Catalytic performance of [Bmim][Co(CO)4] functional ionic liquids for preparation of 1,3-propanediol by coupling of hydroesterification- hydrogenation from ethylene oxide

Article abstract of DOI:10.1016/j.jorganchem.2011.08.022

In this paper, synthesis of 1,3-propanediol (1,3-PDO) through coupling of hydroesterification-hydrogenation from ethylene oxide (EO) catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl [Bmim][Co(CO)₄] functional ionic liquid which was prepared by metathesis reaction between [Bmim]Cl and KCo(CO)₄ has been studied. The structure of [Bmim][Co(CO)₄] was characterized by FT-IR and ¹H NMR. Using [Bmim][Co(CO)₄] as catalyst and [Bmim]PF₆ as solvent, 1,3-PDO was prepared for the first time by coupling of hydroesterifaction of EO and hydrogenation of methyl 3-hydroxypropionate (3-HPM). The yield of 3-HPM can reach 90.8%, while the yield of 1,3-PDO up to 82.9%. The catalyst can be separated from the product mixture by extraction with deionized water and recycled several times without significant loss of catalytic efficiency. A possible reaction mechanism has also been proposed.

Full text of DOI:10.1016/j.jorganchem.2011.08.022

Journal of Organometallic Chemistry 696 (2011) 3668e3672
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Catalytic performance of [Bmim][Co(CO) ] functional ionic liquids for preparation
4
of 1,3-propanediol by coupling of hydroesterification-hydrogenation
from ethylene oxide
*
Zhenmei Guo, Hengsheng Wang, Zhiguo Lv , Zhihui Wang, Tao Nie, Weiwei Zhang
College of Chemical Engineering, Qingdao University of Science and Technology, 266042 Qingdao, Shandong, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 May 2011
Received in revised form
In this paper, synthesis of 1,3-propanediol (1,3-PDO) through coupling of hydroesterification-
hydrogenation from ethylene oxide (EO) catalyzed by 1-butyl-3-methylimidazolium cobalt
tetracarbonyl [Bmim][Co(CO)
between [Bmim]Cl and KCo(CO)
by FT-IR and 1H NMR. Using [Bmim][Co(CO)
prepared for the first time by coupling of hydroesterifaction of EO and hydrogenation of methyl
4
] functional ionic liquid which was prepared by metathesis reaction
has been studied. The structure of [Bmim][Co(CO) ] was characterized
] as catalyst and [Bmim]PF as solvent, 1,3-PDO was
27 July 2011
4
4
Accepted 18 August 2011
4
6
Keywords:
3
8
-hydroxypropionate (3-HPM). The yield of 3-HPM can reach 90.8%, while the yield of 1,3-PDO up to
2.9%. The catalyst can be separated from the product mixture by extraction with deionized water and
1-Butyl-3-methylimidazolium cobalt
tetracarbonyl
recycled several times without significant loss of catalytic efficiency. A possible reaction mechanism has
also been proposed.
Hydroesterification
Methyl 3-hydroxypropionate
Hydrogenation
Ó 2011 Elsevier B.V. All rights reserved.
1,3-Propanediol
1. Introduction
copper-based catalysts have low reaction rates and low product
yields, because activities and stability of the catalyst and selectivity
1
,3-Propanediol (1,3-PDO) as a bifunctional organic compound
to 1,3-PDO were unfavorable. Meanwhile, the mono-catalytic
systems for hydroesterification of EO to 3-HPM intermediate were
less active or stable and were also difficult to recover and recycle
[6e8].
could potentially be used for many synthesis reactions, in particular
as a monomer for polycondensing to produce polyesters, polyethers
and polyurethanes. Polyesters based on 1,3-PDO have unique
features that are difficult to obtain from other glycols. For instance,
poly(trimethylene terephthalate) (PTT), a new polyester based on
Ionic liquids (IL), in particular, consisting of 1-R-3-
methylimidazolium (Rmim) cations and their counter anions,
have attracted more and more attention due to their unique
chemical and physical properties of nonvolatile, nonflammability,
thermal stability, and controlled miscibility [9e17]. Over the last
few years, ionic liquids have successfully been applied as alter-
native solvents for homogeneous catalysis [18]. Recently, the
functional ionic liquid catalysts have become more important in
homogeneous catalysis as catalysts, because functional ionic liquid
catalysts could be superior to traditional catalysts in the catalytic
activity, stability and selectivity for many reactions, but the cata-
lysts cannot be recycled in most cases [9,18e21].
1
,3-PDO, has the elastic recovery of nylon and the chemical resis-
tance of polyester [1]. Various manufacturing processes for 1,3-PDO
have been developed including routes based on acrolein, ethylene
oxide (EO) and glucose or glycerol [2]. The low conversion efficiency
of the acrolein process, as well as the hazardous nature of acrolein,
has spurred a great deal of interest in producing 1,3-PDO from other
chemical sources. In recent years, the EO-based route has been most
intensively studied, through carbonylation of EO followed by
hydrogenation of the intermediate 3-hydroxypropionaldehyde (3-
HPA) or methyl 3-hydroxypropionate (3-HPM) [3,4]. However, the
intermediate 3-HPA was unstable and could formlow polymer-
andethylidene ether easily [5]. Although efforts have been made so
far and some progress has also been achieved, the processes for
preparing 1,3-PDO by hydrogenation of 3-HPM in the presence of
In this paper, we report on the application of [Bmim][Co(CO)4]
functionalized ILs as catalyst for coupling reactions of
hydroesterifaction of EO and hydrogenation of methyl 3-
hydroxypropionate to prepare 1,3-propanediol. Functional ionic
4
liquid [Bmim][Co(CO) ] as a catalytic active organometallic ionic
liquid was first prepared by P.J. Dyson in 2001 [22], but the catalytic
performance of the above mentioned new organometallic
*
Corresponding author. Tel./fax: þ86 532 84022719.
E-mail address: lvzhiguo@qust.edu.cn (Z. Lv).
0
022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.022

Z. Guo et al. / Journal of Organometallic Chemistry 696 (2011) 3668e3672
3669
A
B
C
Scheme 1. The reaction equations of the hydroesterification of EO.
autoclave was purged with CO three times and the contents were
heated to 25 C and maintained 24 h, then precipitate (KCl) was
removed by filtration, and methanol was removed by distillation
under reduced pressure affording an intense blue-green colored
liquid [Bmim][Co(CO) ]. The characterization of [Bmim][Co(CO) ]
4 4
was made on Brucker VERTEX 70 Fourier Transform Infrared
Spectrometer (Liquid Membrane Method) and BrukerDRX-500
A: [Bm im ]Cl
B: KCo(CO)
1
1
891.58
888.96
ꢀ
4
C: [Bm im ][ Co(CO )4]
500 3000 2500 2000
W avenum ber cm
3
1500
1000
500
-
1
4 4
Fig. 1. IR spectrums of KCo(CO) , [Bmim]Cl and [Bmim][Co(CO) ].
Nuclear Magnetic Resonance Spectrometer (500 MHz, D
.3. Hydroesterification/hydrogenation reaction
Hydroesterification reaction of EO was conducted in a 100-mL
2
O).
2
compound was less studied. As far as we are aware, use of this class
of ILs as a catalyst for coupling reactions of hydroesterifaction and
hydrogenation has not been previously reported. Using [Bmim]
stainless steel autoclave equipped with a magnetic drive stirrer
and an electrical heater. For the catalytic experiments, 1.02 mmol of
Catalyst, 2.04 mmol of promoter, 102 mmol (4.49 g) of EO and
[
4 6
Co(CO) ] as catalyst and [Bmim]PF as solvent, 3-HPM was
prepared by hydroesterification of EO and 1,3-PDO was prepared by
hydrogenation of 3-HPM. The catalytic system can be separated
from the product mixture by extraction with deionized water and
recycled three times without significant loss of catalytic efficiency.
A possible reaction mechanism has been proposed，and the
optimum reaction conditions were also obtained by single-factor
experiments.
40.8 mmol of solvent were placed in the autoclave. The reactor was
pressurized with CO, and then heated to a specified temperature.
Hydrogenation reaction of 3-HPM was conducted in a 60-mL
stainless steel autoclave. In a typical experiment, 1.02 mmol of
Catalyst, 2.04 mmol of promoter, 20.4 mmol (2.12 g) of 3-HPM and
2
40.8 mmol of solvent were placed in the reactor. After H was then
charged, the reactor was pressurized to the desired pressure and
was then heated to a specified temperature.
2
. Experimental section
After completion of the reaction, autoclave was cooled with ice-
water and slowly depressurized to atmospheric pressure through
a cold trap, the product mixture was analyzed by means of GC and
GCeMS. The catalyst was then separated from the product mixture
by extraction with deionized water, and then it was dried for next
run. Co leaching was analyzed by means of inductively coupled-
plasmaopticalemission spectroscopy(ICP). Gas chromatographic
analysis was made on a Hewlett Packard 6890 gas chromatograph
equipped with a flame ionization detector and HP-5 capillary
2
.1. General remarks
1
-Chlorobutane, 1-methylimidazole and methanol were simply
distilled under nitrogen atmosphere before being used. Potassium
borohydride and cobalt chloride were obtained from Sinopharm
Chemical Reagent and were used as received without further
purification. Hydrogen (99.9%) and carbon monoxide (99.9%) were
supplied by Heli Gases and were used as received.
Physical data of 3-HPM: molecular weight 104.10, relative
column (0.32
m
m ꢁ 50 m). The identity of reaction products was
ꢀ
ꢀ
density(25 C, H
molecular weight 76.1, relative density(25 C, H
point 211 C.
2
O ¼ 1)1.09, boiling point 145 C. 1,3-PDO:
confirmed with a Hewlett Packard 6890-5973 MSD GCeMass
ꢀ
2
O ¼ 1)1.05, boiling
spectrometer.
ꢀ
3. Results and discussion
2.2. Catalyst preparation
3.1. Catalyst characterization
KCo(CO) was prepared in a 100-mL stainless steel autoclave.
4
After calculated amounts of potassium borohydride and cobalt
chloride were charged into the reactor, the autoclave was purged
with CO three times and pressurized to the desired level. A speci-
1
4
Spectroscopic data of [Bmim][Co(CO) ]: H NMR: d8.68 (s, 1H),
7
(
.44 (m, 1H), 7.42 (m,1H), 4.18 (t, 2H), 3.73 (s, 3H), 1.85 (m, 2H), 1.32
m, 2H), 0.92 (m, 2H). IR: v 3076.12 ( CeH, aromatic), 2961.60 and
n
ꢀ
fied temperature (1e5 C) was maintained in an ice-bath. After 4 h,
KCl and unreacted materials were removed by filtration，affording
a methanol solution of KCo(CO)
4
.
[Bmim]Cl was synthesized by reaction of 1-methylimidazole and
1
-chlorobutane [n(1-methylimidazole):n(1-chlorobutane) ¼ l:1.1].
In a typical experiment, 1-chlorobutane and 1-methylimidazole
were added to a flask and then refluxed for 48 h. Unreacted mate-
rials were removed by washing with ethyl acetate, and then ethyl
acetate was removed by distillation under reduced pressure.
The reaction of K[Co(CO)
a 100-mL stainless steel autoclave. Typically, [Bmim]Cl and meth-
anol solution of KCo(CO) were charged into the reactor. The
4
] and [Bmim]Cl was carried out in
Scheme 2. The reaction equations of the hydrogenation of 3-HPM.
4

3670
Z. Guo et al. / Journal of Organometallic Chemistry 696 (2011) 3668e3672
HOCH
genation were CH
CH OH. The reaction equations were shown as Scheme 1 and
Scheme 2.
2
CH
2
OH, CH
3
OCH
2
CH
2
OCH
3
and the by-products of hydro-
2
]CHCOOCH
3
, CH
3
CH COOCH , CH CH CH OH,
2
3
3
2
2
3
3.3. Reaction mechanism
It is well established that the active species for [Bmim][Co(CO)
4
]
catalyzed hydroesterification of EO and hydrogenation of 3-HPM
þ ꢂ
n 4
was an ionic species, [L ] [Co(CO) ] [23e25], when a Lewis base
(
L) was used as a promoter（e.g. Imidazole，etc.）. The Lewis
þ
acidic cationic species [L
n
]
was thought to be responsible for the
coordination and activation of EO or 3-HPM, while anionic species
ꢂ
[Co(CO)
4
]
was accountable for nucleophilic attack on the less
hindered carbon atom of the coordinated EO or 3-HPM and CO or
insertion, the proposed mechanism is shown in Scheme 3.
H
2
3.4. The catalytic performance of different catalysts
The catalytic performance of different catalysts for hydro-
esterification of EO and hydrogenation of 3-HPM were studied
(
[
Table 1, entries 1e5). Obviously, the catalytic activity of [Bmim]
Co(CO) ] was best among the above-mentioned catalysts. It seemed
4
that the introduction of imidazolium ionic liquid not only increased
the stability of catalyst in operation system, but also avoided catalyst
leaching when it was separated from the product mixture.
Scheme 3. Proposed mechanism of hydroesterification/hydrogenation.
3.5. Effect of the solvents on hydroesterification/hydrogenation
2
870.79
(
n
CeH
,
aliphatic), 1888.96
(
n
C
]
O
d
), 1664.40
C-H), 1169.14 (d
(
n
C
]
C
,
,
aromatic), 1569.90, 1461.43 and 1380.22 (
aromatic), 758.08, 621.03, 554.72.
CeH
Comparing the results of hydroesterification of EO and hydro-
genation of 3-HPM catalyzed by [Bmim][Co(CO) ] in different
4
IR spectrum of KCo(CO)
4
, [Bmim]Cl and [Bmim][Co(CO)
4
] is
solvents, the effect of the solvents on the catalytic performances
was obvious (Table 1, entries 6e10), the catalytic activity was better
when imidazolium ionic liquid was used as a solvent and [Bmim]
shown in Fig. 1. Obviously, there is no peak in IR spectrum (A) of
ꢂ1 ꢂ1
Bmim]Cl from 2000 cm to 1700 cm . IR spectrum (B) reveals
[
ꢂ1
ꢂ
anion in KCo(CO)
a strong band at 1891.58 cm for the [Co(CO)
4
]
4
.
6
PF was the most appropriate solvent for hydroesterification and
IR spectrum (C) shows the strong absorption of carbonyl group at
hydrogenation. Therefore [Bmim]PF
further experiments.
6
was used as a solvent in
ꢂ1
ꢂ
anion in
1
888.96 cm , and illuminates the existence of [Co(CO)
4
]
[
Bmim][Co(CO) ].
4
3.6. Effect of the promoters on hydroesterification/hydrogenation
3.2. Analysis of the reaction products
We tested the promoting effect of the promoter on hydro-
esterification and hydrogenation catalyzed by [Bmim][Co(CO) ].
Obviously, imidazole was highly effective for the ring-opening of
According to the GC and GCeMS analysis, we found that the
by-products of hydroesterification were CH ]CHCOOCH ,
2 3
4
Table 1
Effect of solvents, catalyst and promoter on hydroesterification/hydrogenation.
Entry
Catalyst
Solvent
Promoter
Hydroesterificationa
Hydrogenationb
EO conversion
Selectivity to
3-HPM (%)
3-HPM
conversion (%)
Selectivity to
1,3-PDO (%)
(%)
1
2
3
4
5
6
7
8
9
None
0
0
0
0
0
0
0
0
CoCl
Co (CO)
KCo(CO)
2
2
8
[Bmim]PF
6
Imidazole
Imidazole
78.2
85.3
98.1
73.6
89.2
91.6
97.9
98.1
26.8
52.3
98.1
87.8
88.9
62.7
78.2
92.6
30.8
68.5
72.4
86.5
92.6
16.1
38.6
92.6
80.6
82.7
73.6
82.9
99.2
72.5
84.3
92.9
98.7
99.2
26.8
52.3
99.2
87.8
88.9
70.1
75.8
83.6
16.2
60.9
64.8
81.4
83.6
16.1
38.6
83.6
78.6
76.3
4
[Bmim][Co(CO)
4
]
]
None
methanol
Tetrahydrofuran
[Bmim]BF
[Bmim]PF
[Bmim][Co(CO)
4
4
10
11
12
13
14
15
6
None
Pyridine
Imidazole
Triphenyl phosphine
Tributyl phosphine
[Bmim][Co(CO)
4
]
[Bmim]PF
6
a
ꢀ
Hydroesterification: 75 C, 3.7 MPa CO, 10 h.
b
ꢀ
Hydrogenation: 165 C, 10.5 MPa H
2
, 10 h.

Z. Guo et al. / Journal of Organometallic Chemistry 696 (2011) 3668e3672
3671
1
00
100
90
A
9
8
7
6
0
0
0
0
A
B
80
B
70
A:Selectivity to 3-HPM
B:Conversion of EO
A: Conversion of 3-HPM
B: Selectivity to 1,3-PDO
60
1
50 155 160 165 170 175
3.2 3.4 3.6 3.8 4.0 4.2
Temperature / C
Pressure / MPa
Fig. 6. Effect of temperature on hydrogenation of 3-HPM Imidazole as promoter,
[Bmim]PF as solvent. 10.5 MPa H , 10 h.
Fig. 2. Effect of CO pressure on hydroesterification of EO. [Bmim]PF
Imidazole as promoter, 75 C, 10 h.
6
as solvent,
6
2
ꢀ
EO and activation of 3-HPM. The results are presented in Table 1
entries 11e15).
(
3.7. Reaction conditions
1
00
Hydroesterification of EO was greatly influenced by the varia-
9
8
7
0
0
0
tion of pressure, temperature and reaction time (Figs. 2e4). The
conversion of EO and the selectivity to 3-HPM increased with the
increase of CO pressure, and was only a little change when CO
pressure was more than 3.7 MPa. It seemed that the in situ formed
active species were more stabilized and the inserted reaction of CO
happened readily at higher pressures [26]. Upon increasing
temperature and reaction time, the conversion of EO increased, but
the selectivity to 3-HPM dropped off, because dehydration reaction
of 3-HPM happened readily at higher temperature. The results
indicated that the appropriate reaction conditions for hydro-
A
A: Conversion of EO
B: Selectivity to 3-HPM
B
6
5
70
75
80
Temperature /
C
Fig. 3. Effect of temperature on hydroesterification of EO [Bmim]PF
Imidazole as promoter, 3.7 MPa CO, 10 h.
6
as solvent,
ꢀ
esterification of EO were 75 C, 3.7 MPa CO and 10 h.
As seen in Figs. 5e7, the conversion of 3-HPM and the selectivity
to 1,3-PDO increased with the increase of H pressure. At higher
2
temperature, dehydration reaction of 3-HPM happened readily, so
the selectivity to 1,3-PDO decreased. The conversion of 3-HPM and
the selectivity to 1,3-PDO increased with the increase of reaction
time, but it was feeble when reaction time was more than 10 h.
1
00
A
B
9
8
7
0
0
0
3.8. Recovering and recycling of catalyst
4
Recycling performance of [Bmim][Co(CO) ] was investigated in
[Bmim]PF and using reaction conditions selected based on
6
A: Conversion of EO
B: Selectivity to 3-HPM
previous studies. The water phase, containing product and
unconverted reactants, could be removed by simple phase decan-
tation, the ionic liquid phase containing the catalyst could be
recycled. Only very little amount of the catalyst (0.4e2.6%) leached
into the water phase. Recycling experiments indicated good
6
7
8
9
10
11
12
Time / h
Fig. 4. Effect of time on hydroesterification of EO [Bmim]PF
promoter, 75 C, 3.7 MPa CO.
6
as solvent, Imidazole as
ꢀ
6
stability of the catalyst in the ionic liquid [Bmim]PF with no
significant loss in activity and selectivity during three consecutive
runs. The recycling results were compiled in Table 2.
1
00
1
00
9
0
A
B
9
8
7
6
0
0
0
0
A
B
80
70
A: Conversion of 3-HPM
B: Selectivity to 1,3-PDO
A: Conversion of 3-HPM
B: Selectivity to 1,3-PDO
6
0
9
.0
9.5 10.0 10.5 11.0 11.5
Pressure / MPa
6
7
8
9
10
11
12
Time / h
Fig. 5. Effect of H
Bmim]PF
2
pressure on hydrogenation of 3-HPM Imidazole as promoter,
as solvent. 165 C, 10 h.
Fig. 7. Effect of reaction time on hydrogenation of 3-HPM Imidazole as promoter,
ꢀ
ꢀ
[
6
[Bmim]PF
6
as solvent. 165 C, 10.5 MPa.

3672
Z. Guo et al. / Journal of Organometallic Chemistry 696 (2011) 3668e3672
Table 2
a
4
Recycling performance of [Bmim][Co(CO) ] .
Time
Hydroesterificationb
Hydrogenationc
EO conversion (%)
Selectivity to 3-HPM(%)
3-HPM conversion (%)
Selectivity to 1,3-PDO(%)
1
2
3
98.1
94.3
88.9
92.6
90.5
90.2
99.2
95.3
90.7
83.6
80.5
78.6
a
6
Imidazole as promoter, [Bmim]PF as solvent.
b
ꢀ
Hydroesterification: 75 C, 3.7 MPa CO, 10 h.
c
ꢀ
Hydrogenation: 165 C, 10.5 MPa H
2
, 10 h.
4
. Conclusions
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[
[
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ꢀ
[
[
[
[
[
The appropriate reaction conditions of hydrogenation of 3-HPM
ꢀ
were 165 C, 10.5 MPa H
2
and 10 h. Under the optimum conditions,
the best conversions of 3-HPM were up to 99.2% with selectivity in
the 1,3-PDO up to 83.6%, the catalyst could be recycled three times
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1
[
This research was supported by National Natural Science
Foundation of China (20776071) and Introduced Talents Starting
Foundation of QUST.
(