Mendeleev Commun., 2011, 21, 329–330
Table 2 Influence of the gas phase nature on the product composition.
C2H4
OH
OH
+
OH
OH
Conver-
Gas Pressure/ sion of
Products, yield (mol%)
phase atm
4-octene
(mol%)
OH
1-Pentene 3-Hexene 5-Decene 6-Dodecene
C2H4
+
C2H4 28
31.9
8.5
0.6
0.1
22.0
5.7
28.9
7.7
1.1
0.3
N2
27
Scheme 2
Table 3 Dependence of the yields of the 4-penten-1-ol ethenolysis products on reaction conditions.
Products, yield (mol%)
Propenol 3-Buten-1-ol
Pressure of
ethylene/atm
Substrate-to-catalyst
molar ratio
Conversion of
4-penten-1-ol (mol%)
IL
Time/h
[bmim]PF6
[bmim]PF6
[bmim]PF6
[bmim]BF4
[bmim]BF4
[bmim]BF4
24
24
72
24
72
72
30
60
60
60
60
60
12:1
12:1
12:1
12:1
12:1
3:1
16.5
33.7
51.3
13.8
25.1
80.1
7.6
15.8
31.6
5.7
17.2
73.8
8.7
17.4
19.1
7.8
7.5
5.9
reaction (Scheme 1). Indeed, 1-pentene, 1-butene and propylene
can be produced from 4-octene, 3-octene and 2-octene, respec-
tively.
double bond shift reaction is the initial step of the process, then
the ethenolysis can take place, and the products are 3-buten-1-ol
and propenol (Scheme 2).
Note that the main products are 5-decene and 3-hexene, both
of them being formed in homometathesis of 3-octene, while
the yields of the anticipated ethenolysis products are very low.
Such a difference in the products yields can be explained as
follows. The double bond shift in the formed 3-hexene results in
2-hexene, and further in 1-hexene. Homometathesis of the latter
gives 5-decene. Alternatively, 2-hexene can take part in homo-
metathesis to form starting 4-octene.
Evidently, the double bond shift also takes place in 1-pentene,
which is the main product of the ethenolysis of 4-octene. 1-Hexene
and 1-heptene are the products of ethenolysis of 3-octene and
2-octene and are detected in trace quantities. The double bond
shift in 1-pentene should give 2-pentene which upon metathesis
can produce 3-hexene. Small amounts of heptenes, nonenes, and
undecenes being the products of co-metathesis of different olefins,
were also detected in total yield no more than 0.1–0.2%.
Apparently, starting 4-octene can also undergo degenerate
metathesis conversion, leading to the same 4-octene, and the
reaction proceeding is invisible.
A number of runs with 4-penten-1-ol ethenolysis were carried
out, differing in the nature of the ILs, as well as the pressure of
ethylene, the substrate-to-catalyst ratio and the reaction duration
(Table 3). The data obtained can be interpreted in the following
way. In the beginning of the process, 3-buten-1-ol and propenol
are formed in about equal amounts. Further the propenol yield
becomes higher than that of 3-buten-1-ol. An extremely large
difference can be achieved on increasing the catalyst-to-substrate
ratio. This allows one to suggest that butenol is the intermediate
product in the propenol formation, and the latter is the final
reaction product. Furthermore, the double bond in propenol can
be stabilized by interaction of the p-orbital with the electron pair
of the hydroxyl oxygen.
It is worth to mention that the pentenol conversion depends
almost linearly on the ethylene pressure in the system. It is also
interesting that the homometathesis products are formed in small
amounts under the chosen reaction conditions (their yields are
less than 0.5%). The yields of the ethenolysis products are also
influenced by the type of the IL.
The data obtained show that ethylene reacts with octenes to
a rather insignificant extent. This allows one to suppose that the
use of an inert gas atmosphere (e.g., nitrogen) instead of ethylene
should not affect the 4-octene conversion as well as the composi-
tion of the reaction products. In order to check this suggestion,
ethylene was replaced by dry nitrogen (Table 2).
The results indicated that the reaction proceeding in the
nitrogen atmosphere led to a dramatic suppression of 4-octene
conversion. The reason of such an unexpected result is a rather
good ethylene solubility in the IL media, which, in turn, causes
an increase in the solubility of higher olefins. As a result, the
efficiency of the metathesis process increases as well.
is more
Under the same conditions of ethenolysis, [bmim]PF6
preferential than [bmim]BF4.
In conclusion, neutral ILs such as [bmim]PF6 and [bmim]BF4
with dissolved WCl6 (+SnBu4) can be used as the reaction media
in olefins metathesis and ethenolysis. The unsubstituted acyclic
olefins participate in homometathesis and both the original olefin
and its isomers formed through the step of the double bond shift can
take part in the reaction. In the case of 4-penten-1-ol, ethenolysis
is preferable, with the reaction products being 3-buten-1-ol and
propenol.
References
It stems from these data that the rate of ethenolysis under
the chosen conditions is very low, regardless of the fact that the
presence of ethylene increases the 4-octene conversion. In this
case, the main process is the homometathesis reaction in which
general participants are olefins resulted from the double bond
shift in octenes.
In order for the ethenolysis reaction to proceed, the sub-
strate should be probably changed. For example, in the case of
4-penten-1-ol, homometathesis is suppressed by the influence
of the hydroxyl group. The reaction between ethylene and this
alkenol is apparently the degenerate metathesis. However, if the
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Received: 31st May 2011; Com. 11/3736
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