Oxidation of unsaturated compounds in ionic liquids with the use of cyclodextrin-containing catalytic systems

Article abstract of DOI:10.1134/S0965544107050039

The Wacker oxidation of alkenes-1 in ionic liquids catalyzed by a system containing palladium, and copper complexes and β-cyclodextrins was studied. It was shown that the use of β-cyclodextrins substantially increases the oxidation rate in biphasic systems olefin/ionic liquid. It was found that the proposed catalytic systems possess substrate selectivity, which is determined by the structure of a receptor molecule.

Full text of DOI:10.1134/S0965544107050039

ISSN 0965-5441, Petroleum Chemistry, 2007, Vol. 47, No. 5, pp. 331–336. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © L.V. Andreeva, A.L. Maksimov, A.Ya. Zhuchkova, V.V. Predeina, T.Yu. Filippova, E.A. Karakhanov, 2007, published in Neftekhimiya, 2007, Vol. 47, No. 5,
pp. 362–367.
Oxidation of Unsaturated Compounds in Ionic Liquids
with the Use of Cyclodextrin-Containing Catalytic Systems
L. V. Andreeva, A. L. Maksimov, A. Ya. Zhuchkova, V. V. Predeina,
T. Yu. Filippova, and E. A. Karakhanov
Moscow State University, Faculty of Chemistry, Leninskie gory, Moscow, 119899 Russia
e-mail: max@petrol.chem.msu.ru
Received January 24, 2007
Abstract—The Wacker oxidation of alkenes-1 in ionic liquids catalyzed by a system containing palladium, and
copper complexes and β-cyclodextrins was studied. It was shown that the use of β-cyclodextrins substantially
increases the oxidation rate in biphasic systems olefin/ionic liquid. It was found that the proposed catalytic sys-
tems possess substrate selectivity, which is determined by the structure of a receptor molecule.
DOI: 10.1134/S0965544107050039
Since the discovery of sulfonated triphenylphos-
phine by Kuntz, the development of new catalytic sys-
tems for reactions under biphasic conditions has
become one of the most thriving lines of research in
metal complex catalysis. Application of this concept
assumes that metal complexes are soluble in one phase
and the reactants and products are soluble in the other.
Thus, a catalyst can easily be isolated from the products
and recycled [1–3].
EXPERIMENTAL
In this work, β-cyclodextrin, 1-methylimidazole,
tetrafluoroboric acid, and ethyl sulfate from Aldrich
were used. 3-Butyl-1-methylimidazolium tetrafluorob-
+
–
orate [BMIM] [BF ] was synthesized according to a
4
procedure described in [11], and 1-methylimidazolium
+
–
tetrafluoroborate [çMIM] [BF ] was obtained as
4
described in [12]. 1-Methylimidazolium ethyl sulfate
+
–
[
EtMIM] [SO OEt] was obtained according to the pro-
3
cedure [13]. Modification of β-cyclodextrin by nitrile-
Various solvents, such as water, fluorinated hydro-
carbons, and ionic liquids [3, 4–6] have been used as a
phase for catalyst immobilization. The latter liquids,
owing to their stability and amenability to modification,
turn out to be extremely attractive for use in biphasic
catalysis. However, one of problems faced upon carry-
ing out reactions of nonpolar substrates in the presence
of an ionic liquid is a low concentration of a substrate
in the polar phase in which the catalyst is immobilized.
Even for hexene-1, its concentration only slightly
exceeds 100 mmol/l [6, 7]. As a result, reaction rates for
such substrates turn out to be too low.
containing (β-CD-CN) groups was carried out by a pro-
cedure described in [1]. 2,6-Di-O-methyl-β-cyclodex-
trin (Met-β-CD) was prepared according to [14]. The
substances were characterized by means of H and C
NMR spectroscopy. The composition of modified
cyclodextrins was additionally confirmed by the
MALDI–TOF technique. The analysis was carried out
on a MALDI–TOF–MS Bruker instrument (Germany).
Ionization of particles was induced by an UV laser at an
incident wavelength of 336 nm.
1
13
Oxyethylated β-cyclodextrin containing 28 oxy-
ethyl fragments (β-CD-E ) was synthesized as follows.
28
Earlier, by the example of aqueous-phase catalysis, A 1.135-g portion (1 mmol) of β-cyclodextrin, 0.114 g
it was shown that one of the general ways of solving a of K CO (10 % of cyclodextrin mass) and 4.4 g
50 mmol) of ethylene carbonate were dissolved in
2
3
(
similar problem is the use of compounds capable of
forming inclusion complexes of the host–guest type as
components of catalytic systems. In this case, not only
transfer of substrate to a nonpolar phase but also a
change in regio- and substrate selectivity of a reaction
is achieved [1–2, 8]. We have shown that macrocyclic
receptors, such as calixarenes and cyclodextrins, can
substantially increase the reaction rate of Wacker oxi-
dation under biphasic conditions [9–10].
1
0 ml of tetra-N-methylurea. The mixture was stirred at
1
50°ë in a nitrogen atmosphere for 4 h. After the cessa-
tion of ëé evolution, the solvent was distilled off, and
2
the obtained substance was recrystallized from a 4 : 1
methanol–acetone blend. The yield of the product was
1
1
.7 g (71%). H NMR (δ, ppm, ëD éD) 4.67 (H1 CD);
.12 (H–O–CH CH – 3.7–3.82 (H-3, H6 CD); 3.6–3.7
3
4
2 2
–
(
H5 CD), 3.4–3.55 (H2; H4 −OCH CH O ). It was
2 2
determined by the MALDI–TOF technique that from
In this paper, we present the results of the study the 21 up to 35 oxyethyl groups fall on one cyclodextrin
of catalytic systems based on modified cyclodextrins in molecule. The mean number of oxyethyl groups
ionic liquids.
was 28. Oxyethylated cyclodextrin containing on the
3
31

3
32
ANDREEVA et al.
average five oxyethyl groups was obtained via the reac-
After completion of the experiment, the autoclave
tion of oxirane with cyclodextrin in an alkaline solution was cooled, the pressure was released, and the products
according to [1].
were extracted with diethyl ether. The layer containing
the ionic liquid was recycled for further experiments.
The ethereal layer was analyzed by the GLC technique
using a Chrompack CP9001 chromatograph with a
flame ionization detector and a column with the SE-30
stationary phase (0.3 mm × 50 m).
Experiments on the Wacker oxidation of octene-1,
heptene-1, hexene-1, and styrene were carried out in a
steel autoclave in an oxygen atmosphere at an increased
pressure and a constant temperature with intense stir-
ring of the reaction mixture. The following order of
operations was maintained in the preparation of a cata-
lytic system: the components of the catalytic system, an
ionic liquid, and a substrate in quantities calculated
according to desired molar ratios were loaded into a
RESULTS AND DISCUSSION
As catalyst components that possess the properties
glass cartridge of the autoclave. The autoclave was of a phase-transfer agent, β-cyclodextrins modified by
tightly sealed, thermostated, and an oxygen pressure various oxyethyl, propionitrile, and methyl groups
was increased to 0.5 MPa.
were chosen.
OH
O
HO
HO
O
O
HO
OH
OH
O
O
OH
O
OH
HO
O
HO
HO
O
OH
HO
=
O
OH
2
1
6
HO
3
O
5
OH
OH
O
OH
O
O
HO
4
HO
OH
OH
HO
HO
HO
HO
OH
O
HO
n
O
O
O
O
O
O
O
H CO
OCH3
OCH3
3
OCH
3
H CO
OCH
3
3
H CO
3
NC
O
O O
O
O
O
O
OCH3
OCH
H CO
3
3
H CO
3
OCH
3 OCH3
β-CD-CN
β-CD-E OH
Me-βCD
x
The modifying groups were introduced in order to onitrile groups were synthesized according to the proce-
increase the solubility of β-cyclodextrins in water and in dures described in the literature [14]. Ethoxylated cyclodex-
ionic liquids. Cyclodextrins modified by methyl and propi- trin has been prepared under the scheme presented below:
PETROLEUM CHEMISTRY Vol. 47 No. 5 2007

OXIDATION OF UNSATURATED COMPOUNDS
CH OH
333
CH OH
2
2
O
O
K CO , ethylene carbonate
2
3
O
O
7
7
tetra-N-methyurea, 150°, 4 h
HO
OH
HO
O
O
n
O–
n = 0–2
First, we studied the oxidation of alkenes to methyl ketones practically were not formed despite the forma-
ketones in the presence of a catalyst system including tion of significant amounts of compounds with internal
palladium sulfate and copper dichloride in a solvent double bonds.
that comprised the water/ionic liquid system at various
In the presence of methylated and ethoxylated
volume ratios of ionic liquids, a temperature of 50°ë, a
β-cyclodextrin, the methyl ketone formation rate sub-
reaction time of 30 min, and a high stirring speed.
stantially increased (Fig. 2).
A high regioselectivity of the oxidation reaction is
A similar result was obtained when the reaction was
worth noting. In spite of the fact that isomeric alkenes
are formed at a high rate along with oxidation, corre-
sponding methyl ketone is the only product of oxida-
tion. In the absence of cyclodextrins, the yield of
octanone-2 increases until the volume fraction of the
+
–
carried out in the ionic liquid [Et-MIM] [SO OEt]
3
(
Table 2, Fig. 2). The growth in the oxidation rate can
be explained by the formation of inclusion complexes
of the host–guest type between cyclodextrin and a mol-
ecule of alkene-1, as in the case of Wacker oxidation in
the biphasic water–substrate system [1–2]. In the pres-
ence of cyclodextrins, the yields of products in this case
depended on the conformity of the substrate cavity to
the cavity of the receptor molecule. The change was
minimal for hexene-1 and maximal for heptene-1
+
–
ionic liquid [BMIM] [BF ] in the solvent becomes
4
2
0 vol % (Fig. 1). The reaction rate of octene-1 oxida-
tion increases by more than three times. With the fur-
ther increase in the ionic liquid/water ratio, the yield of
octanone-2 sharply decreases. This finding agrees with
published data on the oxidation of alkenes-1 in ionic
liquids at low oxygen pressures [15]. It seems that in
this case the ionic liquid shows the properties of a
hydrotrope, a compound that substantially increases the
solubility of an organic compound in water owing to the
formation of associates [16]. Note that such behavior is
also characteristic of other reactions in an ionic liquid–
polar solvent mixture [17].
(
Fig. 2). The variation in the reaction rate also
depended on the nature of a modifying group in the
cyclodextrin molecule. Oxyethylated cyclodextrins dis-
played the maximal activity. In this case, the yield of
ketone amounted to 70% for heptene-1 and more than
5
0% for octene-1 at 90°ë already for 30 min. With an
increase in the reaction temperature, the yield of prod-
ucts grows in the absence of cyclodextrins as well.
It should be noted that the addition of cyclodextrin
substantially increases the reaction rate in a biphasic
water/alkene system, whereas the macrocyclic receptor
has a substantially weaker effect on the reaction rate
when an ionic liquid is added.Apparently, this phenom-
enon is due to the formation of inclusion complexes
The employed catalytic system containing
PdCl (CH CN) , CuCl, HMPA, and cyclodextrins in
2
3
2
+
–
[
EtMIM] [SO OEt] could be recycled in the oxidation
of heptene-1 and octene-1 without the loss of activity.
3
The oxidation of styrenes in the absence of small
with molecules of the ionic liquid and with degradation amounts of water proceeded at a very low rate. The
of its associates. As a result of such competition, the addition of 5% water resulted in a substantial increase
concentration of an unsaturated compound in the aque- in the reaction rate (Table 3).
ous phase containing an ionic liquid sharply decreases.
Along with methyl ketone, the main products of the
To run the oxidation reaction of unsaturated com- reaction were the corresponding aldehyde and benzal-
pounds with air oxygen in the absence of significant dehyde, a product of double-bond breaking, whose
amounts of water, we have chosen as the catalyst a quantity increased with an increase in the amount of
complex of PdCl (CH CN) with CuCl and HMPA, water in the system. Note that a similar result was
2
3
2
which is formed in situ in the reaction mixture in the observed by Namboodiri et al. [19] during oxidation of
+
–
ionic liquid [BMIM] [BF ] [18]. Corresponding styrene with hydrogen peroxide in a water/ionic liquid
4
methyl ketone and isomeric alkenes were the main system. When the reaction is carried out in the presence
products of the reaction. It should be emphasized that of copper dichloride, the oxidation rate increases and
oxidation occurs with a high regioselectivity: isomeric benzaldehyde, the product of double-bond breaking, is
PETROLEUM CHEMISTRY Vol. 47 No. 5 2007

3
34
ANDREEVA et al.
TONCDmod/TON
Yield of ketone, %
25
20
15
10
5
0
2.5
+
–
[
EtMIM] [BF ]
4
PdSO /CuCl2
+
–
4
[EtMIM] [SO3OEt]
2
1
1
.0
.5
.0
PdSO /CuCl /Met-β-CD
4
2
PdSO /CuCl /β-CD-E
28
4
2
PdSO /CuCl /β-CD-CN
4
2
0.5
Met-β-CD
β-CD-E5
0
10
20
30
40
Fig. 2. Change in activity during oxidation of octene-1 to
Ionic liquid, vol %
octanone-2 in the presence of various catalytic systems (O2,
0
.5 MPa; 508C, 30 min); PdCl (CH CN) : CuCl : HMPA :
2 3 2
CD : C H = 1 : 1 : 2 : 0.2 : 10; [C H ] = 2 mol/l; TON is
8
18
8 16
Fig. 1. Yield of octanone-2 depending on the system used.
PdSO : CuCl : CD : [C H ] = l : l0 : 2 : 100. Solvent,
water/[BMIM] [BF ] ; [C H ] = 2 mol/l.
the number of moles of the product per mole of the metal in
the absence of CD; and TON is the number of moles
4
2
8
16
8 16
CD-mod
+
–
of the product per mole of the metal in the presence of CD.
4
not formed, so that the reaction proceeds according to substantially higher than in the case of alkenes-1. This
the mechanism traditional for the oxidation of styrene. difference can be explained in terms of high stability
constants for substrates containing the aromatic moiety
with cyclodextrin (Fig. 4).
The use of a catalytic system containing cyclodex-
trins resulted in a sharp growth in the reaction rate and
practically had no effect on the selectivity for reaction
products. Benzaldehyde makes up about half the total
quantity of the products (Fig. 3, Table 4).
Thus, we obtained results to support the concept that
catalytic systems on the basis of macromolecular
In the case of styrenes, the rise in the reaction rate
due to the presence of cyclodextrins in the system was
Table 2. Yields of ketones-2 in the presence of the catalytic
system PdCl (CH CN) : CuCl : HMPA: modified CD : sub-
2
3
2
strate = 1 : 1 : 2 : 0.2 : 10 (t = 30 min)
Table 1. Yields of ketones-2 in the presence of the catalytic sys-
tem PdCl (CH CN) : CuCl : HMPA : substrate = 1 : 1 : 2 : 10
Temperature, °C
2
3
2
Cyclodextrin
Substrate
5
0
90
Temperature, °C
Reaction time,
min
Substrate
Met-β-CD
Octene-1
19%
40%
34%
49%
26%
27%
50%
23%
32%
42%
53%
59%
76%
52%
43%
64%
38%
75%
5
0
90
Heptene-1
Hexene-1
Heptene-1
Octene-1
Octene-1
Heptene-1
Octene-1
Heptene-1
β-CD-E5
Hexene-1
Heptene-1
30
30
43%
12%
70%
14%
53%
39%
76%
40%
β-CD-E28
β-CD-CN
1
20
30
Octene-1
PETROLEUM CHEMISTRY Vol. 47 No. 5 2007

OXIDATION OF UNSATURATED COMPOUNDS
335
Table 3. Yields of the products of the Wacker oxidation of styrene at various water contents1
Selectivity, %
Amount
of water
Tempera-
ture, °C
Reaction Conversion,
Cocatalyst
time, h
%
Benzalde- Phenylace- Acetophe- Phenylacetic
hyde
taldehyde
none
acid
5
5
%
%
CuCl
CuCl
CuCl
CuCl2
CuCl2
50
80
80
80
80
0.5
2
11
38
56
45
53
23
36
63
–
23
5
54
29
27
76
80
30
3
1
1
1
0%
0%
0%
2
7
2
–
24
20
2
–
–
1
The catalyst/substrate ratio is Pd(MeCN) Cl : CuC1 (or CuC1 ) : HMPA : CD : substrate = 1 : 1 : 2 : 0.2 : 10. The total amount of the sol-
2
2
2
vent is 1 ml, the concentration of the Pd(II) complex is 0.1 mmol/l, and the oxygen pressure is 5 atm.
Table 4. Selectivity in oxidation of styrenes. PdCl (CH CN) : CuCl : HMPA : CD : substrate = 1 : 1 : 2 : 0.2 : 10. [Pd(II)] =
2
3
2
0
.1 mmol/l, 30 min. P(O ) = 0.5 MPa
2
Selectivity, %
Substrate
R–CH –C(O)H
2
R–C(O)H
R–C(O)–CH3
and R–CH –C(O)OH
2
C H –CH=CH styrene
β-CDE5
–
49
36
51
9
35
35
42
29
14
6
5
2
CH –C H CH=CH
2
β-CDE5
3
6
4
p-methylstyrene
–
28
52
36
2
36
46
(
CH ) C–C H –CH=CH
β-CDE5
3
3
6
4
2
p-tert-butylstyrene
–
49
2
49
TON1/TON2
5
octene-1
heptene-1
4
3
without β-CD-E5
in the absence of β-CD-E5
Conversion, %
00
1
8
6
4
2
0
0
0
0
0
2
1
0
Styren
Ô-Methylstyrene p-tert-Butylstyrene
Met-β-CD β-CD-E5 β-CD-E28 β-CD-CN
Fig. 3. Change in the reaction rate in the presence of various
cyclodextrins. TON1 is the number of moles of the product
per mole of the metal in the absence of CD, and TON2 is the
number of moles of the product per mole of the metal in the
presence of CD.
Fig. 4. Oxidation of styrenes: PdCl (CH CN) : CuCl :
2
3
2
HMPA : CD : substrate = 1 : 1 : 2 : 0.2 : 10, [Pd(II)] =
0.1 mmol/l, 30 min, P(O ) = 0.5 MPa.
2
PETROLEUM CHEMISTRY Vol. 47 No. 5 2007

3
36
ANDREEVA et al.
receptors have considerable promise for carrying out
reactions with nonpolar substrates in ionic liquids.
8. A. L. Maksimov, T. S. Buchneva, and E. A. Karakhanov,
J. Mol. Catal. A, 217, 59 (2004).
9
. E. A. Karakhanov, A. Ya. Zhuchkova, A. L. Maksimov,
et al., Neftekhimiya 42, 233 (2002) [Pet. Chem. 42, 181
ACKNOWLEDGEMENTS
(2002)].
This work was supported by the Russian Foundation
for Basic Research, project no. 06-03-32889a.
1
0. E. A. Karakhanov, A. Ya. Zhuchkova, T. Yu. Filippova,
and A. L. Maksimov, Neftekhimiya 43, 302 (2003) [Pet.
Chem. 43, 273 (2003)].
1
1
1
1. J. S. Wilkes, J. A. Levisky, R. A. Wilson, and C. L. Hus-
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