Effective conversion sucrose into 5-hydroxymethylfurfural by tyrosine in [Emim]Br

Article abstract of DOI:10.1016/j.molcata.2013.09.003

In this study, the synthesis of 5-hydroxymethylfurfural (5-HMF) from sucrose was carried out in ionic liquids 1-ethyl-3-methylimidazolium bromide ([Emim]Br) catalyzed by amino acids, and tyrosine displays the best activity. Under the optimal reaction conditions, 76.0% yield of 5-HMF from sucrose was obtained at 160 C for 4 h. The uniquely effective activity of tyrosine for sucrose conversion into 5-HMF in [Emim]Br is mainly attributed to its two types of active sites, free base NH₂ and dissociated H⁺ sites. The former one plays a crucial role in the isomerization of glucose to fructose, and the latter one is active in the hydrolysis of sucrose into monosaccharides and dehydration of generated fructose to 5-HMF. Furthermore, the presence of acidic phenol group in tyrosine also has the synergic catalytic effect on sucrose conversion. In addition, with the use of tyrosine catalyst, other carbohydrates to form 5-HMF were also tested, and the effects of solvent, reaction temperature and reaction time on sucrose conversion into 5-HMF were investigated in detail. A possible mechanism for this catalytic process has been proposed.

Full text of DOI:10.1016/j.molcata.2013.09.003

Journal of Molecular Catalysis A: Chemical 379 (2013) 350–354
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Effective conversion sucrose into 5-hydroxymethylfurfural by
tyrosine in [Emim]Br
Kunmei Sua,∗, Xin Liua, Min Dinga, Qiuju Yuana, Zhenhuan Lib,∗, Bowen Chengb,∗
a School of Environment Science and Chemistry Engineering, and Tianjin Key Lab of Fiber Modification & Functional Fiber, Tianjin Polytechnic University,
300160 Tianjin, China
b School of Materials Science and Engineering, Tianjin Polytechnic University, 300160 Tianjin, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, the synthesis of 5-hydroxymethylfurfural (5-HMF) from sucrose was carried out in ionic
liquids 1-ethyl-3-methylimidazolium bromide ([Emim]Br) catalyzed by amino acids, and tyrosine dis-
plays the best activity. Under the optimal reaction conditions, 76.0% yield of 5-HMF from sucrose was
obtained at 160 ◦C for 4 h. The uniquely effective activity of tyrosine for sucrose conversion into 5-HMF
in [Emim]Br is mainly attributed to its two types of active sites, free base NH2 and dissociated H+ sites.
The former one plays a crucial role in the isomerization of glucose to fructose, and the latter one is active
in the hydrolysis of sucrose into monosaccharides and dehydration of generated fructose to 5-HMF. Fur-
thermore, the presence of acidic phenol group in tyrosine also has the synergic catalytic effect on sucrose
conversion. In addition, with the use of tyrosine catalyst, other carbohydrates to form 5-HMF were also
tested, and the effects of solvent, reaction temperature and reaction time on sucrose conversion into
5-HMF were investigated in detail. A possible mechanism for this catalytic process has been proposed.
© 2013 Elsevier B.V. All rights reserved.
Received 13 February 2013
Received in revised form 25 August 2013
Accepted 4 September 2013
Available online 13 September 2013
Keywords:
5-Hydroxymethylfurfural
Tyrosine
Sucrose
Amino acids
Biomass conversion
1. Introduction
salts [5,15], acidic ionic liquid [16–19], strong acid cation exchange
resins [1,10,20,21], zeolites [19,22] and supported heteropolyacids
5-hydroxymethylfurfural (5-HMF) and its derivatives obtained
from renewable biomass resources have the potential to serve as
substitutes for the petroleum-based building blocks that are cur-
rently used in the production of plastics and fine chemicals [1–4].
Up until now, different feedstocks have been used to produce 5-
HMF, including fructose [1,3,4], glucose [3–5], maltose [6], sucrose
[6–8], cellobiose [7–9], inulin [6–8], starch [6,7], cellulose [5,6,9,10]
and raw lignocellulosic biomass [5,9–11]. However, only fructose
can be well converted into 5-HMF by acid catalyzed dehydration
[4,12]. There is no doubt that the direct use of abundantly available
sucrose for the large-scale production of 5-HMF would be a better
ideal.
Generally, conversion of sucrose to 5-HMF involves two steps,
namely, sucrose rapidly hydrolyze to monosaccharide glucose and
fructose followed by the dehydration of fructose and glucose to
give 5-HMF [4]. The dehydration of fructose can be well catalyzed
by strong acids, such as mineral acids and organic acids [1,9,13,14],
[13]. However, those acid catalysts have low activity in glucose
conversion to 5-HMF because they are unfavorable of glucose
insomerization into fructose.
The catalysts of Bronsted bases or Lewis acids are commonly
used for glucose isomerization to fructose [23–27]. However, inor-
ganic bases can reduce stability of monosaccharides and typically
lead to side reaction [5]. Chun et al. [28] produced 5-HMF effi-
ciently (82 3.9 wt%) from sucrose using [omim][Cl] as a reaction
solvent with HCl and chromium catalyst. When zinc chloride/HCl
as a catalyst, 5-HMF yield only reached 58 2.7%. Han et al.
[9] screened a number of metal chlorides for the conversion of
sucrose, and they identified tin chloride as a potentially interest-
ing catalyst. Compared with fructose, sucrose are more difficult to
convert into 5-HMF, but only potentially toxic metals (Cr chlo-
rides) resulted in a better catalytic performance. Therefore, the
development of a non-toxic and efficient catalytic systems for
the conversion of sucrose to 5-HMF has become a challenge
topic.
Amino acids are well-known acid–base bifunctional com-
pounds, and ionic liquids (ILs) have been proven to be excellent
solvents for carbohydrate conversion [4,5]. Herein, we used
acid–base bifunctional amino acid as green catalyst to convert
sucrose to 5-HMF in ionic liquid [Emim]Br, and the sucrose con-
version process via tyrosine was well studied.
∗
Corresponding authors at: School of Materials and Chemical Engineering, Tianjin
Polytechnic University, Tianjin 300160, China. Tel.: +86 022 83955358;
fax: +86 022 83955055.
E-mail addresses: Sukunmei@tjpu.edu.cn (K. Su),
Zhenhuanli1975@yahoo.com.cn, zhenhuanli@sohu.com (Z. Li),
bowen15@tjpu.edu.cn (B. Cheng).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.09.003

K. Su et al. / Journal of Molecular Catalysis A: Chemical 379 (2013) 350–354
351
Table 1
2. Experimental
Catalytic conversion of sucrose into 5-HMF over various amino acid catalysts.
2.1. Materials
Amino acid
Isoelectric points
5-HMF yield (mol%)
Glycine
Alanine
Valine
Leucine
5.97
6.02
5.97
5.98
6.02
6.3
5.70
9.74
3.22
5.02
5.06
5.68
5.67
5.88
20.6
19.1
30.7
33.5
4.55
2.86
43.6
38.7
3.45
25.6
42.4
30.8
76.0
28.4
Sucrose (99%), 5-HMF, N,N-dimethylformamide (DMF), N-ethyl
bromide(>99%), 1-methylimidazole (>99%), morpholine, pyridine,
SnCl4, TiCl4, CrCl2, CrCl3, benzenesulfonic acid, leucine, tyrosine,
tryptophan, proline and the rest of amino acids were purchased
with analysis reagents degree.
Isoleucine
Proline
Glutamine
Lysine
Glutamic acid
Cysteine
Methionine
Serine
Tyrosine
Tryptophan
2.2. Preparation of the ionic liquids (ILs) and catalyst
[Emim]Br was synthesized from the reaction of 1-
methylimidazole with ethyl bromide at 25 ◦C for 24 h. The
synthesis [Emim]Br was purified by acetonitrile and ethyl acetate
to wipe off the residual ethyl chloride and 1-methylimidazole,
and the purified [Emim]Br was dried in vacuum drying oven at
70 ◦C for 24 h. [Bmim]Br synthesis from n-butyl bromide and
1-methylimidazole, [Emor]Br synthesis from ethyl bromide and
morpholine and [EPy]Br synthesis from ethyl bromide and pyridine
followed above process.
H2SO4/ZrO2 and H2SO4/Al2O3 solid acid catalysts were pre-
pared by impregnation method. The active component H2SO4 was
introduced by impregnation of the supports with aqueous solutions
of H2SO4 (1 mol/L). The impregnation lasted for 24 h, and then cat-
alysts were dried at 120 ◦C in air for 4 h, and further calcined at
550 ◦C in air for 4 h.
Conditions: 0.9 g sucrose, 0.49 mmol catalyst, 5 mL [EMIM] Br, 160 ◦C, 4 h.
yield was obtained over isoleucine. The biggest difference between
leucine and isoleucine was their inequable steric hindrance. There-
fore the low catalytic activity of isoleucine might be attributed to its
high steric hindrance. The hydrolysis of sucrose into monosaccha-
ride and the dehydration of fructose to 5-HMF can be well catalyzed
by acid groups, but acidic glutamic acid showed near no activity for
5-HMF synthesis although it contains two carboxylic acids, how-
ever, alkaline lysine can display well activity for sucrose conversion
into 5-HMF.
2.3. Typical experimental procedure
In order to explore the different catalysis of the weak acid
tyrosine, acidic glutamic acid and alkaline lysine in the hydroly-
sis of sucrose into glucose and fructose, isomerization of glucose
to fructose and conversion of fructose to 5-HMF, the different
ionic forms of three amino acids in [Emim]Br solution were
studied. In neutral [Emim]Br solution, the weak acid tyrosine
was ionized into HOPhCH2CH(NH2)COO− and dissociated H+,
but glutamic acid mainly existed in HOOCCH(NH3+)CH2CH2COO−
form, which is due to [Emim]Br pH (6.8–7.1) > pI (the isoelec-
tric point of tyrosine and glutamic acid). Alkaline lysine changed
into H3N+(CH2)4CH(NH2)COO− in [Emim]Br because of [Emim]Br
pH < pI (the isoelectric point of alkaline lysine). Those results
indicated the uniquely effective activity of tyrosine for sucrose con-
version into 5-HMF in [Emim]Br is mainly attributed to its two
types of active sites, free base NH2 and dissociated H+ sites. The
former one plays a crucial role in the isomerization of glucose to
fructose, and the latter one is active in the hydrolysis of sucrose
into monosaccharides and dehydration of generated fructose to 5-
HMF. Furthermore, the presence of acidic phenol group in tyrosine
also has the synergic catalytic effect on sucrose conversion.
The catalytic experiments were performed in the 20 mL flask. In
a typical experiment, 0.9 g sucrose and 0.49 mmol catalysts were
added into 5 mL solvent. After reaction system had been purged
with nitrogen, the reaction mixture was heated in an oil-bath at
160 ◦C for 4 h. After the desired reaction time elapsed, reaction
mixture was cooled to room temperature immediately.
2.4. HMF yield characterization
All reaction products were analyzed by the high perfor-
mance liquid chromatograph (Waters1525 equipped with UV
and a 996 photodiode array detector) and quantified with 1-
chloronaphthalene as interior standard (or calibration curves
generated from commercially available standards). Following a
typical reaction, the product mixture was diluted with 50 mL
CH3OH, centrifuged to sediment insoluble products, and 0.05 mol
1-chloronaphthalene was added into the product solution to
analyze. The concentrations of products were calculated from
HPLC-peak integrations. 5-HMF yield was based on sucrose loading,
and 1-chloronaphthalene was used as interior standard to calculate
5-HMF molar yields.
3.2. Catalytic conversion of sucrose to 5-HMF over various amino
acid at different temperature in [Emim]Br
moles of 5-HMF
2 moles of sucrose
5-HMF yield (mol%) =
× 100%
Here, catalytic conversion of sucrose to 5-HMF over various
amino acid at different temperature in [Emim]Br was well tested
(Fig. 1). Reactions were carried out at different temperature which
ranges from 80 to 180 ◦C, and the optimized temperature for
sucrose conversion to 5-HMF is from 140 to 160 ◦C. 80 ◦C is an
unsuitable temperature for sucrose conversion because at this tem-
perature the rate of sucrose hydrolysis and fructose dehydration is
very slow. Tyrosine can well catalyze 5-HMF synthesis from sucrose
at 120–180 ◦C, and 5-HMF yield achieved maximum 76.0% at 160 ◦C
for 4 h. As for all the used amino acid catalysts, 5-HMF yield signif-
icantly declined at 180 ◦C. In addition, valine and glycine can also
show better activity at low temperature (100–120 ◦C).
3. Results and discussion
3.1. Catalytic conversion of sucrose into 5-HMF over various
amino acid catalysts
The various amino acids were used to catalyze sucrose conver-
sion to 5-HMF at 160 ◦C, and results were summarized in Table 1.
Among the used amino acids, tyrosine effectively promoted 5-HMF
synthesis from sucrose, and 5-HMF yield achieved 76.0%. Although
isoleucine and leucine are isomer, leucine displayed high activ-
ity in sucrose conversion into 5-HMF, however, only 4.6% 5-HMF

352
K. Su et al. / Journal of Molecular Catalysis A: Chemical 379 (2013) 350–354
80
70
80
70
60
50
40
30
20
10
0
A
A
Cysteine
Alanine
60
50
40
30
20
10
0
Methionine
Serine
Tyrosine
80
100
120
140
160
180
50
45
40
35
30
25
20
15
10
5
Valine
B
Glutamine
Glycine
Leucine
Lysine
80
70
60
50
40
30
20
10
0
B
0
80
100
120
140
160
180
Temperature (oC)
Fig. 1. 5-HMF yield from sucrose catalyzed by different amino acid catalysts in
[Emim]Br at various temperature (conditions: 0.9 g sucrose; 0.49 mmol catalyst;
5 mL [Emim]Br solvent; 160 ◦C, 4 h).
Fig. 2. (A) 5-HMF yield from sucrose over different catalysts in [EMIM] Br (condi-
tions: 0.9 g sucrose, 0.49 mmol catalyst, 5 mL [EMIM] Br, 160 ◦C, 4 h); (B) 5-HMF yield
from different substrates over l-tyrosine in [EMIM] Br (conditions: 0.9 g substrate,
0.49 mmol catalyst, 5 mL [EMIM] Br, 160 ◦C, 4 h). 120 indicated 120 ◦C reactions.
3.3. Catalytic conversion of different carbohydrates to 5-HMF
over various catalysts
Tyrosine, metal chlorides and supported acids et al. were used
to catalyze sucrose conversion to 5-HMF at 160 ◦C (Fig. 2A). 5-HMF
yields catalyzed by CrCl2 and SnCl4 were less than 25% at 160 ◦C, and
those can be improved to 36.9% and 38.9% by the decline of reaction
temperature to 120 ◦C because CrCl2 and SnCl4 can catalyze 5-
HMF degradation into levulinic acid at high temperature. Although
SO42−/ZrO2–Al2O3 catalyst was found to act as a bifunctional cata-
lyst with high activity for both hydrolysis and dehydration of starch
[29], low 5-HMF yields of 24.3% and 20.1% were obtained over
H2SO4/ZrO2 and H2SO4/Al2O3, respectively. Among the used cat-
alysts, only tyrosine can effectively catalyze 5-HMF synthesis from
sucrose under same conditions.
We also tested tyrosine catalyst for catalyzing other carbohy-
drates to form 5-HMF (Fig. 2B), and results demonstrated that
tyrosine was uniquely effective to convert sucrose into 5-HMF
while it showed less activity to convert cellulose, cellobiose, lac-
tose and maltose to 5-HMF even at 160 ◦C, which was attributed to
the difference structure of various carbohydrates. In maltose, cel-
lobiose, galctose and cellulose, the monosaccharide units are joined
by 1,4-glycosidic bond which was rather more difficult hydrolysis
than that of 1,2-glycosidic bond. The reasons for that is the glycoside
hydrolysis of disaccharide and polysaccharide to monosaccharide
units via the carbocation are reversible (Scheme 1) and the high sta-
bility of carbocation intermediate of furanose rings (glucose rings
was less stability) is responsible for sucrose 1,2-glycosidic bond
easy cleavage [30,31].
The dehydration of fructose and glucose was also studied by
using tyrosine catalyst in [Emim]Br system. It can be seen that
72.1% yield of 5-HMF was obtained from the dehydration of fruc-
tose, while the yield of 5-HMF from the dehydration of glucose is
only 38.1% because glucose isomerization is a crucial step [32]. This
results suggested that amino group play a crucial role in the isomer-
ization of glucose to fructose and Brønsted COOH acid groups can
well catalyze fructose dehydration to 5-HMF (Scheme 2).
5-HMF yield directing from sucrose achieved 76.0%, but this
result was much better than 5-HMF yield from the mixture of
fructose and glucose (1:1 mol) under same conditions. On the
HOH2C
HO
OH
CH2OH
O
H
2
HO
HO
HOH2C
O
H2O
+
H2O
O
1
H
OH
HO
HOH2C
HO
Stable carbocation
HOH2C
HO
1
OH
OH
CH2OH
O
O
H
HO
HO
HO
H+
H+
fast
CH2OH
fructose
OH
OH
Glucose
slow
HOH2C
HO
2
O
H
HOH2C
HO
1
OH
OH
HOH2C
slow
HO
fast
O
O
CH2OH
H
HO
HO
1
O
O
H
CH2OH
4
OH
O
HO
β-Glycoside bond to
anomeric position
OH
OH
α-Glycoside bond to
anomeric position
O
β-Glycoside bond to
anomeric position
HO
Sucrose
H2O
O
Cellobiose
H2O
Scheme 1. 5-HMF synthesis process from sucrose and cellobiose in presence of bifunctional catalyst [31,32].

K. Su et al. / Journal of Molecular Catalysis A: Chemical 379 (2013) 350–354
353
H
H2O
H
H
O
N
R
H
HO
H
OH
H
amino acid
base group of
amino acid
OH
OH
CH 2OH
HO
H
HOH 2C
OH
CH 2OH
O
O
H
HO
HO
HO
CH 2OH
HOH 2C
HO
HO
OH
+
OH
HO
O
H
1
fructose
OH
CH 2OH
H
Glucose
O
2
O
OH
O
OH
H
CH 2OH
HO
Sucrose
amino acid
HO
H
H
OH
OH
amino acid
H2O
CH 2OH
O
O
isomerization
H
dehydration
O
OH
H
acid group
HO
OH
O
H
OH
OH
CH 2OH
O
OH
HO
H
H
HO
H
H
H
OH
OH
OH
H
H
OH
H
OH
acid group
CH 2OH
fructose
Scheme 2. Sucrose cleavage and glucose isomerization in presence amino acid catalyst.
basis of those results one can hypothesize that there must exist
the synergistic effects between glycosidic bond hydrolysis and
monosaccharide dehydration. Namely, the glycosidic bond cleav-
age reaction was initiated by the trace water in ionic liquid, and
then fructose and glucose were dehydrated to give H2O. A part of
H2O was subsequently consumed by the glycosidic bond hydrol-
ysis, which kept 5-HMF yield decline from loss to levulinic acid
by minimizing 5-HMF exposure to H2O at elevated temperatures
(Scheme 2).
and [EPy]Br. For basic solvent DMF, low 5-HMF yield 27.7% was
obtained. It seems that the basic solvent inhibited the formation of
5-HMF, which should be probably due to the neutralization of the
acid sites in tyrosine the by the basic DMF. DMSO is another better
solvent for 5-HMF synthesis, and 5-HMF yield increased to 59.0%.
Among [Emim]Br, [Bmim]Br, [Emor]Br and [EPy]Br, [Emim]Br is
the best solvent for sucrose conversion, and 5-HMF yield achieved
76.0%, but [Emor]Br and [EPy]Br are unfavorable of 5-HMF synthesis
at high temperature due to their low decomposition temperature.
Although [Bmim]Br was a homologue of [Emim]Br, much lower 5-
HMF was obtain in [Bmim]Br because the ILs with a shorter-chain
cation have a larger dissolving ability than those with a longer-
chain cation when their anions are identical. These results are
consistent with those reported in the literature [33–35]. In addi-
tion, the trace of 1-methylimidazole excision in ionic liquid will
deteriorate 5-HMF synthesis.
3.4. Effect of solvent on sucrose conversion to 5-HMF
Experiments conducted in different solvents (Fig. 3) offer insight
about the role of solvents in converting sucrose into 5-HMF. The
conversion of sucrose into 5-HMF was demonstrated in many
solvents including [Emim]Br, [Bmim]Br, DMSO, DMF, [Emor]Br
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
[Emim]Br
[Bmim]Br
DMSO
DMF
[Emor]Br
[EPy]Br
2h
4h
6h
8h
Solvents
Time (h)
Fig. 3. 5-HMF yield from sucrose catalyzed by tyrosine in various solvent (condi-
Fig. 4. 5-HMF yield from sucrose catalyzed by tyrosine in various time (conditions:
tions: 0.9 g sucrose, 0.49 mmol catalyst, 5 mL solvent, 160 ◦C, 4 h).
0.9 g sucrose, 0.49 mmol catalyst, 5 mL [Emim]Br solvent, 160 ◦C).

354
K. Su et al. / Journal of Molecular Catalysis A: Chemical 379 (2013) 350–354
3.5. The effect of reaction time on the conversion of sucrose to
5-HMF
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4. Conclusions
Tyrosine shows the uniquely effective activity for sucrose con-
version into 5-HMF, and 5-HMF yield from sucrose achieved 76.0%.
The optimized temperature for sucrose conversion to 5-HMF by
amino acids ranges from 140 to 160 ◦C, and the high effective activ-
ity of tyrosine is mainly attributed to its free NH2, dissociated H+
and the presence of acid phenol group. Base NH2 group plays a
great role in glucose isomerization to fructose, and Brønsted COOH
acid group catalyze sucrose hydrolysis and fructose dehydration.
1,2-glycosidic bond is more easily hydrolyzed than 1,4-glycosidic
bond, which results in tyrosine showing higher activity in sucrose
conversion into 5-HMF. In the sucrose conversion to 5-HMF, a part
of H2O formed from fructose and glucose dehydration was subse-
quently consumed by the glycosidic bond hydrolysis, which keeps
5-HMF yield decline from loss to levulinic acid by minimizing 5-
HMF exposure to H2O at elevated temperatures. The basic solvent
inhibits the formation of 5-HMF due to the neutralization of the
acid sites by basic solvent, and neutral [Emim]Br is the best solvent
for sucrose conversion into 5-HMF.
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Acknowledgements
The authors are grateful for the financial support of the National
and Tianjin Natural Science Foundation of China (nos. 21006071,
30900092 and 12JCZDJC29800).
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