Cyclodimerization of α-methylstyrene under homogeneous and heterogeneous acid catalysis conditions

Article abstract of DOI:10.1134/S0965544109040082

The cyclodimerization of α-methylstyrene in the presence of Broensted and Lewis acids was realized. The dependence of the cyclic α-methylstyrene dimer yield on the catalyst nature and structure was established. It was shown that the activity of the catalysts is determined by the strength of their acid sites, and the selectivity for the cyclic α-methylstyrene dimer depends on the nature of the anion (homogeneous acids) or the porous structure (heterogeneous catalysts). Sulfuric acid and silicophosphate exhibit the highest selectivity in the cyclodimerization of α-methylstyrene into 1,1,3-trimethyl-3-phenylindane.

Full text of DOI:10.1134/S0965544109040082

ISSN 0965-5441, Petroleum Chemistry, 2009, Vol. 49, No. 4, pp. 306–310. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © G.N. Kirichenko, N.G. Grigor’eva, V.I. Glazunova, U.M. Dzhemilev, 2009, published in Neftekhimiya, 2009, Vol. 49, No. 4, pp. 324–328.
Cyclodimerization of a-Methylstyrene under Homogeneous
and Heterogeneous Acid Catalysis Conditions
G. N. Kirichenko, N. G. Grigor’eva, V. I. Glazunova, and U. M. Dzhemilev
Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
e-mail: ink@anrb.ru
Received October 2, 2008
Abstract—The cyclodimerization of α-methylstyrene in the presence of Brönsted and Lewis acids was real-
ized. The dependence of the cyclic α-methylstyrene dimer yield on the catalyst nature and structure was estab-
lished. It was shown that the activity of the catalysts is determined by the strength of their acid sites, and the
selectivity for the cyclic α-methylstyrene dimer depends on the nature of the anion (homogeneous acids) or the
porous structure (heterogeneous catalysts). Sulfuric acid and silicophosphate exhibit the highest selectivity in
the cyclodimerization of α-methylstyrene into 1,1,3-trimethyl-3-phenylindane.
DOI: 10.1134/S0965544109040082
According to [1], the dimerization of α-methylsty- 4-methyl-2,4-diphenylpent-1-ene (II), 4-methyl-2,4-
rene in the presence of acid catalysts, as a rule, leads to diphenylpent-2-ene (III), and α-methylstyrene trimers
a mixture of 1,1,3-trimethyl-3-phenylindane (I), (IV):
CH3
(I)
H3C CH3
CH3
H3C C CH2
C6H5
C
CH2
(II)
CH3
CH2
C
C6H5
acid
H C
2
5
6
catalyst
CH3
H3C C CH
C
CH3
(III)
(IV)
C6H5
C6H5
CH3
CH2
C
H5C6
C H
27 30
As known from published data [1–5], the products
and selectivity of the dimerization of α-methylstyrene
depend on the catalyst nature and reaction conditions.
The α-methylstyrene dimerization has been investi-
gated in the presence of various homogeneous and het-
erogeneous acid catalysts, such as formic, phosphoric
and chloroacetic acids, p-toluenesulfonic acid, cation
exchangers, zinc, aluminum and titanium chlorides and
phosphates, as well as zeolites.
Cyclic dimer I is of considerable practical interest
due to its high thermal and radiation stability. On the
basis of I, lubricants, radiation-resistant coolants, jet
fuels with a high heating value, and effective plasticiz-
ers for polymer materials can be obtained [6–8]. In this
context, investigations aiming to develop highly selec-
tive catalysts for its synthesis are of current importance.
The present work is devoted to the investigation into
the cyclodimerization of α-methylstyrene in the pres-
ence of acid catalysts of various natures and structures,
306

CYCLODIMERIZATION OF α-METHYLSTYRENE UNDER HOMOGENEOUS
307
(‡)
(b)
1
2
1
2
100
80
60
40
20
4
3
3
4
0
0.5
1.0
1.5
2.0 70 80 90 100 110 120 130 140 150 160
T, °C
[cat], wt %
Fig. 1. Effect of (a) the amount of H SO and (b) the temperature on the α-methylstyrene conversion and the selectivity for cyclic
2
4
and linear dimerization products (130°C, 2 wt % of catalyst, 1 h): (1) α-methylstyrene conversion, (2) cyclic dimer, (3) linear
dimers, and (4) trimers.
namely, Brönsted acids (sulfuric acid, cation exchang- all dimers I–III is formed. As the amount of acid is
ers, phosphomolybdic acid H3[P(Mo2O7)6], and silico- increased to 2 wt %, I becomes the main product.
phosphate H3PO4/SiO2, ZnHPO4) and aprotic Lewis
The amount of trimers does not increase, a fact that
acids (ZnCl2, AlCl3, íi2O5 · P2O5).
can be explained by the generation of a large number of
carbocations, which interact with monomer molecules
and thereby reduce the chain growth probability.
EXPERIMENTAL
The investigation into the α-methylstyrene dimer-
The α-methylstyrene cyclodimerization was carried
out in a batch reactor at atmospheric pressure in the
temperature range 50–140°ë. Prior to use, α-methyl-
styrene was dried with calcined barium oxide and dis-
tilled under a vacuum; its purity was 99.8 wt %. The
sulfuric acid used had a concentration of 93%. Phosph-
omolybdic acid of the analytical grade was dried at
150°ë. The cation exchangers KU-2 and KU-23 (the
30/100 modification) were treated as described in [9] to
have a static exchange capacity (SEC) of 5.3 (KU-2)
and SEC = 4.9 (KU-23). Aluminum chloride was sub-
lied in a vacuum. Zinc chloride was calcined at 200°ë.
ization catalyzed by the cation exchangers KU-2 and
KU-23 containing SO3H groups on their surface
showed that differences in the structure of the cation-
exchanger matrixes have a substantial influence on the
composition of the reaction products (Figs. 2 and 3).
For example, in the presence of the cation exchanger
KU-2, the reaction proceeds with a high conversion of
α-methylstyrene (94–98%); however, up to 90% of the
linear dimers are formed.
By using the macroporous catalyst KU-23, under
the selected conditions, cyclic dimer I is formed with a
yield of 91–92 wt %. The higher catalytic activity of
KU-23 in comparison with KU-2 can be explained by
the absence of hindrances to the diffusion of α-methyl-
styrene molecules towards active sites inside catalyst
grains. Note that the highest yield of I is achieved at
140°ë, which is the limiting operating temperature of
the cation exchanger; thus, its use is fraught with diffi-
culties due to a short service life and a rapid loss of
activity under these conditions.
The product hydrocarbons were determined by GLC
on a Tsvet chromatograph with a flame-ionization
detector (2 m × 2 mm metal column; stationary phase,
5% SE-30 on Chromaton HMDS; temperature pro-
gramming from 50 to 280°C at a heating rate of
8°C/min; detector temperature, 250°ë, evaporator tem-
perature, 300°ë) and a carrier gas (helium) flow rate of
30 ml/min.
It is known that heteropoly acids, for example, phos-
phomolybdic acid ç3[ê(åÓ2é7)6], display a higher
activity and selectivity than mineral acids in many pro-
cesses [10–11]. The calculated value for the strength of
its proton centers is 1120–1130 kJ/mol, which is con-
siderably higher than that of sulfuric acid (1170 kJ/mol)
[12].
RESULTS AND DISCUSSION
For the synthesis of the linear dimers of α-methyl-
styrene, 50–70% sulfuric acid is usually used. In our
experiments, concentrated (93%) acid was used
(Fig. 1).
As it can be seen, the quantity of the catalyst has a
determining effect on the yield of I. In the presence of presence of phosphomolybdic acid ç3[ê(åÓ2é7)6]
0.1–1.0 wt % of sulfuric acid at 80–130°ë, a mixture of showed its high activity in the reaction; however, the
The study of α-methylstyrene dimerization in the
PETROLEUM CHEMISTRY Vol. 49 No. 4 2009

308
KIRICHENKO et al.
(‡)
(b)
1
3
1
3
100
80
60
40
20
0
2
2
4
4
5
10
15
20
100
110
120
130
140
T, °C
[cat], wt %
Fig. 2. Effect of (a) the amount of KU-2 and (b) the temperature on the α-methylstyrene conversion and the selectivity for cyclic
and linear dimerization products (130°C, 2 wt % of catalyst, 2 h): (1) α-methylstyrene conversion, (2) cyclic dimer, (3) linear
dimers, and (4) trimers.
(‡)
(b)
1
2
1
100
80
60
40
20
0
2
3
3
4
4
20
5
10
15
100
110
120
130
140
T, °C
[cat], wt %
Fig. 3. Effect of (a) the amount of KU-23 and (b) the temperature on the α-methylstyrene conversion and the selectivity for cyclic
and linear dimerization products (130°C, 2 wt % of catalyst, 2 h): (1) α-methylstyrene conversion, (2) cyclic dimer, (3) linear
dimers, and (4) trimers.
selectivity for I was lower than in the reaction with sul- ion necessarily involve proton centers. In the presence
furic acid (Fig. 4).
of aluminum or zinc chloride, a mixture of linear and
cyclic dimers I–III was formed, of which I made up
40–70%.
The maximum yield of I at 130°ë in the presence of
5 wt % catalyst was 57 wt % over a reaction time of
1.5 h. In addition, the formation of considerable
amounts of the α-methylstyrene trimers was observed
in the presence of the heteropoly acid.
The results of the α-methylstyrene dimerization cat-
alyzed by ZnCl2, AlCl3, and ZnHPO4, as well as silicon
and titanium oxides treated with phosphoric acid, are
presented in the table.
It should be pointed out that the α-methylstyrene
conversion in the presence of freshly sublimed alumi-
num chloride was very high and was increased by cata-
lyst activation with HCl and water vapors. The results
We have found that silicophosphate, which is used
for the hydration of ethylene into ethanol in industry, is
a highly effective catalyst for α-methylstyrene
cyclodimerization into I. The specific feature of this
catalyst is that before its impregnation with phosphoric
acid, the support (silica gel) is subjected to special
hydrothermal treatment, as a result of which it acquires
a microporous structure.
The average pore radius after the thermal treatment
was 11 nm, which provided free access for monomer
obtained demonstrate that the protonation of α-methyl- molecules to the catalyst active sites located inside the
styrene followed by its conversion into the carbonium pores. On the silicophosphate surface, the terminal pro-
PETROLEUM CHEMISTRY Vol. 49 No. 4 2009

CYCLODIMERIZATION OF α-METHYLSTYRENE UNDER HOMOGENEOUS
309
(‡)
(b)
1
1
2
100
90
80
70
60
50
40
30
20
10
0
2
3
3
4
4
1
2
3
4
5
60
80
100
120
T, °C
[cat], wt %
Fig. 4. Dependence of the α-methylstyrene conversion and the selectivity for cyclic and linear dimerization products on the (a) HPA
content and (b) temperature (130°C, 5 wt % of catalyst, 1 h): (1) α-methylstyrene conversion, (2) cyclic dimer, (3) linear dimers,
and (4) trimers.
ton acid centers P–OH with PA = 1220 kJ/mol are
present. There are no Lewis acid sites [13].
Regarding fluorine-promoted silica, as well as zinc
and titanium phosphates, all of these catalysts exhibit a
high activity and selectivity in the synthesis of the lin-
ear dimers of α-methylstyrene.
With the use of silicophosphate, the cyclodimeriza-
tion of α-methylstyrene into I can be accomplished
with a yield up to 94.7%, thus opening possibilities for
the development of an efficient industrial process for results, phosphomolybdic and sulfuric acids, as well as
the synthesis of practically important dimer I.
As can be seen from the presented experimental
silicophosphate, display the highest catalytic activity in
The influence of the catalyst nature and temperature on the yield and composition of α-methylstyrene cyclodimerization prod-
ucts (5 wt % of catalyst, 6 h)
Reaction mixture composition
α-Methylstyrene
Selectivity
for cyclic dimer, %
Catalyst
T, °C
α-methyl-
cyclic
dimer
conversion
α-dimer β-dimer
trimers
styrene
ZnCl
50
70
90
50
70
90
50
70
90
50
70
90
50
70
90
50
70
90
16.8
7.3
40.2
35.4
20.5
39.7
25.1
15.7
40.8
52.4
55.7
62.4
62.0
61.4
63.3
61.7
61.0
54.7
50.8
2.9
27.5
15.8
10.7
26.0
16.6
10.5
16.6
26.7
33.6
23.6
29.9
30.5
24.5
31.5
31.0
27.4
25.4
0.9
15.1
40.3
65.2
18.3
50.7
70.4
1.8
0.4
1.2
1.7
0.6
1.4
1.9
0.1
0.3
0.4
–
83.2
92.7
98.1
84.6
93.8
98.5
59.3
82.8
95.5
87.7
95.3
97.1
89.8
96.5
97.6
85.7
96.6
97.5
18.1
43.5
66.5
21.6
54.2
71.5
3.0
2
1.3
AlCl
15.4
6.2
3
1.5
SiO + 5% F
40.7
17.2
4.5
2
3.4
4.1
5.8
6.1
ZnHPO
12.3
4.7
1.7
1.9
4
3.2
0.2
0.3
–
3.4
2.9
4.9
5.1
TiO · P O
2 5
10.2
3.5
2.0
2.2
2
3.1
0.2
0.3
–
3.2
2.4
5.3
5.4
H PO /SiO
2
14.3
3.4
3.6
4.2
3
4
19.2
92.3
1.2
1.4
20.9
94.7
2.5
PETROLEUM CHEMISTRY Vol. 49 No. 4 2009

310
KIRICHENKO et al.
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the cyclodimerization of α-methylstyrene into I. It
should be noted that both the activity and selectivity of
the tested homogeneous catalysts are substantially
affected by the nature of the acid anion and those of the
heterogeneous catalysts are determined by the size of
the pores in which substrate molecules interact and
from where the reaction products diffuse onto the outer
surface.
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acid and silicophosphate are the most active and selec-
tive catalysts for the cyclodimerization of α-methylsty-
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ACKNOWLEDGMENTS
This work was supported by the President of the
Russian Foundation under the program of support of
leading research schools, grant no. NSh-2349.2008.3.
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