Nano-sawdust-OSO3H as a new, cheap and effective nanocatalyst for one-pot synthesis of pyrano[2,3-d]pyrimidines

Article abstract of DOI:10.1007/s13738-015-0655-3

An atom-efficient, three-component synthetic methodology has been developed for the preparation of biologically important pyrano[2,3-d]pyrimidines using nano-sawdust-OSO₃H as a new catalyst. The reaction involves the use of barbituric acid or t

Full text of DOI:10.1007/s13738-015-0655-3

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0655-3
ORIGINAL PAPER
Nano‑sawdust‑OSO3H as a new, cheap and effective nanocatalyst
for one‑pot synthesis of pyrano[2,3‑d]pyrimidines
B. Sadeghi1 · M. Bouslik1 · M. R. Shishehbore1
Received: 22 November 2014 / Accepted: 29 April 2015
© Iranian Chemical Society 2015
Abstract An atom-efficient, three-component synthetic
methodology has been developed for the preparation of
biologically important pyrano[2,3-d]pyrimidines using
nano-sawdust-OSO3H as a new catalyst. The reaction
involves the use of barbituric acid or thiobarbituric acid,
malononitrile and aldehydes. A wide range of aldehydes
is compatible in this reaction, producing excellent yields
in short time. The morphology of nanocatalyst (nano-
sawdust-OSO3H) was observed using a scanning electron
microscopy (SEM). The decomposition steps and thermal
stability of the catalyst were investigated by thermal anal-
ysis techniques (TGA/DTG). The sawdust-OSO3H sur-
face was studied by energy dispersive X-ray spectroscopy
(EDX) method to find out the chemical composition. Also,
the vibrational spectrum analysis (FT-IR) of the catalyst
has been performed.
libraries for drug discovery [1]. Pyrano[2,3-d]pyrimidines
are some examples of multi-component reactions. Pyrimi-
dine derivatives are attractive, because they generally show
biological properties such as antibacterial, antitumor and
analgesic activities [2–4].
In recent years, there has been growing interest in find-
ing inexpensive and effective solid acid nanocatalyst such
as nanocrystalline TiO2-HClO4 [5], nano-TiCl4∙SiO2 [6–9]
nano-SnCl4∙SiO2 [10, 11] nano-BF3∙SiO2 [12–15] HClO4-
SiO2 nanoparticles [16] and nano silica sulfuric acid [17–
23]. Sawdust is one of the most common materials that
used for various chemical industries such as removing
pollutants from water [24], the color removal from textile
industry [25], the removing cationic, anionic and disperse
dyes from aqueous solution [26] and the CuFe2O4/sawdust
composite was used for removal of cyanine acid blue from
aqueous solution [27].
Keywords Pyranopyrimidines ∙ Thiobarbituric acid ∙
Malononitrile ∙ Green chemistry ∙ Nano-sawdust-OSO3H
The sawdust consists of cellulose, lignin and hemicel-
luloses that cellulose is composed of a long chain of glu-
cose molecules, lignin is a complex polymer composed
of phenylpropane units, and hemicelluloses are branched
polymers composed of xylose, arabinose, galactose, man-
nose, and glucose [28–31]. The lignocellulosic material of
sawdust includes a wide variety of hydroxyl groups that
can be used as active sites for the preparation of solid acid
catalysts.
In this study, the sawdust has been used as adsorbent
for the preparation of nano-sawdust-OSO3H whose aver-
age size is small and is well distributed. The presence of
new functional groups on the surface of sawdust–OSO3H
resulted in a dramatic increase of surface polarity and
acidity, thereby improving the catalytic efficiency of the
nano-sawdust-OSO3H.
Introduction
Recently, multi-component, one-pot synthesis have become
one of the most attractive reactions due to their vast appli-
cations such as high selectivity, mild reaction condition and
construction of several bonds in a single operation. These
reactions are widely applied in pharmaceutical chemis-
try for producing different structures and combinatorial
* B. Sadeghi
sadeghi@iauyazd.ac.ir
1
Recently some conditions and catalysts such as micro-
wave irradiation [32], ionic liquids [33], ultrasonic
Department of Chemistry, Yazd Branch, Islamic Azad
University, P.O. Box 89195-155, Yazd, Iran
1 3

J IRAN CHEM SOC
irradiation [34], diammonium hydrogen phosphate [35],
l-proline [36], H14[NaP5W30O110] [37], sulfonic acid nanop-
orous silica (SBA-Pr-SO3H) [38] and choline chloride∙ZnCl2
[39] have been applied for the pyrano[2,3-d]pyrimidine syn-
thesis. Although many of the reported methods are effective,
but, some of them suffer from disadvantages such as harsh
reaction conditions, use of hazardous solvents, long reaction
times, complex working and purification procedures, long
volume of catalyst loading and moderate yields. Therefore,
the development of a simple, mild and efficient method is
still needed. In continuation of our previous research on the
use of solid acids in organic synthesis [14–21], the nano-
sawdust-OSO3H as a new catalyst has been applied for the
synthesis of pyrano[2,3-d]pyrimidine derivatives.
analysis was performed using a TG 209 F1 (Netzsch Ger-
many). The IR spectrum of the catalyst was recorded using
a model Bruker Tensor 27 FT-IR operating in the range
400–4000 cm−1.The EDX analysis was done using a SAMx
analyser. The chemicals for this work were purchased from
Fluka and were used without further purification.
Synthesis of nano‑sawdust‑OSO3H
The sawdust was collected from sawmill in Farrokhi city,
Iran. Sawdust was washed several times to remove adhering
dirt and then dried at 60 °C for 24 h. The dried sawdust was
ground to pass through a 1 mm sieve and labeled as saw-
dust [27]. The nano-sawdust-OSO3H was prepared by com-
bination of chlorosulfonic acid (2.33 g) drop by drop over
10 min via a syringe to sawdust powder (6 g) in a 50 ml
flask at 0 °C. The reaction mixture was then stirred and then
after 30 min, the ashy powder was separated and washed
with diethyl ether. The obtained solid was dried in an oven
at 60 °C for 4 h and then pulverized at the mortar. The size
of particles was obtained below 100 nm using SEM.
Experimental
Melting points were determined with an Electrothermal 9100
apparatus. IR spectra were recorded on a Shimadzu IR-470
1
spectrometer. H NMR spectra were obtained using Bruker
Avance 300. The morphologies of the nanoparticles were
observed using FESEM of a MIRA3 TESCAN microscope
with an accelerating voltage of 15 kV. Thermogravimetric
General procedure for the preparation of compounds
4a‑l
Nano-sawdust-OSO3H (0.02 g) was added to a stirred
mixture of the aromatic aldehyde (1 mmol), malononi-
trile (1 mmol) and barbituric acid or thiobarbituric acid
(1 mmol) in EtOH (5 mL). The materials were mixed and
refluxed for the appropriate time. The progress of the reac-
tion was followed by TLC (n-hexane:ethyl acetate 3:1).
After completion of the reaction, the mixture was filtered
to remove the catalyst. After evaporation of the solvent,
the crude product was re-crystallized from hot ethanol to
obtain the pure compound.
Results and discussion
In continuation of our investigation into the application of
solid acids in organic synthesis, we studied the applica-
tion of sawdust as a green, inexpensive and available sur-
face to synthesis of solid acid nanocatalyst. In this study,
Fig. 1 SEM micrograph of sawdust
O
Ar
Scheme 1 Synthesis of
pyrano[2,3-d]pyrimidines
O
CN
derivatives in the presence
of nano-sawdust-OSO3H as
catalyst
O
HN
HN
nano-sawdust-OSO3H
EtOH, Reflux
+
CH2(CN)2 +
Ar
H
X
NH2
N
H
O
O
2
X
N
H
1a-l
X=O, S
4a-l
3a, b
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J IRAN CHEM SOC
sawdust-OSO3H nanoparticles were prepared and character-
ized (Fig 1). The catalytic activity of nanoparticles was inves-
tigated for synthesis of pyrano[2,3-d]pyrimidines derivatives,
by the condensation of a aldehyde 1a‑l, malononitrile 2 and
barbituric acid or thiobarbituric acid (3a,b) (Scheme 1).
The morphology and size of sawdust and sawdust-
OSO3H were observed by SEM images. As shown in
Fig. 2, the size of nano-sawdust-OSO3H is below 100 nm.
The results of EDX analyses of the sawdust and saw-
dust-OSO3H are given in Table 1.
Chemical analysis of sawdust gave carbon and oxygen
as the major elements with small amounts of gold (Fig. 3).
The elemental analysis by EDX identified the high peak
of sulfur and carbon in the nano-sawdust-OSO3H (Fig. 4).
Presence of sulfur in the EDX indicates the chemical inter-
action of chlorosulfonic acid with the surface of sawdust.
Sawdust-OSO3H nanoparticles were prepared according to
procedure as shown in Scheme 2.
Sawdust-OH + ClSO3H → Sawdust-OSO3H + HCl
The thermal decomposition of the sawdust and nano-
sawdust-OSO3H has been studied using a combination of
thermogravimetry (TGA) and derivative thermogravimetry
(DTG) methods up to 800 °C under nitrogen atmosphere.
The structural transformation is observed by TG curves
which are supported by DTG studies. Thermal analysis has
proved to be useful in determining the structure of nano-
sawdust-OSO3H and the thermal stability as well as the
decomposition mode under controlled heating rate. Three
thermal decomposition mass loss steps are observed for
the nano-sawdust-OSO3H (a) 14.02 % mass loss at 142 °C
related to the loss of the moisture, (b) 12.34 % mass loss
at 190 °C related to the further loss of the moisture and (c)
37.45 % mass loss at 440 °C related to the decomposition
of cellulose and lignin (Fig. 5).
Fig. 2 SEM micrograph of nano-sawdust-OSO3H
Figure 6 is the TG and derivative TG (DTG) profiles
showing the thermal degradation characteristics of sawdust
at a heating rate of 30 ml/min. The initial step of degra-
dation at 66 °C corresponds to 4.24 % mass loss, perhaps
due to the removal of moisture. The second step of decom-
position in DTG curve shows mass losses at 343 °C and
61.11 % perhaps due to the degradation hemicellulose
units. This degradation indicates that the hemicellulose
Table 1 Chemical analysis of sawdust and sawdust-OSO3H
Sawdust
Sawdust-OSO3H
Element
W %
A %
W %
A %
C
O
S
56.85
39.89
–
65.35
34.42
–
42.98
45.85
11.17
52.68
42.19
5.13
Fig. 3 EDX of sawdust
C Kα
6000
5000
4000
3000
2000
1000
0
O Kα
AuM β
α
AuM
AuLα
10
AuLl
keV
0
5
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J IRAN CHEM SOC
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
Fig. 4 EDX of nano-sawdust-
OSO3H
α
S K
α
O K
C K
α
β
S K
keV
0
5
10
3428 cm−1. The C–H stretching vibrations of the aliphatic
systems for cellulose and hemicelluloses units observed at
2932 cm−1. The C=C stretching vibrations of the phenyl
rings in the lignin unit observed at 1645 cm−1. The sym-
metric and asymmetric O=S=O stretching vibrations
appeared at 1066 and 1232 cm−1. The S–O stretching
Sawdust-OH + ClSO3H → Sawdust-OSO3H + HCl
Scheme 2 Preparation of nano-sawdust-OSO3H
units reacted with the chlorosulfonic acid in the nano-
sawdust-OSO3H. The major mass loss of nearly 82 % is
due to the devolatilization of the hemicelluloses, cellulose
and lignin as shown in Fig. 6. The mass loss of 19.38 % at
the third step associated with TDTG peak at 443 °C corre-
sponds to the mass loss of the decomposition of cellulose.
The lignin degradation is observed as a shoulder of the final
peak at 495 °C.
vibrations observed at 850 cm−1
.
In order to determine the optimum quantity of nano-
sawdust-OSO3H, the reaction of barbituric acid, malononi-
trile and benzaldehyde was carried out under reflux in etha-
nol using different quantities of nano-sawdust-OSO3H. As
shown in Table 2, 0.02 g of nano-sawdust-OSO3H gives an
excellent yield in 15 min.
Also, the acid capacity of nano-sawdust-OSO3H as a cri-
terion of H+ sites was determined using acid–base titration.
The value of 0.78 was obtained.
In FT-IR spectrum of nano-sawdust-OSO3H (Fig. 7), the
hydroxyl bands of sawdust and sulfonic acid appeared at
To study the scope of the reaction, a series of aldehydes
with barbituric acid or thiobarbituric acid and malon-
onitrile were examined by nano-sawdust-OSO3H as cat-
alyst. The results are shown in Table 3. In all cases, aro-
matic aldehyde substituted with either electron-donating
Fig. 5 The TGA/DTG curves
of nano-sawdust-OSO3H
samples
1 3

J IRAN CHEM SOC
Fig. 6 The TGA/DTG curves
of sawdust samples
Fig. 7 FT-IR spectrum of nano-
sawdust-OSO3H
Table 2 Optimization of the
reaction conditions for synthesis
of 4a
Entry
Catalyst (amount)
Solvent/condition
Time (min)
Yield
1
2
3
4
5
6
7
8
Nano-Sawdust-OSO3H (0.02 g) CH2Cl2/reflux
Nano-Sawdust-OSO3H (0.02 g) EtOH/reflux
Nano-Sawdust-OSO3H (0.02 g) CH3CN/reflux
Nano-Sawdust-OSO3H (0.02 g) DMF/reflux
Nano-Sawdust-OSO3H (0.02 g) H2O/reflux
Nano-Sawdust-OSO3H (0.01 g) EtOH/reflux
Nano-Sawdust-OSO3H (0.03 g) EtOH/reflux
15
15
15
15
15
15
15
15
Trace
94
Trace
47
83
73
95
Nano-Sawdust-OSO3H (0.02 g) EtOH/reflux
2nd run
92
9
Nano-Sawdust-OSO3H (0.02 g) EtOH/reflux
3rd run
15
87
1 3

J IRAN CHEM SOC
M.P. (°C) Ref.b
Table 3 Synthesis of
pyrano[2,3-d]pyrimidines
Entry
Ar
X
Product
Time (min)
Yielda
1
C6H5
O
O
O
O
O
O
O
O
S
4a
4b
4c
4d
4e
4f
15
8
94
91
86
87
93
92
85
87
83
72
69
75
206–208 (208–210) [32]
232–234 (231–232) [39]
225–227 (226–227) [38]
212–214 (213–215) [32]
259–261 (262–263) [34]
230–232 (237–238) [34]
228–230 (230–231) [35]
272–274 (279–280) [39]
120–122 (116–118) [39]
230–232 (230–233) [39]
236–237 (234–237) [39]
236–238 (232–235) [39]
2
4-ClC6H4
3
4-CH3C6H4
2-ClC6H4
10
20
8
4
5
3-NO2C6H4
4-NO2C6H4
4-BrC6H4
6
10
12
12
22
20
25
20
7
4g
4h
4i
8
4-CH3OC6H4
4-CH3OC6H4
3-NO2C6H4
3-ClC6H4
9
10
11
12
S
4j
S
4k
4l
4-NO2C6H4
S
Ratio of aldehyde (mmol): barbituric acid or thiobarbituric acid (mmol): malononitrile (mmol): catalyst (g)
is 1:1:1:0.02
a
Isolated yield
b
All products are known and were identified by their melting points, IR and 1H NMR spectra
H
Scheme 3 Plausible mecha-
nism for the formation of
pyrano[2,3-d]pyrimidine
derivative
:
:
O
O
CN
CN
CN
CN
nano-sawdust-OSO3H
Ar
CH
C
Ar-CH
Ar-CH
+
-H2O
1
5
2
nano-sawdust-OSO3
Ar
O
O
O
H
CN
HN
HN
5
HN
C
N
Micheal addition
OH
X
N
H
O
X
O
N
H
X
N
H
6
3
Cyclization
Ar
Ar
O
O
O
H
CN
CN
HN
HN
Tautomerism
X
X
NH2
N
H
NH
N
H
O
4
7
solid acid catalyst. The subsequent step was Knoevenagel
condensation between the activated aldehyde and malononi-
trile 2 to form intermediate 5. Then the Michael addition of
barbituric acid or thiobarbituric acid (3a,b) to intermediate
5 would furnish intermediate 6. Finally, the product 4 was
obtained by an intramolecular cyclization and tautomerism.
or electron-withdrawing groups underwent the reaction
smoothly and formed products in approving yields.
With the above-mentioned results in hand, a plausible
mechanism of this reaction was proposed in Scheme 3.
The initiation step of this chain process was begun with the
interaction of aldehyde 1 and nano-sawdust-OSO3H as a
1 3

J IRAN CHEM SOC
Table 4 Comparison of
nano-sawdust-OSO
3H and
Entry
Catalyst
Solvent
Condition
Time
Yield
Ref.
various catalyst in the synthesis
of pyrano[2,3-d]pyrimidine
derivatives
1
2
3
4
5
6
7
8
9
–
H2O
MW
90 °C
US
3–5 min
3–5 h
86–94
82–95
62–78
71–81
68–88
85–90
30–90
42–98
69–94
[32]
[BMIm]BF4
–
DAHPa
[BMIm]BF4
H2O
[33]
1–3 h
[34]
EtOH
EtOH
EtOH
–
r.t
2 h
[35]
l-proline
r.t
30–150 min
30–60 min
5–45 min
30–240 s
8–25 min
[36]
H14[NaP5W30O110
]
Reflux
140 °C
US
[37]
SBA-Pr-SO3H
[38]
Choline chloride∙ZnCl2
Nano-sawdust-OSO3H
EtOH
EtOH
[39]
Reflux
This work
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in literature [32–39]. As shown in Table 4, synthesis of
these compounds catalyzed by nano-sawdust-OSO3H in
EtOH offers production of the corresponding products in
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The present investigation shows that nano-sawdust-OSO3H
a capable nanocatalyst to be used for pyrano[2,3-d]pyrimi-
dine synthesis via one-pot reaction of aldehydes, malononi-
trile and barbituric acid or thiobarbituric acid. Nano-saw-
dust-OSO3H was successfully prepared and characterized
using TGA/DTG, EDX, FT-IR and SEM. Prominent among
the advantages of this method are such as shorter reaction
times, simple work-up, affords excellent yield, and re-usa-
ble for a number of times without appreciable loss of activ-
ity. The present method does not involve any hazardous
organic solvent. Therefore, this procedure could be classi-
fied as green chemistry.
Acknowledgments The research Council of the Islamic Azad Uni-
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for this work.
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