Synthesis of maleic acid from renewable resources: Catalytic oxidation of furfural in liquid media with dioxygen

Article abstract of DOI:10.1016/j.catcom.2010.12.033

Developing novel technologies to obtain fuel and organic chemicals from renewable resources has been the immediate issue in academic and industrial communities. The present work introduces a new route to synthesize maleic acid from the renewable furfural. The current data reveal that, using dioxygen as oxidant, the simple copper salts can catalyze oxidation of furfural to maleic acid in aqueous solution. The combination of copper nitrate with phosphomolybdic acid could achieve a 49.2% yield of maleic acid with selectivity of 51.7%. The major challenge for this route is how to avoid the polymerization of furfural to resins under oxidative conditions.

Full text of DOI:10.1016/j.catcom.2010.12.033

Catalysis Communications 12 (2011) 731–733
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Synthesis of maleic acid from renewable resources: Catalytic oxidation of furfural in
liquid media with dioxygen
Song Shi, Huajun Guo, Guochuan Yin ⁎
School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Developing novel technologies to obtain fuel and organic chemicals from renewable resources has been the
immediate issue in academic and industrial communities. The present work introduces a new route to
synthesize maleic acid from the renewable furfural. The current data reveal that, using dioxygen as oxidant,
the simple copper salts can catalyze oxidation of furfural to maleic acid in aqueous solution. The combination
of copper nitrate with phosphomolybdic acid could achieve a 49.2% yield of maleic acid with selectivity of
Received 5 September 2010
Received in revised form 29 December 2010
Accepted 29 December 2010
Available online 6 January 2011
5
1.7%. The major challenge for this route is how to avoid the polymerization of furfural to resins under
Keywords:
oxidative conditions.
Catalytic oxidation
Renewable furfural
Copper nitrate
Maleic acid
© 2011 Elsevier B.V. All rights reserved.
Dioxygen
1
. Introduction
With the diminishing of the fossil resources, seeking their
reported [20–24], however, to the best of our knowledge, there has
been no report of demonstrating the direct oxidation of furfural using
dioxygen to maleic or fumaric acid in liquid media up to now.
Although maleic acid can be synthesized from the gas vapor oxidation
of furfural at elevated temperature [25], its commercialization to
replace the current benzene and/or butane routes was not reported.
The present work introduces a simple redox metal salt catalyzed
oxidation of furfural to maleic acid in aqueous solution with dioxygen
as oxidant (Eq. (1)). The obtained results reveal that furfural can be
selectively oxidized to maleic acid with minor other oxidation
products.
replacements to obtain fuel and versatile organic chemicals has
been attracting more and more attention than ever, even much more
attention in the future. Biomass, dominantly comprised of carbon,
hydrogen, oxygen and nitrogen, is the largest, annually renewable
carbon resources on earth. Its refining may provide most of
transportation fuel and organic chemicals which are currently
obtained from the fossil feedstock, and in the viable future, it is the
only carbon resource which can play the roles as does the current
fossil feedstock. Exploring novel technologies to utilize biomass as the
replacement of the current fossil feedstock is greatly expanding from
all of the aspects now [1–18]. Furfural is a renewable resource coming
from corncobs, oat, wheat bran, and sawdust etc [19]. Significantly,
these raw materials are rich agricultural byproducts, not competitive
with human beings. Thus, exploring the sub-products from furfural as
the replacements of the fossil resources is greatly attractive. Indeed,
furfural has served as a platform to synthesize a variety of chemicals
including more than 1600 products. Compared with furfural which is
CO H
2
cat.
CHO
+ CO2
+
H O
2
Eq:1
O2
O
CO H
2
2. Experimental
5 4
a C platform, maleic and fumaric acids are the C products which are
currently manufactured from benzene and/or butane through
oxidation. Significantly, maleic and fumaric acids are the starting
materials extensively applied in resins, surface coatings, lubricant
additives, plasticizers, copolymers, and agricultural chemicals. In
literatures, oxidations of furfural with versatile oxidants have been
All of the reagents are of analytic purity grade, and were purchased
from local Sinopharm Chemical Reagent.
2
In a general oxidation reaction, Cu(OAc) (0.2 mmol) and furfural
(0.6 mL) were added to 4 mL of water in a glass tube equipped with a
glass cap having holes. The glass tube was put into a 50 mL stainless
autoclave, then, the autoclave was charged with oxygen (20 atm). The
resulting reaction mixture was magnetically stirred at 98 °C for 14 h in
oil bath. The quantitative product analysis was performed by HPLC
equipped with an UV-detector and a C18 column (250×4.6 mm) with
⁎
Corresponding author. Tel.: +86 27 87543732; fax: +86 27 87543632.
E-mail address: gyin@hust.edu.cn (G. Yin).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.12.033

732
S. Shi et al. / Catalysis Communications 12 (2011) 731–733
Table 1
Then, the counter-ions of the copper(II) cation, which may help to
Catalyst scanning for the furfural oxidation.
modulate the redox properties of the copper(II) cation, were further
investigated for furfural oxidation. Compared with the results from
the control experiment without catalyst, the acetate, sulfate and
nitrate counterparts can improve the yield of maleic acid substan-
tially. In contrast, the chloride anion does not provide any improve-
ment, and the carbonate even gives the negative effect on the catalytic
activity. Particularly, copper sulfate gives a 19.5% yield of maleic acid,
and copper nitrate provides even higher yield (23.9%) of maleic acid
than copper sulfate. However, the addition of extra nitrate to the
reaction mixture does not improve the catalytic activity any more. For
examples, adding additional nitric acid to adjust the pH of the solution
to pH 1.5 provides a 22.2% yield of maleic acid, and additional
potassium nitrate gives only an 18.3% yield of maleic acid. Therefore,
the nitrate anion independently does not promote the conversion of
furfural to maleic acid, and the role it may play is possibly to modulate
the redox potential of copper(II) cation to match the catalytic
oxidation.
Catalyst
Conversion (%)
Yield of maleic acid (%)
–
56.3
26.7
70.0
73.2
90.0
54.8
35.4
72.1
68.8
71.0
62.1
85.9
67.0
49.5
7.2
0.8
0.3
4.1
12.1
6.1
3.1
6.0
4.0
18.6
7.4
Mn(OAc)
Pd(OAc)
AgOAc
2
a
2
FeSO
RuCl
NiCl
4
3
2
V
2
O
5
Co(NO
Cu(OAc)
CuCl
Cu(NO
CuSO
CuCO
3
)
2
2
2
3
)
2
23.9
19.5
1.7
4
3
Reaction conditions: water 4 mL, furfural 0.6 mL, catalyst 0.2 mmol, oxygen 20 atm,
reaction temperature 98 °C, and 14 h.
a
15.9% yield of furoic acid formation.
Addition of versatile additives to improve the catalytic efficiency of
the redox metal catalysts has been extensively applied in various
oxidation studies [26–30]. Here, a list of inorganic and organic
additives has also been tested to improve the catalytic efficiency of
copper nitrate (Table 2). The improvements are almost minor for all of
the N-containing organic additives which were expected to coordi-
nate with the copper(II) cation to modulate its redox properties.
Significantly, heteropolyacids demonstrated different efficiency.
Phosphomolybdic acid improves catalytic efficiency greatly, giving
90.3% conversion, 35.3% yield of maleic acid with 39.3% selectivity,
while phosphotungstic acid and silicotungstic acid generate negative
effect, yielding only 12.1% and 9.8% yield of maleic acid, respectively.
In addition, all of the tested redox inorganic additives also afford
negative effect. Surprisingly, copper nitrate plus iron nitrate provides
an only 4.6% yield of maleic acid, even though the copper(II) or iron
(II) ion alone can provide much higher yield. Apparently, the catalytic
efficiency is not a simple addition of copper nitrate with the additives.
Since the combination of copper nitrate with phosphomolybdic acid
demonstrated impressive improvement on the furfural oxidation to
maleic acid, the optimization between copper nitrate and phosphomo-
lybdic acid has been summarized in Table 3. With 0.8 mmol of
phosphomolybdic acid and 0.4 mmol of copper nitrate, the yield of
maleic acid could be improved up to 49.2% with selectivity of 51.7%, and
the conversion of furfural is 95.2%. Because dioxygen alone in thecontrol
experiment can initiate the polymerization of furfural which exhausts
more than half of substrate (see Table 1), and the catalytic oxidation by
copper nitrate does not generate any significant byproducts such as
fumaric acid and furoic acid, it is pleased to note that copper nitrate can
catalytically convert furfural to maleic acid with high selectivity. For
example, in the case of adding 1,10-phenanthroline, the overall
conversion and yield are 80.1% and 29.5%, respectively (Table 2). After
simply correcting the polymerization in the control experiment, the
an internal standard sample (acrylic acid), and the products were
further confirmed by HPLC-MS. The mobile phase was methanol with
water (v/v 10%:90%) containing KH
The pH of the mobile phase was adjusted to pH 2.4 with H
2
PO
4
buffer (0.01 M) at 1 mL/min.
PO
3
4
.
3
. Results and discussion
Catalytic oxidations of furfural using various simple redox metal
salt catalysts were carried out in aqueous solution with pressured
dioxygen as oxidant, and the results are summarized in Table 1. Under
the reaction conditions, the reactivity of the redox metal salts is
significantly different. After 14 h reaction with 20 atm of dioxygen at
9
8 °C, the color of the reaction mixture generally turns to dark.
Sometimes the black precipitate could be observed after reaction,
which indicates the formation of resins through polymerization.
Among these catalysts, copper acetate provides an 18.6% yield of the
expected maleic acid, iron sulfate gives a 12.1% yield of maleic acid,
whereas the catalysts from other metal sources are substantially poor
2
for maleic acid formation. Except that Pd(OAc) catalyst provides a
1
5.9% yield of furoic acid, only a trace of furoic acid and furmaic acid
products were observed from other metal catalysts. Thereby, the
simple redox metal salts such as copper acetate and iron sulfate can
highly selectively convert furfural to maleic acid under current
conditions. The major competitive process for the selective oxidation
is the polymerization of furfural to generate resins under the oxidative
conditions. In the control experiment without catalyst, the conversion
of furfural is 56.3% with an only 7.2% yield of maleic acid, which
indicates that furfural readily undergoes polymerization to form
resins under the oxidative conditions. Only copper and iron salts are
the potential catalysts for catalytic oxidation of furfural to maleic acid,
and copper acetate demonstrates higher activity than iron sulfate.
Table 2
The combination of copper nitrate with versatile additives in furfural oxidation.
Combination
Conversion (%)
Selectivity of maleic acid (%)
Yield of maleic acid (%)
a
Cu(NO
Cu(NO
Cu(NO
Cu(NO
3
3
3
3
)
)
)
)
2
2
2
2
+ethylenediamine
+triethylamine
+1,10-phenanthroline
+bipyridine
86.9
77.2
80.1
78.6
49.1
38.5
43.7
36
28.9
33.4
36.8
36.0
29.3
21.8
15.8
12.8
33.8
39.3
26.8
25.1
25.8
29.5
28.3
14.4
8.4
6.9
4.6
12.1
35.3
9.8
a
a
a
Cu(NO
3
3
3
3
3
3
3
)
)
)
)
)
)
)
2
+Co
+NiCl
+RuCl
+Fe(NO
2
(SO
4
)
3
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
2
2
2
2
2
2
2
3
3
)
3
+H
+H
+H
3
3
4
PW12
PMo12
SiW12
O
O
O
40·xH
40·xH
40·xH
2
O
2
O
2
O
35.8
90.3
36.6
3 2
Reaction conditions: water 4 mL, furfural 0.6 mL, Cu(NO ) 0.2 mmol, additives 0.2 mmol, oxygen 20 atm, reaction temperature 98 °C, and 14 h.
a
3 2
Cu(NO ) 0.4 mmol, additives 0.4 mmol.

S. Shi et al. / Catalysis Communications 12 (2011) 731–733
733
Table 3
for converting furfural to maleic acid are currently under investigation
in our laboratories.
Optimization of the combination between copper nitrate and phosphomolybdic acid.
H
3
PMo12
O
40
Cu(NO
(mmol)
3
)
2
Conversion
(%)
Selectivity of maleic
acid (%)
Yield of maleic
acid (%)
(mmol)
Acknowledgements
0
0
0
0
0
0
0
0
0
.1
0.1
0.2
0
0.2
0.4
0
0.4
0
0.4
88.5
86
35.6
27.8
33.9
44.1
36.6
40.3
43.8
43.3
51.7
31.5
23.9
24.7
34.9
27.7
36.4
41.7
38.4
49.2
Support from the fund of Huazhong University of Science and
Technology is deeply appreciated. Product identification through
HPLC-MS analysis was performed in Analytical and Testing Center,
Huazhong University of Science and Technology by Ms Xiaoman Gu.
.2
.2
72.9
79.1
75.7
90.3
95.2
88.7
95.2
.4
.4
.8
.8
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4
. Conclusions
[
This work demonstrates an early example of obtaining maleic acid
[
[
from renewable furfural by catalytic oxidation in liquid media, which
provides an alternative route to the current fossil feedstock based
oxidation technologies. The combination of the copper nitrate with
phosphomolybdic acid can selectively transfer furfural to maleic acid
with a 49.2% yield and 51.7% selectivity of maleic acid, while the
conversion of furfural is 95.2%. The major challenge comes from the
polymerization of furfural to resins under oxidative conditions. How
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