Nano-WO3-supported sulfonic acid: New, efficient and high reusable heterogeneous nano catalyst

Article abstract of DOI:10.1016/j.molcata.2014.09.020

Nano-WO₃-supported sulfonic acid [n-WO₃-SO₃H (n-WSA)] is easily prepared from the reaction of nano WO₃ with chlorosulfonic acid as sulfonating agent. This new catalyst is characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy, thermal gravimet-ric analysis (TGA), pH analysis and Hammett acidity function. Nano-WO₃-supported sulfonic acid isused as an efficient and recyclable catalyst for some organic reactions such as synthesis of 1,8-dioxo-octahydroxanthene, tetrahydrobenzoxanthene and benzimidazolo quinazolinone derivatives. All of thereactions are very fast and the yields are excellent. The used catalyst was easily separated and reused for 10 runs without appreciable loss of its catalytic activity.

Full text of DOI:10.1016/j.molcata.2014.09.020

Accepted Manuscript
Title: Nano-WO3-supported sulfonic acid: New, efficient and
high reusable heterogeneous nano catalyst
Author: Ali Amoozadeh Salman Rahmani
PII:
S1381-1169(14)00423-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.09.020
MOLCAA 9281
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
19-6-2014
13-9-2014
16-9-2014
Please cite this article as: A. Amoozadeh, Nano-WO3-supported sulfonic acid: New,
efficient and high reusable heterogeneous nano catalyst, Journal of Molecular Catalysis
A: Chemical (2014), http://dx.doi.org/10.1016/j.molcata.2014.09.020
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• Nano-WO3-supported sulfonic acid has been reported.
• The n-WSA works very well for different organic reactions with excellent yields.
• The advantages of n-WSA are high efficiently, reusability and operational simplicity.
• The n-WSA was easily separated and reused for several runs without loss activity.
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Nano-WO3-supported sulfonic acid: New, efficient and high recyclable
heterogeneous nano catalyst
Ali Amoozadeh* and Salman Rahmani*
Department of Chemistry, Semnan University, Semnan, Zip Code: 35131-19111, Iran, Fax: +98 (233)
3354110, Tel.: +98 (233) 3366177, e-mail: aamozadeh@semnan.ac.ir, salmanrahmani64@yahoo.com
2
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Nano-WO3-supportedsulfonic acid:New, efficient andhighreusable
heterogeneous nanocatalyst
Ali Amoozadeh* and Salman Rahmani*
Department of Chemistry, Semnan University, Semnan, Zip Code: 35131-19111, Iran, Fax: +98 (233)
3354110, Tel.: +98 (233) 3366177, e-mail: aamozadeh@semnan.ac.ir,salmanrahmani64@yahoo.com
Abstract
Nano-WO3-supported sulfonic acid [n-WO3-SO3H (n-WSA)]is easily prepared from the reaction of
nanoWO3 with chlorosulfonic acid as sulfonating agent.This new catalystis characterized by X-ray
diffraction (XRD), field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy, thermal
gravimetric analysis (TGA), pH analysis and Hammett acidity function. Nano-WO3-supported sulfonic acid
is used as an efficient and recyclable catalyst forsome organic reactions such as synthesis of1,8-dioxo-
octahydroxanthene, tetrahydrobenzoxanthene and benzimidazoloquinazolinone derivatives. All of the
reactions are very fast and the yields are excellent. The used catalyst was easily separated and reused for 10
runs without appreciable loss of its catalytic activity.
Keywords: Nano-WO3-supported sulfonic acid, Heterogeneous nano catalyst, Multi component reaction,
Green chemistry.
1. Introduction
The “green chemistry” principles of chemical reactions have encouraged the use of reusable strong solid
acids as alternatives for such unrecyclable “liquid acids” catalysts such as sulfuric acid, nitric acid,etc.
Though the use of new solid acid catalystshas been widely developed, there is still a need to discover new
methodologies for the immobilization of sulfonic acid.These solid acids are suitable options economically
and industrially because of their special properties such as using less toxicity and readily available
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precursors, simple and non-energy-intensive methods for recovery and reuse of catalyst[1]. In this context,
the use of nanoparticles as heterogeneous catalysts has attracted considerable attention because of the
interesting structural features and high levels of catalytic activity associated with these materials [2].
Furthermore, nanoparticle materials are considered to be a bridge between homogeneous and heterogeneous
catalysts[3]. In addition, the application of transition metal nanoparticles as catalysts for organic reactions
has been attracting wide interest as nanoparticle-based catalytic systems can exhibit superior catalytic
activities than the corresponding bulk materials. Transition metal oxides have been efficiently played an
important role as catalysts in organic reactions. These high reactivities are due to high surface areas
combined with unusually reactive morphologies.
Among various transition metals, tungsten is one of the important metals on our globe, and consequently,
one of the most economical and environmentally well-suited ones.Moreover, tungsten is not toxic and
additionally, the tungsten trioxide is commercially available.
The tungsten trioxide (WO3) is commonly regarded as a material for many promising applications, in
several research fields, due to their multiple potential applications such as catalytic activity for water
purification[4], metathesis between ethene and 2-butene[5], esterification of propionic acid[6], photocatalytic
activity[7], NO2 sensing[8], photocatalytic O2 production[9], oxidation of cyclopentene to
glutaraldehyde[10], gas sensing properties [11] and adsorption of methylene blue from water [12] and other
application such as heterogeneous catalysts, chromogenic devices, solar-energy devices, field electron
emission. In spite of the aforementioned advantages, unpredictably, in comparison with some other transition
metals until lately, tungsten has been comparatively unheeded as a catalyst in the organic synthesis.
Based on the mentioned facts, it has been decided to improve the catalytic properties of nano-WO3 by
reacting it with chlorosulfonic acid to produce nano-WO3-supported sulfonic acid (n-WSA) (Scheme
1).Sulfonation with chlorosulfonic acid is convenient, fast and efficient method for heterogenization of
homogeneous catalysts[13-15] that has attracted more much attention after Zolfigol's report on the
preparation of silica sulfuric acid (SSA) [16].
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O
ClSO3H
O S OH
O
OH
HCl
CH2Cl2, r.t.
= nano-WO3
Scheme 1.Preparation of nano-WO3-SO3H (n-WSA).
2. Experimental
2.1. Materials and Instruments
Chemicals were purchased from the Merck chemical companies. Thin-Layer Chromatography (TLC) on
commercial plates of silica gel 60 F254 was used to monitor the progress of reactions. The products were
1
13
1
13
characterized by FT-IR spectra, HNMR, CNMR and CHN analyzer. H and CNMR spectra which were
recorded on Bruker Advance Spectrometer 400 & 500 MHz using CDCl3-d and DMSO-d6 as solvent. The
chemical shifts are expressed in parts per million (ppm) and tetramethylsilane (TMS) was used as an internal
reference. Elemental analyses were performed by Perkin Elmer CHN analyzer, 2400 series II. Melting points
were recorded on a THERMO SCIENTIFIC 9100 apparatus.
2.2. Characterization methods of nano-WO3-SO3H (n-WSA)
2.2.1. X-ray diffraction spectrum
Wide angle X-ray diffraction spectrum for the n-WSA powder sample was obtained using a Siemens
D5000 (Siemens AG, Munich, Germany) X-ray diffractometer using Cu-Ka radiation of wavelength 1.54 Å.
2.2.2. Filed emission scanning electron microscopy
A particle size study of n-WSA sample was carried out using Philips XL30 field emission scanning
electron microscope (Royal Philips Electronics, Amsterdam, The Netherlands) instrument operating at 10
kV. The sample was mounted on a double sided adhesive carbon disk and sputter-coated with a thin layer of
gold to prevent sample charging problems.
2.2.3. Infrared spectra
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The n-WSA sample was mixed with KBr powder and compressed into a pellet, wherein, the n-WSA
powder was evenly dispersed. Fourier transform infrared spectrum was recorded on Shimadzo FT-IR 8400
instrument.
2.2.4. Thermo gravimetric analyses
Thermo gravimetric analyses (TGA) were conducted on a Du Pont 2000 thermal analysis apparatus under
air atmosphere at a heating rate of 5 °C/min.
2.3. Preparation of nano-WO3
10 mL of ammonia solution (25 wt%) was added to the CTAB solutions while stirring. After getting a
homogenous solution, 0.117 mol of WCl6 1000 mL−1 of CTAB solution was added with vigorous stirring.
After stirring for 4 h, the products were aged at ambient temperature for 72 h. The final product was filtered,
washed with deionized water and absolute ethanol in order to remove surfactant, residual reactants and by
products and then calcinated at 500°C for 2 h[17].
2.4. Preparation of nano-WO3-SO3H (n-WSA)
A suction flask equipped with a constant-pressure dropping funnel and a gas inlet tube for conducting
HCl gas over an adsorbing solution (i.e., water) was used, charged with the nano-WO3 (4 g, 17 mmol) in dry
CH2Cl2 (20 ml). Then chlorosulfonic acid (1 ml, 15 mmol) (CAUTION: a highly corrosive and water
absorbant. Be careful when using this liquid. Protective gloves, protective clothing and eye and face
protection equipment are also needed.)was added dropwisely over a period of 30 min at room temperature.
HCl gas immediately evolved from the reaction vessel. Stirring was continueduntilHCl evolution was seized.
After the addition was completed, the mixture was shaken for 30 min. A darkgreen powder of nano-tungsten
trioxide-supported sulfonic acid was obtained. Then, the CH2Cl2 was removed under reduced pressure and
the solid powder was washed with ethanol (10 mL) and dried at 70 °C.
The prepared n-WSA stored in vacuum desiccator over anhydrous silica gel, then, was dried in 120 °C for
6 hours. The mmol of H+ per gram of catalyst (3.7 mmol/ gram of n-WSA) was determined by the titration of
0.1 gram of sample with a standard solution of NaOH (0.1 N). For this purpose, the surface acidic protons of
nano-WO3-SO3H (100 mg) were ion-exchanged with a saturated solution of NaCl (10 mL) by sonication.
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This process was repeated twice more, yielding 30 mL of proton-exchanged brine solution. Therefore, to
determine the loading of acid sites on the synthesized catalyst, the obtained solution was titrated by NaOH
(0.1 M) solution in presence of phenol red indicator solution or pH meter.
2.5. General procedure for synthesis of 1,8-dioxo-octahydroxanthene derivatives
In a typical experiment, various aromatic aldehyde (1 mmol), 1,3-cyclic diketon (2mmol) and catalyst
(0.019 g) in solvent free condition were taken in a 25 ml round bottomed flask.The flask was stirred at 100
oC for an appropriate time. The reaction mixture was cooled, eluted with hot ethanol (5 mL), centrifuged and
filtrated to collect the formed precipitate. The crude product was recrystallized from ethanol to yield pure
1,8-dioxo-octahydroxanthene derivatives.
2.6. General procedure for synthesis of tetrahydrobenzoxanthene derivatives
In a typical experiment, various aromatic aldehyde (1 mmol), 1,3-cyclic diketon (1 mmol), β-naphtol (1
mmol) and catalyst (0.019 g) in solvent free condition were taken in a 25 ml round bottomed flask.The flask
o
was stirred at 100 C for an appropriate time. The reaction mixture was cooled, eluted with hot ethanol (5
mL), centrifuged and filtrated to collect the formed precipitate. The crude product was recrystallized from
ethanol to yield pure tetrahydrobenzoxanthene derivatives.
2.7. General procedure for synthesis of benzimidazoloquinazolinone derivatives
In a typical experiment, different aromatic aldehyde (1 mmol), 1,3-cyclic diketon (1 mmol), 2-amino-
benzimidazole (1 mmol) and catalyst (0.019 g) in solvent free condition were taken in a 25 ml round
o
bottomed flask.The flask was stirred at 100 C for an appropriate time. The reaction mixture was cooled,
eluted with hot ethanol (5 mL), centrifuged and filtrated to collect the formed precipitate. The crude product
was recrystallized from ethanol to yield pure benzimidazoloquinazolinone derivatives.
3. Results and Discussion
3.1. Characterization of nano-WO3-SO3H
3.1.1. X-ray diffraction spectra
The nano-WO3 powder can be easily synthesized by reported procedure[17].Fig. 1a shows the XRD
patterns of nano-WO3 powder before modification.The following peak signals with miler indices (001),
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(020), (200), (120), (111),(021), (201), (220), (221), (320), (131), (002), (040), (400), (140), (022), (202),
(240), (420), (222), (240) and (430) in Fig. 1a confirm the formation ofnano tungsten trioxide crystal phase
which coincides with JCPD 201324 standard. The crystal size of the nanoWO3 powder was also determined
from X-ray pattern using the Debye-Scherrer formula given as t=0.9λ/B1/2cosθ, that t is the average crystal
size, λ the X-ray wavelength used (1.54 Å), B1/2 the angular line width at half maximum intensity and θ the
Bragg′s angle. The average crystal size of the nano-WO3 powder for2θ = 24.32 ºis calculated to be around
21.67nm.Fig.1b illustrates XRD patterns of the samples of modifiednanoWO3. As shown in Fig.1b, the peak
intensities of nano-WO3-SO3H (n-WSA) are almost the same as those ofnanoWO3(Fig. 1a) and sulfonate
modification dose not change the phase ofnanoWO3.
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Fig.1. The X-ray diffraction pattern of (a) the nano-WO3 powder and (b) n-WSA.
3.1.2. Field emission scanning electron microscopy
The field emission scanning electron microscopy (FE-SEM) images of nano-WO3 powder reveals
thespherical nano-WO3 powder with average particle sizes of about75-80 nm(Fig.2).
Fig.2. The FE-SEM image of nano-WO3.
It was revealed by the FE-SEM images of n-WSAthat the spherical n-WSA powder average particle sizes
was about60-75 nm (Fig. 3). Compared to Fig. 2, as shown in Fig. 3, its cleared that the surface of the as-
synthesized n-WSA are not smoothed indicating that the modification process has performed successfully.
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Fig.3. The FE-SEM image of n-WSA.
3.1.3. FT-IR spectra
The FT-IR spectra of nano-WO3 powder and n-WSA are shown in Figure4. In the graph a of Fig. 4, the
absorbance bands at around 777 and 838 cm-1 is due to W-O-W vibration, 1629 cm-1 W-OH vibrationand the
absorbance bands at around 3400-3500 cm-1 was certified to the adsorbed water (Fig. 4, graph a and b) which
is consistent with the reported IR spectra for nano-WO3[7]. In the graph b of Fig. 4, the absorption range in
1177-1284 and 1012-1070 cm-1 was certified the O=S=O asymmetric and symmetric stretching modes lies
respectively and the S-O stretching mode lies in 577-615 cm-1 showing the presence of sulfonic acid
functional group which is consistent with the reported IR spectra for -SO3H[18].
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Fig. 4. The FT-IR spectra of (a) The nano WO3 powder and (b) n-WSA.
3.1.4. Thermo gravimetric analysis
Thermo gravimetric analysis (TGA) of n-WSA in comparison with nano WO3 is shown in Fig. 5. The
TGA curve of WO3 (Fig. 5a) displays a weight loss (5 wt.%) below 100 °C which corresponds to the loss of
the physically adsorbed water. Also, there is a slight weight loss (1 wt.%) between 100 °C and 800 °C, which
possibly corresponds to the dehydroxylation of WO3.
In the TGA curve of n-WSA (Fig. 5b) exist two regions corresponding to different mass lose ranges. In
the first region,a mass loss approximately 4% weight occurred below 140 °C that displayed that was
attributable to the loss of trapped water from the catalyst. A mass loss of approximately 16% weight occurred
between 140 and 250 °C that was related to the sudden mass loss of SO3H groups[18, 19]. Also, from the
TGA, it can be understood that n-WO3-SO3H has a greater thermal stability (up 150 °C) confirming that it
could be safely used in organic reactions at temperatures in the range of 80-130 °C.
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Fig.5. TGA cure of (a) nano-WO3and (b) n-WSA.
3.1.5. Surface acidity studies
The Hammett acidity function (H0) can effectively express the acidity strength of an acid in organic
solvents[20]. It can be calculated using the following equation:
H0= pK(I)aq + log([I]s/[IH+]s),
Here, ‘I’ represents the indicator base (mainly substituted nitroanilines) and [IH+]s and [I]s are
respectively the molar concentrations of the protonated and unprotonated forms of the indicator. The pK(I)aq
values are already known (for example the pK(I)aq value of 4-nitroaniline is 0.99) and can be obtained from
many references. According to the Lambert-Beerlaw, the value of [I]s/[IH+]s can be determined and
calculated using the UV-visible spectrum. In this experiment, 4-nitroaniline was chosen as the basic
indicator, and CCl4 was chosen as the solvent because of its aprotic property. The maximal absorbance of the
unprotonated form of 4-nitroaniline was observed at 329 nm in CCl4. As Fig. 6 shows, the absorbance of the
unprotonated form of the indicator in n-WO3-SO3H was weak as compared to the sample of the indicator in
CCl4, which indicated that the indicator was partially in the form of [IH+].
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Fig.6. Absorption spectra of (a) 4-nitroaniline (indicator) and (b) n-WSA (catalyst) in CCl4.
The obtained results are listed in Table 1, which shows the acidity strength of nano-WO3-SO3H. These
results of the Hammett acidity function (H0) also confirm the synthesis of nano-WO3-SO3H with a high
density of acid sites (-SO3H groups)on the surface of nano-WO3-SO3H (Table 1).
Table 1. Calculation of Hammett acidity function (H0) of n-WSA.
Entry
1
2
Catalyst
Amax
1.83
0.512
[I]s (%)
100
27.17
[IH+]s (%)
0
72.83
H0
-
1.13
-
n-WSA
Condition for UV-visible spectrum measurement: solvent, CCl4;
indicator, 4-nitroaniline (pK(I)aq= 0.99), 1.44*10-4mol/L; catalyst, n-WSA (20 mg), 25 °C.
To compoare the relative acidity of n-WSA, Hammet acidity of various amount of n-WSA (0-25 mg) was
compared with sulfuric acid at 50 mM concentration (by the methodology described in the literature [21]).
The obtained results were shown in the Fig. 7. From Fig. 7 it is clear that the n-WSA prossess similar acidity
as sulfuric acid. Also,from the obtained results, we can investigated the contributed supported sulfonic acid
for reactions.
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Fig. 7. Comparison of Hammett functions of various amount of n-WSA in water with Sulfuric Acid (50 mM) (4-
nitroaniline (44.8 mM) as indicator pKa= 0.99, Amax= 380 nm).
The obtained results of characterization methods showed that the nano-WO3-supported sulfonic acid is
prepared and different characterization methodsalso show that the sulfunic acid groups (-SO3H) have been
supported on the surface of nano-WO3. Indeed, nano-WO3 functions as a Lewis acid and sulfonic acids
functions as the Brønsted. Brønsted acids could usually provide a hydrogen bond which can initiate the
catalytic procedure. In our new solid acid supported catalyst, we have conserved both of these
properties.Based on the obtained results,we expected better catalytic activity for nano-WO3-supported
sulfonic acid comparing with nano-WO3. Toconfirm this hypothisis, the catalytic ability of nano-WO3-
supported sulfonic acid is tested in some of organic reactions.
3.2. Using nano-WO3-SO3H in some organic reactions
In continuation of our studies on developing inexpensive and environmentally benign methodologies for
organic reactions [22, 23],nano-titania-supported sulfonic acid[13]as heterogeneous solid acid nano catalyst
was studied where the results were also very satisfactory.
In thepresent work, nano-WO3-supported sulfonic acid was easily prepared andused as a highly efficient,
heterogeneous, reusable and inexpensive solid acid catalystfor synthesis of 1,8-dioxo-octahydroxanthene,
tetrahydro-benzoxanthene and benzimidazolo-quinazolinone derivatives.
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3.2.1. Synthesis of 1,8-dioxo-octahydroxanthene derivatives
The synthesis of xanthenes, especially dioxo-octahydroxanthenes, has emerged as a powerful tool
in organic synthesis due to their broad applications in different fields[24-27].The prepared n-WSA has
been tested for the synthesis of 1,8-dioxo-octahydroxanthene derivatives by condensation between para-
chlorobenzaldehyde (1) (1 mmol) and dimedone (2) (2 mmol) under solvent free condition as a model
reaction (Scheme 2).
O
O
Ar
O
O
n-WSA (0.019 g)
R1
R1
ArCHO
1
2
Solvent Free, 100 °C
O
R1
R2
R2
R2
3, 4, 5
1
2
2a:
2b:
2c:
R = R = H
1
2
R = R = Me
1
2
R = H, R = Ph
Scheme 2. Synthesis of 1,8-Octahydroxanthene derivatives.
To justify the efficiency of the n-WSA, the model reaction was carried out in presence of different
amount of n-WSA in solvent free condition at 90 ºC and compared it by nano-WO3 (Table 2).
Table 2.Optimization of catalyst amount for the synthesis of 1,8-dioxo-octahydroxanthenea.
Entry
Catalyst
Amount of catalyst (g)
Yieldb (%)
1
2
-
-
21
49
62
75
81
89
89
25
Nano-WO3-SO3H
Nano-WO3-SO3H
Nano-WO3-SO3H
Nano-WO3-SO3H
Nano-WO3-SO3H
Nano-WO3-SO3H
Nano-WO3
0.011
0.013
0.015
0.017
0.019
0.021
0.019
3
4
5
6
7
aReaction condition: 1 (1 mmol), 2 (2mmol), reaction time: 1 h, under solvent free condition at 90 ºC.
bIsolated yield.
The obtained results showed that n-WSA performed well to give desired product within 60 min in 89%
yield at 90 ºC under solvent free condition (Table 2, entry 5) and is a more suitable option than tungsten
trioxide (Table 2, entry 7). The greater catalytic activity of n-WSA was most likely related to the SO3H
groups of the catalyst, which could provide efficient acidic sites.
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In the next step, the effect of temperature in presence of 0.019 g of n-WSA was investigated. The results
showed that the best temperature was 100 ºC (Table 3, entry 7). By increasing the temperature to 110 oC, the
achieved yield was decreased to 92% (Table 3, entry 8), so the experiences were followed at 100oC.
Table 3.Optimization of other conditions for the synthesis of 1,8-dioxo-octahydroxanthenea.
Entry
1
2
Temperature (ºC)
Solvent
Yieldb (%)
Trace
21
RT
40
-
-
3
60
-
39
4
5
70
80
-
-
64
83
6
90
-
89
7
8
9
10
11
12
13
14
15
100
110
100
100
100
100
100
100
100
-
-
93
92
58
63
50
42
37
21
EtOH
PEG
MeOH
CH3CN
Toluen
CH2Cl2
H2O
12
aReaction condition: 1 (1 mmol), 2 (1 mmol), n-WSA (0.019 g), reaction time: 1 h.
bIsolated yield.
Eventually to making sure that the solvent free condition is appropriate, it has been decided to investigate
the effect of different classical solvents such as EtOH, PEG, MeOH, CH3CN, Toluene, CH2Cl2 and H2O at
100 °C (Table 3, entries 9-15). As it is shown in Table 3, using these solvents gave significantly lower yields
and longer reaction times. Increasing the reaction times did not improve the yields. So the best yield of
product was provided in solvent free conditions.
After optimizing the conditions, the scope of method was successfully studied by using a various
aromatic aldehydes (including aldehydes with electron-releasing substituents, electron-withdrawing
substituents and halogens on the aromatic ring) and cyclic 1,3-diketone compounds. The results
aresummarized in Table 4.
Table 4. Synthesis of 1,8-dioxo-octahydroxanthene derivatives by n-WSAa.
Time
(h)
1.05
0.85
0.9
Yieldb
(%)
90
94
92
Melting point (◦C)
Entry
Ar
R1
R2
Product
Found
Reported
1
2
3
4
5
-C6H5
4-O2N-C6H4
4-Br-C6H4
4-H3C-C6H4
4-H3CO-C6H4
H
H
H
H
H
H
H
H
H
H
3a
3b
3c
3d
3e
213-215
234-236
222-225
244-246
190-191
[28]
[28]
-
-
1.05
1.1
89
88
190-192[29]
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6
7
8
9
-C6H5
2-O2N-C6H4
3-O2N-C6H4
4-O2N-C6H4
4-F-C6H4
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
5a
5b
5c
5d
1.1
0.85
0.8
0.8
0.9
1
1
1.2
1.25
1.3
1.25
1.05
1.3
1.25
1.2
1.25
1.25
1.05
92
90
93
94
92
93
91
89
89
90
87
92
86
85
91
90
90
93
203-204
244-245
168-169
222-224
206-207
237-239
264-267
230-232
212-214
242-244
246-247
234
268-271
256-258
196-198
204-208
212-215
234-236
205-206 [30]
246-248 [31]
167-168 [30]
221-223 [30]
208-209 [31]
236-237 [32]
263-265 [33]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
4-Cl-C6H4
4-Br-C6H4
2-H3C-C6H4
4-H3C-C6H4
4-H3CO-C6H4
4-HO-C6H4
2-Naphtaldehyde
2-OH-5-BrC6H3
C6H5-CH=CH-
-C6H5
-
216-217 [33]
241-243 [33]
246-248 [31]
234-235 [34]
-
-
-
-
-
-
H
H
H
H
Ph
Ph
Ph
Ph
4-H3C-C6H4
4-H3CO-C6H4
4-Cl-C6H4
aReaction conditions: aromatic aldehyde (1 mmol), cyclic-diketone (2mmol), n-WSA (0.019 g)under solvent-free at 100
oC.
bIsolated yield.
The present method not only affords the products in excellent yields but also avoids the problems
associated with catalyst cost, handing, safety and pollution.
As indicated in Table 4, the reaction works easily for a vast variety of aromatic aldehydes with both
electron-donating and electron-withdrawing groups and different cyclic diketone to give corresponding 1,8-
dioxo-octahydroxanthene derivatives in good to excellent yields. In almost all cases, the reactions proceeded
smoothly within 50-80 min. However, it is notable that substituted aromatic aldehydes with electron-
withdrawing groups increase the rate of reaction (Table 2 entries 2, 3, 7-12 and 23) probably by activating
the carbonyl group as electrophile center. Contrarily in the case of electron-donating groups, the reaction was
more slowly (Table 2, entries 3, 5, 13-19, 21 and 22).
A plausible mechanism for the synthesis of 1,8-dioxo-octahydroxanthenesin presence of n-WSA as
catalystis shown in Fig. 8.
17
Page 17 of 29

O
R2
O
O
S
O
O
H
S
O
R1
O
O
OH
H
O
O
R3
R3
R2
OH
H
R1
-H2O
O
O
R1
H
O
O
O
O
OH
R2
R3
H
O
S
R1
(III)
R2
R1
R2
(IV)
(II)
O
O
O
R1
R2
(I)
R3
R3
R3
O
O
O
O
O
O
O
S
-H2O
-H2
R1
R1
R1
R1
H
OH
R1
R1
H
O
O
O
H
R2 OH
R2
O
R2
R2
H
(VI)
R2
OH R2
O
O
(V)
S
(VII)
O
= nano-WO3
Fig. 8.Possible mechanism for the synthesis of 1,8-dioxo-octahydroxanthene derivatives in presence of n-WSA as
catalyst.
In the proposed mechanism, initially, the carbonyl group of aromatic aldehyde is activated by SO3H
groups of nano-WO3-SO3H to give intermediateII. Then, 1,3-cyclic diketone attacksthe activated aldehyde
and affords intermediate III. Following, by removing H2O from intermediate III, the IV as a Mickel acceptor
is prepared. One more time, the SO3H group of nano-WO3-SO3H activates intermediate IV. Then, Michael
addition of dimedone with intermediate IV gives V. Intermediate V changes to VI after ring closing reaction
and removing catalyst. Finally by removing H2O from compound VI, final 1,8-dioxo-octahydroxanthene
derivativesVIIis produced. The proposed mechanism illustrate clearelythe catalytic role of nano-WO3SO3H.
As indicated in the Figure 8, the SO3H groups play important role in the catalytic activity of nano-WO3-
SO3H.
18
Page 18 of 29

Reusability of the catalyst was checked by recovered n-WSA and reused for eight consecutive reactions
and obtained the yield 90-93%. This indicates that as -SO3H groups has fixed on the surface of nano-WO3, it
does not lose its activity and could be recycled 10 times(Fig. 9).Further, pH analysis of the recovered catalyst
showed loading of 3.35 mmol H+/g. This result suggests that the nature of the catalyst remains intact after
each run and leaching of the acid species did not occur during the course of the reaction.
Fig. 9. Reusability of n-WSA for the synthesis of 1,8-dioxo-octahydroxanthenes, Reaction conditions:para-
chlorobenzaldehyde (1 mmol), dimedone (2mmol), reaction time: 1 h at 100 ºC in solvent free condition.
Various methods have been reported for the synthesis of 1,8-dioxo-octahydroxanthenes, including,
condensation of aromatic aldehydes and 1,3-cyclic diketones in presence of different catalysts. A comparison
between the result of the proposed catalyst and some of the recently used catalysts for synthesis of
octahydroxanthene derivatives is summarized in Table 5.
Table 5.Comparison of the characteristic of new synthesized catalyst with some reported catalysts.
Entry
Amount of Catalyst
Time (h)
Yield
(%)
Trace
Trace
95
90
95
91
87
88
78
92
94
Catalyst
Condition
Solvent
1
2
3
4
5
6
7
8
9
Nano-ZnO
Nano-NiO
10 mol%
10 mol%
10 mol%
0.1 g
0.2 g
0.1 g
0.2 g
0.1 g
0.4 g
0.2 g
2
2
2.5
6.5
1
100 ºC
100 ºC
70
Reflux
Ultrasonic
80 ºC
80 ºC
80 ºC
100 ºC
Reflux
100 ºC
100 ºC
-
-
[CMIM][HSO4] [35]
NaHSO4.SiO2[36]
MCM-41-SO3H [32]
[Hmim]TFA [37]
[cmmim][BF4] [38]
CAN/HY-Zeolite [39]
Dowex-50W [40]
Amberlyst-15 [41]
Fe+3-montmorillonite [42]
Proposed catalyst
H2O
CH3CN
H2O
-
3
2.5
1.5
1.5
5
6
1
-
-
-
10
11
12
CH3CN
Et-OH
-
0.05 g
0.019 g
93
19
Page 19 of 29

Although, some of these methods have convenient protocols with good to high yields, the majority of
these methods suffer at least from one of the following disadvantages such as the use of toxic organic
solvents, excess reagents, long reaction time and harsh reaction conditions. Table 5 shows that the
heterogeneous solid acid catalyst of nano-WO3-SO3H is the best in comparison to the other mentioned
catalysts. The proposed new catalyst has some advantages in comparison with the other catalyst including
shorter reaction time, easy separation, low consumption of organic solvents, reusability and ability to
perform reactions in solvent free conditions. It is a stable solid acid catalyst with high densities of sulfuric
acid groups that can be easily synthesized in the laboratory and can be reused for several times.
3.2.2. Synthesis of tetrahydrobenzoxanthene derivatives
As Xanthenes and compounds based on these core templates are important heterocycles that are known to
possess multiple biological, pharmaceutical and other activities [43, 44],it was decided to develope the
catalytic activity of n-WSA by investigating their synthesis. For this purpose,tetrahydrobenzoxanthene was
synthesized by condensation between benzaldehyde (1) (1 mmol), dimedone (2) (1 mmol) and β-naphtole (6)
(1 mmol) under solvent free condition as a model reaction (Scheme 3).
Ar
O
O
O
OH
n-WSA (0.019 g)
ArCHO
1
R1
Solvent Free, 100 °C
R1
R2
O
R2
1
2
6
2a:
2b:
2c:
R = R = H
7, 8, 9
1
2
R = R = Me
1
2
R = H, R = Ph
Scheme 3. Synthesis of tetrahydrobenzoxanthene derivatives.
In table 6, the activity of n-WSA is compared with the nano-WO3 and other catalyst.
Table 6. Comparison of nano-WO3-SO3H with some reported catalysts.
Amount of
Catalyst
-
0.019 g
0.019 g
10 mol%
10 mol%
7 mol%
5 mol%
Time
(min)
90
85
85
85
85
50
120
Yield
(%)
15
31
91
Trace
Trace
89
Entry
Catalyst
Condition
Solvent
1
2
3
4
5
6
7
-
100 ºC
100 ºC
100 ºC
100 ºC
100 ºC
110 ºC
50 ºC
-
-
-
-
-
-
Nano-WO3
Nano-WO3-SO3H
Nano-ZnO
Nano-NiO
Trityl Chloride [45]
CeCl3.7H2O-NaI [46]
CH3OH
93
20
Page 20 of 29

8
9
NH2SO3H [47]
H14[NaP5W30O110][48]
TCT [49]
InCl3[50]
P2O5[50]
HClO4-SiO2[51]
Sr(OTf)2[52]
pTSA/[bmim]BF4[53]
20 mol%
0.4 mol%
5 mol%
30 mol%
20 mol%
0.1 g
120 ºC
120 ºC
80 ºC
120 ºC
120 ºC
80 ºC
150
120
60
30
40
60
300
180
-
-
-
-
-
-
85
88
92
84
76
95
85
90
10
11
12
13
14
15
10 mol%
10 mol%
80 ºC
80 ºC
ClCH2CH2Cl
-
The obtained results showed that the n-WSA (91%,yield) was a more suitable option rather than the nano-
WO3 (31%, yield).In comparison with the other mentioned catalysts, the presence new catalyst has some
advantages including shorter reaction time, easy preparation and separation, low consumption of organic
solvents, lower temperature of reaction and amount of catalyst, reusability and ability to perform reactions in
solvent free conditions and high yield of products. It is a useful solid acid nanocatalyst with high densities of
sulfuric acid groups that can be easily prepareded.
To examine the limitation and the scope of the reaction, the synthesis of different
tetrahydrobenzoxanthene derivatives heve been investigated. The obtained results are summarizedin Table 7.
Table 7. Synthesis of tetrahydrobenzoxanthene derivatives by n-WSAa.
Time
(min)
90
95
100
88
85
85
85
80
80
80
85
80
80
75
75
80
80
80
85
90
90
80
85
80
Yieldb
(%)
90
88
89
90
91
92
91
94
94
87
91
92
92
93
94
93
92
92
88
86
85
83
88
90
90
Melting point (◦C)
Entry
Ar
R1
R2
Product
Found
Reported
190-192 192-193 [54]
205-207 206-207 [54]
182-184 181-182 [54]
244-246 243-245 [54]
207-209 208-209 [54]
208-210 209-211 [54]
212-214 214-215 [54]
235-236 234-235 [54]
237-238 236-237 [54]
1
2
3
4
5
6
7
8
-C6H5
4-H3C-C6H4
4-H3CO-C6H4
2-Cl-C6H4
4-Cl-C6H4
4-F-C6H4
4-Br-C6H4
3-O2N-C6H4
4-O2N-C6H4
2-Naphtyl
-C6H5
2-Cl-C6H4
2-O2N-C6H4
3-O2N-C6H4
4-O2N-C6H4
4-F-C6H4
4-Cl-C6H4
4-Br-C6H4
4-H3C-C6H4
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
7a
7b
7c
7d
7e
7f
7g
7h
7i
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
H
H
7j
190-191
-
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
Ph
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
9a
9b
9c
148-150 151-153 [55]
178-180 179-180 [55]
222-224
223-225[55]
169-171 168-170 [55]
177-179 178-180 [55]
182-184 184-185 [56]
180-181 180-182 [55]
186-188 186-187 [57]
177-178 176-188 [55]
4-H3CO-C6H4 CH3
202-204
222-225
204-205[55]
223-225[55]
4-HO-C6H4
2-Naphtyl
-C6H5
4-F-C6H4
4-Cl-C6H4
CH3
CH3
H
H
H
228-230 228-230 [56]
118-124
181-183
234-235
-
-
-
Ph
Ph
80
21
Page 21 of 29

26
27
28
4- O2N-C6H4
4-H3C-C6H4
4-H3CO-C6H4
H
H
H
Ph
Ph
Ph
9d
9e
9f
75
85
85
92
85
83
183-186
198-200
191-192
-
-
-
aReaction conditions: 1 (1 mmol), 2 (1mmol), 6 (1 mmol) and n-WSA (0.019 g) in solvent-free at 100 oC.
bIsolated yield.
As indicated in Table 7, the new conditions are very suitable for a vast varity of tetrahydrobenzoxanthene
derivatives.
A plossible mechanism for thesynthesis of tetrahydrobenzoxanthenes is shown in Fig. 10.
O
O
S
O
S
O
O
H
S
O
H
O
O
O
O
H
O
R3
OH
OH
H
H
R2
O
OH
O
R1
R3
O
R3
(II)
(III)
(I)
(IV)
R2
O
R1
(V)
R3
R3
R3
O
O
O
O
S
R1
-H2O
OH
R1
R1
H
O
H
O
OH
R2
O
O
R2
OH R2
(VII)
O
O
S
O
(VI)
(VIII)
= nano-WO3
Fig. 10. Proposed mechanism for the synthesis of tetrahydrobenzoxanthenes in presence n-WSA.
In the possible mechanism (Fig. 10), initially, activated carbonyl group of aromatic aldehyde (II) is
attacked by B naphtol (i) to afford intermediate III.Dehydration of III, provides chalkonIV as a Mickel
acceptor. The intermediate IV is activated by SO3H groups of nano-WO3-SO3H. Then, Michael addition of
dimedone (V) with intermediate IV gives intermediateVI which could be changed to VII after ring closing
reaction and removing catalyst. Finally by removing H2O from VII, product VIII is produced. The proposed
mechanism illustrate the catalytic role of nano-WO3SO3H. As indicated in the Figure 9, the SO3H groups of
nano-WO3-SO3H plays principal role in the catalytic activity of nano-WO3-SO3H.
22
Page 22 of 29

The recyclability of the catalyst was tested with five consecutive synthesis of tetrahydrobenzoxanthene by
using recovered n-WSA and desired product obtained in 89-91% yield(Fig.11).
Fig. 11. Reusability of n-WSA for the synthesis of tetrahydrobenzoxanthenes, Reaction conditions:benzaldehyde (1
mmol), dimedone (1 mmol), β-naphtole (1 mmol), reaction time: 85 min at 100 ºC in solvent free condition.
3.2.3. Synthesis of benzoimidazoloquinazolinone derivatives
As benzoimidazoloquinazolinones are important because of their wide range of biological activities,
application in medicinal chemistry, agrochemicals and pharmaceutical industry as herbicides and active
pharmaceuticals[58-60] and to explore the efficiency of n-WSA, it wastested it for their synthesis by
condensation between benzaldehyde (1) (1 mmol), dimedone (2) (1 mmol) and 2-amino benzimidazole (10)
(1 mmol) under solvent free condition as a model reaction (Scheme 4).
Ar
O
O
O
N
N
n-WSA (0.019 g)
R2
NH2
Ar-CHO
1
N
Solvent Free, 100 °C
N
H
N
H
R1
R2
R1
1
2
10
11, 12, 13
2a:
2b:
2c:
R = R = H
1
2
R = R = Me
1
2
R = H, R = Ph
Scheme 4. Synthesis of 3,3-dimethyl-12-phenyl-3,4,5,12-tetrahydrobenzo[4,5]imidazo[2,1-b]quinazolin-1(2H)-one
derivatives.
One more time the activity of n-WSA was compared with the nano-WO3and some other catalyst (Table
8).
23
Page 23 of 29

Table 8. Comparison of nano-WO3-SO3H with some reported catalysts.
Time
(min)
15
15
15
15
15
360
10
Yield
(%)
12
34
94
Trace
Trace
64
Entry
Catalyst
Condition
Solvent
1
2
3
4
5
6
7
-
Nano-WO3
Nano-WO3-SO3H
Nano-ZnO
Nano-NiO
- [61]
100 ºC
100 ºC
100 ºC
100 ºC
100 ºC
-
-
-
-
-
Reflux
Reflux
DMF
CH3CN
I2[62]
84.6
Microwave
120 ºC-100 psi
8
Silica gel [63]
3
-
95
9
SBA-Pr-SO3H [64]
H6P2W18O62[65]
NH2SO3H [66]
Ionic Liquid [67]
- [68, 69]
10
15
20
360
5
-
90
91
90
84
58
89
10
11
12
13
14
Reflux
Reflux
Heating
Reflux
CH3CN
CH3CN
-
DMF
DMF
- [61]
Microwave
5
The obtained results showed that the n-WSA (94%, yield) works better than the nano-WO3 (34%,
yield).One more time, our new catalyst has some advantages in comparison with the other catalyst such as
easy preparationand separation, low consumption of organic solvents, recoverability and reusability,
operational simplicity and solvent free conditions.
To examine the limitation and the scope of the reaction, the synthesis of benzoimidazoloquinazolin
derivatives have been investigated. The obtained results are summarized in Table 9.
Table 9. Synthesis of benzoimidazoloquinazolinderivatives by n-WSAa.
Melting point (◦C)
Entry
Ar
R1
R2 Product Time (min) Yieldb (%)
Found
318-319
Reported
>300[62]
1
2
3
4
5
6
7
8
9
-C6H5
4-H3C-C6H4
4-H3CO-C6H4 CH3 CH3
4-O2N-C6H4
4-F-C6H4
4-Cl-C6H4
4-Br-C6H4
4-HO-C6H4
-C6H5
CH3 CH3
CH3 CH3
11a
11b
11c
11d
11e
11f
11g
11h
12
15
18
20
12
12
14
14
16
15
15
94
92
90
95
94
95
95
91
92
93
328-330 330-332 [61]
317-318 318-320[61]
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
334-336
324-326
337-339
312-314
>300 [62]
-
340 [61]
>300 [62]
332-334 330-332 [64]
H
H
H
Ph
312-313
335-336
-
-
10
-C6H5
13
aReaction conditions: 1 (1 mmol), 2 (1mmol), 2-amino benzimidazole (1 mmol), n-WSA (0.019 g)under solvent-free
conditions at 100 oC.
bIsolated yield.
As showed in Table 8, fortunately the new catalyst also works very well for a vast varity of
benzoimidazoloquinazolin derivatives.
A proposed mechanism for the synthesis of benzoimidazoloquinazolins is shown in Fig. 12.
24
Page 24 of 29

O
S
O
R3
O
S
O
O
O
OH
H
O
H
H
O
O
HN
O
O
HO
O
H
R2
R1
N
H2N
R3
(III)
R1
R2
R1
R2
(IV)
(II)
(I)
R3
O
O
R3
S
O
R3
H
O
HO
R1
H
O
O
O
HN
HO
OH R2
N
S
OH
N
-H2O
-H2O
R1
N
R1
O
HN
N
N
H
R2
N
R2
N
H
H
(VII)
(VI)
(V)
= nano-WO3
Fig. 12. Proposed Mechanism for the synthesis of benzoimidazoloquinazolins by n-WSA.
The reusability of the catalyst was tested with five consecutive synthesis of benzoimidazoloquinazolin by
using recovered n-WSA and desired product obtained in 91-94% yield(Fig.13).
Fig.13.Reusability of n-WSA for the synthesis of benzimidazoloquinozoline,Reaction conditions: benzaldehyde (1
mmol), dimedone (1mmol), 2-amino benzimidazole (1 mmol),reaction time: 15 min at 100 ºC in solvent free condition.
25
Page 25 of 29

4. Conclusion
In summary, for the first timenano-WO3-supported sulfonic acid was introduced as a new heterogeneous
solid acid nano catalyst. This new catalyst has been efficiently used for the synthesis of 1,8-dioxo-
octahydroxanthenes, tetrahydrobenzoxanthene and benzoimidazoloquinazolinin multi component
reactionsunder solvent-free conditions. Allthe reactions works easily for a variety of aldehydes with both
electron-donating and electron-withdrawing groups to give corresponding products in excellent yields. The
catalyst was reused for 10 consecutive cycles with consistent activity. The excellent catalytic performance,
easy preparation and separation of the catalyst make it a good heterogeneous solid acid nano catalyst for
organic synthesis and transformations.
Acknowledgements
We gratefully acknowledge the department of chemistry of Semnan University for supporting this work.
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