Oxidation of 5-hydroxymethylfurfural to maleic anhydride with molecular oxygen

Article abstract of DOI:10.1039/c0gc00837k

5-Hydroxymethylfurfural (HMF) was converted to maleic anhydride in 52% yield via selective oxidation with molecular oxygen using VO(acac)₂ as catalyst in liquid phase. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0gc00837k

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COMMUNICATION
Oxidation of 5-hydroxymethylfurfural to maleic anhydride with molecular
oxygen†
Zhongtian Du,a Jiping Ma,a,b Feng Wang,a Junxia Liua,b and Jie Xu*a
Received 22nd November 2010, Accepted 13th December 2010
DOI: 10.1039/c0gc00837k
5-Hydroxymethylfurfural (HMF) was converted to maleic
anhydride in 52% yield via selective oxidation with molecu-
lar oxygen using VO(acac)2 as catalyst in liquid phase.
Maleic anhydride (MA) is a versatile chemical intermediate used
to produce a variety of products such as unsaturated polyester
resins, 1,4-butanediol, fumaric acid, and tetrahydrofuran.1,2
The global production capacity is more than one million tons
per year.1 In industry, MA is mainly produced via selective
oxidation of benzene, o-xylene or n-butane under relatively high
temperature; e.g. catalytic oxidation of n-butane to MA is usually
◦
performed at 400–450 C, and the selectivities of MA are 67–
75 mol% at 70–85% conversions of n-butane.2 All these routes
above depend on petroleum-based feedstocks. Herein we provide
Scheme 1 Several routes for the selective oxidation of HMF.
a potential biomass-based route for the preparation of MA.
systems for catalytic oxidation of benzyl alcohols with molecular
oxygen.10 When the oxidation of HMF was performed using
VO(acac)2 as catalyst under 0.1 MPa oxygen in acetonitrile,‡ the
main product was DFF. Unexpectedly, MA appeared rather
than FDCA under higher oxygen pressure. Both the conversions
of HMF and the yields of MA were significantly enhanced when
the pressure of oxygen was increased from 0.1 MPa to 1.0 MPa
(Fig. 1) The yield of MA remained roughly constant when the
oxygen pressure was further raised to 1.5 MPa. These results
suggested that high pressure of oxygen facilitated the conversion
of HMF into MA.
The solvent also played an important role for the oxidation
of HMF to MA (Table 1). 52% yield of MA was obtained in
acetonitrile at 90 ◦C in 4 h (entry 2), meanwhile 14% yield
of DFF was detected too. Besides acetonitrile, acetic acid was
preferred for the formation of MA (entry 4). The yields of MA
were about 7% in DMF and TFT respectively (entries 5 and 6),
which were much less than that in acetonitrile or acetic acid.
These results further confirmed the great influence of oxygen
pressure on vanadium-catalyzed oxidation of HMF, as good
yields of DFF were achieved under lower oxygen pressure in
these solvents according to the previous reports.6 About 19%
of HMF was converted and little MA was detected in DMSO
(entry 7). When dichloromethane was used as the solvent, much
oxygen was consumed, however, only 16% of MA was received
and black insoluble was observed (entry 8 and ESI† Fig. S16).
The effects of solvents on vanadium-catalyzed oxidation were
also described in many literatures previously.10–12
Biomass is viewed as a promising feedstock for the chemical
industry in the future.3 Conversions of biomass into chemicals
have become a hot topic recently; many “roadmaps” with far-
sightedness were plotted.3 For example, carbohydrates, includ-
ing fructose, glucose and cellulose, could be converted into 5-
hydroxymethylfurfural (HMF),4 which is a versatile platform
chemical. Many researchers concentrated on the oxidation of
HMF to 2,5-diformylfuran (DFF) or 2,5-furandicarboxylic acid
(FDCA) (Scheme 1),5–8 as these furan products could be used as
polymer monomers.9 The molecules of both MA and HMF
contain furyl rings in the basic structure, thus it would be
interesting to convert HMF into MA from the viewpoint of
sustainable chemistry. This transformation could be achieved via
oxidative C–C bond cleavage of HMF. In this communication,
we report VO(acac)2 catalyzed oxidation of HMF to MA with
molecular oxygen in liquid phase.
HMF, which can be taken as a heteroaromatic alcohol,
was usually oxidized to DFF using vanadium-based catalysts
(Scheme 1).6 Recently we developed several vanadium-based
aState Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, Dalian, 116023, P. R. China.
E-mail: xujie@dicp.ac.cn; Fax: (+86)-411-84379245;
Tel: (+86)-411-84379245
bGraduate University of the Chinese Academy of Sciences, Beijing,
100039, P. R. China
† Electronic supplementary information (ESI) available: Detailed ex-
perimental procedures, product analysis, additional results and origianl
data traces. See DOI: 10.1039/c0gc00837k
554 | Green Chem., 2011, 13, 554–557
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Table 1 Catalytic oxidation of HMF in different solventsa
Yield of main furan
products (mol%)b
Conversion of
Entry
Solvent
HMF (mol%)
MA
DFF
1c
2
CH3CN
CH3CN
CH3CN
CH3COOH
DMF
<1
99
97
>99
96
96
—
52
50
50
7
—
14
15
<1
11
6
3d
4
5
6
TFT
7
7
8
DMSO
CH2Cl2
19
>99
<1
16
9
<1
a Reaction conditions: 2.5 mmol HMF, 0.125 mmol VO(acac)2, 5 ml
solvent, 1.0 MPa O2, 90 ◦C, 4 h. Acetonitrile contained 1% acetic acid.
TFT: a,a,a-trifluorotoluene; DMF: N,N-dimethyl-formamide. b The
yields were calculated as the molar ratio of their amounts to the initial
amount of HMF. The yield of MA included maleic acid. c Without
catalyst. d 5 mol% 2,6-di-tert-butyl-p-cresol was added.
Fig. 2 Effect of reaction temperature. Reaction conditions: 2.5 mmol
HMF, 0.125 mmol VO(acac)2, 5 ml acetonitrile, 1.0 MPa O2, 4 h.
Fig. 3 Oxidation of HMF to MA catalyzed by different transition
metals. Reaction conditions: 2.5 mmol HMF, 0.125 mmol [M], 5 ml
acetonitrile, 90 ◦C, 1.0 MPa O2, 4 h.
Fig. 1 Effect of oxygen pressure. Reaction conditions: 2.5 mmol HMF,
0.125 mmol VO(acac)2, 5 ml acetonitrile, 90 ◦C, 4 h.
Furthermore, the reaction temperature could affect the oxi-
dation efficiency as well as products distribution (Fig. 2). When
the reaction was performed under 70 ◦C, the conversions of
HMF were not more than 50% in 4 h. Interestingly, when
the temperature was raised from 90 ◦C to 130 ◦C, the yields
of MA gradually decreased from 52% to 20% meanwhile the
yields of DFF increased from 14% to 52%. Higher reaction
temperature favoured the formation of DFF rather than MA.
This observation was consistent with the previous reports on
vanadium-catalyzed oxidation of HMF to DFF. In those papers,
oxidations of HMF to DFF were usually performed at around
130–150 ◦C.6
Besides VO(acac)2, some other vanadium compounds
also exhibited activities for catalytic oxidation of HMF
to MA. About 30–43% yields of MA were obtained
using VO(pic)2 [bis(pyridine-2-carboxylato)oxovanadium(IV)],
VO(mal)2 [bis(maltolato)oxovanadium(IV)] and VOSO4 respec-
tively under the same conditions (Fig. 3). In contrast to
vanadium compounds, transition metals such as FeSO4, CuSO4,
Mn(acac)2, MoO2(acac)2, Co(acac)2 and Co(OAc)2 were much
less effective for catalytic oxidation of HMF into MA, and the
yields of MA were less than 2%. These results indicated that
vanadium species were unique for catalytic C–C bond cleavage
of HMF. To the best of our knowledge, this is the first report on
vanadium-catalyzed oxidation of HMF to MA with molecular
oxygen.
Then an important issue arose: the formation route of MA
from HMF. Generally, aldehydes such as benzaldehyde tend
to form corresponding acids with molecular oxygen via autox-
idation, especially in the presence of transition metal ions.13
The aldehyde group of HMF seemed to be the breakthrough
point to form MA via an autoxidation/decarboxylation reaction
pathway. If this hypothesis was right, DFF should be easily
converted to MA in good yield under the same conditions.
Unexpectedly, most of DFF remained stable and only 2% of MA
was obtained when DFF was oxidized (ESI† Fig. S14 and S15).
No MA was detected when FDCA was employed as substrate.
Furthermore when a typical free radical inhibitor (5 mol% 2,6-
di-tert-butyl-p-cresol) was added, both the oxidation process of
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HMF and the products distribution were almost not affected
(Table 1, entry 3), suggesting that the main reaction course
might not be a free-radical one. From the oxidation products
of HMF (or DFF), no FDCA was detected by both NMR
and esterification method (ESI† pp. 10–14). These experiments
showed that the aldehyde group of HMF was relatively stable
under oxygen atmosphere, which was quite different from that
of benzaldehyde. All these results above indicated that MA
was probably not formed via decarboxylation reaction, i.e. the
oxidation of HMF to MA did not involve DFF or FDCA as the
key intermediate. The VO(acac)2 catalyzed oxidation of HMF
was quite different from those using Co/Mn/Br/Zr, Pt-based
or Au-based catalytic systems.5,7,8 In those examples, FDCA or
its derivatives were often generated via further oxidation of the
aldehyde group as proposed by the authors.
In contrast to DFF, MA was obtained in 24% yield when
5-(hydroxymethyl)furfuryl alcohol (HMFA) was oxidized. Fur-
thermore, some products derived from C–C bond cleavage were
also observed when the oxidation of furfuryl alcohol or 5-
methylfurfuryl alcohol was performed respectively under the
same reaction conditions. Thus the presence of aldehyde group
was not necessary for C–C bond cleavage. If a mixture of HMFA
and DFF (10 mol% HMFA and 90 mol% DFF) was subject to
oxidation, only 4% yield of MA was detected, which showed
that the presence of HMFA could not significantly promote
the oxidation of DFF to MA either. Therefore, the formation
of MA was related to the hydroxymethyl group of HMF itself
rather than the aldehyde group.
In a HMF molecule, the aldehyde group and furyl ring forms a
p-conjugated system, leaving the hydroxymethyl group out (Fig.
4). Calculation results indicate that the C–C bond [C(4)–C(7)]
connecting the hydroxymethyl group is longer than [C(1)–C(6)]
near the aldehyde group; thus it is more easily broken from C(4)–
C(7). From a different standpoint, the carbon-oxygen bond
[C(1)–O(5) or C(4)–O(5)] of HMF contains a s bond and p bond
and the corresponding bond length is between that of typical C–
O and C O bonds. Thus, the right part of HMF [O(5)–C(4)–
C(7)–O(9)] can be viewed as a quasi a-hydroxy ketone. Catalytic
oxidative C–C bond cleavage of typical a-hydroxy ketones by
vanadium compounds has been demonstrated by J. M. Bre´geault
and T. Momose et al. before.11 Therefore the inherent structure
Fig. 4 Calculated bond lengths of HMF.
of HMF might account for the C–C bond cleavage from the C–C
bond [C(4)–C(7)] connecting hydroxymethyl group.
The other key issue is the distribution of products. In our
recent report, HMF was converted to DFF in excellent yield
under 0.1 MPa O2.14 The vanadium-catalyzed oxidation of
HMF under high pressure of oxygen was quite different. The
corresponding products via oxidation became complex due to
the unique structure of HMF, which contains an aldehyde group,
a hydroxymethyl group and a furyl ring. Some possible products
were listed in Scheme 2. Besides MA and maleic acid, formic
acid and carbon dioxide were detected as C1-products in this
study, which further confirmed the C–C bond cleavage of HMF.
About 14% of DFF was also obtained, which suggested that
the oxidation of the hydroxymethyl group of HMF occurred
at the same time as C–C bond cleavage. This agrees with the
studies on vanadium-catalyzed oxidation of alcohols.10,12 About
10% byproducts were mainly derived from the esterification of
formic acid and HMF. Others (about 24%) were not detectable
using GC. As mentioned above, though nearly 100% HMF was
converted in CH2Cl2, most of HMF was transformed to a black
resinous substance, which was almost insoluble in common
solvents such as CH2Cl2, acetone or acetonitrile (ESI† Fig.
S16). It was visible when CH2Cl2 was used, however we could
not exclude the occurrence of similar products, which could
not be detected by GC, in other solvents. Once formic acid
was formed, diverse side reactions might be followed under the
reaction conditions. This explanation was in accordance with
the properties of furan compounds. Resinification of furfural or
furfuryl alcohol in the presence of acid/oxygen is known.9
Scheme 2 Possible products from oxidation of HMF. (Those in boxes were determined to exist).
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Based on the experiments mentioned above, we proposed
a pathway for VO(acac)2 catalyzed oxidation of HMF with
molecular oxygen (Scheme 3). Both oxidation of hydroxymethyl
group and C–C bond cleavage took place simultaneously. When
the oxidation was performed under 0.1 MPa O2, the oxidation
of HMF to DFF prevailed (route b). In this work, the C–C bond
adjacent to the hydroxymethyl group was easily broken under 1.0
MPa O2 atmosphere; after the cleavage of C–C bond, a second
a-hydroxy ketone might form on the other side via resonance
(ESI† Fig. S9). Then further oxidation would lead to MA as the
main product (route a). Oxidation of the hydroxymethyl group
to an aldehyde group also occurred; however, DFF was relatively
stable against further oxidation into FDCA or MA.
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Scheme 3 Proposed reaction pathways for oxidation of HMF catalyzed
by VO(acac)2.
In summary, HMF was oxidized to maleic anhydride with
molecular oxygen using VO(acac)2 as catalyst in liquid phase.
The C–C bond cleavage occurred due to the hydroxymethyl
group of HMF itself rather than the aldehyde group. This work
provides a possibility for the preparation of MA from biomass-
based feedstocks via oxidation of HMF. Further study of this
transformation is currently underway.
The work was supported by the National Natural Science
Foundation of China (projects 20736010 & 20803074); We also
thank Dr G. J. Zhao and Dr J. Hu for their help in theoretical
studies.
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14 Very recently, we reported an efficient catalytic system for aerobic
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Y. P a n g , ChemSusChem, DOI: 10.1002/cssc.201000273.
Notes and references
‡ Acetonitrile contained 1% acetic acid.
1 K. Weissermel and H. J. Arpe, Industrial Organic Chemistry, Com-
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