Homogeneous hydroformylation of long chain alkenes catalyzed by water soluble phosphine rhodium complex in CH3OH and efficient catalyst cycling

Article abstract of DOI:10.1039/c8ra08787c

The hydroformylation of long chain alkenes catalyzed by a water soluble Rh/TPPTS complex (TPPTS: sodium salt of sulfonated triphenylphosphine) in methanol was investigated. The mixture of rhodium precursor HRh(CO)(TPPTS)₃, ligand TPPTS, methanol and a long chain alkene becomes a single phase under reaction conditions, which make the hydroformylation reaction proceed homogeneously. Both the conversion of long chain alkene and the selectivity to aldehydes (including the aldehydes forming methylacetals) could reach up to 97.8% and 97.6%, respectively, with 3323 h^?1 of TOF (TOF: turnover frequency is defined as the moles of converted alkene per mole of Rh per hour). After the solvent methanol was removed under the reaction temperature, two phases were formed automatically. The colourless product phase could be efficiently separated from the precipitate rhodium catalyst phase by centrifuge. The catalyst was reused for five times without obvious loss of rhodium and the catalytic activity. The rhodium leaching in product mixture was less than 0.03% of the total rhodium.

Full text of DOI:10.1039/c8ra08787c

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PAPER
Homogeneous hydroformylation of long chain
alkenes catalyzed by water soluble phosphine
Cite this: RSC Adv., 2019, 9, 7382
rhodium complex in CH OH and efficient catalyst
3
cycling
Yan-li Liu, Jian-gui Zhao, Yuan-jiang Zhao, Hui-Min Liu, Hai-yan Fu, Xue-li Zheng,
*
Mao-lin Yuan, * Rui-xiang Li
and Hua Chen
The hydroformylation of long chain alkenes catalyzed by a water soluble Rh/TPPTS complex (TPPTS:
sodium salt of sulfonated triphenylphosphine) in methanol was investigated. The mixture of rhodium
3
precursor HRh(CO)(TPPTS) , ligand TPPTS, methanol and a long chain alkene becomes a single phase
under reaction conditions, which make the hydroformylation reaction proceed homogeneously. Both
the conversion of long chain alkene and the selectivity to aldehydes (including the aldehydes forming
ꢀ1
methylacetals) could reach up to 97.8% and 97.6%, respectively, with 3323 h of TOF (TOF: turnover
frequency is defined as the moles of converted alkene per mole of Rh per hour). After the solvent
methanol was removed under the reaction temperature, two phases were formed automatically. The
colourless product phase could be efficiently separated from the precipitate rhodium catalyst phase by
centrifuge. The catalyst was reused for five times without obvious loss of rhodium and the catalytic
activity. The rhodium leaching in product mixture was less than 0.03% of the total rhodium.
Received 23rd October 2018
Accepted 16th February 2019
DOI: 10.1039/c8ra08787c
rsc.li/rsc-advances
transfer limitations. Nevertheless, long chain alkenes (pC
have signicantly lower solubility in the aqueous solution of the
For more than 80 years, the chemical industry has relied on the catalyst, which correspondingly leads to lower reaction rates in
hydroformylation reaction to convert alkenes, CO and H
into aqueous-organic biphasic systems, making it difficult and
aldehydes which were widely used in making plasticizers, phar- economically unviable. Many approaches have been developed to
6
)
1
. Introduction
2
1
–10
maceuticals, lubricants, amines and so on.
Nowadays, the overcome the barrier from phase transfer in aqueous-organic
11,12
production capacity is beyond 12 million tons annually.
biphasic systems such as using cosolvents, surfactants and
Rhodium-based homogeneous catalyst was found to be far more ionic liquids to increase the miscibility or the interfacial area
active to hydroformylation of alkene because of its superior between two solvents, but they have some disadvantages, such as
2
3–27
activity, allowing the process at a lower temperature and pressure, emulsion or a higher catalyst leaching.
Therefore, seeking for
13
and the ability to control the selectivity. However, the traditional a catalytic system which could cover the advantage of homoge-
homogeneous catalysis confronts difficulties related to the sepa- neous (good reactivity) and biphasic catalysis (easy separation) is
28
ration of products from a catalyst as well as the recycling of the highly desirable. As well known, the amount of rhodium and
14
catalyst. Especially with regard to long chain alkenes, the thermal ligand used in hydroformylation is quite low, so it may be ex-
separation of the products with high boiling points would put pected that a low boiling point polar solvent (i.e., methanol)
thermal stress for the temperature-sensitive catalyst and result in could be selected to dissolve water soluble phosphine rhodium
slow degradation of the catalyst under these conditions.
complex, ligand and alkene under the reaction temperature and
Aqueous-organic biphasic catalysis possessing many advan- could be helpful for the formation of homogeneous hydro-
tages such as convenient separation of product, environmentally formylation. Once the hydroformylation nished, the low boiling
15–22
friendly and economy,
was successfully applied to the polar solvent was evacuated under lower temperature than that of
hydroformylation of ethene and propene on plant because their product aldehydes. Rhodium catalyst precipitated as the form of
solubilities in the aqueous phase are sufficient to allow the solid since it is difficult to dissolve in the product aldehydes, and
hydroformylation to occur at an acceptable rate without phase- then the resulting mixture became solid (catalyst)–liquid (alde-
hydes) two phases. Therefore, the catalyst could be readily
separated and reused for the next cycle.
Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of
Chemistry, Sichuan University, Chengdu 610064, P. R. China. E-mail: cdscyml@
Herein, methanol is chosen to improve the hydroformylation
of long chain alkenes catalyzed by a water soluble Rh/TPPTS
1
63.com; zhengxueli@scu.edu.cn; Fax: +86-28-8541-2904
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complex. This is the rst example on taking advantages of both long chain alkenes catalyzed by water soluble phosphine
31
homogeneous reaction and heterogeneous separation of cata- rhodium complex. In this study, different low boiling polar
lyst from product.
solvents were investigated in the hydroformylation of 1-dode-
cene using HRh(CO)(TPPTS)3 as a rhodium precursor and
TPPTS as a water soluble phosphine. Based on our previous
study on the hydroformylation of 1-dodecene catalyzed by Rh/
2. Experimental
2
.1 Materials
Ligand TPPTS (sodium salt of sulfonated triphenylphosphine, reaction parameters. The side reactions mainly include 1-
Fig. 1) and rhodium precursor HRh(CO)(TPPTS)
were prepared dodecene isomerization to generate internal dodecenes and 1-
All the solvents were purchased dodecene hydrogenation to dodecane, and then the acetalation
32
ꢂ
TPPTS, 2.0 MPa of syngas and 80 C was selected as initial
3
29,30
according to the literatures.
33
from Kelong Chemical Co. of Chengdu and used without any reaction of the formed aldehydes to methylacetals. As pre-
additional purication. 1-Hexene, 1-octene, 1-decene, 1-dode- sented in Table 1, the solvents and their amounts have great
cene, cyclohexene, norbornene and dicyclopentadiene were inuence on the hydroformylation of 1-dodecene. Among them,
purchased from Sigma-Aldrich. Hydrogen (H
2
, 99.99%) and methanol exhibited superior performance to other solvents, the
carbon monoxide (CO, 99.9%) were obtained from Southwest reason might be that the rhodium precursor, ligand TPPTS and
Institute. The composition of reaction mixture was determined 1-dodecene had a better solubility in methanol under the
by means of gas chromatography (PANNA A91, KB-1: 30 m ꢁ reaction temperature, and thus creating a single phase in which
0
.25 mm ꢁ 0.50 mm, FID). Rhodium leaching in the product the homogeneous hydroformylation of long chain alkenes
mixture was analyzed by inductively coupled plasma atomic proceeded smoothly. The conversion of 1-dodecene could reach
3
1
emission spectroscopy (ICP-AES). P NMR spectra were recor- up to 99.7% (Table 1, entry 6). The results also showed that
ded on the Bruker AVANCE III HD 400 M.
when the amount of methanol increased from 1.0 mL to 5.0 mL,
the activity increased, the reason is that the reaction system
turned from a biphase into a homogeneous phase, which
resulted in quick reaction. Further increasing the volume of
methanol to 10.0 mL, the content of methylacetals in products
is decreased due to the decrease of catalyst concentration. Aer
hydroformylation, the reaction mixture presented a single
phase (shown in Fig. 2). When methanol was removed from the
reaction mixture under the reaction temperature, the remained
mixture became two phases and the upper one was the product
phase which could be separated efficiently from the bottom
solid rhodium catalyst phase (shown in Fig. 2). The results
suggested that the strategy to make homogeneous hydro-
formylation of long chain alkenes with water soluble Rh/TPPTS
complex and easy separation of products is feasible, just
through using an appropriate low boiling point polar solvent.
The molar ratio of phosphine to rhodium was one of the
important factors affecting the activity and regioselectivity of
hydroformylation. It can be seen from Table 2 that the conver-
sion of 1-dodecene rose fast with the increase in the molar ratio
of phosphine to rhodium, however, the content of aldehydes in
products increased initially and then decreased. Also, as the
molar ratio of phosphine to rhodium increased to 25, the
content of methylacetals in products increased from 5.2 to
2
.2 Hydroformylation and catalyst recycling
Long chain alkene hydroformylation experiments were carried
out in a 25 mL stainless steel autoclave equipped with
a magnetic stirrer. Typically HRh(CO)(TPPTS) , TPPTS, long
3
chain alkene and a low boiling point polar solvent were loaded
into the autoclave, which was sealed, purged with syngas
(
H : CO ¼ 1.0 : 1.0) for three times and charged to the desired
2
pressure and heated to the preset temperature. Then the stirrer
was started and the time was recorded. Aer the reaction was
complete, the autoclave was cooled down to room temperature,
and the gas was carefully released. The products were analyzed
by GC (PANNA A91 on a KB-1 capillary column 30 m ꢁ 0.25 mm
ꢁ
0.50 mm, FID).
Aer hydroformylation, the methanol in the product mixture
was removed via distillation under the reaction temperature
and the remained mixture became two phases. The upper
product phase was separated from the lower precipitate catalyst
phase by centrifuge and ltration. Then the distillated meth-
anol and a new portion of long chain alkene were introduced for
the next catalytic reaction.
3
. Results and discussion
13.5%. While further increasing the molar ratio of P/Rh to 30,
the content of methylacetals in products did not ascend since
the excess ligand could not be fully dissolved in 10.0 mL of
methanol. It is well known that the presence of phosphine
ligand would affect the coordination equilibrium of catalytic
Long chain alkenes have signicantly lower solubility in the
aqueous solution of the catalyst, which correspondingly leads to
lower reaction rates in biphasic catalytic system, and cosolvent
was found to have a great impact on the hydroformylation of
34
active species. When the molar ratio of P/Rh increased,
HRh(CO)(TPPTS)2 catalytic active species increased, which
resulted into higher reactivity. The optimum molar ratio of P/Rh
was 20. The conversion of 1-dodecene and the selectivity to
aldehydes (including the aldehydes converting to methyl-
acetals) could reach up to 99.7% and 99.2%, respectively.
The effect of temperature on the hydroformylation of 1-
dodecene was also investigated and the results were shown in
Fig. 1 Structure of TPPTS.
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a
Table 1 Effects of solvent and its volume
b
c
d
e
f
ꢀ1
Entry
Solvent
Volume (mL)
Conv. (%)
Ald. (%)
Ace. (%)
L/B
TOF (h
)
1
2
3
4
5
6
7
8
9
No
THF
CH
CH
EtOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
0.0
10.0
10.0
10.0
10.0
10.0
1.0
2.0
3.0
4.0
5.0
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3
CN
Cl
2
2
10.0
99.7
3.3
67.3
75.4
83.4
99.7
99.6
99.8
90.1
87.3
92.7
84.2
98.4
95.6
92.6
77.4
79.3
83.5
92.8
0.0
6.5
0.0
1.4
3.7
6.1
20.1
18.3
15.5
6.5
3.0
2.5
2.1
2.7
2.6
2.5
2.1
2.3
2.4
2.5
333
3323
110
2243
2513
2780
3323
3320
3327
3020
1
1
1
1
1
0
1
2
3
4
6.0
8.0
12.0
a
ꢀ3
ꢂ
Reaction conditions: Rh ¼ 1.35 ꢁ 10 mmol, [P]/[Rh] ¼ 20.0, S/C ¼ 3333, 1-dodecene ¼ 1.0 mL, P ¼ 2.0 MPa (CO : H
2
¼ 1.0 : 1.0), T ¼ 80.0 C, t ¼
b
c
d
e
1
.0 h. Percent of converted alkene, determined by GC. Content of aldehydes in products. Content of methylacetals in products. Ratio of the
f
linear aldehyde to the branched aldehyde in products. Turnover frequency dened as the moles of converted alkene per mole of Rh per hour.
Table 3. It seemed that the reaction temperature also displayed 3, entry 10, 58.0%). In addition, the effect of reaction time on
a signicant role in this hydroformylation. The conversion of 1- the 1-dodecene hydroformylation was obvious, the initial rate is
dodecene increased sharply when the reaction temperature much higher (see Table 3, entry 3), prolonging the reaction time
ꢂ
increased from 60 to 80 C (Table 3, entries 1, 2 and 6). This may was favourable for the formation of methylacetals (Table 3,
be due to the fact that the solubilities of rhodium precursor,
TPPTS and 1-dodecene increase with the rise of reaction
temperature. Meanwhile, higher temperature is favorable for
a
Table 2 Influence of the molar ratio of phosphine to rhodium
35
b
c
d
e
f
ꢀ1
hydroformylation and the formation of catalytic active species.
Entry P/Rh Conv. (%) Ald. (%) Ace. (%) L/B
TOF (h )
ꢂ
Further enhancing the reaction temperature to 100 C has an
obvious increase of content of methylacetals in product (Table
1
2
3
4
5
6
7
0.0
5.0
55.0
74.1
99.5
99.1
99.7
99.1
99.1
62.5
62.1
83.5
88.9
92.7
82.7
82.8
5.2
5.6
5.9
6.3
6.5
2.7
2.7
2.5
2.5
2.5
2.4
2.4
1833
2470
3317
3303
3323
3303
3303
10.0
15.0
20.0
25.0
30.0
13.5
13.5
a
ꢀ3
Reaction conditions: Rh ¼ 1.35 ꢁ 10 mmol, S/C ¼ 3333, 1-dodecene
1.0 mL, methanol ¼ 10.0 mL, P ¼ 2.0 MPa (CO : H ¼ 1.0 : 1.0), T ¼
¼
2
ꢂ
b
c
d
e
8
0.0 C, t ¼ 1.0 h. See Table 1. See Table 1. See Table 1. See
f
Table 1. See Table 1.
Table 3 Influences of reaction temperature and time on 1-dodecene
a
hydroformylation
ꢂ
b
c
d
e
f
ꢀ1
Entry T ( C) t (h) Conv. (%) Ald. (%) Ace. (%) L/B TOF (h
)
1
2
3
4
5
6
7
8
9
1
1
60.0 1.0 12.3
70.0 1.0 28.8
80.0 0.25 40.2
80.0 0.5 61.0
80.0 0.75 77.4
80.0 1.0 99.7
80.0 2.0 99.8
80.0 4.0 99.7
90.0 1.0 99.7
100.0 1.0 99.6
100.0 1.0 99.6
88.4
94.5
97.5
94.5
91.5
92.7
74.1
43.7
65.9
36.5
94.5
2.2
2.0
0.0
2.2
5.4
1.9
2.5
410
960
2.7 5359
2.4 4066
2.5 3440
2.5 3323
2.1 1663
6.5
23.4
53.8
30.4
58.0
0.0
1.6
831
2.0 3323
1.3 3320
2.5 3320
0
1
g
a
ꢀ3
Reaction conditions: Rh ¼ 1.35 ꢁ 10 mmol, [P]/[Rh] ¼ 20.0, S/C ¼
333, 1-dodecene ¼ 1.0 mL, methanol ¼ 10.0 mL, P ¼ 2.0 MPa
3
b
c
d
e
(CO : H
2
¼ 1.0 : 1.0). See Table 1. See Table 1. See Table 1. See
f g
Fig. 2 Picture of before and after reaction.
Table 1. See Table 1. 30 mL of triethylamine was added.
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a
Table 4 Hydroformylation of other long chain alkenes
b
c
d
e
f
ꢀ1
Entry
Alkene
Conv. (%)
Ald. (%)
Ace. (%)
L/B
TOF (h
)
1
2
3
4
1-Hexene
1-Octene
1-Decene
1-Dodecene
Cyclohexene
Norbornene
Dicyclopentadiene
97.8
98.0
99.0
99.7
93.5
92.5
93.0
90.6
93.8
95.1
92.7
92.3
94.6
95.5
7.0
5.2
3.9
6.5
0.0
0.0
0.0
2.3
2.5
2.4
2.5
—
3260
3267
3300
3323
390
g
5
h
6
—
—
385
388
i
7
a
ꢀ3
ꢂ
b
Reaction conditions: Rh ¼ 1.35 ꢁ 10 mmol, [P]/[Rh] ¼ 20.0, S/C ¼ 3333, P ¼ 2.0 MPa (CO : H
2
¼ 1.0 : 1.0), T ¼ 80.0 C, t ¼ 1.0 h. See Table 1.
c
d
e
f
g
ꢀ3
See Table 1. See Table 1. See Table 1. See Table 1. Rh ¼ 2.70 ꢁ 10 mmol, [P]/[Rh] ¼ 20.0, S/C ¼ 1667, P ¼ 2.0 MPa (CO : H ¼ 1.0 : 1.0), T ¼
i
2
ꢂ
h
ꢀ3
ꢂ
1
1
20.0 C, t ¼ 4.0 h. Rh ¼ 2.70 ꢁ 10 mmol, [P]/[Rh] ¼ 20.0, S/C ¼ 1667, P ¼ 2.0 MPa (CO : H
2
¼ 1.0 :1 .0), T ¼ 120.0 C, t ¼ 4.0 h. Rh ¼ 2.70 ꢁ
ꢀ3
ꢂ
0
mmol, [P]/[Rh] ¼ 20.0, S/C ¼ 1667, P ¼ 2.0 MPa (CO : H
2
¼ 1.0 : 1.0), T ¼ 120.0 C, t ¼ 4.0 h.
entry 8, 53.8%). In order to obtain higher content of aldehydes upper colorless product phase was easily separated from the
in product mixture, different base was added in the hydro- lower solid catalyst phase aer centrifuge. The above recycled
formylation to prevent the formation of acetal side products and methanol, solid rhodium catalyst and a new portion of alkene
triethylamine showed a good result (Table 3, entry 11), the were then added to the autoclave to start the next cycle (see
conversion and the selectivity to aldehydes could reach up to Fig. 3). In order to avoid the effect of operational loss of
9
h
9.6% and 94.5%, respectively, and the TOF could achieve 3320 rhodium precursor and ligand TPPTS in the catalyst recycling
ꢀ1
.
experiments, the amount of Rh and the molar ratio of P/Rh were
ꢀ
3
In considering the fact that the excellent catalytic perfor- enlarged to 4.05 ꢁ 10 mmol and 50.0, respectively. Results in
mance of the studied catalytic system during 1-dodecene Fig. 4 indicated that the catalyst could be reused for ve runs
hydroformylation, the hydroformylation of other long chain without evident loss in activity and selectivity for aldehydes
alkenes and cycloolens in the studied catalytic system were (including the aldehydes converting to methylacetals). However,
also investigated. As presented in Table 4, excellent conversion the activity began to decrease aer ve cycles. The main reason
of alkenes was maintained. Results further revealed that the may be that the ligand TPPTS was partly oxidized with air
studied catalytic system can also be applied to the hydro- during the catalyst separation from products, which was proved
3
1
formylation of other long chain alkenes and cycloolen, proving by the P NMR characterization of the precipitate catalyst
the generality of this catalytic system in hydroformylation. residue aer hydroformylation (see Fig. 5, OTPPTS : TPPTS
Encouraged by these excellent results, the recycling effi- oxide). Also, another reason resulted from the operational loss
ciency of the studied catalytic system used in 1-hexene hydro- of rhodium precursor and TPPTS was inevitable during their
formylation was explored. Aer hydroformylation, the reaction separation. Fortunately, the leaching of Rh in the organic phase
mixture presented a single phase. The remained mixture was below ppm. As demonstrated in Fig. 2, when methanol was
became two phases when methanol was recycled from reaction removed from the mixture aer hydroformylation, the resulting
mixture by distillation under the reaction temperature. The mixture showed a liquid–solid biphasic state, which might hint
that the employment of methanol indeed realized homoge-
neous hydroformylation and heterogeneous separation of
products from catalysts. This strategy developed an innovation
for the hydroformylation of long chain olens. Ideally, the
Fig. 3 Catalyst cycle.
3 3
Fig. 4 Catalyst recycling with HRh(CO)(TPPTS) /TPPTS in CH OH.
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of Specialized Laboratory, College of Chemistry, Sichuan
University for the analysis work.
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Fig. 5
P NMR of rhodium catalyst before and after reaction (a)
before reaction; (b) after product separation.
5
6
7
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Conflicts of interest
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Chem., 1997, 116, 27.
There are no conicts to declare.
2
1 B. Cornils, J. Mol. Catal. A: Chem., 1999, 143, 1.
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Acknowledgements
2
The authors thank the nancial support from the National
Natural Science Foundation of China (No. 201202108, 24 F. Hapiot, S. Menuel, H. Bricout, S. Tilloy and E. Monier,
1871187), from the Opening Project of Key Laboratory of Green Appl. Organomet. Chem., 2015, 29, 580.
Chemistry of Sichuan Institutes of Higher Education (No. 25 H. Fu, M. Li, H. Chen and X. Li, J. Mol. Catal. A: Chem., 2006,
LZJ1402), from the Sichuan University Outstanding Scholar
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Research Fund (No. 2015SCU04A05, 2018SCUH0079) and from 26 X. Jin, K. Zhao, F. Kong, F. Cui and D. Yang, Catal. Lett.,
the Key Program of Sichuan Science and Technology Project 2013, 143, 839.
No. 2018GZ0312, 2019YFG0146). We are grateful to the Centre 27 M. Chevry, T. Vanb ´e sien, S. Menuel, E. Monier and
2
(
of Testing & Analysis and the Comprehensive Training Platform
F. Hapiot, Catal. Sci. Technol., 2017, 7, 114.
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