Silica-supported boric acid assisted conversion of mono- and poly-saccharides to 5-hydroxymethylfurfural in ionic liquid

Article abstract of DOI:10.1039/c4ra01771d

Silica-supported boric acid has been prepared and applied as heterogeneous catalyst for the direct conversion of inexpensive and biorenewable mono- and polysaccharides to 5-hydroxymethylfurfural (HMF) in ionic liquid under much milder conditions. Fructose, glucose, sucrose, inulin, and cellulose were successfully converted to HMF with moderate to excellent conversion. The catalyst and the solvent system can be recycled for up to four consecutive cycles without a significant loss in conversion. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra01771d

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Silica-supported boric acid assisted conversion
of mono- and poly-saccharides to 5-
Cite this: RSC Adv., 2014, 4, 14414
hydroxymethylfurfural in ionic liquid†‡
Mayanka Walia, Upendra Sharma, Vijai K. Agnihotri*ab and Bikram Singh*ab
ab
ac
Silica-supported boric acid has been prepared and applied as heterogeneous catalyst for the direct
conversion of inexpensive and biorenewable mono- and polysaccharides to 5-hydroxymethylfurfural
Received 28th February 2014
Accepted 7th March 2014
(
HMF) in ionic liquid under much milder conditions. Fructose, glucose, sucrose, inulin, and cellulose were
DOI: 10.1039/c4ra01771d
successfully converted to HMF with moderate to excellent conversion. The catalyst and the solvent
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system can be recycled for up to four consecutive cycles without a significant loss in conversion.
C6-sugars (i.e., hexoses) by eliminating three moles of water
molecules at an elevated temperature. Fructose is produced
Introduction
8
In response to the presently existing threats regarding the from glucose isomerisation whereas glucose is generally
global warming caused by greenhouse gas emissions as well as produced by hydrolysis of starch, which is a main constituent of
9
continuous depletion of fossil fuel reserves, much effort has food material such as potato, rice, and maize. Therefore, non-
been devoted to the development of technologies that facilitate digestible carbohydrate resources such as cellulose, hemi-
the conversion of renewable biomass resources into trans- celluloses, lignin and inulin are the ideal substrates for the
1
0,11
portation fuels and chemical intermediates (e.g. alcohols, production of HMF.
But it is more difficult to produce HMF
1
aldehydes, acids). Therefore, there is an urgent need for the from glucose and its polymer since the isomerisation step i.e.,
development of cost-effective processes by which these bio- glucose to fructose conversion is the main step in HMF
sustainable substrates can be transformed into value added production form glucose and its polymers. HMF can be
chemicals. Nature produces more than 75% of carbohydrates produced by ionic liquid-assisted dehydration of sugars and
from the total biomass out of which less than 5% used in food carbohydrates has been of high interest during recent years.
and non-food sectors. Carbohydrate-based biomass, a widely Ionic liquids are presented as promising solvents as they are
distributed and inexpensive resource, constitutes one of the capable of dissolving cellulose and other biomass components
12
13
2
3
most abundant groups of organic compounds. The potentiality and can signicantly improve the selectivity as well as the yield
14
of these compounds as the sustainable substitutes is well of HMF assertively.
recognized for building blocks derived from petrochemicals in
Recently, various catalytic methods have been developed for
4
4
the production of plastics and ne chemicals. One molecule of the production of HMF from carbohydrates. Mostly, Lewis acid
particular interest, 5-hydroxymethylfurfural (HMF) has been catalysts have been applied for the conversion of saccharides to
15
identied as one of the most promising platform compounds, HMF in various ionic liquids. Zhang's group has reported
which undergo a variety of reactions and form a series of conversion of sugar to HMF with 68–70% yield in a system con-
derivatives which can be converted into a wide range of indus- sisting of 1-ethyl-3-methyl-imidazolium chloride [emim]Cl and a
1
6
trially important chemicals, such as alternative biofuels, diesel CrCl
fuel additives, solvents and biopolymers.
2
catalyst. HMF synthesis from glucose was also accom-
Conventionally, plished by common Lewis acid, SnCl in 1-ethyl-3-methyl-
HMF is produced from the acid-catalyzed dehydration of imidazolium tetrauoroborate ([emim]BF
5–7
4
17
)
4
and bulky NHC
N-heterocyclic carbene) metal ligands. One report also avail-
able by using dimethylacetamide (DMA), NaBr, a Lewis acid and
18
(
19
a
2
CrCl with a signicant enhancement of HMF yield up to 81%.
Academy of Scientic & Innovative Research, CSIR-Institute of Himalayan Bioresource
Technology, Palampur, Himachal Pradesh-176 061, India. E-mail: kantvijai@yahoo. HMF has also been synthesized from fructose by using bronsted
com; bikram_npp@rediffmail.com
20
acidic ionic liquids as a catalyst with yield up to 72%. Acidic
b
Natural Plant Products Division, CSIR-Institute of Himalayan Bioresource
ionic liquid 1-(4-sulfonic acid) butyl-3-methylimidazolium
hydrogen sulfate has been also used as a catalyst for HMF
conversion from fructose with 100% conversion and 95% yield.
-Methylimidazolium-based and N-methylmorpholinium-based
Technology, Palampur, Himachal Pradesh-176 061, India
c
Indian Institute of Technology Bombay, Powai, 400 076, India
21
†
1
‡
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra01771d
1
protic ionic liquids has also been employed as a catalyst for the
IHBT communication no. 3575.
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conversion of fructose and sucrose to HMF with 74.8% and
Results and discussion
22
47.5% respectively. For the HMF preparation from fructose,
effect of ionic liquids with different cations and anions has also In continuation to our previous study, silica supported boric
23
been studied. The production of HMF from glucose in 63% acid was prepared by the similar strategy and characterized
24
35
yield was also reported using enzyme by two step method. First accordingly. We began our investigation for the HMF forma-
step involved isomerisation of glucose to fructose in the presence tion taking glucose as a model substrate. For the conversion
of glucose isomerase and borate ions, followed by the acid cata- HMF from glucose, rstly glucose isomerised to fructose and
lyzed dehydration of fructose to HMF using HCl as a catalyst in a then there is elimination of three water molecules (Scheme 1).
ꢀ
biphasic system. Other reports on HMF production showed the When the reaction was carried out at 90 C with SSBA or at
ꢀ
HMF yields of 42% at a 73% conversion by combining a solid acid 120 C without SSBA, traces of HMF was obtained as the desired
catalyst, amberlyst-15 and a solid base catalyst, Mg–Al hydro- product (Table 1, entry 1 and 3). Increasing the reaction
2
5
ꢀ
talcite, in N,N-dimethylformamide, Glucose dehydration in temperature to 120 C resulted in complete conversion of
26
water by using CrCl
2
-Im-SBA-15 as a catalyst yield 50% of HMF.
glucose aer 3 h as observed by thin layer chromatography
HMF yields of 57% at 79% conversion of glucose using a Lewis (TLC) (Table 1, entry 2); 81% GC conversion (isolated yield 60%)
acidic Sn-beta zeolite and HCl in a water–NaCl–THF biphasic of HMF was observed for glucose. No product was observed
27
reaction system and HMF yield of 61% from glucose using when silica gel and boric acid were used separately instead of
28
3 2
AlCl $6H O as the catalyst in a biphasic system. HMF produc- SSBA clearly demonstrating the catalytic role of SSBA (Table 1,
tion from cellulose has also been studied by using mesoporous entries 4 and 5). When the reaction was performed using ionic
titania (MTN) and zirconia (MZrN) nanoparticles with 18.2% and liquids 1-butyl-3-methylimidazolium tetrauoroborate [bmim]
29
2
9.2% yield. However, most of these methods required use of BF , 1,3-dimethylimidazolium hydrogen carbonate solution
4
toxic and expensive metal catalysts, strong acids and most [50% solution in MeOH : H O (2 : 3)] [1,3-dimim]HCO3 and
2
importantly resulted in low HMF yield. Ionic liquids ([mmim] water as a solvent; no reaction was observed in any of the case
4 4 4 4
HSO , [mmbim]HSO , [hmbim]HSO and [psmbim]HSO ) have (Table 1, entries 6–8). When the reaction was performed using
also been studied as a catalyst for the conversion of fructose to sodium tetraborate with ionic liquid 1-butyl-3-methyl-
30
HMF using DMSO as a solvent. Most of these methods are imidazolium hydrogen sulphate [bmim]HSO4, only 10%
applicable for the monosaccharides such as fructose and glucose conversion was observed (Table 1, entry 9). These results
but non-digestible carbohydrate resources such as cellulose, showed that the H BO –SiO in conjunction with ionic liquid
3
3
2
hemicelluloses, lignin and inulin are the ideal substrates for the [bmim]HSO4 is the procient catalytic system for HMF
production of HMF. There is a strong desire for the development production from carbohydrates.
of general method for this transformation without using any
toxic or strong acid catalyst.
In the present study, we have also investigated the most
preferred reaction conditions for the production of HMF taking
In recent years, boric acid has been used in organic synthesis different mono-, di- and polysaccharides as test substrates
because it is commercially available, moisture and air stable, (Table 2). In case of fructose excellent GC conversion 88% was
ꢀ
non toxic, environmentally benign, cheap and easy to handle. obtained at 90 C even in short reaction time i.e. 1.5 h. The
The operational simplicity and non corrosiveness of boric acid product (HMF) was isolated by column chromatography using
makes it as an attractive catalyst. Boric acid has been reported ethyl acetate : methanol (9.5 : 0.5) as a solvent. The puried
for the conversion of fructose and glucose into HMF with low product was identied on the basis of HRMS and NMR data.
31,32
yield.
Using the catalytic system, boric acid–NaCl, and HRMS calculated for C H O is 127.0395 and observed as
6 7 3
methyl isobutyl ketone as extractive solvent, a yield of 60% in 127.0404.
HMF was achieved from fructose, while only 14% was obtained
from glucose. Ionic liquids have remarkable unique properties inulin and cellulose, higher conversion was observed at 120 C
such as high thermal stability and high solubilising ability, than at 90 C. Interestingly, the present catalytic conditions
Although in case of other carbohydrates such as sucrose,
ꢀ
ꢀ
which enable carbohydrates to be dissolved at high concentra- were found to be highly efficient for the conversion of the
33
tion and serving as solvents that are potentially recyclable. disaccharide sucrose and afforded HMF in 80% conversion; just
Therefore ionic liquids are growing as a most preferred reaction 3 h were required for its transformation. When the reaction was
34
media for the synthesis of HMF from sugars. Nevertheless, the carried out without catalyst, 72% of HMF conversion was
existing processes suffered from limited substrates scope, observed in case of fructose, however no reaction was observed
longer reaction time and most importantly lower yield of HMF. in case of glucose and sucrose without catalyst.
To the best of our knowledge, there is no report available in
Further to examine the applicability of our catalyst, the same
literature for the conversion of carbohydrate to HMF with much reaction was carried out with biopolymers; inulin and cellulose.
improved conversion by using silica supported boric acid (SSBA)
as a heterogeneous catalyst. Surface-catalyzing dehydration of
carbohydrates on supported boric acid can decrease product
contamination and aid the development of greener route in
HMF synthesis. To circumvent the aforementioned limitations,
herein, we report mild silica supported boric acid promoted
conversion of carbohydrates to HMF in ionic liquid.
Scheme 1 Dehydration of glucose into HMF.
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a
Table 1 Conversion of glucose to HMF in different ionic liquids, at different temperatures and with different catalyst
ꢀ
b
Entry
Catalyst
Solvent
Temperature ( C)
Yield (%)
c
1
2
3
4
5
6
7
8
9
SSBA
SSBA
—
Boric acid
Silica gel (60–120)
SSBA
SSBA
SSBA
[bmim]HSO
[bmim]HSO
[bmim]HSO
[bmim]HSO
4
4
4
4
4
90
120
120
120
120
120
120
120
120
Traces
81
Traces
nd
nd
nd
nd
Traces
10
[bmim]HSO
d
[bmim]BF
4
e
[1,3-dimim]HCO
3
H
2
O
Sodium tetraborate
[bmim]HSO
4
a
ꢀ
b
Reaction conditions: glucose (100 mg), ionic liquid (1 g), catalyst (15 mg, 0.02 mmol of boric acid), 120 C, 3 hd. GC based conversion aer
c
derivatization to corresponding acetyl derivative.
tetrauoroborate. 1,3-Dimethylimidazolium hydrogen carbonate solution [50% solution in MeOH : H O (2 : 3)] nd: not detected.
1-Butyl-3-methylimidazolium hydrogen sulphate.
1-Butyl-3-methylimidazolium
e
2
Table 2 Applicability of catalytic system, [bmim]HSO
for the conversion of different saccharides to HMF
4
+ H
3
BO
3
–SiO
2
of cellulose, 0.04 mmol of SSBA was used and 18% of HMF
conversion was observed.
a
Regarding the mechanistic study of the reaction, we propose
32
similar type of mechanism as reported earlier (Scheme 2).
Possibly silica support increases the Lewis acid character of
boric acid which increases its reactivity for the isomerisation of
glucose into fructose and also helps in the hydrolysis of glyco-
sidic linkage of di or polysaccharides.
b
Substrate
Product
Time/h
Yield (%)
Recyclability of the catalytic system
c
Fructose
HMF
HMF
HMF
HMF
HMF
HMF
2
1.5
3
3
5
72
88
81
80
88
18
Recyclability of the [bmim]HSO + H BO –SiO catalytic system
was carried out aer the product HMF was separated from the
4
3
3
2
Fructose
Glucose
Sucrose
Inulin
d
Cellulose
7
a
Reaction conditions: carbohydrate (100 mg), ionic liquid (1 g), catalyst
ꢀ
15 mg, 0.02 mmol of boric acid), 120 C, 1.5–7 h. GC based
c d
b
(
conversion. Without SSBA. Catalyst (25 mg, 0.04 mmol of boric acid).
For the direct transformation of inulin (polymer of fructose)
into HMF involves two reactions. First step for the hydrolysis of
inulin into monosaccharide, fructose and second step involves
11
the dehydration of fructose to nal product, HMF. From the
GC data using internal standard, it was observed that inulin
completely hydrolyzed to its monomer, which in turn converted
to the nal product HMF with 88% GC conversion. Whereas in
case of cellulose (polymers of glucose), direct conversion
involves three reactions i.e. Firstly, hydrolysis into mono-
saccharide glucose, second reaction involves isomerisation
from aldose-type sugar (glucose) to ketose-type sugar (fructose)
and nally, exclusive formation of HMF occurs by the dehy-
Scheme 2 Proposed mechanism for the formation of HMF using
12
dration of this ketose-type sugar, fructose. For the conversion SSBA.
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inulin and sodium tetraborate were purchased from Sigma-
Aldrich. All other chemicals used were of analytical grade and
purchased from Merck India Ltd. Reaction mixture analyses
were performed on Shimadzu GC 2010, AOC-20i auto-sampler
coupled with a DB-5 capillary column, (30 m ꢁ 0.25 mm i.d.,
ꢀ
0
.25 mm) and FID. The initial temperature of column was 40 C
ꢀ
ꢀ
ꢂ1
held for 5 min and programmed to 230 C at 4 C min , then
held for 5 min at 230 C; the sample injection volume was 2 ml in
ꢀ
Scheme 3 Catalytic conversion of saccharides into HMF and subse-
quent acetylation.
HPLC grade dichloromethane. Helium was used as carrier gas
at a ow rate of 1.1 ml min on split mode (1 : 50). Products
ꢂ1
identied by GC, were conrmed by analysis of mono-
saccharides and HMF standards. HMF was also isolated by
1
13
column chromatography and identied by H and C NMR
Bruker Avance-300 spectrometer) and mass spectroscopic
(
techniques.
General experimental procedure
Synthesis of silica-supported boric acid (SSBA). Boric acid
(

3.0 g) with 60 ml water was taken in a 250 ml round bottom
ask and heated to 60–80 C. To this, silica gel (60–120 mesh,
ꢀ
2
7.0 g) was added gradually with constant stirring and reuxed
Fig. 1 Recycling of [bmim]HSO
reaction. Reaction conditions for each run: glucose (100 mg,
4
and catalyst for the dehydration
for 5 h. Water was evaporated under vacuum and the residue
was stirred at 100 C for 6–7 h under vacuum to give free owing
white powder.
Typical procedure for the conversion of saccharides to HMF.
A mixture of saccharide (100 mg) and H BO –SiO (15 mg, 0.02
ꢀ
0
.55 mmol), catalyst (15 mg, 0.02 mmol recycled) [bmim]HSO
4
(1 g,
35
ꢀ
recycled), reaction time ¼ 3 h, temperature ¼ 120 C.
3
3
2
mmol of boric acid) was heated in ionic liquid [bmim]HSO
4
reaction mixture by extracting ve times with ethyl acetate.
Product was separately derivatized by acetylation (Scheme 3) for
GC analysis every time. Aer each run, HMF was extracted with
ethyl acetate and the catalytic system ([bmim]HSO + H BO –
ꢀ
(
1 g) at 120 C for 3 h under nitrogen atmosphere. Aer the
reaction, the reaction ask was cooled in an ice bath; the
3
6
reaction mixture was acetylated in situ with pyridine : acetic
anhydride (1 : 1, v/v) for 16 h at room temperature (Scheme 3).
Aer acetylation reaction, water was added and the product
was extracted with the ethyl acetate. The derivatised product
mixture was analysed by GC and hexadecane used as the
internal standard. In case of cellulose, aer the completion of
acetylation reaction, nal product was extracted with ethyl
acetate; the aqueous layer was dried and weighed. HMF
conversion was calculated on the basis of the initial substrate
amount and the amount of the product.
4
3
3
SiO ) was dried under vacuum before using for the next. The
2
catalytic system can be recycled for four times without any
signicant decrease in the conversion of HMF (Fig. 1).
Therefore, silica-supported boric acid catalyst has been
established as a promising catalyst for carbohydrates because of
its high efficient activity, long catalyst life, reusability and easy
recovery. However, this method of HMF production will only be
industrial useful if it is scalable.
Conclusion
amount of HMF
Yield of HMF ¼
ꢁ 100
In conclusion, an efficient catalytic system has been devel-
oped for the excellent conversion of carbohydrates to HMF.
The catalytic system in combination with ionic liquid is
applicable for mono-, di- and polysaccharides and can be
recycled up to four times. Therefore, this could be an effective
and environmentally safe catalytic system for the conversion
starting amount of cellulose
The product (HMF) was isolated by column chromatography.
The puried product was identied on the basis of HRMS and
1
NMR data. H NMR (MeOD) d
H
: 7.38 (1H, d, J ¼ 3.5 Hz, H-3),
6
.59 (1H, d, J ¼ 3.5 Hz, H-4), 9.54 (1H, s, H-6), 4.62 (2H, s, H-7).
of carbohydrates to HMF as there is no use of strong and toxic 13
acids.
C NMR d ¼ 123.7 (C-3), d ¼ 109.8 (C-4), d ¼ 178.4 (C-6), d ¼
C
C
C
C
3
7
5
6.6 (C-7), d ¼ 152.8 (C-2), d ¼ 162.2 (C-5).
C
C
Experimental
General information
Acknowledgements
Fructose, glucose, sucrose, boric acid, silica and cellulose were The authors are grateful to the Director, CSIR-IHBT Palampur
purchased from S.D. Fine-Chem. Ltd (Mumbai, India). Ionic (HP), India for continuous encouragement and for providing
liquid, [bmim]HSO
4
,
[bmim]BF
4
,
[1,3-dimim]HCO
3
,
HMF, necessary facilities during the course of the investigation.
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