Efficient aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran, and synthesis of a fluorescent material

Article abstract of DOI:10.1002/cssc.201000273

Furan fluorescence: 5-Hydroxymethylfurfural, available from biomass, is efficiently oxidized to 2,5-diformylfuran by using molecular oxygen, under mild conditions. The oxidation is catalyzed by Cu(NO₃)₂/ VOSO₄. The renewable, rather than petroleum-based, furan dialdehyde is used for the synthesis of a fluorescent material.

Full text of DOI:10.1002/cssc.201000273

DOI: 10.1002/cssc.201000273
Efficient Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-
Diformylfuran, and Synthesis of a Fluorescent Material
Jiping Ma,[a, b] Zhongtian Du,[a] Jie Xu,*[a] Qinghui Chu,[c] and Yi Pang*[c]
The present organic-chemical and polymer industries mainly
depend on resources derived from fossil fuels.[1] Hence, the
transformation of abundant biomass resources into chemicals
is attractive from the viewpoint of sustainable chemistry.[2]
Many efforts have recently been made to produce 5-hydroxy-
methylfurfural (HMF), which is viewed as a key platform chemi-
cal,[3] from carbohydrates. 2,5-Diformylfuran (DFF), one of the
most important derivatives of HMF, is a furan dialdehyde, and
various applications of DFF have been described, including its
use as starting material for synthesis of the pharmaceuticals,
macrocyclic ligands, and others.[4] Furthermore, it can be used
as a monomer for preparation of many functional materials.[5]
For example, Gandini and co-workers described a polymer of
DFF and ortho-phenylenediamine,[5a] while Amarasekara et al.
reported the synthesis and characterization of a 2,5-diformyl-
furan–urea resin.[5c] Thus, the direct conversion of HMF to DFF
via selective oxidation is attractive and important.
formation concerning the selective oxidation of HMF to DFF. In
particular, a good selectivity for DFF can be achieved by using
vanadium-catalyzed systems.[9] However, more efficient and
economical catalytic systems, especially for use in mild condi-
tions, remain to be developed. In essence the conversion of
HMF to DFF can be viewed as the oxidation of a heteroaromat-
ic alcohol. We have recently disclosed several vanadium-based
catalytic systems for the oxidation of benzyl alcohols with mo-
lecular oxygen.[10] Based on these results, we report herein a
homogenous catalytic system, Cu(NO3)2/VOSO4, that oxidizes
HMF to DFF in a facile manner, with good yields under mild
conditions (Scheme 1).
Compared to methods that use a stoichiometric quantity of
oxidant,[6] the catalytic oxidation of HMF to DFF by using mo-
lecular oxygen as terminal oxidant is an intriguing prospect,
for both economical and environmental reasons. However,
owing to the presence of both a furan ring and an aldehyde
group in the molecule, the oxidation of HMF often involves
many side reactions, for example, overoxidation, decarbonyla-
tion, and cross-polymerization. The efficient conversion of HMF
into DFF via catalytic oxidation with molecular oxygen is a
great challenge. Recently, much progress has been made in
the development of catalytic systems, such as Co/Mn/Zr/Br,[7]
Pt-Bi/C,[8] and vanadium-based catalysts.[9] Carlini et al. reported
an HMF conversion of 84% and a DFF selectivity of 97% with
vanadyl phosphate as catalyst, at 1508C.[9b] Corma and co-
workers designed immobilized vanadyl–pyridine complexes;
82% HMF conversion was achieved, with DFF 99% selectivity,
at 1308C.[9c] These works have provided us with important in-
Scheme 1. Oxidation of HMF to DFF.
Vanadium compounds are widely used for the catalytic oxi-
dation of organic compounds: the VIV/VV redox cycle is often
proposed during the catalytic oxidation of alcohols with mo-
lecular oxygen.[11,12] Because Cu(NO3)2 is a strong oxidant, its
use to assist the formation of VV species during oxidation with
molecular oxygen is interesting. We chose VOSO4 as vanadium
source because of its unique performance during catalytic
oxidation of benzyl alcohols.[10]
Neither Cu(NO3)2 nor VOSO4 alone exhibited a high efficiency
towards the catalytic oxidation of HMF, as shown in Table 1,
entries 1 and 2. Under the same conditions, HMF conversion
was enhanced remarkably when Cu(NO3)2 and VOSO4 were
used in combination (entries 3–5). An HMF conversion of up to
99%, with 99% DFF selectivity, could be obtained within 1.5 h
by using only 2 mol% Cu(NO3)2/VOSO4 (1:1 molar ratio) as the
catalyst (entry 3). When the oxidation was carried out with less
catalyst (catalyst/HMF=0.005), a high conversion of HMF into
[a] J. Ma, Dr. Z. Du, Prof. J. Xu
State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Dalian, 116023 (PR China)
Fax: (+86)411-84379245
E-mail: xujie@dicp.ac.cn
Table 1. Aerobic catalytic oxidation of HMF.[a]
[b] J. Ma
Entry Catalyst
Molar ratio
catalyst/HMF [8C] [h] [mol%]
T
t
Conversion Selectivity[b]
Graduate University of the Chinese Academy of Sciences
Beijing 100039 (PR China)
[mol%]
[c] Dr. Q. Chu, Dr. Y. Pang
1
2
3
4
5
Cu(NO3)2
VOSO4
Cu(NO3)2/VOSO4 0.02
Cu(NO3)2/VOSO4 0.005
Cu(NO3)2/VOSO4 0.02
0.02
0.02
80
80
80
80
1.5 trace
1.5 10
1.5 99 (96)
–
31
99
99
99
Institution Department of Chemistry &
Maurice Morton Institute of Polymer Science
The University of Akron
5
99
99
RT[c] 48
Akron, OH 44325 (USA)
Fax: (+1)322-972-8263
E-mail: yp5@uakron.edu
[a] Reaction conditions: 10 mmol HMF, molar ratio Cu/V=1, 0.1 MPa O2,
5 mL acetonitrile. The value in parenthesis is the isolated yield of DFF.
[b] Selectivity towards DFF. [c] Room temperature.
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201000273.
ChemSusChem 2011, 4, 51 – 54
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51

DFF could still be achieved after 5 h (entry 4). The oxidation
even proceeded at room temperature, and good results were
obtained after a reaction time of 48 h (entry 5). In addition to
the use of mild reaction conditions and the high efficiencies
achieved, the inorganic catalyst could also be easily removed
after oxidation, rendering this process rather attractive.
was formed, owing to chlorination). These results suggest that
HMF is oxidized to DFF directly by a VV species, rather than
VOSO4.[13]
VV species were formed under the employed reaction condi-
tions, although initially VIV in the form of VOSO4 was used. We
applied UV/Vis spectroscopy to detect the VV species after che-
lation.[14] VIV, CuII, and NO3 species do not interfere with this
À
Further studies showed that DFF remained stable under the
oxidative conditions employed. After complete conversion of
the HMF after 1.5 h, the selectivity of the reaction towards DFF
was still nearly 99% even after prolonging the reaction time to
5 h (Figure 1). 2,5-Furandicarboxylic acid was not detected by
detection method. Firstly, VOSO4 and Cu(NO3)2 were stirred in
acetonitrile under an O2 atmosphere in the absence of HMF.
The Cu(NO3)2/VOSO4 reaction mixture was then pretreated
with 4-(2-pyridylazo)resorcinol (PAR), iodo-nitro-tetrazolium
chloride (INT), and 1,2,-diaminocyclohexane-N,N,N’,N’-tetra-
acetic acid (CDTA), and examined by UV/Vis spectroscopy (see
Supporting information). In acetonitrile, the absorption band
of PAR appears at ca. 385 nm, and is assigned to a p-p* elec-
tronic transition. After adding the Cu(NO3)2/VOSO4 reaction
mixture a new absorption band appeared at ca. 552 nm
(Figure 2), characteristic of complex of VV with PAR and INT.[14]
Figure 1. Time course of the reactions. Conditions: 10 mmol HMF, 0.2 mmol
VOSO4, 0.2 mmol Cu(NO3)2, 0.1 MPa O2, 5 mL acetonitrile, 808C.
NMR analysis. However, HMF conversions of only 21–78% were
achieved when Ni(NO3)2, Co(NO3)2, Ce(NO3)3, NaNO3, or
Fe(NO3)3 was employed instead of Cu(NO3)2, even after 5 h
under 0.5 MPa O2. Thus, the combination of VOSO4 with
Cu(NO3)2 was the most effective one among the tested metal
nitrates (see Supporting information, Figure S1). The type of
vanadium compound had a strong effect on the HMF oxida-
tion reaction, also. The combination of VOSO4 and Cu(NO3)2 ap-
pears to exhibit a unique chemistry: VOSO4 showed a much
higher efficiency than NaVO3, VOPO4, VO(OEt)3, VO(acac)2, and
VO(pic)2 [bis(pyridine-2-carboxylato)oxo-vanadium(IV)]. The
HMF conversions were lower than 33% when the vanadium
compounds mentioned above were used (Table S1). Similar ob-
servations were described in previous reports on the catalytic
oxidation of alcohols.[10] Notably, Cu(NO3)2/VOCl3 was also effec-
tive towards the catalytic oxidation of DFF (Table S1, entries 3
and 4). Moreover, 85% HMF conversion and 97% DFF selectivi-
ty were achieved when the reaction time was prolonged to
3 h. This result indicates that the initial valence of vanadium
(IV or V) is not a crucial factor.
Figure 2. UV/Vis spectra after treating the Cu(NO3)2/VOSO4 reaction mixture
with different volumes of Cu(NO3)2/VOSO4 reaction mixture.
All spectra intersected at ca. 460 nm, forming a clear isosbestic
point and suggesting that only one new species is formed. No
absorption band was observed around 552 nm when VOSO4 or
Cu(NO3)2 was treated with the same procedure (Figure S7
and S8). 51VNMR provided additional evidence for the exis-
tence of VV species. Because VIV is paramagnetic, mononuclear
VIV species cannot be detected by 51V NMR.[15] No 51VNMR
signal was apparent from the VOSO4 sample (Figure S9). In
contrast, the Cu(NO3)2/VOSO4 reaction mixture exhibited
strong 51VNMR signals (Figure S10). All of these results indicate
that a VIV/VV redox cycle is probably involved, consistent with
previous reports on vanadium-catalyzed oxidation of alcohols
with molecular oxygen.[12] The Cu(NO3)2 facilitates the genera-
tion of VV species from VOSO4. This may explain the enhanced
performance of Cu(NO3)2/VOSO4 even under mild conditions.
The ease of DFF production from HMF prompted us to
explore the furan counterpart of related, important polymers,
such as fluorescent materials.[16] One potential application is to
transform the aldehyde group into benzoxazole, a heterocyclic
We carried out the oxidation reaction with a stoichiometric
amount of VOSO4 or VOCl3 under a nitrogen atmosphere
(Scheme S1). VOSO4 by itself was not an active oxidant for the
direct oxidation of HMF to DFF: no oxidation of HMF was ob-
served. In contrast, HMF was nearly completely converted and
a DFF yield of 46% was achieved when 1 equiv VOCl3 was
stirred with HMF for 5 h, even at RT (about 44% of byproducts
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ChemSusChem 2011, 4, 51 – 54

ring that is often seen in thermally stable rigid-rod polymers
and optical materials.[17] Thus, the reaction of DFF with 2-
amino-4-bromophenol afforded the benzoxazole dibromide 2,
which then underwent Suzuki coupling[18] with 9,9-dihexyl-
fluorene-2,7-bis(trimethyleneborate) to afford the polymer 3a
(Scheme 2; Mw =5077, PDI=1.3, Figure S11). A THF solution of
the polymer exhibited an absorption maximum lmax =366 nm,
Experimental Section
Typical procedure for HMF oxidation (Table 1, entry 3): Vanadyl
sulfate (34.3 mg, 0.2 mmol), cupric nitrate trihydrate (48.3 mg,
0.2 mmol), and HMF (1.26 g, 10 mmol) were charged into a 50 mL
autoclave, and acetonitrile (5 mL) was added. After the autoclave
was closed, oxygen was added (0.1 MPa). The autoclave was then
was heated to 808C within ca. 20 min. The reaction temperature
was maintained at 808C for 1.5 h. Oxygen was recharged if con-
sumed during the oxidation. The autoclave was cooled to room
temperature and depressurized carefully. A sample of the reaction
mixture was taken for GC analysis. Conversion and selectivity were
determined based on area normalization without any purification.
Crucial data were reconfirmed by NMR (Figure S3 and S4). Products
were confirmed by GC-MS, NMR, and by comparison of their GC re-
tention times with those of authentic samples. When GC showed
that the conversion of HMF was more than 99%, acetonitrile was
removed by rotary evaporator after filtration. The crude product
was purified by chromatography on silica gel using ethyl acetate
and petroleum (3:5) as eluant. DFF was obtained as white solid
1
(1.19 g, yield 96%). H NMR (400 MHz, [D6]DMSO, 298 K): d=9.82
(2H), 7.68 ppm (2H); 13C NMR: d=122.10, 153.66, 180.73 ppm.
Scheme 2. Synthesis of polymer 3a.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (projects 20736010 and 20803074).
and strong blue fluorescence (emission peak lem =462 nm and
quantum yield f =0.57; Figure 3). In comparison with its
fl
isoelectronic structure 3b (lmax =329 and 381 nm; lem =425
and 449 nm),[17b] the emission of the furan derivative 3a is at
longer wavelength and significantly broader, revealing the
notable effect of the furan moiety on the electronic band
structure and optical characteristic of p-conjugated materials.
In summary, we report a highly efficient catalytic system
consisting of Cu(NO3)2/VOSO4. HMF is oxidized to DFF in high
yield with molecular oxygen under mild conditions. As an ex-
ample, DFF was used as dialdehyde for the synthesis of a blue-
emitting fluorescent material. The potential applications of DFF
remain to be explored and the detailed catalytic mechanism
also needs to be further studied.
Keywords: biomass · fluorescence · oxidation · polymers ·
vanadium
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Received: August 25, 2010
Revised: October 12, 2010
Published online on November 25, 2010
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