Multiphase catalysis using water-soluble metal complexes in supercritical carbon dioxide

Article abstract of DOI:10.1039/a903528a

Hydrogenation of cinnamaldehyde was performed in a supercritical carbon dioxide-water biphasic catalyst system, which eliminates gas-liquid-liquid mass transfer and gives better activity and selectivity.

Full text of DOI:10.1039/a903528a

Multiphase catalysis using water-soluble metal complexes in supercritical
carbon dioxide
a
b
a
a
Bhalchandra M. Bhanage, Yutaka Ikushima, Masayuki Shirai and Masahiko Arai*
a
Institute for Chemical Reaction Science, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
E-mail: marai@icrs.tohoku.ac.jp
Tohoku National Industrial Research Institute, Nigatake, Miyagino-ku, Sendai 983-8551, Japan
b
Received (in Cambridge, UK) 4th May 1999, Accepted 28th May 1999
Hydrogenation of cinnamaldehyde was performed in a
supercritical carbon dioxide–water biphasic catalyst system,
which eliminates gas–liquid–liquid mass transfer and gives
better activity and selectivity.
Hydrogenation of a, b-unsaturated aldehydes to give un-
saturated alcohols with high selectivity is a challenging task due
to several possible side reactions using heterogeneous metal
supported catalysts.9 However, good selectivity and activity
,10
3
were reported with Ru–PPh based catalysts using homogenous
and biphasic catalyst systems.11 Table 2 summarizes the present
results for hydrogenation of cinnamaldehyde using several
catalyst systems.† Under the conditions used, unsaturated
alcohol (UOL) and saturated aldehyde (SAL) were the main
products with other very minor products. All the catalysts were
2
Supercritical carbon dioxide (scCO ) is considered as an
ecologically benign and economically feasible reaction medium
1
for metal catalyzed reaction. It has several advantages such as
nonflammability, lack of toxicity, absence of a gas–liquid phase
boundary and possible simplifications in work up. This makes
scCO
chemical properties of scCO
range by adjusting the pressure and temperature. Use of
organometallic catalysts in scCO is interesting, as demon-
2
an alternative to conventional solvents. The physico-
reduced with H
catalytic species. The catalytic chemistry for hydrogenation of
a,b-unsaturated aldehydes using Ru–TPPTS [TPPTS
P(C SO Na) ] has already been explored well by earlier
2
for 1 h at 40 °C in order to form the active
2
can be tuned within a certain
=
2
6
H
4
3
3
2
11
strated in some previous works. Water-soluble organometallic
catalysis has widened the scope of homogeneous catalysis in
practice as it gives easy separation of catalyst and reactants/
products, which is an important step towards the development
investigators. In homogeneous reaction systems gas–liquid
mass transfer is a key rate determining parameter. In the case of
toluene solvent, 29% conversion was obtained with 92%
selectivity to UOL. Homogeneous catalysis in general suffers
from the major drawback of catalyst and product separation and,
hence, the concept of biphasic catalysis has emerged. When this
system is converted to a biphasic mode of operation keeping all
parameters constant, the conversion of cinnamaldehyde drops
from 29% to 11%, retaining the selectivity performance (Table
2, run 3). The important parameters such as gas–liquid–liquid
mass transfer and liquid–liquid mass transfer (i.e. solubility of
substrate in catalyst phase) are key factors in controlling the rate
of reaction. In this case the substrate, cinnamaldehyde, has finite
solubility in the catalyst phase, and therefore that is not a major
limitation unlike hydroformylation of higher olefins in a
biphasic mode of operation.3 When this reaction is subjected
3
of environmentally friendly processes. Hoechst AG is operat-
ing a 300,000 tonnes per annum plant for hydroformylation of
propylene using Rh and a water-soluble phosphine complex in
a biphasic mode of operation. Several new concepts such as use
4
5
of co-solvents and surface active ligands, interfacial catalysis
6
using catalyst binding ligands, supported aqueous phase
7
8
catalysis, and supported ethylene glycol phase catalysis have
emerged to improve poor reaction rates, which are due to
limitations in liquid–liquid mass transfer and/or solubility of
2
reactants. Considering the advantages of scCO as a reaction
medium and water-soluble metal complexes, there is a need to
combine these two approaches to develop a truly environmen-
tally friendly process (see Table 1). This eliminates the use of
organic solvents and also gives easy catalyst/product separation
and catalyst recycling. Here we demonstrate integration of
biphasic catalysis and supercritical carbon dioxide using
hydrogenation of an a,b-unsaturated aldehyde, cinnamalde-
hyde. This gives significant enhancement in the reaction rate
and selectivity to cinnamyl alcohol and easy separation of the
catalyst and reactants/products.
–6
to scCO
the RuCl
is mainly due to the very poor solubility of the phosphine ligand
in scCO . Visual observation through a sapphire window
confirms that solid catalyst particles are suspended in scCO
2
as medium instead of an organic solvent like toluene,
3
–PPh catalyst system performs very poorly (run 2). It
3
2
2
.
Since there is no interaction of catalyst and reactants, a poor
reaction rate is observed. Presently, many researchers are
working on enhancing the solubility of phosphine ligands in
Table 1 Catalysis using metal complexes
System
Type
Advantages
Disadvantages
Homogeneous
Gas–liquid
Gas–liquid–liquid
High activity and selectivity
Catalyst/product separation; gas–liquid mass
transfer; organic solvent needed
Low reaction rates for water insoluble
substrates; gas–liquid–liquid mass transfer
limits rate of reaction; organic solvent
needed
Biphasic
High selectivity; high activity possible with water
soluble substrates; easy catalyst separation and
recycling
(organic–water)
SAPC
Gas–liquid–liquid
High activity and selectivity; product separation by
phase separation; easy catalyst recycling
High selectivity; high activity possible with water
soluble substrates; easy catalyst separation and
recycling; organic solvent not needed
Organic solvent needed; stability of catalyst
film on solid support
Poor solvating ability of many supercritical
fluids
(on solid support)
Biphasic
Supercritical
fluid–liquid
(supercritical
solvent–water)
SAPC in
supercritical
solvent
Supercritical
fluid–liquid (on
solid support)
High activity and selectivity; product separation by
phase separation; easy catalyst recycling; use of
organic solvent is avoided
Poor solvating ability of many supercritical
fluids
Chem. Commun., 1999, 1277–1278
1277

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Table 2 Hydrogenation of cinnamaldehyde using various catalyst systemsa
Pressure/MPa
Selectivity (%)
Catalyst
precursor
Solvent
system
Conversion
(%)
Run Reaction type
Ligand
scCO
2
H
2
UOL
SAL
1
2
3
4
5
6
7
8
a
Homogeneous
Homogeneous
Biphasic
Biphasic
Biphasic
Biphasic
SAPC
RuCl
RuCl
RuCl
RuCl
RhCl
3
3
3
3
3
PPh
PPh
3
toluene
—
140
—
140
140
140
—
40
40
40
40
40
40
40
40
29
1.5
11
38
35
22
13
44
92
89
92
99
—
—
93
96
8
11
8
3
scCO
toluene–water
2
TPPTS
TPPTS
TPPTS
TPPTS
TPPTS
TPPTS
scCO
scCO
scCO
2
2
2
–water
–water
–water
0.5
100
100
7
Pd(OAc)
2
RuCl
RuCl
3
toluene–water
scCO –water
SAPC
3
2
140
4
3
Reaction conditions: Catalyst precursor: 0.012 mmol; ligand/Ru: 8; T = 40 °C; cinnamaldehyde: 7.8 mmol; toluene (for 1,3,7): 25 cm ; time: 2 h; water:
3
0.5 cm ; silica (for 7,8): 1.5 g.
by using flourous substituents.12 Biphasic catalytic
–water (runs 4–6) give much better
conversion than conventional biphasic reactions (11 to 38%)
and normal homogenous modes of operation (29 to 38%). This
catalyst system differs from conventional gas–liquid and gas–
liquid–liquid catalytic hydrogenation, since gas–liquid and gas–
liquid–liquid mass transfer are completely eliminated in the
back pressure regulator. The reaction was started by stirring the mixture
with a magnetic stirrer and continued for 2 h. After reaction, the pressure
was released and the reaction mixture was analyzed via GC (Shimadzu GC-
scCO
systems such as scCO
2
2
8
A, Ucon Oil 8HB 2000 Uniport B, 6 m). Details of the experimental
apparatus and procedures are described elsewhere (ref. 14).
1
Chem. Rev., 1999, 99; G. Kaupp, Angew. Chem., 1994, 106, 1519;
Angew Chem., Int. Ed. Engl., 1994, 33, 1452; M. Poliakoff, S. M.
Howdle and S. G. Kazarian, Angew. Chem., 1995, 107, 1409; Angew.
Chem., Int. Ed. Engl., 1995, 34, 1275; P. G. Jessop, T. Ikaria and R.
Noyori, Science, 1995, 269, 1065.
case of scCO
supercritical mixture of H
is 3.2 M, while the concentration of H
pressure is only 0.4 M.13 This property of scCO
2
as solvent. The concentration of hydrogen in a
(85 bar) and CO (120 bar) at 50 °C
in THF under the same
allows a
2
2
2
2
2 P. G. Jessop, T. Ikariya and R. Noyori, Nature, 1994, 368, 231; A.
Furstner, D. Koch, K. Langemann, W. Leitner and C. Six, Angew
Chem., Int. Ed. Engl., 1997, 36, 2466; J. W. Rathke, R. J. Klingler and
T. R. Krause, Organometallics, 1991, 10, 1350.
reduction in viscosity and an increase in diffusion rate as
compared with the liquid phase, so that transport to and from the
catalyst phase is no longer a limiting factor. This causes
significant rate enhancement as observed in Table 2 and might
3
Applied Homogeneous Catalysis by Organometallic Complexes, ed. B.
Cornils and W. A. Herrmann, VCH, Weinheim, 1996; B. Cornils, W. A.
Herrmann and R. W. Eckl, J. Mol. Catal. A, 1997, 116 27; W. A.
Herrmann and B. Cornils, Angew. Chem., Int. Ed. Engl., 1997, 36,
be advantageous in improving selectivity performance. RuCl
as metal precursor gives 99% selectivity towards UOL (run 4),
while RhCl and Pd(OAc) give 100% selectivity towards SAL.
3
3
2
1
048.
Earlier investigators have already examined this feature.
Supported aqueous phase catalysis (SAPC) in which the metal
complex is supported on a solid surface like silica has been
successfully used for biphasic reactions which have substrate
4
R. M. Deshpande, Purwanto, H. Delmas and R. V. Chaudhari, Ind.
Chem. Eng. Res., 1996, 35, 3927; Purwanto and H. Delmas, Catal.
Today, 1995, 24, 135.
5 H. Ding and B. E. Hanson, J. Chem. Soc., Chem. Commun., 1994, 2747;
H. Ding, B. E. Hanson and J. Bakos, Angew. Chem., Int. Ed. Engl., 1995,
2
solubility limitations. SAPC can also be used in scCO as
3
4, 1645.
solvent and better activity and selectivity were observed when
compared with toluene as solvent (12.4 to 44%). Although the
application of SAPC is not particularly attractive in the case of
hydrogenation of cinnamaldehyde (since it has finite solubility
in the catalyst phase), it may be more attractive in the case of
water insoluble substrates.
6
7
R. V. Chaudhari, B. M. Bhanage, R. M. Deshpande and H. Delmas,
Nature, 1995, 373, 501; US Pat. 5498801 (1996); 5650546 (1997).
J. P. Arhancet, M. E. Davis, J. S. Merola and B. E. Hanson, Nature, 1989
3
39, 454; J. P. Arhancet, M. E. Davis, J. S. Merola and B. E. Hanson,
J. Catal., 1990, 121, 327.
8 K. T. Wan and M. E. Davis, Nature, 1994, 370, 449.
In conclusion, scCO
2
–water was shown to be a good
9 P. Gallezot and D. Richard, Catal. Rev.-Sci. Eng., 1998, 40, 81 and
references cited therein; V. Ponec, Appl. Catal. A., 1997, 149, 27.
0 M. Arai, H. Takahashi, M. Shirai, Y. Nishiyama and T. Ebina, Appl.
Catal. A., 1999, 176, 229; M. Arai, A. Obata, K. Usui, M. Shirai and Y.
Nishiyama, Appl. Catal. A., 1996, 146, 381; M. Arai, K. Usui, M. Shrai
and Y. Nishiyama, Stud. Surf. Sci. Catal., 1995, 91, 923; M. Arai, K.
Usui and Y. Nishiyama, J. Chem. Soc., Chem. Commun., 1993, 1853.
1 J. M. Grosselin, C. Mercier, G. Allmang and F. Grass, Organometallics,
alternative solvent system for conventional biphasic catalytic
systems. This eliminates gas–liquid–liquid mass transfer limita-
tions due to the very high solubility of reactant gases in
1
2
scCO .
We thank the Japan Society for Promotion of Science (JSPS)
for financial support.
1
1
991, 10, 2126; M. Hernandez and P. Kalck, J. Mol. Catal. A, 1997, 116,
1
17 and 130; A. J. Carrasquel, J. Marino, F. A. Lopez, D. E. Paez, I.
Notes and references
Rojas and N. Valecia, J. Mol. Catal. A, 1997, 116, 157; F. Joo, J.
Kovacs, A. C. Benyei and A. Katho, Catal. Today, 1998, 42, 441.
†
Typical experimental procedure for an experiment involving the scCO
2
–
water biphasic catalytic system is as follows: RuCl (0.012 mmol) and
TPPTS (0.096 mmol) dissolved in water (0.5 cm ) were charged to a 50 cm
3
12 D. Koch and W. Leitner, J. Am. Chem. Soc., 1998, 120, 13398; D. R.
Palo and C. Erkey, Ind. Eng. Chem. Res., 1998, 37, 4203.
13 Hydrogen and Deuterium, ed. C. L. Young, Solubility Data Series,
Pergamon, Oxford, 1981, vol. 5/6.
14 Y. Ikushima, N. Saito, K. Hatakeda, S. Ito, M. Arai and K. Arai, Ind.
Eng. Chem. Res., 1992, 31 569; Y. Ikushima, N. Saito and M. Arai,
J. Phys. Chem., 1992, 96, 2293.
3
3
reactor maintained at 40 °C. Hydrogen (10 bar) was introduced into the
reactor and left for 1 h. Cinnamaldehyde (7.8 mmol) was introduced into the
reactor after depressurizing the hydrogen. Hydrogen (40 bar) and liquid
carbon dioxide were subsequently introduced into the reactor using a
JASCO Model 880-PU syringe pump and compressed to the desired
pressure (180 bar). The pump delivered the CO
ml min . Pressure control was achieved using a JASCO Model 880-81
2
at a flow rate of 3.5
21
Communication 9/03528A
1278
Chem. Commun., 1999, 1277–1278