Hydrogen Peroxide Assisted Selective Oxidation of 5-Hydroxymethylfurfural in Water under Mild Conditions

Article abstract of DOI:10.1002/cctc.201701302

An effective and selective method for the oxidation of 5-hydroxymethylfurfural (HMF) by using hydrogen peroxide (H₂O₂) as the liquid oxygen source and activated-carbon-supported ruthenium (Ru/AC) as the catalyst was developed. This reaction system allowed HMF to be oxidized in water under mild reaction conditions efficiently, as it was shown to have lower mass-transfer resistance than gaseous oxygen-assisted oxidation systems. In addition, we could selectively control the components of the oxidation products by adjusting the reaction conditions. We optimized several reaction parameters such as the reaction temperature (75 °C), time (t=1 or 6 h), base additive (sodium carbonate), and the HMF/catalyst ratio (50 or 10) to attain the desired products in maximum yields. Thus, 5-formyl-2-furoic acid was obtained in a high yield up to 92 % with a HMF/catalyst ratio of 50 and a reaction time of 1 h, whereas 2,5-furandicarboxylic acid was obtained in a maximum yield of 91.3 % with a HMF/catalyst ratio of 10 and a reaction time of 6 h. A possible mechanism for the selective oxidation of HMF was also discussed. We envision that the H₂O₂-mediated oxidation systems proposed in this study would be of great benefit to other organic oxidation systems.

Full text of DOI:10.1002/cctc.201701302

Accepted Article
Title: H2O2-assisted Selective Oxidation of 5-Hydroxymethylfurfural
(HMF) in Water under Mild Conditions
Authors: Ching-Tien Chen, Chi Van Nguyen, Zheng-Yen Wang, Yoshio
Bando, Yusuke Yamauchi, Amanullah Fatehmulla, Aslam
Farooq, Takuya Yoshikawa, Takao Masuda, and Kevin Chia-
Wen Wu
This manuscript has been accepted after peer review and appears as an
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the VoR from the journal website shown below when it is published
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Link to VoR: http://dx.doi.org/10.1002/cctc.201701302
A Journal of
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10.1002/cctc.201701302
ChemCatChem
DOI: 10.1002/cctc.201((will be completed by the editorial staff))
H2O2-assisted Selective Oxidation of 5-Hydroxymethylfurfural
(HMF) in Water under Mild Conditions
Ching-Tien Chen,[a] Chi Van Nguyen,[a] Zheng-Yen Wang,[a] Yoshio Bando,[b] Yusuke Yamauchi,[b]
Amanullah Fatehmulla,[c] Aslam Farooq,[c] Takuya Yoshikawa,[d] Takao Masuda,[d] and Kevin C.-W.
Wu*[a,e]
An effective and selective oxidation of 5-hydroxymethylfurfural (HMF) using hydrogen peroxide (H2O2) as the liquid oxygen source and
activated carbon supported ruthenium (Ru/AC) as the catalyst was demonstrated in this work. This reaction system allows HMF to be
oxidized in water and mild reaction conditions efficiently since it has relatively less mass-transfer resistance compared to gaseous oxygen-
assisted oxidation systems. In addition, we could selectively control the components of oxidation products by adjusting the reaction
conditions. We optimize several reaction parameters such as the reaction temperature (75 °C), times (t = 1 or 6 hr), additive base (sodium
carbonate), and the ratios of HMF/catalyst (50 or 10) in order to attain the desired products with the maximum yield. The results showed that
5-formyl-2-furoic acid (FFCA) with a high yield up to 92% could be obtained at the conditions of HMF/catalyst = 50 and t = 1 hr while 2,5-
furandicarboxylic acid (FDCA) with the maximum 91.3% yield could be obtained at the conditions of HMF/catalyst = 10 and t = 6 hr. A
possible mechanism of such selective oxidation of HMF is also discussed. We envision that the H2O2-mediated oxidation systems proposed
in this study would be a great benefit to other organic oxidation systems.
5-hydroxymethylfurfural (HMF), a renewable resource from
lignocellulosic biomass conversion, is considered as one of the
most valued additive chemicals.[1] Comprised of a hydroxyl
group, an aldehyde group, and a ring structure, HMF is a
platform for converting into useful compounds such as levulinic
acid[2] and 2,5-dimethylfuran (DMF)[3] through ring-opening and
hydrogenation/hydrogenolysis, respectively. In addition, the
aerobic oxidation of HMF to 2,5-furandicarboxylic acid (FDCA)
has attracted much attention recently.[4] One of the most
important reasons is that FDCA has the potential of replacing
terephthalic acid (PTA), an organic diacid compound for
synthesizing conventional plastic products such as polyethylene
terephthalate (PET),[5] thus can be a renewable building block
for polymers.
formyl-2-furoic acid (FFCA), as shown in Scheme 1.[4b] At the
first oxidation step, DFF or HMFCA intermediate could be
formed based on the catalyst employed.[4b] However, the
formation of DFF was more favourable than HMFCA due to the
easily oxidized alcohol group. Thus, high selectivity of DFF (over
90%) can be achieved from HMF or via an one-pot conversion
of fructose.[6] FFCA, through further oxidation of DFF or HMFCA,
is a main chain of FDCA production and also the rate limiting
7]
step.[4a,
In order to eliminate the intermediates, previous
studies usually applied high temperatures (over 120 °C)[8] and
pressures (over 2 MPa)[9] in closed systems to increase the
solubility of gaseous oxygen. Even though a high yield (over
90%) of FDCA could be obtained in several cases, the utilization
of high-pressure gas generates the risk of explosion, which is
less favourable for industrial applications.
The conventional aerobic oxidation of HMF to FDCA
contains several alcohol and aldehyde oxidation steps with the
involvement of the intermediates 5-hydroxymethyl-2-
furancarboxylic acid (HMFCA), 2,5-diformylfuran (DFF), and 5-
[a]
C.-T. Chen, C. V. Nguyen, Z.-Y. Wang, Prof. Dr. K. C.-W. Wu
Department of Chemical Engineering
National Taiwan University
No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
Fax: (+886)2-2362-304
E-mail: kevinwu@ntu.edu.tw
[b]
Y. Bando, Y. Yamauchi
International Center for Materials Nanoarchitectonics (MANA),
National Institute for Materials Science (NIMS), 1-1 Namiki,
Tsukuba, Ibaraki 305-0044 Japan
[c]
[d]
A. Fatehmulla, A. Farooq
Department of Physics and Astronomy, College of Science, King
Saud University, Riyadh 11451, Saudi Arabia
Prof. Dr. T. Yoshikawa, Prof. Dr. T. Masuda
Division of Applied Chemistry, Graduate School of Engineering,
Hokkaido University,
Sapporo, 060-8628, Japan
Prof. K.C.-W. Wu
Department of Chemistry, Chung Yuan Christian University,
Chung Li, 32023, Taiwan
Scheme1. Oxidation of HMF to FFCA and FDCA through two different
pathways.
Very recently, the Ebitani group and others have reported
that Au-based catalysts are capable of HMF-to-FDCA aerobic
oxidation with high yields under milder conditions.[10] In addition,
scientists have found out that by adding bases in the reaction
systems aldehyde groups in HMF can be catalysed into acid
groups through the nucleophilic attack of OH- groups, thus high
[e]
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/cctc.20xxxxxxx.
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10.1002/cctc.201701302
ChemCatChem
yields (over 80%) of FDCA
could be obtained even under
low pressures (e.g. 1 bar).[11]
However, with the presence
of bases in the systems, the
synthesis of a complicated
catalyst such as bi-metals (Bi-
Pt/TiO2,[12] Pt-Pb/Carbon)[13]
or those with
core/shell
(Pd/C@Fe3O4)[14]
can mediate
structure
that
alcohol/aldehyde oxidation of
HMF becomes difficult to
batch system, it is worth of mentioning that a semi-batch system
where H2O2 was added dropwisely into the system could
strongly improve the catalytic conversion of HMF. As shown in
Entry 6, when only 1.5 ml of 35% H2O2(aq) was added dropwisely,
we could obtain an increasing yield of 64% for FFCA. This result
shows that a continuous involvement of H2O2 is crucial to
complete the conversion of HMF to the desired products.
We have previously screened many kinds of catalysts (i.e.
different metals loaded activated carbon materials) for HMF
conversion. As shown in Table S1, the results showed that
ruthenium (Ru)-loaded activated carbon (i.e. Ru/AC or RuPt/AC)
exhibited higher values in HMF conversion and products yield,
as compared to other noble metal-loaded AC materials such as
Pt/AC, NiPt/AC, CoPt/AC, and PdPt/AC. The recycle ability of
the prepared Ru/AC was discussed in Fig. S1.
For the reaction environment, we found that as the
temperature increased, the conversion of HMF and the yield of
products also increased (See Table S2). The most suitable
reaction temperature is decided to be 75 ºC. Temperatures
above 75ºC are not suitable for the presenting aqueous system
due to drastic evaporation of the solvent.
The effect of the amount of the base (i.e. Na2CO3) in this
reaction system was also studied (See Table S3). It is shown
that when the reaction was conducted without any base, both
the HMF conversion and the product yield were relatively low.
This result reveals the importance of the Na2CO3 base in this
system, and the conversion of HMF was not high in the absence
of a base. When the HMF/Na2CO3 ratio was 1: 0.5, the presence
of DFF in the solution indicated that the efficiency of HMF
oxidation was not strong enough, since DFF is one of products
after an oxidation step (Scheme 1). Further increasing the base
makes the reaction of DFF move forward, thus resulting in
higher FFCA yield. The highest FFCA yield appeared when the
ratio is 1: 1. However, the yield of FDCA did not change much
as the ratio was increased.
achieve. Besides, these systems still involve two-phase (i.e.
liquid-gas) reactions that require specially designed reactors
and high volume of gaseous oxygen.[4b, 7, 11a] Consequently, an
effective, full liquid phase system of HMF conversion would be
scientifically challenging but optimum for chemical industries in
the future.
A liquid oxygen source (i.e. hydrogen peroxide or H2O2) has
been an alternative approach widely applied in industrial
manufacture, thanks to its affordable price, safe storage and
high active oxygen content.[15] Most of the applications of H2O2
are involved as an oxidizing agent for oxidation reaction such as
Baeyer-Villiger oxidation reaction,[15b] alcohol oxidation,[16]
[17]
[18]
phenol hydroxylation,
oxidation of sulphides and
cyclohexane oxidation.[19] Hydrogen peroxide was recently
employed in biomass conversion successfully, such as the
production of gluconic acid from glucose,[15a] succinic acid from
levulinic acid,[20] and oxidation of furfural into maleic acid or
furmaric acid.[21] However, difficulties in controlling its selectivity
and quickly decomposing in base or metal catalysts are its
drawbacks.[15b] Thus, both the selection of catalysts or catalytic
system set ups for general oxidation reactions still remain a
challenge when H2O2 is used as an oxidizing agent.
In this study, we design an aqueous phase catalytic system
for HMF oxidation. Instead of using oxygen gas, we choose
H2O2 as the liquid oxidant to decrease the mass transfer
resistance and provide high reactivity. H2O2 was chosen as an
ideal liquid oxidant among others since it only generates water
and oxygen gas after decomposition. This system is operated
under atmospheric pressure and temperature below 100 ºC that
provides easy and safe controls.
First, we optimized the reaction conditions of HMF oxidation.
As comparing Entry 1 with 2 in Table 1, it is found that a basic
environment could trigger the decomposition of HMF, but no
product was found. However, after adding the Ru/AC catalyst
(Entry 3), the conversion of HMF was increased and a trace
amount of DFF could be obtained. In contrast, as we introduced
H2O2 to the system (no Ru/AC catalyst), almost all of the HMF
was decomposed (conversion was 93%, as presented in entry
4), but there was still no observation of desired products such
as DFF, HMFCA, FFCA or FDCA. These results indicate that
both base (i.e. Na2CO3) and oxidant (i.e. H2O2) promote the
decomposition of HMF, and the catalysts (i.e. Ru/AC) endorses
the conversion of HMF to the desired products. In entry 5, when
all of Na2CO3, H2O2 and Ru/AC were present in the system, we
could get 94% HMF conversion but more desired products such
as FFCA (37%) and DFF (14%). In such a batch system where
a certain amount of H2O2 was added in one time, we observed
a lot of bubbles generated in the solution, indicating H2O2 was
quickly decomposed to oxygen gas and water. In contrast of
As for the effect of H2O2 concentration, we found that the
conversion of HMF was low when the reaction was performed in
absence of H2O2 (See Table S4). About 9% of FFCA yield was
observed after reaction, indicating that there were a few
amounts of HMF oxidized by the Ru/AC catalyst. In this case,
few oxygen gas dissolved in the solution could be used as the
oxidant. When increasing the H2O2 concentration to 5%, the
HMF conversion was greatly increased to 100%, and the yield
of FFCA was also increased to 79%. Although there was still 5%
of DFF at this condition, which implies the oxidation efficiency
was not high enough, we could overcome this problem by simply
increasing the concentration of of H2O2 to 10%. These results
indicate that the presence and liquid oxygen source (i.e. H2O2)
and its concentration are critical in our oxidation system.
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10.1002/cctc.201701302
ChemCatChem
Figure 1. Effects of (a) the amount of Ru and (b) the amount of
HMF on the yields of FFCA and FDCA.
Figure 2. Yields of FFCA and FDCA at various time periods at
a molar ratio of HMF/Ru = 10. Reaction condition: 75 ºC, Ru/AC
(10 wt% Ru, 25 mg), H2O (13.5 ml), HMF/Na2CO3 = 1 : 1, and
35% H2O2(aq) was added dropwisely with the rate = 1.6 ml/h.
Conversions of HMF in this figure are all 100%.
Based on our optimization of reaction conditions, we
found that FFCA could be synthesized quickly from HMF but the
FFCA-to-FDCA reaction was relatively slower. This feature
makes it possible to selectively stop the reaction for desired
products (i.e. FFCA or FDCA), because both of them are
precious block chemicals. Two factors
were found to be critical for selective
production of FFCA and FDCA. As shown
in Fig. 1(a), on one hand, we found the
amounts of Ru (wt%) on AC affected the
selective oxidation of HMF to FFCA or
FDCA. More Ru on AC (from 2% to 10%)
would result in higher FDCA yields (i.e.
from 1.7% to 26.0%). On the other hand,
when increasing the amount of HMF (from
0.3 to 0.8 mmol), more FFCA could be
obtained (from 69.5% to 75.0%), as shown
in Fig. 1(b). Because FFCA is the
intermediate of HMF-to-FDCA, more
amounts of Ru on AC (i.e. more catalysts)
would catalyze the conversion, and more
HMF (i.e. more reactants) would lead to
incomplete conversion when the catalyst amount and reaction
time are limited. We further adjust both HMF and Ru wt% and
use the HMF/Ru ratio to study the selective oxidation of HMF.
As shown in Table S5 and S6, when we fixed the HMF/Ru ratio
at 20, the similar product compositions proved that HMF/Ru
molar ratio is the key factor for determining product selectivity in
our system. In other words, the effect of adding less reactant
gives almost the same results as adding more catalyst. We
believe that the amount of HMF that one mole of Ru could react
per unit time should be a constant in our system. When HMF/Ru
was decreased to 10, given that more catalysts could provide
more active sites, HMF would convert to FFCA and then further
convert to FDCA. In contrast, when the HMF/Ru ratio was
increased to 60, the reactant HMF was not completely
consumed (i.e. trace amount of HMF remained). As a result, we
control the HMF/Ru ratio at 50 to ensure complete conversion of
HMF, and we can obtain FFCA in 84% yield within 1 hour. For
getting FDCA, we extended the reaction time to 6 hours, and
FDCA with the highest yield of 91% could be obtained under 75
ºC and atmospheric pressure, as shown in Fig. 2. We also
checked our catalysts through FT-IR analysis to prove that our
product will not be adsorbed in the pore of Ru/AC after reaction,
as shown in Fig. S2.
To demonstrate the high efficiency of our system using liquid
oxygen source (i.e. H2O2), we compare our results with that
using gaseous oxygen as the oxidant. As shown in Table S7,
the system using gaseous oxygen while remaining other
reaction conditions the same could only produce trace amount
of FDCA. This result indicated that the oxygen molecules
generated from H2O2 would interact with the reactant (i.e. HMF)
and catalyst (i.e. Ru/AC) more efficiently than gaseous oxygen
molecules that are required to be dissolved in solution prior to
reaction.
It is reported that strong base would facilitate the production
of FDCA, but at the same time HMF is easily decomposed to
other side products in strong alkaline environment.[18] Therefore,
it is important to find out the most suitable base for our system.
We used different bases including sodium bicarbonate (NaHCO3,
pKa = 10.3), sodium carbonate (NaCO3, pKa = 10.33) and
sodium hydroxide (NaOH, pKa = 13.8), and the results are listed
in Table 2. For the cases of 1 hour reaction, it could be found
that the base with lower pKa (i.e. NaHCO3) gives a higher FFCA
yield, and the one with higher pKa (i.e. NaOH) resulted in more
FDCA. However, NaOH was too strong so about 30% of HMF
was degraded instead of oxidation. Consequently, a weak base
like NaHCO3 is more suitable in our system. When we further
extended the reaction time to 3 hours, the amount of FFCA
decreased and the amount of FDCA increased, indicating the
successful FFCA-to-FDCA conversion.
To further improve the yield of FDCA, we came out an idea
that is to separate the HMF-to-FDCA reaction into a sequential
HMF-to-FFCA and FFCA-to-FDCA reaction. In the first HMF-to-
FFCA reaction we used NaHCO3 (i.e. the weak base) to
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10.1002/cctc.201701302
ChemCatChem
a clear solution, and the solution was added to the activated
carbon solution. After stirring for another 20 min, the solution
was moved to a rotating evaporator to remove the water
gradually under reduced pressure and 30 °C. When most of the
water was removed (i.e. powder-formed activated carbon could
be observed), the temperature was increased to 70 °C and held
for 30 min to further drying of the samples. The material was
then reduced to metal state by calcination under hydrogen gas
flow. We use mixed gas containing 95% of nitrogen and 5% of
hydrogen with a flow rate of 60 ml/min. The temperature was
raised from 20 °C to 450 °C within 90 min, and held at 450 °C
for 4 h. The reduced Ru-on-activated carbon (denoted as
Ru/AC) was then collected after cooling. The oxidation state of
Ru in the synthesized Ru/AC samples was examined with XPS
measurement (Fig. S3).
synthesize FFCA with a high yield. After that, for the second
FFCA-to-FDCA reaction, we then added NaOH (i.e. the strong
base) into the solution. The strong base can provide more Na+
ions that can prevent the catalyst from deactivating and more
OH- ions that can promote the FFCA-to-FDCA reaction. The
results are shown in Table 3. From entry 1 and 2, low yields of
FDCA indicated that NaHCO3 was not strong enough for the
deionization of FDCA. In addition, in entry 6, even we removed
the used Ru/AC catalyst and added fresh Ru/AC catalyst for the
FFCA-to-FDCA reaction, we only observed a little improvement
of the FDCA yield, indicating that fresh Ru/AC catalyst was still
deactivated and lost the efficiency very soon when the FDCA
was formed. However, when we used NaOH as the base for the
FFCA-to-FDCA reaction, we can convert most of the FFCA into
FDCA within 2 hours (Entry 3, 4, 5). As comparison, if we
introduce fresh Ru/AC catalyst and NaOH into the system at the
same time, FDCA yield of 76% could be obtained (Entry 7) in a
total 3-hour reaction. Consequently, we can conclude that a
strong base such as NaOH is necessary for the FFCA-to-FDCA
reaction.
Oxidation of HMF
In a typical oxidation reaction of HMF,
0.0378 g of HMF (0.3 mmol) and 0.0250 g of catalyst was
prepared in a two-neck round bottom flask. Then 13.5 ml of de-
ionized water and 1 ml of 0.3 M sodium carbonate (Na2CO3)
aqueous solution were added. After that, the round bottom flask
containing the reaction media was then put into an oil bath to
control the reaction temperature. A
rubber stopper was used to cap the vial
and a needle was inserted on it for
maintaining the pressure at 1 atm (i.e.
open system). Finally, to start the
reaction, 1.5 ml of H2O2(aq) was added
to the solution dropwisely in a rate of
1.6 ml/h by syringe pump. The reaction
was carried out at various times under
stirring. The shortest reaction time was
one hour because we examined that all
H2O2(aq) could be consumed within one
hour.
Analysis of products
After
reaction, the catalyst was separated
from the solution by filtration, and then
In conclusion, we propose an effective liquid-phase
oxidation system for selective HMF oxidation to either FFCA or
FDCA with high yields. Compared to other metal catalysts, we
found that ruthenium (Ru)-based catalysts show the best
performance with the presence of our liquid oxidant, hydrogen
peroxide (H2O2). No gas flow is required during the reaction;
instead, we added hydrogen peroxide dropwisely into the
system. We found the main factors affecting product
composition are the molar ratio of HMF to Ru and the reaction
time. We can selectively produce FFCA or FDCA by simply
adjusting these two factors. The reactions are in low
temperature, atmospheric pressure, weak base environment,
and short reaction time with high catalytic efficiency, and the
catalysts are easy to synthesize, which make this reaction
system more feasible for industrial FDCA production in the
future.
the solution was directly analyzed by High Performance Liquid
Chromatography (HPLC), which was equipped with RI detector
and a Transgenomic COREGel 87H3 (300 mm × 7.8 mm)
column. The retention time for HMF, HMFCA, DFF, FFCA, and
FDCA are 36.5, 24.5, 47.3, 28.6, and 20.7 minute, respectively.
The yield of products is defined as the mole of product produced
over the mole of reactant added. The conversion of HMF is
defined as the mole of HMF consumed after the reaction over
the mole of HMF added.
mole of product produced
Yield % =
×100%
mole of HMF added
mole of HMF consumed
mole of HMF added
Conversion % =
×100%
Acknowledgements
We would like to thank the Ministry of Science and Technology
(MOST) of Taiwan (104-2628-E-002-008-MY3; 105-2218-E-
155-007; 105-2221-E-002-003-MY3; 105-2221-E-002-227-MY3;
105-2622-E-155-003-CC2) and the Aim for Top University
Project at National Taiwan University (105R7706) for the
funding support. The authors extend their appreciation to the
International Scientific Partnership Program (ISPP) at King
Saud University (KSU) for funding this research work through
ISPP-0066. K.C.W.W. acknowledges the special appointed
professorship from Hokkaido University for his stay in Sapporo.
Experimental Section
Chemicals Hydrogen peroxide solution (H2O2, 35% w/w) is
purchased from Showa. Ruthenium (III) chloride hydrate
(RuCl3·nH2O, 38% - 42% Ru basis) and other materials are all
purchased from Sigma-Aldrich.
Preparation of catalysts
activated carbon was mixed with 15 ml of water and stirred for
20 min. Then, ruthenium chloride was dissolved in water to form
At first, 0.2
g
of grinded
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10.1002/cctc.201701302
ChemCatChem
[21]
N. Araji, D. D. Madjinza, G. Chatel, A. Moores, F.
Jérôme, K. D. O. Vigier, Green Chem. 2017, 19, 98-
101.
Keywords: Selective oxidation • 5-hydroxymethyl furfural
(HMF) • Hydrogen peroxide • 5-formyl-2-furoic acid (FFCA) •
2,5-furandicarboxylic acid (FDCA)
Received: ((will be filled in by the editorial staff))
Published online: ((will be filled in by the editorial staff))
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10.1002/cctc.201701302
ChemCatChem
COMMUNICATION
Ching-Tien Chen, Chi Van Nguyen,
Zheng-Yen Wang, Yoshio Bando,
Yusuke Yamauchi, Amanullah
Fatehmulla, Aslam Farooq, Takuya
Yoshikawa, Takao Masuda, and Kevin
C.-W. Wu*
Selective Oxidation of 5-Hydroxymethylfurfural (HMF): We propose an
effective liquid-phase oxidation system for selective HMF oxidation to either FFCA
or FDCA with high yields using Ru/AC and H2O2 as the catalyst and oxidant,
respectively.
Page No. – Page No.
Selective Oxidation of 5-
Hydroxymethylfurfural (HMF) in Water
under Mild Conditions
This article is protected by copyright. All rights reserved.