PEGPHOT: A new well-defined molecular weight polyether-substituted triphenylphosphite and its application in biphasic hydroformylation

Article abstract of DOI:10.1007/s10562-011-0603-5

This work describes the synthesis and characterization of PEGPHOT (tri-(4-triethylenoglycol-monomethyletherphenyl)phosphite) and its use in the rhodium-catalyzed hydroformylation of different olefins. In the hydroformylation of 1-hexene, it was possible t

Full text of DOI:10.1007/s10562-011-0603-5

Catal Lett (2011) 141:977–981
DOI 10.1007/s10562-011-0603-5
PEGPHOT: A New Well-Defined Molecular Weight Polyether-
Substituted Triphenylphosphite and its Application in Biphasic
Hydroformylation
•
Jose Ribeiro Gregorio Ricardo Gomes da Rosa
•
´
Ana Nery Furlan Mendes Joan Carles Bayon
´
•
´
´
Received: 23 December 2010 / Accepted: 10 April 2011 / Published online: 23 April 2011
Ó Springer Science+Business Media, LLC 2011
Abstract This work describes the synthesis and
characterization of PEGPHOT (tri-(4-triethylenoglycol-
monomethyletherphenyl)phosphite) and its use in the
rhodium-catalyzed hydroformylation of different olefins. In
the hydroformylation of 1-hexene, it was possible to carry out
10 recycles of the catalytic system without significant loss in
activity.
1 Introduction
Hydroformylation is an important and clean process to
produce aldehydes, which are important intermediates in
the chemical industry [1]. A major drawback of this reac-
tion is the catalyst recovery. The most successful strategy
to overcome this problem is the use of liquid–liquid
biphasic systems [2–8]. An example of these systems is
the combination of a nonpolar organic phase and a high
polarity solvent like poly(ethylene-oxide) (PEG) [9, 10].
This polymer has shown good performance in segregating
some metal catalysts from low polarity products, allowing
recovery and recycling of the metal complex. Many
examples of PEG-based biphasic systems using Rh, Ru and
Pd catalysts have been recently reported [11–18]. As in
other liquid–liquid biphasic systems, the recovery effi-
ciency of the catalyst depends on the difference between
the polarity of the products and the catalyst. These polarity
requirements could be a problem when the products of a
particular reaction show a medium to high polarity,
like aldehydes produced in the oxo process. To circum-
vent this problem, we herein present the synthesis of
tri-(4-triethylenoglycolmonomethyletherphenyl)phosphite
(PEGPHOT). To the best of our knowledge, this ligand is
the first ever described bearing PEG tails with a well-
defined molecular weight.
Keywords Biphasic catalytic system Á Hydroformylation Á
Rhodium Á PEO Á PEG
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-011-0603-5) contains supplementary
material, which is available to authorized users.
´
J. R. Gregorio (&) Á R. G. da Rosa
´
Instituto de Quımica, Universidade Federal do Rio Grande do
Sul, Av. Bento Gonc¸alves, 9500, 91501-970 Porto Alegre,
RS, Brazil
e-mail: jrg@iq.ufrgs.br
R. G. da Rosa
e-mail: ricardo.gomes@ufrgs.br
The phosphite PEGPHOT was synthesized in a purity
higher than 98% in two steps according to Scheme 1.
To evaluate the ligand as a modifier for the rhodium-
based catalytic system, we performed the hydroformylation
of 1-hexene (model substrate), 1-decene, styrene and
methyl oleate using PEG-400 as a solvent, which is liquid
at room temperature.
A. N. F. Mendes
´
´
Centro Universitario Norte do Espırito Santo, Departamento de
Ciencias Matematicas e Naturais, Universidade Federal do
ˆ
´
´
Espırito Santo, Rodovia BR 101 Norte, km 60, 29932-540 Sa˜o
Mateus, ES, Brazil
e-mail: ananeryfm@gmail.com
´
J. C. Bayon
Departament de Quımica, Universitat Autonoma de Barcelona,
´
`
08193 Bellaterra, Barcelone, Spain
e-mail: JoanCarles.Bayon@uab.es
123

´
J. R. Gregorio et al.
978
procedure [19]. Under argon, a mixture of 3.00 g
(27.3 mmol) of the hydroquinone, 0.31 g (2.85 mmol) of
the quinone, 4.47 g (27.3 mmol) of triethyleneglycolmo-
nomethylether and 0.33 mL of concentrated H2SO4 was
prepared. The mixture was vigorously stirred at 80 °C for
24 h. After this time, the sample was dissolved in dichlo-
romethane and washed with water. The organic phase was
then dried with MgSO4 and the solvent was removed. The
viscous dark residue was purified by distillation under
reduced pressure (230 °C, 1 mmHg) to give a 60% yield of
a 98% purity product. The intermediate was characterized
as follows:
1H NMR (CDCl3, 250 MHz): 7.06 (s, 1H), 6.78–6.65
(m, 4H), 3.97 (t, 2H), 3.77 (t, 2H), 3.59–3.73 (m, 6H), 3.53
(t, 2H), 3.34 (s, 3H).
13C NMR (CDCl3, 63 MHz): 152.2, 150.4, 116.0, 115.6,
71.7, 70.5, 70.4, 69.8, 67.9, 58.8.
MS [m/z (relative intensity)]: 256 (M?, 16%); 147
(14%); 110 (37%); 103 (19%); 59 (100%); 45 (11%); 29
(9%).
Scheme 1 Synthesis of PEGPHOT
2 Experimental
2.1 General
2.3 Ligand Synthesis
All operations were performed under an argon atmosphere
using standard Schlenk flask techniques. Solvents were
dried and distilled before use. The gases H2 (AGA,
99.999%) and CO (Air Products, 99%) were used without
purification.
The phosphite PEGPHOT was prepared according to the
following procedure: 4.68 g of 4-triethyleneglycolmono-
methyletherphenol (18.3 mmol), previously dried twice by
azeotropic distillation with toluene, and 2.55 mL of tri-
ethylamine (18.3 mmol) were dissolved in 20 mL of dry
THF. The solution was cooled by means of an ice bath and
a solution of 0.92 g (6.7 mmol) of PCl3 in 20 mL of THF
was added dropwise over 30 min. The ice bath was
removed and the mixture was stirred overnight and then
refluxed for 2 h. The resulting mixture was filtered from
the ammonium salt through a small silica column (dried at
130 °C overnight) and the solvent was evaporated under
vacuum to furnish PEGPHOT as a clear oil in 80% yield.
The final ligand was characterized as follows:
Gas chromatography–mass spectrometry experiments
were carried out with a G1800A Hewlett Packard gas
chromatograph and the ionization mode was electron
impact. Separations were accomplished on an HP-5 capil-
1
lary column (30 m 9 0.25 mm 9 0.25 lm). 31P, H and
13C NMR spectra were obtained with a Bruker Avance-250
instrument (s, singlet; d, doublet; t, triplet; q, quadruplet;
1
m, multiplet). Chemical shifts of the H and 13C NMR
spectra are reported in ppm (d) relative to tetramethylsilane
(TMS) using CDCl3 as an internal reference. The 31P NMR
spectra were recorded with 85% H3PO4 as an external
reference.
1H NMR (CDCl3, 250 MHz): 7.00 (d, 6H), 6.86 (d, 6H),
4.07 (t, 6H), 3.81 (t, 6H), 3.59–3.75 (m, 18H), 3.49-3.56
(m, 6H), 3.35 (s, 9H).
The conversion and selectivity of the hydroformylation
reactions were determined using a gas chromatographic
technique on a Shimadzu 17A GC system equipped with a
DB-5 column (30 m 9 0.25 mm 9 0.25 lm) and FID
detector. Helium was the carrier gas. For methyl oleate,
13C NMR (CDCl3, 63 MHz): 155.1, 144.8, 121.4, 115.2,
71.6, 70.5, 70.3, 69.4, 67.6, 58.7.
31P NMR {1H} (CDCl3, 101.3 MHz): 129.2.
ESI?: 796.34; calculated 796.84 (along with this signal,
another peak at 819.3 due to the sodium adduct was
observed).
1
these parameters were determined by H NMR, as descri-
bed below.
2.4 Hydroformylation and Recycling of the Catalytic
System
2.2 General Procedure for the Preparation of
4-triethyleneglycolmonomethyletherphenol (HPEG)
Under an argon atmosphere, a mixture of RhCl3.3H2O
(1.92 9 10-2 mmol), PEG-400 (4 g) and PEGPHOT
(0.192 mmol) was stirred at room temperature. After
The precursor 4-triethyleneglycolmonomethyletherphenol
(HPEG) was prepared according to a modified published
123

PEGPHOT: A New Well-Defined Molecular Weight
979
30 min, 1-hexene (2.4 mL, 19.2 mmol) was added and the
resulting mixture was transferred to an argon purged
stainless steel mini-reactor (100 mL) by a cannula without
additional solvent and under an argon atmosphere. The
reactions were carried with magnetic stirring. The reactor
was sealed, purged three times with H2 and pressurized
with H2 and CO as described below (Tables 1, 2, 3). The
reactor was heated by means of an oil bath and the tem-
perature was monitored with an adapted thermocouple. The
catalytic reactions were cooled to room temperature and
the reactor was vented. Next, the homogeneous reaction
mixture was transferred by cannula to a Schlenk tube under
argon. The unconverted substrate and products were
quantitatively (within experimental GC error) extracted
with vigorous magnetic stirring using 3 9 3 mL of dry
n-heptane. The extracts were analyzed by GC. For recy-
cling experiments, the polar phase containing the catalytic
system was dried under vacuum and transferred back to the
reactor, and then fresh alkene was added. For methyl ole-
ate, the procedure was similar, but the analysis was made
80 °C. Table 2 shows that at this temperature, the catalytic
activity and selectivity were retained after a greater number
of recycles, which implied an increase in the TON.
Using this modification, we were able to perform four
recycles (five reactions) while maintaining the same alde-
hyde linearity ratio ([ 72%), and no loss in conversion or
total aldehyde selectivity was observed (Fig. 1). We also
noticed that by lowering the temperature, the catalyst
leaching (observed during the extraction procedure for
reactions performed at 100 °C) was no longer visible, as
observed previously [11]. The formation of branched
aldehydes should come from the tandem isomerization-
hydroformylation process, which was considerable, espe-
cially after the 4th recycle. This behavior should be related
to phosphite inactivation during each recycle workup due
to some PEG’s residual water. Indeed, the oxidation of
both phosphines and phosphites by water under similar
reaction conditions has been already demonstrated [29].
Also, the aldehydes generated as products could react with
phosphites modifying their coordination behavior [30, 31].
1
by H NMR and APT on a small sample; the remaining
sample was passed through silica-gel (using dichloro-
methane as an eluent), dried under vacuum and stocked.
3 Results and Discussion
The starting operational conditions were based on the lit-
erature [20–28]: 100 °C, 40 bar, 5 h, L/Rh = 10, substrate/
Rh = 1000 and CO/H2 = 1. We observed excellent con-
versions from the 1st to the 7th cycles. However, despite
the high yields in total aldehydes, the system showed dif-
ferent product distributions along the recycles (Table 1).
This was likely due to some thermal decomposition of
either the solvent (PEG) or ligand, which was reinforced by
the presence of the catalyst’s color in the n-heptane phase
after some recycles.
To overcome the thermal decomposition problems
described above, the reaction temperature was lowered to
Fig. 1 Product distribution along the recycles for the hydroformyl-
ation of 1-hexene under the reaction conditions in Table 2
Table 1 Preliminary results of the hydroformylation of 1-hexene using PEGPHOT and the biphasic system PEG-400/n-heptane
Number of recycles
C (%)a
Isomers (%)a, b
Hexane (%)a
1-Heptanal (%)a
2-MH (%)a
2-EP (%)a
TON
0
1
2
3
4
5
6
7
96
96
0
0
0
0
0
0
0
0
1
1
1
2
1
0
0
5
72
68
60
53
52
52
51
51
22
25
29
34
36
37
37
35
5
6
960
960
98
10
11
11
11
12
9
980
100
100
98
1000
1000
980
98
980
80
800
Reaction conditions RhCl3.3H2O (0.01923 mmol); substrate/Rh = 1000; ligand/Rh = 10; PEG-400 (4 g); 100 °C; 5 h; 40 bar (CO/H2 = 1:1);
C Conversion, 2-MH 2-methylhexanal, 2-EP 2-ethylpentanal, data calculated by GC; 2-hexene and 3-hexene. See text for recycling details
a
b
123

´
J. R. Gregorio et al.
980
Table 2 Hydroformylation of 1-hexene with RhCl3.3H2O/PEGPHOT using the biphasic system PEG-400/alkene
Number of recycles
C (%)a
Isomers (%)a, b
Hexane (%)a
1-Heptanal (%)a
2-MH (%)a
2-EP (%)a
TON
0
1
2
3
4
5
6
7
8
9
10
97
96
96
98
98
98
97
98
98
97
97
3
3
3
2
1
0
1
1
1
1
1
4
5
3
4
2
0
2
2
2
1
2
76
76
76
75
72
69
62
61
56
56
56
17
16
17
17
21
26
30
31
33
35
35
0
0
1
1
4
5
6
5
8
7
6
960
950
930
960
980
980
970
980
980
970
970
Reaction conditions RhCl3.3H2O (0.01923 mmol); substrate/Rh = 1000; ligand/Rh = 10; PEG-400 (4 g); 80 °C; 5 h; 40 bar (CO/H2 = 1:1);
C Conversion, 2-MH 2-methylhexanal, 2-EP 2-ethylpentanal, data calculated by GC; 2-hexene and 3-hexene. See text for recycling details
a
b
Table 3 Hydroformylation of different olefins with RhCl3.3H2O/PEGPHOT using the biphasic system PEG-400/alkene
Olefin
Conversion (%)
Aldehydes (%)
Isomers (%)
Hydrogenation (%)
n/iso
1-Hexene
1-Decene
Styrene
97
90
85
92c
93
86
82
50c
3a
10a
4
4.4
5.0
0.2
ND
4
–
18
50c
Methyl oleateb
ND
Reaction conditions RhCl3.3H2O (0.01923 mmol); substrate/Rh = 1000; ligand/Rh = 10; PEG-400 (4 g); 80 °C; 5 h; 40 bar; CO/H2 = 1:1.
Product distribution calculated by GC, except when indicated; 2-hexene and 3-hexene or 2-decene and 3-decene, respectively; Reaction
a
b
c
performed using the following conditions: 100 °C; ligand/Rh = 10. Double bonds/Rh = 745; 40 bar; CO/H2 = 2:1; 5 h; Calculated by
1H NMR, see text
Table 3 shows the versatility of the present system for
different kinds of olefins. RhCl3.3H2O/PEGPHOT was an
excellent catalyst for the hydroformylation of 1-hexene, but
also 1-decene, styrene and methyl oleate in PEG-400. For
1-decene, the only hydroformylation products observed
were 1-undecanal and 2-methydecanal, aside from
2-decene and 3-decene, which were formed by substrate
isomerization. For styrene, some hydrogenation was
observed and a typical n/iso ratio of the aldehydes was
achieved with this substrate.
4 Conclusions
In summary, PEGPHOT is a well-defined phosphite ligand
that can be easily prepared from readily accessible
reagents. Its use with an Rh-based catalyst in liquid PEG-
400 media for the biphasic hydroformylation of alkenes has
been demonstrated. Further work to investigate the evolu-
tion of the catalytic species in the recycling experiment, as
well as to extend this strategy to other phosphorus ligands
and reactions are in progress.
Methyl oleate was hydroformylated under the optimized
reaction conditions previously described [32]. In this case,
even in the presence of an excess of CO, a significant
amount of the hydrogenation product was observed. Fur-
thermore, because the conversion was measured by 1H
NMR [32], it was not possible to quantify the amount of
9- and 10-formylestearate or other aldehydes formed from
previously isomerized substrate. Although the catalytic
system RhCl3.3H2O/PEGPHOT proved to be very efficient
for the hydroformylation of terminal olefins, it needs to be
optimized for internal ones. It is important to emphasize
that the reactions conditions are very mild compared to
most of the previously published reports on related cata-
lytic systems [15, 20–28].
Acknowledgments The authors acknowledge PRONEX/CNPq/
FAPERGS-04/0887-0, FAPERGS 04/1117.9, Spanish DGI (project
CTQ2005-09187-C02-01) CNPq (projects 474050/2007-6, 473917/
´
2008-4 and 310967/2009-0) and INCT-Catalise for their financial
support, as well as CAPES and CYTED (Project V9) for fellowships
to A.N.F.M.
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