Synthesis of linear aldehydes from internal olefins in water

Article abstract of DOI:10.1039/b418350a

We show here, for the first time, that the carbonylation of internal olefins in a biphasic water system is possible. It is shown that control of the pH and CO partial pressure are important factors for successful reactions. Interestingly, the water-soluble catalyst leads to significantly higher regioselectivity compared to similar catalysts soluble in organic solvents. The obtained nli-selectivities exceed aD known literature data and the catalyst can be easily reused several times. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b418350a

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Synthesis of linear aldehydes from internal olefins in water{
Holger Klein, Ralf Jackstell and Matthias Beller*
Received (in Cambridge, UK) 9th December 2004, Accepted 14th February 2005
First published as an Advance Article on the web 9th March 2005
DOI: 10.1039/b418350a
the hydroformylation of internal olefins have been mainly
We show here, for the first time, that the carbonylation of
internal olefins in a biphasic water system is possible. It is
shown that control of the pH and CO partial pressure are
important factors for successful reactions. Interestingly, the
water-soluble catalyst leads to significantly higher regioselec-
tivity compared to similar catalysts soluble in organic solvents.
The obtained n/i-selectivities exceed all known literature data
and the catalyst can be easily reused several times.
developed by ligand design.10 Elegant examples include the
diphosphite ligands of UCC11 and Dupont/DSM,12 the
Xantphos ligands of van Leeuwen and co-workers,13 the acylpho-
sphite ligands of Bo¨rner et al.14 and substituted NAPHOS ligands,
that were introduced by us.15 However, to the best of our
knowledge there exists no example for a selective hydroformyla-
tion of internal olefins to linear aldehydes in water.
Here, we describe for the first time such reactions, which
proceed with hitherto unknown n/i-selectivity (.99:1), for the
synthesis of linear aldehydes from internal olefins. In addition, we
demonstrate that the control of pH in biphasic hydroformylations
allows for faster and more selective transformations of terminal
and internal olefins, which broadens the applicability of this method.
In the course of our investigations into the rhodium-catalysed
hydroformylation and hydroaminomethylation of internal olefins,
we reported that 2,29-bis(diphenylphosphinomethyl)-1,19-bi-
naphthalene (NAPHOS16) and similar phosphines allow for the
conversion of internal olefins in homogeneous phase.15 Based on
this work the question arose, whether water-soluble NAPHOS-
ligands in presence of rhodium complexes are able to catalyse the
reaction of internal olefins to linear aldehydes. Sulfonated
NAPHOS (so-called BINAS17) was introduced by Herrmann
et al. and shows high activity and n/i-selectivity in the rhodium-
catalysed hydroformylation of propene.18 However, such ligands
have never been successfully applied in hydroformylations of
internal olefins. Thus, it was not surprising that initial tests on the
hydroformylation of 2-pentene (Table 1), in the presence of
0.05 mol% Rh(CO)2acac and 0.25 mol% BINAS, were disappoint-
ing.19 Applying conditions that are typical for the hydroformyla-
tion of propene (T 5 125 uC, p 5 30 bar, CO:H2 5 1:1), a mixture
of aldehydes is obtained in only 12% yield (Table 1, entry 1).
However, by lowering the synthesis gas pressure to 10 bar, olefin
isomerization is faster and the yield of n-hexanal is significantly
increased (Table 1, entry 2). The very high n/i-selectivity of 97:3
and the marginal hydrogenation of pentene (,0.3%) and aldehyde
(0.7% hexanols) are noteworthy.
A fundamental problem of homogeneous catalysis is the simple
and efficient separation and recycling of the catalyst from starting
materials and products. The application of a biphasic system of
water and a non-miscible organic solvent constitutes probably the
most elegant and practical solution to this problem.1 Here, the
catalyst should be water-soluble and easily isolated by simple
phase separation. The industrial feasibility of this concept has
been successfully proven by the large scale production of
butyraldehyde (.300 000 t/a) via hydroformylation of propene
(Ruhrchemie/Rhoˆne-Poulenc process).2 Unfortunately, most cata-
lytic reactions have significantly reduced rates in water compared
to standard organic solvents. For example, aliphatic olefins other
than propene or 1-butene cannot be efficiently carbonylated in
water so far.3
Therefore in recent years other solvents have become important
as reaction media for two-phase-reactions.4 Examples are liquid
CO2,5 fluorous phases6 and especially ionic liquids.7 Nevertheless,
water is the ideal green solvent with regard to availability, price
and toxicity. Hence, it is desirable to develop concepts which allow
for a more general use of this type of biphasic catalysis.
One of the most important goals in current hydroformylation
research is the selective conversion of internal olefins to linear
aldehydes (Scheme 1).8 Such transformations offer the opportunity
to use cheaper mixtures of internal and terminal olefins as
feedstock and to save time and energy, which is needed for the
additional purification steps.9 So far, known catalyst systems for
Next, the influence of the partial pressures of carbon monoxide
and hydrogen were systematically studied. Selected results are
shown in Table 1. It became clear that, by reduction of the carbon
monoxide pressure down to 2 bar, an increase in both activity and
n/i-selectivity can be achieved. A lower pressure of CO leads to
increased hydrogenation side reactions. On the other hand, varia-
tions of the CO:H2 ratio seem to have a negligible influence on the
test reaction. Then the influence of the pH of the water phase on
the hydroformylation was examined in more detail.20 So far there
is no such study for internal olefins known to the best of our
knowledge. Surprisingly, the aldehyde yield in the buffered system
(phosphate buffer pH 6–9) was in all cases higher, compared to the
non-buffered reaction mixture (Table 1, entries 5–9).
Scheme 1 Rhodium-catalysed isomerisation–hydroformylation of inter-
nal olefins.
{ Dedicated to Prof. Dr Gu¨nther Wilke on the occasion of his 80th
birthday.
*matthias.beller@ifok.uni-rostock.de
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Table 1 Biphasic hydroformylation of 2-pentene with Rh-BINAS catalysta
b
pR (bar)
Entry
p0(CO) (bar)
p0(H2) (bar)
Additive
n-Hexanal (%)
n:i
88:12
Hexanols (%)
1
2
3
4
5
6
7
9
10
11
12
13
a
11
3
3
2
2
2
2
2
2
11
3
9
30
10
18
18
18
18
18
18
18
18
18
18
—
—
—
—
11
33
33
48
59
72
73
62
75
69
59
42
0.2
0.7
0.8
1
2
4
3
3
4
3
97:3
97:3
98:2
98:2
99:1
99:1
99:1
.99:1
99:1
98:2
98:2
10
10
10
10
10
10
10
10
10.5
Buffer (pH: 6)
Buffer (pH: 7)
Buffer (pH: 8)
Buffer (pH: 9)
Triethanolamine (1 ml)
TMEDA (0.5 ml)
Triethylamine (1 ml)
Triisooctylamine (1 ml)
2
2
1.5
2
1
Reaction conditions: 40 ml organic (anisole) and 40 ml aqueous phase; 73.0 mmol 2-pentene; 2-pentene:BINAS:Rh 5 2000:5:1; 125 uC; 24 h.
Pressure at reaction temperature.
b
Table 2 Recycling of the catalysta
Especially at pH 7 and 8 a significant increase of the aldehyde
yield (72–73%; TON 5 1460, TOF 5 61 h21) and an excellent
regioselectivity (99:1) are observed. This is the highest regioselec-
tivity that has been described for a hydroformylation of any internal
olefin to date. Interestingly, this excellent regioselectivity is only
achieved in water. When the tetra-n-butylammonium BINAS salt
was used as the ligand, in a one-phase-system (anisole:NMP 5 1:1)
and under the same reaction conditions [p0(CO) 5 2 bar,
p0(H2) 5 10 bar, pR 5 18 bar, T 5 125 uC, t 5 24 h], the
n/i-selectivity was only 85:15, and the yield of n-hexanal was only
52%. The possible reason for the higher n/i-selectivity in water is so
far unclear, although one might speculate about the increased
steric size of the ligand due to sulfonation and hydrogen bonding
to water molecules.
Entry
Hexanals (%)
n:i
Hexanols (%)
1b
2
3
4
5
6
7
a
63
64
71
68
66
63
59
99:1
99:1
99:1
99:1
99:1
99:1
99:1
3
3
3
3
3
2
2
Reaction conditions: p0 (CO) 5 2 bar, p0 (H2) 5 10 bar; T 5
18 bar; 73.0 mmol 2-pentene,
2-pentene:Rh 5 2000:1; t 5 24 h. BINAS:Rh 5 5, after every
125 uC;
p
(125 uC)
5
b
reaction 1 equivalent (relating to Rh) of ligand was added.
shown, that the catalyst phase is stable over a reaction time of at
least one week!
We assume that the main reason for the higher reactivity under
basic conditions is an easier preformation of the active catalyst
species, as was described by Joo´ et al. for hydrogenations using
chloride containing Rh-complexes.21 The lower yield in the non-
buffered solvent system is explained by a sharp decrease of the pH
in the aqueous catalyst solution (pH , 5) due to the acidity of the
Rh-hydride complex, and the formation of CO2 and HCO2H by
water-gas shift reaction. This example clearly demonstrates the
importance of pH control for transition metal-catalysed reactions in
aqueous media.22
Finally, we tested other olefins under similar conditions
(Table 3). Particularly interesting is the hydroformylation of
2-butene because of the industrial importance of inexpensive C4-
mixtures (.20M tons crack-C4/a). With this olefin similar good
results are obtained as with 2-pentene. The somewhat lower
n/i-selectivity (98:2) can be explained by the higher vapour pressure
of butenes, which causes an increase of the partial pressure of
carbon monoxide during the reaction.
Also, 1-pentene yields hexanals in good yield (78%) and
outstanding n/i-selectivity (.99:1). As stated in the introduction,
a particular challenge is the hydroformylation of mixtures of
olefins (Table 3, entries 4–6). Indeed, a mixture of octenes that
contained only 3.6% 1-octene, gave 10% nonanals. In this case the
reaction in a one-phase-system with the tetra-n-butylammonium
BINAS salt under identical conditions, gave a higher yield of 20%
but, as in case of 2-pentene, a significantly lower n/i-selectivity
(77:23). Clearly, the use of water as solvent does not only allow for
an easier catalyst recycling but also for higher selectivity towards
the desired linear isomer. By using longer reaction times or a
higher reaction temperature (140 uC) the aldehyde yield is
increased to 33%. With pure 2-octene at 140 uC (entry 7) a
somewhat higher yield (47%) and regioselectivity (99:1) are
obtained due to its easier isomerization to 1-octene.
Excellent results for the hydroformylation of 2-pentene can be
also obtained in the presence of amines (Table 1, entries 10–11). By
applying triisooctylamine as an additive it became again
apparent, that the increase in the reactivity is not due to the
transfer of the catalyst (as ammonium BINAS salt) into the
organic phase.
Obviously biphasic catalysis is advantageous compared to single
phase catalysis, when it is possible to reuse the catalyst system
several times. In order to demonstrate the reusability of the
aqueous catalyst phase, six recycling experiments with a buffered
solution (pH 5 9) were carried out (Table 2). The initial increase in
yield (Table 2, entries 2–3) is due to a drop of the pH to the
optimal value (7–8). The following decrease in the yield can be
mainly explained by the further descent of the pH. Indeed, pH-
control of the catalyst phase after the seventh experiment showed a
pH value of about 6. During the recycling experiments it was also
In addition styrene, which typically forms the branched alde-
hyde, is hydroformylated predominantly with the Rh-BINAS
2284 | Chem. Commun., 2005, 2283–2285
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Table 3 Hydroformylation of different olefinsa
b
pR (bar)
Entry
Substrate
T (uC)
p0(CO) (bar)
p0(H2) (bar)
t (h)
Aldehyde (%)
n:i
Alcohol (%)
1
2
3
4
5
6
7
8
a
2-Butenec
1-Pentene
2-Pentene
Octenesd,e
Octenesd,e
Octenesd,e
2-Octened
Styrenef
125
110
125
125
125
140
140
125
2
4
2
2
2
2
2
1.5
10
8
19
18
18
16
16
16
16
15
24
16
24
24
72
24
24
6
68
78
74
10
33
33
47
87
b
98:2
99:1
99:1
97:3
98:2
98:2
99:1
84:16
4
1
3
0.1
2
3
3
1
10
10
10
10
10
10.5
Reaction conditions: aqueous phase: buffer (pH: 8), 73 mmol olefin, olefin:BINAS:Rh 5 2000:5:1. Pressure at reaction temperature.
144 mmol 2-butene (E/Z-mixture), 2-butene:BINAS:Rh 5 4000:5:1. Aqueous phase: 19 ml H2O + 1 ml triethanolamine + 20 ml PEG 300.
Octene mixture (1:2:3:4 5 4:46:34:13). 36.5 mmol styrene, styrene:BINAS:Rh 5 5000:10:1, addition of styrene at reaction temperature.
c
e
d
f
system to give phenylpropanals in 87% yield (TOF 5 725 h21
;
and C. Claver, Kluwer Academic Publishers, Dordrecht, 2000, pp. 57–
59; (b) C. D. Frohning and C. W. Kohlpaintner, in Applied
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W. A. Herrmann, VCH, Weinheim, 1996, 1st edn., vol. 1, p. 40.
11 E. Billig, A. G. Abatjoglou and D. R. Bryant, (UCC) EP 213639, 1987,
US 4748261, 1988.
12 P. M. Burke, J. M. Garner, K. A. Kreutzer, A. J. J. M. Teunissen,
C. S. Snijder and C. B. Hansen, (DSM/Du Pont) WO 97/33854, 1997.
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Angew. Chem., 1999, 111, 349-351; L. A. van der Veen, P. C. J. Kamer
and P. W. N. M. van Leeuwen, Angew. Chem. Int. Ed., 1999, 38,
336–338; (b) L. A. van der Veen, P. C. J. Kamer and P. W. N. M. van
Leeuwen, Organometallics, 1999, 18, 4765–4777.
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Angew. Chem., 2001, 113, 3505–3508; H. Klein, R. Jackstell,
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n:i 5 84:16). Due to the easier hydrogenation of styrene, a lower
catalyst concentration is advantageous compared to the other
experiments.
In conclusion, we have shown here for the first time that the
carbonylation of internal olefins in a biphasic water system is
possible. It is shown that control of the pH and CO partial
pressure are important factors for successful reactions.
Interestingly, the water-soluble catalyst leads to significantly higher
regioselectivity compared to similar catalysts soluble in organic
solvents. The obtained n/i-selectivities exceed all known literature
data and the catalyst can be easily reused several times.
This work was sponsored by the German Federal Ministry of
Education and Research (BMBF), the state Mecklenburg-Western
Pomerania and the ‘‘Fonds der Chemischen Industrie (FCI)’’. We
thank Dr Franz Nierlich and Dr Klaus-Diether Wiese (Degussa
AG) for general discussions. Mrs Susann Buchholz, Dr Christine
Fischer and Dr Wolfgang Baumann (all IfOK) are thanked for
excellent analytical service.
16 K. Tamao, H. Yamamoto, H. Matsumoto, N. Miyake, T. Hayashi and
M. Kumada, Tetrahedron Lett., 1977, 16, 1389–1392.
17 Mixture of the sodium salts of different regioisomers with a sulfonation
degree between 6 and 8.
Holger Klein, Ralf Jackstell and Matthias Beller*
Leibniz-Institut fu¨r Organische Katalyse an der Universita¨t Rostock e.
V., Buchbinderstr. 5-6, D-18055 Rostock, Germany.
E-mail: matthias.beller@ifok.uni-rostock.de
18 (a) H. Bahrmann, K. Bergrath, H.-J. Kleiner, P. Lappe, C. Naumann,
D. Peters and D. Regnat, J. Organomet. Chem., 1996, 520, 97–100; (b)
H. Bahrmann, H. Bach, C. D. Frohning, H.-J. Kleiner, P. Lappe,
D. Peters, D. Regnat and W. A. Herrmann, J. Mol. Catal. A: Chem.,
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19 The hydroformylation experiments were carried out in a 300 ml Parr
autoclave at a stirring speed of 1200 min21. The volume of the
reaction mixture was 80 ml (40 ml organic and 40 ml aqueous phase).
Rh(CO)2acac was used as the catalyst precursor and the Rh
concentration in the aqueous solution was 0.91 mM. After adding
all starting materials under argon into the cooled autoclave (ice bath),
the indicated CO- and H2-pressures were applied and stirring
was started. After reaching the reaction temperature, the pressure in
the autoclave was kept constant by delivery of synthesis gas
(CO:H2 5 1:1) via a pressure regulator. After the reaction time
the autoclave was cooled to room temperature and samples
were taken from the organic phase and analyzed by gas
chromatography. Products were identified by comparison with
authentic samples.
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Angew. Chem. Int. Ed., 1999, 38, 3026–3028; (b) C. Do¨bler,
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10 (a) P. C. J. Kamer, J. N. H. Reek and P. W. N. M. van Leeuwen, in
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This journal is ß The Royal Society of Chemistry 2005
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