An efficient one-pot three-component synthesis of 7-amino-2, 4-dioxo-5-aryl-1,3,4,5-tetrahydro-2 H-pyrano[2,3-d]pyrimidine-6-carbonitriles catalyzed by SnO2/SiO2 nanocomposite

Article abstract of DOI:10.1007/s11164-020-04273-x

Abstract: We have developed a SnO₂/SiO₂ catalyzed efficient and rapid protocol for the synthesis of pyrano[2,3-d]pyrimidinone derivatives by the three-component cyclocondensation of aromatic benzaldehydes, malononitrile, and barbitur

Full text of DOI:10.1007/s11164-020-04273-x

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04273-x
An efcient one‑pot three‑component synthesis oꢀ 7‑amino
‑
2,4‑dioxo‑5‑aryl‑1,3,4,5‑tetrahydro‑2H‑pyrano[2,3‑d]
pyrimidine‑6‑carbonitriles catalyzed by SnO /SiO
2
2
nanocomposite
Ajeet A. Yelwande1 · Machhindra K. Lande1
Received: 8 July 2020 / Accepted: 12 September 2020
©
Springer Nature B.V. 2020
Abstract
We have developed a SnO /SiO catalyzed efcient and rapid protocol ꢀor the syn-
2
2
thesis oꢀ pyrano[2,3-d]pyrimidinone derivatives by the three-component cyclo-
condensation oꢀ aromatic benzaldehydes, malononitrile, and barbituric acid in
ethanol at room temperature. Nanocomposite SnO /SiO catalytic materials were
2
2
synthesized using the sol–gel method. The synthesized catalytic materials were well
characterized by using a transmission electron microscope, X-ray diꢁraction spec-
troscopy, scanning electron microscopy, energy dispersive spectroscopy, Fourier
transꢀorm inꢀrared spectroscopy, temperature-programmed desorption (NH -TPD),
3
and Brunauer–Emmett–Teller theory. This protocol has several advantages such as
high yield, simple workup procedure, non-toxic, clean, and easy recovery and reus-
ability oꢀ the catalytic system.
Graphic abstract
An efcient catalytic system has been developed ꢀor the synthesis oꢀ pyrano[2,3-d]
pyrimidinone derivatives ꢀrom one-pot three-component cyclocondensation oꢀ aro-
matic benzaldehydes, malononitrile, and barbituric acid in ethanol at room tempera-
ture using 15 wt% SnO /SiO .
2
2
Extended author inꢀormation available on the last page oꢀ the article
Vol.:(012
1
3456789)
3

A. A. Yelwande, M. K. Lande
Keywords SnO /SiO · Nanocomposite · Sol–gel · Pyrano pyrimidinones ·
2
2
Cyclocondensation
Introduction
A catalyst is a substance that enhances the rate oꢀ a chemical transꢀormation without
being consumed in the process. Catalysts may be in a gaseous, liquid, or solid state.
In homogeneous catalysis, the catalyst is molecularly dispersed in the same phase
(
usually gaseous or liquid) as the reactants. In heterogeneous catalysis, the reactants
and the catalyst are in diꢁerent phases, separated by a phase boundary. The most
commonly used heterogeneous catalysts are solids, and the reactants are in gase-
ous or liquid states. On the other hand, most oꢀ the processes using homogeneous
catalysts occur in a liquid phase. The ꢀact that the catalyst is in a distinct phase with
respect to the reaction medium accounts ꢀor the major advantage oꢀ the heteroge-
neous catalysts over the homogeneous as it makes the separation oꢀ heterogeneous
catalysts simple and cost-eꢁective compared to the homogeneous catalysts [1].
Solid inorganic acids have been used ꢀor various chemical processes and cata-
lytic systems because catalysis has played a major role in preventing pollution in our
environment. Recently, a wide range oꢀ solid acids and their supported ꢀorms have
been reported and extensively reviewed ꢀor various chemical processes [2, 3]. Owing
to their possible utilization as alternatives to liquid inorganic acids in industry, solid
acid catalysts have received much consideration [4–6]. They have the advantages oꢀ
easy separation oꢀ the catalyst ꢀrom the liquid reaction media, applicable recycla-
bility, low corrosion, green chemical procedures, and improved product selectivity
[
7–9].
SnO SiO nanocomposite has several advantages such as high thermal stabil-
2
/
2
ity, high surꢀace area, small in size, and non-toxic; thereꢀore, it has been used as
a catalyst in various types oꢀ reactions such as aminolysis oꢀ styrene oxide with
aniline ꢀor the Meerwein–Ponndorꢀ–Verley reduction oꢀ 4-tert-butylcyclohex-
anone [10], hydroxylation oꢀ phenols [11], Baeyer–Villiger oxidations [12], Meer-
wein–Ponndorꢀ–Verley reductions [13], sugar isomerization [14], epimerization
[
[
15], oxidative dehydrogenation oꢀ cyclohexane [16], and Cannizzaro-type reactions
17].
The non-aqueous synthesis oꢀ SnO /SiO material is not well studied till date,
2
2
and only a ꢀew reports are available ꢀor its synthesis. The ꢂrst describes a proce-
dure based on the reaction oꢀ TEOS with Tin (IV) acetate in anhydrous acetic acid
[
18]. Another report introduces a twin polymerization method ꢀor the production
oꢀ SnO /SiO [19]. The nanosized SnO particles have been prepared by using diꢀ-
2
2
2
ꢀ
erent chemical methods such as precipitation and sol–gel [20, 21]. Tin oxide and
tin oxide-supported metal oxide have been extensively used as solid acid or redox
catalysts ꢀor the oxidative dehydrogenation oꢀ propane, CO oxidation, esteriꢂcation
reaction, reduction oꢀ NO/NO to N , and hydrogenation reaction oꢀ nitrate [22–24].
2
2
Tin oxide has been more commonly used as a catalyst ꢀor the oxidation oꢀ organic
compounds [25].
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Multicomponent reactions (MCRs) have attracted considerable attention due to
their ease oꢀ perꢀormance, high yield, and especially synthetic ꢀeasibility and ef-
ciency [26–32]. MCRs include three or more starting materials reacting in a single
ꢃask to ꢀorm a new product, where basically all the atoms contribute to the newly
ꢀ
ormed product. Due to the diverse biological activity oꢀ compounds in this class,
there is great interest in their synthesis. There is a continuous widespread interest in
the synthesis oꢀ pyrano-pyrimidinones because oꢀ the diverse biological properties
associated with this system [33–46]. Compounds with such annulated uracils have
antitumor, antihypertensive, antibacterial, and ꢀungicidal activities, some oꢀ them
exhibit antimalarial, antiꢀungal, analgesics, and herbicidal properties [47–54].
Previous methods ꢀor the synthesis oꢀ 7-amino-2,4-dioxo-5-aryl-1,3,4,5-tetrahy-
dro-2H-pyrano[2,3-d]pyrimidine-6-carbonitriles have been reported in which a two-
component reaction between arylidene malononitrile with barbituric acid occurred
under harsh thermal conditions [55]. Also, a microwave-assisted one-pot three-com-
ponent cyclocondensation oꢀ barbituric acids, benzaldehyde derivatives, and alkyl
nitrile in the absence or presence oꢀ triethylamine [56] has been reported. However,
some oꢀ these methods are plagued by one or many drawbacks such as long reac-
tion time, use oꢀ volatile solvents, low yields, and harsh reaction conditions [57].
Thereꢀore, it is necessary to develop an improved route ꢀor the synthesis oꢀ pyrano-
pyrimidinones under mild reaction conditions.
Academic as well as industrial chemists are constantly trying to ꢂnd appropriate
sustainable replacements ꢀor expensive, toxic, hazardous, and environmentally dam-
aging catalysts. Thus, more convenient, high-yielding, and eco-ꢀriendly catalysts are
always in demand. Hence, many eꢁorts have been developed during the last decade
ꢀ
or accomplishing MCR by using environmentally benign heterogeneous catalysts.
Heterogeneous catalysts have high selectivity, which is very desirable in chemical
synthesis, as it may oꢁer several advantages such as avoidance oꢀ protection steps,
minimization oꢀ side reactions, as well as step oꢀ the reaction [58–65].
In continuation oꢀ our studies ꢀor the synthesis oꢀ solid acids nanocomposite
materials and nanomagnetic catalysts and our quest toward the development oꢀ a
new heterogeneous catalytic system ꢀor the synthesis oꢀ bioactive heterocycles
[
66–73]. Here, we report a SnO /SiO catalyzed synthesis oꢀ pyrano[2,3-d]pyrimidi-
2 2
none derivatives using multicomponent cyclocondensation oꢀ aldehydes, malononi-
trile, and barbituric acid in ethanol at room temperature (Scheme 1). The noticeable
advantage oꢀ the present work is that the method is simple, ꢀast, and environmentally
benign, and the catalyst was recovered and reused several times ꢀor the preparation
oꢀ pyrano-pyrimidinones.
Results and discussion
To optimize the reaction conditions, the reaction oꢀ benzaldehyde, malononitrile,
and barbituric acid is considered as a model reaction to examine the eꢁect oꢀ various
solvents, such as acetone, toluene, acetonitrile, methanol, and ethanol with SnO /
2
SiO catalytic materials. Among all the solvent screened ꢀor the condensation, it was
2
1
3

A. A. Yelwande, M. K. Lande
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Table 1 Eꢁect oꢀ various
Time (min)a
Yield (%)b
Entry
Solvent
solvents
2
2
2
2
2
a
a
b
c
d
e
Acetone
Methanol
Ethanol
Toluene
Acetonitrile
120
75
60
130
70
50
85
94
60
87
All reactions were carried out using SnO /SiO at room temperature
2
2
b
Isolated yields
Table 2 Eꢁect oꢀ various
Yield (%)a
Entry
Catalyst
Time (min)
amount oꢀ catalyst
3a
3b
3c
3d
3e
3ꢀ
–
200
180
90
80
60
–
SiO2
SnO2
10 wt% SnO /SiO2
15 wt% SnO /SiO2
20 wt% SnO /SiO2
35
80
90
94
92
2
2
70
2
Reaction conditions Benzaldehyde (1 mmol), malononitrile
(
1 mmol), barbituric acid (1 mmol), catalyst (0.1 g), and ethanol
1
5 mL
a
Isolated yields
observed that ethanol ꢀound to be an excellent medium and ꢀurnishing the product in
excellent yield (Table 1).
Aꢀter optimization oꢀ the solvent eꢁect, we have also studied the optimization
oꢀ the amount oꢀ catalyst. However, in the absence oꢀ the catalyst, the ꢀormation oꢀ
the desired product was not observed, Table 2 (entry (3a)). Initially, pure SiO was
2
used as a catalyst ꢀor the model reaction, and the results obtained were very poor.
Aꢀter that, pure SnO was also used ꢀor the reaction, and the results with respect to
2
yields were good but the time required to complete the reaction was high. As we
used 15 wt% SnO /SiO catalysts, the time required ꢀor the completion oꢀ the reac-
2
2
tion ultimately reduced with an increase in the yield oꢀ the product. Interestingly, it
was observed that diꢁerent wt% (10, 20) oꢀ SnO support on SiO ꢀurnishes the poor
2
2
yields oꢀ the product, and longer reaction time is needed ꢀor the completion oꢀ the
reaction. Hence, 15 wt% SnO /SiO (0.1 g) was sufcient to carry out the reaction.
2
2
The model reaction was also carried out by non-conventional methods like ultra-
sonication and microwave irradiation. In ultrasonication, the time required ꢀor the
completion oꢀ the reaction is 55 min with 85% yields. Similarly, the model reaction
was also carried out by microwave irradiation, and the completion oꢀ the reaction
takes place in 8 min aꢁording 82% yields. So, ꢀrom our experimental study, it was
observed that the reaction condition 15 wt% SnO /SiO in ethanol at room tempera-
2
2
ture is more ꢀavorable compared to ultrasonication and microwave irradiation.
1
3

A. A. Yelwande, M. K. Lande
Table 3 shows the comparative study oꢀ diꢁerent catalysts, the merit oꢀ the pre-
sent work that SnO /SiO nanocomposite catalyst consists oꢀ non-toxic, clean, green
2
2
synthesis, and simple workup procedure, and the catalyst can be recovered easily.
To explore the scope and generality oꢀ the present method, a variety oꢀ diꢁer-
ent substituted aromatic aldehydes possessing electron-rich and electron-deꢂcient
groups as well as heterocyclic aldehydes gave good-to-excellent yields (90–95%)
and the reaction was completed within 60–80 min in ethanol at room temperature
(
Table 4).
Then, we turned our attention toward the recovery and reusability oꢀ the catalyst
Fig. 1) as it is important ꢀrom an industrial and economical point oꢀ view. The cata-
(
lyst was separated, washed with n-hexane, and dried at 80 °C ꢀor 2 h beꢀore the next
catalytic run. The reusability oꢀ the catalyst was investigated three times, and it was
ꢀound to retain almost consistent activity (Table 4, entry 4a).
To explain this mechanism, Knoevenagel condensation ꢀollowed by cyclization
leading to xanthene derivatives is accredited to the exclusive role oꢀ SnO /SiO as
2
2
a catalyst and is shown in Fig. 2. As SnO /SiO is an acidic catalyst, initially ben-
2
2
zaldehyde 1a was partially bound with SnO /SiO to activate carbonyl carbon ꢀol-
2
2
lowed by C=C bond ꢀormation with active methylene group oꢀ malononitrile 2 to
ꢀ
orm intermediate I. In the second step, the C–C bond ꢀormation oꢀ intermediates I
with 3 to give the ꢀormation oꢀ intermediates II. In the next step, the intramolecular
cyclization oꢀ intermediates II occurs to give intermediates III. In the last step, the
protonation oꢀ the NH group to give the ꢂnal product 4a and the regeneration oꢀ the
catalyst.
Experimental
All Chemicals were purchased either ꢀrom Merck or Fluka and used without ꢀur-
ther puriꢂcation. All products are known compounds and were characterized by
1
comparing H nuclear magnetic resonance (NMR) spectroscopic data and melting
points with literature values. Uncorrected melting points oꢀ all compounds were
1
measured in an open capillary in a parafn bath. H NMR spectra were recorded
1
using a Bruker instrument ( H at 400 MHz) in dimethyl sulꢀoxide (DMSO)-d6 sol-
vent with tetramethylsilane (TMS) an internal standard. Thin-layer chromatogra-
phy (TLC) was perꢀormed with silica gel 60 F254 plates with ultraviolet (UV) light
ꢀ
or visualization. The morphology oꢀ the sample was characterized with CM-200
PHILIPS transmission electron microscopy (TEM) operated at 200 kV, resolution at
0
.23 nm. FT-IR spectra were recorded on JASCO-FT-IR/4100, Japan, in KBr disc.
The X-ray diꢁraction (XRD) patterns were recorded on Bruker 8D advance X-ray
diꢁractometer using monochromator Cu-Kα radiation (40 kV and 30 mv) oꢀ wave-
length=1.5405 Å. Conventional scanning electron microscopy (SEM) images and
energy dispersive spectroscopy (EDS) were obtained on JEOL; JSM-6330 LA oper-
ated at 20.0 kV and 1.0000 nA. Temperature-programmed desorption (NH -TPD)
3
measurements were carried out on a Micrometrics Instrument corporation Chem-
isoꢀt TPx V1.02 unit 1 (2750). The surꢀace area oꢀ the samples was characterized by
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
1
3

A. A. Yelwande, M. K. Lande
Table 4 15 wt% SnO /SiO catalyzed synthesis oꢀ pyrano-pyrimidinones reaction oꢀ benzaldehydes,
2
2
malononitrile, and barbituric acid
Time (min)a
Yield (%)a
Entry Aldehydes
Product
M.P (°C)
94 (93, 93, 92)b
2
07–209
4
a
60
2
37–239
4
b
50
55
70
65
95
95
91
91
2
2
2
29–231
25–227
26–228
4
c
4d
4
e
4
f
50
80
60
95
92
90
258–260
4
g
212–214
240–242
4
h
Reaction conditions Benzaldehydes (1 mmol), malononitrile (1 mmol) barbituric acid (1 mmol), catalyst
(
0.1 g), and ethanol 15 mL
Isolated yields
Yield aꢀter consecutive cycles
a
b
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Fig. 1 The recyclability oꢀ SnO /SiO in the synthesis oꢀ pyrano[2,3-d]pyrimidinone
2
2
Fig. 2 Plausible mechanism ꢀor the synthesis oꢀ pyrano[2,3-d]pyrimidinone
the BET analysis perꢀorming the adsorption oꢀ nitrogen at 77 K with Micrometrics
ASAP 2010.
Preparation of pure Silica (SiO2)
Silica samples were synthesized by using the sol–gel process. A quantity oꢀ
(
2.408 g) tetraethyl ortho-silicate (TEOS) was taken in an autoclave bottle to which
1
% Cetyl trimethyl ammonium bromide (CTAB) in 20 mL ethanol was added drop-
wise with constant stirring. The reaction mixture was maintained at pH~10 using
aqueous ammonia. This mixture was then hydrothermally treated at 60 °C ꢀor 12 h
1
3

A. A. Yelwande, M. K. Lande
in an autoclavable bottle. Aꢀter drying at 110 °C ꢀor 7 h in an oven, the obtained
powder was pulverized using mortar and pestle and ꢂnally calcined at 400 °C ꢀor
2
h.
Preparation of SnO /SiO catalyst
2
2
Series oꢀ SnO /SiO nanocomposite catalytic materials were synthesized by using
2
2
the sol–gel method. Generally, 15 wt% SnO /SiO catalysts were synthesized by
2
2
using (0.846 g) oꢀ Tin (IV) chloride dissolved in 20 mL double distilled water, and
tetraethyl orthosilicate (TEOS) solution (2.408 g) was added dropwise in an auto-
clave bottle. The resulting mixture was stirred and 1% solution oꢀ cetyltrimethylam-
monium bromide (CTAB) in 20 mL ethanol was added dropwise with constant stir-
ring. The reaction mixture was maintained at pH~10 using aqueous ammonia. This
mixture was then hydrothermally treated at 60 °C ꢀor 12 h in an autoclavable bottle.
Aꢀter drying at 110 °C ꢀor 7 h in an oven, the obtained powder was pulverized using
mortar and pestle and ꢂnally calcined at 400 °C ꢀor 2 h. Similarly, 10 and 20 wt%
SnO /SiO catalysts were prepared in the same manner.
2
2
General procedure for the synthesis of pyrano‑pyrimidinones 4(a–h)
A mixture oꢀ aldehydes (1 mmol, 0.106 g), malononitrile (1 mmol, 0.06 g) and bar-
bituric acid (1 mmol, 0.128 g) catalytic amount oꢀ 15 wt% SnO /SiO (0.1 g) in eth-
2
2
anol (15 mL) was stirred ꢀor the speciꢂed times mentioned in Table 4. The progress
oꢀ the reaction was monitored by TLC (petroleum ether:ethyl acetate=7:3 as elu-
ent). Aꢀter completion oꢀ the reaction, the reaction mixture was heated to solubilize
the products. The catalyst is insoluble in ethanol; thus, the separation oꢀ the catalyst
was easier by simple ꢂltration. The ꢂltrate was concentrated under reduced pressure,
and the crude product obtained was recrystallized ꢀrom ethanol to aꢁord pure prod-
ucts 4(a–h) (Scheme 1).
Spectroscopic data of representative compounds
7
‑Amino‑2,3,4,5‑tetrahydro‑2,4‑dioxo‑5‑phenyl‑1H‑pyrano[2,3‑d]pyrimidine‑6‑car-
1
bonitrile 4a H NMR (400 MHz, DMSO-d ): δ 4.44 (s, 1H), 5.81 (2H, br, s, NH ),
6
2
−
1
6
3
.91–8.28 (m, 5H), 10.38 (1H, br s, NH), 12.06 (1H, br s, NH). IR (KBr, cm ):
+
203, 3174, 3076, 2202, 1710, 1630. ES-MS: m/z 283. 05 (M ).
7
‑Amino‑5‑(4‑bromophenyl)‑2,3,4,5‑tetrahydro‑2,4‑dioxo‑1H‑pyrano[2,3‑d]pyrimi-
1
dine‑6‑carbonitrile 4c H NMR (400 MHz, DMSO-d ): δ 4.42 (s, 1H), 5.69 (2H,
6
br, s, NH ), 6.88–820 (m, 4H), 11.05 (1H, br s, NH), 12.09 (1H, br s, NH) IR (KBr,
2
−1
cm ): 3207, 3153, 3091, 2195, 1693, 1678.
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Catalyst characterizations
XRD analysis
Figure 3a–e shows the XRD patterns oꢀ synthesized materials. Figure 3a shows a
broad peak at 22.27° corresponding to the amorphous nature oꢀ silica. Figure 3b
ꢀ
or SnO nanoparticles represents the XRD patterns ꢀor SnO which show the
2
2
presence oꢀ highly crystalline and sharp intense peaks, which are in good agree-
ment with that obtained by JCPDS card no. 41-1445 [82] with lattice parameter
a = 4.743 Å and c = 3.1859 Å. The crystal planes (110), (101), (211), (002), (310),
and (301) were prominently seen in XRD indicating the polycrystalline nature oꢀ
powder, suggesting the tetragonal lattice symmetry oꢀ these SnO nanoparticles.
2
No impurity phase was observed in all synthesized materials.
The same diꢁraction pattern was observed ꢀor all series oꢀ SnO /SiO materials
2
2
shown in Fig. 3c–e. It was ꢀound that as the loading oꢀ Sn in samples increases, a
gradual increase exists in the peaks intensity (at 2θ = 26.60°) ꢀor the plane (110)
corresponding to the presence oꢀ SnO . Similarly, it was ꢀound that broad peaks at
2
2
2.71° in SnO /SiO correspond to the presence oꢀ amorphous silica. From this,
2
2
it is clearly seen that SnO crystalline nanoparticles aꢀter depositing SiO on its
2
2
surꢀace enhance porosity.
The average crystallite size (D) is determined ꢀrom the XRD spectra using
Scherrer’s ꢀormula. The Scherrer equation [83–85] can be written as ꢀollows:
(a)
(
(
b)
c)
(
(
d)
e)
0
1
0
1
2
1
110
101 20
21
220
31
30
20
32
20
30
40
50
60
70
80
2
θ (Degree)
Fig. 3 (a–e) XRD patterns oꢀ (a) SiO , (b) SnO and (c) 10 wt% SnO /SiO , (d) 15 wt% SnO /SiO , (e)
2
2
2
2
2
2
2
0 wt% SnO /SiO
2 2
1
3

A. A. Yelwande, M. K. Lande
ꢀ
= Kꢁ∕(ꢂcosꢃ)
where τ is the mean size oꢀ the ordered (crystalline) domains, which may be smaller
or equal to the grain size; K is a dimensionless shape factor, with a value close to
unity. The shape ꢀactor has a typical value oꢀ about 0.9; λ is the X-ray wavelength;
β is the line broadening at halꢀ the maximum intensity (FWHM); θ is the Bragg
angle (in degrees). Average crystallite size oꢀ the SnO material was determined
2
ꢀ
rom the 110 plane at 2θ=26.6° by using the Scherrer equation as shown in Table 5.
It was seen that a pure sample oꢀ SnO showed the crystallite size as 12.40 nm. As
2
the loading oꢀ Sn increases, a gradual decrease in the crystallite size ꢀrom 31.60 to
2
5.05 nm was observed ꢀor 10% and 15%, respectively. Aꢀter that, ꢀor a 20% sample,
small increase in the crystallite size 28.35 nm was observed.
TEM analysis
The morphological analysis oꢀ the synthesized material studied by TEM is depicted
in Fig. 4a1–a4. The average particle size oꢀ all samples was investigated using the
main linear intercept method by drawing random lines on the TEM photographs and
counting the number oꢀ grain boundaries. Figure 4a1 shows that mesoporous silica
having a particle size between 288 and 320 nm shows the presence oꢀ varying spher-
ical shape which is a characteristic property oꢀ silica. Figure 4a2 shows the presence
oꢀ ꢃake-like SnO nanoparticles with an average particle size oꢀ about 7–9 nm [86].
2
Figure 4a3 shows that the SnO nanoparticles clearly deposited on spherical-shaped
2
SiO composite and thereꢀore their particle size has ultimately reduced to about
2
2
5–30 nm. The particle size calculated ꢀrom TEM was in close agreement with the
particle size calculated ꢀrom XRD and SEM. The typical SAED pattern ꢀor SnO
2
nanoparticle is depicted in Fig. 4a4 which indicates the presence oꢀ (110), (200),
(
211), and (310) planes, respectively, and predicts the tetragonal lattice symmetry oꢀ
SnO nanoparticles as evidenced ꢀrom the XRD analysis.
2
SEM–EDS analysis
Figure 5b1–b3 shows the SEM analysis oꢀ synthesized materials. Figure 5b1 dem-
onstrates that the surꢀace morphological investigation oꢀ mesoporous silica shows
good agglomeration oꢀ particles with a spherical shape, whereas Fig. 5b2 shows that
Table 5 Average crystallite size
Entry
Sample
Average
oꢀ SnO material determined
2
crystallite size
ꢀ
rom the 110 plane by using the
(
nm)
Scherrer equation
1
2
3
4
5
SiO2
SnO2
10% SnO /SiO2
15% SnO /SiO2
–
12.40
31.60
25.05
28.35
2
2
20% SnO /SiO2
2
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Fig. 4 a1–a4 TEM image oꢀ a1 SiO , a2 SnO , a3 15 wt% SnO /SiO , a4 diꢁraction patterns oꢀ SnO
2
2
2
2
2
Fig. 5 b1–b3 SEM image oꢀ b1 SiO , b2 SnO , b3 15 wt% SnO /SiO
2
2
2
2
SnO nanoparticles indicate a compact arrangement structure due to the uniꢀorm
2
size which is responsible ꢀor importing irregular shapes [87]. The nanocomposite
oꢀ 15 wt% SnO /SiO (Fig. 5b3) shows the presence oꢀ some porosity which may
2
2
be due to the insertion oꢀ SnO particles on the surꢀace oꢀ SiO . This has helped in
2
2
enhancing the catalytic activity oꢀ the material. The elemental analysis oꢀ 15 wt%
SnO /SiO (Fig. 6) shows the presence oꢀ constituent elements Sn, O, and Si con-
2
2
ꢂrmed on the basis oꢀ atom %, 3.65, 54.93, and 41.44, respectively. This indicates
that the required stoichiometric ratio in the catalyst is maintained.
1
3

A. A. Yelwande, M. K. Lande
Fig. 6 EDS pattern oꢀ 15 wt% SnO /SiO2
2
FT‑IR analysis
Dry sample (10 mg) was ground with oven-dry KBr (200 mg), and the resulting
homogeneous mixture (100 mg) was taken in the sample holder. The prepared sam-
ple was put in JASCO-FT-IR/4100, spectrometer and scanned between IR ranges
−
1
4
000 and 400 cm . Fig. 7a–e shows the FT-IR spectra oꢀ the prepared catalytic
materials. Figure 7a shows the FT-IR spectrum oꢀ pure SnO having an absorp-
2
−1
tion band at 3205 cm which is due to the Sn–OH stretching vibration, and the
−1
band at 1634 cm is assigned ꢀor the Sn-OH bending vibration. Figure 7b shows
−
1
that the FT-IR spectrum oꢀ pure SiO gives inꢀrared region at 3408 cm due to the
2
−
1
−1
Si–OH stretching vibration, 1620 cm due to the Si–OH bending mode, 1093 cm
−1
ꢀ
or Si–O stretching vibration, and 806 cm due to the Si–O–Si bending vibrational
−1
mode. The strong absorption band at 631 cm is due to the antisymmetric Sn–O–Sn
vibrational mode oꢀ SnO . Similar results were reported in the literature by Desh-
2
pande et al. [88]. Similarly, Fig. 7c–e shows that the inꢀrared bands at 3408, 1620,
093, 806, and 631 cm− are attributed to the SnO /SiO ꢀramework.
1
1
2
2
TPD analysis
NH -TPD measurements were carried out by (i) pre-treating oꢀ samples ꢀrom room
3
temperature to 150 °C in Helium ꢃow 25 cc/min ꢀor 1 h; (ii) adsorption oꢀ ammo-
nia at room temperature; (iii) Desorption oꢀ adsorbed ammonia with a heating rate
−1
oꢀ 10 °C min starting ꢀrom the adsorption temperature ꢀrom 50 to 500 °C. The
NH -TPD desorption was used to determine the acidic properties oꢀ solid cata-
3
lysts. This provides inꢀormation about the total concentration and strength oꢀ acidic
sites (Bronsted and Lewis). From the TPD analysis, it was ꢀound that the ammonia
desorbed in two diꢁerent regions. In the ꢂrst region, 0.06238 mmol/g oꢀ NH des-
3
orbed at 259 °C to the presence oꢀ Lewis acidic sites, while in the second region
0
.08625 mmol/g oꢀ NH desorbed at 507.1 °C ꢀrom Bronsted acidic sites. Hence,
3
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
(
(
e)
d)
(
c)
(
b)
(
a)
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
Fig. 7 a–e FT-IR patterns oꢀ a SnO , b SiO , c 10 wt% SnO /SiO , d 15 wt% SnO /SiO , e 20 wt%
2
2
2
2
2
2
SnO /SiO
2
2
the total strength oꢀ acidic sites present in 15 wt% SnO /SiO was ꢀound to be
2
2
0
.149 mmol/g (Fig. 8). It indicates that both Bronsted and Lewis acidic sites are pre-
sent in SnO /SiO composite materials.
2
2
Fig. 8 TPD proꢂle oꢀ 15 wt% SnO /SiO2
2
1
3

A. A. Yelwande, M. K. Lande
Fig. 9 BET surꢀace area oꢀ 15 wt% SnO /SiO2
2
Table 6 The acid strength and surꢀace area
2
Entry
Catalyst
Total acidity (mmol/g)
0.149
Surꢀace area (m /g)
1
15 wt% SnO /SiO
331.5814
2
2
BET surface area
The N2-BET surꢀace areas oꢀ 15 wt% SnO /SiO material were characterized and
2
2
shown in Fig. 9 and summarized in Table 6. The amount oꢀ N gas adsorbed-des-
2
orbed at a given pressure allows to determine the surꢀace area oꢀ the material. The
isotherm ꢀor the prepared material indicates that a large volume was adsorbed on the
2
surꢀace oꢀ the material. The BET surꢀace area observed is 331.5814 m /g; similarly,
2
Single Point Surꢀace Area at P/Po 0.20128441 was ꢀound to be 327.5305 m /g. It
indicates that the material has a large surꢀace area, and hence, this material shows a
higher catalytic activity.
Similarly, BJH Adsorption Average Pore Diameter (4V/A): 22.1828 nm which
indicates a large increase in pore size and surꢀace area. The same result ꢀrom XRD
3
was observed, i.e., 25.05 nm. The pore volume is ꢀound to be 0.744036 cm /g, as
shown in Fig. 10. It indicates that the ꢀormation oꢀ a porous surꢀace, as well as the
smaller pore volume oꢀ the material, may be due to the penetration oꢀ the silica into
the pores oꢀ the SnO , which can be clearly seen in SEM and TEM images.
2
Reusability oꢀ catalyst
The catalyst was tested ꢀor its reusability with 15 wt% SnO /SiO catalytic mate-
2
2
rial. It was observed that there were no changes in its catalytic activity till the
1
3

An efcient one‑pot three‑component synthesis oꢀ 7‑amino‑2,…
Fig. 10 BJH adsorption average pore diameter oꢀ 15 wt% SnO /SiO2
2
third cycle. It was clearly seen in the XRD oꢀ the material. There is a slight
decrease in the crystalline nature oꢀ the catalyst, but all peaks are matched with
the XRD oꢀ the ꢀresh sample (Fig. 11).
1
5 wt % SnO /SiO2
2
(
Reused)
1
5 wt % SnO /SiO2
2
(
Fresh)
0
1
1
10
0
20
1
21
0
22
0
1
2
21
1
31
30
20
3
2
0
30
40
50
60
70
80
2
θ (Degree)
Fig. 11 XRD pattern oꢀ reused 15 wt% SnO /SiO2
2
1
3

A. A. Yelwande, M. K. Lande
Conclusion
In summary, an efcient catalytic system has been developed ꢀor the synthesis oꢀ
pyrano[2,3-d]pyrimidinone derivatives ꢀrom one-pot three component cycloconden-
sation oꢀ aromatic substituted benzaldehyde, malononitrile, and barbituric acid in
ethanol at room temperature using 15 wt% SnO /SiO . The present method oꢁers
2
2
remarkable advantages such as non-toxic, non-corrosive, and inexpensive reaction
conditions. Simple recovery and reusability oꢀ the catalyst make the reaction suc-
cessꢀul under environmental benign conditions.
Acknowledgements The authors are thankꢀul to the Head, Department oꢀ Chemistry, Dr. Babasaheb
Ambedkar Marathawada University, Aurangabad, India ꢀor providing the laboratory ꢀacility.
Compliance with ethical standards
Conꢁict oꢀ interest There are no conꢃict oꢀ interest to declare.
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Aꢀliations
Ajeet A. Yelwande1 · Machhindra K. Lande1
*
Ajeet A. Yelwande
ajeetye@gmail.com
1
Department oꢀ Chemistry, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad 431004, India
1
3