70—75%). In
the presence of zeolites ZVN and VKZ in chlorobenzene, styrene forms a mixture of oligomers
(n = 2—7), among which the dimers prevailed, while without the solvent oligomers with an
average molecular weight of ∼1510 are formed.
Key words: styrene, oligomerization, dimerization in bulk, dimerization in solvent, cyclic
and linear dimers, oligomers, zeolites, pentasils.
Styrene dimers are promising as regulators of polymer
chain growth, plasticizers of polymers and Plexiglas, a basis
of synthetic lubricants, and components of epoxide, varnishꢀ
andꢀpaint, and poly(vinyl chloride) materials.1—4 Strong
acids, namely, AcClO4, CF3SO3H, and pꢀMeC6H4SO3H
are usually used5—7 for the synthesis of styrene dimers,
although it is shown8,9 that zeolites Y and Beta are highly
active in styrene dimerization. The linear dimer of styrene,
viz., (E)ꢀ1,3ꢀdiphenylbutꢀ1ꢀene, was obtained with the
selectivity up to 80% in the presence of zeolite Y at 70 °C,
whereas zeolite Beta is more selective (84—90%) with
respect to the formation of cyclic styrene dimers: cisꢀ and
transꢀ1ꢀmethylꢀ3ꢀphenylindanes.
The use of pentasils in styrene dimerization is unknown.
Since these zeolites possess10 stronger acid sites than zeoꢀ
lites Y and Beta, it was of interest to study the catalytic
properties of the pentasils in styrene dimerization.
In the present work, we studied the transformations of
styrene in the presence of pentasils of two different strucꢀ
tural types: MTW (zeolite ZSMꢀ12) and MFI (zeolites
ZVN11,12 and VKZ13,14). The data obtained on the activity
and selectivity of the catalysts in styrene dimerization
were compared to their acidic properties and molecularꢀ
sieve characteristics.
Al2O3 = 28) produced at the OAO ''Angarskii zavod katalizatorov
i organicheskogo sinteza'' and VKZ (SiO2/Al2O3 = 40) synthesized
by the hydrothermal method from alkaline aluminosilicate gel
using hexamethylenediamine as an organic additive.
Before experiments on styrene oligomerization, the catalyst
samples were heated in air for 4 h at 540 °C. Styrene (OAO
''Salavatnefteorgsintez'') were distilled. Chlorobenzene was
dehydrated using a standard method.
Styrene oligomerization was carried out in a periodical
isothermal reactor at 80—130 °C in the presence of 5—40 wt.%
catalyst in chlorobenzene and without a solvent. The initial
styrene concentration in chlorobenzene [M]0 was 2.2 mol L–1
.
1H and 13C NMR spectra were recorded on a Bruker
AVANCEꢀ400 spectrometer (1H, 400.13 MHz; 13C, 100.62
MHz) in CDCl3. Highꢀresolution mass spectra were measured
on a Fisons Trio 1000 instrument, whose chromatograph was
equipped with a DB 560 quartz column (50 m); the temperature
of the column was increased from 50 to 320 °C with a programmed
heating rate of 4 °C min–1; electron impact (70 eV). GLC
analysis was carried out on an HRGS 5300 Mega Series
chromatograph (Carlo Erba) with a flameꢀionization detector
(capillary column 25 m, SEꢀ30 phase, temperatureꢀprogrammed
heating from 50 to 280 °C at a rate of 8 °C min–1, detector
temperature 250 °C, evaporator temperature 300 °C, helium as
a carrier gas, 30 mL min–1). Analysis by highꢀperformance liquid
chromatography (HPLC) was performed on an HPꢀ1090 chroꢀ
matograph with a refractometric detector and a Plgel 100 Å
polystyrene column using toluene as an eluent, a toluene flow
Experimental
rate of 0.8 mL min–1, and a tape velocity of 1.5 cm min–1
.
The current concentration of styrene and quantitative
composition of the dimeric fraction were determined by GLC.
The time of dimer elution (min) was as follows: (Z)ꢀ1,3ꢀdiꢀ
phenylbutꢀ1ꢀene, 15.2; cisꢀ1ꢀmethylꢀ3ꢀphenylindane, 15.6;
transꢀ1ꢀmethylꢀ3ꢀphenylindane, 15.9; (E)ꢀ1,3ꢀdiphenylbutꢀ
Samples of the pentasils in the Hꢀform were studied:
industrial catalysts ZSMꢀ12 (SiO2/Al2O3 = 34) and ZVN (SiO2/
* Dedicated to Academician A. I. Konovalov on his 75th birthꢀ
day.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 59—63, January, 2009.
1066ꢀ5285/09/5801ꢀ0059 © 2009 Springer Science+Business Media, Inc.

60
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
Grigor´eva et al.
1ꢀene, 17.1. The time of elution of trimers ranged from 26.2 to
28.4 min (12 peaks).
Results and Discussion
For the identification of the styrene dimers, the cyclic dimer
1ꢀmethylꢀ3ꢀphenylindane was synthesized as a mixture of two
isomers according to an earlier described procedure.15 Linear
dimers were identified in a mixture of all the four isomers with
the following compositions (wt.%): (Z)ꢀ1,3ꢀdiphenylbutꢀ1ꢀene
(1a), 1.7; (E)ꢀ1,3ꢀdiphenylbutꢀ1ꢀene (1b), 74.1; cisꢀ1ꢀmethylꢀ
3ꢀphenylindane (2a), 10.9; transꢀ1ꢀmethylꢀ3ꢀphenylindane
(2b), 13.3.
The molecularꢀweight distribution of products of styrene
oligomerization was determined by HPLC. Styrene dimers and
trimers were isolated by vacuum distillation for calibration. The
molecular weights of the dimers and trimers and the highꢀ
molecularꢀweight fraction with the degree of oligomerization
n = 14 were determined by Rast´s method.16 The other nꢀmers
were determined by the polystyrene calibration, which was
carried out by the standards obtained from Aldrich.
Oligomerization of styrene in the presence of the
pentasils occurs with the formation of the dimers of
(Z)ꢀ (1a), (E)ꢀ1,3ꢀdiphenylbutꢀ1ꢀene (1b), cisꢀ (2a)
and transꢀ1ꢀmethylꢀ3ꢀphenylindane (2b) (Scheme 1) and
higherꢀmolecularꢀweight oligomers.
The composition and yield of the reaction products
depend substantially on the structural type of pentasil and
reaction conditions, and specifically whether the oligoꢀ
merization occurs in solution or in bulk.
Highꢀmolecularꢀweight compounds with a molecular
weight of ∼1510 are formed in the absence of solvent
under the action of zeolites ZVN and VKZ (20 wt.%,
110 °C). The catalyst is rapidly deactivated by the oligoꢀ
mers formed and, hence, the conversion of styrene is not
high: 20—35 wt.% (Fig. 1, a, b).
Unlike this, styrene oligomerization in the bulk in
the presence of zeolite ZSMꢀ12 occurs with the styrene
conversion higher than 90 wt.%. The dimers are predomiꢀ
nantly formed (80%), and the amount of higherꢀmolecuꢀ
larꢀweight oligomers is small and the degree of oligoꢀ
merization is restricted by tetramers (Fig. 1, c). The
fraction of linear isomers among the dimers is 75%.
The (Z)ꢀisomer of 1,3ꢀdiphenylbutꢀ1ꢀene (1a) is formed
in considerable amounts (up to 10%) in the presence of
zeolite ZSMꢀ12, whereas only a more stable (E)ꢀisomer
(1b) was identified on the other zeolites.
The results of styrene oligomerization in a chlorobenzene
solution (20 wt.% catalyst, 110 °C, [M]0 = 2.2 mol L–1)
in the presence of the pentasils are shown in Figs 1, a—c.
It is seen that zeolite ZSMꢀ12 manifests the maximum
activity in the reaction, while on zeolites VKZ and ZVN
the styrene conversion is considerably lower: 61.0 and
28.0 wt.%, respectively.
The differences observed in the catalytic activity are
not related to the acidic properties of the pentasils, beꢀ
cause the strength of the Brönsted acid sites (BAS) in
these catalysts is the same (1165 kJ mol–1) and the BAS
concentration in zeolite ZVN is even higher than that in
zeolite ZSMꢀ12 (135 and 106 μmol g–1, respectively).19
1,3ꢀDiphenylbutꢀ1,2ꢀenes (1a,b). The 1H NMR spectrum of
the mixture contained a group of overlapped signals from the
isomers, δ: 7.50—7.80 (m, H arom.). (Z)ꢀIsomer (1a). 1H NMR,
characteristic signals, δ: 1.75 (d, 3 H, Me); 4.35 (m, 1 H, CH);
6.84, 7.0 (both m, 1 H each, =CH). 13C NMR, characteristic
signals, δ: 23.2 (Me), 38.1 (C(3)butene), 129.9 (C(1)butene), 137.3
(C(2)butene). MS, m/z (Irel (%)): 208 (44.6), Kovac`´ index Ik
1
1687. (E)ꢀIsomer (1b). H NMR, characteristic signals, δ: 1.85
(d, 3 H, Me); 4.0 (q, 1 H, CH); 6.77 (m, 1 H, =CH, J = 16 Hz);
6.81 (d, 1 H, =CH, J = 16 Hz). 13C NMR, characteristic signals,
δ: 21.5 (Me), 42.9 (C(3)butene), 127.4 (C(1)butene), 135.56
(C(2)butene). MS, m/z (Irel (%)): 208 (64.6), Kovac`´ index Ik
1795. The spectral characteristics are close to those described in
literature.17
1
1ꢀMethylꢀ3ꢀphenylindanes (2a,b). The H NMR spectrum
of the mixture contained a group of overlapped signals from
the isomers, δ: 7.50—7.80 (m, 9 H, H arom.). cisꢀIsomer (2a).
1H NMR, characteristic signals, δ: 1.78 (d, 3 H, Me); 1.93, 2.99
(both m, 1 H each, CH2); 3.50 (m, 1 H, CHМe); 4.52 (t, 1 H,
CHPh). 13C NMR, characteristic signals, δ: 19.5 (Me), 38.6
(C(1)), 46.9 (C(2)), 50.9 (C(3)). MS, m/z (Irel (%)): 208 (85.3),
Kovac`´ index Ik 1702. transꢀIsomer (2b). 1H NMR, characteristic
signals, δ: 1.69 (d, 3 H, Me); 2.49, 2.61 (both m, 1 H each,
CH2); 3.68 (q, 1 H, CHМe); 4.73 (t, 1 H, CHPh). 13C NMR,
characteristic signals, δ: 20.8 (Me), 38.4 (C(1)), 45.0 (C(2)),
49.9 (C(3)). MS, m/z (Irel (%)): 208 (100), Kovac`´ index Ik 1719.
The spectral characteristics are close to those described in
literature.18
Scheme 1

Styrene diꢀ and oligomerization on pentasils
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
61
C (%) 14´
In addition, it is known that within the same structural
type of zeolites an increase in the SiO2/Al2O3 molar ratio
(М) induces a decrease in the concentration of acid sites
and, therefore, the activity of zeolite VKZ (М = 40) in the
reaction should be lower than that in the case of zeolite
ZVN (М = 28). In fact we observe an opposite situation:
the styrene conversion in the presence of zeolite VKZ is
by 2—3 times higher than that in the presence of zeolite
ZVN. The low activity of the pentasils with the MFI
structure in styrene dimerization is caused by specific
features of their framework topologies. The sizes of pores
in zeolites of the MFI type (equidimensional tubes with
a diameter of 0.56 nm and sinusoidal channels with a
diameter of the aperture of 0.51×0.55 nm) make it
possible the dimers to form but impede substantially
diffusion of products from the pores. Therefore, styrene
oligomerization in the presence of zeolites of the MFI type
involves, most likely, the surface acid sites, accounting
for 30% of the total number of BAS.20
a
80
2
60
Y
40
Y´
3
20
4
5
C (%)
b
14´
Oligomers with a broad molecularꢀweight distribution
(n = 2—5 on zeolite VKZ and n = 2—7 on zeolite ZVN) are
formed under the action of pentasils of the MFI type. This
also can confirm that the reaction occurs on the external
catalyst surface that contains no steric restrictions for chain
growth. Predominantly cyclic dimers 2a,b (ratio 1 : 2 = 38 : 62)
are formed on the VKZ zeolite, whereas linear dimer 1b
(ratio 1 : 2 = 67 : 33) is formed on zeolite ZVN.
Compared to zeolites ZVN and VKZ, the system
of pores in zeolite ZSMꢀ12 is formed by broad straight
channels (the diameter of the aperture is 0.56×0.59 nm),
which favors the removal of the formed oligomer molecules
from the catalyst channels. At the same time, the sizes
of channels of zeolite ZSMꢀ12 restrict the formation of
molecules with the degree of oligomerization n ≥ 3. As a
result, the major products of styrene conversion on zeoꢀ
lite ZSMꢀ12 are dimers (up to 83.0%), among which
linear isomers 1a,b predominate (the ratio 1 : 2 is 78 : 22).
Minor amounts of trimers (up to 15.0%) and tetramers
(1.5—2.0%) are formed on the surface active sites.
The ratio of the products varies, depending on the
reaction conditions (Fig. 2). An increase in the temperaꢀ
ture (80—130 °C) and catalyst amount (5—40 wt.%)
decreases the fraction of linear isomers 1a,b in the comꢀ
position of the dimers and increases the amount of cyclic
dimers 2a,b. The amount of triꢀ and tetramers increases
insignificantly.
80
60
40
20
2
Y
Y´
3
4
5
6
7
c
C (%)
Y´
Y
2
2´
80
60
40
20
3´
3
4´
4
Isomeric composition of the styrene dimers in the
presence of zeolites ZSMꢀ12 and ZVN as a function of
the reaction time is given in Table 1. The starting product
was the fraction isolated by vacuum distillation. The fracꢀ
tion had the following composition: 9.6 wt.% cyclic dimers
2a,b and 90.4 wt.% linear isomers 1a,b. As can be seen,
in the presence of both catalysts, the amount of both
(Z)ꢀ and (E)ꢀisomers of linear dimers decreases due to
intramolecular ring closure (Scheme 2).
Fig. 1. Conversion of styrene and molecularꢀweight distribution
of the oligomers in chlorobenzene and without solvent (symbols
with hachures) formed in the presence of pentasils (20 wt.%
catalyst, 110 °C, [M]0 = 2.2 mol L–1, 1 h): ZVN (a), VKZ (b),
and ZSMꢀ12 (c); Y is the styrene conversion; 2, 3, 4, 5, 6, 7, and
14 is the selectivity of formation of the diꢀ, triꢀ, tetraꢀ, pentaꢀ,
hexaꢀ, heptaꢀ, and 14ꢀmers, respectively.

62
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
Grigor´eva et al.
C (%)
a
Scheme 2
1
80
60
40
20
2
Table 1. Isomeric composition of the styrene dimers under the
action of zeolites ZSMꢀ12 and ZVN as a function of the reaction
time (Т = 110 °C, 20 wt.% catalyst)
3
4
Cataꢀ
lyst
t/h 2a/2b Isomeric composition (wt.%) 1 : 2
2a
2b
1b
1a
Initial
composition
0
0.92
4.6
5.0
88.4
2.0 90 : 10
80
90
100
110
120 T/°C
ZSMꢀ12
1
3
5
1.07
1.11
1.08
6.2
6.8
6.7
5.8
6.1
6.2
86.7
85.7
85.7
1.3 88 : 12
1.4 87 : 13
1.4 87 : 13
C (%)
b
1
ZVN
2
5
7
1.17
1.13
1.07
6.3
6.1
6.1
5.4
5.4
5.7
87.4
87.5
87.2
0.9 88 : 12
1.0 88 : 12
1.0 88 : 12
80
60
40
20
0
Thus, due to an optimum combination of the acidic
properties and molecularꢀweight characteristics, the
use of zeolite ZSMꢀ12 makes it possible to perform
the dimerization of styrene both with and without solvent
with a high selectivity of formation of linear dimers
(70—75%) and the monomer conversion up to 100 wt.%.
In the presence of zeolites VKZ and ZVN, styrene
oligomerization in the bulk affords oligomers with a moꢀ
lecular weight of ∼1510, and a mixture of oligomers
(n = 2—7) with the predomination of dimers is formed in
chlorobenzene. The low activity and selectivity of these
zeolites are due to the fact that the reaction occurs on the
external catalyst surface.
2
3
4
10
20
[Catalyst] (wt.%)
Fig. 2. Influence of the reaction parameters on the styrene conꢀ
version and selectivity of formation of the reaction products in the
presence of zeolite ZSMꢀ12 in chlorobenzene: 1, styrene conꢀ
version; 2, 3, and 4, selectivity of formation of compounds 1 and
2 and oligomers with n = 3—4, respectively; (a) 20 wt.% catalyst,
[M]0 = 2.2 mol L–1, 1 h; (b) 110 °C, [M]0 = 2.2 mol L–1, 1 h.
This work was financially supported by the Division
of Chemistry and Materials Science (Program No. 8
''Development of Scientific Foundations for New Chemiꢀ
cal Technologies with Production of Pilot Batches of
Substances and Materials'').
As a result, the ratio 1 : 2 changes from 90 : 10 to 87 : 13
(on zeolite ZSMꢀ12). The ring closure rate is lower in the
presence of zeolite ZVN.
In addition to the increase in the amount of cyclic
dimers, the ratio of cis/trans isomers (2a/2b = 1.07—1.17) also
changes compared to the starting product (2a/2b = 0.92).
The formation of cisꢀisomer 2a is considered6 to be therꢀ
modynamically more favorable, because only in this conꢀ
formation the both substituents can be in the equatorial
position relative to the indane ring.
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in revised form November 17, 2008