Conversion of glucose in CPL-LiCl to 5-hydroxymethylfurfural

Article abstract of DOI:10.1002/cjoc.201090299

5-Hydroxymethylfurfural (HMF), an important versatile sugar derivative, is also considered a key intermediate between petroleum-based industrial organic chemistry and bio-based carbohydrate chemistry. Here, we report that caprolactam (CPL) containing lithium chloride (LiCl) is a privileged solvent that enables the synthesis of the renewable platform chemical 5-hydroxymethylfurfural (HMF) from purified glucose. Metal halides in CPL-LiCl are catalysts, among which CrCl₃, CrCl₂, SnCl₄ and SnCl₂ are found to be uniquely effective, leading to the conversion of glucose to HMF with yields of 55%-67%. The simplicity of this chemical transformation of glucose contrasts markedly with the complexity of extant processes and provides a new paradigm for the use of biomass as a raw material for a renewable energy and chemical industries.

Full text of DOI:10.1002/cjoc.201090299

NOTE
†
Conversion of Glucose in CPL-LiCl to 5-Hydroxymethylfurfural
Chen, Tianming(陈天明)
Lin, Lu*(林鹿)
State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou,
Guangdong 510640, China
5-Hydroxymethylfurfural (HMF), an important versatile sugar derivative, is also considered a key intermediate
between petroleum-based industrial organic chemistry and bio-based carbohydrate chemistry. Here, we report that
caprolactam (CPL) containing lithium chloride (LiCl) is a privileged solvent that enables the synthesis of the re-
newable platform chemical 5-hydroxymethylfurfural (HMF) from purified glucose. Metal halides in CPL-LiCl are
catalysts, among which CrCl , CrCl , SnCl and SnCl are found to be uniquely effective, leading to the conversion
3
2
4
2
of glucose to HMF with yields of 55%— 67%. The simplicity of this chemical transformation of glucose contrasts
markedly with the complexity of extant processes and provides a new paradigm for the use of biomass as a raw ma-
terial for a renewable energy and chemical industries.
Keywords biomass, glucose, CPL-LiCl, halides, 5-hydroxymethylfurfural (HMF)
Introduction
has been demonstrated in water, traditional organic sol-
8
9,10
11-13
vents, multiphase systems,
Zhao et al. reported that chromium catalysts in alky-
and ionic liquids.
The present consumption of fossil fuels has led to
significant levels of environmental pollution and rapidly
diminishing petrochemical reserves. The diminishing
fossil fuel reserves and the globe warming effects have
become major concerns. The search for sustainable, al-
ternative energy is of critical importance.
Biofuels are highly attractive as the only sustainable
source of liquid fuels currently. However, the replace-
12
limidazolium chloride ionic liquids, such as
1-ethyl-3-methylimidazolium chloride ([EMIM]Cl),
enable synthesis of HMF from glucose, a less expensive
feedstock, in good yield. While promising, this method
depends on expensive ionic liquid solvents. In our re-
search, we sought to address these concerns by mini-
mizing the use of ionic liquids for HMF production.
1
,2
3
ment of petroleum feedstock by biomass is limited by
the lack of highly efficient methods to selectively con-
vert carbohydrates to chemical compounds for the bio-
4
fuel production. A practical catalytic process that can
transform the abundant biomass into versatile chemicals
would also provide the chemical industry with renew-
5
able feedstocks. Biomass-derived carbohydrates repre-
sent a promising carbon-based alternative as an energy
source and a sustainable chemical feedstock. However,
more efficient processes need to be developed for the
selective conversion of carbohydrates into useful or-
ganic intermediates.
Noting that the chloride counterions in [EMIM]Cl
1
4
The five-membered ring compound, 5-hydroxy-
methylfurfural (HMF), is one of the top bio-based plat-
form compounds. HMF can be converted to a novel
form only weak ion pairs, we reasoned that other
nonaqueous solvents containing a high concentration of
chloride ions could be as effective as [EMIM]Cl for
HMF synthesis. We were aware that CPL containing
LiCl is one of solvents that can dissolve purified simple
sugars. These useful properties likely stem from the as-
3
biofuel molecule 2,5-dimethylfuran via selective hy-
drogenation. Thus, making HMF with renewable feed-
stock is highly demanding. Because glucose is liable to
6
+
form a stable six-membered pyranoside structure, it
sociation of lithium ions with CPL to form CPL•Li
failed to form HMF with satisfactory yields under those
macrocations, resulting in a high concentration of
weakly ion-paired chloride ions. Here, we report that
using CPL-LiCl as a solvent enables the efficient syn-
7
known conditions. In the case of HMF, its formation by
the dehydration of fructofuranose is straightforward and
*
E-mail: lclulin@scut.edu.cn; Tel.: 0086-020-22236719; Fax: 0086-020-22236719
Received July 12, 2010; revised and accepted August 17, 2010.
Project supported by the National Key Basic Research Program (No. 2010CB732201) from the Ministry of Science and Technology of China.
†
Dedicated to the 60th Anniversary of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
Chin. J. Chem. 2010, 28, 1773— 1776
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1773

Chen & Lin
NOTE
thesis of HMF in a single step from glucose. The
CPL-LiCl solvent is cheaper and more easily prepared
than traditional ionic liquids. Preparation of
Ion-exclusion chromatographic separation of HMF
Deionized water (2.0 g) was mixed with above reac-
tion mixture (4.254 g) containing HMF (182 mg). This
solution was loaded onto a column of ion-exclusion
resin (Dowex 50X8-200, Li+ form, 70 cm×1.5 cm) and
eluted with deionized water at a rate of 3 cm/min. Frac-
tions (25 mL) were collected and analyzed by IC. IC
analysis indicated that ＞75% of the HMF was recov-
ered in the HMF-containing fractions.
5-hydroxymethylfurfural from glucose in CPL-LiCl has
the prospect of industrialization.
Experimental
General
Commercial chemicals were of reagent grade or bet-
ter and were used without further purification. Reactions
were performed in glass vessels heated in a tempera-
ture-controlled oil bath with magnetic stirring.
Results and discussion
Influence of the reaction medium’s composition on
the 5-HMF yield
5-Hydroxymethylfurfural was from Energy Chemical
Company.
N,N-Dimethylacetamide (DMA)-LiCl has been
Analytical methods
shown to be an effective solvent for the dehydration of
glucose to 5-HMF. We found that CPL-LiCl also is an
effective solvent for the dehydration of glucose to
15
All reaction products were analyzed by ion chroma-
tography (IC) and quantified with calibration curves
generated from commercially available standards. After
handling samples simply, HMF and glucose were ana-
lyzed using Dionex ICS-3000 ion-exchange chroma-
tography with electrochemical detector (Figure 1). The
glucose and HMF were separated on a CarboPacTM
PA1 column (i.d. 2 mm×250 mm) by using isocratic
elution consisting of 70 mmol/L sodium hydroxide at a
flow rate of 0.35 mL/min. The experimental results
showed that linear correlations of glucose and HMF
5-HMF. Therefore, mixtures of CPL and LiCl were used
as the solvent for the process, and the effect of the sol-
vent composition was studied. The experimental results
are shown in Table 1. We found HMF yield was 27.3%
from glucose in the absence of LiCl. With the addition
of LiCl or LiBr to CPL, we obtained substantial yield of
HMF (40%—67%). But we found a bit of HMF yields
(10%—14%) with the addition of ZnCl to CPL. It can
2
be seen that the mole ratio in CPL-LiCl or CPL-LiBr
had some influence on the molar yield of HMF. A high
HMF yield was obtained in 3∶1 (mole ratio) CPL-LiCl
or CPL-LiBr. The results demonstrate that CPL-LiCl or
CPL-LiBr mixture are effective solvent for the dehydra-
tion of glucose to 5-HMF
2
were observed, and the correlation coefficient r was
over 0.999.
a
Table 1 Influence of solvent composition on the 5-HMF yield
Solvent
Catalyst,
mol%
Molar
yield/%
27.3
56.1
39.2
66.7
56.2
51.3
42.8
61.5
13.4
14.1
9.7
T/℃
Time/h
(
mole ratio)
CPL
CrCl
CrCl
CrCl
CrCl
CrCl
CrCl
CrCl
CrCl
CrCl
3
3
3
3
3
3
3
3
, 6
, 6
, 6
, 6
, 6
, 6
, 6
, 6
, 6
100
100
100
100
100
100
100
100
100
100
100
3
3
3
3
3
3
3
3
3
3
3
CPL-LiCl (5∶1)
CPL-LiCl (4∶1)
CPL-LiCl (3∶1)
CPL-LiCl (2∶1)
CPL-LiBr (5∶1)
CPL-LiBr (4∶1)
CPL-LiBr (3∶1)
Figure 1 Chromatogram of the standard mixture. 1—HMF
(
0.6424 mg/L); 2—glucose (1.001 mg/L).
Typical workup procedure
LiCl (0.424 g, 0.01 mol) was dissolved in CPL
CPL-ZnCl (5∶1)
3
2
(
3.395 g, 0.03 mol) at 100 ℃. The reaction mixture was
stirred at 120 ℃ for 1.5 h, cooled to 80 ℃. Thereafter,
CPL-ZnCl (4∶1)
3
CrCl , 6
2
3 2
CrCl •6H O (0.035 g, 0.131 mmol) and glucose (0.4 g,
CPL-ZnCl
2
(3∶1)
3
CrCl , 6
2
.222 mmol) were added. The reaction mixture was
a
Glucose was reacted at a concentration of 10% relative to the
total mass of the reaction mixture. Catalyst loading is relative to
glucose. Yields are based on IC analysis.
stirred at 100 ℃ for 3 h. At 1 h intervals, aliquots of
the reaction mixture were removed for IC analysis.
HMF yields for optimized reactions of sugars were re-
produced to within 2%—3%.
1
774
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 1773— 1776

Conversion of Glucose in CPL-LiCl to 5-Hydroxymethylfurfural
Conversion of glucose into HMF in CPL-LiCl
treated with various metal halide and acid catalysts
Table 2 Influence of various metal halide and acid catalysts on
the 5-HMF yield
a
Figure 2 is a histogram showing conversion results
for glucose in CPL-LiCl, pretreated with various metal
halide catalysts. As shown in the figure, Glucose con-
version was high for the metal halide catalysts tested.
These metal halide showed a conversion of glucose of
Solvent
Catalyst,
mol%
Molar
yield/%
46.2
31.4
58.7
45.2
54.8
41.4
64.7
54.3
41.9
28.6
55.4
41.7
9.7
T/℃
Time/h
(
mole ratio)
CPL-LiCl (5∶1)
CPL-LiCl (4∶1)
CPL-LiCl (3∶1)
CPL-LiCl (2∶1)
CPL-LiCl (5∶1)
CPL-LiCl (4∶1)
CPL-LiCl (3∶1)
CPL-LiCl (2∶1)
CPL-LiCl (5∶1)
CPL-LiCl (4∶1)
CPL-LiCl (3∶1)
CPL-LiCl (2∶1)
CPL-LiCl (3∶1)
CPL-LiCl (3∶1)
CPL-LiCl (3∶1)
CrCl
CrCl
CrCl
CrCl
2
2
2
2
, 6
, 6
, 6
, 6
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
8
5% or greater. However, HMF yields were low using
AlCl or CuCl . HMF yields from conversion of glucose
were also low using acids (e.g., H SO ) as catalysts.
Four catalysts, CrCl , CrCl , SnCl and SnCl , gave
3
2
2
4
3
2
4
2
4
SnCl , 6
HMF yields of 55%—67%, good efficiency for conver-
sion of glucose. The experimental results are shown in
Table 2. HMF yield for CPL-LiCl solvent systems not
SnCl
SnCl
SnCl
SnCl
SnCl
SnCl
SnCl
4
4
4
2
2
2
2
, 6
, 6
, 6
, 6
, 6
, 6
, 6
, 6
containing CrCl
tently 15% or less. Although Zhao et al. reported that
CrCl was markedly less effective than CrCl , we found
3
, CrCl
2
, SnCl
4
or SnCl1
2
were consis-
2
2
3
that chromium in either oxidation state gave a similar
yield. Stannum in either oxidation state also gave a
similar yield.
Chromium and stannum likely enables conversion of
glucose to HMF by catalyzing the isomerization of glu-
AlCl
CuCl
H SO , 6
3
12,16
2
, 6
7.3
cose into fructose (Figure 3).
The fructose is then
converted to HMF. Our observations suggest that the
yields of HMF from glucose in reactions utilizing chro-
mium or stannum correlate with metal coordination.
Highly coordinating ligands such as amines decrease the
yields of HMF. On the other hand, halide ligands en-
hance HMF yields. Our data suggest that the halide ad-
ditives must balance two roles in the conversion of glu-
cose into HMF: serving as ligands for chromium or
stannum and facilitating the selective conversion of
fructose. In contrast, chloride potentially offers the op-
timal balance of nucleophilicity and coordinating ability,
enabling unparalleled transformation of glucose into
HMF.
12.6
2
4
a
Glucose was reacted at a concentration of 10% relative to the
total mass of the reaction mixture. Catalyst loading is relative to
glucose. Yields are based on IC analysis.
Figure 3 Putative mechanisms for the chromium-catalyzed or
stannum-catalyzed transformation of glucose into HMF.
Conclusion
Catalytic dehydration of glucose to 5-HMF using
CrCl as the catalyst in CPL-LiCl mixtures by heating
3
was investigated. CPL-LiCl mixtures were shown to be
effective for the dehydration of glucose to 5-HMF. A
high 5-HMF yield of 66.7% was obtained for a 3 h reac-
tion time in (3∶1 mole ratio) CPL-LiCl mixtures at 100
℃.
Figure 2 Glucose conversion in CPL-LiCl (3∶1) treated with
numerous catalysts. Glucose was reacted at a concentration of
10% relative to the total mass of the reaction mixture. Catalyst
loading is reacted at a concentration of 6% relative to the mol of
glucose. The reaction systems were heated to 100 ℃ for 3 h.
Yields are based on IC analysis.
We demonstrated that CrCl , SnCl and SnCl also
are excellent catalysts for the conversion of glucose into
2
4
2
Chin. J. Chem. 2010, 28, 1773— 1776
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
1775

Chen & Lin
NOTE
HMF in the CPL-LiCl mixtures. Formation of the
five-membered-ring chelate complex of Cr (or Sn) and
glucose may play a key role in the formation of HMF.
The efficient, cheaper, low toxicity and reusable cata-
lytic system has great potential for application.
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