One-pot synthesis of 2-amino-3-cyanopyridines and hexahydroquinolines using eggshell-based nano-magnetic solid acid catalyst via anomeric-based oxidation

Article abstract of DOI:10.1007/s11164-019-04049-y

Abstract: In the present research, the eggshell as a hazardous waste by European Union regulations was converted to a valuable catalyst, namely nano-Fe₃O₄@(HSO₄)₂. The as-prepared catalyst, first, was characterized using different techniques, including Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Back-titration method confirmed the loading of a high surface density of acidic group, namely 8.8?mmol HSO₄ per gram of the catalyst. The catalytic property of the as-prepared catalyst was examined in the synthesis of 2-amino-3-cyanopyridines via anomeric-based oxidation (ABO), and hexahydroquinolines derivatives. High yield, short reaction time, solvent-free condition, waste to wealth, and optimization with the design of experiment are the major advantages of the present work. Taken together, these results suggest the conversion of waste to wealth products around the world and usage in organic transformation. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-019-04049-y

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-04049-y
One‑pot synthesis of 2‑amino‑3‑cyanopyridines
and hexahydroquinolines using eggshell‑based
nano‑magnetic solid acid catalyst via anomeric‑based
oxidation
Tahere Akbarpoor1 · Ardeshir Khazaei1 · Jaber Yousef Seyf2 · Negin Sarmasti1 ·
Maryam Mahmoudiani Gilan1
Received: 6 August 2019 / Accepted: 23 November 2019
© Springer Nature B.V. 2019
Abstract
In the present research, the eggshell as a hazardous waste by European Union reg-
ulations was converted to a valuable catalyst, namely nano-Fe3O4@(HSO4)2. The
as-prepared catalyst, frst, was characterized using diferent techniques, including
Fourier-transform infrared spectroscopy (FT-IR), X-ray difraction (XRD), energy-
dispersive X-ray spectroscopy (EDX), feld emission scanning electron microscopy
(FESEM), and transmission electron microscopy (TEM). Back-titration method
confrmed the loading of a high surface density of acidic group, namely 8.8 mmol
HSO4 per gram of the catalyst. The catalytic property of the as-prepared catalyst was
examined in the synthesis of 2-amino-3-cyanopyridines via anomeric-based oxida-
tion (ABO), and hexahydroquinolines derivatives. High yield, short reaction time,
solvent-free condition, waste to wealth, and optimization with the design of experi-
ment are the major advantages of the present work. Taken together, these results
suggest the conversion of waste to wealth products around the world and usage in
organic transformation.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-019-04049-y) contains supplementary material, which is available to authorized users.
* Ardeshir Khazaei
khazaei_1326@yahoo.com
1
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
2
Department of Chemical Engineering, Hamedan University of Technology, Hamedan, Iran
Vol.:(0123456789)
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T. Akbarpoor et al.
Graphic abstract
Keywords Eggshell · Nano-Fe3O4@Ca(HSO4)2 · Hexahydroquinoline · 2-amino-3-
cyanopyridine
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One-pot synthesis of 2-amino-3-cyanopyridines and…
Introduction
Multicomponent reactions (MCRs) are chemical transformations which involve
three or more reactants to react, providing diverse arrays of compounds. MCR is
an important component in organic transformations and plays a key role in syn-
thesis of heterocyclic moieties which in turn leads to chemical libraries contain-
ing a variety of biologically active components [1, 2]. On the other hand, MCRs
are economically viable, high convergence with high bond-forming-index (BFI)
[3] which has seen a resurgence of interest. Quinoline and its derivatives are a
primary moiety in several natural products and medications, widely utilized in the
pharmaceutical synthesis [4]. Quinolines with a 1,4-dihydropyridine (1,4-DHP)
framework have numerous pharmaceutical properties [5]. Several methods have
been proposed for the synthesis of quinolines, but each of them has shortcomings
that include long reaction times, use of organic solvents, poor performance, harsh
reaction conditions, expensive catalysts, etc. [6].
2-aminopyridines (2-APs) are key initial moieties in the synthesis of nitro-
gen heterocyclic compounds [7]. For instance, 2-aminopyridines are used in the
synthesis of pharmaceuticals, such as piroxicam, sulfapyridine, tenoxicam, and
tripelennamine [8]. Some decorated 2-AP is called 2-amino-3-cyanopyridines
(2-A-3-CPs) which have interesting pharmacological properties [9]. The prepa-
ration of 2-A-3-CP can be traced back to the work of Kambe and Saito in the
modifed Chichibabin synthesis [10]. They synthesized 2-A-3-CP from separated
arylidene malononitrile intermediate in a multicomponent reaction (MCR). Their
methodology has disadvantages, including the use of benzene as a solvent, long
reaction time, and low to moderate yield. 2-A-3-CPs have biological activities
such as dual-target activities against VEGFR2 and Src [11], a potent inhibitor of
HIV-1 integrase [12], antimicrobial agents [12], novel IKK-β inhibitors [13], A2A
adenosine receptor antagonists [14], and antiproliferative efect.
Although several methodologies have been reported for the synthesis of these
molecules in the literature [15], these methods are limited to moderate yield, and
long reaction time and use of volatile organic solvents (benzene [10], toluene [16],
ethanol [13, 16–18], acetic acid [19], and 1,4-dioxane [20], 2,2,2-trifuoroethanol
[21], dimethoxyethane [22]). On the other hand, 2-A-3-CP derivatives are synthe-
sized using various catalyst, including the use of TBBDA and PBBS in solvent-
free condition [9], Ti(dpma)(NMe2)2, Ti(dpm)(NMe2)2, and DMU [16, 23], cop-
per nanoparticles [24], grindstone technology [25], ytterbium perfuorooctanoate
[17], nano-Fe3O4 [18], [Fe3O4-SiO2-(CH2)3Im]C(CN)3 [26], cellulose sulfuric
−
acid [27], Pd(OH)2 [22], ClO4 /Al-MCM-41 [28], graphene oxide [29], urease
[30], hexadecyldimethylbenzyl ammonium bromide (HDMBAB) [31], Cu(I) [32],
and fructose/maltose [33]. But many of the methods are sufering from drawbacks
such as longer reaction time, especially difculty in catalyst preparation and sepa-
ration. Our research group, recently, developed nano-Fe3O4@(HSO4)2 from the
eggshell powder as a solid acid catalyst so that it was used in the synthesis of
indazolo[1,2-b]-phthalazinetrione derivatives [34]. Accordingly, the aim of this
research project has therefore been to investigate the efcacy of nano-Fe3O4@
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T. Akbarpoor et al.
(HSO4)2 in the synthesis of hexahydroquinolines and 2-amino-3-cyanopyridines
derivatives. On the other hand, this research examines the signifcance of solvent-
free condition, diferent solvents, temperature, and the amount of catalyst on the
yield and the time of the chosen organic transformations.
Experimental section
General remarks
Ferrous chloride tetrahydrate (FeCl2·4H2O), ferric chloride hexahydrate
(FeCl3·6H2O), ammonia (28 vol %), benzaldehyde, acetophenone, dimedone, etha-
nol, acetone, chloroform, and chlorosulfonic acid prepared from Merck Company.
The reaction progress was monitored by TLC (EtOAc/n-hexane, 3/10) method. The
1HNMR, 13CNMR, and IR techniques together with a melting point were used to
characterize the synthesized compounds. Spectral data provided in supporting
information.
Preparation of Fe3O4 nanoparticles
The co-precipitation method [35] was used for preparation of the Fe3O4 magnetic
nanoparticles. First, a solution was prepared by dissolving 11.3 g FeCl3·6H2O and
5.6 g FeCl2·4H2O in 100 mL deionized water at 80 °C. After the complete dissolu-
tion of the mentioned iron salts, 25 mL of ammonia was added to the mixture at
once. A black dispersion of nano-Fe3O4 was obtained during 2 h at 80 °C under
nitrogen atmosphere. Afterward, the resultant magnetic nanoparticles were collected
using an external super magnet. The black magnetic nanoparticles were washed sev-
eral times with water and acetone and fnally dried in the oven.
Preparation of eggshell powder
Eggshells were immersed in boiling distilled water for 2 h and washed with it. The
eggshells were dried in an oven at 120 °C for 2 h and milled using a cutting mill
and then dried at 120 °C to obtain a constant weight. To remove any residue organic
compounds, to a 100 mL dichloromethane in a 250-mL Erlenmeyer fask the egg-
shell powder was added and the mixture was homogenized in an ultrasound bath for
2 h. The eggshell powder was dried in an oven at 120 °C after separation through
fltration.
Preparation of Fe3O4@eggshell
A mixture was prepared by adding 1 g of the prepared eggshell powder in the
previous step to 100 mL water and stirred for 10 min. Then, 0.5 g of prepared
nano-Fe3O4 was added to the mixture and dispersed using an ultrasound bath for
15 min and fnally continuously stirred for 2 h at 60 °C. Eggshell powder (CaCO3)
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One-pot synthesis of 2-amino-3-cyanopyridines and…
attaches to the nano-Fe3O4 surface via electrostatic (columbic) and electrodynam-
ics forces [36]. These forces are strong enough to prevent separation of CaCO3
from the nano-Fe3O4 core. Finally, the resultant nano-Fe3O4@eggshell was dried
in an oven at 90 °C after fltration.
Preparation of Fe3O4@Ca(HSO4)2
To 100 mL of dried CH2Cl2, 1 g Fe3O4@eggshell was added and stirred for
15 min. Then, controlling the mixture temperature at 0 °C, 0.66 mL chloro-
sulfonic acid was gently added to the mixture. The temperature of the reaction
should be hold at 0 °C to remove all gas from the reaction. The reaction mixture
was stirred continuously for 24 h after exhausting all gases. The reaction between
CaCO3 and ClSO3H is as follows: ClSO3H + CaCO3 → CaCl2 + Ca(HSO4)2 + HCl
[34]. The obtained Fe3O4@Ca(HSO4)2 nanoparticles were separated from the
mixture via a super magnet; then, it was dried in an oven after washing several
times with water and CH2Cl2. Observation of gas generation during addition of
chlorosulfonic acid confrms the production of HCl [34]. The procedure for the
synthesis of nano-Fe3O4@Ca(HSO4)2 is shown in Fig. 1.
General synthesis of 2‑amino‑3‑cyanopyridines derivatives
At solvent-free condition, 1 mmol benzaldehyde, 1 mmol acetophenone,
1.5 mmol ammonium acetate, and 1 mmol malononitrile (benchmark reaction 1)
together with the 0.05 g as-prepared catalyst were added to a test tube at 90 °C
(optimum reaction condition). Until the completion of reaction progress, it was
monitored by a thin-layer chromatography (TLC) technique. The magnetic cata-
lyst, then, was separated using a super magnet and dried in an oven after washing
with water and ethanol. The fnal product was purifed trough recrystallization in
ethanol.
Fig. 1 Synthesis of nano-Fe3O4@Ca(HSO4)2
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T. Akbarpoor et al.
General procedure for the synthesis of hexahydroquinoline derivatives
At solvent-free condition, 1 mmol aldehyde, 1 mmol ethyl acetoacetate, 1 mmol
dimedone, and 1.5 mmol ammonium acetate (benchmark reaction 2) together with
0.05 g catalyst were added to a test tube at 90 °C (optimum reaction condition).
The progress of the reaction was checked via TLC, and after the completion of the
reaction, the magnetic nanoparticles were separated using a super magnet, washed
with water and ethanol, and dried in an oven. Finally, the pure product was obtained
through recrystallization in ethyl acetate. All hexahydroquinoline derivatives were
synthesized at the optimum reaction condition which was obtained for benchmark
reaction 2.
Results and discussion
In the present research, frst, the eggshell powder was coated on the surface of mag-
netic nano-Fe3O4, and then CaCO3 as the main part of the eggshell was converted
to Ca(HSO4)2 through reaction with ClSO3H. Accordingly, a solid nano-magnetic
acid catalyst (Fe3O4@Ca(HSO4)2) was synthesized and used in the organic trans-
formations. That is, the eggshell turned into a solid, green, and environmentally
friendly solid acid catalyst [34]. Based on the back-titration method, 5.18 mmol
–SO4H group was loaded per gram of the prepared catalyst. Of more interest here
was the evaluation of catalytic activity of the as-synthesized catalyst in the synthesis
of 2-amino-3-cyanopyridine and hexahydroquinoline derivatives.
Characterization of the as‑prepared catalyst
In this research, the infrared spectroscopy (IR), feld emission scanning electron
microscopy (FESEM), transmission electron microscopy (TEM), and energy-disper-
sive X-ray spectroscopy (EDX) techniques were used for characterization of the as-
synthesized catalyst.
Infrared (IR)
To identify the presence of various functional groups in the as-prepared catalyst,
the IR spectroscopy was used. Figure 2 shows the IR spectra of nano-Fe3O4, egg-
shell, nano-Fe3O4@eggshell, and nano-Fe3O4@Ca(HSO4)2 from top to down,
respectively. The IR spectrum of Fe3O4@eggshell inherits some functional
groups as present in the IR spectra of Fe3O4 and eggshell. The wave number of
1152 cm−1 is related to S=O in the –SO3H group. In addition, wave numbers from
3000 to 3600 cm−1 confrm the OH of the –SO3H group. These results imply the
conversion of CaCO3 to Ca(HSO4)2 in the synthesis of nano-magnetic catalyst.
The functional groups shown by a vertical dash-dotted rectangles (868, 1411, and
2522 cm−1) are present in the eggshell, nano-Fe3O4@eggshell, and nano-Fe3O4@
1 3

One-pot synthesis of 2-amino-3-cyanopyridines and…
Fig. 2 IR spectra of Fe3O4, eggshell, Fe3O4@eggshell, and Fe3O4@Ca(HSO4)2
Ca(HSO4)2. This can be attributed to incomplete conversion of CaCO3 in the
presence of chlorosulfonic acid [37]. The generated Ca(HSO4)2 is solid so that
the ClSO3H has to difuse through solid Ca(HSO4)2 to complete the reaction.
Accordingly, the reaction between ClSO3H and CaCO3 is controlled through dif-
fusion which in turn leads to an incomplete reaction.
Fig. 3 Field emission scanning electron microscopy (FESEM) and transmission electron microscopy
(TEM) of the as-synthesized nano-Fe3O4@Ca(HSO4)2 MNPs
1 3

T. Akbarpoor et al.
Field emission scanning electron microscopy (FESEM) and transmission electron
microscopy (TEM)
The FESEM and TEM are useful techniques in size, shape, and morphology char-
acterization of nanoparticles. TEM provides so useful information, in particular,
about the structure of the hybrid materials. Figure 3 illustrates the FESEM (left) and
TEM (right) images of the as-synthesized nano-Fe3O4@Ca(HSO4)2. FESEM repre-
sents a spherical shape, while TEM shows a core–shell structure for the nanoparti-
cles. Nano-Fe3O4, and Ca(HSO4)2 form the core and shell part of the nanoparticles,
respectively. The aggregation of nanoparticles in TEM image can be attributed to
the hydrogen bond formation between HSO4 groups on the nanoparticles surface.
The TEM image provides evidence for the formation of the as-synthesized catalyst
with a core–shell structure.
Energy‑dispersive X‑ray spectroscopy (EDX)
The EDX technique provides some information about chemical elements and their
relative composition. The accuracy of the obtained results can be afected by some
various factors such as the chemical nature of the sample. Figure 4 shows the EDX
spectrum of the as-prepared catalyst. The O, C, Fe, S, and Ca are the major constitu-
ent atoms, providing consistent evidence for the synthesis procedure. To measure
the surface density of HSO4 groups, back-titration technique was used. 30 mL water,
frst, was added to a 0.1 g of the as-synthesized catalyst, and the resultant mixture
was stirred for 1 h. 10 mL NaOH, then, was added to the mixture and stirred up to
the point at which the solution pH was fxed. The solid catalyst, then, was sepa-
rated from the mixture using an external magnet. Two drops of chemical indicator,
fnally, (phenolphthalein) was added into the mixture, and the solution was titrated
Fig. 4 The energy-dispersive X-ray spectroscopy (EDX) of Fe3O4@Ca(HSO4)2 MNPs
1 3

One-pot synthesis of 2-amino-3-cyanopyridines and…
Table 1 Efect of various
Entry
Solvent
Time (min)
5
Yielda (%)
60 °C
solvents on the time and yield
of reaction 1 (in the presence of
a catalyst)
1
–
85
2
3
4
5
6
EtOAc
CH3CN
H2O
n-Hexane
EtOH
Trace
Trace
–
Trace
Trace
aIsolated yield
Table 2 Efect of various
Entry
Solvent
Time (min)
Yielda (%)
60 °C
solvents on time and yield of
reaction 2 (in the presence of a
catalyst)
1
–
5
10
10
60
7
94.64
49.23
46.23
–
68.6
77.84
2
3
4
5
6
EtOAc
CH3CN
H2O
n-Hexane
EtOH
5
aIsolated yield
against 1.2 mL HCl 0.1 N. Hence, the surface density of acidic groups identifed
as 8.8 mmol/g catalyst ((10×0.1−1.2×0.1)/0.1). This quantity shows a large sur-
face density toward the many cases of SO3H-based reported catalyst in the litera-
ture [34]. The more acidic group leads to a more active catalyst in favor of organic
transformations.
Evaluation of the catalytic activity of nano‑Fe3O4@Ca(HSO4)2
Efect of solvent on the reaction
In order to investigate the efect of solvents on the reaction yield, two benchmark
reactions were considered. The reaction among benzaldehyde, acetophenone,
ammonium acetate, and malononitrile (reaction 1) and also the reaction among
benzaldehyde, ethyl acetoacetate, dimedone, and ammonium acetate (reaction 2)
were selected as representative reactions. The Fe3O4@Ca(HSO4)2 was used as the
nano-catalyst, and the reactions were carried out in various solvents, including etha-
nol, ethyl acetate, acetonitrile, water, and n-hexane. The results of the investigated
experiments are listed in Tables 1 and 2 for reaction 1 and reaction 2, respectively.
Generally, the usage of solvents leads to the low reaction yield. For each benchmark
reaction, six cases were tested: reaction at the solvent-free condition, and in the
1 3

T. Akbarpoor et al.
presence of ethyl acetate, acetonitrile, water, n-hexane, and ethanol as solvent. The
as-prepared catalyst was used in all six experiments. The solvent-free condition pro-
vides the lowest time and highest reaction yield for both benchmark reaction 1 and
benchmark reaction 2. For the frst benchmark reaction, we fnd no product in the
presence of all six tested solvents. It should be emphasized that benzaldehyde has a
dual role, including solvent and reactant in the benchmark reaction 1 and benchmark
reaction 2. In the matter of this, the solvent-free condition was chosen for further
analysis of the reactions.
Optimization of the reaction condition
Although the optimization of the reaction condition can be done using one-factor-
at-a-time method, this method is not efcient, and the cross-efect of factors is not
seen. Hence, the central composite design (CCD), in the present work, as a response
surface method was used to optimize the both benchmark reaction conditions. Based
on the numerical optimization techniques, the optimal condition for benchmark
reaction 1 was achieved at 90 °C and 0.05 mol percent of the catalyst. The best value
of the temperature and the amount of the catalyst are 71 °C and 0.05 mol percent,
respectively, for the benchmark reaction 2. Figure 5 provides the 2D and 3D graphs
of the benchmark reaction 1 (a and b) and benchmark reaction 2 (c and d) for yield
versus temperature and the amount of the catalyst, respectively. In both reactions,
the yield has a direct relation with the amount of catalyst, while there is an optimum
Fig. 5 a 2D and b 3D graphs for yield versus temperature and the amount of the catalyst. (a and b for
benchmark reaction 1; c and d for benchmark reaction 2)
1 3

One-pot synthesis of 2-amino-3-cyanopyridines and…
point for the yield versus temperature. The obtained optimum reaction conditions
were used to synthesize the diferent derivatives.
It is assumed that the optimum reaction condition to be the same for all the
2-amino-3-cyanopyridines derivatives. Accordingly, diferent benzaldehydes with
acetophenone, ammonium acetate, and malononitrile were reacted in the presence
of the as-prepared catalyst at the optimum condition (0.05 and 90 °C). The reac-
tion times and yields were between 5 and 15 min, and 53–89, respectively (Table 3).
Table 3 Synthesized diferent 2-amino-4,6-diphenylnicotinonitrile derivatives at the optimum bench-
mark reaction condition
product
1
2
3
4
5
m.p.
Yield
Time
182-184
180-187
89.4
183-187
66.68
8
246-251
65.58
10
188-191
71.75
8
85
5
10
product
6
7
8
9
10
m.p.
Yield
Time
198-200
79.34
10
195-197
77.65
10
138
62
241-243
75.80
10
135-138
65
10
8
15
product
11
12
13
14
m.p.
Yield
Time
137-139
166-168
63
128
67.69
13
232-237
67.71
10
189-191
89.07
5
75
5
10
product
16
17
18
19
20
m.p.
Yield
Time
247-262
63.54
5
242-243
89.07
15
192-194
53
8
161-163
63.04
10
190-191
78.85
13
product
21
22
m.p.
Yield
Time
202-203
85.18
13
193-194
85.14
10
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T. Akbarpoor et al.
Table 4 Synthesized diferent hexahydroquinoline derivatives at the optimum benchmark reaction condi-
tion
product
1
2
3
4
5
m.p.
Yield
Time
218-220
94.64
3
205-207
84.54
5
205-206
87.63
5
186-189 [40]
260-266
86.88
5
75
5
product
6
7
8
9
10
m.p.
Yield
Time
242-244 [41]
240-243 [40]
234-236 [42]
257-260
91.52
5
206-208
96.5
7
91.54
7
85.4
7
95
9
product
11
12
m.p.
Yield
Time
257-262
98.4
7
231-234
67.97
9
These results imply that the as-prepared catalyst involved in the control step of the
reaction which in turn leads to the reduction of activation energy and the reaction
time. Yield, time, melting point, and the structures of synthesized derivatives are
illustrated in Table 3. In a similar manner, the hexahydroquinoline derivatives were
synthesized at the optimal reaction condition (0.05 and 71 °C). Results are listed
in Table 4, with the reaction times and yields between 3 and 9 min, and 68–98%,
respectively. Table 4 illustrates the yield, time, melting point together with the struc-
ture of hexahydroquinoline derivatives. Results confrm the efciency and involve-
ment of the as-prepared catalyst in the slowest step of the reaction. Reducing organic
transformation times leads to an increase in the number of recipe cycles in the
industrial production. Conversion of waste to wealth (preparation of the catalyst)
and utilizing it in the synthesis of 2-amino-3-cyanopyridines and hexahydroquino-
line derivatives are the major objective of the present work.
Proposed mechanism
The suggested plausible mechanism for the synthesis of 2-amino-3-cyanopyridines
is shown in Fig. 6, and the possible mechanism for hexahydroquinoline is shown in
Fig. 7. Interaction of oxygen atom electrons in benzaldehyde with HSO4 groups on
the catalyst surface provides an active site to attack the malononitrile, and dimedone
to benzaldehyde in benchmark reaction 1, and benchmark reaction 2, respectively.
1 3

One-pot synthesis of 2-amino-3-cyanopyridines and…
Fig. 6 The proposed mechanism for 2-amino-3-cyanopyridine
Fig. 7 Possible mechanism for hexahydroquinoline
1 3

T. Akbarpoor et al.
(a)
(b)
Fig. 8 FT-IR spectra of the original and recycled catalyst in the synthesis of a HHQ and b 2-A-3-CP
This plausible interaction triggered the multicomponent reaction which, in turn,
leads to the formation of products. It should be emphasized that the production of
2-amino-3-cyanopyridines derivatives take places through anomeric-based oxida-
tion (ABO) mechanism [38]. Intermediates I and II have diastereomers which are
shown in Fig. 6. It has been shown that the R (I) isomer has a higher oxidation rate
than S (II) isomer. In the ABO mechanism, in the other hand, H2 is generated which
is attributed to the hydride transfer owing to the internal molecular orbital (MO)
electron transfer in agreement with Marcus theory [39–41].
Retrieval of the catalyst
An efcient catalyst has to perform its role several times without reduction in its
activity. Accordingly, the as-prepared catalyst performance was examined in the pre-
sent work. After the completion of the benchmark reactions, added to the mixture
was 20 mL of hot ethanol to dissolve all components except the catalyst. So, the as-
prepared catalyst was recovered using an external magnet and dried in an oven after
washing several times with ethanol. Recovered catalyst was used in three cycles, and
the reaction yield was recorded for both benchmark reactions (94, 93, and 91% for
the benchmark reaction 1 and 85, 87, and 79% for the benchmark reaction 2). This
result confrms the stability of the as-prepared catalyst in diferent cycles. The FT-IR
technique, also, was used to investigate the stability of the catalyst in each cycle. The
identical FT-IR spectra (Fig. 8a and b) in all cycles confrm the chemical stability of
the as-prepared catalyst.
Conclusion
The current study found a route to the conversion of eggshell waste to a valuable
solid catalyst. Diferent metrics confrmed the stability and efciency of the as-pre-
pared solid acid catalyst in the organic transformations. The as-prepared catalyst,
strictly speaking, has a high potential to be used in organic synthesis. The opti-
mum reaction condition, as the present work, should be identifed via the design of
1 3

One-pot synthesis of 2-amino-3-cyanopyridines and…
experiment. Using the as-prepared catalyst, the reaction time can be considerably
reduced. High yield, short reaction time, solvent-free condition, wastes to wealth
conversion, and optimization with the design of expert are the major advantages of
the present work. Hope this work motivates the researcher to prepare catalyst from
the available waste in the world. So, further investigation and experimentation into
waste to wealth conversion is strongly recommended.
Acknowledgements The authors gratefully acknowledge the Bu-Ali Sina University Research Council
and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis
(CEDEFMCS) for providing support for this work.
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