CL-150131
Received: February 9, 2015 | Accepted: March 1, 2015 | Web Released: June 5, 2015
Heteropolyacids as Efficient Catalysts for the Synthesis of Precursors to Ethylene Glycol
by the Liquid-phase Carbonylation of Dimethoxymethane
Junpeng Wang,1,2 Jianhua Liu,1 Heyuan Song,1 and Jing Chen*1
1State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, P. R. China
2University of Chinese Academy of Sciences, Beijing 100049, P. R. China
(E-mail: chenj@licp.cas.cn)
Methyl methoxyacetate (MMAc), a precursor to ethylene
glycol (EG), was synthesized successfully via the liquid-phase
carbonylation of dimethoxymethane (DMM) catalyzed by
heteropolyacids (HPAs). The experiment results showed that
H3PW12O40 (PW12) exhibited the best catalytic performance for
the carbonylation of DMM, and its high catalytic activity was
attributed to the synergistic effect between its superior acidic
strength and the high polarity of the solvent.
In this work, a green and reusable heteropolyacid (PW12)
was selected as an efficient catalyst for the synthesis of MMAc
via the liquid-phase carbonylation of DMM under relatively
mild conditions; the high catalytic activity of PW12 may be
attributed to the synergistic effect between its superior acidic
strength and the high polarity of the solvent.
In order to screen the best catalyst, four different HPAs
(PW12, SiW12, PMo12, and SiMo12) and some other catalysts
were examined preliminarily for the carbonylation of DMM
with CO (Scheme 1). The final products were quantitatively
analyzed by GC using a known amount of ethyl acetate as the
internal standard (Table 1). The product, MG, probably origi-
nated from the hydrolysis of DMM to HCHO and methanol,
followed by further carbonylation of HCHO with CO
(Scheme 2). Because MMAc and MG are both precursors to
EG, the total selectivity of MMAc and MG was calculated. The
highest DMM conversion (99.1%) and total selectivity (80.9%)
of MMAc and MG were obtained when using PW12 as the
catalyst. As shown in Table 1, the total selectivity improved
with increasing HPA acidic strength; therefore, the acid strength
of the HPAs seemed to be a key parameter in the carbonylation
of DMM. SiW12, PMo12, and SiMo12 possessed approximately
equal acidic strength, but the molybdic HPAs exhibited lower
MMAc selectivity than the tungstic HPAs. This may be
attributed to the greater reducibility of molybdic acids.9 The
deep blue color of the reaction solutions catalyzed by PMo12 and
SiMo12 provided evidence for the formation of heteropoly blues,
which were a result of the reduction of molybdic acids. The
reduction of HPAs leads to an increase in the basicity of the
polyanion21,22 and causes a further negative influence on acid
catalytic activity. The catalytic performance of PW12 was clearly
Ethylene glycol (EG), one of the essential commodity
chemicals, is widely used as a raw material in the production
of polyester resins, fibers, medicines, antifreezes, and other
products.1 The main method of producing EG is the hydration of
ethylene oxide, which can be obtained by the partial oxidation
of ethylene.2 However, as a result of the increasing shortage
of petroleum, considerable attention has been paid to finding
alternative starting materials, in place of ethylene, for producing
EG. Synthesis gas, a less expensive mixture of CO and H2
generated from fossil fuels and biomass, as a starting feedstock
for producing EG is a hopeful alternative. EG can be produced
from formaldehyde and syngas through the carbonylation of
formaldehyde to glycolic acid, followed by esterification to
methyl glycolate (MG) and hydrogenation to the target
product.3-9 However, since the reaction rate of formaldehyde
carbonylation is limited by the low solubility of CO in the used
solvent, the reaction pressure has to be relatively high.10
Both formaldehyde and dimethoxymethane (DMM) are
derivatives of the C1 compound of methanol. The carbonylation
of DMM with carbon monoxide produces methyl methoxyace-
tate (MMAc) in contrast to the production of glycolic acid for
formaldehyde carbonylation. MMAc and glycolic acid are both
precursors to EG. MMAc can be readily converted into EG in
two consequent steps,11,12 the gist of which comprises the
hydrogenation of MMAc to 2-methoxyethanol and the hydrol-
ysis of 2-methoxyethanol to EG. Recently, Bell and co-workers
reported for the first time the vapor-phase carbonylation of
DMM over H-Faujasite (an acid zeolite) to synthesize MMAc
with a selectivity of 79% and a yield of 20%.13 Liu and his
partners tested a Nafion-H catalyst for the vapor-phase carbon-
ylation of DMM that exhibited a high MMAc selectivity of
about 90% but a low DMM conversion of 15% at 80 °C and
about 3 MPa.14 Several attempts at the synthesis of MMAc
through the carbonylation of DMM with CO have been carried
out in the liquid phase.15-20 In these cases, however, the use of
severely corrosive strong mineral acid or very high reaction
pressure could not be avoided. To our certain knowledge, few
reports have been published on the carbonylation of DMM by
heteropolyacids (HPAs).
HPAs
CH3OCH2COOCH3
CH3OCH2OCH3 + CO
solvent
(MMAc)
(DMM)
HPAs: H PW
O
12 40
(abbreviate as PW
12
)
3
H SiW
O
12 40
(abbreviate as SiW
)
12
4
H PMo
3
O
12 40
(abbreviate as PMo
)
12
H SiMo
O
(abbreviate as SiMo )
4
12 40 12
Scheme 1. The carbonylation of DMM with CO catalyzed by
heteropolyacids.
CO
HCHO
CH3OCH2OCH3
(DMM)
HOCH2COOH
HOCH2OOCHC3
(MG)
H2O
H2O
CH3OH
H2O
2CH3OH
Scheme 2. Probable reaction route for the formation of MG
from DMM.
© 2015 The Chemical Society of Japan