A nano silver-xerogel (Ag nps@modified TEOS) as a newly developed nanocatalyst in the synthesis of benzopyranopyrimidines (with secondary and primary amines) and: Gem -bisamides

Article abstract of DOI:10.1039/c7dt00822h

Silver nanoparticles have been prepared from a chemical reduction approach and supported on modified TEOS (tetraethylorthosilicate) xerogels to be studied as a nanocatalyst in the conversions of benzopyranopyrimidines (with primary as well as secondary am

Full text of DOI:10.1039/c7dt00822h

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A nano silver-xerogel (Ag nps@modified TEOS) as a
newly developed nanocatalyst in the synthesis of
benzopyranopyrimidines (with secondary and
primary amines) and gem-bisamides†
Cite this: DOI: 10.1039/c7dt00822h
Gurpreet Kour and Monika Gupta
*
Silver nanoparticles have been prepared from a chemical reduction approach and supported on modified
TEOS (tetraethylorthosilicate) xerogels to be studied as a nanocatalyst in the conversions of benzopyrano-
pyrimidines (with primary as well as secondary amines along with the mechanism by trapping the imine
intermediate) and also in the synthesis of gem-bisamides. Different conditions for the performance of the
nanocatalyst have been screened and tolerance with respect to variable functionalities has been observed,
1
resulting in excellent yields; and confirmation of products synthesized has been done using studies like H
NMR, 13C NMR and mass analysis. Also, SEM-EDX and TEM of the nanocatalyst have been performed to
know the internal and external morphology, size and elemental composition. UV and XRD analysis to
confirm the silver nanoparticles’ and xerogel’s presence, TGA to study the thermal stability and FTIR to study
the modification pattern of the nanocatalyst have been undertaken and presented in this work.
Received 7th March 2017,
Accepted 12th April 2017
DOI: 10.1039/c7dt00822h
rsc.li/dalton
azole synthesis,10 phenolysis of epoxides11 and alkyne–azide-
1. Introduction
1,3-dipolar cycloaddition.12 Silver nanoparticles have been
Widening the scope of silver nanoparticles in their application least explored with respect to organic conversions which pro-
in synthetic purposes in the field of nanocatalysis, the present vides a greater scope to unveil its application, this provides the
work is in continuation of our previous work on nanocatalysis.1,2 basis for the present work.
Size reduction makes a material worthy of providing a high per-
Benzopyranopyrimidines have diverse potential applications,
formance active binding site, minimizing the energy barriers as they possess properties like analgesic,13 anti-inflammatory,14
and providing selectivity to the optimized reactions. The benefits in vitro anti-aggregating,15 and cytotoxic activity against cancer
of moving to the nanoscale are perhaps the best. Nanocatalysts cell lines.16 Apart from these biological significances, they have
are better than conventional catalysts as their extremely small been studied to have optical and emissive dye properties.17
size yields a tremendous surface area-to-volume ratio and their Many catalysts like ionic liquids, acids, magnetic nanoparticles,
fabrication on the nanoscale achieves properties not found oxychlorides etc. have been used for their preparation but each
within their macroscopic counterparts. Interest in nanocatalysis of them suffers from some limitations like non-recyclability,
in recent years has been focussed on the fabrication of such harsher conditions, and a longer reaction time. So, our present
nanocatalysts that exhibit 100% selectivity for a desired product, work on silver nanocatalysts removes all the limitations and
thereby removing by-products and eliminating waste. Such a also studies the mechanism. Moreover, it is for the first time
selective conversion is often called green chemistry or green that such a conversion has been studied with primary amines.
technology. Nanocatalysis can aid in the designing of catalysts
gem-Bisamides, whether symmetrical or unsymmetrical,
with efficient activity, greater selectivity, and high stability.
have been viewed as interesting moieties to be synthesized for
To date, silver nanoparticles have been studied to catalyze their beneficiary applications studied earlier in controlling
the synthesis of β-enaminones,3 and in oxidative cyclization,4 hypertension18 in peptidomimetic structures19,20 and as CB2
Diels’ Alder cycloaddition of 2-hydroxychalcones,5 reduction of receptor inverse agonists.21,22 This conversion has been
nitroarenes,6–8 oxidation of 1,2-propanediol,9 A-3 coupling, tri- studied by the usage of acid or solid acid catalysts; but this is
for the first time we are presenting this conversion with a
noble metal (silver) and in addition to the catalyst being nano
Department of Chemistry, University of Jammu, Jammu-180006, India.
in size, the role of solvent is highly important for the action of
E-mail: monika.gupta77@rediffmail.com
nanocatalysts. This has been studied using a range of solvents
†Electronic supplementary information (ESI) available: The spectral data of all
and temperature conditions mentioned ahead.
the products. See DOI: 10.1039/c7dt00822h
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In addition to the nanocatalytic activity studied in the present flask and stirred for 2 h at 60 °C on a magnetic stirrer. This
work, the prepared Ag nps@TEOS xerogel has more potential for round bottom flask was placed in an oven at 60 °C for 5 h.
further research in the field of medical sciences and in optically A xerogel was obtained, as shown in the images [Fig. 1(a)].
advanced materials. Silica xerogels obtained from sol–gel syn- This xerogel was immersed in 25 mL ethanol to get rid of any
thesis are biodegradable and as such are quite capable as drug acidic impurities and was again dried at 60 °C for 5 h.
delivery systems. Both silver nanoparticles and silica xerogels Xerogels obtained so were further treated with 1.5 mmol of
have been used in biosensing applications.28,29 Silica xerogels 2-iodoaniline in ethanol at 80 °C for 12 h maintaining the pH
have been studied for their useful optical properties such as high at 9–10 using KOH. The modified material obtained thus was
refractive indices and transparency to visible light.30 Combining filtered under vacuum and dried in an oven at 100 °C.
the two with modification actually combines the positive charac-
2.1.2 Synthesis of silver nanoparticles. 1 mmol of silver
ters of both silica xerogel and silver nanoparticles resulting in a nitrate was solubilised in 25 mL ethanol and was added to a
much more efficient material than its parent material. So, these stirred aqueous solution of sodium borohydride (3 mmol)
potential applications of the Ag nps@TEOS xerogel make it an taken in a round bottom flask with the temperature main-
industrially important nanomaterial. There are many secondary tained between 0 and 5 °C and the pH maintained between
amines present in our biological systems which include biogenic 9 and 10 under a nitrogen atmosphere.
amines e.g. epinephrine. As the present work involves the role of
2.1.3 Synthesis of modified TEOS supported silver catalyst.
Ag nps@TEOS xerogel as nanocatalyst in the synthesis of second- The prepared silver nanoparticle colloidal solution was poured
ary amine derivatives (i.e. synthesis of benzopyranopyrimidines onto 5 g modified TEOS with 50 mL diethyl ether (dried) as the
using secondary amines), so this property of Ag nps@modified solvent was taken in a round bottom flask (100 mL) and stirred
TEOS xerogel makes it a potential candidate to investigate its for 4 h at room temperature. Finally the prepared catalyst was
application scope in biological systems too by affecting the filtered under vacuum and dried at 50 °C for 5 h (Scheme 1).
amounts of secondary amines in biological systems. Such a com-
bination to synthesize the Agnps@modified TEOS xerogel also
lessens the risk of metal toxicity leading to conditions such as
2.2 General procedure for the synthesis of
benzopyranopyrimidines
argyria, argyrosis, liver damage, and kidney damage caused by
ions of silver nanoparticles to living organisms31 by efficiently
Salicylaldehyde (2 mmol), amine (1 mmol) and malononitrile
(1 mmol) were placed in a 50 mL round bottom flask and
stabilizing silver nanoparticles in their zero oxidation state.
stirred thermally at 60 °C in an oil bath on a magnetic stirrer
Also, due to the recyclability of the nanocatalyst in the
and the reaction was catalyzed using 0.1 g of Ag nps@modified
studied conversions, it can never be ignored as a renewable
TEOS as the catalyst with ethanol (2 mL) as the solvent. The reac-
energy source in the form of a catalyst.
tions were run for the appropriate times and were monitored
using the thin layer chromatography technique. With the com-
pletion of the reaction, the reaction mixture was diluted with
ethyl acetate (25 mL) and was warmed and filtered off to remove
the catalyst from the reaction mixture. This warm filtrate was
2 Experimental
2.1 Synthesis of nanocatalyst (Ag nps@modified TEOS)
2.1.1 Synthesis of modified TEOS. 5 mL TEOS, 5 mL then subjected to evaporation to one-third of its original amount
ethanol and 5 mL dilute HCl were taken in a round bottom which on cooling yielded the crude product. The crude product
Fig. 1 (a) TEOS xerogel (b) Ag nps@modified TEOS xerogel nanocatalyst.
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dified TEOS. This was heated to reflux under a condensed
atmosphere and stirred with a magnetic stirrer for the desired
time. The reaction was worked up after the completion as indi-
cated by TLC eluted in pet. ether : ethyl acetate. The working
up involved diluting the reaction mixture with ethyl acetate
(20 mL), warming and then filtering off the filtrate to separate
the catalyst. This was followed by three times cold water wash-
ings and then drying over sodium sulphate overnight. Finally,
the sodium sulphate was filtered off and the filtrate was evapo-
rated to obtain the crude product, which gave the pure com-
pound on recrystallization in ethanol. The compounds thus
1
obtained were authenticated by studies like HNMR, 13CNMR
and mass analysis.
3. Results and discussion
As the iodide group in 2-iodoaniline can be easily displaced to
result in the desired modification, the modification using
2-iodoaniline gives –NH2 as free ends that can stabilize silver
nanoparticles in their zero oxidation state very well by a con-
tinuous flow of electrons. As the modification increases the
chain length, the adsorbed silver nanoparticles can show their
better performance as nanocatalysts. This formed the basis for
modifying the xerogel with 2-iodoaniline.
Scheme 1 Synthesis of Ag nps@modified TEOS xerogel.
3.1 Ag nps@modified TEOS xerogel nanocatalyst
characterization
3.1.1 SEM-EDX analysis. This analysis shows the various
topographic images of the nanocatalyst and elemental compo-
sition (Fig. 2 and 3). SEM images at various magnifications
show a rough xerogel surface with reflecting silver nano-
particles adhered to the xerogel surface [Fig. 2(a) and (b)].
Fig. 3 shows the EDX analysis spectrum which shows the
was then recrystallized using ethanol to obtain pure products.
These products were then confirmed by melting point determi-
nations, 1HNMR, 13CNMR and mass analysis techniques.
2.3 General procedure for the synthesis of gem-bisamides
2 mmol of benzamide and 1 mmol of aldehyde were dissolved presence of carbon, nitrogen, silicon, oxygen and silver
in toluene (2 mL) and to this was added 0.1 g of Ag nps@mo- elements in the nanocatalyst.
Fig. 2 SEM images of Ag nps@modified TEOS xerogel.
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Fig. 3 EDX spectrum of Ag nps@modified TEOS xerogel.
3.1.2 TEM analysis. The TEM analysis reveals various para- 9.66% at 500 °C. So, this analysis confirms the nanocatalyst to
meters of the internal morphology of the catalyst. Fig. 4(a) be used under all the chosen conditions for all the mentioned
shows silver nanoparticles of different sizes, with an average of organic conversions (Fig. 8).
28 nm. Fig. 4(b) and (d) show silver nanoparticles glued on the
3.1.7 ICP-AES analysis. The given sample was digested in
surface of the modified xerogel which has a somewhat tubular 8 ml HNO3 and made up to 50 ml. The filtered solution was
appearance as perceived from the image. A dark field image analyzed with the ICP-AES system which showed the presence
(Fig. 4c) has also been obtained which shows the crystallinity of 7.39 wt% silver loaded on the modified TEOS xerogel.
of silver nanoparticles and reflection from silver nanoparticles
3.2 Testing nanocatalyst for the synthesis of
benzopyranopyrimidines
as small as 4–11 nm and confirms the presence of much
smaller nanosize particles than those seen in Fig. 4(a).
3.1.3 UV-Vis analysis. A plasmon near 400 nm was shown
by the nanocatalyst, which appears due to the presence of xerogel nanocatalyst was tested to be used in the one-pot syn-
silver nanoparticles (Fig. 5).3
thesis of benzopyranopyrimidines. We chose the reaction of
3.2.1 With secondary amines. The Ag nps@modified TEOS
3.1.4 FTIR analysis. The complete FTIR analysis has been piperidine, salicylaldehyde and malononitrile as the reaction
summed up in the table given below Fig. 6, showing all stretch- under observation for optimization of conditions. The reaction
ing and bending vibrations for the appropriate bonds and was carried out under ambient conditions of temperature but
modifications present in the synthesized Ag nps@modified no reaction product was observed to be formed, as seen from
TEOS xerogel.
the TLC even after a 12 h run. So we raised the temperature
3.1.5 XRD analysis. The XRD analysis shows peaks at 38°, parameter to 60 °C and saw the formation of product after
44°, 66° and 77°, which correspond to the 111, 200, 220 and 10 min, which reached completion after 45 min in ethanol;
311 planes4 of silver nanoparticles (Fig. 7).
the yield observed was comparable to the excellent one
3.1.6 Thermogravimetric analysis. This analysis shows an depicted in the literature. Now, to approach some greener
initial weight loss of 5.11% at 192 °C, which can be attributed parameters and to observe the reaction under conditions pro-
to physically adsorbed water. This weight loss reaches up to posed by the literature until now, we observed the same reac-
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Fig. 4 TEM images of Ag nps@modified TEOS xerogel.
tion under solvent-free conditions at ambient temperature and
at 60 °C and at 80 °C. The same test reaction was observed
with water as the solvent at R.T., 60 °C, 80 °C and 100 °C. The
yields obtained are presented in Table 1 and they show that
the chosen reaction condition holds the best possibility of
catalyst activity. To understand how the prepared material
functions as a catalyst in the proposed synthesis we compared
it with unmodified supported silver nanoparticles and with
other catalysts too, as mentioned in Table 2. Bare Ag nano-
particles have shown better results in less time than Ag
nps@TEOS (without modification). The reason for this can be
attributed to the almost homogeneous nature of Ag nano-
particles. But when supported directly on the TEOS xerogel, it
may have hampered the activity of Ag nps as active sites, thus
increasing the reaction time and lowering the yields. But the
modification of the TEOS xerogel with 2-iodoaniline resulted
in an increased chain length, allowing Ag nanoparticles to
Fig. 5 UV–Visible analysis of Ag nps@modified TEOS xerogel.
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Fig. 6 FTIR spectrum of Ag nps@modified TEOS xerogel.
Fig. 7 XRD analysis of Ag nps@modified TEOS xerogel.
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Fig. 8 Thermogravimetric analysis graph of Ag nps@modified TEOS xerogel.
Table 1 Optimization of reaction conditions using piperidine (1 mmol),
salicylaldehyde (2 mmol), malononitrile (1 mmol), and 0.1 g Ag nps@mo-
dified TEOS xerogel
perform efficiently in lowering reaction times and increasing
yields. This comparison convinced us to use the Ag nps@mo-
dified TEOS xerogel nanocatalyst as a suitable catalyst for the
required conversion under the chosen set of conditions. In
addition, a series of reactions with various secondary amines
and substituted salicylic aldehydes were carried out to see
whether the Ag nps@modified TEOS xerogel nanocatalyst
holds good to stand the variable functionalities. The data
(Table 4) support the selective nature of the Ag nps@modified
TEOS xerogel nanocatalyst as a good catalyst for the selected
conversion. Piperidine (pKa = 11.2) is much more basic than
dimethylamine (pKa = 10.74), along with the stability of the
product formed with a six membered heterocycle compared to
open chain products, this forms the basis for piperidine to
show a much higher product yield than dimethyl amine.
Moreover, diethyl amine yielded no product because of the
steric hindrance created by two ethyl groups restricting the
product formation. A comparison of the present work with the
already reported literature methods is presented in Table 3.
3.2.2 With primary amines. Under the optimized set of
conditions, the nanocatalyst was reacted with primary amines
viz. aniline, p-chloro aniline, p-nitro aniline and p-methoxy
aniline as variables. It was observed that no reaction took
S. no.
Solvent
Temperature (°C)
Time
% Yield
1
2
3
4
5
6
7
8
9
Solvent-free
Solvent-free
Solvent-free
Water
Water
Water
Water
Ethanol
Ethanol
R.T.
60
80
R.T.
60
80
100
R.T.
60
12 h
12 h
6.30 h
12 h
12 h
12 h
8 h
—
—
65
—
—
40
50
—
93
12 h
45 min
Table 2 Control experiments with counterparts of Ag nps@modified
TEOS under the optimized and similar set of conditions
S. no.
Catalysts
Time
% Yields
1
2
3
4
TEOS xerogel
Ag nps
Ag nps@TEOS xerogel
Ag nps@TEOS modified xerogel
6 h
60 min
2.5 h
—
85
70
93
45 min
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Table 3 Comparison of the catalytic activity of the Ag nps@modified TEOS xerogel nanocatalyst with other reported catalysts for the one-pot syn-
thesis of pyranopyrimidines
Catalyst
Conditions
Time
% Yield
Drawback
LiClO4 (20 mol%)13
Sodium formate14
EtOH, R.T.
EtOH, R.T.
Solvent-free, R.T.
Solvent-free, R.T.
Ultrasound, solvent-free
Thermal, 60 °C, ethanol
24 h
12 h
9 min
14 min
5 min
45 min
93
83
86
93
96
93
Non-recyclable catalyst, a long run time
Non-recyclable catalyst, a long run time, low yield
Low yield
APTES-MNPs34
Brønsted acid ILs33
Chlorosulfonic acid32
Ag@TEOS nanocomposite
Expensive catalyst
Non-recyclable catalyst, harsh conditions
Recyclable catalyst, easy work-up, mild conditions
(edge of the present work)
Table 4 Ag nps@modified TEOS xerogel nanocatalyst catalyzed syn-
thesis of benzopyranopyrimidines using secondary aminesa
Table 5 Ag nps@modified TEOS xerogel nanocatalyst catalyzed syn-
thesis of benzopyranopyrimidines using primary aminesa
S. no.
1
Aldehyde
Primary amine
Time (h)
8
% Yieldb
—
2
3
4
8
8
3
—
—
63
S. no. Aldehyde
1
Secondary amine % Yieldb M.pt/Lit. M.Pt.
93
167–169/168–17013
2
3
90
85
192–194/196–19814
188–190/185–18927
a Reaction conditions: Salicylic aldehyde (2 mmol), malononitrile
(1 mmol), primary amine (1 mmol), 0.1 g Ag nps@modified TEOS
xerogel, ethanol (2 ml), 60 °C. b Isolated yields.
4
5
6
85
—
90
172–174/177–17913
—
should be enough basic comparable to secondary amines to
stand the conversion.
175–177/178–18014
3.3 Testing nanocatalyst for the synthesis of gem-bisamides
Ag nps@modified TEOS was also screened for catalytic activity
in the synthesis of bisamides. To reach the appropriate set of
conditions, the conditions of temperature, solvent and
7
79
210–212/214–21614 amount of catalysts were varied. All the data along with yield%
are summed up in Table 6, which shows that the chosen con-
ditions resulted in an efficient % yield of the product in com-
paratively less time than the existing methods. Firstly the
solvent-free condition was studied with varying temperatures
a Reaction conditions: Salicylic aldehydes (2 mmol), malononitrile
(1 mmol), amine (1 mmol), 0.1 g Ag nps@modified TEOS xerogel,
ethanol (2 ml), 60 °C. b Isolated yields.
of 80 °C and 100 °C and catalyst amounts of 0.1 g and 0.2 g.
There was no reaction even after a 12 h run. The next solvent
tried was THF at reflux which gave a yield of 45% which never
increased despite increasing the amount of catalyst from 0.1 g
to 0.2 g; ethanol at reflux with 0.1 g and 0.2 g of catalyst also
place with aniline, p-chloro aniline and p-nitro aniline but gave no reaction for a 12 h run. Ethanol–water (1 : 1) at 70 °C
p-methoxy aniline gave product formation in a comparatively also gave no reaction. The last solvent we tried was toluene at
lower yield and longer reaction time than in the case of sec- 110 °C. To our surprise, the solvent provided the perfect
ondary amines (Table 5). An intermediate too has been medium for the catalyst to show its efficiency and we obtained
trapped in this case. So, here we propose that a primary amine excellent yields in comparatively lesser time (Table 6). So here,
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Table 6 Optimization of reaction conditions
Table 8 Agnps@modified TEOS xerogel nanocatalyst in the synthesis
of gem-bisamidesa
Catalyst Time
(h)
%
Yield
S. no. Solvent
Temperature (g)
1
2
3
4
5
6
7
8
—
—
—
—
80
80
100
100
60
60
80
0.1
0.2
0.1
0.2
0.1
0.2
0.1
0.2
0.1
0.1
0.1
0.2
0.1
0.2
12
12
12
12
6
—
—
—
—
40
40
—
—
—
—
—
—
93
93
Time
Product (h)
%
Tetrahydrofuran
Tetrahydrofuran
Ethanol
Ethanol
Water
S. no. Aldehyde
1
Yieldb M. Pt/Lit. M. Pt.
6
12
12
12
12
12
12
1.40
1.40
1.40
2.30
3.30
93
90
91
202–204/205–20723
80
9
100
100
70
70
110
110
2
3
244–246/24023
10
11
12
13
14
Water
Ethanol : water (1 : 1)
Ethanol : water (1 : 1)
Toluene
230–232/230–23223
Toluene
4
5
3.30
2.30
93
83
210–212/216–21823
195–197/195–19824
Table 7 Comparison with parallel analogues
6
7
2.30
2.15
90
90
194–196/198–20024
258–260/263–26423
S. no.
Catalysts
Time (h)
% Yields
1
2
3
4
TEOS xerogel
Agnps
Agnps@TEOS xerogel
Agnps@TEOS modified xerogel
24
—
60
70
93
12 h
12 h
1.40
9
2
91
89
230–232/230–23224
252–254/255–25724
10
2.30
11
12
1.30
1.30
3
90
86
89
206–208/206–20823
205–207/208–21023
210–212/215–21624
we come up with a perspective for the role of solvent to be very
important for such a conversion. The control experiments with
parallel analogues were carried out too and the data are pres-
ented in Table 7. Furthermore, the bisamide conversion was
carried out with different aldehyde substrates like aliphatic,
aromatic and heteroaromatic aldehydes and the catalytic
activity of the Ag nps@modified TEOS xerogel was truly
efficient in all the studied cases (Table 8). A comparison with
earlier reported methods is summarized in Table 9.
13
H
a Reaction conditions: Aldehyde (1 mmol), benzamide (2 mmol),
Agnps@modified TEOS xerogel (0.1 g), toluene (2 ml), 110 °C.
b Isolated yields.
nps@modified TEOS xerogel nanocatalyst activates the amide
by maintaining an electron flow to produce an imine inter-
mediate A, which is then attacked at the CvN bond by
another amide moiety activated by the nanocatalyst in non-
polar toluene and under high temperature conditions to
produce the desired product (Scheme 3). The CvN bond gets
attacked by the –NH2 group rather than CvO because the
CvN bond site is sterically more facile than the sterically hin-
dered CvO bond.
3.4 Proposed mechanisms
3.4.1 Proposed mechanism for the synthesis of benzopyrano-
pyrimidines catalyzed by Ag nps@modified TEOS xerogel.
The mechanism has been studied by trapping the imine inter-
mediate A when a primary amine viz. p-methoxyaniline was
used for the synthesis. So, a confirmed pathway is proposed
here that the synthesis in the case of primary as well as sec-
ondary amines involves a Knoevenagel condensation between
one molecule of salicylic aldehyde and malononitrile giving
away an immino intermediate A; this intermediate is attacked
by the amine (primary or secondary) to give another inter-
mediate B. This B intermediate attacks the other salicylic alde-
3.5 Recyclability of Ag nps@modified TEOS
3.5.1 Recyclability in the synthesis of benzopyranopyrimi-
hyde moiety under the influence of the nanocatalyst to give a dines. This was studied using salicylaldehyde (2 mmol), piper-
cyclized intermediate C which, upon proton transfer in the idine (1 mmol) and malononitrile (1 mmol) as the test reaction
presence of ethanol, finally results in the formation of for five runs (Fig. 9).
benzopyranopyrimidines (Scheme 2).
3.5.2 Recyclability in the synthesis of gem-bisamides. This
3.4.2 Proposed mechanism for the synthesis of gem-bis- was studied using benzaldehyde (1 mmol) and benzamide
amides. To enable an amide to attack an aldehyde, the Ag (2 mmol) as test substrates for five runs (Fig. 9).
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Table 9 Comparison with earlier reported methods
S. no.
Catalyst
Conditions
Time
% Yield
Drawback
1
2
3
4
5
Boric acid23
Toluene, reflux
Solvent-free, 100 °C
Acetone, R.T.
Solvent-free, 100 °C
Toluene, 110 °C
16 h
92
75
68
90
93
Non-recyclable, a long run time
Low yield
Low yield
Low yield
SiO2–PPA25
70 min
120 min
2 h
26
BF3·OEt2
C/TiO2–SO3H24
Ag nps@modified TEOS xerogel
1 h 40 min
Excellent yield, less time, recyclable (edge)
Scheme 2 Proposed mechanism for the synthesis of benzopyranopyrimidines catalyzed by the Ag nps@modified TEOS xerogel.
Scheme 3 Proposed mechanism for the synthesis of gem-bisamides.
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8.0 Hz, Ar), 7.13 (q, 2H, J = 8.0 Hz, Ar), 7.26 (t, 1H, J = 8.0 Hz,
Ar), 7.33 (q, 2H, J = 8.0 Hz, Ar), 8.24 (d, 1H, J = 8.0 Hz, Ar),
13.08 (s, 1H, OH). 13C NMR (100 MHz, CDCl3): δ (ppm) 25.1,
48.5, 66.4, 98.0, 116.7, 117.8, 118.5, 119.3, 120.3, 125.0, 128.6,
129.1, 129.5, 133.3, 150.2, 160.2, 161.0, 163.6, 164.5.
MS ESI+ 362.04.
5.3 N,N′-Benzylidenebisbenzamide
1H NMR (400 MHz, DMSO): δ 7.04 (t, J = 8 Hz, 1H, CH), 7.31
(t, J = 8 Hz, 1H, ArH), 7.38 (t, J = 8 Hz, 2H, ArH), 7.48 (m, 6H,
ArH), 7.89 (d, J = 8 Hz, 2H, ArH), 9.07 (d, J = 8 Hz, 2H, NH).
13C NMR (100 MHz, DMSO): δ 59.0, 126.8, 127.2, 128.8, 132.1,
134.1, 138.9, 166.2.
Fig. 9 Recyclability of Ag nps@modified TEOS xerogel in the synthesis
of benzopyranopyrimidines (piperidine as the test substrate) and gem-
bisamides (benzaldehyde as the test substrate).
MS ESI+ 353 (M + 23).
5.4 N,N′-(3,4-Dimethoxyphenylmethylene)dibenzamide
Each time the amount of the catalyst was reduced due to
manual mishandling and for each run the amounts of the
corresponding reactants were adjusted. After each trial, the
catalyst was washed with warm water and ethanol followed by
drying in an oven at 50 °C to be reused for the next time.
1H NMR (400 MHz, DMSO): δ (ppm): 3.76 (6H, s, OCH3), 6.96
(q, 3H, J = 8 Hz), 7.11 (s, 1H), 7.48 (d, 4H, J = 8 Hz), 7.54 (d,
2H, J = 4 Hz), 7.84 (d, 4H, J = 8 Hz), 8.94 (d, 2H, J = 8 Hz, NH).
13C NMR (100 MHz, DMSO): δ (ppm): 165.9, 149.0, 148.9,
141.5, 134.4, 133.2, 131.9, 119.2, 111.9, 111.0, 59.1.
MS ESI+ 413.03 (M+).
4. Conclusion
So, we conclude the work with some new findings of silver
nanoparticles in the form of Ag nps@modified TEOS xerogel
as a recyclable nanocatalyst in the synthesis of benzopyrano-
pyrimidines and gem-bisamides in less time with efficient
yields. Moreover, the synthesis of benzopyranopyrimidine with
p-methoxybenzaldehyde has been successfully achieved too
and the mechanistic insights are also confirmed by the trap-
ping of the imine intermediate. Also the potential application
of the Ag nps@modified TEOS xerogel makes the synthesis of
such a nanocatalyst worthwhile.
Acknowledgements
We are thankful to IIT Mumbai for SEM-EDX and TEM ana-
lyses, to SAIF, Kochi for XRD and FTIR analyses and to the
Department of Chemistry, University of Jammu, for providing
facilities for UV, TGA and NMR analyses. Also, we are thankful
to IIIM Jammu for providing mass spectral analysis.
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