Sulfonation of carbonized xylan-type hemicellulose: A renewable and effective biomass-based biocatalyst for the synthesis of O- and N-heterocycles

Article abstract of DOI:10.1039/c8nj01329b

The application of biomass-based carbonaceous solid acids in catalysis is attracting increasing attention in the field of chemistry. In this study, a heterogeneous carbon-based solid acid biocatalyst (CXH-SO₃H) with regular spherical structure was synthesized from xylan-type hemicellulose (XH) by a simple two-step method. The catalyst was successfully applied in the synthesis of O- and N-heterocycles with yields of 80-99% and 60-97%, respectively. In view of environment and economy, CXH-SO₃H shows the merits of environmental friendliness, easy operation, simple work-up, excellent yields, and the avoidance of use of organic solvents and expensive catalysts. Moreover, the as-synthesized solid acid catalyst could be used for several cycles without significant loss in its catalytic activity. The results of FT-IR, XRD, and SEM showed that no distinct differences in physico-chemical structures of CXH-SO₃H were observed. Thus, the eco-friendly CXH-SO₃H catalyst is a promising candidate for green synthesis of O- and N-heterocycles from low-cost feed-stocks and has good prospect in partially substituting commercially available solid and liquid acid catalysts and precious metal catalysts.

Full text of DOI:10.1039/c8nj01329b

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Page 1 of 32
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Sulfonation of Carbonized Xylan-type Hemicellulose: A
Renewable and Effective Biomass-based Biocatalyst for the
Synthesis of O- and N-Heterocycles
a
a,*
a,*
b
Jiliang Ma, Xinwen Peng, Linxin Zhong, Runcang Sun
a
State Key Laboratory of Pulp and Paper Engineering, South China
University of Technology, Guangzhou, China.
b
Institute of Biomass Chemistry and Utilization, Beijing Forestry
University, Beijing, China.
*
Corresponding authors’ Eꢀmail: fexwpeng@scut.edu.cn (Xinwen Peng),
and lxzhong0611@scut.edu.cn (Linxin Zhong), Tel.: +86ꢀ020ꢀ87111861;
Fax: +86ꢀ020ꢀ87111861.

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Abstract
The application of biomassꢀbased carbonaceous solid acid in catalysis is
attracting more and more attention in the field of chemistry. In this work,
a heterogeneous carbonꢀbased solid acid biocatalyst (CXHꢀSO H) with
3
regular spherical structure was synthesized from xylanꢀtype
hemicellulose (XH) by a simple twoꢀstep method. The catalyst was
successfully applied in the synthesis of Oꢀ and Nꢀheterocycles with
yields of 80ꢀ96%, 98ꢀ99% and 60ꢀ97%, respectively. In the view of
environment and economy, the CXHꢀSO H shows the merits of
3
environmental friendliness, easy operation, simple workꢀup, excellent
yields and the avoidance of organic solvents and inexpensive catalysts.
Moreover, the asꢀsynthesized solid acid catalyst could be used for several
cycles without significant loss of its catalytic activity. The results of
FTꢀIR, XRD and SEM showed that no obvious difference in
physicoꢀchemical structures of CXHꢀSO H were observed. Thus, the
3
ecoꢀfriendly CXHꢀSO H catalyst is promising for green synthesis of Oꢀ
3
and Nꢀheterocycles from lowꢀcost feedꢀstocks and has good prospect in
partially substituting commercially available solid acid, liquid acid
catalysts and precious metal catalysts.
Keywords: Carbonꢀbased solid acid, Xylanꢀtype hemicelluloses, Oꢀ and
NꢀHeterocycles, Benzoxanthenes, 4ꢀArylꢀNHꢀ1,2,3ꢀtriazoles

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1
. Introduction
Oxygen and nitrogen heterocycles are structures frequently found in a
1
large number of biologically active products. The interest of the
scientific community in synthesis of oxygen and nitrogen heterocycles
has been enormous. As important components of these heterocycles,
xanthenes and 1,2,3ꢀtriazoles attract significant attention for their
2
important biological activities. Furthermore, xanthenes and its
3
derivatives can also be employed as brilliant fluorescent dyes,
4
pHꢀsensitive fluorescent materials, and antagonists in photodynamic
5
therapy. Thus, synthesis of these two compounds are of great importance.
To this end, great efforts have been devoted to synthesizing these
2b
heterocycles with different catalysts, such as [CTA]Fe/MCMꢀ41,
6
7
2d
8
2e
9
proline triflate, ionic liquids, [Ir(cod)Cl] , Rh (Oct) , CuI, AgSbF .
2
2
4
6
Currently, acid catalysts were frequently used in these heterocycles
10
synthesis based on their mild acidity. However, most of these protocols
suffer from undesirable employment of harsh reaction conditions, long
reaction time, tedious workꢀups, toxic organic solvents and using
transitionꢀmetal catalysts. Hence, developing a mild and practical
catalytic system for the preparation of xanthenes and 1,2,3ꢀtriazoles
remains a challenge.
Recently, developing metalꢀfree catalysts is of great relevance for
industryꢀuniversityꢀresearch cooperation in the view of green and
11
sustainable chemistry point. In this scenario, functional carbon materials
1
2
have became a focus of whole society. They can serve as “green” and
efficient options for catalytic transformations. To this end, great efforts
have been devoted to synthesizing novel carbon materials that have an
excellent catalysis activity. Among these processes, biopolymers as raw
materials to produce highꢀperformance and environmentally friendly

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catalysts have attracted considerable amount of attentions due to their low
cost, abundance and renewability. Since the biomassꢀbased carbonaceous
13
solid acid catalyst from ꢀglucose was first reported by Toda et al.,
D
much efforts have been devoted to developing a variety of carbonꢀbased
14
catalysts from raw biomass with a high cellulose/hemicellulose content
by thermal or hydrothermal carbonization. Although cellulose is a good
biodegradable material in the synthesis of carbonꢀbased catalyst, this
process is not an economical and advisable option for utilization of
cellulose when compared with the present applications of cellulose (Fig.
15
S1).
Hemicelluloses are the second most abundant renewable polymers in
1
6
lignocellulosic biomass. Unlike cellulose, in which the monomer unit is
chemically homogeneous, hemicelluloses are a series of heterogeneous
polysaccharides with diverse structures. In addition, these
polysaccharides are different from each other in the light of structure,
17
physical and physicochemical properties. Therefore, how to use the
hemicelluloses to develop functional materials is a challenge. In the early
reports, hemicelluloses can be converted to many valueꢀadded chemicals,
such as ethanol, furfural, levulinivic acid, 5ꢀhydroxymethylfurfural (HMF)
18
and xylitol. Similarly, many hemicellulosesꢀbased materials have been
19
reported in literature. The US Department of Energy estimated that
about 400 million tons of hemicelluloses are available in the USA each
2
0
year. Moreover, it is reported that about 15 million tons of
hemicelluloses are produced annually from the USA pulp and paper
1
9
industry. However, many of these hemicelluloses are not utilized for
valueꢀadded applications. The partial carbonization of hemicelluloses to
produce carbons is a promising way for the utilization of hemicelluloses.
These functional carbons are rich in oxygen and hydrogen that are

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11d, 13
beneficial for the further sulfonation.
The sulfonated carbons are
21
11d
promising candidates for synthesis, biomass conversion and biodiesel
1
3
production.
In the present work, we report a simple and eficient procedure for oneꢀpot
synthesis of oxygen and nitrogen heterocycles using CXHꢀSO H as an
3
effective, neutral, heterogeneous, and reusable acidic catalyst under mild
conditions (Scheme 1). The preparation method of CXHꢀSO H is quite
3
simple and suit for mass product with low cost. The established process
represents a new protocol for rational utilization of the waste
hemicellulose from the pulp and paper industry biomass, which may hold
great potential in industrial applications.
Scheme 1 The CXHꢀSO H was applied in the synthesis of benzoxanthenes (A),
3
4ꢀarylꢀNHꢀ1,2,3ꢀtriazoles (B), and 7ꢀhydroxyꢀ4ꢀmethylcoumarin (C).
2
. Results and discussion
The functional group of CXHꢀSO H was detected by FTꢀIR. As
3
ꢀ
1
illustrated in Fig. 1Aꢀa, the broad band observed at 3430 cm is assigned
to ꢀOH group linked with the neighbor oxygen or sulfuric acid by
hydrogen bonds, indicating that these acidic groups are located in close

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2
2
ꢀ1
ꢀ1
proximity. The peaks at around 1177 cm and 1037 cm are ascribed to
23
the stretching of O=S=O in ꢀSO H groups.
3
Fig. 1 The characterization of fresh CXHꢀSO H and the fifth reused CXHꢀSO H: (A)
3
3
FTꢀIR spectra, (B) XRD patterns, (C) XPS spectra of CXHꢀSO
3
H, (D) O1S, (E) S2P,
and (F) EDX.
As can be seen from the XPS results, the elements C, O and S are
observed in the lowꢀresolution XPS spectrum of CXHꢀSO H (Fig. 1C).
3
The highꢀresolution O1S and S2P are shown in Fig. 1D and 1E,
respectively. In addition, the presences of the aboveꢀmentioned elements

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are also observed from EDX (Fig. 1F), which well agrees with the results
of XPS and FTꢀIR.
In order to quantify the sulfonic group in CXHꢀSO H, acidꢀbase titration
3
and EA experiments were performed and the results are shown in Table 1.
The content of sulfur determined by EA is about 3.55 wt%, indicating
that 1.10 mmol/g ꢀSO H in CXHꢀSO H. This value was slightly higher
3
3
than that from acidꢀbase titration, suggesting that some sulfur species are
probably not in the acidic form.
3
Table 1 Acid density of CXHꢀSO H
a
b
c
S content
SO H density
SO H density
3
3
Sample
(
wt%)
(mmol/g)
1.10
(mmol/g)
1.08
3
CXHꢀSO H
3.55
a
b
c
Determined by EA. Calculated from the S content. Determined by acidꢀbase
titration.
In addition, acetic acid lignin, alkali lignin and industrial lignin were also
treated via the same step to obtain sulfonation of carbonized acetic acid
lignin (CAALꢀSO H), sulfonation of carbonized alkali lignin (CALꢀSO H)
3
3
and sulfonation of carbonized industrial lignin (CILꢀSO H). As shown in
3
Fig. 2, the asꢀprepared three types of ligninꢀbased solid acids show a
smooth surface and irregular block morphology (Fig. 2Aꢀ2F), while
CXHꢀSO H exhibites regular spherical morphology (from 8 to 30 ꢁm)
3
with smooth surface (Fig. 2G and 2H). Meanwhile, EA results (Table S1)
show that the content of sulfur element in CXHꢀSO H is significantly
3
higher than those of ligninꢀbased solid acids. This result demonstrates
that CXHꢀSO H has more acide sites.
3

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Fig. 2 SEM spectra of CAALꢀSO H (A and B), CALꢀSO H (C and D), CILꢀSO H (E
3
3
3
3
and F) and CXHꢀSO H (G and H).
Table 2 Effect of biocatalyst dosage on the oneꢀpot condensation of benzaldehyde
a
with 2ꢀnaphthol and dimedone
o
b
Entry
Catalyst (mol%)
Temperature ( C)
Time (h)
Yield (%)
1
2
3
4
5
0
90
90
90
90
90
2
2
2
2
2
trace
74
2.16
3.24
4.32
5.40
85
88
89
a
Typical reaction conditions: benzaldehyde (0.5 mmol), 2ꢀnaphthol (0.5 mmol),
b
dimedone (0.6 mmol). Isolated yield.
The feasibility for the green synthesis of benzoxanthenes catalyzed by
CXHꢀSO H was investigated. Initially, the experiments were performed
3
by using benzaldehyde (0.5 mmol), 2ꢀnaphthol (0.5 mmol) and
o
5
2
,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (0.6 mmol) as substrates at 90 C for
h under solventꢀfree condition. The results are summarized in Table 2.
Only trace product was detected in the absence of biocatalyst (Table 2,
entry 1). However, a yield of 74% could be obtained by using

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CXHꢀSO H (2.16 mol%) as a biocatalyst, indicating a good catalytic
3
performance of CXHꢀSO H. Encouraged by the result, the effect of
3
amount of CXHꢀSO H on the synthesis of benzoxanthene was explored.
3
The results showed that the yield of 2a increased with the increasing
amount of CXHꢀSO H (Table 2, entries 2ꢀ5); however, an increase in the
3
amount of CXHꢀSO H from 4.32 to 5.40 mol% did not lead to significant
3
change in the yield (Table 2, entries 4ꢀ5). Thus, 4.32 mol% CXHꢀSO H
3
was optimal for this reaction from atom economy.
a
Table 3 Effects of reaction time and temperature on the synthesis of benzoxanthenes
o
b
Entry
Catalyst (mol %)
Temperature( C)
Time (h)
Yield (%)
1
2
3
4
5
6
4.32
4.32
4.32
4.32
4.32
4.32
70
80
3
3
2
2
1
1
64
81
80
88
84
85
80
90
90
110
a
Typical reaction conditions: benzaldehyde (0.5 mmol), 2ꢀnaphthol (0.5 mmol),
b
dimedone (0.6 mmol). Isolated yield.
Thereafter, the effects of temperature and time on the reaction were also
investigated. The results are given in Table 3. As the temperature rises,
the yield of 2a shows an increasing trend (Table 3, entries 1ꢀ2, 3ꢀ4). In
addition, the output of 2a increased along with the extension of reaction
time under the same condition (Table 3, entries 2ꢀ3, 4ꢀ5). According to
o
the above results, 2 h and 90 C were chosen as the optimum reaction
time and temperature for sequent reactions.

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Reaction conditions: aldehudes (0.5 mmol), 2ꢀnaphthol (0.5 mmol), cyclic
o
1
,3ꢀdicarbonyl (0.6 mmol), CXHꢀSO H (4.32 mol %), 90 C, 2 h.
3
3
Scheme 2 Oneꢀpot synthesis of benzoxanthenes catalyzed by CXHꢀSO H.
To examine the extent of the application of biocatalyst in this
condensation reaction, the threeꢀcomponent reaction of a variety of
aldehydes, 2ꢀnaphthol and cyclic 1,3ꢀdicarbonyl compounds in the
presence of CXHꢀSO H was also investigated in the optimal condition
3
(
Scheme 2). The procedure was highly effective for the synthesis of
benzoxanthene. Most importantly, aromatic aldehydes having either
electron donating or withdrawing substituents reacted efficiently and gave
good to excellent yields (83ꢀ96%). Aliphatic aldehydes could also react

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smoothly to afford a good yield under the same reaction condition. On the
other hand, 1,3ꢀcyclohexanedione could also achieve good results. Thus,
CXHꢀSO H could act as an efficient biocatalyst for the synthesis of
3
benzoxanthene.
Table 4 Brief comparison of yields for the oneꢀpot reaction of benzaldehyde,
2ꢀnaphthol and dimedone from various methods
Temperature
Yield
(%)
Entry
Catalyst
Solvent
MeOH
o
Time
2 h
Reference
34a
(
C)
1
CeCl ·7H O
50
50
90
3
2
2
3
Sr(OTf)
2
MeOH
neat
5 h
85
84
34b
34c
a
TPPMS/CBr
4
100
150
80 min
[
2
Cu(bpdo) ·2H
2
4
2+
b
neat
55 min
85
34d
O] /SBAꢀ15
c
5
6
7
8
9
PVPP OTf
toluene
neat
110
120
5 h
85
87
89
88
87
90
34e
34f
32d
34g
32e
34h
.
B(HSO
4
)
3
10 min
50 min
45 min
4
Trityl Chloride
neat
110
pꢀTSA
neat
120
NaHSO
4
·SiO
2
DCE
neat
reflux
100
d
1
0
1
2
nꢀWSA
90 min
Fe
3
O
4
/CSꢀAg
1
1
water
neat
80
90
30 min
2 h
94
88
32c
NPs
CXHꢀSO
3
H
This work
a
b
TPPMS/CBr : Triphenylphosphineꢀmꢀsulfonate/carbon tetrabromide. bpdo: 2,2’
4
c
d
bipyridine, 1,1’ꢀdioxide. PVPP
.
OTf: Polyvinylpolypyrrolidoniume triflate. nꢀWSA:
nanoꢀWO ꢀSO H.
3
3
To have a better understanding of our catalytic system, the effectiveness
of CXHꢀSO H was compared to those of catalysts reported previously for
3
the
2ꢀphenylꢀ9,9ꢀdimethylꢀ8,9,10,12ꢀtetrahydrobenzo[a]xantheneꢀ11ꢀone, as
shown in Table 4. Generally, the yield in this work is similar to those
synthesis
of
1

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reported previously. Although some of them have excellent yields,
additional solvents (MeOH, toluene, and DCE et al.) were used (Table 4,
entries 1, 5, 9), or the reaction time was relatively long (Table 4, entry 9).
Although Fe O /CSꢀAg NPs could obtain a higher yield than CXHꢀSO H
3
4
3
within a short time, but the synthesis of the catalyst was very tedious and
required additional solvent (Table 4, entry 11). Furthermore, the catalytic
activity of XH source for the prepararion of CXHꢀSO H catalyst was also
3
investigated. In this work, the xylanꢀtype hemicellulose obtained from
bamboo, eucalyptus, and pulping and papermaking industry were used to
prepare CXHꢀSO H catalysts under the same conditions. All the
3
CXHꢀSO H catalysts showed a good catalytic activity for the ecoꢀfriendly
3
synthesis
2ꢀPhenylꢀ9,9ꢀdimethylꢀ8,9,10,12ꢀtetrahydrobenzo[a]xanthenꢀ11ꢀone
Table S2). Therefore, the source of raw materials of CXHꢀSO H
of
1
(
3
catalysts doesn't influence the catalytic activity.
The excellent catalysis activity of CXHꢀSO H inspired us to explore its
3
catalytic activity for synthesis of coumarins. Coumarin and their
derivatives are important oxygen heterocycles in the realm natural and
synthetic organic chemists mainly due to their various biological
24
properities and pharmaceuticals applications such as antilipoperoxidant,
25
26
27
28
antimicrobial,
antithrombotic,
anticancer,
antiꢀHIV
and
29
antioxidant, etc. Moreover, they have been commercialized as lasers for
30
31
fluorescent labels, fluorescent probes and enzymatic measurements.
Therefore, synthesis of coumarins is of great importance. For coumarins
synthesis, the condensation reaction was carried out by mixing resorcinol
and ethyl acetoacetate or methyl acetoacetate with the yield of 98% and
9
9%, respectively (Scheme 1C).

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Reaction conditions: nitroolefin (0.3 mmol), NaN
3
(0.45 mmol), CXHꢀSO
3
H (3.24
o
mol %), DMSO (1.5 mL), 60 C, 4 h.
Scheme 3 Oneꢀpot synthesis of 4ꢀarylꢀNHꢀ1,2,3ꢀtriazoles catalyzed by CXHꢀSO H
3
The model reaction of synthesis of nitrogen heterocycles was carried out
by mixing transꢀ3ꢀnitrostyrene, NaN , and CXHꢀSO H in DMSO and
3
3
gave a yield of 72% (Table S3, entry 1). Encouraged by this result, the
experimental condition was optimized and the corresponding results were
shown in Table S3 and Table S4. From the perspective of green
chemistry, the optimal results for the transformation were observed when
transꢀ3ꢀnitrostyrene (0.3 mmol) and NaN (0.45 mmol) reacted in DMSO
3
o
at 60 C for 4 h in the presence of CXHꢀSO H (3.24 mol%).
3
Subsequently, a series of nitroolefin and NaN were explored in the
3
presence of CXHꢀSO H. As seen from Scheme 3, the catalysis of
3
CXHꢀSO H was highly effective for the synthesis of
3
4
ꢀarylꢀNHꢀ1,2,3ꢀtriazoles. A variety of nitroolefins with either
electronꢀdonating or electronꢀwithdrawing groups were converted to
ꢀarylꢀNHꢀ1,2,3ꢀtriazoles in excellent yields (60ꢀ97%). It is found that, as
4

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compared with the nitroolefin with electronꢀdonating groups in Scheme 3,
the yield of nitroolefin with electronꢀwithdrawing groups was lower.
The recyclability and reusability of catalysts are key factors for green
synthesis. In this work, the reusability of CXHꢀSO H was explored by
3
using benzaldehyde, 2ꢀnaphthol and dimedone as model substrates under
the optimized condition. As depicted in Fig. 3, CXHꢀSO H exhibited an
3
excellent catalytic stability, and it could be reused for five times without a
significant loss in catalytic activity. After reaction, the biocatalyst could
be reused by simple filtration, washing and drying. In addition, the
structural characteristic of the reused biocatalyst was checked by FTꢀIR
(
Fig. 1Aꢀb), XRD (Fig. 1Bꢀb), and SEM (Fig. 4C, 4D). The characteristic
peaks of the fifth reused biocatalyst show no significant difference from
that of fresh CXHꢀSO H (Fig. 1A), indicating that the reuse of
3
CXHꢀSO H did not change the chemical structure of CXHꢀSO H.
3
3
3
Fig. 3 Recycle of CXHꢀSO H
The phase structure of the fresh CXHꢀSO H and the recycled CXHꢀSO H
3
3
after five cycles were determined by XRD. As indicated in Fig. 1Bꢀa, the
o
fresh biocatalyst exhibited a broad diffraction peak at 2θ = 20ꢀ30 , which

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is assigned to the amorphous carbon structure of CXHꢀSO H. The broad
3
diffraction peak of the fifth reused biocatalyst showed little difference
(
Fig. 1Bꢀb), indicating that the reuse of CXHꢀSO H did not change the
3
crystallographic property of CXHꢀSO H.
3
The morphologies of fresh CXHꢀSO H and the recycled CXHꢀSO H after
3
3
five cycles were observed by SEM, and the results are presented in Fig. 4.
Both the fresh CXHꢀSO H and the reused CXHꢀSO H are regular
3
3
spherical particles, demonstrating the good stability of CXHꢀSO H during
3
catalysis.
Fig. 4. SEM images of fresh CXHꢀSO H (A and B) and the fifth reused of
3
3
CXHꢀSO H (C and D)
A
plausible
mechanism
for
the
synthesis
of
1
2ꢀphenylꢀ9,9ꢀdimethylꢀ8,9,10,12ꢀtetrahydrobenzo[a]xantheneꢀ11ꢀone
3
2
catalyzed by CXHꢀSO H is shown in Fig. 5. According to literatures we
3
suppose that the reaction might proceed via the initial formation of
3
2e, 33
orthoꢀquinone methides (4),
which was formed by the nucleophilic
addition of activated 2ꢀnaphthol (2) to the activation of the carbonyl
group of benzaldehyde (1), in the presence of CXHꢀSO H. Then, the
3

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intermediate 4 was activated as a Michael acceptor, which was attacked
by nuclephile dimedone in the presence of CXHꢀSO H. Finally, the
3
condensation process resulte in the formation of 7 which was cyclyzed to
8
and subsequently produced target product 9 upon dehydration.
Fig.
2ꢀphenylꢀ9,9ꢀdimethylꢀ8,9,10,12ꢀtetrahydrobenzo[a]xantheneꢀ11ꢀone catalyzed by
CXHꢀSO
5
A
plausible
mechanism
for
synthesis
of
1
3
H
3
. Conclusions
The present work describes the synthesis and characterization of a novel
heterogeneous CXHꢀSO H biocatalyst that exhibited an excellent
3
catalytic activity. The biocatalyst showed a high catalytic potential for the
ecoꢀfriendly multicomponent synthesis of oxygen and nitrogen
heterocycles. Furthermore, the procedure had several advantages, such as
ease of preparation and handling of the biocatalyst, simple workꢀup
procedure, mild reaction conditions, high product yield and the use of
inexpensive, environmentally friendly, and renewable biomass.
Compared with the commercially available solid acid catalysts and liquid
acid catalysts, CXHꢀSO H showed much better performance. Therefore,
3
CXHꢀSO H is promising to partially replace commercially available solid
3

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acid catalysts and liquid acid catalysts in the synthesis of oxygen and
nitrogen heterocycles.
4
. Experimental
4
.1 General information
Xylanꢀtype hemicelluloses were obtained from byꢀproduct of pulping and
papermaking industry. Aldehyde, 2ꢀnaphthol, cyclic 1,3ꢀdicarbonyl
compounds and NaN used were analysis grade and were purchased from
3
Aladdin Industrial Corporation. Nitromethane, sodium chloride,
magnesium sulfate anhydrous and other reagents used were analysis
grade and were provided by Guangzhou Chemical Reagent Factory,
China. All chemicals were used without further purification. Xꢀray
diffraction (XRD) patterns were obtained using a Bruker D8 Focus
Diffractometer equipped with Cu Kα radiation (λ = 0.15418 nm). The
voltage and current were 40 kV and 40 mA, respectively. Scanning
electron microscope (SEM) images were derived on a Zeiss EVO 18
(
Jena, Germany) operated at a 10 kV acceleration voltage. XPS
measurements were conducted on a Kratos Axis Ultra DLD spectrometer
employing amonochromated Al Kα Xꢀray source (hν = 1486.6 eV). IR
spectra were recorded on a Nicolet 6700 FTꢀIR spectrophotometer using
KBr pellets. Element analysis (EA) was performed on a Vario EI III
elementar.
4
.2 Preparation of Sulfonation of Carbonized Xylan-type
Hemicelluloses (CXH-SO H)
3
o
3
g of XH was carbonized at 350 C for 90 min under nitrogen
atmosphere to produce the incomplete carbonization product CXH.
Thereafter, the CXH was added into concentrated H SO with a ratio of
2
4
o
solid to liquid = 1: 30 (g: mL), and heated at 150 C for 15 h under

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DOI: 10.1039/C8NJ01329B
nitrogen atmosphere to introduce ꢀSO H groups. The mixture was
3
immediately cooled to room temperature and diluted with 2000 mL
deionized water, followed by filtrating and washing with hot deionized
o
water (＞80 C) until no sulfate ions were detected in the washed water.
Finally, the resulting biocatalyst CXHꢀSO H was collected and dried in a
3
o
vacuum oven at 80 C for 24 h to remove excess moisture.
4
.3 General Procedure for the Synthesis of Benzoxanthenes
In a typical experimental procedure, CXHꢀSO H (4.32 mol%) was added
3
to a mixture of aldehyde (0.5 mmol), 2ꢀnaphtol (0.5 mmol), and
1
,3ꢀcyclohexadione (0.6 mmol) in a 15 mL pressure flask with a magnetic
o
stirring bar. The reaction processed at 90 C for 2 h, as indicated by TLC
for a complete reaction. Upon the completion of the reaction, ethyl
acetate (10 mL) was added when the reaction system was cooled to room
temperature, and fully crushed, rested for a period of time, and then
filtered. The solid biocatalyst was washed with ethyl acetate (10 mL) for
two times and used for subsequent cycles after drying under vacuum.
Finally, the combined filtrate was evaporated under reduced pressure and
the target products were obtained by column chromatography on silica
gel using ethyl acetate/hexane as an eluent. All products were
characterized by NMR spectroscopy.
1
2-Phenyl-9,9-dimethyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
1
(
2a): H NMR (600 MHz, CDCl ): δ = 8.02 (d, J = 12.0 Hz, 1H),
3
7
1
1
1
.79ꢀ7.76 (m, 2H), 7.45ꢀ7.34 (m, 5H), 7.21ꢀ7.18 (m, 2H), 7.09ꢀ7.06 (m,
H), 5.75 (s, 1H), 2.57 (s, 2H), 2.28 (dd, J = 18.0 Hz, J = 36.0 Hz, 2H),
1
2
1
3
.12 (s, 3H), 0.97 (s, 3H); C NMR (151 MHz, CDCl ): δ = 196.74,
3
63.77, 147.67, 144.68, 131.41, 131.33, 128.74, 128.34, 128.30, 128.15,

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1
3
26.91, 126.15, 124.80, 123.59, 117.62, 116.95, 114.19, 50.81, 41.31,
4.63, 32.14, 26.21, 27.05.
1
2-(4-Fluorinephenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xant
1
hen-11-one (2b): H NMR (600 MHz, CDCl ): δ = 7.77 (d, J = 6.0 Hz,
3
1
1
0
1
1
4
H), 7.39ꢀ7.34 (m, 2H), 7.32ꢀ7.26 (m, 5H), 6.88ꢀ6.85 (m, 2H), 5.71 (s,
H), 2.57 (s, 2H), 2.27 (dd, J = 18.0 Hz, J = 36.0 Hz, 2H), 1.12 (s, 3H),
1
2
1
3
.97 (s, 3H); C NMR (151 MHz, CDCl ): δ = 196.85, 163.87, 161.96,
3
60.34, 147.70, 140.52, 131.21, 129.83 (d, J = 7.55.0 Hz), 128.96, 128.43,
27.02, 124.94, 123.49, 117.34, 117.01, 115.06, 114.92, 114.06, 50.84,
1.37, 33.95, 32.20, 29.27, 27.04.
1
2-(4-Chlorophenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xanthe
1
n-11-one (2c): H NMR (600 MHz, CDCl ): δ = 7.89 (d, J = 6.0 Hz, 1H),
3
7
2
.78ꢀ7.75 (m, 2H), 7.42ꢀ7.24 (m, 5H), 7.13ꢀ7.12 (m, 2H), 5.68 (s, 1H),
.55 (s, 2H), 2.24 (dd, J = 18.0 Hz, J = 36.0 Hz, 2H), 1.10 (s, 3H), 0.95
1
2
13
(
s, 3H); C NMR (151 MHz, CDCl ): δ = 196.87, 164.06, 147.67, 143.19,
3
1
1
31.87, 131.46, 131.15, 129.75, 129.05, 128.43, 128.34, 127.06, 124.97,
23.39, 116.99, 116.98, 113.75, 50.76, 41.32, 34.08, 32.13, 29.25, 27.04.
1
2-(4-Bromophenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xanthe
1
n-11-one (2d): H NMR (600 MHz, CDCl ): δ = 7.88 (d, J = 12.0 Hz,
3
1
1
0
1
1
2
H), 7.77ꢀ7.74 (m, 2H), 7.42ꢀ7.27 (m, 5H), 7.24ꢀ7.20 (m, 2H), 5.66 (s,
H), 2.54 (s, 2H), 2.24 (dd, J = 12.0 Hz, J = 36.0 Hz, 2H), 1.10 (s, 3H),
1
2
1
3
.95 (s, 3H); C NMR (151 MHz, CDCl ): δ = 196.76, 164.07, 147.68,
3
43.72, 131.45, 131.29, 131.15, 130.15, 129.06, 128.44, 127.08, 124.98,
23.39, 120.06, 116.98, 116.92, 113.68, 50.79, 41.33, 34.22, 32.18, 29.25,
7.09.
1
2-(4-Nitrophenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xanthen
1
-
11-one (2e): H NMR (600 MHz, CDCl ): δ = 8.02 (d, J = 12.0 Hz, 2H),
3

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7
2
.84ꢀ7.80 (m, 3H), 7.53ꢀ7.51 (m, 2H), 7.44ꢀ7.26 (m, 3H), 5.82 (s, 1H),
.59 (s, 2H), 2.27 (dd, J = 18.0 Hz, J = 48.0 Hz, 2H), 1.13 (s, 3H), 0.95
1
2
13
(
s, 3H); C NMR (151 MHz, CDCl ): δ = 196.66, 164.57, 151.80, 147.69,
3
1
1
46.24, 131.49, 130.93, 129.55, 129.28, 128.59, 127.29, 125.15, 123.53,
23.02, 116.98, 115.94, 112.88, 50.68, 41.31, 34.79, 32.16, 29.22, 26.96.
1
2-(p-Tolyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xanthen-11-on
1
e (2f): H NMR (600 MHz, CDCl ): δ = 7.99 (d, J = 6.0 Hz, 1H),
3
7
6
3
.75ꢀ7.71 (m, 2H), 7.41 (m, 1H), 7.34ꢀ7.31 (m, 2H), 7.23ꢀ7.21 (m, 2H),
.97ꢀ6.95 (m, 2H), 5.66 (s, 1H), 2.54 (s, 2H), 2.24 (dd, J = 18.0 Hz, J =
1
2
13
6.0 Hz, 2H), 2.18 (s, 3H), 1.09 (s, 3H), 0.96 (s, 3H); C NMR (151
MHz, CDCl ): δ = 196.91, 163.79, 147.73, 141.91, 135.68, 131.53,
3
1
1
31.47, 128.97, 128.74, 128.40, 128.31, 126.99, 124.88, 123.72, 117.93,
17.07, 114.43, 50.97, 41.45, 34.34, 32.29, 29.30, 27.30, 21.01.
1
2-(4-Methoxyphenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xant
1
hen-11-one (2g): H NMR (600 MHz, CDCl ): δ = 7.97 (d, J = 12.0 Hz,
3
1
1
1
1
1
4
H), 7.76ꢀ7.72 (m, 2H), 7.41ꢀ7.24 (m, 5H), 6.70ꢀ6.69 (m, 2H), 5.65 (s,
H), 3.66 (s, 3H), 2.54 (s, 2H), 2.25 (dd, J = 18.0 Hz, J = 30.0 Hz, 2H),
1
2
1
3
.10 (s, 3H), 0.96 (s, 3H); C NMR (151 MHz, CDCl ): δ = 196.93,
3
63.62, 157.73, 147.63, 137.12, 131.44, 131.34, 129.31, 128.60, 128.32,
26.89, 124.80, 123.64, 117.83, 116.98, 114.36, 113.53, 55.00, 50.87,
1.33, 33.77, 32.19, 29.24, 27.13.
1
2-(3-Methoxyphenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xant
1
hen-11-one (2h): H NMR (600 MHz, CDCl ): δ = 7.99 (d, J = 6.0 Hz,
3
1
H), 7.75ꢀ7.72 (m, 2H), 7.42ꢀ7.23 (m, 3H), 7.08ꢀ7.06 (m, 1H), 6.93ꢀ6.90
(
(
(
m, 2H), 6.59ꢀ6.57 (m, 1H), 5.69 (s, 1H), 3.68 (s, 3H), 2.53 (s, 2H), 2.25
1
3
dd, J = 18.0 Hz, J = 30.0 Hz, 2H), 1.09 (s, 3H), 0.96 (s, 3H); C NMR
1
2
151 MHz, CDCl ): δ = 196.76, 163.86, 159.38, 147.68, 146.26, 131.41,
3
1
31.37, 129.02, 128.77, 128.30, 126.92, 124.82, 123.60, 120.92, 117.49,

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1
2
16.97, 114.57, 114.07, 111.19, 54.91, 50.84, 41.33, 34.57, 32.16, 29.18,
7.16.
1
2-(2-Methoxyphenyl)-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xant
1
hen-11-one (2i): H NMR (600 MHz, CDCl ): δ = 8.28 (d, J = 6.0 Hz,
3
1
H), 7.72ꢀ7.66 (m, 2H), 7.43ꢀ7.23 (m, 4H), 7.03ꢀ7.00 (m, 1H), 6.79ꢀ6.72
(
m, 2H), 5.96 (s, 1H), 3.93 (s, 3H), 2.57 (s, 2H), 2.20 (dd, J = 12.0 Hz, J
1
2
1
3
=
36.0 Hz, 2H), 1.10 (s, 3H), 0.98 (s, 3H); C NMR (151 MHz, CDCl ):
3
δ = 196.76, 164.21, 156.30, 147.63, 133.30, 131.84, 131.22, 130.56,
1
1
28.29, 128.14, 127.57, 126.69, 124.60, 123.95, 120.68, 118.28, 116.91,
13.61, 111.48, 55.84, 50.87, 41.43, 32.17, 29.40, 26.96.
1
2-(3-Methoxy-4-hydroxylphenyl)-9,9-dimethyl-8,9,10,12tetrahydrob
1
enzo[a]xanthen-11-one (2j): H NMR (600 MHz, CDCl ): δ = 7.98 (d, J
3
=
12.0 Hz, 1H), 7.79ꢀ7.75 (m, 2H), 7.45ꢀ7.31 (m, 3H), 7.01 (m, 1H),
6
1
.68ꢀ6.64 (m, 2H), 5.65 (s, 1H), 3.83 (s, 3H), 2.56 (s, 2H), 2.28 (dd, J =
1
13
8.0 Hz, J = 30.0 Hz, 2H), 1.12 (s, 3H), 0.98 (s, 3H); C NMR (151
2
MHz, CDCl ): δ = 197.07, 163.73, 147.74, 146.08, 143.81, 136.97,
3
1
1
2
31.47, 131.42, 128.73, 128.36, 126.92, 124.86, 123.67, 121.01, 117.76,
16.98, 114.44, 114.09, 111.33, 55.88, 50.91, 41.40, 34.14, 32.24, 29.28,
7.12.
1
2-Methyl-9,9-dimethyl-8,9,10,12tetrahydrobenzo[a]xanthen-11-one
1
(
2k): H NMR (600 MHz, CDCl ): δ = 8.08 (d, J = 6.0 Hz, 1H), 7.81 (d, J
3
=
6.0 Hz, 1H), 7.69 (d, J = 6.0 Hz, 1H), 7.57ꢀ7.54 (m, 1H), 7.45ꢀ7.43 (m,
1
2
H), 7.19 (d, J = 6.0 Hz, 1H), 4.60ꢀ4.57 (m, 1H), 2.52 (s, 2H), 2.36 (s,
13
H), 1.36 (d, J = 6.0 Hz, 3H), 1.17 (s, 3H), 1.15 (s, 3H); C NMR (151
MHz, CDCl ): δ = 197.50, 164.94, 147.28, 131.39, 131.14, 128.55,
3
1
3
28.00, 126.81, 124.78, 123.03, 119.96, 117.03, 114.63, 51.01, 41.34,
2.21, 29.44, 27.17, 23.33, 22.97.

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1
1
2-Phenyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one (2l): H NMR
(
600 MHz, CDCl ): δ = 8.00 (d, J = 6.0 Hz, 1H), 7.79ꢀ7.76 (m, 2H),
3
7
2
.44ꢀ7.35 (m, 5H), 7.21ꢀ7.18 (m, 2H), 7.09ꢀ7.07 (m, 1H), 5.78 (s, 1H),
13
.76ꢀ2.63 (m, 2H), 2.48ꢀ2.35 (m, 2H), 2.05ꢀ1.94 (m, 2H); C NMR (151
MHz, CDCl ): δ = 196.92, 165.49, 147.70, 144.98, 131.41, 131.31,
3
1
1
28.75, 128.41, 128.29, 128.19, 126.90, 126.17, 124.80, 123.60, 117.62,
16.89, 115.47, 36.96, 34.56, 27.64, 20.18.
1
1
2-(p-Tolyl)-8,9,10,12tetrahydrobenzo[a]xanthen-11-one (2m):
H
NMR (600 MHz, CDCl ): δ = 7.96 (d, J = 6.0 Hz, 1H), 7.73ꢀ7.70 (m, 2H),
3
7
1
2
1
1
.39ꢀ7.29 (m, 3H), 7.22ꢀ7.20 (m, 2H), 6.96 (d, J = 6.0 Hz, 1H), 5.69 (s,
H), 2.70ꢀ2.57 (m, 2H), 2.44ꢀ2.30 (m, 2H), 2.17 (s, 3H), 2.00ꢀ1.89 (m,
13
H); C NMR (151 MHz, CDCl ): δ = 197.12, 165.53, 147.61, 142.07,
3
35.62, 131.39, 131.29, 128.88, 128.63, 128.25, 128.23, 126.86, 124.75,
23.58, 117.75, 116.85, 115.58, 36.89, 34.11, 27.60, 20.88, 20.14.
1
2-(4-Chlorophenyl)-8,9,10,12tetrahydrobenzo[a]xanthen-11-one
1
(
2n): H NMR (600 MHz, CDCl ): δ = 7.89 (d, J = 6.0 Hz, 1H),
3
7
2
.80ꢀ7.77 (m, 2H), 7.45ꢀ7.28 (m, 5H), 7.16ꢀ7.14 (m, 2H), 5.73 (s, 1H),
13
.76ꢀ2.63 (m, 2H), 2.49ꢀ2.36 (m, 2H), 2.08ꢀ1.93 (m, 2H); C NMR (151
MHz, CDCl ): δ = 197.20, 165.89, 147.65, 143.44, 131.90, 131.45,
3
1
1
31.11, 129.80, 129.05, 128.41, 128.36, 127.05, 124.96, 123.40, 116.97,
15.03, 36.86, 34.06, 27.64, 20.17.
1
2-(4-Nitrophenyl)-8,9,10,12tetrahydrobenzo[a]xanthen-11-one (2o):
1
H NMR (600 MHz, CDCl ): δ = 8.02 (d, J = 6.0 Hz, 2H), 7.81ꢀ7.78 (m,
3
3
H), 7.52ꢀ7.48 (m, 2H), 7.43ꢀ7.35 (m, 3H), 5.83 (s, 1H), 2.78ꢀ2.66 (m,
13
2
H), 2.48ꢀ2.36 (m, 2H), 2.10ꢀ1.92 (m, 2H); C NMR (151 MHz, CDCl ):
3
δ = 196.76, 166.19, 152.02, 147.63, 146.18, 131.42, 130.86, 129.48,
1
3
29.30, 128.52, 127.20, 125.07, 123.47, 122.99, 116.91, 115.88, 114.07,
6.80, 34.70, 27.61, 20.08.

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1
2-(4-Bromophenyl)-8,9,10,12tetrahydrobenzo[a]xanthen-11-one (2p):
1
H NMR (600 MHz, CDCl ): δ = 7.86 (d, J = 12.0 Hz, 1H), 7.74ꢀ7.71 (m,
3
2
H), 7.39ꢀ7.25 (m, 5H), 7.21ꢀ7.19 (m, 2H), 5.68 (s, 1H), 2.69ꢀ2.56 (m,
13
2
H), 2.43ꢀ2.30 (m, 2H), 2.00ꢀ1.86 (m, 2H); C NMR (151 MHz, CDCl ):
3
δ = 196.84, 165.61, 147.59, 143.93, 131.36, 131.22, 131.04, 130.15,
1
3
28.99, 128.35, 126.98, 124.88, 123.31, 120.01, 116.84, 116.81, 114.85,
6.84, 34.09, 27.55, 20.10.
4
7
.4
General
Procedure
for
the
Synthesis
of
-Hydroxy-4-methylcoumarin
In a typical procedure, a mixture of resorcinol (1 mmol), ethyl
acetoacetate or methyl acetoacetate (1 mmol), and CXHꢀSO H (3.24
3
mol%) was successively charged into a 15 mL pressure flask with a
magnetic stirring bar. Then the reaction system was placed in an oilꢀbath
o
(
85 C) for the desired reaction time with magnetic stirring, and the
progress of the reaction was monitored by TLC. After the completion of
reaction, the reaction mixture was cooled to room temperature and added
with cold ethanol (10 mL). The biocatalyst was then separated by
filtration and iceꢀcold distilled water was poured into the reaction mixture
to precipitate the crude product. The collected crude product was
recrystallized
ꢀhydroxyꢀ4ꢀmethylcoumarin. The product was confirmed by NMR
spectroscopy.
from
ethanol,
producing
high
quality
7
7
-Hydroxy-4-methylcoumarin
1
H NMR (600 MHz, DMSOꢀd ): δ = 10.54 (s, 1H), 7.56 (d, J = 6.0 Hz,
6
1
H), 6.81 (d, J = 12.0 Hz, 1H), 6.73 (s, 1H), 6.12 (s, 1H), 2.37 (s, 3H);
1
3
C NMR (151 MHz, DMSOꢀd ): δ = 161.25, 160.39, 154.94, 153.47,
6
1
26.54, 112.93, 112.10, 110.35, 102.29, 18.14.

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4
.5 General Procedure for the Synthesis of 4-Aryl-NH-1,2,3-triazoles
CAUTION: All the experiments were performed in a wellꢀventilated
fume hood and behind a blast shield. CXHꢀSO H (3.24 mol%) was
3
carefully added to a mixture of nitroolefin (0.3 mmol) and NaN3 (0.45
mmol) in DMSO (1.5 mL) under stirring. Thereafter, the mixture was
o
stirred at 60 C for 2 h, and the progress of the reaction was monitored by
TLC. After the completion of reaction, the solid biocatalyst was removed
by filtration and washed with ethyl acetate for several times, and used for
subsequent cycles after drying under vacuum. The filtrate was extracted
with saturated NaCl solution, and then the organic layer was dried over
anhydrous MgSO and evaporated in vacuo. Finally, the target products
4
were obtained by column chromatography on silica gel using ethyl
acetate/hexane as an eluent. All products were characterized by NMR
spectroscopy.
1
4
-Phenyl-NH-1,2,3-triazole (3a): H NMR (600 MHz, DMSOꢀd ), 1
6
drop TFA: δ = 14.95 (s, 1H), 8.25 (s, 1H), 7.86 (s, 2H), 7.45 (s, 2H), 7.35
1
3
(
s, 1H); C NMR (151 MHz, DMSOꢀd ), 1 drop TFA: δ = 145.9, 130.5,
6
1
28.9, 128.1, 127.2, 125.5.
-(p-Tolyl)-NH-1,2,3-triazole (3b): H NMR (600 MHz, DMSOꢀd ), 1
1
4
6
drop TFA: δ = 14.94 (s, 1H), 8.23 (s, 1H), 7.75 (s, 2H), 7.26 (d, J = 6.0
13
Hz, 2H), 2.32 (s, 3H); C NMR (151 MHz, DMSOꢀd ), 1 drop TFA: δ =
6
1
46.2, 137.5. 130.5, 129.5, 127.8, 125.5, 20.8.
-(4-Methoxyphenyl)-NH-1,2,3-triazole (3c): H NMR (600 MHz,
1
4
DMSOꢀd ), 1 drop TFA: δ = 14.98 (s, 1H), 8.21 (s, 1H), 7.79 (d, J = 12.0
6
13
Hz, 2H), 7.02 (d, J = 6.0 Hz, 2H), 3.79 (s, 3H); C NMR (151 MHz,
DMSOꢀd ), 1 drop TFA: δ = 159.2, 126.9, 122.7, 114.3, 55.1.
6

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1
4
-(4-Fluorinephenyl)-NH-1,2,3-triazole (3d): H NMR (600 MHz,
DMSOꢀd ), 1 drop TFA: δ = 14.98 (s, 1H), 8.24 (s, 1H), 7.91 (s, 2H),
6
1
3
7
1
.29 (s, 2H); C NMR (151 MHz, DMSOꢀd ), 1 drop TFA: δ = 162.8,
6
61.2, 145.5, 130.7, 127.7 (J CF = 58.89 Hz), 119.3, 115.9 (J CF = 19.63
Hz).
1
4
-(4-Bromophenyl)-NH-1,2,3-triazole (3e): H NMR (600 MHz,
DMSOꢀd ), 1 drop TFA: δ = 15.06 (s, 1H), 8.30 (s, 1H), 7.83 (d, J = 6.0
6
1
3
Hz, 2H), 7.66 (d, J = 6.0 Hz, 2H); C NMR (151 MHz, DMSOꢀd ), 1
6
drop TFA: δ = 145.2, 131.6, 131.0, 130.0, 127.6, 121.2.
1
4
-(4-Chlorophenyl)-NH-1,2,3-triazole (3f): H NMR (600 MHz,
DMSOꢀd ), 1 drop TFA: δ = 15.05 (s, 1H), 8.29 (s, 1H), 7.90 (d, J = 6.0
6
1
3
Hz, 2H), 7.53 (d, J = 12.0 Hz, 2H); C NMR (151 MHz, DMSOꢀd ), 1
6
drop TFA: δ = 145.2, 132.7, 131.0, 129.0, 127.3, 119.8.
1
4
-(NH-1,2,3-Triazol-4-yl)benzonitrile (3g): H NMR (600 MHz,
DMSOꢀd ), 1 drop TFA: δ = 15.24 (s, 1H), 8.43 (s, 1H), 8.08 (d, J = 6.0
6
13
Hz, 2H), 7.93 (s, 2H); C NMR (151 MHz, DMSOꢀd ), 1 drop TFA: δ =
6
1
43.9, 133.0, 132.3, 131.9, 126.3, 121.3, 118.8.
1
Methyl-4-(NH-1,2,3-triazol-4-yl)benzoate (3h): H NMR (600 MHz,
DMSOꢀd ), 1 drop TFA: δ = 15.19 (s, 1H), 8.38 (s, 1H), 8.03 (s, 4H),
6
1
3
3
1
.86 (s, 3H); C NMR (151 MHz, DMSOꢀd ), 1 drop TFA: δ = 142.7,
6
33.3, 129.4, 127.6, 120.6, 111.8, 55.5.
1
4
-(3-Methoxy-4-hydroxylphenyl)-NH-1,2,3-triazole (3i): H NMR (600
MHz, DMSOꢀd ), 1 drop TFA: δ = 14.76 (s, 1H), 9.19 (s, 1H), 8.13 (s,
6
13
1
H), 7.38 (s, 1H), 7.28 (s, 1H), 6.82 (s, 1H), 3.83 (s, 3H); C NMR (151
MHz, DMSOꢀd ), 1 drop TFA: δ = 148.4, 147.2, 130.6, 122.3, 118.7,
6
1
16.3, 110.2, 56.1, 29.50.
4
.6 Recyclability experiments

New Journal of Chemistry
Page 26 of 32
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DOI: 10.1039/C8NJ01329B
A mixture of benzaldehyde (0.5 mmol), 2ꢀnaphtol (0.5 mmol), dimedone
0.6 mmol), and CXHꢀSO H (4.32 mol%) was charged into a 15 mL
(
3
pressure flask with a magnetic stirring bar. The reaction system was then
o
stirred at 90 C for 2 h. Upon the completion of the reaction, ethyl acetate
(
10 mL) was added when the reaction system was cooled to room
temperature to precipitate CXHꢀSO H. The CXHꢀSO H was filtered off
3
3
and washed with ethyl acetate for several times. The recovered
o
CXHꢀSO H was then dried under vacuum at 80 C for 24 h and used
3
directly for the next run. Finally, pure product was obtained by
evaporation of the solvent, followed by column chromatography on silica
gel using ethyl acetate/hexane as an eluent. The product was confirmed
by NMR spectroscopy.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We wish to thank for the National Natural Science Foundation of China
(
21336002, 31430092, 21506068), Guangdong Natural Science Funds for
Distinguished Young Scholar (2016A030306027, 2017A030306029),
Tipꢀtop Scientific and Technical Innovative Youth Talents of Guangdong
Special Support Program (2015TQ01C488), State Key Laboratory of
Pulp and Paper Engineering and Fundamental Research Funds for the
Central Universities.
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