Please do not adjust margins
Green Chemistry
Page 4 of 6
DOI: 10.1039/C5GC02440D
COMMUNICATION
Journal Name
assumption that sulphanilic acid could equally facilitate the complicated carbohydrates dehydration into high value-added
hydrolysis of 1,4-glycosidic bond in cellulose, we argue that this chemical platform 5-HMF in one-pot. To further show the
bifunctional organocatalyst might also act as a catalyst for the ability of this catalytic system, the durability of the system was
highly challenging conversion of cellulose or even untreated investigated in glucose dehydration. It has been shown that
lignocellulosic biomass to 5-HMF under our described conditions. sulphanilic acid in aqueous condition is able to catalyze the
To study this possibility, the reaction of cellulose without any dehydration reaction of glucose into 5-HMF in five consecutive
pretreatment was conducted under the conditions indicated in reaction runs and exhibited consistent activity (Figure 1).
entry 17, Table 1. The reaction conversion was easily calculated by
measuring the weight of cellulose consumed during the reaction. In
this manner, 67% of cellulose converted and 37% 5-HMF was
produced as determined by HPLC analysis (Table 1, entry 21). This
result verified that sulphanilic acid is also able to simultaneously
depolymerize the cellulose structure through 1,4-glycosidic bond
hydrolysis and also two-step isomerization and dehydration
reactions to form 5-HMF product. In order to increase the HMF
yield, in the next step, the reaction was repeated in the presence of
Figure 1 Durability of sulphanilic acid catalyst (24 mol%) in aqueous solvent for glucose
48 mol% sulphanilic acid catalyst. In this case, 5-HMF was produced
dehydration (50 mg glucose, 150 ºC, 60 min).
with up to 52% yield at 83% cellulose conversion (Table 1, entry 22).
Increasing either the reaction time or temperature above 60 min
The present catalyst system is distinguished from previous
and 150 ºC resulted in lower 5-HMF yield, suggesting that 150 ºC
and 60 min are optimal temperature and reaction time, respectively
work in that we obtain high yields of 5-HMF from simple
(fructose) to complex (cellulose) carbohydrates and even
(Table 1, entries 23-24). Encouraged by these promising and
untreated lignocellulosic biomass (e.g. Straw and Barely Husk)
unprecedented results, we surmised whether it was possible to run
without the need for potentially hazardous metal salts, under
the same reaction using waste lignocellulosic biomass residues such
absolutely organocatalytic mode of operation. Despite the
as straw and barley husk and obtain satisfactory 5-HMF yield from
genuinely homogeneous feature that results in excellent
these materials within acceptable reaction times.
kinetic profile, sulphanilic acid itself could be easily recycled
For this reason, 25 mg of each oven-dried substrate was used
and reused and display high stability and durability under the
without any pretreatment in the same reaction conditions to
described reaction conditions. More importantly, the use of
glucose dehydration using 48 mol% sulphanilic acid catalyst. Prior to
water as the main component of solvent system even in the
the calculation of reaction conversion and furfural yields, the
case of insoluble complex biomass and the absence of
amount of cellulose, hemicellulose, and lignin was estimated using
TG analysis (Table S1, Figure S1-S4).28 It has been shown that both
employing expensive ionic liquids make this protocol
environmentally benign and economically attractive
lignocellulosic materials gave the corresponding 5-HMF in
alternative for this important transformation. Because it is
approximately 41% yield which is highly comparable to HMF yield
easy to scale up the above described transformation by using a
prepared from microcrystalline cellulose (Table 2, entries 1-2).
suitable designed reactor, this system can provide 5-HMF
Table 2. Lignocellulosic biomass constituents and dehydration reaction products.a
easily and quickly in the required volume, as well as in pure
form without the need for any pre-treatment (for complex
Entry
Biomass
A
B
C
Con.
(%)b
HMF
(%)c
Furfural
(%)c
LA
(%)
(%)
(%)
(%)d
biomass and waste agricultural residue) or complicate
separation strategy. This concept will open a new challenging
area in design of several types of organocatalytic ion-pared
catalysts for the above-mentioned strategically important
transformations.
1
2
Straw
32
27
27
14
28
25
47
33
41
41
50
41
5
8
Barley
husk
a
The amount of each constituent (A: Cellulose, B: Hemicellulose, C: Lignin) was
determined based on TG analysis (Figure S1-S4); Reactions were performed using
25 mg lignocellulosic biomass, 48 mol% sulphanilic acid in 3 mL biphasic solvent
Acknowledgements
b
at 150 ºC, for 60 min. Conversion was calculated after weighing the remained
dried biomass. c HMF and furfural yields were calculated according to the amount
The authors greatly acknowledge Iran National Science
Foundation (INSF) through grant no. G014, and IASBS research
council for the financial support of this work.
d
of hexose and pentose units in each feed-stock, respectively. The amounts of
Levulinic acid were estimated using HPLC analysis (See ESI for details).
Furthermore, the presence of hemicellulose in both feed-stocks led
to the formation of furfural from pentose dehydration. In this Notes and references
context, both straw and barley husk in the same reaction conditions
1
D. Lüthi, M. Le Floch, B. Bereiter, T. Blunier, J.-M. Barnola, U.
Siegenthaler, D. Raynaud, J. Jouzel, H. Fischer, K. Kawamura
and T. F. Stocker, Nature, 2008, 453, 379.
produced furfural in 50 and 41% yields, respectively (Table 2,
entries 1-2).
2
A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J.
Cairney, C. A. Eckert, W. J. Frederick, J. P. Hallett, D. J. Leak,
These observations strongly rely on the robustness of
sulphanilic acid as efficient catalyst for a variety of simple to
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins