Novel functional ionic liquids as metal-free, efficient and recyclable catalysts for the carbonylation of formaldehyde

Article abstract of DOI:10.1007/s10562-014-1199-3

Methyl glycolate (MG) was synthesized as a precursor to ethylene glycol from the catalytic carbonylation of formaldehyde followed by esterification with methanol by using metal-free, efficient and recyclable SO₃H- functionalized ionic liquids (BAILs) as catalysts. Among the studied BAILs, N-butyl-N-(3-sulfonylpropyl) thiomorpholine-1,1-dioxide triflate showed excellent activity and MG selectivity. The effects of reaction parameters such as reactant, solvent, catalyst loading, molar ratio of H₂O to H ₂CO, temperature, pressure, and reaction time were studied. MG was obtained in high yield under mild conditions. At 160 C, 5.0 MPa, and reactant mole ratio of BAIL:H₂CO:H₂O = l:40:80, 98 % conversion of formaldehyde was achieved with 94 % selectivities of MG. Catalysts did not show any significant deterioration in performance in repeated use up to eight batches. Graphical Abstract: Methyl glycolate (MG) was synthesized from the carbonylation of formaldehyde followed by esterification with methanol using metal-free, efficient and recyclable SO₃H-functionalized ionic liquids (BAILs) as catalysts. MG was obtained in excellent yield under mild conditions. The catalyst was reused up to eight consecutive recycles without apparent loss in its catalytic activity. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1199-3

Catal Lett (2014) 144:711–716
DOI 10.1007/s10562-014-1199-3
Novel Functional Ionic Liquids as Metal-Free, Efficient
and Recyclable Catalysts for the Carbonylation of Formaldehyde
•
Heyuan Song Fuxiang Jing Ronghua Jin
•
•
•
Zhen Li Jing Chen
Received: 25 October 2013 / Accepted: 20 January 2014 / Published online: 8 February 2014
Ó Springer Science+Business Media New York 2014
Abstract Methyl glycolate (MG) was synthesized as a
precursor to ethylene glycol from the catalytic carbonyl-
ation of formaldehyde followed by esterification with
methanol by using metal-free, efficient and recyclable
SO3H-functionalized ionic liquids (BAILs) as catalysts.
Among the studied BAILs, N-butyl-N-(3-sulfonylpropyl)
thiomorpholine-1,1-dioxide triflate showed excellent
activity and MG selectivity. The effects of reaction
parameters such as reactant, solvent, catalyst loading,
molar ratio of H2O to H2CO, temperature, pressure, and
reaction time were studied. MG was obtained in high yield
under mild conditions. At 160 °C, 5.0 MPa, and reactant
mole ratio of BAIL:H2CO:H2O = l:40:80, 98 % conver-
sion of formaldehyde was achieved with 94 % selectivities
of MG. Catalysts did not show any significant deterioration
in performance in repeated use up to eight batches.
product of the chemical industry manufactured on a large
scale used in the production of polyester resins and fibers
and antifreeze. The conventional process for producing EG
is based on the partial oxidation of ethylene to ethylene
oxide which is then hydrated to ethylene glycol. [1] The
economy of the conventional process is highly dependent
on the ethylene price. The dependence on ethylene as raw
material has promoted the investigation of alternative EG
production processes based on synthesis gas, which is a
less expensive feedstock. Since the 1970s, because of the
scarcity of oil, efforts have been made to replace oil by
abundant and cheap natural gas or coal in the preparation of
EG, and great progress has been achieved. [2–5] Of these,
carbonylation of formaldehyde with CO via MG to EG
using sulphuric acid as a catalyst was developed by Du
Pont company [4, 6–9], the drawback of rigorous reaction
conditions and heavy corrosion limited the development of
this method. This process was improved by the use of
concentrated H2SO4 and metal carbonyl cations [such as
Cu(CO)?n or Ag(CO)?2 ], which enabled the carbonylation to
proceed under relatively mild conditions. [7, 9, 10] How-
ever, a strong inorganic liquid acid medium was still
inevitably employed. To overcome the disadvantages
caused by liquid acids, the more environmentally friendly
solid acids, such as resins [5, 11], zeolite [12, 13] and
heteropolyacids [14, 15], have been employed. MG yield
up to 78 % could be obtained at an initial CO pressure of
24 MPa using Amberlyst 15 as catalyst. Unfortunately, the
reported catalytic systems still suffered from one or more
disadvantage, including poor reactivity (low catalytic
activity and selectivity), and high reaction pressures.
Recently, ionic liquids (ILs) have attracted much
attention as alternative solvents and environmentally
benign catalysts for chemical transformations. BMIm[PF6]
and BMIm[BF4] have been reported as effective solvents
Keywords Formaldehyde Á Carbonylation Á Methyl
glycolate Á Ethylene glycol Á Ionic liquids
1 Introduction
Carbonylation of formaldehyde with CO is a powerful
method for the synthesis of methyl glycolate (MG), which
is a precursor to ethylene glycol (EG). EG is a major
H. Song Á F. Jing Á R. Jin Á Z. Li (&) Á J. Chen (&)
State Key Laboratory for Oxo Synthesis and Selective
Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou 730000, People’s Republic of
China
e-mail: zhenli@licp.cas.cn
J. Chen
e-mail: shy@licp.cas.cn
123

712
H. Song et al.
for carbonylation of formaldehyde using p-TsOH as cata-
lyst. Although significant progress has been made, some
transition metal compounds (such as CF3SO3Ag) were still
used in the catalytic system [16]. Very recently, we have
reported that Brønsted acidic ionic liquids (BAILs) can be
used as catalysts directly for the carbonylation of formal-
dehyde. For example, by using BAIL, 1-(4-sulfobutyl)-3-
methylimidazolium trifluoromethanesulfonate, as catalyst,
the highest MG yield of 98 % could be obtained under a
CO pressure of 5.0 MPa after 8 h with 10:5:2 molar ratio
of H2O:H2CO:BAIL [17]. In continuation of our endeavour
in green synthesis and using ILs as recyclable and eco-
friendly catalysts, herein, we designed and synthesized
several novel SO3H-functionalized ILs based on thi-
omorpholine-1,1-dioxide cation (Scheme 1) and investi-
gated their potential uses as catalysts for the direct
carbonylation of formaldehyde. It may be noted that this
method is eco-friendly and economical, because it does not
involve corrosive H2SO4 or any costly metal catalysts and
SO3H-functionalized IL catalyst could be reused for at
least eight times without any significant decrease in cata-
lytic activity.
standard. Chemical shifts are reported in parts per million
(ppm, d) and referenced to D2O (d = 4.88). Elementary
analyses were obtained with an elementar Vario EL cube
instrument.
2.1.1 BAIL1
1H NMR (400 MHz, D2O) d 0.58–0.62 (t, J = 8.0 Hz, 3H),
0.78–0.81 (m, J = 7.1 Hz, 2H), 1.01–1.10 (h, J = 9.0 Hz,
2H), 1.34–1.42 (q, J = 10.7 Hz, 2H), 1.80–1.87 (q,
J = 7.4 Hz, 2H), 2.62–2.65 (q, J = 6.5 Hz, 2H), 3.14–3.19
(q, J = 6.7 Hz, 2H), 3.29–3.45 (t, 4H), 3.68–3.70 (t,
J = 4.0 Hz, 4H). 13C-NMR (100 MHz, D2O): d 12.56,
17.43, 18.75, 23.00, 45.06, 46.78, 56.73, 57.36, 59.17,
119.62
(JC–F = 315.1 Hz).
Anal.
Calcd
for
C12H24NO8S3F3: C, 31.11; H, 5.22; N, 3.02. Found: C,
31.16; H, 5.12; N, 3.05.
2.1.2 BAIL2
1H NMR (400 MHz, D2O) d 0.63–0.66 (t, J = 7.7, 6.2 Hz,
3H), 1.05–1.12 (m, J = 7.2 Hz, 2H), 1.39–1.47 (h,
J = 8.0 Hz, 2H), 1.85–1.92 (q, J = 9.3 Hz, 2H), 2.67–2.71
(q, J = 5.3 Hz, 2H), 3.20–3.24 (q, J = 5.3 Hz, 2H),
3.40–3.34 (q, J = 8.0 Hz, 2H), 3.44–3.45 (t, J = 4.4 Hz,
4H), 3.74–3.76 (t, J = 4.0 Hz, 4H). 13C-NMR (100 MHz,
D2O): d 12.65, 17.42, 18.78, 22.98, 45.06, 46.82, 56.71,
57.34, 59.04. Anal. Calcd for C11H25NO9S3: C, 32.12; H,
6.12; N, 3.40. Found: C, 32.17; H, 6.02; N, 3.37.
2 Experimental
2.1 Ionic Liquids Preparation
The BAILs were prepared according to the previous liter-
ature. [18] A stoichiometric amount of 1,3-propyl sultone
was added dropwise to a solution of 4-butylthiomorpho-
line-1,1-dioxide in toluene, and then the mixture was stir-
red at 60 °C for 8 h. The white solid zwitterion was washed
repeatedly with toluene to remove non-ionic residues and
dried in vacuum. Then the zwitterion and corresponding
acid were mixed in a molar ratio of 1:1 in anhydrous tol-
uene, and stirred magnetically at 60 °C for 8 h, followed
by washing with toluene and drying in vacuo to obtain the
final BAILs. The 1H NMR spectra and 13C NMR spectra in
D2O were recorded on an Avance TM III-400 MHz NMR
spectrometer using tetramethylsilane (TMS) as internal
2.1.3 BAIL3
1H NMR (400 MHz, D2O) d 0.79-0.83 (t, J = 5.3 Hz, 3H),
1.21–1.30 (m, J = 7.2 Hz, 2H), 1.54–1.62 (h, J = 8.0 Hz,
2H), 2.01–2.08 (q, J = 9.3 Hz, 2H), 2.22 (s, 1H),
2.82–2.86 (q, J = 5.3 Hz, 2H), 3.35–3.39 (q, J = 5.3 Hz,
2H), 3.51–3.58 (q, J = 9.3 Hz, 2H), 3.56–3.60 (t,
J = 8.0 Hz, 4H), 3.88–3.90 (t, J = 4.0 Hz, 4H),
7.19–7.21(d, J = 8.0 Hz, 2H), 7.52–7.54 (d, J = 8.0 Hz,
2H). 13C-NMR (100 MHz, D2O): d 12.87, 17.65, 19.02,
20.60, 23.20, 45.26, 47.01, 56.86, 57.55, 59.21, 125.51,
Scheme 1 Carbonylation of
formaldehyde with CO
catalyzed by novel functional
ionic liquids
123

Novel Functional Ionic Liquids as Catalysts for the Carbonylation of Formaldehyde
713
129.57, 139.87, 142.50. Anal. Calcd for C18H31NO8S3: C,
44.53; H, 6.43; N, 2.88. Found: C, 44.47; H, 6.39; N, 2.93.
based ionic liquid, BAIL4, as a catalyst. Moderate to best
results were obtained when the reaction was carried out in
presence of 2.5 % SO3H-functionalized thiomorpholine-
1,1-dioxide-ion based BAILs. A key parameter influencing
catalyst efficacy in these systems proved to be the count-
eranion—triflate salt (entry 1) is clearly superior to the
other BAILs having the same cation (entries 2 and 3)
evaluated in this study.
2.1.4 BAIL4
1H NMR (400 MHz, D2O) d 0.42–0.45 (t, J = 7.4 Hz, 3H),
0.80–0.87 (m, J = 5.6 Hz, 2H), 1.34–1.42 (h, J = 3.2 Hz,
2H), 1.82–1.90 (h, J = 8.0 Hz, 2H), 2.45–2.47 (t,
J = 4.0 Hz, 2H), 3.71–3.75 (t, J = 7.2 Hz, 2H), 3.88–3.92
(t, J = 7.2 Hz, 2H), 7.05–7.07 (d, J = 8.0 Hz, 2H), 8.31 (s,
1H). 13C-NMR (100 MHz, D2O): d 12.45, 18.63, 25.02,
31.02, 47.23, 47.75, 49.36, 119.87 (JC–F = 315.1 Hz),
122.25, 122.57, 135.13. Anal. Calcd for C12H21N2O6S2F3:
C, 35.13; H, 5.16; N, 6.82. Found: C, 35.23; H, 5.08; N,
6.55.
The carbonylation of formaldehyde can be explained by
the formation of methylol cation through protonation of
H2CO and the generation of acylium cation by the insertion
of CO to methylol cation. The acylium cation is stabilized
by water as glycolic acid and then esterification takes place
in presence of methanol to produce MG. Carbonylation of
formaldehyde and esterification are all typical acid-cata-
lyzed reactions. Therefore, the outcome of the reaction
system depends very much on the acidity of catalyst. It is
expected that the counterion plays a very significant role in
determining the acidity of BAILs—in particular the
2.2 General Procedure for the Carbonylation
of Formaldehyde
-
The carbonylation of formaldehyde with CO was carried
out in a 100 mL magnetically stirred autoclave equipped
with a Teflon liner and a Teflon coated magnetic stirring
bar. In a typical experiment, formaldehyde (30 mmol),
BAILs (0.75 mmol), water (60 mmol) and solvent (4 mL)
were charged into the autoclave, then CO ([99.95 %) was
introduced with initial pressure of 4.0–6.0 MPa at room
temperature after flushed three times with CO. The con-
tents of the reactor were stirred and heated to 140–190 °C
and held at this temperature for 4–8 h. After reaction, the
autoclave was cooled to room temperature and depressur-
ized. For the esterification of glycolic acid to MG, excess
methanol (4 mL) was added into the autoclave and refluxed
for 2 h at 80 °C. The final products were identified and
quantitatively analyzed by gas chromatography/mass
spectrometry (GC/MS) (Agilent 7890A/5975C) and GC
(Agilent 6890 equipped with a SE-54 capillary column),
respectively. A known amount of n-hexane was added as
an internal standard to the product mixture before the GC
analysis. Unconverted formaldehyde was detected as
dimethoxymethane. For the recycling of catalyst, dim-
ethoxymethane, methanol and products were separated
from the reaction system by distillation under vacuo of
10 mmHg at 90 °C, the BAILs and sulfolane were recov-
ered and reused directly for subsequent reactions.
CF3SO3 anion is known to endow SO3H-functionalized
-
ILs with significantly stronger acidity than HSO4 and
-
p-(CH3)C6H4SO3 counterions. On the other hand, the
nucleophilicity of CF3SO3- anion is very poor which helps
to stabilize the carbonium ion intermediate.
With an active catalyst in hand we next wished to
evaluate the influence of monomeric formaldehyde sour-
ces, namely trioxane, paraformaldehyde and 50 % of
aqueous formaldehyde solution on the reaction and the
results are summarized in Table 2. When using trioxane or
paraformaldehyde as the sources of formaldehyde, about
97–98 % H2CO conversion and C92 % MG selectivity
could be achieved. For the reaction of using 50 % of
aqueous formaldehyde solution as a monomeric formal-
dehyde source, although the H2CO conversion reaches
96 %, the yield and selectivity of MG are not high. Cor-
respondingly, the highest MG yield (92 %) appears in the
reaction with trioxane as the formaldehyde source.
The effect of solvent is summarized in Table 3. It was
found that solvents showed different behaviors in the
reaction mixture, which possibly relates to the different
Table 1 Preliminary catalyst evaluation of different BAILs
Entrya ILs
H2CO
conversion
(%)
Yield (%)
Selectivity
of MG (%)
MG MMAc MF
1
2
3
4
a
BAIL1 98
BAIL2 94
92
86
67
62
4.2
5.8
3.0
0.2
1.3 94
3 Results and Discussion
1.8 92
4.4 90
0.8 99
BAIL3 75
BAIL4 63
The one-pot two-step reaction of carbonylation of formal-
dehyde with CO followed by subsequent esterification was
examined preliminarily to optimize the reaction conditions
(Table 1). Lowest conversion (63 %) and MG yield (62 %)
were obtained using SO3H-functionalized imidazolium-ion
Reaction conditions of carbonylation: trioxane (10 mmol), solvent
sulfolane (4 mL). BAIL:H2CO = 1:40 (molar ratio), H2O:H2CO =
2:1 (molar ratio), 160 °C, 5.0 MPa CO, 8 h
123

714
H. Song et al.
Table 2 Influence of different monomeric formaldehyde sources on the reaction
Entrya
Supplier of formaldehyde
H2CO conversion (%)
Yield (%)
MG
Selectivity of MG (%)
MMAc
MF
1
2
3
a
(CH2O)3
98
97
96
92
89
82
4.2
7.1
1.3
0.6
0.8
94
92
85
(CH2O)n
CH2O, 50 %
13.8
Reaction conditions of carbonylation: H2CO (30 mmol), solvent sulfolane (4 mL). BAIL1: H2CO = 1:40 (molar ratio), H2O:H2CO = 2:1
(molar ratio), 160 °C, 5.0 MPa CO, 8 h
Table 3 Effect of solvent on the carbonylation of formaldehyde
Entrya
Solvent
H2CO conversion (%)
Yield (%)
MG
Selectivity of MG (%)
MMAc
MF
1b
2b
3
–
94
96
98
66
95
3.0
82
89
92
52
85
1.4
8.4
6.3
4.2
0.0
0.0
0.0
2.6
0.8
1.3
0.5
0.5
0.0
88
93
94
79
90
47
Sulfolane
Sulfolane
4
1,4-Dioxane
Tetrahydrofuran
Dimethylsulfoxide
5
6
a
Reaction conditions of carbonylation: trioxane (10 mmol), solvent (4 mL). BAIL1:H2CO = 1:40 (molar ratio), H2O:H2CO = 2:1(molar
ratio), 160 °C, 5.0 MPa CO, 8 h
b
Reaction conditions of carbonylation: trioxane (10 mmol), solvent (4 mL). BAIL1:H2CO = 1:25 (molar ratio), H2O:H2CO = 2:1(molar
ratio), 170 °C, 6.0 MPa CO, 8 h
stability of reaction intermediate in different solvents. It
can be seen that the dipolar aprotic solvent sulfolane pos-
sesses distinct advantages as a medium for this reaction
system. Higher yield of MG (92 %) is obtained in sulfolane
(entry 3) than in other organic solvents (entries 4–6) under
the same conditions. Much lower yield of MG has been
obtained in the 1,4-dioxane solvent (entry 4), probably due
to its low polarity. Dimethylsulfoxide is inert under the
present conditions (1.4 % MG yield) (entry 6). The reac-
tion proceeded under solvent-free conditions gave moder-
ate yield of MG (83 %), yet produced large amounts of
byproducts such as MMAc and MF. The fact that MG yield
in sulfolane is substantially higher under the present reac-
tion conditions, indicates that the good yield results from
the stabilization effect of the acylium cation in sulfolane
[17]. In addition, the catalyst of SO3H-functionalized IL
bearing thiomorpholine-1,1-dioxide and the reactants show
higher solubility in sulfolane.
resulted in a 99 % conversion (entry 1). The selectivity of
MG showed a maximum with the molar ratio of BAIL1 to
H2CO increases. This type of behavior usually indicates the
presence of other side reactions which produce a large
number of byproducts. Hence, the optimal molar ratio of
BAIL1 to H2CO is 1:40. It was already known that water
participates in the reaction as reactant for formation of
glycolic acid and can significantly promote Koch carbon-
ylation. For the effect of different molar ratios of water to
H2CO (entries 2, 4 and 5), the results indicate that the yield
was enhanced when increasing the amount of water
because the excess of one of the reactants makes the
equilibrium shifting towards the products side. However,
further increase of the molar ratio to as high as 4:1 resulted
in a decrease in yield due to the decrease in the concen-
tration of catalyst. From the data in Table 4, we can see
that temperature has a dramatic effect on the carbonylation
of formaldehyde (entries 2, 6 and 7). The yield of MG is as
low as 42 % at 140 °C. With the increasing of the tem-
perature, the reaction is significantly enhanced and reached
the good yield of MG as 90 % at 180 °C, further increase
of the temperature, the yield of MG was almost the
same (entry 8). The influence of CO pressure to the yield of
MG was not obvious (entries 2, 9 and 10). However,
increasing the reaction time had an advantageous influence
on the yield of MG (entries 2, 11 and 12), the highest yield
being obtained after 8 h.
To optimize the reaction conditions of the carbonylation
of formaldehyde with CO, the effect of catalyst dosage,
molar ratio of H2O to H2CO, reaction temperature, reaction
pressure and reaction time were also investigated with
catalyst BAIL1 and the results are summarized in Table 4.
The catalyst dosage had a great effect on the reaction.
When molar ratio of BAIL1 to H2CO increased from 1:80
to 1:40 (entries 2 and 3), the conversion of formaldehyde
increased from 92 to 94 %, and a further increase to 1:20
123

Novel Functional Ionic Liquids as Catalysts for the Carbonylation of Formaldehyde
715
Table 4 Effect of different reaction conditions using BAIL1 as catalyst
Entrya
BAIL1:H2CO
(mol ratio)
H2O:H2CO
(mol ratio)
PCO
(MPa)
Temp.
(°C)
Time
(h)
H2CO
conversion (%)
Yield (%)
Selectivity of
MG (%)
MG
MMAc
MF
1
1:20
1:40
1:80
1:40
1:40
1:40
1:40
1:40
1:40
1:40
1:40
1:40
2:1
2:1
2:1
1:1
4:1
2:1
2:1
2:1
2:1
2:1
2:1
2:1
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
4.0
6.0
5.0
5.0
160
160
160
160
160
140
180
190
160
160
160
160
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
4.0
8.0
99
94
92
91
86
46
98
99
94
96
83
98
88
88
85
83
80
42
90
90
87
89
79
92
9.8
4.2
3.5
7.8
2.1
0.6
7.6
8.1
5.1
5.7
2.4
4.2
0.6
2.1
3.5
0.7
3.6
3.0
0.4
1.4
2.5
1.9
3.2
1.3
89
93
92
91
93
92
92
90
92
92
93
94
2
3
4
5
6
7
8
9
10
11
12
a
Reaction conditions of carbonylation: trioxane (10 mmol), solvent sulfolane (4 mL)
efficient and recyclable catalyst for the carbonylation of
formaldehyde (Fig. 1).
4 Conclusion
In summary, a series of novel SO3H-functionalized ILs
bearing thiomorpholine-1, 1-dioxide was synthesized and
applied to the direct carbonylation of formaldehyde with-
out any additives. BAIL1 exhibited the best activity and
this catalytic system could be recycled at least eight times
after separating the unreacted materials and products from
reaction system and no significant decrease in catalytic
activity was observed. The present study shows that these
structurally novel BAILs have a potential application in the
production of ethylene glycol.
Acknowledgments We are grateful for the financial support from
the National Natural Science Foundation of China (No. 21133011)
and National Basic Research Program of China (973 Program) (No.
2011CB201404).
Fig. 1 Conversion of formaldehyde and selectivity of MG after
consecutive batches. Reaction conditions of carbonylation:
BAIL1:H2CO=1:40 (molar ratio), H2O:H2CO=2:1 (molar ratio),
160 °C, 6.0 MPa CO, 8 h
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batch reaction under the same conditions. As expected,
BAIL1 could be reused for 8 times at least and there was no
obvious decrease in the conversion of formaldehyde and
selectivity of MG, which indicated that BAIL1 was high
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