Novel silica sodium carbonate (SSC): Preparation, characterization and its first catalytic application to the synthesis of new dihydropyrano[2,3-c]pyrazoles

Article abstract of DOI:10.1016/j.catcom.2014.05.029

In this study, a novel and highly efficient catalyst was produced from a reaction between silica chloride and sodium hydrogen carbonate. This novel catalyst was named silica sodium carbonate (SSC), and was characterized by FT-IR, XRD, XRF and TG-DT analys

Full text of DOI:10.1016/j.catcom.2014.05.029

Novel silica sodium carbonate (SSC): Preparation, characterization and its first
catalytic application to the synthesis of new dihydropyrano[2,3-c] pyrazoles
Khalil Eskandari, Bahador Karami, Saeed Khodabakhshi
PII:
DOI:
Reference:
S1566-7367(14)00210-6
doi: 10.1016/j.catcom.2014.05.029
CATCOM 3923
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8 April 2014
30 May 2014
31 May 2014
Please cite this article as: Khalil Eskandari, Bahador Karami, Saeed Khodabakhshi,
Novel silica sodium carbonate (SSC): Preparation, characterization and its first catalytic
application to the synthesis of new dihydropyrano[2,3-c] pyrazoles, Catalysis Communica-
tions (2014), doi: 10.1016/j.catcom.2014.05.029
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ACCEPTED MANUSCRIPT
Novel silica sodium carbonate (SSC): Preparation, characterization and its
first catalytic application to the synthesis of new dihydropyrano[2,3-c]
pyrazoles
Khalil Eskandari*, Bahador Karami*, Saeed Khodabakhshi
Department of Chemistry, P. O. Box 353, Yasouj University, Yasouj, 75918-74831, Iran
*Corresponding author: Tel: +98 7412223048, Fax: +98 7412242167
E-mail addresses: karami@mail.yu.ac.ir, khalileskandari@yahoo.com
Abstract
In this study, a novel and highly efficient catalyst was produced from reaction between silica
chloride and sodium hydrogen carbonate. This novel catalyst was named silica sodium
carbonate (SSC), and was characterized by FT-IR, XRD, XRF, TG-DTA analysis, atomic
absorption and titration with HCl (0.01 N). Furthermore, herein, first application of SSC as a
green, highly efficient and recyclable catalyst to synthesis of new 1,4-dihydropyrano[2,3-
c]pyrazoles is successfully examined. Compared to the classical reactions for the synthesis of
1,4-dihydropyrano[2,3-c]pyrazoles, presented procedure using SSC has some advantages
than others such as obtaining excellent yields of products, short reaction times, green and
safety procedure, easy handling and reusability of catalyst.
Keywords: Silica sodium carbonate; Catalyst; Green; Dihydropyranopyrazole; Aqueous
media
1. Introduction
From perspective of green chemistry, and increasing emphasis on the reduction of
environment pollution, application of clean technologies in chemical synthesis have been
inevitable [1,2]. Also, the handling of clean and safe technologies will require a level of
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innovation and new technologies [3]. Nowadays, catalytic technologies have been found a
great interest for chemists due to catalysts not only have played a vital role in the economic
development of the chemical industries but also have rapidly developed environmental
pollution control [4,5].
Recently, synthesis of supported catalysts as clean materials has attracted significant
attentions [6,7]. Supported catalysts have some advantage such as avoids formation of
inorganic salts, recyclable, non-toxic, easy to handle, safe to store, long life time, easy and
inexpensive removal from reaction mixture by filtration or centrifugation and tolerates a wide
range of temperatures and pressures [6,7]. Therefore, the necessity of using eco-friendly
heterogeneous supported catalysts in organic synthesis being understood [8]. Usually,
charcoals, alumina, silica, or polymers being used as supports for preparation of supported
catalysts which among them silica has many other advantages such as no swelling, good
mechanical stabilities, and ease of scalability. In fact, these heterogeneous catalysts decrease
reactor and plant corrosion problems and are more environmentally safe.
Dihydropyrano[2,3-c]pyrazole was first time synthesized by Junek and Aigner from reaction
between 3-methyl-1-phenylpyrazolin-5-one and tetracyanoethylene [9]. Followed it, Otto and
co-workers reported a base catalyzed two-component Michael type reaction between 4-
arylidiene-1-phenyl-1H-pyrazol-5-one and malononitrile to the synthesis of dihydropyrano
[2,3-c] pyrazoles [10]. Thereafter, several groups reported that weak bases can also be used
for this Michael type cyclization [11,12]. Nowadays, dihydropyrano[2,3-c]pyrazoles are
known as important class of biologically active heterocyclic compounds. They have shown
numerous virtues such as antimicrobial [13], antibacterial [14], antifungal [15], anti-
inflammatory [16], herbicidal agents [17], analgesic [18], and biodegradable agrochemicals
like insecticidal [19]. Also, some substituted pyrano[2,3-c]pyrazoles have been found to be
effective antiplatelet molecules that effect K+ induced calcium dependent aortal contaction
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[20]. Herein we wish to report an efficient novel heterogeneous basic eco-friendly catalyst
which was successfully applied to synthesis of new dihydropyrano[2,3-c]pyrazoles. We
called this novel heterogeneous catalyst silica sodium carbonate (SSC) that was prepared in
an alternative two step route from silica gel (1) using thionyl chloride (2), silica chloride 3
and sodium bicarbonate (4) (Scheme 1).
Scheme 1. Alternative two step preparation of SSC
After SSC was prepared, act as powerful basic catalyst to efficient synthesis of
dihydropyrano[2,3-c]pyrazoles. SSC as a heterogeneous Brønsted base successfully catalyzed
alternative Knoevenagel condensation, Michael addition reaction and intramolecular
cyclization between 3-methyl-1-phenyl-2-pyrazolin-5-one (5), malononitrile (6), and aryl
aldehydes 7 in good to excellent yields (Scheme 2).
Scheme 2. SSC catalyzed green synthesis of dihydropyrano[2,3-c]pyrazoles
2. Experimental
Chemicals were purchased from Aldrich (USA) and Merck (Germany) chemical companies.
X-ray diffraction (XRD) analysis was carried out using a D8 ADVANCE X-ray
diffractometer using Co-Kα radiation (λ = 1.7890 Å) (Bruker, Germany). X-ray Fluorescence
(XRF) spectroscopy was recorded by X-ray fluorescence analyzer, S4 Pioneer (Bruker,
Germany). Thermogravimetric (TG) analysis was carried out with a STA 6000 system
(PerkinElmer, USA). TG analysis was performed with a 9.8 mg sample in alumina pans
under a dynamic argon atmosphere between 30 and 700 °C, and the experiment was run at a
rate of 10 °C/min. Melting points were measured on an elecrtothermal KSB1N apparatus
(Krüss, Germany). IR spectra were obtained using a FT-IR-680 plus spectrometer (JASCO,
1
Japan) at the scanning range of 400-4000 cm–1. H NMR and 13C NMR spectra were
determined on a FT-NMR Bruker Avance Ultra Shield Spectrometer (Bruker, USA) at
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1
13
400.13 MHz (for H NMR) and 100.62 MHz (for C NMR) using DMSO-d6 as the solvent
and TMS as the internal standard. Elemental analyses (C, H, N) were performed with a
Heraeus CHN–O Rapid analyzer (Wellesley, MA, USA). TLC was performed on TLC-Grade
silica gel-G/UV 254 nm plates (Merck, Germany) (eluent: n-hexane/ethyl acetate ϕr = 1:1).
2.1. Preparation of novel SSC
To equipped 250 mL round bottom flask with reflux condenser, which by hoses interface
connected to a pot of water, was added 10 g silica gel 60 (63-200 µm) that was previously
dried at 120 °C for 6 hours. Then 40 mL thionyl chloride was added dropwise to this flask
which perched in an ice bath (CAUTION). After addition of thionyl chloride, reaction
mixture was egressed from ice bath, stirred for 0.5 hour in room temperature and 48 hours
under reflux conditions. Afterwards, reaction mixture was filtrated to obtain silica chloride.
In next step, to a stirred 250 mL round bottom flask under reflux conditions containing 10 g
sodium bicarbonate and 25 mL n-hexane, 10 g of silica chloride (after drying at 120 °C for 6
hours) was added. After 24 h, reaction mixture was filtrate to separation of catalyst and solid
product was washed with distilled water to remove remaining sodium bicarbonate. 50 mL
distilled water in ten times, each time 5 mL was used until filtrate become quite neutral.
Finally, after drying catalyst at 100 °C for 12 h, 14 g SSC was obtained that characterized by
FT-IR and XRD spectroscopy, XRF analysis, TG-DTA analysis, atomic absorption and
titration with HCl (0.01 N).
2.2. General procedure to synthesis of dihydropyrano[2,3-c]pyrazoles
To mixture of 6 mL water and ethanol (1:2) in a round bottom flask, 1.25 mmol (0.082 g)
malononitrine and 1.00 mmol aryl aldehyde were added. Then 0.01 mmol (0.018 g) SSC was
added to this mixture. After stirring reaction mixture for 2 hours at 80 °C, 0.88 mmol (0.153
g) 3-methyl-1-phenyl-2-pyrazolin-5-one was added to reaction mixture. Reaction progress
was controlled by TLC. After 20-40 min reaction was completed. Then, reaction mixture for
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separation of catalyst was filtrated and catalyst was washed with ethanol, dried at 120 for 2 h
and was reused in another reaction. Filtrate poured on a few small pieces ices in a small
beaker to appear product as pure crystals. Then crystalline product was filtrated, collected
1
and characterized by FT-IR, H NMR, 13C NMR, elemental analyses (C, H, N) and via
comparison of their melting points with the reported ones for known compounds.
3. Results and discussion
Considering the importance aspects of green chemistry, performing laboratory procedures to
synthesis of organic compounds in green and eco-friendly conditions, spite of being efficient,
has found significant attentions by chemists. Accordingly, several attempts took place to
preparation and utilization of heterogeneous, safe, effective and eco-friendly catalysts. For
example Nafion-H®, silica sulfuric acid [21] and silica chloride [22] have been made by
researcher groups for several organic reactions. In connection to previous findings about
organic transformation using green heterogeneous catalysts, such as silica supported
zirconium oxychloride (ZrOCl2·8H2O/SiO2), silica tungstic acid (STA), molybdate sulfuric
acid (MSA), and tungstatesulfuric acid (TSA) [23-25], herein we wish to report a novel,
highly efficient and eco-friendly basic catalyst which was successfully applied to synthesis of
new dihydropyrano[2,3-c]pyrazoles. As can be seen in Scheme 1, from the reaction of readily
available materials such as silica gel (1) and thionyl chloride (2), silica chloride 3 has been
prepared [26]. Accordingly, we found that sodium bicarbonate can react with 3 to give silica
sodium carbonate (SSC). It is noteworthy that reaction is clean and easy. From the synthetic
point of view, the nucleophilic substitution at silicon is also attractive. SSC was characterized
by X-ray fluorescence (XRF), X-ray diffraction (XRD), FT-IR spectra, atomic absorption and
titration with HCl (0.01 N). As can be seen from Table 1, XRF data of SSC show the
composition of the catalyst as 68.96 (%W/W) Si (Entry 1) and 12.20 (%W/W) Na (Entry 2).
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Fig. 1 shows the XRD patterns of SSC which exhibits the presence of sodium carbonate
phase supported on amorphous silica as a broad peak around 40° (2θ) (θ is the Bragg's angle).
Also, the broad peaks around 10°, 34°, 36° and 43° (2θ) from the smaller inset could be
attributed to linking of Si to the OCO2Na. The observed peak with the equivalent Bragg's
angle at 2θ = 21.1° is correlated to amorphous silica [27]. Other typical and acute peaks at 2θ
= 26.0, 30.0, 30.6, 35.5, 40.3, and 47.7 corresponded to NaHCO3 reflection (crystal face
indices: 210,–111,111,121,320, and 301) could be clearly detected, which attributed to the
characteristic patterns of NaHCO3 (PDF#15-0700). Furthermore, the peak at 2θ = 34.3 is in
good agreement with the strongest diffraction (110) of Na (JCPDS#22-0948). Therefore, the
appearances of these peaks affirm the connection of −OCOONa in the SSC.
The mixing FT-IR spectra for the anhydrous sodium bicarbonate, silica chloride, and SSC
are shown in Fig. 2. This comparable spectrum shows the characteristic bonds of anhydrous
sodium bicarbonate and silica chloride. Also, the appearance of two distinguished adsorption
bonds at 1640 and 1455 cm−1 in the catalyst spectrum reveals incorporation of sodium
bicarbonate to the silica chloride. To further confirmation of SSC structure, the
thermogravimetric analysis (TG-DTA) of this catalyst was also performed at temperatures
ranging from 30 °C to 700 °C (Fig. 3). This analysis showed four weight losses. The first one
appearing below 100 °C (6.2%) is attributed to the elimination of water and alcoholic
solvents from the solid surface. The second one as the main weight loss (about 16%)
appearing between 100 and 200 °C. From this weight loss, nearby 6% is corresponds to the
endothermic peak of the departure of surface and micropore-absorbed water and silanol
groups hydrogen-bonded to molecular water [28] and the remaining (about 10%) is correlated
to decomposing of –OCOONa and releasing CO2 [29]. From this weight loss the percentage
of carbonates obtained about 10%. The third one appearing between 200 and 500 °C (about
5.3%) is related to removal of organic functional groups located inside the solid network,
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remained micropore-absorbed water and partial hydrogen-bonded silanol groups [28]. Also
the last weight loss between 500 and 680 °C (about 5.1%) is corresponded to dehydroxylation
process [30]. Finally above 680 °C weight percent remain constant and residual mass obtain
67.4%. As can be understood, these data are in good agreement with the results of IR analysis
and confirmed the incorporation of −OCOONa groups into the silica framework.
As well as, the studying of catalyst by atomic absorption spectroscopy, showed the existence
of sodium in catalyst structure that is in accordance with XRF spectroscopy. In continuous,
we evaluated the amounts of sodium bicarbonate supported on SiO2 using two methods,
including (a) titration with 0.01 N HCl (neutralization reaction) and (b) calculating the weight
difference between primary solid acid loosed chloride and new SSC. After these experiments,
we found that 1 g catalyst includes 0.14 g –OCO2Na. Regarding to the molecular weight of
CO3Na (83 g), therefore, 0.006 g of catalyst is equivalent to 0.01 mmol CO3Na.
Table 1. XRF data of SSC
Fig. 1. Powder X-ray diffraction pattern of SSC
Fig. 2. FT-IR spectra for the comparison of SiO2Cl, SSC and NaHCO3
Fig. 3. Thermogravimetric (TG) analysis with mass changes of a) -6.2, b) -16.0, c) -5.3 and d)
-5.1 %, and e) residual mass 67.4% (700 °C) and differential thermal analysis (DTA) of the
SSC.
In regard of the importance of using novel eco-friendly heterogeneous catalyst in organic
synthesis, herein, after characterization of the catalyst, we decided to use the SSC for the
synthesis of some dihydropyrano[2,3-c]pyrazoles. In fact, the wide applicability of some
dihydropyrano[2,3-c]pyrazoles [13-20] attracted the interest of various organic researchers
with the aim of finding improved methods for the synthesis of these compounds. In
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connection with our studies on synthesis of heterocyclic compounds [31-34], we found that
SSC can be used as a powerful, safe and recyclable catalyst for alternative Knoevenagel and
Michael reaction between malononitrile (6), aryl aldehydes 7 and 3-methyl-1-phenyl-2-
pyrazolin-5-one (5) in aqueous media to the synthesis of dihydropyrano[2,3-c]pyrazoles 8 in
good to excellent yields (Scheme 2).
Generally, in this protocol, the SSC has considerable and special features. For example, high
recyclability, being compatible with environment, and a small amount of required catalyst are
some virtues of catalyst.
With an emphasis on aspects of green chemistry, we decide to perform reaction in aqueous
media. For this purpose, the progress of reaction in aqueous media was studied for synthesis
of compound 8e (model reaction) (Table 2). From resulting data of this experiment, the
mixture of EtOH/H2O (2:1) at 80 °C which result to obtain product with highest yield was
opted as optimum conditions for reaction media.
Table 2. Finding the best green solvent for reaction media
In the next step, to enhance reaction efficiency and economic saving, the amount of required
catalyst for the reaction should be optimized. To this end, the model reaction was carried out
in the presence of different amounts of catalyst under obtained above conditions (Table 3).
Considering obtained results from Table 2, 1 mol% of catalyst was chosen as most effective
amount of catalyst for this reaction.
Table 3. Optimization of molar ratio of the catalyst for the model reaction
After finding optimal conditions for the reaction, in order to show the generality of the
method, the reaction was loaded with 3-methyl-1-phenyl-2-pyrazolin-5-one (5), malononitrile
(6) and a wide range of aryl aldehydes 7 in the presence of 1 mol% SSC as basic catalyst and
obtained results were summarized in Table 4.
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Table 4. Synthesis of dihydropyrano[2,3-c]pyrazole derivatives using SSC (1 mol%) at 80 °C
in aqueous media
3.1. Catalyst recyclability
One of the overtaking of this procedure which has achieved interest for chemists and
industrialists is catalyst recyclability, reusability and small amount of required catalyst. SSC
(as heterogeneous catalyst) is able to reuse in further reaction, after previous reaction run, (up
to five times) without remarkable loss of activity (Fig. 4).
Fig. 4. Recyclability results of SSC for model reaction.
We proposed a mechanism for the SSC catalyzed synthesis of dihydropyrano[2,3-c]pyrazoles
(Scheme 3). As can be seen from reaction mechanism, dihydropyrano[2,3-c]pyrazole 8 is
formed through alternative Knoevenagel condensation and Michael addition reaction and
intramolecular cyclization between malononitrile 6, aryl aldehyde 7 and 3-methyl-1-phenyl-
2-pyrazolin-5-one 5 using catalytic amount of SSC which in all steps act as accelerator and
driving force.
Scheme 3. Proposed mechanism for the synthesis of dihydropyrano[2,3-c]pyrazoles by the
use of SSC
4. Conclusion
In conclusion, we found SSC as an effective and environmentally safe heterogeneous
Brønsted base which successfully catalyzed alternative Knoevenagel condensation, Michael
addition reaction and intramolecular cyclization between 3-methyl-1-phenyl-2-pyrazolin-5-
one, malononitrile, and aryl aldehydes in good to excellent yields. Furthermore, SSC can be
used as catalyst, in reactions that needs basic media or basic catalyst. Therefore, believed it
can be found much interest and application in organic syntheses in future. Present protocol
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not only originates the products with excellent yields in short reaction times but also avoids
some problems such as catalyst cost, pollution, handling, and safety. Also, conventional
work-up of products and high recyclability of catalyst are other attractive features of this
procedure.
Acknowledgement
We are thankful to Yasouj University for partial support of this work.
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Table captions in sequence
Table 1. XRF data of SSC
Table 2. Finding the best green solvent for reaction media
Table 3. Optimization of molar ratio of the catalyst for the model reaction
Table 4. Synthesis of dihydropyrano[2,3-c]pyrazole derivatives using SSC (1 mol%) at 80 °C
in aqueous media
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Table 1
Compound
Concentration (%W/W)
Si
Na
Ca
Zn
Cl
S
68.96
12.20
7.08
5.61
2.51
1.58
F
1.12
Al
Mn
Sr
Fe
Mg
Cu
Ti
0.510
0.457
0.139
0.124
0.090
0.062
0.057
Total
100.50
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Table 2
Entry
1
Solvent
H2O
H2O
H2O
EtOH
EtOH
Temp. (°C) Time (min) Yield (%)
r.t.
80
180
120
120
180
120
120
120
120
120
120
60
35
50
50
45
70
45
60
75
70
70
50
70
86
82
80
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Reflux
r.t.
Reflux
r.t.
EtOH/H2O (1:2)
EtOH/H2O (1:2)
EtOH/H2O (1:2)
EtOH/H2O (1:2)
EtOH/H2O (1:2)
EtOH/H2O (2:1)
EtOH/H2O (2:1)
EtOH/H2O (2:1)
EtOH/H2O (2:1)
EtOH/H2O (2:1)
70
80
90
Reflux
r.t.
70
60
80
30
90
60
Reflux
60
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Table 3
Catalyst amount
Entry
Time (min)
Yield (%)
(mol%)
1
2
3
4
5
-
180
25
25
30
30
45
94
88
88
86
1
2
3
4
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Table 4
Time
(min)
Yielda
(%)
Mp (°C),
(lit.)
Entry
Aldehyde
Product
1
25
90
158-159
2
25
88
175-176
3
35
92
167-169
4
35
88
170-171
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171-173
5
25
94
(168-170)b
145-146
6
25
92
(144-146)b
174-175
7
35
88
(170-172)b
176-177
8
35
86
(176-178)b
9
35
88
169-170
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10
35
90
159-160
aIsolated Yield
bReported m.p [35]
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Figure and Scheme captions in sequence
Scheme 1. Alternative two step preparation of SSC
Scheme 2. SSC catalyzed green synthesis of dihydropyrano[2,3-c]pyrazoles
Fig. 1. Powder X-ray diffraction pattern of SSC
Fig. 2. FT-IR spectra for the comparison of SiO2Cl, SSC and NaHCO3
Fig. 3. Thermogravimetric (TG) analysis with mass changes of a) -6.2, b) -16.0, c) -5.3 and d)
-5.1 %, and e) residual mass 67.4% (700 °C) and differential thermal analysis (DTA) of the
SSC.
Fig. 4. Recyclability results of SSC for model reaction.
Scheme 3. Proposed mechanism for the synthesis of dihydropyrano[2,3-c]pyrazoles by the
use of SSC
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Scheme 1
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Scheme 2
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Scheme 3
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Graphical abstract
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ACCEPTED MANUSCRIPT
Highlights
 A novel and highly efficient heterogeneous catalyst is prepared
and introduced.
 Novel prepared catalyst was called SSC.
 SSC was characterized by FT-IR, XRD, XRF analysis, atomic
absorption and titration.
 SSC successfully catalyzed green synthesis of dihydropyrano[2,3-
c]pyrazoles.
 SSC show high catalytic activity and reusability up to fifth times.
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