Aqueous-phase hydroformylation of 1-octene: Styrene latices as phase-transfer agents

Article abstract of DOI:10.1002/anie.200602386

(Figure Presented) An elegant method for the aqueous-phase hydroformylation of 1-octene with a water-soluble Rh catalyst and amphiphilic latex particles as phase-transfer agents has been developed (see scheme). In this way, substantial concentrations of the olefin in the aqueous catalyst-containing phase were reached, and thus reasonable turn-over frequencies under mild reaction conditions could be achieved.

Full text of DOI:10.1002/anie.200602386

Angewandte
Chemie
Homogeneous Catalysis
DOI: 10.1002/anie.200602386
Aqueous-Phase Hydroformylation of 1-Octene:
Styrene Latices as Phase-Transfer Agents**
Katharina Kunna, Christian Müller, Joachim Loos, and
Dieter Vogt*
The Co- and Rh-catalyzed hydroformylation of olefins to
aldehydes has become one of the most important commercial
applications of homogeneous catalysis. However, one of the
major problems is the catalyst recovery from the reaction
mixture. Acommercial solution was applied in 1984 with the
[
1]
RCH/RP process, which is an aqueous-phase hydroformyl-
ation that converts propene to n-butyraldehyde
À1
(
ca. 0.8 Mta ) and isobutyraldehyde in the presence of
[
HRh(CO)(tppts) ] (see Scheme 3 for tppts). The modified
3
rhodium catalyst is dissolved in the aqueous phase, and
propene is significantly soluble in water. Thus, the catalyst is
recovered without any significant loss by separation of the
organic product layer from the aqueous phase. However, the
process is limited to olefins with short alkyl chains since the
solubilities of olefins in water decrease with increasing
number of carbon atoms, and the hydroformylation is there-
fore limited by the rate of mass transfer. Thus, higher olefins
(
> C ) are not suited for the RCH/RP process.
6
Several approaches have been proposed in the literature
for the hydroformylation of higher olefins. Examples include
anchoring rhodium catalysts to resins, polymeric supports, or
[
1a,2]
denrimers;
the use of ligands with amphiphilic proper-
[
3]
ties; or performing the reaction in the presence of cyclo-
dextrins, calix[4]arenes, cosolvents, (CTAB) micelles,
or in ionic liquids.
[
4]
[4]
[5]
[6]
[
7]
We report herein on the use of microsuspensions (also
called microemulsions) as phase-transfer agents in the hydro-
formylation of 1-octene. Microsuspensions or latices are
thermodynamically stable dispersions of submicron polymer
particles in water. Latices are synthesized by microemulsion
polymerization of suitable monomers or mixtures of mono-
mers dispersed in water in the presence of a surfactant.
[
*] Dipl.-Chem. K. Kunna, Dr. C. Müller, Prof. Dr. D. Vogt
Schuit Institute for Inorganic Chemistry and Catalysis
Eindhoven University of Technology
P.O. Box 513, 5600 MB Eindhoven (The Netherlands)
Fax: (+31)40-245-5054
E-mail: d.vogt@tue.nl
Dr. J. Loos
Laboratory of Polymer Technology and Material and Interface
Chemistry
Eindhoven University of Technology
5600 MB Eindhoven (The Netherlands)
[**] Prof. Dr. A. van Herk (TU/e) is gratefully acknowledged for helpful
discussions. We thank A. J. P. M. Staring for technical assistance
and Umicore for a generous gift of [Rh(acac)(CO) ]. The Dutch
2
National Research School Combination Catalysis (NRSCC) is
gratefully acknowledged for financial support.
Angew. Chem. Int. Ed. 2006, 45, 7289 –7292
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Communications
Conventional latices consist of a lipophilic core of organic
polymers and a hydrophilic surfactant, which provides charge
stabilization to the colloidal dispersion. The size of the
particles ranges from 4 to 100 mm, and their shape depends on
the composition and type of surfactant, giving structures such
as spheres, rods, or disks. The latex particles are stabilized by
the hydrophilic surfactant, while the lipophilic core can
absorb organic compounds.
We expect that these amphiphilic properties provide the
possibility to use latices as phase-transfer agents in a biphasic
hydroformylation of higher olefins using the water-soluble
Figure 1. TEM images of latices 1a (a) and 1b (b).
Table 1: Diameters of the latex particles 1a–c.
catalyst [HRh(CO)(tppts) ]. Thus, the polystyrene-based
3
[
8]
latices 1a–c were prepared by free-radical polymerization
Scheme 1). All latices are composed of the amphiphilic
(
[
a]
Sample
D [nm] (TEM)
h
D [nm] (DLS)
h
1
1
1
a
b
c
25Æ3
78Æ2
43Æ5
302
273
218
[a] Measured at 258C.
Aqueous-phase hydroformylation experiments were car-
ried out using the water-soluble catalyst system tppts/[Rh-
acac)(CO) ] (Scheme 3; acac = acetylacetonate) and the
Scheme 1. Synthesis of polystyrene-based latices 1a (R=H), 1b
R=SO Na), and 1c (R=CH NMe BF ).
(
3
2
3
4
(
2
macromonomer styr-PEG3000 (polyethylene glycol) and the
crosslinker DVB (divinylbenzene) as a stabilizing agent
(
Scheme 2). Produced in this way, the latices consist of a
Scheme 3. The ligand tppts.
latices 1a–c as phase-transfer agents. To gain insight into
the kinetics of the hydroformylation reaction, gas uptake of
Scheme 2. The structures of the nonionic (1a), anionic (1b), and
cationic (1c) latices (DVB part is omitted for clarity).
CO/H was measured automatically during the course of the
2
reactions (Figure 2). Notably, the gas-uptake curves represent
the conversion of 1-octene into aldehydes as no hydrogena-
lipophilic core and a hydrophilic shell, and the only variation
is the presence of different substituents R on the styryl groups.
These specific structures are supposed to act as phase-transfer
agents and transport the water-insoluble olefin into the water
phase.
The hydrodynamic diameters (D ) of the latex particles
h
were calculated by means of transmission electron micro-
[
9]
scopy (TEM; Figure 1)
(
and dynamic light scattering
[
10]
DLS). The particle sizes that were measured with TEM
[
11]
were smaller than those measured with DLS, which is most
likely a result of shrinkage of the particles during sample
preparation (Table 1).
The ability of the latices to act as phase-transfer agents
was further investigated by means of partitioning experi-
ments. In all cases a significant solubility of the organic
compounds in the microsuspension was observed, while the
latices preferably interacted with 1-octene instead of nonanal
Figure 2. Gas uptake of CO/H and conversion of 1-octene in the
Rh(tppts)-catalyzed aqueous-phase hydroformylation of 1-octene.
2
[
12]
by a factor of 2.5.
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Angew. Chem. Int. Ed. 2006, 45, 7289 –7292

Angewandte
Chemie
tion products (octane, alcohols) were observed as by-prod-
ucts. From the gas-uptake curves it is obvious that in all cases
catalytic activity was observed in the presence of latex
particles but that the different styryl salts had a dramatic
influence on the conversion of 1-octene.
The organic phase was further analyzed by means of gas
chromatography. The obtained yields of aldehydes are some-
what lower compared to the theoretical ones, owing to their
solubility in the microsuspension. The results are summarized
in Table 2. In the absence of any latex particles, the hydro-
5 was obtained, along with a decrease in activity to 44%
(Table 2, entry 5).
In summary, we investigated the possibility of polystyr-
ene-based latices to act as phase-transfer agents in the
aqueous-phase hydroformylation of 1-octene. It was thereby
observed that the substituent R of the styryl salts has a
significant influence on the conversion of 1-octene. Conse-
quently these catalytic systems provide new options in the
field of continuous aqueous organometallic catalysis. Further
investigations on the use of higher olefins (> C ) and on
8
variations of both ligand and latex particles are currently
being carried out.
Table 2: Rhodium-catalyzed aqueous-phase hydroformylation of 1-oct-
ene.
[
a]
[
b]
[c]
[d]
Entry
Ligand + additive
Conversion [%]
Yield [%]
l/b
–
Experimental Section
The ligand tppts and 1-octene were purchased from Aldrich and
purified by flash chromatography (Al O ); the latter was distilled
1
2
3
4
5
6
tppts
–
9.0
11
70
44
99
–
2
3
tppts+1a
tppts+1b
tppts+1c
4.5
7.38
49
35
90
1.9
2.0
3.4
5.1
2.9
over CaH2 and degassed. The polystyrene-based latices were
synthesized by emulsion polymerization of styrene as described
below.
[
e]
f]
tppts+1c
tppts+1c
[
8]
[
General preparation of polystyrene-based latices 1a–c:
A
[
14]
solution of the internal styrene salt (12 mmol) in degassed and
deionized water (80 mL) was placed into an autoclave equipped with
a mechanical stirrer. The solution was heated to 808C and stirred at
[
(
a] Reaction conditions: 1-octene (150 mmol), tppts (0.21 mmol), [Rh-
acac)(CO) ] (0.035 mmol), water/organic phase 1:2.3, S/P/Rh 5000:6:1,
latex (100 mg solid content), dodecane external standard (15 mmol),
CO/H2 1:1, p=20 bar, T=808C, t=140 h, stirring rate 600 rpm.
b] Determined by gas uptake (see also Figure 2). [c] Determined by
GC analysis; corresponds to yield of aldehyde in the organic phase.
d] Ratio linear/branched product. [e] tppts (0.71 mmol), Rh/L 1:20.
f] Latex (500 mg solid content).
2
100 rpm. After the temperature was reached, styrene (49 mmol),
[
15]
divinylbenzene (1.85 mmol), and the initiator
added. The stirring rate was increased to 300 rpm. After 10 minutes
the mixture became milky, indicating formation of the microsuspen-
(0.48 mmol) were
[
[
16]
[
[
sion. The macromonomer functional PEG3000 (1.23 mmol) in water
20 mL) was added and the suspension was stirred for 4 h. During this
(
process several samples were taken to measure the solid contents and
consequently to monitor the conversion. Finally, the latex was cooled
to room temperature and stored at 48C. The latices were purified by
dialysis over 3–4 days by using a membrane with a pore size of 25–
formylation of 1-octene with CO/H (1:1) in water using tppts/
2
[
Rh(acac)(CO) ] at 808C and 20 bar pressure showed no
2
30 Š. In case of bigger particles, centrifugation was performed. The
conversion at all (Table 2, entry 1). The addition of 1a to the
reaction mixture increased the conversion of 1-octene to 9%
during the 140-hour reaction time (Table 2, entry 2), and
addition of 1b increased conversion to 11% (Table 2,
entry 3). Interestingly, when the same reaction was carried
out using 1c as the phase-transfer agent (Table 2, entry 4), the
conversion of 1-octene increased to 70%. By using a higher
amount of latex as phase-transfer agent, the conversion of 1-
octene increased to 100% with an observed turnover
particles were analyzed by means of TEM and DLS.
General procedure for the aqueous-phase hydroformylation of 1-
octene: The reactor was charged with water (11 mL), [Rh-
[
17]
(acac)(CO)
100 mg, 2 mL), giving a Rh/tppts ratio of 1:6. The catalyst was
]
(0.0356 mmol), tppts (0.21 mmol)
,
and latex
2
(
preformed at 08C and 20 bar CO/H for 3 h at 600 rpm. Subsequently,
2
the substrate 1-octene (150 mmol, Rh/S 1:5000) was added by a
dropping funnel, and the conversion was measured by gas uptake of
[18]
CO/H2. After 140 h the reaction was stopped by cooling the reactor
to room temperature and venting. The organic layer was analyzed by
gas chromatography on a PONAcolumn (length 50 m, d = 0.2 mm,
film 0.5 mm, J&W Scientific).
À1
frequency of 150 h (Table 2, entry 6). These results nicely
demonstrate the mass-transfer limitation of the aqueous-
phase hydroformylation of 1-octene.
Received: June 14, 2006
Published online: October 9, 2006
The strikingly better performance of the ammonium-
modified latex particle 1c may be explained by a preferred
association of the sulfonated catalyst complex with the
ammonium groups of these latex particles, thereby associating
the catalyst with the phase-transfer agent and thus enhancing
Keywords: biphasic catalysis · hydroformylation · latices ·
.
microemulsion · polystyrene
[
6]
the hydroformylation reaction. This association might be
described as a combination of electrostatic, van der Waals,
and hydrophobic interactions. In fact, remarkable stable
complexes of cationic ammonium substrates and polysulfo-
nated host molecules have been observed before and are well
[1] a) Multiphase Homogeneous Catalysis (Eds.: B. Cornils, W. A.
Hermann, I. T. Horvµth, W. Leitner, S. Mecking, H. Olivier-
Bourbigou, D. Vogt), Wiley-VCH, Weinheim, 2005, p. 166;
b) P. W. N. M. van Leeuwen in Homogeneous Catalysis—Under-
standing the Art (Ed.: P. W. N. M. van Leeuwen), Kluwer,
Amsterdam, 2004; c) C. Claver, P. W. N. M. van Leeuwen in
Rhodium Catalyzed Hydroformylation (Eds.: P. W. N. M. van
Leeuwen, C. Claver), Kluwer, Amsterdam, 2000.
[
13]
documented in the literature.
Further investigation of the product mixture revealed an l/
b ratio of about 2, as expected for monodentate PR /Rh
3
systems. To increase the linearity, the L/Rh ratio was
increased from 6:1 to 20:1. In this way an l/b ratio of about
Angew. Chem. Int. Ed. 2006, 45, 7289 –7292
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www.angewandte.org
7291

Communications
[
2] T. Jongsma, H. Van Aert, M. Fossen, G. Challa, P. W. N. M.
van Leeuwen, J. Mol. Catal. 1993, 83, 37 – 50.
[
3] a) B. E. Hanson, H. Ding, C. W. Kohlpaintner, Catal. Today
1998, 42(4), 421 – 429; b) B. Fell, G. Papadogianakis, J. Mol.
Catal. 1991, 66, 143 – 154.
[
4] S. Shimizu, S. Shirakawa, Y. Sasaki, C. Hirai, Angew. Chem.
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[5] P. Purwanto, H. Delmas, Catal. Today 1995, 24, 135 – 140.
[6] A. Rijsager, B. E. Hanson, J. Mol. Catal. A 2002, 189, 195 – 202.
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[
8] R. Sablong, J. I. van der Vlugt, R. Thomann, S. Mecking, D.
Vogt, Adv. Synth. Catal. 2005, 347, 633 – 636.
[
9] TEM experiments were performed on a Fei Tecnai 20 after
deposition and drying a droplet of the latex dispersion on a
carbon-coated copper grid.
[
10] DLS experiments were performed on a Malvern 4700 DLS
Particle-Size Analyzer.
[
[
11] C. Yi, Z. Zu, J. Appl. Polym. Sci. 2005, 96, 824 – 828.
12] Amixture of 1-octene and n-nonanal was treated with an
aqueous latex suspension under hydroformylation conditions,
and the distribution between the phases was determined by GC
analysis (external standard: dodecane). Furthermore, the stabil-
ity of the microsuspension was tested at different temperatures
and stirring rates. Optimal conditions without any significant
coagulation were found at 808C and 600 rpm.
[
[
[
13] See, for example: C. Bonal, Y. Israꢀli, J. Morel, N. Morel-
Desrosiers, J. Chem. Soc. Perkin Trans. 2 2001, 1075 – 1078.
14] 1a: no styryl salt; 1b: sodium 4-vinylbenzylsulfonate; 1c: 4-
vinylbenzyltrimethylammonium tetrafluoroborate.
15] 1a: VA-086 (2,2’-azobis[2-methyl-N-(2-hydroxyethyl)]propion-
amide); 1b,c: V-50 (2,2’-azobis(2-methylpropionamide) dihy-
drochloride).
[
16] 4-Vinylbenzylstyrene PEG3000 was synthesized according to: K.
Ito, S. Yokoyama, F. Arakawa, Y. Yukawa, T. Iwashita, Y.
Yamasaki, Polym. Bull. 1986, 16, 337 – 344.
[
[
17] 0.71 mmol tppts were used in Table 2, entry 5.
18] Calibration of CO/H [mL] was performed by hydroformylation
2
of 1-octene using Sixantphos/[Rh(acac)(CO) ] catalyst in tolu-
2
ene.
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Angew. Chem. Int. Ed. 2006, 45, 7289 –7292