High acidity cellulose sulfuric acid from sulfur trioxide: A highly efficient catalyst for the one step synthesis of xanthene and dihydroquinazolinone derivatives

Article abstract of DOI:10.1039/c9ra05748j

A cellulose sulfonate catalyst (HS-cellulose sulfonate) with high stability, excellent catalytic activity and high acidity value (about 1.55 mmol g^-1) was successfully prepared by SO₃ gas phase sulfonation. The basic morphology and nanostructure of the catalyst were determined by HRTEM, XRD, IR, TG, etc. In addition, the catalyst was applied to the catalytic reaction of a dihydroquinazolinone derivative and a xanthene compound, and very valuable results were obtained. The development and preparation of cellulose sulfonate catalysts provide a good approach for the development and application of cellulose, and also an important application of green organic catalytic synthesis methodology.

Full text of DOI:10.1039/c9ra05748j

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High acidity cellulose sulfuric acid from sulfur
trioxide: a highly efficient catalyst for the one step
synthesis of xanthene and dihydroquinazolinone
derivatives†
Cite this: RSC Adv., 2019, 9, 28718
Xiaofei Yue,‡ Zhiqiang Wu, ‡ Gang Wang, Yanping Liang, Yanyan Sun,
*
Manrong Song, Haijuan Zhan, Shuxian Bi and Wanyi Liu
A cellulose sulfonate catalyst (HS-cellulose sulfonate) with high stability, excellent catalytic activity and high
acidity value (about 1.55 mmol gꢀ1) was successfully prepared by SO3 gas phase sulfonation. The basic
morphology and nanostructure of the catalyst were determined by HRTEM, XRD, IR, TG, etc. In addition,
the catalyst was applied to the catalytic reaction of a dihydroquinazolinone derivative and a xanthene
compound, and very valuable results were obtained. The development and preparation of cellulose
sulfonate catalysts provide a good approach for the development and application of cellulose, and also
an important application of green organic catalytic synthesis methodology.
Received 25th July 2019
Accepted 4th September 2019
DOI: 10.1039/c9ra05748j
rsc.li/rsc-advances
certain limitations. For example, the prepared cellulose sulfonic
acid has a lower acid value (the number of H+ sites on the cellulose
–SO3H was determined by acid-base titration to be 0.50 meq gꢀ1);
Introduction
In recent years, catalysts and reagents containing –SO3H have
received considerable attention and use in organic synthesis.1–4
Examples include mesoporous-amorphous silica,5 mesoporous-
amorphous carbon6 and magnetic nanoparticles,7 etc. This is
because they have unique properties, such as wide universality,
cheap and easy to obtain raw materials, simple post-processing,
and they are eco-friendly. At the same time, they have the advan-
tage of being non-toxic and non-corrosive.
Therefore, a great amount of research has been devoted to
a diverse range of biodegradable materials, such as xanthan
sulfuric acid,8 starch sulfuric acid,9 sulfuric acid-modied PEG
(PEG-SO3H),10–12 and meglumine13 which have been exploited as
solid-support acid catalysts for acid-catalyzed transformations.
Cellulose sulfonic acid (CSA)14 is also the most interesting bio-
support catalyst containing –SO3H and has been used in some
organic synthesis conversions, such as cycloaddition,15 diazotiza-
tion,16 dehydration reaction, etc17,18. However, the rst preparation
of cellulose sulfonic acid was reported by Ahmad. S., et al.14 The
method is mainly through chlorosulfonic acid as a sulfonating
reagent. Although this method is convenient and fast, it still has
the chlorosulfonic acid is expensive and the use risk is increased;
the catalyst is used in a large amount, and the catalytic reaction
time is long. Rajitha. B., et al.19 and Javad. S., et al.20 used cellulose
sulfonic acid as a catalyst for organic synthesis. Similarly, in these
reaction processes, the reaction time is longer, the amount of the
catalyst is large, and the cycle life is limited. Therefore, it is key to
solve the above problems from the source to nd a method capable
of producing high quality, green, and durable cellulose sulfonic
acid. It is worth noting that in this work we have made the process
of synthesizing biomass-based solid sulfonic acids more environ-
mentally friendly and green. In addition, the catalyst has excellent
versatility and catalytic activity in catalytic organic synthesis, and
also effectively avoids some disadvantages of conventional
catalysts.
Dihydroquinazolinone and xanthene derivatives have very
important applications as anticancer,21 anti-HIV,22 and anti-
bacterial23 agents etc. due to their good biological and phar-
macological activities. At present, the main catalysts for the
synthesis of dihydroquinazolinone derivatives include I2/
DMF,24 triuoroacetic acid (TFA),25 InCl3,26 GO nanosheets,27 etc.
The xanthene derivative synthesis method mainly includes
Yb(OTf)3,28 cellulose sulfuric acid,29 [PVP-SO3H]Cl,30 etc.
However, there are some disadvantages in the above catalytic
synthesis methods. For example, the catalyst is expensive, the
amount is large, and it is not easy to recycle; a large amount of
toxic solvent is used; the reaction time is long and the yield is
lower. Therefore, we still need to develop a more efficient,
simple and green approach.
State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical
Engineering, National Demonstration Center for Experimental Chemistry Education,
College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan
750021, P. R. China. E-mail: liuwy@nxu.edu.cn; Tel: +86 130 9951 9169
† Electronic supplementary information (ESI) available: Segmental details of the
experimental procedures, the catalyst characterization results (HRTEM, IR,
XRD, SEM, TEM, and TG), and the spectral data of the obtained compounds
(1H-NMR and 13C-NMR) are shown in this le. See DOI: 10.1039/c9ra05748j
‡ These authors contributed equally in this work.
28718 | RSC Adv., 2019, 9, 28718–28723
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We have developed a high acidity cellulose sulfate (HS-
RSC Advances
cellulose sulfate) as a biosupport catalyst by gas phase
sulfonation of sulfur trioxide (as shown in Scheme 1). In
addition, the heterogeneous catalyst is easy to prepare,
insoluble in an organic solvent, easily separated from the
reaction medium, has a high acid density and reactivity, and
is more stable.
Results and discussion
Characterization of HS-cellulose sulphate
By analyzing the SEM photographs (Ce; CSA) before and aer
cellulose sulfonation (Fig. 1A and B), it was observed that Ce
appeared as a relatively smooth micron-sized massive particle
with obvious delamination and accumulation. The structure of
CSA is characterized by relatively coarse micron-scale rods and
a rough surface structure. This is attributed to sulfonation
leading to modication of the cellulose surface structure and
partial degradation of the linear polymer layer structure. In
addition, the cellulose surface before and aer sulfonation has
no obvious pore structure, and the ber width is about 3–10 mm.
It was observed by TEM (Fig. 1C) that the main layered structure
of cellulose aer sulfonation remained relatively intact, but the
surface structure of the cellulose and the internal structure of
the shallow layer changed to some extent. This is because the
sulfonating agent SO3 interacts with the –OH group of cellulose,
which not only generates new functional groups C–OSO3H, but
also that adsorption of SO3 on the surface of cellulose leads to
the formation of H2SO4 which then favours the partial degra-
dation of the cellulose structure. In other words, the above
mechanism of action is more favorable for the depolymeriza-
tion of the cellulose layered structure and leads to rather modify
the structure of the shallow layer of cellulose. In summary, we
found that the SO3 gas sulfonation method not only changes the
surface structure and functional groups of cellulose, but also
contributes to the depolymerization of the internal structure of
cellulose to some extent. In addition, it was observed by HRTEM
(Fig. 1D) that cellulose sulfonic acid has a certain lattice spacing
(1.029 nm and 1.043 nm, which is consistent with the litera-
ture31), and different lattice fringes and crystal faces appear.
This shows that the sulfonation of the sulfur trioxide gas phase
not only uses a small amount of sulfonating agent and
a controllable sulfonation reaction, but also obtains an acid site
with an ordered surface structure while obtaining a sulfonate
acid bond in the cellulose supermolecule. This structural trait
makes it possible to be used as a highly efficient catalyst.
Fig. 1 SEM image of cellulose (Ce; A) and the fresh HS-cellulose
sulphate (CSA; B). TEM and HRTEM image of fresh HS-cellulose
sulphate (C and D).
By comparing the infrared spectra of CSA with different
sulfonation times (shown as Fig. 2a and b), we found that
a longer sulfonation time means a deeper degree of depoly-
merization of the cellulose glucose unit, a more complex
sulfonated product because of the formed sulydryl groups,
and a deeper carbonization phenomenon (Fig. S1†). Therefore,
we chose 10 min as the optimal sulfonation time. The IR
spectrum (Fig. 2c) of the catalyst showed a broad peak for an
ꢀ
–O–H absorption band at the peaks at 3350 cmꢀ1 and a –CH2
absorption peak at 2898 cmꢀ1. The peaks at 1114, 1062, and
898 cmꢀ1 indicated C–O stretching, C–C skeletal vibration, and
C–H ring stretching of the glucose unit, respectively.32 Three
new bands appeared in the IR spectrum at 1276, 1233 and
590 cmꢀ1 corresponding to the O]S]O asymmetric and
symmetric stretching vibrations and S–O stretching vibration of
the sulfonic acid groups.33 At the same time, the new peaks at
1721 cmꢀ1 and 898 cmꢀ1 are C]O structural characteristic
peaks,34 which means cellulose has been depolymerized slightly
Fig. 2 FT-IR of different sulfonation times of cellulose (a) and (b);
Scheme 1 Synthesis of HS-cellulose sulphate from a-cellulose by SO3 before and after sulfonation of cellulose (Ce and CSA; c); and XRD of
gas.
before and after sulfonation of cellulose (Ce and CSA; d).
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during sulfonation, and partially formed the structure of a pol- (Scheme 2). For most solvents, including water, the product is
yhydroxyaldehyde or a polysulfonicaldehyde.35 It is worth noting obtained in high yields at higher temperatures (90 ꢁC), indi-
that our method of synthesizing biomass-based solid sulfonic cating that the catalyst interacts well with the organic solvent
acid has a much higher sulphate content. From chemical (Table 1, entries 1–9), with the exception of DMSO. The amount
titration and elemental analysis it was found that the number of of solvent used has a minor effect on the product yield of the
H+ sites on the cellulose-SO3H was 1.48 mmol gꢀ1 and model reaction (entries 10–12). It is worth noting that temper-
1.55 mmol gꢀ1, respectively.
ature has a large effect on the reaction, and the appropriate
The powder XRD pattern (Fig. 2d) of the matrix showed temperature signicantly increases the product yield (entries
characteristic diffraction peaks for the cellulose eigenstate at 13–14). Increasing the amount of catalyst signicantly increases
14.9ꢁ, 22.5ꢁ and 34.4ꢁ.36 Aer sulfonation, HS-cellulose sulphate product yield (entries 15–16). Based on the consideration of the
has two peaks at 16.5ꢁ and 20.7ꢁ, respectively, in addition to the green chemistry guidelines, we chose to use water as the solvent
ꢁ
original peak shape. The small new peak indicates that the and use 10 mg HS-cellulose sulphate catalyst at 60 C for the
original crystal structure of cellulose has been damaged to some most optimal reaction conditions.
extent, but the original crystal structure is still retained. This
To investigate the substrate range of the catalyst, we
corresponds to test results such as HRTEM. In summary, the synthesized a series of dihydroquinazolinone derivatives (as
results of these tests show that the catalyst has a unique shown in Table 2) using different aromatic aldehydes and 2-
structure.
aminobenzamide. The results show that both the electron-
To assess the thermal stability of HS-cellulose sulphate, TG withdrawing and aromatic aldehydes of the electron-donating
experiments were carried out and are shown in Fig. 3. It can be group can participate in the reaction, and a good yield can be
seen from the thermogravimetric TG curve that the catalyst is obtained (Table 2, entries 1–18). Although the corresponding
roughly divided into four stages of weightlessness. The rst yield of p-phenylbenzaldehyde is low, it can also reach 80%
stage loses weight from a small range of 92 ꢁC to 126 ꢁC, and the (entry 7) due to the electronic effect of the substituents. It is
weight loss is about 4.0%. It is speculated that it may be the important that the acid-labile substrates, such as p-dimethyla-
evaporation of physically adsorbed water on the surface of HS- minobenzaldehyde, also yield good yields of the desired
cellulose sulphate. The second stage starts to lose weight product (entry 3). This is very signicant. The thio-
ꢁ
quickly at around 121 C until the weight loss is about 33.5% phenecarbaldehyde can also react well with 2-aminobenzamide
ꢁ
until 205 C. The analysis may be the sample-bonded sulfonic to give good yields (entry 14). It is worth noting that 2-amino-
acid decomposition process; the third phase is a slow weight benzamides with different substituents react with aromatic
ꢁ
ꢁ
loss phase between 210 C and 325 C, and the weight loss is aldehydes to produce unique effects (entries 15–20). Among
about 15.1%, which may be the depolymerization process of the them, 4-nitro-2-aminobenzamide has the best effect, while the
cellulose polymer. The nal stage is between 330–615 ꢁC, which 5-Cl and 5-OCH3 substituents are not effective (entries 19–20).
could be attributed to the decomposition of cellulose. The In general, the HS-cellulose sulphate catalyst is excellent in
weight losses found by the TG measurements agreed well with catalyzing the synthesis of dihydroquinazolinone derivatives.
those anticipated for the decomposition of cellulose sulfonic
acid to cellulose and the sulfonic acid group. The results show cellulose sulphate, we synthesized
To further investigate the universality of the catalyst HS-
series of xanthene
a
that the catalyst has good thermal stability.
compounds by using Scheme 3 as a model reaction. Through
conditional screening, the optimal conditions for the model
reaction are determined (Table S1,† entry 4). It was conrmed that
the reaction was carried out under heating without a solvent.
Almost all aromatic aldehydes can be reacted with 2-naphthol in
the absence of solvent to form the corresponding xanthene deriv-
atives, which is very valuable (Table 3, entries 1–21). The advantage
is that the catalyst is used in a small amount (10 mg, 4.0 mmol%),
the reaction time is short (1.0–1.5 h), and the yield of all target
compounds is as high as 94% or more (entries 1–14). It is note-
worthy that acetaldehyde and propionaldehyde can also react with
2-naphthol to produce the target product with yields of 76% and
80% (entry 15 and 16), respectively. Similarly, 2-naphthol with
Catalytic performance evaluation of HS-cellulose sulphate
from sulfur trioxide gas phase sulfonation
First, we chose to synthesize dihydroquinazolinones as a model
reaction to investigate the optimal conditions for the reaction
Scheme
2
HS-cellulose
sulfate
catalytic
synthesis
of
Fig. 3 TG analysis of cellulose (Ce) and HS-cellulose sulphate (CSA).
28720 | RSC Adv., 2019, 9, 28718–28723
dihydroquinazolinones.
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Table 1 Optimization of conditions for the synthesis of the quinazo-
linone reaction using the HS-cellulose sulphate catalyst
Entrya
Catalyst/mg
Temperature/ꢁC
Solvent
Yieldb/%
Scheme
compounds.
3
HS-cellulose sulfate catalytic synthesis of xanthene
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
10
10
10
1
1
5
90
90
90
90
90
90
90
90
90
60
60
60
60
30
60
60
Ethanol
Methanol
IPA
DCE
DMSO
THF
Ethyl acetate
Acetonitrile
Water
Water
Water
98
97
94
99
60
98
96
96
98
82
92
90
46
12
75
99
Similarly, one of the evaluation criteria for the efficient use of
catalysts is whether the catalyst can be recycled. We examined
the cyclical use of both model reactions for the HS-cellulose
sulphate catalyst synthesis (Table 2, entry 1 and Table 3, entry
1). The results show that the HS-cellulose sulphate catalyst can
be recycled in two reaction systems. Although the yield of the
target product decreased aer the catalyst was recycled 3 times,
it was still able to maintain a yield of more than 80%, which is
fortunate. The deactivation of the HS-cellulose sulphate catalyst
is due to several possibilities. One is that during the catalytic
process, the catalyst is not collected due to the small amount of
the catalyst. The second is that the sulfonic acid group is
a hydrophilic group, and the water formed during the reaction
dissolves part of the catalyst, resulting in deactivation of the
catalyst. Similarly, we have shown from the results of the
infrared and elemental analysis (Fig. S2 and Table S2†) that the
catalyst has a certain loss during use, and the S content ratio in
9
10c
11d
12e
13
14
15
16
Water
Water
Water
Water
10
Water
a
Reaction conditions: aldehyde (0.5 mmol), 2-aminobenzamide (0.5
mmol), catalyst: HS-cellulose sulfate; solvent dosage: 1.5 mL; IPA:
b
isopropanol. DCE: dichloroethane. THF: tetrahydrofuran. Isolated
c
d
yield. The solvent dosage is 0.5. The solvent dosage is 1.0 mL.
e
The solvent dosage is 2.0 mL.
different substituents reacts with aromatic aldehydes to produce
different effects (entries 17–24). The effect obtained with 6-Br-
naphthol is better (entries 17–21), while the 1-Br, 8-NH2 and 6-
COOH substituents are not effective (entries 22–24).
Table 3 The HS-cellulose sulphate catalyzed synthesis of xanthene
compounds under solvent-free conditions
Entrya R1
R2
Product Time (h) Yieldb (%)
Table
2 HS-cellulose sulfate catalyzed synthesis of dihy-
droquinazolinones derivatives in water
1
2
3
4
5
6
7
8
–C6H5
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
6-Br
6-Br
6-Br
6-Br
6-Br
1-Br
8-NH2
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.1
1.0
1.0
1.5
1.5
1.5
1.5
1.5
2.0
2.0
2.5
2.0
1.5
6.0
6.0
6.0
97(94,89,86)c
98
97
97
94
95
97
94
96
97
96
95
94
95
80
76
Entrya R1
R2
Pro Time (h) Yieldb (%)
4-NO2–C6H4
3-NO2–C6H4
4-Br–C6H4
2-Br–C6H4
3-Br–C6H4
4-Cl–C6H4
3-Cl–C6H4
2-Cl–C6H4
4-CN–C6H4
4-F–C6H4
4-C6H5–C6H4
4-CH3–C6H4
2,4-Cl2–C6H3
–C3H7
1
–C6H5
H
3a 0.7
3b 1.5
3c 1.5
3d 1.0
3e 1.0
94 (90, 88, 82)c
2
4-CH3–C6H4
4-N(CH3)2–C6H4
4-OCH3–C6H4
4-NO2–C6H4
4-COOH–C6H4
4-C6H5–C6H4
4-F–C6H4
H
H
H
H
H
H
H
87
98
86
87
91
80
89
85
92
98
83
95
88
91
90
89
92
N.R
Trace
3d
4
5
9
6
3f
2.0
7d
8
3g 2.0
3h 1.0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
9d
10d
11
12
13
14
15
16
17
18
19
20
4-Br–C6H4
4-Cl–C6H4
2-Cl–C6H4
3-Cl–C6H4
4-OH–3-OCH3–C6H4
–C4H3S
H
H
H
H
H
H
4-NO2
4-NO2
4-NO2
4-NO2
5-Cl
3i
3j
1.5
1.5
3k 2.0
3l 2.0
–C2H5
–C6H5
3m 1.0
3n 2.0
3o 1.5
3p 1.5
3q 1.5
80
84
68
80
4-CH3–C6H5
4-F–C6H5
4-Cl–C6H5
3-Br–C6H5
–C6H5
–C6H5
5s
5t
5u
5v
5w
4-CH3–C6H5
4-Cl–C6H5
2-Cl–C6H5
–C6H5
91
3r
3s 6.0
6.0
2.0
N.R
Trace
Trace
–C6H5
–C6H5
–C6H5
5-OCH3 3t
6-COOH 5x
a
Reaction conditions: aromatic aldehyde (0.5 mmol), aminobenzamide
(0.5 mmol), HS-cellulose sulphate (10 mg), 60 ꢁC; water (1.5 mL). The
a
Reaction conditions: aromatic aldehyde (1.0 mmol), 2-naphthol (1.0
reactions were run until completion as indicated by TLC. N.R: no mmol), HS-cellulose sulphate (10 mg), and 100–110 ꢁC. The reactions
1
reaction. All the compounds are known, characterized by H NMR and were run until completion as indicated by TLC. N.R: no reaction. All
b
c
d
13C NMR. Isolated yield. The recovered catalyst cycle yield. The the compounds are known, characterized by 1H NMR and 13C NMR.
b
solvent was water : ethanol ¼ 1 : 1.
Isolated yield. c The recovered catalyst cycle yield.
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the catalyst drops from the initial 4.65% to 1.64%. This ulti-
mately leads to a decrease in activity aer the catalysts are used
three times.
The high efficiency catalysis and multiple cycle performance
of the HS-cellulose sulphate catalyst has a very important rela-
tionship with the structure of the catalyst itself. Aer the a-
cellulose is sulfonated with liquid SO3, its original cellulose
surface structure is destroyed, and a large amount of the –SO3H
groups are present on the surface, while a part of the cellulose
sulfonate appears. It has abundant catalytic active groups and
dispersed active sites and stability properties aer being
sulfonated for 10 min, whether it is the surface structure of the
catalyst or the acidity value of the material. Just as mentioned
above, signicant lattice streaks on the surface of the material
are a novel nano-scale catalyst formed by sulfur trioxide gas
phase sulfonation of a-cellulose. The structure–activity rela-
tionship of this nanomaterial has rarely been reported before.
Fig. 4 The gas phase sulfonation equipment from sulfur trioxide. ((A)
The spherical condenser and exhaust gas absorption device (cotton
and KOH). (B) The cellulose mixed with glass beads.)
bottle. Then, HS-cellulose sulphate (10 mg, 4.0 mmol%) was
added to it. The resulting mixture was stirred magnetically at
110–115 ꢁC, and aer solidication of the reaction mixture and
also at the same temperature, it was vigorously stirred with
a small rod. Aer completion of the reaction, as monitored by
TLC, the reaction mixture was cooled to room temperature, and
the EtOAc (2 ꢂ 3 mL) was added. The cellulose sulfuric acid was
ltered off and collected for the next reaction. The ltrate was
concentrated to dryness, and the crude solid product was crys-
tallized from EtOH to afford the pure xanthene compounds. All
Experimental section
Preparation of HS-cellulose sulphate from sulfur trioxide gas
phase sulfonation
The generation of sulfur trioxide and its sulfonation reaction
were carried out in a 250 mL three-neck ask with a graduated
Soxhlet extractor and a gas absorption device. In advance, in the
Soxhlet extractor with a diameter of about 4 cm, the lled glass
beads (0.5–1.0 cm in diameter) are coated with about 1 cm thick
cellulose powder with about 0.5 cm (about 0.5 g). In turn, a total
of 2 g cellulose powder and glass beads were added. Then 10–
20 g phosphorus pentoxide was added to the ask. At room
temperature, concentrated sulfuric acid of 20–30 mL was added
by a constant pressure drop funnel, and about 10 min drops
were slowly heated to three bottles. Heating to about 180 ꢁC,
sulfur trioxide gas enters the upper end smoothly from the side
of the Soxhlet extractor, and naturally condenses to 40–45 ꢁC
and ows into the lled ber material. At this time, the sulfur
trioxide sulfonation reaction begins.
1
compound structures were analyzed by H-NMR and 13C-NMR.
Procedure for the synthesis of the dihydroquinazolinone
derivatives
The aminobenzamide (0.5 mmol), HS-cellulose sulphate (10
mg), water 1.5 mL, and aldehyde (0.5 mmol) were separately
added to a Schlenk tube and stirred with heating at 60 ꢁC until
the end of the reaction (TLC was used to follow the reaction).
The ethanol (2 ꢂ 3 mL) was added to the reaction system, and
the catalyst was collected for the next reaction by simple ltra-
tion. The ltrate was concentrated and subjected to column
chromatography (with an eluent ratio of petroleum ether : ethyl
acetate of 1 : 1) and puried. All compound structures were
Aer sulfonation, 10–20 min, the total approaching 1 mL of
liquid sulfur trioxide was collected and three bottle heating kits
were removed (Fig. 4). The reaction material was removed into
a beaker, 10 mL of water was added to soak, and the mixture was
then ltered and washed with 4 ꢂ 10 mL deionized water and
1
analyzed by H-NMR and 13C-NMR.
ꢁ
followed by vacuum drying (50 C, 24 h) to afford 2.8 g of HS-
cellulose sulphate as a pale yellow powder. The number of H+
sites on the cellulose-SO3H was determined by acid-base titra-
tion to be 1.48 mmol gꢀ1, while the sulfur content of the
samples was 1.55 mmol gꢀ1 as judged by conventional
elemental analysis. The similarity between these two values
indicated that most of the sulfur species in the sample were part
of the sulfonic acid groups. The elemental sulphur content of
HS-cellulose sulphate indicated a comparatively much higher
sulphate content in the sulfur trioxide-derived HS-cellulose.
Conclusions
The application of a high acidity cellulose sulfuric acid catalyst
(HS-cellulose sulfonate) prepared from sulfur trioxide provides
new ideas and methods for green organic synthesis. In partic-
ular, as a kind of sulfonated biomass-based solid acid catalyst, it
proves to be an efficient catalyst for the synthesis of pharma-
ceutical intermediate quinolinone in water and xanthene
derivatives in solvent-free conditions. The excellent catalytic
performance and stability of HS-cellulose sulfonate depend on
the specic sulfonation of cellulose which has a large effect on
its matrix structure. Further depolymerization and reorganiza-
Procedure for the synthesis of the xanthene compounds
A mixture of 2-naphthol (2 mmol) and aromatic aldehyde (1 tion of the cellulose structure provides the possibility of deep
mmol) was heated and stirred at 110 ꢁC in a chicken heart sulfonation of cellulose in gas sulfur trioxide, which is also
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Conflicts of interest
The authors declare no competing nancial interest.
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Acknowledgements
This work was supported by the Major Innovation Projects for
Building First-class Universities in China’s Western Region (No.
ZKZD2017003), the National First-rate Discipline Construction
Project of Ningxia (No. NXYLXK 2017A04) and the National
Natural Science Foundation of China (No. 21862013).
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