Acid-catalysed direct transformation of cellulose into methyl glucosides in methanol at moderate temperatures

Article abstract of DOI:10.1039/b925723c

Cellulose can be transformed into methyl glucosides in methanol with yields of 50-60% in the presence of several acid catalysts under mild conditions (≤473 K); H₃PW₁₂O₄₀ provides the highest turnover number (～73 in 0.5 h)

Full text of DOI:10.1039/b925723c

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Acid-catalysed direct transformation of cellulose into methyl glucosides
in methanol at moderate temperaturesw
Weiping Deng, Mi Liu, Qinghong Zhang,* Xuesong Tan and Ye Wang*
Received (in Cambridge, UK) 8th December 2009, Accepted 22nd January 2010
First published as an Advance Article on the web 6th February 2010
DOI: 10.1039/b925723c
Cellulose can be transformed into methyl glucosides in methanol
with yields of 50–60% in the presence of several acid catalysts
under mild conditions (r473 K); H3PW12O40 provides the
highest turnover number (B73 in 0.5 h) for the formation of
methyl glucosides among many acid catalysts examined.
The production of chemicals or fuels from renewable biomass
resources has attracted much attention because of the worldwide
demand for a decreased dependence on fossil resources.1 As the
most abundant source of biomass and because of its non-edible
Scheme 1 Catalytic conversion of cellulose to methyl glucosides in
nature, cellulose is a promising alternative for the sustainable
methanol.
production of chemicals and fuels.2 However, the direct
utilization of cellulose is still a challenge because of its robust
can be converted efficiently in methanol medium to methyl
crystalline structure. Processes for high-temperature pyrolysis or
glucosides (with a- and b-isomers), which are important
intermediates for the production of fine chemicals,1a in the
gasification of cellulose to bio-oils or syngas have been
developed,1 but these processes suffer from problems of high-
presence of an acid catalyst at r473 K (Scheme 1).
energy input and low selectivity. The transformation of cellulose
Non-catalytic degradations of cellulose were reported to
under mild conditions into glucose or a ‘‘platform’’ molecule,3
proceed in supercritical methanol under severe conditions,
which may be facilely converted into chemicals or fuels, is more
attained at 623 K and 43 MPa.8 We used much milder reaction
desirable. The hydrolysis of cellulose to glucose can be catalyzed
and the highest yield of methyl glucosides of B30% was
by enzymes at ambient temperatures,4 but the enzymatic route
conditions (r473 K and N2 pressure of 3 MPa, see ESIw for
still remains a slow and expensive process. Many studies have
experimental details), and under such conditions, no conversion
been contributed to the hydrolysis of cellulose catalyzed by
of cellulose (crystallinity, 85%) was observed in methanol. We
mineral acids at relatively lower temperatures (o523 K).5
first examined the catalytic performances of various dilute liquid
Although high yields of glucose can be achieved using
mineral or organic acids including HCl, HNO3, H2SO4, H3PO4
and CF3COOH with a concentration of 2.2–6.7 mmol LÀ1
concentrated H2SO4 (30–70%), the hydrolysis of cellulose with
(H+ concentration = 6.7 mmol LÀ1) for the conversion of
cellulose in methanol. Table 1 shows that the dilute H2SO4
provides a significant yield to methyl glucosides (48%, entry 4).
On the other hand, only very small amounts of products were
formed using HNO3 and CF3COOH, and no conversion of
cellulose was observed using other liquid mineral or organic acids.
We speculate that the relatively stronger acidity (lower pKa) and
the higher boiling point of H2SO4 may contribute to the out-
standing performance of the diluted H2SO4 (see Table S1, ESIw).
Methyl levulinate, which was likely formed by the subsequent
conversions of methyl glucosides (see Scheme S1, ESIw), was also
observed with a lower yield in the presence of dilute H2SO4. Note
that the concentration of H2SO4 used here is about one order of
magnitude lower than those typically used for the dilute acid-
catalyzed hydrolysis of cellulose (B50 mmol LÀ1) in water.5a
dilute acids (o1%), which is more feasible at a commercial scale,
affords lower glucose yields.5 Solid acids such as carbon materials
bearing SO3H groups and layered transition metal oxides (e.g.,
HNbMoO6) have also been examined for the hydrolysis of
cellulose, but the yield of glucose is low.6 Higher glucose yield
(40–60%) could only be attained in the conversion of the
cellulose with a decreased crystallinity after a pretreatment with
trifluoroacetic acid or ball milling.5,6c The use of ionic liquids as
reaction media could also enhance the efficiency for cellulose
conversions in the presence of an acid catalyst.7
The development of efficient approaches for the direct
transformation of cellulose, especially cellulose with a high
crystallinity, under mild conditions still remains a significant
challenge. Herein, we report our new finding that cellulose
State Key Laboratory of Physical Chemistry of Solid Surfaces,
National Engineering Laboratory for Green Chemical Productions
of Alcohols, Ethers and Esters, College of Chemistry and Chemical
Engineering, Xiamen University, Xiamen 361005, China.
E-mail: zhangqh@xmu.edu.cn, wangye@xmu.edu.cn;
Fax: +86-592-2183047; Tel: +86-592-2186156
w Electronic supplementary information (ESI) available: Experimental
details, properties of liquid acids, scheme for the formation of methyl
Table
1 further demonstrates that the Keggin-type
heteropolyacids, i.e., H4SiW12O40 and H3PW12O40, exhibit
catalytic performances similar to dilute H2SO4 for cellulose
transformation in methanol (entries 6 and 7). Some hetero-
polyacids, e.g., H3PW12O40, are expected to possess Brønsted
acidity stronger than H2SO4.9 However, reports on the utilization
of these heteropolyacids for the degradation of cellulose are
very scarce.10 A recent study showed that H3PW12O40 could
levulinate, effect of reaction time and XRD patterns of H3PW12O40
See DOI: 10.1039/b925723c
.
ꢀc
This journal is The Royal Society of Chemistry 2010
2668 | Chem. Commun., 2010, 46, 2668–2670

View Article Online
Table 1 Catalytic performances of various acid catalysts for the
conversion of cellulose to methyl glucosides in methanola
Yieldb (%)
M-a-G M-b-G ML
Entry Catalyst
Conv. (%)
1
2
3
4
5
6
7
8
HClc
0
1.0
0
76
2
95
95
2
39
100
100
0
0.20
0
0
0.10
0
0
0
0
2.8
0
3.0
5.3
0
c
HNO3 c
H3PO4c
H2SO4
28
20
0.090 0.040
CF3COOHc
H4SiW12O40
H3PW12O40
H-ZSM-5
Sulfated ZrO2
Nafion
28
25
0.50
9.0
19
15
26
26
29
36
20
18
0.30
7.0
14
11
18
19
23
26
9
0
10
11
12
13
14
15
9.2
9.0
7.0
4.0
3.0
2.0
Amberlyst-15
Carbon (cell.)-SO3H-98%d 90
Fig.
1
Effect of reaction time on catalytic performances of
Carbon (lig.)-SO3H-98%d
Lig.-SO3H-64%e
78
78
90
H3PW12O40 for the conversion of cellulose in methanol. Reaction
conditions: temperature, 468 K; cellulose, 0.50 g; methanol, 20 mL;
Lig.-SO3H-17%e
[H+], 2.6 mmol LÀ1
.
a
Reaction conditions: temperature, 468 K; catalyst, 0.10 g; cellulose,
b
We investigated the catalytic behaviours of three typical
catalysts, i.e., H2SO4, H3PW12O40 and lig.-SO3H-17%, for the
conversion of cellulose in methanol in more detail. In each
case, the increase in the H+ concentration first increased the
product yields, but a too high H+ concentration did not favor
the formation of methyl glucosides (Table 2). Yields of methyl
glucosides of 48, 53 and 61% were attained in the presence of
0.20 g; methanol, 20 mL; time, 1 h. M-a-G, M-b-G and ML denote
methyl-a-glucopyranoside, methyl-b-glucopyranoside and methyl
c
levulinate, respectively. Temperature, 473 K; [H+], 6.7 mmol LÀ1
;
d
cellulose, 0.50 g; methanol, 30 mL; time, 0.5 h. Prepared by
carbonization of cellulose (cell.) or lignin (lig.) at 723 K in N2 followed
e
by sulfonation in 98% H2SO4 at 353 K. Prepared by direct
sulfonation of lignin in 64 or 17% H2SO4 at 483 K.
H2SO4 ([H+], 6.7 mmol LÀ1), H3PW12O40 ([H+], 2.6 mmol LÀ1
)
and lig.-SO3H-17% ([H+], 5.0 mmol LÀ1), respectively. The
yield of methyl levulinate increased with the H+ concentration
in the cases of H2SO4 and H3PW12O40 at the expense of the
yields of methyl glucosides, suggesting that methyl levulinate was
formed by the acid-catalysed conversions of methyl
glucosides. The turnover number (TON) for the formation
of methyl glucosides was evaluated by the moles of methyl
glucosides formed per mole of H+. H3PW12O40 demonstrated
the highest TON; a TON of 73 was attained in 0.5 h with a
yield of 47% for the formation of methyl glucosides. The
catalyze the hydrolysis of a ball-milling pretreated cellulose to
glucose with a yield of 15% in aqueous medium.10 In our
system, H3PW12O40 catalyzed the conversion of cellulose to
methyl glucosides with a yield of 43%. The handling of
H3PW12O40 would be more facile than that of H2SO4, and it
does not require corrosion-resistant reactor.
Solid acids have also been examined for the transformation
of cellulose in methanol. Zeolite H-ZSM-5 showed a very low
reactivity possibly because its pore size is too small (0.55 nm)
to be accessed by cellulose. Sulfated ZrO2, which is known to
be a superacid, showed a medium activity, producing methyl
glucosides with a yield of 16% (Table 1, entry 9). The
polymeric resin-based materials containing SO3H groups such
as Nafion and Amberlyst-15 afforded relatively higher
activities probably because of the larger pores of these acidic
resins.7c The amorphous carbon bearing high density of SO3H
groups prepared by partial carbonization of cellulose at 723 K
in N2 followed by sulfonation in concentrated H2SO4 was
reported to be a superior catalyst for the saccharification of
cellulose in water medium.6a This carbon material, denoted as
carbon (cell.)-SO3H-98%, demonstrated a good performance
in our reaction, giving a yield of 44% to methyl glucosides
(Table 1, entry 12). The carbon material derived from the
carbonization of lignin followed by sulfonation in 98% H2SO4
(denoted as carbon (lig.)-SO3H-98%) was also effective for the
conversion of cellulose into methyl glucosides. Furthermore,
the direct sulfonation of lignin by 17% H2SO4 under refluxing
conditions followed by washing with water and drying
(denoted as lig.-SO3H-17%) resulted in an efficient catalyst
with a better yield to methyl glucosides (62%) (Table 1,
entry 15). These carbon materials with SO3H groups,
especially the lig.-SO3H-17%, dispersed better in methanol,
and this may result in the better catalytic performances.
Table 2 Effect of the H+ concentration on catalytic behaviours of
three typical catalysts for the conversion of cellulose in methanola
Yieldc (%)
H+ conc.b/
mmol LÀ1 Conv. (%)
TONd
M-a-G M-b-G ML
Catalyst
e
H2SO4
0.67
2.7
7
30
2.5
10
1.7
7.0
0
0
6.5
6.5
6.7
76
87
95
76
28
24
19
27
31
29
26
16
35
31
20
2.8 7.4
19
33
1.0
2.6
4.2
5.0
16
13
20
22
20
17
11
26
20
14
15
0
2.2
1.0
73
H3PW12O40
86
3.0 31
6.0 18
11 13
1.0 15
3.0 19
2.0 10
100
100
72
82
90
Lig.-SO3H-17%f 2.6
5.0
7.5
a
Reaction conditions: temperature, 468 K; cellulose, 0.50 g; methanol,
b
20 mL; time, 0.5 h. The H+ concentration was regulated by changing
the concentration of liquid acids or the weight of solid acids, the H+
concentration for solid acids was determined by an acid–base titration.6a
c
M-a-G, M-b-G and ML denote methyl-a-glucopyranoside, methyl-
d
b-glucopyranoside and methyl levulinate, respectively. TON was
calculated by the moles of methyl glucosides formed per mole of
H+
e
f
Temperature, 473 K; methanol, 30 mL. Time, 2 h.
.
ꢀc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 2668–2670 | 2669

View Article Online
Table 3 Comparison of cellulose conversions in methanol and in water in the presence of several typical acid catalystsa
In water medium
Yieldb (%)
H+ conc./mmol LÀ1 Conv. (%) Glucose Fructose HMF TONc Conv. (%) M-a-G M-b-G ML TONc
In methanol medium
Yieldb (%)
Catalyst
d
H2SO4
H4SiW12O40
H3PW12O40
6.7
3.5
2.6
28
20
16
30
9.6
7.1
6.0
4.3
4.2
3.0
2.4
1.2
0.6
0.5
2.6
1.5
3.1
3.6
3.7
76
85
86
82
28
33
31
35
20
24
22
26
2.8
2.0
3.0
3.0
7.4
25
31
19
Lig.-SO3H-17%e 5.0
12
a
b
Reaction conditions: temperature, 468 K; cellulose, 0.50 g; water (or methanol), 20 mL; time, 0.5 h. HMF, M-a-G, M-b-G and ML denote
c
5-hydroxymethyl furfural, methyl-a-glucopyranoside, methyl-b-glucopyranoside and methyl levulinate, respectively. TON was calculated by the
moles of glucose or methyl glucosides formed per mole of H+
.
d
e
Temperature, 473 K; methanol, 30 mL. Time, 2 h.
effects of reaction time for the three catalysts have also been
examined. Fig. 1 shows the result for the H3PW12O40 ([H+],
2.6 mmol LÀ1). The increase in reaction time first increased the
yield of methyl glucosides, but a too long reaction time
decreased the yield of methyl glucosides and increased those
of methyl levulinate and other degradation products, further
indicating the existence of consecutive conversions of methyl
glucosides to methyl levulinate. Similar tendencies have also
been observed for the other two catalysts (see Table S2, ESIw).
The conversion of cellulose in methanol was compared with
that in water under the same reaction conditions in the
presence of an acid catalyst. In water medium, fructose and
5-hydroxymethyl furfural (HMF) were formed as by-products
of glucose. The yield and the TON of glucose obtained in the
conversion of cellulose in water were significantly lower
than those of methyl glucosides attained in methanol in the
presence of any catalyst in Table 3, demonstrating that the
employment of methanol as a reaction medium is beneficial to
the degradation of cellulose to monosaccharides.
the concentrated product mixture. More than 80% of
H3PW12O40 could be recovered by such a simple procedure.
We clarified that the activity and the structure of the recovered
H3PW12O40 did not undergo significant changes (see Fig. S1,
ESIw). The conversion of cellulose could also proceed in
ethanol in the presence of H3PW12O40. We attained ethyl
glucosides with a yield of 42% at 468 K.
In conclusion, we have presented a novel catalytic approach
for the transformation of cellulose into methyl glucosides in
methanol under relatively mild conditions (r473 K). Dilute
H2SO4, heteropolyacids (i.e., H3PW12O40 and H4SiW12O40)
and several solid acids bearing SO3H groups can all catalyze
this transformation with good yields (440%). Among these
catalysts, H3PW12O40 provides the highest TON for the
formation of methyl glucosides. It is clarified that the
conversion of cellulose in methanol is more facile than that
in water, and methyl glucosides formed in methanol are more
stable against further degradations than glucose in water.
This work was supported by the NSF of China (20625310,
20873110, 20923004), the National Basic Program of China
(2010CB732303 and 2005CB221408), and the Key Scientific
Project of Fujian Province (2009HZ0002-1).
It should be noted that the ratio of methyl-a-glucopyranoside
to methyl-b-glucopyranoside is around 1.4–1.5 during cellulose
conversions in methanol in the presence of each catalyst. This
may suggest that the intermolecular transformations between
the a and the b isomers proceed rapidly. We performed the
conversion of methyl-a-glucopyranoside (3.0 mmol) in methanol
(20 mL) in the presence of H3PW12O40 catalyst ([H+] =
2.6 mmol LÀ1) at 468 K for 0.5 h. The remaining methyl-a-
glucopyranoside was 1.5 mmol, and 1.1 mmol of b isomer was
formed, giving a ratio of methyl-a-glucopyranoside to methyl-b-
glucopyranoside of B1.4. Simultaneously, 0.40 mmol of the
reactant was transformed into methyl levulinate (0.12 mmol)
and other unknown degradation products (0.28 mmol). This
confirms the easy intermolecular transformation between the a
and the b isomers, and also implies that there is an upper limit for
the yield of methyl glucosides due to their further conversions. As
a comparison, we also examined the conversion of glucose in the
presence of H3PW12O40 under the same reaction conditions
except for using water instead of methanol, and found that more
glucose (B1.2 mmol) was converted to degradation products.
Thus, methyl glucosides in methanol medium are more stable
against further degradations than glucose in water.
Notes and references
1 (a) G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2007, 107,
2411; (b) J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew.
Chem., Int. Ed., 2007, 46, 7164; (c) C. H. Christensen, J. Rass-
Hansen, C. C. Marsden, E. Taarning and K. Egeblad,
ChemSusChem, 2008, 1, 283.
2 (a) D. Klemm, B. Heublein, H.-P. Fink and A. Bohn, Angew. Chem.,
Int. Ed., 2005, 44, 3358; (b) M. Stocker, Angew. Chem., Int. Ed., 2008,
47, 9200; (c) P. L. Dhepe and A. Fukuoka, ChemSusChem, 2008, 1, 969.
3 B. Kamm, Angew. Chem., Int. Ed., 2007, 46, 5056.
4 Y. P. Zhang and L. R. Lynd, Biotechnol. Bioeng., 2004, 88, 797.
5 (a) H. Zhao, J. H. Kwak, Y. Wang, J. A. Franz, J. M. White and
J. E. Holladay, Energy Fuels, 2006, 20, 807; (b) H. Zhao,
J. E. Holladay, Y. Wang, J. M. White and Z. C. Zhang,
J. Biobased Mater. Bioenergy, 2007, 1, 210.
6 (a) S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi,
H. Kato, S. Hayashi and M. Hara, J. Am. Chem. Soc., 2008,
130, 12787; (b) A. Takagaki, C. Tagusagawa and K. Domen,
Chem. Commun., 2008, 5363; (c) A. Onda, T. Ochi and
K. Yanagisawa, Green Chem., 2008, 10, 1033.
7 (a) C. Li and Z. K. Zhao, Adv. Synth. Catal., 2007, 349, 1847;
(b) M. Mascal and E. B. Nikitin, Angew. Chem., Int. Ed., 2008, 47,
7924; (c) R. Rinaldi, R. Palkovits and F. Schuth, Angew. Chem.,
Int. Ed., 2008, 47, 8047.
8 Y. Ishikawa and S. Saka, Cellulose, 2001, 8, 189.
9 J. Macht, M. J. Janik, M. Neurock and E. Iglesia, Angew. Chem.,
Int. Ed., 2007, 46, 7864.
The recovery and repeated uses of H3PW12O40 catalyst after
the conversion of cellulose in methanol were attempted. After
the reaction, the remaining methanol was first removed by
evaporation, and then, the recrystallized H3PW12O40 was
separated by a simple filtration after adding diethyl ether into
10 K. Shimizu, H. Furukawa, N. Kobayashi, Y. Itaya and
A. Satsuma, Green Chem., 2009, 11, 1627.
ꢀc
This journal is The Royal Society of Chemistry 2010
2670 | Chem. Commun., 2010, 46, 2668–2670