Bifunctional Imidazole-Benzenesulfonic Acid Deep Eutectic Solvent for Fructose Dehydration to 5-Hydroxymethylfurfural

Article abstract of DOI:10.1007/s10562-020-03309-6

Abstract: Imidazole (Im) and benzenesulfonic acid (BSA) formed deep eutectic solvents (DESs) were used as acidic catalyst and solvent for the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF). The DES formation involved an acid–base neutralization to produce equimolar salt from BSA and Im, and subsequent interaction between equimolar salt as hydrogen bond acceptor and excessive BSA as hydrogen bond donor. The BSA-rich DES [Im:1.5BSA] with a 1:1.5 molar ratio of Im:BSA and 10% dosage exhibited high catalytic activity for fructose dehydration with a 5-HMF yield of 90.1% at 100?°C after a very short reaction time (3?min). The bifunctionality of [Im:1.5BSA] for promoting reaction rates and catalytic activity of fructose dehydration has been identified by tuned acidity of DESs and hydrogen bond interaction among fructose, 5-HMF, and DESs demonstrated by conductor-like screening model for real solvents (COSMO-RS) theory. Graphic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-020-03309-6

Catalysis Letters
https://doi.org/10.1007/s10562-020-03309-6
Bifunctional Imidazole‑Benzenesulfonic Acid Deep Eutectic Solvent
for Fructose Dehydration to 5‑Hydroxymethylfurfural
Chencong Ruan1 · Fan Mo1 · Hao Qin1 · Hongye Cheng1 · Lifang Chen1 · Zhiwen Qi1
Received: 25 March 2020 / Accepted: 5 July 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Imidazole (Im) and benzenesulfonic acid (BSA) formed deep eutectic solvents (DESs) were used as acidic catalyst and solvent
for the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF). The DES formation involved an acid–base neutrali-
zation to produce equimolar salt from BSA and Im, and subsequent interaction between equimolar salt as hydrogen bond
acceptor and excessive BSA as hydrogen bond donor. The BSA-rich DES [Im:1.5BSA] with a 1:1.5 molar ratio of Im:BSA
and 10% dosage exhibited high catalytic activity for fructose dehydration with a 5-HMF yield of 90.1% at 100 °C after a
very short reaction time (3 min). The bifunctionality of [Im:1.5BSA] for promoting reaction rates and catalytic activity of
fructose dehydration has been identifed by tuned acidity of DESs and hydrogen bond interaction among fructose, 5-HMF,
and DESs demonstrated by conductor-like screening model for real solvents (COSMO-RS) theory.
Graphic Abstract
Keywords Fructose · 5-HMF · Dehydration · Deep eutectic solvent · COSMO-RS
1 Introduction
* Lifang Chen
lchen@ecust.edu.cn
The depletion of fossil fuels and increasing environmen-
* Zhiwen Qi
zwqi@ecust.edu.cn
tal concerns have raised an urgent necessity for efcient
transformation of cellulosic biomass feedstocks into sus-
tainable bioenergy [1]. Great eforts have been devoted to
direct conversion of carbohydrates to 5-hydroxymethylfur-
fural (5-HMF), one of the top value-added biomass-derived
1
Max Planck Partner Group at the State Key Laboratory
of Chemical Engineering, School of Chemical Engineering,
East China University of Science and Technology, 130
Meilong Road, Shanghai 200237, China
Vol.:(0123456789)
1 3

C. Ruan et al.
platform chemicals. Containing a hydroxyl and an aldehyde
groups, 5-HMF can be converted into biofuel precursors and
high value-added chemicals. As one of the most reactive car-
bohydrates for dehydration, fructose is a preferred feedstock
for 5-HMF synthesis due to its abundant natural source of
carbon [2].
dehydration of fructose to 5-HMF. In addition, various reac-
tion conditions including reaction time, temperature, fruc-
tose loading, and DES acidity were also evaluated.
2 Experimental
Generally, fructose dehydration to 5-HMF requires the
presence of strong acid catalysts in rigorous reaction condi-
tions [3]. However, owing to the existence of active alde-
hyde group, side reactions such as further rehydration and
degradation of 5-HMF readily occurred and resulted in low
5-HMF selectivity and yield [4]. Accordingly, ionic liquids
(ILs) as reaction medium or/and catalyst for fructose dehy-
dration have gained increasing attention due to their superior
properties, e.g., negligible vapor pressure, solvating abil-
ity, and chemical stability [5–7]. It was found that Brønsted
acidic ILs were highly efcient for fructose dehydration to
5-HMF. Nevertheless, ILs with complicated preparation pro-
cesses, high cost, and low biodegradability have restricted
their practical application [8].
2.1 DES Preparation and Characterization
The Im-BSA DESs were prepared based on our previous
work [20]. Typically, Im and BSA with specifc mole ratio
were mixed, heated to 80 °C, and kept at this temperature
with magnetically stirring. Then a homogeneous clear liquid
was obtained and meant the formation of DES. The prepared
DES was characterized by 1H nuclear magnetic resonance
(NMR) in deuterium oxide at room temperature and Fourier-
transform infrared (FT-IR) using KBr discs.
2.2 Reaction Procedure for Fructose Dehydration
In order to overcome these limitations, deep eutectic sol-
vents (DESs) with the advantages of ILs have been emerged
and developed. Typically, DESs, formed through hydrogen
bond interaction between hydrogen bond acceptor (HBA,
quaternary ammonium or phosphorus salt) and hydrogen
bond donor (HBD, organic acid or alcohol), can remarkably
decrease the melting point relative to individual components
[9]. Owing to their low price and melting points, the dehy-
dration of fructose into 5-HMF using DESs as media has
been developed, in which hydrogen bond can be formed by
organic acid or alcohol and fructose, and thus promote its
transformation rates [10]. For example, fructose dehydra-
tion using choline chloride (ChCl)-based DES as solvent and
sulfonated amorphous carbon–silica (SACS) as catalyst had
a 100% selectivity to 5-HMF [11]. ChCl and p-toluene sul-
fonic acid formed DES as both solvent and catalyst obtained
a 90.7% of 5-HMF yield [12]. Additionally, 5-HMF yield
also easily reached up to 90.0% in acid catalyzed processes
using ChCl-based DESs, but they took a long reaction time
[13–15]. In order to promote the efciency of fructose con-
version, acid–base bifunctional heteropolyacids (Ly2HPW)
showed a high 5-HMF yield of 92.3% in [ChCl/fructose]
DES after only 1 min [16]. Although ChCl is widely used as
HBA in these reported DESs, the stabilities of these DESs
are poor owing to HCl release during these prepared pro-
cesses [17]. Thus, the exploration of halogens free DESs for
efcient fructose dehydration is desirable.
In a typical run, 10 g of DES was added into a round-bot-
tomed fask and preheated to 100 °C using oil-bath, and
then 1.0 g of fructose was added with vigorous stirring
at 600 rpm. After the reaction, the reaction mixture was
quenched rapidly in order to prevent any further reactions,
diluted by distilled water, and then separated by centrifuga-
tion. In recycling experiments, 5-HMF was separated by liq-
uid–liquid extraction and ethyl acetate was used as extracting
agent. The remained liquid was treated by rotary evaporator
at 60 °C to remove water and ethyl acetate, and fnally the
DES was recovered. The solid by-product humin was washed
by distilled water twice and dried at 50 °C for 24 h.
For the liquid phase products, 5-HMF was analyzed using
LC-2010AHT SHIMADZU liquid chromatograph equipped
with a UV–vis detector recorded at 284 nm and a Benson
polymeric BP-OA column. The mobile phase was H2SO4
aqueous solution (pH=3) with fow rate of 0.8 mL/min and
the analysis was carried out at 45 °C for 40 min and quanti-
fed by external standard method. Fructose was conducted
by 1H NMR spectrometry in deuterium oxide at 25 °C [21,
22]. Each sample was detected with a spectral width of
20 ppm, a relaxation delay of 30 s, a scan number of 32,
and an acquisition time of 4 s. The fructose was determined
by internal standard method using dimethyl sulfoxide as an
internal standard.
Imidazole-based ILs were widely used as catalyst or/and
solvent in some chemical reactions [18, 19]. Herein, imi-
dazole (Im) and benzenesulfonic acid (BSA) were selected
to form halogens free DESs, whose formation process was
identifed in detail. The bifunctional Im-BSA DESs as both
catalyst and solvent were systemically investigated for the
3 Results and Discussion
3.1 Formation Process of DES
According to the two-step formation mechanism of imi-
dazole-based DES reported in our previous work [20], the
1 3

Bifunctional Imidazole-Benzenesulfonic Acid Deep Eutectic Solvent for Fructose Dehydration…
formation process of Im-BSA DES was assumed and experi-
mentally verified. Equimolar salt [Im:BSA] is obtained
through an acid–base neutralization between BSA and Im,
and subsequently corresponding DES is formed by the equi-
molar salt as HBA and excessive BSA as HBD.
and 7.05 ppm (single, 2H–C=CH–) are observed in Im
[24]. Notably, all hydrogens slightly shift to low magnetic
feld, which results from π–π conjugation between benzene
and imidazole rings for [Im:BSA] [25]. Relative to the
shifts of BSA, obvious downshifts of the chemical shifts
of the H2, H3, and H4 positions in the imidazole ring are
observed, which dominantly ascribes to the protonation of
Im in [Im:BSA] [26]. The results indicate that equimolar
salt [Im:BSA] is formed through an acid–base neutralization
between Im and BSA.
The prepared [Im:BSA], individual Im and BSA were
1
characterized by H NMR to investigate the formation of
equimolar salt. As shown in Fig. 1, the peaks at 7.66, 7.44,
and 7.40 ppm correspond to the chemical shifts of H5 (dou-
blet, –C=CH–), H6 (triplet, –C=CH–), and H7 (triplet, 2H,
–CH=C–) in BSA, respectively [23]. The chemical shifts of
H2, H3 and H4 positions at 7.68 ppm (single, N=CH–N)
Figure 2 shows FT-IR spectra of Im, BSA, equimolar salt
[Im:BSA], and DES [Im:1.5BSA]. Stretching peak of C=N
in Im is observed at around 1670 cm−1, while the reduced
intensity in [Im:BSA] indicates the protonation of Im [27].
The peak of S=O stretching vibration located at 1229 cm−1
in BSA splits into two sharp peaks at 1223 and 1177 cm−1
in [Im:BSA], which is caused by the electrostatic interaction
between sulfonate group and imidazolium cation [28]. These
changes also illustrate the acid–base neutralization between
Im and BSA. Then, DES is formed by interaction of equimo-
lar salt and excess BSA. Thus, we can observe the peak shift
from 1177 cm−1 in [Im:BSA] to 1166 cm−1 in [Im:1.5BSA],
which indicates the formation of hydrogen bond between
BSA and equimolar salt [29]. The bending vibration of N–H
at 902 cm−1 in [Im:BSA] shifted to a lower wavenumber of
891 cm−1 in [Im:1.5BSA] also confrms the strong interac-
tion between Im+ and BSA [30, 31]. The results demonstrate
the strong interaction between equimolar salt and BSA, and
the formation of DES [Im:1.5BSA].
3.2 Properties of DES
Fig. 1 1HNMR spectra of a Im, b BSA, and c equimolar salt
The acidity of catalyst is a crucial factor to infuence cata-
lytic performance of fructose dehydration. Thus, pH value
[Im:BSA]
Fig. 2 FT-IR spectra of a Im,
b BSA, c [Im:BSA], and d
[Im:1.5BSA]
1 3

C. Ruan et al.
in aqueous solution (1 mol/L) was measured to evaluate
the acidity of Im-BSA DESs at diferent molar ratios. The
equimolar salt is a very weak acid (pH=5.16), while DESs
present strong acidity owing to the presence of excessive
BSA. For example, with increased BSA content of DESs,
the pH values of [Im:1.1BSA] and [Im:1.5BSA] drop to 1.46
and 0.97, respectively. With further increase in BSA content
up to [Im:2BSA], pH value slightly reduces to 0.70. There-
fore, the acidity can enhance with increased BSA content of
DESs, which indicates that BSA rich DESs may be suitable
for the dehydration of fructose to 5-HMF.
located in both HBA and HBD regions indicates the strong
ability to form hydrogen bond between fructose and either
molecules with polar region. Accordingly, complicated
hydrogen bond network can be formed among fructose,
[Im:BSA], and BSA-rich DESs. As a result, fructose is read-
ily soluble in [Im:BSA] and BSA-rich DESs, and fructose
dehydration may be improved owing to the solvent efect
of DESs. Similarly, there are peaks in both polar regions
for 5-HMF, so hydrogen bond can also be formed between
5-HMF and [Im:BSA] or BSA-rich DESs.
The stability of DESs is also vital from the viewpoint
of reaction operation. Representatively, the mass loss of
[Im:1.5BSA] was determined by thermogravimetric analy-
sis (TGA, Fig. 4) under a nitrogen fow of 200 ml/min. The
total weight loss can be divided into four parts from 40 to
600 °C. The weight loss at the frst stage below 145 °C is
8.5%, ascribing to physically adsorbed moisture [36]. There
is almost no weight loss in the second part from 145 to
238 °C, indicating the thermal stability of [Im:1.5BSA]. It
starts to decompose through two stages owing to organic
groups in DES. Therefore, the prepared DES is potential to
be used as catalyst and solvent under reaction temperature
below 238 °C.
The solvation ability of DES and fructose was also ana-
lyzed by conductor-like screening model for real solvents
(COSMO-RS), which is an efcient tool to investigate inter-
action among discussed molecules. In COSMO-RS theory,
σ-profle is commonly divided into three regions (Fig. 3),
HBD region at − 0.03 ~ − 0.0084 e/Å2, HBA region at
0.0084–0.03 e/Å2, and non-polar region at 0.0084–0.0084
e/Å2 [32, 33]. Moreover, the deeper color means the stronger
HBA (red) and HBD (blue) ability. Thus, as one of the most
signifcant characteristic in COSMO-RS, the polarity of Im+,
BSA−, BSA, fructose, and 5-HMF can be described by their
σ-profles.
BSA has one wide peak in HBD region and one large
peak close to the boundary of nonpolar and HBA region,
indicating its strong HBD and very weak HBA abilities,
respectively. BSA− dominantly distributed in HBA region
indicates strong HBA ability and Im+ only illustrates HBD
ability. Thus, strong hydrogen bond between BSA and
BSA− of equimolar salt and weak hydrogen bond between
BSA and Im+ can be formed, confrming the aforementioned
FT-IR analysis.
3.3 Catalytic Activity for Fructose Dehydration
Fructose can be dehydrated to 5-HMF in the presence of var-
ious acid catalysts such as mineral acids, organic acids, solid
acids, etc. [37]. Thus, BSA-rich DESs with suitable acidity
and solvation ability were applied to catalyze the dehydra-
tion of fructose to 5-HMF. The efect of reaction time on
fructose dehydration was investigated with mass ratio (10:1)
of [Im:1.5BSA] to fructose under a reaction temperature of
100 °C. As shown in Fig. 5, a 66.1% yield of 5-HMF and a
70.1% of fructose conversion are obtained after only 1 min
As for fructose, its solubility in DES is also mainly asso-
ciated with hydrogen bond [34, 35]. Two pronounced peaks
Fig. 3 σ-Profles of Im+, BSA−, BSA, fructose, and 5-HMF
Fig. 4 TGA curve for [Im:1.5BSA]
1 3

Bifunctional Imidazole-Benzenesulfonic Acid Deep Eutectic Solvent for Fructose Dehydration…
[ChCl:4phenol] as solvent and SACS as catalyst (Table 1,
entry 1) [11]. The reaction time is reduced to 60 min using
DES [ChCl:p-TSA] as both solvent and catalyst (Table 1,
entry 2) [12]. In another strategy, fructose as both reac-
tant and one component of formed DES together with
ChCl, reaction time depends on applied catalysts (Table 1,
entries 3–5) [13, 14, 16]. Notably, 5-HMF yield is high up
to 92.3% after the reaction time of 1 min (Table 1 entry
5), but the catalyst preparation of Ly2HPW is especially
complicated [16]. Here, bifunctional DES [Im:1.5BSA]
as both catalyst and solvent shows high catalytic activ-
ity with a 5-HMF yield (90.1%) under the reaction time
of only 3 min (Table 1, entry 6). As for solvent efect,
the existence of hydrogen bond between sulfonic group
and fructose plays important roles to efciently promote
the reaction rate of fructose dehydration and improve the
catalytic activity [39, 40]. Moreover, the acidity of the
catalyst has a vital infuence on fructose dehydration [40,
41]. [Im:1.5BSA] with the strong acidity would be respon-
sible for its high catalytic activity with high 5-HMF yield.
Herein, we fnd that the acidity of BSA-Im DES is tun-
able by changed molar ratio of Im to BSA. Therefore, the
efect of DES acidity on fructose conversion and 5-HMF
yield was investigated to gain optimal Im:BSA molar ratio.
As illustrated in Fig. 6, [Im:1.5BSA] with pH value of 0.97
shows the best catalytic performance with the highest yield
of 90.1% and fructose conversion of 95.1% in 3 min, while
the maximum yield of [Im:1.1BSA] and [Im:1.3BSA] are
78.2% and 83.4% within 7 and 5 min, respectively. Equi-
molar salt [Im:BSA] has negative catalytic activity for
fructose dehydration and couldn’t activate the reaction due
to its very weak acidity. Meanwhile, the reaction rate is
also promoted with increased BSA content of DESs. The
conversion rate of fructose using [Im:1.5BSA] is far higher
than those of [Im:1.3BSA] and [Im:1.1BSA]. However,
continuous increase in BSA content up to [Im:1.7BSA],
the maximum yield of 5-HMF decreases to 84.3% and
fructose conversion is similar to that of [Im:1.5BSA]. The
result indicates that humin may be also promoted in a par-
ticularly high acidity of the reaction system.
Fig. 5 Time course study for fructose dehydration. Reaction condi-
tions: 1 g of fructose and 10 g of [Im:1.5BSA] at 100 °C
and indicate that the prepared DES is highly active for fruc-
tose dehydration to 5-HMF. With prolonging reaction time
to 3 min, fructose conversion increases to 95.1% and 5-HMF
yield reaches the maximum value (90.1%). Fructose con-
version maintains constant with continual prolongation of
reaction time, while 5-HMF yield gradually decreases due
to the polymerization of 5-HMF through aldol condensa-
tion to humin and oligomeric precursors [38]. No levulinic
acid and formic acid is detected because DES can prevent
5-HMF from further rehydration [11]. In addition, humin
yield gradually increases with increased reaction time, which
indicates that [Im:1.5BSA] as acid catalyst preferentially
catalyzes high concentrated 5-HMF into humin rather than
residue fructose.
In addition, the reaction time of fructose dehydration
is greatly reduced to 3 min and more efcient than previ-
ously reported from reaction rates (Table 1). Many stud-
ies have reported that catalytic performance of fructose
dehydration is closely related to employed catalysts and
reaction media, i.e. solvation efect of DESs [39–41]. A
67.0% of 5-HMF yield can be obtained after 240 min using
Table 1 DESs-based system for
Entry
Catalytic system
Temperature Time (min)
(°C)
Yield (%)
References
the dehydration of fructose to
5-HMF
1
2
SACS/[ChCl:4phenol]
[ChCl:p-TSA]
HCl/[ChCl:fructose]
Amberlyst-15/[ChCl:fructose]
Ly2HPW/[ChCl/fructose]
[Im:1.5BSA]
110
80
100
100
110
100
240
60
240
120
1
67.0
90.7
90.3
94.2
92.3
90.1
[11]
[12]
[13]
[14]
[16]
This work
3
4a
5
6
3
aIn the DES/MeCN (methyl cyanide) biphasic system
1 3

C. Ruan et al.
When pure BSA is used as catalyst, the maximum yield
of 5-HMF is only 29.1%. Im and fructose can form DES
and no catalytic activity for fructose dehydration has ever
been detected [42]. It is worthwhile to note that fructose
conversion in pure BSA is lower than [Im:1.5BSA] and
[Im:1.7BSA] due to the fact the ability of hydrogen bond
between BSA and fructose is lower than that between DES
and fructose, which can be clearly seen in σ-profles (Fig. 3).
Therefore, bifunctional BSA-rich DESs as acid catalyst and
solvent intensively infuence reaction rates and catalytic
activities of fructose dehydration via tuned acidity of DESs
and hydrogen bond interaction among fructose, 5-HMF, and
DESs.
The acidity of DESs has a vital efect on catalytic perfor-
mance of fructose dehydration. Thus plausible mechanism
for fructose dehydration in acidic medium can be proposed
(Fig. 7). The frst step is the protonation of tertiary hydroxyl
group of fructose [43]. In BSA rich DESs, the hydrogen
proton from SO3H group of BSA can activate the dehydra-
tion reaction, which is followed by the release of H2O mol-
ecule. Thus the intermediate, furanosyl oxocarbenium ion
is formed. Then BSA− anion as a nucleophile attacks C2
position of fructose, and the intermediate is deprotonated
to form an enol, which is subsequently converted into alde-
hyde through keto-enol tautomerism [44]. Finally, two H2O
molecules are eliminated to produce 5-HMF.
The efect of reaction temperature ranging from 80 to
110 °C on fructose conversion and 5-HMF yield was studied
using the optimized bifunctional [Im:1.5BSA]. As shown
in Fig. 8, with an increase in the reaction temperature from
80 to 100 °C, the rate of fructose conversion increases, the
maximum yield of 5-HMF enhances from 80.2 to 90.1% and
the optimal reaction time is also reduced. Generally, high
reaction temperature can efciently promote reaction rate of
fructose dehydration to 5-HMF, leading to high 5-HMF yield
and reduced reaction time. Further raising the reaction tem-
perature to 110 °C, the maximum yield of 5-HMF decreases,
Fig. 6 Efect of DES acidity on a 5-HMF yield and b fructose con-
version. Reaction conditions: 1 g of fructose and 10 g of DES at
100 °C
Fig. 7 Proposed mechanism for the dehydration of fructose to 5-HMF
1 3

Bifunctional Imidazole-Benzenesulfonic Acid Deep Eutectic Solvent for Fructose Dehydration…
Fig. 9 Efect of fructose loading amount on fructose conversion and
5-HMF yield. Reaction conditions: 10 g of [Im:1.5BSA] at 100 °C for
3 min
attributed to high 5-HMF concentration in reaction mixture
caused by initial high fructose concentration, which leads to
the occurrence of unwanted side reactions [12, 39].
The recycling experiments were conducted using recov-
ered [Im:1.5BSA] under consistent reaction conditions, simi-
lar to fresh DES. However, 5-HMF yield decreases to 85.1%,
which can be ascribed to the fact that a small amount of BSA
should be extracted into extracting agent, when 5-HMF was
separated from DES using liquid–liquid extraction resulting
in a decrease of DES acidity. In prospective work, efcient
separation technique should be focused and investigated to
recover DES in order to reduce the loss of BSA in DESs.
Fig. 8 Efect of temperature on a 5-HMF yield and b fructose con-
version. Reaction conditions: 1 g of fructose and 10 g of [Im:1.5BSA]
while the rate of fructose conversion maintains increasing
and the optimal reaction time continues to decrease. It is
known that high reaction temperature can improve reaction
rates including fructose conversion and parasitic products,
humin and soluble polymers [45]. Furthermore, the hydro-
gen bond interaction between DES and 5-HMF for stabiliz-
ing 5-HMF and inhibiting side reactions would be broken at
the elevated temperature, which makes the polymerization
of 5-HMF easy and results in fast decrease of 5-HMF [46].
Substrate to catalyst or solvent ratio (wt/wt) is an impor-
tant parameter, which can refect the efciency of substrate
(fructose) conversion (Fig. 9). With increased weight ratio
of fructose to [Im:1.5BSA] from 1:10 to 1:2.5, fructose
conversion decreases from 95.1% to 82.0%, which could be
due to insufcient hydrogen proton released by [Im:1.5BSA]
for activating fructose dehydration. Meanwhile, a signif-
cant reduction can be observed in 5-HMF yield from 90.1 to
55.1%, indicating that high fructose loading would defnitely
infuence 5-HMF yield and selectivity. The reason may be
4 Conclusions
Bifunctional Im-BSA DESs as catalyst and solvent are inves-
tigated for fructose dehydration to 5-HMF. The formation
process of DESs is identifed by the formation of equimolar
salt [Im:BSA] and subsequent DESs from [Im:BSA] and
excessive BSA through hydrogen bond interaction. The acid-
ity of DESs can be tuned by adjusting molar ratio of Im to
BSA. The solvent efect of DESs is due to hydrogen bond
formation between Im+ and/or BSA− species of DES and
fructose. Thus, bifunctional BSA-rich DESs as acid cata-
lyst and solvent can efciently promote reaction rate and
catalytic activity of fructose dehydration via tuned acidity
of DESs and hydrogen bond interaction among fructose,
5-HMF, and DESs. In all, the bifunctional [Im:1.5BSA] for
highly active dehydration of fructose to 5-HMF provides a
perspective for the preparation of potential DESs and their
practical applications in the dehydration of fructose.
1 3

C. Ruan et al.
bifunctional HPA nanocatalysts induced by choline chloride. RSC
Adv 4:63055–63061
Acknowledgements The fnancial support from Shanghai Municipal
Natural Science Foundation (Grant No. 19ZR1412500) and National
Natural Science Foundation of China (Grant No. 21776074) is greatly
acknowledged.
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Compliance with Ethical Standards
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Conflict of interest The authors declare no conficts of interest.
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