Biomass derived β-cyclodextrin-SO3H carbonaceous solid acid catalyst for catalytic conversion of carbohydrates to 5-hydroxymethylfurfural

Article abstract of DOI:10.1016/j.apcata.2015.04.021

A new β-cyclodextrin-SO₃H carbonaceous solid acid catalyst was synthesized in an ecofriendly manner and was found efficient for conversion of carbohydrates into 5-hydroxymethylfurfural. Numbers of different solvents systems were screened for efficient formation of HMF. The results showed that the β-cyclodextrin based-SO₃H catalyst resulted in 96% 5-hydroxymethylfurfural (HMF) yield from fructose while glucose gave a 47% HMF yield in DMSO in pretty good yields and high selectivity. Polysaccharides such as sucrose and inulin also gave about 85% and 92% yield of HMF. The catalyst was readily recovered and reused for atleast three runs without any significant impact on yields of products. The main advantages of this protocol include practical simplicity, high yields, recyclable catalyst, safety and cheapness of benign solvents.

Full text of DOI:10.1016/j.apcata.2015.04.021

Accepted Manuscript
Title: Biomass derived ␤-Cyclodextrin-SO H Carbonaceous
3
Solid Acid Catalyst for Catalytic Conversion of Carbohydrates
to 5-hydroxymethylfurfural
Author: Raju S. Thombal Vrushali H. Jadhav
PII:
S0926-860X(15)00254-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.04.021
APCATA 15358
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
28-1-2015
27-3-2015
14-4-2015
Please cite this article as: R.S. Thombal, V.H.J. Biomass derived rmbeta-
Cyclodextrin-SO H Carbonaceous Solid Acid Catalyst for Catalytic Conversion of
3
Carbohydrates to 5-hydroxymethylfurfural, Applied Catalysis A, General (2015),
http://dx.doi.org/10.1016/j.apcata.2015.04.021
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Highlights



 -Cyclodextrin derived carbonaceous catalyst was synthesized for the production of
5
-hydroxymethylfurfural (HMF).
 Fructose gave about 96% yield of HMF while glucose gave a 47% HMF yield in
DMSO with high selectivity.
 Polysaccharides such as sucrose and inulin also gave about 85% and 92% yield of
HMF.

 The catalyst can be readily recovered and reused for at least three runs without any
significant impact on yields of products.
1
Page 1 of 15

Biomass derived -Cyclodextrin-SO H Carbonaceous Solid Acid
3
Catalyst for Catalytic Conversion of Carbohydrates to 5-
hydroxymethylfurfural
Raju S. Thombal and Vrushali H. Jadhav *
Department of Organic Chemistry, National Chemical Laboratory (CSIR-NCL), Pune-411008, India.

BSTRACT

new-Cyclodextrin-SO
3
H carbonaceous solid acid catalyst was synthesized in an
ecofriendly manner and was found efficient for conversion of carbohydrates into 5-
hydroxymethylfurfural. Numbers of different solvents systems were screened for efficient
3
formation of HMF. The results showed that the -cyclodextrin based-SO H catalyst resulted
in 96% 5-hydroxymethylfurfural (HMF) yield from fructose while glucose gave a 47% HMF
yield in DMSO in pretty good yields and high selectivity. Polysaccharides such as sucrose
and inulin also gave about 85% and 92% yield of HMF. The catalyst was readily recovered
and reused for atleast three runs without any significant impact on yields of products. The
main advantages of this protocol include practical simplicity, high yields, recyclable catalyst,
safety and cheapness of benign solvents.
O
OH
HO
OH
HO
OH
Fructose
Or
OH
O
O
HO
HO
-cyclodextrin-SO H
3
O
HO
H
OH OH
Glucose
Solvent, 140-180 °C
HMF
Or
Good Yields
99% Selectivity
OH
>
O
HO
HO
O
OH
n
Polysaccharides
Keywords: -Cyclodextrin, carbonaceous, catalyst, 5-hydroxymethylfurfural.
1. Introduction
Today almost whole world is dependent on fossil fuels for energy sources. With the
*
Corresponding author. Email: vh.jadhav@ncl.res.in, Tel: +91 (20) 25902275
2
Page 2 of 15

increasing population there will be a concern that these fossil fuels will be used up soon.
Hence there is a need to look at alternative energy sources in the biosphere. Biomass
comprising of 75% carbohydrates is the only renewable source available widely, which has
the potential to replace current non-renewable fossil resources. Now-a-days, most attractive
and promising approach is to convert biomass derived carbohydrates to furanic aldehydes
such as HMF as it is a promisable candidate and serves as a platform compound for fine
chemicals, plasticizers and polymers [1-10]. As seen from the literature, dehydration of
fructose into HMF is very easy and efficient [11]. However fructose is not abundant in nature
and also very expensive. Hence, HMF cannot be manufactured from fructose on large scale.
On the contrary, glucose is the most abundant feedstock for production of HMF. There are
also some catalytic systems in which fructose is readily converted to HMF and are ineffective
for conversion of glucose to HMF [12, 13] In 2007, Zhao et al.[14] for the first time reported
dehydration of glucose to HMF in CrCl
such as SnCl , AlCl , GeCl , MgCl , ScCl
, NA-p, Ag 40, H-ZSM-5 were used for dehydration of glucose to HMF
2
as a catalyst. Later homogeneous catalyst systems
4
3
4
2
3
, YbCl and heterogeneous catalyst system such as
3
2-
SO
4
/ZrO
2
3
PW12O
with moderate yields of 40 to 70 % [15, 16]. Heterogeneous catalytic processes have
advantages over homogeneous catalysis such as straight forward catalyst separation, catalyst
regeneration, relatively low cost which make them more applicative in industrial production
[17-20].
An amorphous carbon material consisting of small polycyclic aromatic carbon sheets
with a high density of sulfonic acid (SO H) sites are especially attractive heterogeneous
3
catalysts now-a-days due to their low cost, metal-free composition, and expected high
stability and high reusability [21, 22]. Indeed, materials produced by this approach have
shown very promising catalytic activity for many acid-catalyzed reactions than commercial
3
Page 3 of 15

catalysts like zeolites, niobic acid or Amberlyst-15 [23]. Intrigued by these studies [24, 25]
and our continuing work in this field [26, 27], we choose readily available -cyclodextrin as a
carbon precursor and p-TSA as a sulphonating agent. Naturally occurring -cyclodextrin can
be prepared by enzymatic hydrolysis of starch which comes from biomass [28].
Cyclodextrins are cyclic oligomers of seven D-glucose units linked in a (1-4) manner and
have a pre organized structure. Hence after sulphonation of -cyclodextrin we expected more
polycyclic aromatic sheets to be formed and hence high density of sulphonated sites to be
attached on the carbonaceous material ultimately showing more acidic character of the
catalyst. In this study, we have prepared -cyclodextrin-SO
3
H catalyst by one step
hydrothermal carbonization of -cyclodextrin and p-TSA under mild reaction conditions and
shown its application in the synthesis of HMF from fructose, glucose and polysaccharides.
The hydrothermal carbonization promoted the structure to undergo decomposition,
hydrolysis, dehydration, and a molecular rearrangement reaction to produce a polycylic
aromatic structure embedded with active –SO
3
H, –COOH and -OH sites. A schematic
diagram for preparation of -cyclodextrin-SO
3
H carbonaceous catalyst is shown in Figure 1
OH
HO
O
O
O
OH
3
SO H
HO
OH
O
OH
HO
HO
O
OH
O
O
pTSA, 180 °
HO
OH
C
OH
O
HO
OH
neat
OH
O
OH
OH
HOOC
COOH
OH
O
OH
OOH
OH
O
O
SO
3
H
sp
2
carbons
HO
O
OH
-cyclodextrin-SO H carbonaceous catalyst
3
-cyclodextrin
O
O
Fructose/Glucose/
Polysaccharides
HO
H
HMF
Figure 1. Preparation of -cyclodextrin-SO H carbonaceous catalyst and its application in HMF synthesis.
3
4
Page 4 of 15

2. Experimental
2.1. Catalyst Preparation
Typically g of -cyclodextrin powder was mixed with 18 g of p-TSA and was
heated in an oil bath at 180 °C for 24 h under nitrogen. After 24 h, the catalyst was kept open
to air and further heated for 24 h to remove all the volatile compounds adsorbed on the
surface of the material. Deionised water was added to it and the catalyst was filtered and
further washed several times with deionised water to remove the excess sulphate ions and
°
then finally washed with ethanol. The black powder thus obtained was oven dried at 100 C
for 12 h. This black powder was found to be insoluble in DMSO, DMF, DMA, and all
organic solvents even at boiling temperatures.
2.2. Catalyst Characterization
The catalyst thus obtained was characterized with FT-IR (Spectrum 400), Elemental
analysis from EDAX (Quanta 200 3D, FEI), PXRD (Panalytical X'Pert Pro), NH
3
TPD
(Thermo Scientific TPD RO 1100), Raman (LabRAM HR 800), HRTEM (Tecnai G2 FEI),
13
C cross-polarization (CP) magic angle spining NMR (Jeol ECX 400, at a frequency of 100
MHz with a spinning rate of 8 KHz), BET surface area (Quantachrome Autosorb iQ),
Elemental analysis C, H and O (Thermo Scientific, Flash EA 1112). The acid densities were
measured by acid base titration.
2.3. HMF Synthesis
In a typical synthesis, 100 mg of carbohydrates, 100 wt% of cyclodextrin-SO
3
H
catalyst were taken in a round bottom flask under nitrogen, to which was added 10 mL of
solvent. The reaction was then heated at given temperature for given time with magnetic
stirring. After specified time, the reaction mass was centrifuged to separate the catalyst, and
the solution was further analyzed by HPLC (Agilent 1200 Series) equipped with column
5
Page 5 of 15

Phenomenex Gemini RP C18 5, (250 mm X 4.6 mm). A mixture of water and acetonitrile
93:7) was used as a mobile phase with a flow rate of 1 mL/min.
(
The retention times observed were as follows: solvent peaks: 3.5 to 4.5, 5-
hydroxymethylfurfural: 7.5, furfuraldehyde: 10.5 (Figure S8, Supp Inf). The amounts of
HMF were determined by HPLC using furfuraldehyde as an internal standard. The HMF
1
formation was also confirmed using H NMR (Figure S9, Supp Inf).
3. Results and Discussion
3.1. Carbonaceous material properties
-1
The FT-IR spectrum (Figure S1, Supp Inf) showed characteristic peaks at 1008 cm
-1
and 1032 cm which are attributed to O=S=O stretching vibrations in -SO
3
H groups and peak
-1
at 1174 cm for SO
3
H stretching. This indicates that the sulfonic acid groups have been
-1
successively incorporated on the catalyst surface. Peaks at 1610 cm attributed for C=C
-1
stretching vibrations in aromatic carbons and peak at 1680 cm attributed for C=O stretching.
-1
Peak at 1714 cm attributed to presence of C=O stretching vibration of –COOH group.
-1
Bands at 2950 to 2875 cm attributed for C-H stretching band. Bands due to O-H stretching
-1
were observed at 3421 cm . The XRD pattern (Figure S2, Supp Inf) of a -cyclodextrin-
SO H catalyst exhibited broad diffraction peak at 2θ angles of 15°-30° which can be
3
assigned to C(002) planes and a weak peak at 2θ angles of 38°-48° that are typical for
amorphous carbon composed of aromatic carbon sheets oriented in a considerably random
fashion [29]. The energy dispersive X-ray analysis (EDAX) analysis (Figure S3, Supp Inf)
showed sulphur composition to be 2.99 %. The ammonia desorption studies (Figure S4, Supp
Inf) showed the total acid density to be 2.7 mmol/g. The total acid density and the sulphonic
acid density of -cyclodextrin-SO
3
H based on acid base titration was found to be 3.0 mmol/g
6
Page 6 of 15

and 1.24 mmol/g respectively. Raman spectrum (Figure S5, Supp Inf) showed two peaks, G
-1
band at around 1580 cm due to active Raman vibration of E2g symmetry and D band at
-1
around 1350 cm due to carbon sheet stacking of the incomplete carbonized catalyst structure
which explains the presence of polycyclic aromatic carbon sheets with an intensity ratio of
3
0.81. The broad intense D band in -cyclodextrin-SO H also indicates the presence of
amorphous material in the sample, consistent with the presence of the broad peak in the XRD
pattern. [30]. HRTEM (Figure S6, Supp Inf) showed aggregates of particulate morphology.
13
C CP/MAS NMR spectrum (Figure S7, Supp Inf) showed chemical shifts at 130, 155 and
180 ppm in the NMR spectrum indicating presence of polycyclic aromatic carbon atoms,
phenolic -OH and –COOH groups respectively [31, 32]. Broad peaks observed at 130 ppm
and 155 ppm obscures the peak due to aromatic carbons attached to -SO H. BET surface
3
areas and pore size were calculated using the standard Brunauer-Emmett-Teller (BET)
2
equation and was found to be 1.36 m /g and 66.7 A ° (Table 1). Elemental analysis showed
composition of C, H and O to be 70.6 %, 3.7 % and 22.6 % respectively.
Table 1. The structure and surface properties of -cyclodextrin-SO
3
H catalyst
0
Catalyst
Surface area
Pore size (A )
Acid density
(mmol/g)
3
SO H amount
(mmol/g)
2
(m /g)

-cyclodextrin- SO
3
H
1.36
66.7
3.0
1.24
3.2 Optimization of reaction conditions in HMF formation
The performance of -cyclodextrin-SO H as an acid catalyst was tested for the
3
conversion of carbohydrates to HMF. Initially we started to investigate the catalytic activity
for this new catalyst for the dehydration of fructose to HMF in DMSO, as DMSO is versatily
known to give good yields of HMF from fructose. In an optimized reaction, 100 mg of
fructose and 100 wt% catalyst was placed in a round bottom flask, to it was added 10 mL of
7
Page 7 of 15

DMSO and the reaction mixture was heated at 140 °C for 2 h. HMF was seen to be formed
with 100% selectivity from HPLC analysis. The same reaction was then repeated on glucose
as an substrate. In this case also HPLC analysis showed formation of HMF. These results
3
indicate that the sulphonic acid groups on the -cyclodextrin-SO H played a vital role in
HMF formation from fructose as well as glucose. The same reaction was carried out on
glucose without addition of catalyst in DMSO as a solvent, and in this case no HMF
formation was observed.
We further studied the effect of reaction temperature, reaction time and catalyst
3
concentration on the performance of -cyclodextrin-SO H in DMSO. For this, fructose and
glucose were reacted with -cyclodextrin-SO
3
H at different temperatures i.e 100 °C, 140 °C
and 180 °C. Aliquots at intervals were taken out and studied for formation of HMF using
HPLC. It was observed that reaction time and reaction temperature had an significant
influence on HMF yields. In case of fructose, the reaction was slower at 100 °C and much
faster at 140 °C and reached a maximum HMF formation at 140 °C in 2 h, while at 180 °C
HMF formation was not so efficient (Figure 2). While, in the case of glucose, HMF was
formed in traces at 100 °C and 140 °C (Figure 3). At higher temperature of 180 °C glucose
reached a maximum HMF formation in 5 h. It was found that heating for longer time and
higher temperature had an negative impact on HMF yields due to formation of side products.
The catalyst concentration was also studied to get maximum HMF formation. Catalyst
concentration of 10 wt%, 50 wt% and 100 wt% was studied in DMSO as shown in Figure 4.
It was found that 100 wt% of metal catalyst gave maximum HMF formation in fructose as
well as glucose.
8
Page 8 of 15

Figure 2 and 3. Study of formation of HMF 1 from D- fructose and D-glucose using -cyclodextrin-SO
3
H
catalyst at different temperature in DMSO.
Figure 4. Study of formation of HMF from fructose and glucose using different concentrations of -
cyclodextrin-SO H catalyst in DMSO.
3
3.3 HMF formation from carbohydrates
After setting the optimum conditions for HMF formation from fructose and glucose,
3
we further tried to explore the -cyclodextrin-SO H catalyst in various solvents so as to
obtain higher yields and the results are summarized in Table 2 and 3. Fructose gave excellent
yields of HMF in DMSO, DMF, NMP and DMA as shown in Table 2. Highest yield of about
96% was obtained in DMSO. Polar solvents like GVL, nitromethane, sulpholane,
isopropanol, ethylene glycol, CH CN and [BMIM]Cl gave moderate to good yields of HMF
3
from fructose. It can be seen that water is not a suitable solvent for HMF formation as water
is not favourable for dehydration reactions and hence promotes side reactions. The -
3
cyclodextrin-SO H was also effective in converting glucose to HMF in good yields. In case
of glucose, an maximum yield of HMF formation of about 47% was observed in DMSO as
seen in Table 3. Solvents like DMF, NMP, DMA, sulpholane, and [BMIM]Cl gave moderate
yields of HMF in the range of 24 to 37%. All the reactions proceeded with almost > 99%
selectivity.
9
Page 9 of 15

Table 2. Fructose to HMF using -cyclodextrin-SO
3
H catalyst.
a
Entry
Substrate
Solvent
Time (h) Yield (%)
Temp (°C)
1
2
3
4
5
6
7
8
9
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
DMSO
140
140
140
140
100
140
140
100
140
140
140
100
2
2
2
2
2
2
2
2
2
2
2
2
96
92
84
79
74
72
85
63
25
-
DMF
NMP
GVL
Nitromethane
Sulpholane
DMA
Isopropanol
Ethylene glycol
Water
1
1
0
1
2
[BMIM]Cl
76
45
1
3
CH CN
a
Yields are based on HPLC analysis.
Table 3. Glucose to HMF using -cyclodextrin-SO H catalyst.
3
a
Entry Substrate Solvent
Temp (°C) Time (h) Yield (%)
1
2
3
4
5
Glucose
Glucose
Glucose
Glucose
Glucose
Glucose
DMSO
DMF
180
180
180
180
5
5
5
5
5
5
47
37
24
29
28
32
NMP
DMA
Sulpholane 180
[BMIM]Cl 180
6
a
Yields are based on HPLC analysis.
No rehydration by-products such as levulinic acid and formic acids were detected in any of
the samples. The catalyst was found to efficiently convert less expensive and easily available
polysaccharides (sucrose, inulin and starch) to HMF as shown in Table 4. 85% yield of HMF
1
0
Page 10 of 15

was obtained from sucrose, whereas inulin gave about 92% yield of HMF. Starch gave about
0% yield of HMF.
1
Table 4. Polysaccarides to HMF using -cyclodextrin-SO H catalyst.
3
a
Entry
Substrate
Solvent
Time (h)
Yield (%)
Temp (°C)
140
1
2
Sucrose
Inulin
DMSO
DMSO
DMSO
2
2
5
85
92
10
140
3
Starch
140
a
Yields are based on HPLC analysis.
3.4 Catalyst reusability
The stability of the catalyst is of great importance for practical use, so the cycle usage
test of -cyclodextrin-SO
reaction, the catalyst was separated by centrifugation, washed with water and ethanol, dried at
00 °C for 2 h to remove the adsorbed by-products prior to reuse in the next run. The
catalytic activity of the catalyst for the conversion of fructose to HMF in DMSO showed
3
H was conducted and the results are listed in Figure 5. After the
1
st
nd
rd
constant activity when reused 3 times. 1 run showed 94% yield of HMF while 2 and 3 run
both showed 93% yield of HMF from D-fructose indicating good stability of the catalyst.
a
Yields are based on HPLC analysis.
Figure 5. Yields of F when -cyclodextrin-SO H catalyst was reused
3
4. Conclusion
In summary, we have developed a novel sulphonated carbonaceous material having -
SO
H, -COOH and -OH groups by one step hydrothermal carbonization of -cyclodextrin
3
1
1
Page 11 of 15

and p-toulene sulphonic acid under mild and ecofriendly conditions. Such carbonaceous
catalyst having high acid strength was found effective for conversion of carbohydrates to
HMF in DMSO with pretty good yields and high selectivity. The catalyst showed good
reusability too. The catalyst can also be used industrially due to its green preparation, high
activity, selectivity and reusability.
Acknowledgements
V.H.J. thanks DST, New Delhi for the INSPIRE Faculty Award and Fast Track
Grant. V.H.J also thanks Dr. Sourav Pal, Director, NCL for providing all the infra-structural
facilities.
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4
Page 14 of 15

Graphical Abstract
3
Biomass derived -Cyclodextrin-SO H Carbonaceous Solid Acid Catalyst for Catalytic
Conversion of Carbohydrates to 5-hydroxymethylfurfural
Raju S. Thombal and Vrushali H. Jadhav *
Department of Organic Chemistry, National Chemical Laboratory (CSIR-NCL), Pune-411008, India.

3
new-Cyclodextrin-SO H carbonaceous solid acid catalyst was synthesized in an
ecofriendly manner and was found efficient for conversion of carbohydrates into 5-
hydroxymethylfurfural. Numbers of different solvents systems were screened for efficient
3
formation of HMF. The results showed that the -cyclodextrin based-SO H catalyst resulted
in 96% 5-hydroxymethylfurfural (HMF) yield from fructose while glucose gave a 47% HMF
yield in DMSO which are pretty good yields with high selectivity. Polysaccharides such as
sucrose and inulin also gave about 85% and 92% yield of HMF. The catalyst can be readily
recovered and reused for atleast three runs without any significant impact on yields of
products. The main advantage of this protocol includes clean reactions, practical simplicity,
high yields, recyclable catalyst, safety and cost effective starting materials.
O
OH
HO
OH
HO
OH
Fructose
Or
OH
O
O
HO
HO
-cyclodextrin-SO
3
H
O
HO
H
OH OH
Glucose
0
Solvent, 140-180 C
HMF
Good Yields
99% Selectivity
Or
OH
>
O
HO
HO
O
OH
n
Polysaccharides
Keywords: -Cyclodextrin, carbonaceous, catalyst, 5-hydroxymethylfurfural.
1
5
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