Nonaqueous Biphasic Hydroformylation of Long Chain Alkenes Catalyzed by Water Soluble Phosphine…
439
chemicals industries [5–9]. Rhodium complexes have been
examined as the most effective homogenous catalysts for
hydroformylation as they display high activity and selectiv-
SO3Na
SO3Na
NaO3S
NaO3S
P
P
SO Na
ity under milder reaction conditions [10]. However, a serious
shortcoming of homogeneous catalysis is the cumbersome
separation by distillation of reaction products from catalyst.
Aqueous media are now viewed as excellent means to effect
nearly complete catalyst separation and recovery [11–16], but
3
NaO3S
SO Na
3
SO Na
3
SO3Na
the poor solubility of long chain alkenes (>C ) in water is of
TPPTS
Fig. 1 Structure of TPPTS and BISBIS
BISBIS
6
potential limitation. In addition, this process is not suitable for
water-sensitive substrates.
Recently, as a nontoxic, biodegradable and inexpensive sol-
vent of low volatility, polyethylene glycol (PEG) has attracted
much interest as a recycling solvent [17, 18].
The content of rhodium in products mixture was detected by
inductively coupled plasma-atomic emission spectroscopy
(ICP-AES).
Among rhodium catalyzed hydroformylation of long chain
alkenes in PEG, the tested catalysts are commonly rhodium
complexes with phosphines containing PEG chain or rhodium
polyethylene glycolate complex, so as to increase the solubility
and affinity of the catalyst to PEG. Results obtained show that
the regioselectivity for linear aldehyde is low, alongside, the
rhodium leaching into product phase is high (up to 10 wt% of
the initial amount). To the best of our knowledge, the hydro-
formylation of long chain alkenes catalyzed by rhodium cata-
lyst with water soluble phosphine BISBIS or TPPTS (TPPTS:
sodium salt of sulfonated triphenylphosphine, BISBIS: sodium
salt of sulfonated 2,2′-bis(diphenylphosphinomethyl)-1,1′-
biphenyl) in PEG has not been described yet.
2.2 Hydroformylation and Catalyst Recycling
All hydroformylation was carried out in a 60 mL stainless
steel autoclave equipped with a magnetic stirrer. HRh(CO)
(TPPTS) , TPPTS or BISBIS, PEG and long chain alkene
3
were introduced to the autoclave under a nitrogen atmos-
phere. The autoclave was closed, flushed with syngas three
times, and then pressurized with syngas (H :CO=1:1) to
2
desired pressure and heated to needed temperature for a speci-
fied time. After the reaction was finished, the autoclave was
cooled to room temperature and carefully depressurized. The
product phase was separated from the PEG phase containing
water soluble rhodium catalyst by simple phase separation.
The products were analyzed by GC (PANNA A91, KB-1,
Herein, water soluble phosphine rhodium catalyzed the
hydroformylation of long chain alkenes in PEG (Scheme 1) is
chosen to investigate the reaction performance, phase behavior
and catalyst recycling.
3
0 m×0.25 mm×0.50 µm, FID). In catalyst recycling experi-
2
Experimental
ments, the PEG phase and new portion of long chain alkene
were introduced to the autoclave under a nitrogen atmos-
phere. The other operations were the same as the former
hydroformylation.
2.1 Materials
Ligands TPPTS, BISBIS (Fig. 1) and rhodium precursor
HRh(CO)(TPPTS) were prepared according to literatures [19,
3 Results and Discussion
3
2
0]; DEG (Diethylene glycol), PEG-200, PEG-400 and PEG-
6
00 (the number refers to the average molecular weight) were
As well known, bidentate phosphine ligands are crucial for
regioselectivity control toward linear aldehyde, because their
specific bite angle can improve the regioselectivity [21, 22].
In this report, 1-dodecene was chosen as a probe substrate,
BISBIS as a water soluble bidentate phosphine ligand to
investigate the reaction performance in PEG. Based on our
previous research on rhodium catalyzed hydroformylation
with BISBIS [23, 24], 3.0 MPa of syngas and 120 °C were
purchased from Kelong Chemical Co. of Chengdu. All chemi-
cals were used without any additional purification; 1-octene,
1
-decene and 1-dodecene were purchased from Sigma-Aldrich;
hydrogen (H , 99.99%) and carbon monoxide (CO, 99.9%)
2
were obtained from Southwest Institute. The composition of
reaction mixture was determined by means of gas chromatog-
raphy (PANNA A91, KB-1: 30 m×0.25 mm×0.50 µm, FID).
Scheme 1 Hydroformylation of
O
HRh(CO)(TPPTS) /BISBIS
3
O
H
long chain alkenes
or TPPTS
+
CO + H2
+
R
R
H
PEG
R
linear aldehyde
branched aldehyde
1
3