One-pot conversions of lignocellulosic and algal biomass into liquid fuels

Article abstract of DOI:10.1002/cssc.201200031

The one-pot conversion of lignocellulosic and algal biomass into a liquid fuel, 2,5-dimethylfuran (DMF), has been achieved by using a multicomponent catalytic system comprising [DMA]⁺[CH₃SO₃] ^- (DMA=N,N-dimethylacetamide), Ru/C, and formic acid. The synthesis of DMF from all substrates was carried out under mild reaction conditions. The reaction progressed via 5-hydroxyemthylfurfural (HMF) in the first step followed by hydrogenation and hydrogenolysis of HMF with the Ru/C catalyst and formic acid as a hydrogen source. This report discloses the effectiveness of the Ru/C catalyst for the first time for DMF synthesis from inexpensive and readily abundant biomass sources, which gives a maximum yield of 32 % DMF in 1 h. A reaction route involving 5-(formyloxymethyl)furfural (FMF) as an intermediate has been elucidated based on the ¹H and ¹³C NMR spectroscopic data. Another promising biofuel, 5-ethoxymethylfurfural (EMF), was also synthesized with high selectivity from polymeric carbohydrate-rich biomass substrates by using a Bronsted acidic ionic liquid catalyst, that is [DMA]⁺[CH₃SO₃]^-, by etherification of HMF in ethanol. Copyright

Full text of DOI:10.1002/cssc.201200031

DOI: 10.1002/cssc.201200031
One-Pot Conversions of Lignocellulosic and Algal Biomass
into Liquid Fuels
Sudipta De, Saikat Dutta, and Basudeb Saha*[a]
The one-pot conversion of lignocellulosic and algal biomass
into a liquid fuel, 2,5-dimethylfuran (DMF), has been achieved
time for DMF synthesis from inexpensive and readily abundant
biomass sources, which gives a maximum yield of 32% DMF in
1 h. A reaction route involving 5-(formyloxymethyl)furfural
by using
a multicomponent catalytic system comprising
[DMA]+[CH3SO3]À (DMA=N,N-dimethylacetamide), Ru/C, and
formic acid. The synthesis of DMF from all substrates was car-
ried out under mild reaction conditions. The reaction pro-
gressed via 5-hydroxyemthylfurfural (HMF) in the first step fol-
lowed by hydrogenation and hydrogenolysis of HMF with the
Ru/C catalyst and formic acid as a hydrogen source. This report
discloses the effectiveness of the Ru/C catalyst for the first
(FMF) as an intermediate has been elucidated based on the H
1
and 13C NMR spectroscopic data. Another promising biofuel,
5-ethoxymethylfurfural (EMF), was also synthesized with high
selectivity from polymeric carbohydrate-rich biomass sub-
strates by using a Brønsted acidic ionic liquid catalyst, that is
[DMA]+[CH3SO3]À, by etherification of HMF in ethanol.
Introduction
The conversion of abundant and renewable lignocellulose into
liquid fuels for transport applications is the aspiration of cur-
rent bioenergy research.[1,2] A long-standing issue is to produce
liquid fuels from renewable sources including cellulose and
lignocellulosic biomass by an economically and environmental-
ly acceptable route.[3,4] The chemical transformation of biomass
into biofuel involves a multistep process, namely, 1) pretreat-
ment of biomass into cellulosic components, 2) acid-catalyzed
hydrolysis of cellulose into sugar components and 3) catalytic
transformation of sugars into fuel components via 5-hydroxy-
methylfurfural (HMF) as an intermediate.[5] Recent studies have
shown that lignocellulosic biomass can be dissolved in an ionic
liquid (IL) and converted into fuels without the need to isolate
the cellulosic components.[6] Dumesic et al. first reported the
synthesis of 2,5-dimethylfuran (DMF), a promising liquid fuel,
from fructose by hydrogenation–hydrogenolysis of the HMF in-
termediate.[7]
5-chloromethylfurfural from sugar and biomass.[12,13] However,
these processes involved multistep reactions and required an
additional separation step. Recently, EMF was synthesized from
macroalgae-derived agar[14] and sugar derivatives using acidic
IL catalysts.[15]
As reported by Dumesic et al., the first step of the direct
conversion of fructose to DMF (71% yield) involved acid-cata-
lyzed dehydration to HMF followed by hydrogenation and hy-
drogenolysis of HMF with a Cu–Ru/C catalyst.[7] Binder and
Raines reported the synthesis of DMF from untreated corn
stover, giving a 9% DMF yield based on the cellulose content
of the corn stover.[16] This two-step synthesis of DMF involved
the CrCl3–HCl-catalyzed transformation of corn stover into
HMF, followed by hydrogenation–hydrogenolysis of HMF to
DMF by the Cu-Ru/C catalyst in the presence of H2. In this pro-
cess, a toxic chromium salt along with a mineral acid was used
as the catalyst for the degradation of corn stover into HMF.
Recently, Yang and Sen reported the conversion of biomass-de-
rived carbohydrates to 5-methylfurfural (MF)[17] and a promising
liquid fuel 2,5-dimethyltetrahydrofuran (DMTHF)[18,19] with
good yields using homogeneous RuCl3 and RhCl3 catalysts. The
same authors have also used a heterogeneous Pd/C catalyst
for the synthesis of MF from fructose.[17] Chidambaram and Bell
reported a two-step approach for the catalytic conversion of
glucose to DMF with a Pd/C catalyst in ILs, which gave a maxi-
Bioethanol, the only renewable liquid fuel currently pro-
duced in large quantities, suffers from several limitations, in-
cluding low energy density, high volatility, and contamination
by the absorption of atmospheric water. Compared to bioetha-
nol, DMF is considered as an ideal liquid fuel because of its su-
perior energy density (30 kJcmÀ3) and high research octane
number (RON=119).[8] DMF is immiscible with water and
easier to blend with gasoline than ethanol. Recently, biomass-
derived DMF has been successfully tested as a biofuel in
a
single-cylinder gasoline direct-injection (GDI) research
[a] S. De, Dr. S. Dutta, Prof. Dr. B. Saha
Laboratory of Catalysis, Department of Chemistry
University of Delhi, University Road
Delhi 110007 (India)
engine.[9] The performance of DMF was satisfactory against
gasoline in terms of combustion, ignition, and emission charac-
teristics. 5-Ethoxymethyl-2-furfural (EMF)[10] is another promis-
ing biofuel with a high boiling point (2358C) and comparable
energy density (8.7 kWhLÀ1) to that of standard gasoline
(8.8 kWhLÀ1) and diesel (9.7 kWhLÀ1).[11] EMF was prepared via
Fax: (+91)011-27667794
E-mail: bsaha@chemistry.du.ac.in
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201200031.
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S. De, S. Dutta, and B. Saha
mum 47% conversion of glucose with 32% DMF selectivity.[20]
However, a potential drawback of this method was that the IL
decreased the solubility of H2. Hence, a high pressure of H2
(6.2 MPa) was required, which made the process energy inten-
sive. Under similar reaction conditions, the Ru/C catalyst failed
to produce DMF from HMF.[20] Thananatthanachon and Rauch-
fuss reported a effectiveness of the Pd/C catalyst for the one-
pot conversion of fructose to DMF with a maximum 51% over-
all DMF yield.[21]
thyl)furan (BHMF) followed by the hydrogenolysis of BHMF to
DMF. In an earlier report, the synthesis of BHMF from fructose
was carried out by using a Pd/C catalyst and FA as a hydrogen
source.[20] In the present study, the hydrogenation–hydrogeno-
lysis steps were performed using the Ru/C catalyst in the pres-
ence of two equivalents of FA and a catalytic amount of con-
centrated H2SO4. Detailed reaction conditions and yields of
DMF from various substrates are summarized in Table 1. In the
case of fructose, 30% DMF was obtained from a reaction con-
ducted with oil-bath heating (Table 1, entry 1). In addition,
32% HMF intermediate, 20% FMF intermediate, and 12% LA
were also present in the product solution as identified from
the 1H NMR spectrum (Figure S4). Based on quantified DMF,
unconverted intermediates, and LA, the total conversion of
fructose can be calculated to be 94%. As microwave (MW)-as-
sisted biomass transformation has been effective for selective
conversions to HMF,[25,26] the present one-pot transformation of
fructose to DMF was also carried out under MW-assisted heat-
ing. The first step involved the synthesis of HMF in the pres-
ence of FA as a dehydration catalyst at 1508C for 10 min. In
a consecutive step, the intermediate HMF was converted to
DMF by hydrogenation and hydrogenolysis reactions using the
Ru/C catalyst at 758C for 45 min in THF. The reaction produced
a maximum yield of 32% DMF (Table 1, entry 2). A comparative
analysis of the results shown in entries 1 and 2 of Table 1 re-
vealed that the MW-assisted heating experiment produced
32% DMF in 55 min as compared to 30% DMF in 17 h with oil-
Herein, we report the effectiveness of the Ru/C catalyst for
the conversion of fructose and biomass into DMF. Our strategy
is to execute the multistep DMF synthesis from an HMF plat-
form[22] in a single vessel. We used formic acid (FA) as a H2
source and a deoxygenating agent. The IL [DMA]+[CH3SO3]À
(DMA=N,N-dimethylacetamide) was found to be effective for
the hydrolysis and dehydration of untreated biomass into HMF
in the first step of the sequential transformation. To address
the sustainability issue, we used inexpensive and readily avail-
able lignocellulosic biomass substrates, for example, sugarcane
bagasse and agar.
Results and Discussion
The Ru/C catalyst has long been known for its effectiveness in
the hydrogenolysis of polyols to alkanes.[23,24] In all cases, the
active carbon support acts as a binder for the facile hydroge-
nation. The weak RuÀC(support) interaction in the catalyst can
also greatly influence the reactivity of the Ru species. As dis-
cussed above, the active carbon-supported Pd catalyst showed
moderate activity in the preparation of DMF from fructose;[21]
however, the Ru/C catalyst was ineffective in producing DMF
from HMF in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl)
under H2 (6.2 MPa).[20] To examine the catalytic effectiveness of
Ru/C in the presence of a sustainable hydrogen storage agent,
FA, the present DMF synthesis from biomass and biomass-de-
rived carbohydrate has been investigated under mild condi-
tions. The Ru/C catalyst with 5 wt% Ru loading was prepared
by ultrasonicating a RuCl3·3H2O and activated charcoal mixture
followed by the reduction of the metal precursor with NaBH4
(see the Experimental Section). Characterization of the Ru/C
catalyst by means of powder XRD and high-resolution TEM
(HRTEM, Figures S1 and S2 in the Supporting Information)
showed the presence of metallic Ru on the activated carbon
surface. Preliminary experiments to study the effectiveness of
the Ru/C catalyst for the one-pot transformation of HMF to
DMF were performed in the presence of FA as a hydrogen
source and a catalytic amount of concentrated H2SO4. The
1H NMR spectrum of the product solution using mesitylene as
an internal standard revealed the formation of 37% DMF along
with 43% 5-(formyloxymethyl)furfural (FMF) intermediate, 12%
unconverted HMF, and 3% levulinic acid (LA, Figure S3). LA is
the rehydration product of HMF with water. The formation of
DMTHF and MF was not evidenced under our mild reaction
conditions, as observed under high-pressure conditions
(2.1 MPa H2) for the conversion of fructose with RuCl3 and Pd/
C catalysts.[17–19] The catalytic transformation of HMF to DMF
takes place by the hydrogenation of HMF to bis(hydroxyme-
1
bath heating. The H NMR spectra revealed that the transfor-
mation of HMF to DMF occurred via the formation of FMF as
an intermediate. The 1H NMR spectra of the reaction mix-
ture showed one singlet at d=9.65 ppm corresponding to the
ÀCHO proton and two doublets at d=7.21 and 6.61 ppm cor-
responding to the furan ring protons of FMF (Figures S5 and
S6). The formyloxy functionalization of the ÀCH2OH group of
HMF (Scheme 1) led to the formation of FMF before the addi-
Scheme 1. Formation of FMF intermediate during DMF synthesis.
tion of Ru/C catalyst and H2SO4. In the presence of Ru/C, FA,
and H2SO4, the sequential hydrogenation and hydrogenolysis
reactions occurred and DMF was obtained as the desired prod-
uct.
This one-pot DMF synthesis was extended to a-cellulose. As
shown in Table 1, the Brønsted-acidic IL [DMA]+[CH3SO3]À was
used as a catalyst in the first step for the conversion of a-cellu-
lose into HMF in a DMA/LiCl solvent at 1508C under oil-bath
heating. In the second step, FA was added for the formylation
of HMF. In the third step of this one-pot reaction, FMF was
converted into the desired product, DMF, in the presence of
Ru/C and a catalytic amount of H2SO4. The yield of DMF from
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Conversion of Biomass into Liquid Fuels
Table 1. DMF preparation from different substrates.
Entry
1
Substrate
fructose
Amount Step 1
Step 2
T [8C] t [min] reagent
Step 3
T [8C] t [min] reagent
DMF yield
[g]
reagent
T [8C] t [min] [g] ([%])[a]
0.72
FA (2 mL)
150 120
Ru/C (0.8 g)
75
900
45
60
5
–
–
–
–
0.116 (30)
0.031 (32)
0.054 (14)
0.011 (16)
0.049
H2SO4 (28 mL)
THF (8 mL)
Ru/C (0.2 g)
H2SO4 (8 mL)
THF (2 mL)
FA (0.8 mL)
2 (MI[b]
)
)
)
)
fructose
0.18
0.65
0.12
FA (0.5 mL)
150
10
60
10
60
10
60
10
75
–
–
3
a-cellulose
a-cellulose
[DMA]+[CH3SO3]À (0.065 g) 150
DMA/LiCl (6.5 g)
150
150
150
Ru/C (0.4 g)
H2SO4 (14 mL)
THF (6 mL)
Ru/C (0.1 g)
H2SO4 (3 mL)
THF (1.5 mL)
Ru/C (0.4 g)
H2SO4 (14 mL)
THF (6 mL)
Ru/C (0.1 g)
H2SO4 (4 mL)
THF (1.5 mL)
Ru/C (0.8 g)
H2SO4 (35 mL)
THF (10 mL)
Ru/C (0.2 g)
H2SO4 (5 mL)
THF (1.2 mL)
75 900
4 (MI[b]
[DMA]+[CH3SO3]À (0.012 g) 150
DMA/LiCl (1.2 g)
FA (0.2 mL)
FA (1.0 mL)
75
45
5
sugarcane bagasse 0.50
sugarcane bagasse 0.10
[DMA]+[CH3SO3]À (0.05 g)
DMA/LiCl (8.0 g)
150
150
150
60
5
75 900
6 (MI[b]
[DMA]+[CH3SO3]À (0.01 g)
DMA/LiCl (1.5 g)
FA (0.25 mL) 150
75
45
0.011
7
agar
agar
1.00
0.15
[DMA]+[CH3SO3]À (0.1 g)
DMA/LiCl (6.0 g)
FA (2.0 mL)
FA (0.4 mL)
150
150
60
5
75 900
0.143 (24)
0.024 (27)
8 (MI[b]
[DMA]+[CH3SO3]À (0.015 g) 150
DMA/LiCl (1.0 g)
75
45
[a] GC analysis. DMF molar percentage was calculated with respect to the starting substrates. [b] Irradiation at 300 W.
a-cellulose was 14% over 17 h (Table 1, entry 3). The total con-
version of a-cellulose after the first step was 39% with the for-
mation of 18% total reducing sugar, as determined by the
phenol–H2SO4 method.[27] In addition to DMF, unconverted
HMF and FMF intermediates may also be present in the final
crude product as observed in the conversion of a pure HMF
sample. The conversion of a-cellulose under MW-assisted heat-
ing produced 16% DMF in a total reaction time of 1 h (Table 1,
entry 4). The yield of DMF from a-cellulose is significantly
lower than that obtained from fructose, which could be due to
the robust crystalline structure of a-cellulose, which consists of
a 3D network of hydrogen bonding interactions.[6,28] Therefore,
the degradation of cellulose into hexose units was carried out
with a strongly acidic IL catalyst, [DMA]+[CH3SO3]À. Our previ-
ous study has shown that the maximum yield of HMF from a-
cellulose was 29% when using the [DMA]+[CH3SO3]À catalyst.[29]
Nevertheless, a-cellulose is a new biorenewable substrate
capable of producing DMF under the present reaction
conditions.
ments produced 0.049 and 0.011 g of DMF from 0.5 and 0.1 g
of starting sugarcane bagasse in 17 and 1 h, respectively
(Table 1, entries 5 and 6). This result shows that the Ru/C cata-
lyst is quite effective considering that sugarcane bagasse con-
tains only 25% hemicellullose, 50% cellulose (i.e., a total of
about 75% carbohydrate), and 25% lignin.[30] The conversion
of cellulose to HMF is more difficult than that of hemicellulose
due to the difference in their microcrystalline structures, which
makes cellulose more resistant to hydrolysis than hemicellulo-
ses.[31] In the oil-bath heating experiment, the total conversion
of sugarcane bagasse after the first reaction step was 52%
with the formation of 20% total reducing sugar as determined
by using the phenol–H2SO4 method.[27]
A
13C NMR investigation
of the reaction products of the second reaction step of sugar-
cane bagasse conversion confirmed the formation of FMF from
its characteristic signals at d=178.0 and 160.1 ppm corre-
sponding to ÀOCHO and ÀCHO groups, respectively (Fig-
ure 1a). Figure 1b shows the 13C NMR spectra of the final DMF
product along with some unconverted FMF intermediate. In
this process, the use of FA as a hydrogen source as well as
a deoxygenating agent enabled the three-step reaction to be
performed in one pot. The amount of FA (0.8–1.0 mL) required
for the conversion of cellulose and sugarcane bagasse sub-
strates was less than that used for the fructose conversion
(2 mL). This is because the role of FA in the conversion of cellu-
lose and sugarcane bagasse substrates was limited to form-
yloxy ester (ÀCH2OCHO) formation, whereas in the case of fruc-
tose conversion, FA also acted as a dehydration catalyst for
HMF formation in the first step. Due to the robust crystalline
structure of a-cellulose with its 3D network of hydrogen bond-
The substrate scope of this method for the one-pot synthe-
sis of DMF was extended to sugarcane bagasse and agar. As
shown in Table 1, both oil-bath and MW-assisted heating ex-
periments were performed to compare the DMF yields. In the
case of sugarcane bagasse, [DMA]+[CH3SO3]À was used for the
in situ conversion of this untreated biomass into HMF at 1508C
for 1 h under oil-bath heating. In the second step, FA was
added for the formylation of the HMF intermediate. In the sub-
sequent step, Ru/C, H2SO4, and THF were added to facilitate
the hydrogenation–hydrogenolysis of HMF to produce the
product, DMF. The oil-bath and MW-assisted heating experi-
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S. De, S. Dutta, and B. Saha
ate A. The subsequent deoxygenation of intermediate A by
the Ru/C catalyst led to the formation of intermediate B. The
final product, DMF, was formed via the formyloxy ester (inter-
mediate C) of intermediate B in the presence of FA and H2SO4
followed by another deoxygenation step in the presence of
the Ru/C catalyst. Scheme 2 summarizes the formylation, hy-
drogenation, and hydrogenolysis steps discussed above.
Thananatthanachon and Rauchfuss reported that the Pd/C-
FA catalytic system afforded overall 51% DMF from fructose.[21]
Chidambaram and Bell attempted HMF conversion with the
Ru/C catalyst in [EMIM]Cl under 6.2 MPa H2. DMF was not de-
tected in the final product mixture.[20] We found that carbon-
supported, highly dispersed Ru nanoparticles of 5–8 nm are
quite effective for DMF synthesis, giving a maximum 32% DMF
yield from fructose.
The facile conversion of macroalgal polymeric carbohydrates
into biofuels is a promising area of research.[32] The synthesis
of DMF from macroalgae-derived agar using a suitable catalyst
is a challenging goal. To overcome this challenge, we have
tested the one-pot reaction for the conversion of macroalgae-
derived agar into DMF under oil-bath and MW-assisted heat-
ing. As described in the experimental section and summarized
in Table 1, the [DMA]+[CH3SO3]À catalyst was used for the con-
version of agar into HMF. The subsequent additions of FA, Ru/
C, and H2SO4 in Steps 2 and 3 resulted in the formation of
24% DMF in 17 h under oil-bath heating (Scheme 3, Table 1,
Figure 1. a) 13C NMR (CDCl3) spectrum of the reaction mixture showing FMF
intermediate during the progression of a reaction between sugarcane bag-
asse and [DMA]+[CH3SO3]À catalyst in DMA/LiCl (10 wt%) and subsequent
heating with FA. b) 13C NMR spectrum (CDCl3) of the final oily product ob-
tained from sugarcane bagasse as a starting substrate.
Scheme 3. One-pot conversion of macroalgae-derived agar into DMF.
ing interactions,[6,28] the [DMA]+[CH3SO3]À catalyst was used for
hydrolysis and subsequent dehydration of cellulose and sugar-
cane bagasse substrates into HMF. We found that FA was inef-
fective for in situ HMF formation from cellulose and sugarcane
entry 7). The conversion of agar after the first reaction step
was 67% with the formation of 23% total reducing sugar. In
addition to DMF, unconverted HMF and FMF intermediates are
also expected to be present in the final crude product in the
same ratio as that observed for the conversion of pure HMF.
The same reaction under MW-assisted heating produced 27%
DMF in 1 h (Table 1, entry 8).
1
bagasse. In both reactions, H and 13C NMR spectra of the reac-
tion mixture revealed the formation of FMF intermediate after
the addition of FA. In the presence of the Ru/C catalyst,
FA acted as a hydrogen source for the hydrogenation of the
ÀCHO group of HMF (Step 1 in Scheme 2) to form intermedi-
A previous report demonstrated the formation of a maximum
10% yield of HMF from agar powder using a solid Brønsted-
acidic Dowex 50WX8 catalyst in [EMIM]Cl.[14] To improve the
degradation of the polymeric unit present in agar, we have
used the [DMA]+[CH3SO3]À catalyst in the present study, which
indeed accelerated the in situ HMF formation as evidenced
from the 24% yield of DMF.
In addition to the broad substrate scope of the present one-
pot DMF synthesis combining the three steps, we have devel-
oped a synthesis method for the efficient conversion of HMF
and inexpensive biomass to EMF, another promising biofuel,
by using [DMA]+[CH3SO3]À as an acid catalyst for the etherifica-
tion of HMF in ethanol. We began with HMF (0.5 g) as a sub-
strate, which was reacted with [DMA]+[CH3SO3]À catalyst
(0.05 g) in ethanol (10 mL) at 1208C. As shown in Table 2
Scheme 2. Transformation of sugar and biomass-derived HMF to DMF.
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Conversion of Biomass into Liquid Fuels
ing a mixture of EMF and EL in a 9:1 ratio (Table 2, entry 4). A
comparative analysis of the results shown in Table 2 revealed
that the reaction with sugarcane bagasse produced more EMF
than that with cellulose fibers under identical reaction condi-
tions. We have also investigated the formation of EMF as
a function of reaction time by monitoring the progression of
Table 2. EMF preparation from HMF and biomass substrates.[a]
Entry Substrate ([g])
[DMA]+[CH3SO3]À EtOH
t
Yield[b]
[g]
[mL] [h] [g] ([%])
1
2
3
4
HMF (0.5)
fructose (2.0)
cellulose fibers (1.0)
0.05
0.20
0.20
10
20
15
15
15 0.56 (92)
16 1.09 (64)
20 0.21 (22)
20 0.28
1
1
the reaction by using H NMR spectroscopy. H NMR spectra of
the reaction mixture were recorded at regular time intervals in
the presence of mesitylene as an internal standard. The yield
of the products (EMF+EL) was determined by comparing the
signal intensity of the ÀCHO proton (d=9.59 ppm) of EMF
with that of the mesitylene aromatic ring proton at d=
6.78 ppm. The yield of HMF was recorded as a function of reac-
tion time for all substrates. The results plotted in Figure 2
reveal that HMF is a preferred substrate for the quantitative
conversion to EMF with 90% selectivity, whereas the strong 3D
network of H bonds[6] in the structure of cellulose precludes its
facile hydrolysis.
sugarcane bagasse (1.0) 0.20
[a] Reaction conditions: T=1208C. [b] Isolated yield comprising EMF+EL
in a 9:1 ratio.
(entry 1), almost quantitative conversion of HMF was achieved
in 15 h under oil-bath heating. The oily liquid product was pu-
rified by using column chromatography. The isolated yield of
purified product was 0.56 g. Analysis of the isolated product
1
by means of H and 13C NMR spectroscopy revealed the forma-
tion of EMF in a 9:1 ratio with ethyl levulinate (EL).[33] The ratio
of EMF to EL in the isolated product was determined by com-
paring the signal intensities of the ÀOCH2CH3 peaks. The rea-
sons for the simultaneous formation of EMF and EL could be
1) catalysis of the ring-opening of EMF by the Brønsted-acidic
[DMA]+[CH3SO3]À catalyst and 2) esterification of LA, which was
formed as a byproduct from the rehydration of HMF. The pres-
ent one-pot synthesis of EMF from biomass refrained from the
[14]
use of toxic CrCl2 and concentrated HCl[10] used in previously
reported methods. A recent study reported the formation of
EL as a major product from the conversion of a series of sub-
strates including HMF, fructose, and glucose over 22 h in the
presence of sulfonic-functionalized IL catalyst.[15] However, the
same reaction produced EMF as the major product when car-
ried out for 2 h. In the present study, EMF was obtained as
a major product from the reaction between [DMA]+[CH3SO3]À
and HMF, suggesting that the acid strength of the catalyst was
enough for the complete etherification of HMF in ethanol and
hence that the LA formation, esterification of which led to EL,
was minimal.
The effectiveness of the [DMA]+[CH3SO3]À catalyst was fur-
ther investigated for the synthesis of EMF from fructose, cellu-
lose fibers, and inexpensive biomass waste, sugarcane bagasse,
at 1208C under oil-bath heating. A reaction between fructose
(2.0 g) and [DMA]+[CH3SO3]À (0.2 g) in ethanol for 16 h gave
1.09 g isolated product (Table 2, entry 2).
1H NMR spectral data of the purified product revealed the
complete conversion of the in situ-formed HMF into a mixture
of EMF and EL in a 9:1 ratio (Figures S11 and S12). In the case
of cellulose, a reaction between cellulose fibers (1.0 g) and
[DMA]+[CH3SO3]À (0.2 g) in ethanol at 1208C produced 0.21 g
isolated oily product in 20 h (Table 2, entry 3). The progression
of the reaction was monitored by the appearance and disap-
pearance of the proton signal of the ÀCHO group of the inter-
mediate HMF. The results again showed the complete conver-
sion of in situ-generated HMF into a mixture of EL and EMF.
The [DMA]+[CH3SO3]À catalyst was also effective for the conver-
sion of sugarcane bagasse into EMF in ethanol. The one-pot re-
action between [DMA]+[CH3SO3]À (0.2 g) and sugarcane bag-
asse (1.0 g) at 1208C gave 0.28 g isolated oily product contain-
Figure 2. EMF formation curves as a function of reaction time (h) for differ-
ent substrates catalyzed by [DMA]+[CH3SO3]À in ethanol.
Conclusions
We have described the one-pot synthesis of promising bio-
fuels, 2,5-dimethylfuran (DMF) and 5-ethoxymethylfurfural
(EMF), from a range of readily available biomass substrates.
The first step of the one-pot reaction involved in situ 5-hy-
droxyemthylfurfural (HMF) synthesis using formic acid (FA) as
a catalyst for fructose and the [DMA]+[CH3SO3]À (DMA=N,N-di-
methylacetamide) catalyst for cellulose and untreated biomass.
In the subsequent steps, HMF was transformed into DMF by
hydrogenation and hydrogenolysis reactions using FA and Ru/
C. We found that the Ru/C catalyst is quite effective, giving
a maximum yield of 32% DMF from fructose and 27% from
agar. We have identified 5-(formyloxymethyl)furfural as an in-
1
termediate during the reactions by means of H and 13C NMR
spectroscopy. The Brønsted-acidic IL catalyst, [DMA]+[CH3SO3]À,
was also effective for the clean synthesis of 5-ethoxymethylfur-
fural (EMF), another potential biofuel, from HMF, fructose, sug-
arcane bagasse, and agar in ethanol. Under mild reaction con-
ditions, HMF was quantitatively converted to EMF with high se-
lectively. Investigations are underway to examine the effective-
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S. De, S. Dutta, and B. Saha
CDCl3): d=2.24 (s, 6H, 2CH3), 5.82 ppm (s, 2H, CH); 13C NMR
(100 Hz, CDCl3): d=13.45 (CH3), 105.91 (CH), 150.15 ppm (CH).
ness of new catalysts (e.g., bimetallic carbon or clay-supported
catalysts) and hydrogen sources for the efficient hydrogena-
tion–hydrogenolysis of HMF to DMF.
Preparation of DMF from a-cellulose: a-Cellulose (0.65 g) and
[DMA]+[CH3SO3]À (0.065 g) were mixed with DMA/LiCl (6.5 g) in
a round-bottomed flask. The reaction mixture was heated to reflux
with continuous stirring at 1508C for 1 h. After 1 h, FA (0.8 mL) was
added, and the mixture was heated to reflux for another 1 h at
1508C. The resulting dark solution was cooled to room tempera-
ture and diluted with THF (6 mL). After adding a catalytic amount
of H2SO4 (14 mL) and Ru/C (0.4 g) to the resulting solution, the mix-
ture was heated to reflux at 758C for 15 h. After completion of the
reaction, the Ru/C catalyst was recovered by filtration. The filtrate
was diluted with H2O (5 mL), and the organic layer was extracted
into diethyl ether. The product was obtained from the organic
layer after removing THF and diethyl ether by vacuum distillation
at 808C.
Experimental Section
Materials
d-Fructose, a-cellulose, 2,5-dimethylfuran, formic acid, and activat-
ed carbon were purchased from Sigma–Aldrich. RuCl3·3H2O and
agar powder were obtained from SRL, India. DMA, THF, diethyl
ether, and LiCl were purchased from Spectrochem, India. Sugar-
cane bagasse was collected from a local sugarcane juice shop. Cel-
lulose and sugarcane bagasse were oven-dried to constant weight
at 808C prior to use.
Preparation of DMF from sugarcane bagasse: Sugarcane bagasse
(0.50 g) and [DMA]+[CH3SO3]À (0.050 g) were mixed with DMA/LiCl
(8.0 g) in a round-bottomed flask. The reaction mixture was heated
to reflux with continuous stirring at 1508C for 1 h. FA (1.0 mL) was
added, and heating was continued for another 1 h at 1508C. The
mixture was cooled to room temperature, and unreacted sugar-
cane bagasse was removed from the solution by filtration. The fil-
trate was mixed with THF (6 mL), concentrated H2SO4 (14 mL), and
Ru/C (0.4 g). The resulting solution was heated to reflux with con-
tinuous stirring at 758C for 15 h. After completion of the reaction,
the Ru/C catalyst was recovered by filtration. The filtrate was dilut-
ed with H2O (4 mL), and the organic layer was extracted into dieth-
yl ether. The desired product was obtained from the organic layer
after removing THF and diethyl ether by vacuum distillation at
808C.
Characterization
HRTEM images of Ru/C were recorded by using a TECNAI G2T30,
u-TWIN instrument with a tungsten filament as the electron
source. Powder XRD data for Ru/C were collected by using
a Rigaku Miniflex 2 instrument. Conversions of d-fructose, cellulose,
and sugarcane bagasse to DMF under MW-assisted heating were
performed by using a CEM Matthews WC Discover microwave reac-
tor, model no. 908010 DV9068, equipped with programmable pres-
sure and temperature controller. H and 13C NMR spectra were col-
1
lected by using a JEOL JNM ECX-400 P 400 MHz instrument, and
data were processed by using the JEOL DELTA program, version
4.3.6. DMF yields were measured by using a Shimadzu GC-2014
chromatograph equipped with a flame ionization detector (FID)
detector. Conversions of a-cellulose, sugarcane bagasse, and agar
substrates during DMF synthesis were determined by the change
of substrate weight before and after the first step of the reaction.
Preparation of DMF from agar: [DMA]+[CH3SO3]À and agar powder
(1.0 g) (1.0 g) were mixed with DMA/LiCl (6 g) in a round-bottomed
flask. The reaction mixture was heated to reflux at 1508C for 1 h.
FA (2.0 mL) was added and stirring was continued for 1 h at 1508C.
The mixture was cooled to room temperature, and unreacted agar
was removed by filtration. The filtrate was mixed with THF (10 mL),
concentrated H2SO4 (35 mL) and Ru/C (0.8 g) and heated to reflux
at 758C for 15 h. The desired product was extracted as described
in the preparation from sugarcane bagasse.
Preparation of Ru/C
RuCl3·3H2O (130 mg) and activated charcoal (1.0 g, 100 mesh size)
were added to a mixture of THF and H2O (100 mL, 1:1, v/v). After
the mixture was ultrasonicated for 1 h and mechanically stirred for
another 10 h, a solution (10 mL) containing an equivalent amount
of NaBH4 and Na2CO3 with respect to RuCl3·3H2O was added drop-
wise, and the mixture was stirred for 1 h at 108C. The material was
collected by filtration, washed with distilled water and ethanol,
and dried in a vacuum oven at 608C.
Preparation of DMF from HMF: A suspension of HMF (0.1 g), FA
(0.31 mL), H2SO4 (6 mL), THF (4 mL), and Ru/C (0.16 g) was heated
to reflux at 758C with continuous stirring for 15 h. After cooling
the solution to room temperature, the Ru/C was separated by fil-
tration, and the filtrate was mixed with H2O (1 mL). The organic
phase was extracted into diethyl ether. A crude product containing
a mixture of DMF, unconverted HMF, FMF intermediate, and LA
was obtained after removing THF and diethyl ether by vacuum dis-
tillation at 808C.
Preparation of DMF under oil-bath heating
Preparation of DMF from fructose: Fructose (0.72 g) and FA
(2.0 mL) were mixed in a round-bottomed flask and heated to
reflux with continuous stirring at 1508C for 2 h. The resulting dark
solution was cooled to room temperature and diluted with THF
(8 mL). A catalytic amount of concentrated H2SO4 (28 mL) and Ru/C
(0.8 g) were then added to the dark solution. The mixture was
heated to reflux at 758C for an additional 15 h. After cooling the
solution to room temperature, the Ru/C catalyst was separated by
filtration. The filtrate containing the desired product was mixed
with H2O (5 mL). The organic phase was extracted into diethyl
ether (3ꢁ5 mL). A crude product containing a mixture of DMF, un-
converted HMF, and FMF intermediates and LA was obtained after
removing THF and diethyl ether by vacuum distillation at 808C.
Preparation of DMF under microwave-assisted heating
Preparation of DMF from fructose: A MW tube was charged with
fructose (0.18 g) and FA (0.5 mL). The loaded tube was inserted
into the MW reactor preset at 1508C for 10 min. After 10 min, THF
(2 mL), concentrated H2SO4 (8 mL), and Ru/C (0.2 g) were added,
and the reaction was continued under MW irradiation at 758C for
45 min. The reaction mixture was cooled to room temperature,
and the solid catalyst was removed by filtration. The filtrate was di-
luted with H2O (3 mL), and the organic layer was extracted into di-
ethyl ether. The desired product was obtained from the organic
1
Characteristic peaks for DMF in the NMR spectra: H NMR (400 Hz,
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Conversion of Biomass into Liquid Fuels
layer after removing THF and diethyl ether by vacuum distillation
at 808C.
product was isolated and characterized as described in the prepa-
ration from HMF.
Preparation of DMF from a-cellulose: [DMA]+[CH3SO3]À (0.012 g), a-
Cellulose (0.12 g), and DMA/LiCl (1.2 g) were loaded into a MW
tube. The loaded tube was inserted into the MW reactor preset at
1508C for 10 min. After 10 min, FA (0.2 mL) was added, and the re-
action was continued for another 5 min at the same temperature.
To the resulting dark solution, THF (1.5 mL), concentrated H2SO4
(3 mL), and Ru/C (0.1 g) were added, and the reaction was contin-
ued under MW irradiation at 758C for 45 min. The desired product
was extracted as described in the preparation from fructose.
Preparation of EMF from cellulose: Cellulose fibers (1.0 g) were sus-
pended in ethanol (15 mL) in a 100 mL round-bottomed flask. To
this was added [DMA]+[CH3SO3]À (0.20 g), and the reaction mixture
was heated to reflux with continuous stirring at 1208C for 20 h.
The oily liquid product was isolated and characterized as described
in the preparation from HMF.
Preparation of EMF from sugarcane bagasse: Sugarcane bagasse
(1.0 g) was suspended in ethanol (15 mL) in a 100 mL round-bot-
tomed flask. To this was added [DMA]+[CH3SO3]À (0.20 g), and the
reaction mixture was heated to reflux with continuous stirring at
1208C for 20 h. The oily liquid product was isolated and character-
ized as described in the preparation from HMF.
Preparation of DMF from sugarcane bagasse: Sugarcane bagasse
(0.10 g), [DMA]+[CH3SO3]À (0.01 g), and DMA/LiCl (1.5 g) were
loaded into a MW tube. The loaded tube was inserted into the MW
reactor preset at 1508C for 10 min. After 10 min, FA (0.25 mL) was
added, and the reaction was continued for another 5 min at the
same temperature. The mixture was cooled to room temperature,
and unreacted sugarcane bagasse was removed by filtration. The
filtrate was mixed with THF (1.5 mL), a catalytic amount of concen-
trated H2SO4 (4 mL) and Ru/C (0.1 g), and the reaction was contin-
ued under MW irradiation at 758C for another 45 min. The desired
product was extracted as described in the preparation from
fructose.
Determination of DMF yield
The yield of DMF was measured by using a GC (Shimadzu GC-
2014) equipped with a FID detector and Zebron (ZB-35) capillary
column (0.32 mm, inner diameter 0.25 mmꢁ30 m). Essential param-
eters of the GC analysis were as follows: Injection volume 1.0 mL,
inlet temperature 2708C, detector temperature 3008C, and a split
ratio of 1:100. The initial column temperature of 508C (2 min) was
increased with temperature ramp of 108CminÀ1 to the final tem-
perature of 2808C. The diethyl ether extractant of the reaction mix-
ture was diluted with methanol for the GC run. DMF was identified
by using its retention time in comparison to an authentic sample.
The peak of the gas chromatogram was integrated, and the actual
concentration of each component was obtained from the precali-
brated plot of peak area against concentration.
Preparation of DMF from agar: [DMA]+[CH3SO3]À (0.015 g), agar
powder (0.15 g), and DMA/LiCl (1 g) were loaded into a MW tube.
The loaded tube was then inserted into the MW reactor preset at
1508C for 10 min. After 10 min, FA (0.4 mL) was added, and the re-
action was continued for another 5 min at the same temperature.
The mixture was cooled to room temperature, and unreacted agar
was removed by filtration. The filtrate was mixed with THF
(1.2 mL), a catalytic amount of concentrated H2SO4 (5 mL) and Ru/C
(0.2 g), and the reaction was continued under MW irradiation at
758C for another 45 min. The desired product was extracted as de-
scribed for the preparation from fructose.
Acknowledgements
We acknowledge Ms. Minakshi Singh, Department of Chemistry,
Mewar University, Rajasthan, India for GC measurement of DMF
yields. B.S. is grateful to the University Grant Commission (UGC),
India for financial support and the University of Delhi. S. Dutta
thanks UGC, India for a DS Kothari Postdoctoral Fellowship. S. De
thanks UGC, India for a Junior Research Fellowship.
Preparation of EMF
Preparation of EMF from HMF: The synthesis of EMF from HMF
was carried out in a 100 mL round-bottomed flask under oil-bath
heating. The flask was charged with HMF (0.5 g), [DMA]+[CH3SO3]À
(0.05 g),and ethanol (10 mL) and heated to reflux with continuous
stirring at 1208C for 15 h. The reaction mixture was cooled to
room temperature, ethanol was evaporated under vacuum, and
the oily residue was column chromatographed with a silica gel
(200–400 mesh) as the stationary phase and a mixed dichlorome-
thane/diethyl ether solvent (2:1, v/v) as the mobile phase. After
separating [DMA]+[CH3SO3]À, the oily liquid product was character-
Keywords: biomass
·
heterogeneous
catalysis
·
hydrogenolysis · ionic liquids · liquid fuel
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Published online on && &&, 0000
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FULL PAPERS
Biomass breakdown in one pot: The
one-pot conversion of lignocellulosic
and algal biomass into liquid fuel, 2,5-
dimethylfuran, has been achieved by
using a multicomponent catalytic
S. De, S. Dutta, B. Saha*
&& – &&
One-Pot Conversions of
Lignocellulosic and Algal Biomass into
Liquid Fuels
system comprising [DMA]+[CH3SO3]À
(DMA=N,N-dimethylacetamide), Ru/C,
and formic acid. A reaction route has
1
been elucidated based on H and 13C
NMR spectroscopic data. Another prom-
ising biofuel has also been synthesized
by using [DMA]+[CH3SO3]À as catalyst.
ChemSusChem 0000, 00, 1 – 9
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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