Metathesis of hex-1-ene in ionic liquids

Article abstract of DOI:10.1070/MC2004v014n02ABEH001870

The WCl₆ + BMIMBF₄ and NaReO₄ + BMIMCl-AICl₃ (BMIM is l-butyl-3-methylimidazolium) systems are effective catalysts for the metathesis of hex-1-ene to form oct-4-ene.

Full text of DOI:10.1070/MC2004v014n02ABEH001870

,
2004, 14(2), 59–60
Metathesis of hex-1-ene in ionic liquids
Alexander V. Vasnev,* Alexander A. Greish and Leonid M. Kustov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 095 137 2935; e-mail laigwat@pisem.net
1
0.1070/MC2004v014n02ABEH001870
The WCl + BMIMBF and NaReO + BMIMCl–AlCl (BMIM is 1-butyl-3-methylimidazolium) systems are effective catalysts
6
4
4
3
for the metathesis of hex-1-ene to form oct-4-ene.
Olefin metathesis is the disproportionation of unsaturated hydro-
carbons based on the exchange of alkylidene groups between
two olefin molecules. The well-known catalysts for the process
Table 1 Hex-1-ene metathesis in various catalytic systems (20 °C; 1 h;
hex-1-ene:ionic liquid:catalyst molar ratio of 1:0.8:0.08; 500–600 rpm).a
1
are either Re-, Mo- and W-containing heterogeneous com-
Hex-1-ene
conversion
Yield (mol%)
Other
products
2
Catalytic system
pounds or organometallic comlpexes of metals such as Ru, W
(
%)
oct-4-ene dec-5-ene
and Mo.3 The metathesis of olefins is accompanied by side
reactions such as double bond shift, polymerization and solvent
alkylation reactions.
,4
NaReO4 + BMIMBF4
0.5
0.2
—
—
—
—
NaReO +
100.0
5.4
Polymers
4
BMIM–AlCl 1:2
Ionic liquids are unique systems, which are considered as an
alternative to traditional solvents or homogeneous catalysts. For
example, the metathesis of non-conjugated dienes for the syn-
3
NaReO4 +
4.9
0.1
—
BMIMCl–AlCl 1:1.05
3
thesis of alicyclic compounds was studied.5 The carbenium
complexes of Ru (so-called Grubbs catalysts) were used as the
catalysts, and neutral ionic liquids (BMIMBF , BMIMPF and
–8
WCl + BMIMBF
12.8
8.4
—
4.2
—
—
6
4
WCl +
100.0
Polymers
6
BMIMCl–AlCl , 1:1.05
3
4
6
aBut-2-ene and ethylene were also formed in accordance with the reaction
stoichiometry.
X
N
N
reaction (as the next product of bond shift in hex-2-ene). How-
ever, in this case, hex-3-ene must be the main reaction product
because of degenerate metathesis.
X = BF , PF , OTf
4
6
BMIMOTf, where BMIM is 1-butyl-3-methylimidazolium) were
taken as reaction media.
†
The results obtained in the metathesis of hex-1-ene in both
The metathesis of pent-2-ene in the presence of tungsten-
containing compounds promoted by organoaluminium com-
neutral (BMIMBF ) and acidic (BMIMCl–AlCl ) ionic liquids
4
3
with various catalysts are given in Table 1.
9
pounds was described. The reaction was performed in an ionic
NaReO + BMIMCl–AlCl (1:1.05) and WCl + BMIMBF
4 3 6 4
liquid characterised by high Lewis acidity (BMIMCl–AlCl3,
are the most active systems in the metathesis reaction. At the
same time, PdCl and RhCl dispersed in BMIMCl–AlCl and
1
:1.1 mol).
2
3
3
We studied the metathesis of hex-1-ene in the presence of
catalysts dissolved in ionic liquids as reaction media. Both
neutral (BMIMBF ) and acidic (BMIMCl–AlCl ) ionic liquids
BMIMBF ionic liquids are inactive in the reaction.
4
NaReO dissolved in an ionic liquid with a high concentration
4
of AlCl gave no metathesis products, and oligomers and poly-
4
3
3
were used. The effect of Lewis acidity on the catalyst activity
mers were the main products of the reaction. This fact is con-
sistent with published data on the activity of acidic ionic liquids
in olefin oligomerisation.12 The above reactions took place in
the WCl + BMIMCl–AlCl system (1:1.05), and in the pure
was studied using the BMIMCl–AlCl ionic liquid with com-
3
ponent ratios of 1:2 and ~1:1. These compositions correspond
–
–
7
to the AlCl4 and Al Cl anions, as found by spectroscopic
2
6
3
methods.10 The catalysts were WCl , NaReO and palladium
ionic liquid BMIMCl–AlCl (1:1.05). These results suggest that
6
4
3
and rhodium chlorides. It was of interest to test these compounds,
which form organometallic complexes that are presumably active
in hex-1-ene metathesis.
†
Synthesis of ionic liquids. BMIMCl. A mixture of 0.3 mol of N-methyl-
imidazole and 0.3 mol of butyl chloride was refluxed for 20 h in an argon
atmosphere. The reaction product BMIMCl was formed as a separate
phase. The salt was washed with dry acetone (3×100 ml). A white solid
Hex-1-ene and the ionic liquids are practically immiscible
and form two-phase reaction mixtures. WCl and NaReO were
6
4
(0.26 mol) was obtained. Yield 86%.
found to exhibit catalytic activity in the metathesis reaction.
Note that the main reaction product was oct-4-ene rather than
dec-5-ene, which is the expected product of hex-1-ene dis-
proportionation (Scheme 1).
BMIMBF . 0.25 mol of ammonium tetrafluoroborate (NH BF ) was
4
4
4
added to 0.25 mol of BMIMCl in 120 ml of dry acetone in an Ar atmo-
sphere. The reaction mixture was vigorously stirred at 20 °C for 72 h.
The precipitate (NH Cl) was filtered off, and the solution of BMIMBF
4
4
Thus, the first step of the reaction is the double bond iso-
merisation of hex-1-ene into hex-2-ene, and the rate of the
double bond shift reaction is higher than that of the metathesis
reaction. Therefore, the starting olefin to be converted in the
metathesis reaction is mainly hex-2-ene. The equilibrium con-
centrations of hex-1-ene, hex-2-ene and hex-3-ene in the reac-
in acetone was evaporated in a vacuum. The ionic liquid (0.21 mol) was
obtained. Yield 84%.
BMIMCl–AlCl3. 0.114 mol [in the case of BMIMCl–AlCl3 (1:2)] or
0
.06 mol [in the case of BMIMCl–AlCl (1:1.05)] of AlCl was gradually
3
3
added to 0.057 mol of BMIMCl for 2–3 h at 20 °C. Ionic liquids
(
0.057 mol) were obtained. Yield 100%.
Hex-1-ene metathesis. The experiments were carried out in a cylin-
1
1
tion mixture at 20 °C are equal to 1, 66 and 33%, respectively.
It is anticipated that hex-3-ene also takes part in the metathesis
3
drical 15 cm vessel after purging dry nitrogen for 0.5 h. In the course
of purging, the components (hex-1-ene, ionic liquids and catalysts in a
molar ratio of 1:0.11:0.125, in some runs, Bu Sn) were placed in the
4
vessel. The vessel was sealed and the reaction mixture was vigorously
stirred (20 °C; 500–600 rpm). After the experiments (standard time of
1
h), the vessel was cooled to 0 °C, and the reaction mixture was
analysed by GLC.
Analysis of reaction products. The metathesis products were analysed
by GLC on a packed column (3 m×3 mm) with SE-30 on Chromosorb;
an SE-30 capillary column (30 m) and a Carbowax 20M capillary
column (40 m) using the method of internal standards.
(
degenerate metathesis)
Scheme 1 Hex-1-ene metathesis in ionic liquids.
–
59 –

,
2004, 14(2), 59–60
Table 2 Formation of hex-1-ene (and hex-2-ene) metathesis products in
WCl + BMIMBF (20 °C; hex-1-ene, ionic liquids and catalysts in a molar
ratio of 1:0.8:0.08; 500–600 rpm).
Table 3 Effect of Sn Bu on the catalyst activity in hex-1-ene metathesis
4
6
4
(20 °C; 1 h; hex-1-ene, ionic liquids and catalysts, in a molar ratio of
a
a
1:0.8:0.08; 500–600 rpm).
Hex-1-ene
Yield (mol%)
dec-5-ene
Hex-1-ene
conversion
(%) oct-4-ene dec-5-ene (%)
Yield (mol%)
Selectivity
for oct-4-ene
Catalytic
system
Bu Sn/
mol%
4
Time/h
conversion
%)
(
oct-4-ene
Total
1
2
5
.0
.5
.0
12.8
22.9
27.4
8.4
17.7
22.2
4.2
4.8
5.0
12.5
22.5
27.2
WCl +
BMIMBF4
0
10
30
12.8
21.7
25.0
8.4
21.2
24.3
4.2
0.4
0.6
65.3
97.7
97.2
6
aBut-2-ene and ethylene were also formed in accordance with the reaction
stoichiometry.
NaReO +
BMIMCl–
0
10
5.4
12.1
12.2
4.9
11.6
11.9
0.2
0.1
0.1
90.7
95.9
97.5
4
AlCl (1:1.05) 30
3
oligomerisation and polymerisation reactions are catalysed by
aBut-2-ene and ethylene were also formed in accordance with the reaction
stoichiometry.
selectivity of the process remained at a high level.
AlCl , but the latter processes do not take place in ionic liquids
3
with the BMIMCl:AlCl ratio of 1:1. The use of a 5% excess of
3
AlCl in the NaReO + BMIMCl–AlCl (1:1.05) system leads
3
4
3
Thus, we can conclude that the WCl + BMIMBF4 and
6
to the appearance of the catalytic activity in hex-1-ene meta-
thesis. The main reason consists in the presence of strong
acid sites related to AlCl , which can activate NaReO (in the
NaReO + BMIMCl–AlCl3 systems exhibit high catalytic
4
activity in the olefin metathesis reaction. Note that the initial
step of the reaction is the double bond isomerisation of hex-1-ene
into hex-2-ene, and the main product of the reaction is oct-4-ene.
A considerable increase in the product yields can be achieved
3
4
heterogeneous catalytic system Re O /Al O , the source of this
2
7
2
3
1
3
acidity is the Al O support).
2
3
In the acidic system NaReO + BMIMCl–AlCl (1:1.05), the
4
3
by adding small amounts of Bu Sn to the system. The oct-4-ene:
4
main product was oct-4-ene, as a product of hex-2-ene meta-
thesis, with the oct-4-ene:dec-5-ene ratio of 50. On the contrary,
in the neutral WCl –BMIMBF system, both olefines were
dec-5-ene ratio can be increased by Bu Sn additives. When the
4
reaction is carried out in the NaReO + BMIMCl–AlCl system,
4
3
6
4
this ratio remains almost unchanged, and the selectivity of the
process reaches an extremely high value (almost 97%).
formed in comparable quantities, though oct-4-ene was the
main product. Heptenes and nonenes (products of hexene isomer
co-metathesis) were formed in these systems in 0.2 and 0.1%
yields, respectively.
In order to evaluate the catalytic activity of the test ionic
systems, we found the ratios between the highest possible
yields of oct-4-ene and dec-5-ene and the yields obtained under
References
1
R. L. Banks and G. C. Bailey, Ind. Eng. Chem., Prod. Res. Develop.,
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3
4
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6
+
BMIMBF system are given in Table 2.
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4
3
, 3785.
2
7%. The WCl + BMIMBF system is more active than that
6 4
6
7
D. Semeril, H. Olivier-Bourbigou, C. Bruneau and P. H. Dixneuf,
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based on NaReO + BMIMCl–AlCl (1:1.05). For the former
4
3
system, the yield of oct-4-ene after 1 h of the reaction is 37% of
the value obtained after 5 h, and the yield of dec-5-ene is 82%.
For the latter systems, the yield of oct-4-ene under the same
conditions is only about 18%.
8
9
Q. Yao and Y. Zhang, Angew. Chem., Int. Ed. Engl., 2003, 42, 3395.
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1 Yu. M. Zhorov, Izomerizatsiya olefinov (Isomerization of Olefins),
Khimiya, Moscow, 1977 p. 204 (in Russian).
The yield of dec-5-ene in the WCl + BMIMBF4 system
6
1
1
remained unchanged after the first hour of the process; oct-4-ene
was formed subsequently as the metathesis product.
The activity of metathesis catalysts is known to increase upon
adding small amounts of tin-containing compounds. There-
fore, experiments with the WCl + BMIMBF and NaReO +
12 Y. Chauvin, B. Gilbert and J. Guibard, J. Chem. Soc., Chem. Commun.,
1
990, 23, 1715.
13 G. Doledec and D. Commereuc, J. Mol. Catal. A: General, 2000, 161,
6
4
4
+
BMIMCl–AlCl systems promoted by tetrabutyltin were per-
125.
3
formed. The results of the experiments are given in Table 3.
The addition of 10–30 mol% tetrabutyltin to the WCl +
6
+
BMIMBF system results in the yield of oct-4-ene about
4
2
.5–3.0 times higher than that obtained in the standard experi-
ment. At the same time, the yield of dec-5-ene significantly
decreased (by a factor of about 10). This resulted in a con-
siderable increase in selectivity for oct-4-ene. When tetrabutyl-
tin was added to the NaReO + BMIMCl–AlCl (1:1.05) sys-
4
3
tem, the yield of oct-4-ene was 2.5 times higher, whereas the
Received: 28th November 2003; Com. 03/2196
–
60 –