Green bio-based synthesis of Fe2O3@SiO2-IL/Ag hollow spheres and their catalytic utility for ultrasonic-assisted synthesis of propargylamines and benzo[b]furans

Article abstract of DOI:10.1002/aoc.4029

A novel magnetic hybrid system containing nano-magnetic Fe₂O₃ hollow spheres, silica shell, [pmim]Cl ionic liquid and silver nanoparticles was synthesized and characterized. The silver nanoparticles were prepared via biosynthesis usi

Full text of DOI:10.1002/aoc.4029

Received: 28 May 2017
DOI: 10.1002/aoc.4029
Revised: 14 July 2017
Accepted: 17 July 2017
F U L L P A P E R
Green bio‐based synthesis of Fe2O3@SiO2‐IL/Ag hollow
spheres and their catalytic utility for ultrasonic‐assisted
synthesis of propargylamines and benzo[b]furans
Samahe Sadjadi1
| Majid M. Heravi2
| Masoumeh Malmir2
1 Gas Conversion Department, Faculty of
Petrochemicals, Iran Polymer and
Petrochemicals Institute, PO Box 14975‐
112, Tehran, Iran
2 Department of Chemistry, School of
Science, Alzahra University, PO Box
1993891176, Vanak, Tehran, Iran
A novel magnetic hybrid system containing nano‐magnetic Fe2O3 hollow
spheres, silica shell, [pmim]Cl ionic liquid and silver nanoparticles was synthe-
sized and characterized. The silver nanoparticles were prepared via biosynthe-
sis using Achillea millefolium flower as reducing and stabilizing agent. The
hybrid system was successfully used as an efficient and reusable catalyst for
promoting green ultrasonic‐assisted A3 and KA2 coupling reactions as well as
benzo[b]furan synthesis. It was found that decoration of the magnetic core with
non‐magnetic moieties decreased the maximum saturation magnetization.
However, the catalyst was still superparamagnetic and could be simply sepa-
rated from the reaction mixture using an external magnet. The heterogeneous
nature of the catalyst was also confirmed by studying its reusability and stability
and the leaching of silver. Use of aqueous media, high yields, short reaction
times, broad substrate tolerance and low required amount of catalyst are the
merits of this protocol.
Correspondence
Samahe Sadjadi, Gas Conversion
Department, Faculty of Petrochemicals,
Iran Polymer and Petrochemicals
Institute, PO Box 14975‐112, Tehran, Iran.
Email: samahesadjadi@yahoo.com
Majid Heravi, Department of Chemistry,
School of Science, Alzahra University, PO
Box 1993891176, Vanak, Tehran, Iran.
Email: mmh1331@yahoo.com
KEYWORDS
A3 and KA2 coupling reactions, benzo[b]furan, biosynthesis, magnetic nanoparticles, propargylamine
1 | INTRODUCTION
high surface areas and low densities. In this regard, the
most challenging issue is the aggregations of hollow
Core–shell magnetic nanoparticles exhibit exceptional
properties including high surface area, remarkable mag-
netic susceptibility and coercivity.[1] They have found
various applications in a diverse range of research fields
such as sensors, drug delivery, diagnosis, immobilization
of biologically active species, magnetic separation and
most importantly catalysis.[2–4] Utilization of magnetic
nanoparticles in catalysis facilitates the recovery and
separation of the catalyst and makes the procedure
cost‐effective and clean.[5–7] To date, various magnetic
nanoparticles and magnetic core–shell hybrids with a
variety of sizes, morphologies and magnetic properties
have been developed. In this context, hollow magnetic
nanoparticles are attracting increasing attention due to
their outstanding features such as tiny particle sizes,
magnetic nanoparticles, which can be suppressed by
surface modification and introduction of organic
functionalities.[6]
In the last decade, multicomponent reactions have
received considerable attention as an effective way to
achieve molecular complexity through simple and readily
available starting materials in one‐pot procedures.[8] As
important starting materials, acetylenes have a diverse
range of applications in multicomponent reactions and
organic transformations, such as click reactions, Suzuki,
Heck and Sonogashira reactions, A3 coupling reactions,
etc. Among organic reactions, an A3 coupling reaction, a
three‐component coupling reaction of aldehydes, amines
and alkynes, is a promising pathway for the synthesis of
propargylamines. Propargylamines are considered as
Appl Organometal Chem. 2017;e4029.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4029

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SADJADI ET AL.
important intermediates with utility for the synthesis of
more complicated chemicals including biologically
attractive nitrogen‐containing compounds such as herbi-
cides, fungicides, restricted peptide isosteres, pyrroles,
indolizines, oxotremorine analogues as well as natural
products.[9–13] Generally, in the literature, diverse meth-
odologies using various catalysts such Zn‐, Ir‐, Ni‐, Cu‐,
Ag‐, Au‐ and Fe‐based catalysts have been reported for
promoting A3 coupling reactions.[9,14–16] In this line, some
novel catalysts including sulfonate‐based Cu(I) metal–
organic frameworks,[17] Cu2O/nano‐CuFe2O4,[18] Cu(II)
Schiff base complex immobilized on graphene oxide,[19]
CuI catalysts supported on protonated trititanate nano-
tubes,[20] copper nanoparticles supported on starch micro-
particles,[21] Cu(II) chloride,[22] magnetic Fe3O4@Au
nanoparticles[23] and magnetically separable CuO nano-
particles supported on graphene oxide[24] have been
recently introduced.
The main challenges in most of these previously
reported protocols are the need for high temperature, long
reaction times, inert atmosphere, some toxic solvents or
costly media such as ionic liquids or transition or precious
metals and the homogeneous nature of the catalyst.[25]
Therefore, developing a novel, efficient, rapid and green
protocol for the synthesis of propargylamines is of great
importance.
simplicity, rapidness, minimization of waste, high yields
and purity of products.
In continuation of systematic research on the develop-
ment of efficient and heterogeneous nanocatalysts[33–37]
for promoting various chemical transformations and
introducing green and cost‐effective protocols,[6,33,38]
herein we report a novel magnetic hybrid catalyst,
h‐Fe2O3@SiO2‐IL/Ag, prepared through the synthesis of
nanomagnetic Fe2O3 hollow spheres followed by coating
them with a silica shell, conjugation of [pmim]Cl ionic
liquid and immobilization of Ag(0) nanoparticles via a
biosynthetic approach. The catalytic utility of the novel
catalyst for promoting green and ultrasonic‐assisted
synthesis of propargylamines from reaction of amine,
phenylacetylene and aldehyde (Scheme 1a) as well as the
synthesis of benzo[b]furans through reaction of amine,
phenylacetylene and salicylaldehydes (Scheme 1b) is
studied. Furthermore, the reusability and stability of
the catalyst as well as silver leaching are investigated
to elucidate the nature of the catalysis. Notably, the
comparison of the performance of h‐Fe2O3@SiO2‐IL/Ag
with some of the previously reported ones was
accomplished.
2 | EXPERIMENTAL
A3 coupling reactions can be exploited for the synthe-
sis of benzofurans. These heterocycles are important
pharmacophores and clinically applied drugs, which are
prepared via A3 coupling reaction followed by intramolec-
ular cyclizations.[26,27] In this context various catalysts
such as CuI nanoparticles[28,29] and hierarchically porous
sphere‐like copper oxide[30] can be applied. Therefore,
designing novel and efficient methods for the preparation
of these compounds is of great interest.
Utilization of ultrasonic irradiation as an efficient,
green and clean unconventional procedure for promoting
organic transformations is a growing field in green
chemistry.[31,32] In ultrasonic chemistry, the cavitation
effect is of great influence. Such ultrasonic irradiation
can result in the formation of high local temperatures
and pressures inside bubbles which accelerate mass trans-
fer and turbulent flow in the liquid.[32] Ultrasonic‐assisted
procedures benefit from various advantageous including
2.1 | Materials and instrumentation
All chemicals, including FeCl3⋅6H2O, sodium acetate
trihydrate, trisodium citrate dihydrate, tetraethyl
orthosilicate (TEOS), toluene, acetone, ethanol, ethylene
glycol, urea, AgNO3, NH3⋅H2O, aldehydes, amines and
phenylacetylene, were of analytical grade, purchased
from Sigma‐Aldrich and used without further purifica-
tion. The progress of all organic reactions was monitored
using TLC with commercial aluminium‐backed plates of
silica gel 60 F254, using UV light. Melting points were
determined in open capillaries using an Electrothermal
1
9100 without further corrections. H NMR spectra were
obtained using a Bruker DRX‐400 spectrometer at 400
and 100 MHz, Supporting information.
The catalyst was characterized using various tech-
niques including scanning electron microscopy (SEM)/
energy‐dispersive X‐ray (EDX) analysis, Fourier
SCHEME 1 A3 and KA2 coupling
reactions for the synthesis of (a)
propargylamines and (b) benzo[b]furans

SADJADI ET AL.
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transform infrared (FT‐IR) spectroscopy, vibrating sample
magnetometry (VSM), X‐ray diffraction (XRD), thermo-
gravimetric analysis (TGA), Brunauer–Emmett–Teller
(BET) measurements and inductively coupled plasma
atomic emission spectrometry (ICP‐AES). SEM/EDX
images were obtained with a Tescan instrument, using
Au‐coated samples and an acceleration voltage of 20 kV.
FT‐IR spectra were recorded with a PerkinElmer Spec-
trum 65 instrument. BET analysis was carried out using
a Belsorp Mini II instrument. The degassing process was
performed by heating the catalyst at 423 K for 3 h. Room
temperature powder XRD patterns were obtained using a
Siemens D5000 with Cu Kα radiation from a sealed tube.
TGA was carried out using a Mettler Toledo instrument
with a heating rate of 10 °C min−1 from 50 to 800 °C
under nitrogen atmosphere. The magnetic properties of
the catalyst and h‐Fe2O3 were characterized using VSM
(Lakeshore7407) at room temperature. The ultrasonic
apparatus used for in this work was a Bandelin HD 3200
with output power of 150 W and tip TT13.
the unreacted silica and purify h‐Fe2O3@SiO2 core–shell,
it was washed three times with EtOH–H2O and then dried
at 80 °C for 12 h in an oven.
2.4 | Synthesis of 1‐methyl‐3‐
(trimethoxysilylpropyl)imidazolium
chloride ([pmim]cl)
[pmim]Cl was prepared according to the literature.[40]
Typically, N‐methylimidazole (1 mol) was mixed with
(3‐chloropropyl)trimethoxysilane (1 mol) at room temper-
ature. Then, the resulting mixture was refluxed at 95 °C
overnight. Upon completion of the reaction, the mixture
was cooled to ambient temperature. The pure [pmim]Cl
was obtained after washing with diethyl ether and drying
under vacuum at 40 °C.
2.5 | Synthesis of h‐Fe2O3@SiO2‐IL
To synthesize h‐Fe2O3@SiO2‐IL (Figure 1c), 2 (2 g) was
dispersed in EtOH (250 ml) and then sonicated for 0.5 h.
After that, the suspension was stirred vigorously at room
temperature in a round‐bottom flask. Subsequently, a
solution of [pmim]Cl (6 g) in deionized water (100 ml)
and NH3⋅H2O (1 ml) was introduced to the suspension
and the resulting mixture was stirred for 36 h. After com-
pletion of the reaction, the resulting product was magnet-
ically collected and washed three times with EtOH–H2O.
The wet powder was then dissolved in 50 ml of methanol
and stirred at room temperature for 0.5 h. During the stir-
ring process, 50 ml of diethyl ether was added into the
flask. Then, the final product (3) was magnetically col-
lected, washed three times with diethyl ether and dried
at 80 °C for 12 h in an oven.
2.2 | Synthesis of Nanomagnetic Fe2O3
hollow spheres
The nanomagnetic Fe2O3 hollow spheres (h‐Fe2O3) were
prepared via a previously reported solvothermal pro-
cess.[6] Briefly, FeCl3⋅6H2O (5 mmol) was dissolved in eth-
ylene glycol (70 ml) in a flask. Then, a mixture of
trisodium citrate dihydrate (1.5 mmol), sodium acetate
(30 mmol) and urea (17 mmol) was added to the solution.
Subsequently, the brown mixture was stirred energetically
for 1 h, transferred to a Teflon‐lined stainless steel auto-
clave (150 ml capacity) and kept at 220 °C overnight.
Upon completion of the process, the reactor was cooled
and the resulting product (1; Figure 1a) was filtered,
washed three times with EtOH–H2O and dried at 80 °C
for 24 h in an oven.
2.6 | Preparation of Achillea millefolium
flowering plant extracts
Fresh leaves of A. millefolium were collected from Alborz
city, Iran. Initially, the A. millefolium flowers (2 g) were
crushed in a porcelain mortar. The obtained powder was
then suspended in deionized water (100 ml) and boiled
at 80 °C for 1 h. The concentrated extract (4; Figure 1e)
was then cooled and filtered.
2.3 | Synthesis of h‐Fe2O3@SiO2 Core–
Shell
The preparation of h‐Fe2O3@SiO2 was performed accord-
ing to a previously reported method[39] with slight modifi-
cation. Typically, h‐Fe2O3 (1 g) was dispersed in a mixture
of ethanol (50 ml), deionized water (20 ml) and NH3
(6 ml). Notably, the pH of the resulting mixture was kept
at ca 11. Subsequently, to achieve high dispersion, the
mixture was sonicated at ambient temperature for 0.5 h.
Then, TEOS (2 g) was added slowly into the obtained light
brown mixture, which was continuously stirred at room
temperature for 12 h in air. At the end of the process,
the as‐prepared h‐Fe2O3@SiO2 core–shell (2; Figure 1b)
was simply collected using an external magnet. To remove
2.7 | Loading of ag nanoparticles on h‐
Fe2O3@SiO2‐IL: Synthesis of h‐Fe2O3@SiO2‐
IL/Ag
Synthesis and immobilization of silver nanoparticles were
achieved through the following procedure. Initially,
h‐Fe2O3@SiO2‐IL (1 g) was introduced into a solution of
Ag(NH3)2NO3 (0.1 g) in deionized water (20 ml). The

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SADJADI ET AL.
FIGURE 1 Possible formation process of h‐Fe2O3@SiO2‐IL/Ag hollow spheres
resulting mixture was then stirred at room temperature
for 0.5 h. It is postulated that electrostatic attraction kept
the [Ag(NH3)2]+ ions adsorbed on the surfaces of h‐
Fe2O3@SiO2‐IL. To reduce the silver salt and furnish
Ag(0) nanoparticles, A. millefolium extract was employed
as a reducing and stabilizing agent. Typically, the fresh
extract (2 ml) was added into the suspension. The
mixture was then stirred for 12 h. Finally, the product
(5; Figure 1d) was magnetically collected, washed three
times with EtOH–H2O and dried at 60 °C for 12 h. The
general synthetic procedure of h‐Fe2O3@SiO2‐IL/Ag is
illustrated in Figure 1.

SADJADI ET AL.
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Then, the resulting mixture was subjected to ultrasonic
irradiation at a power of 100 W. The progress of the reac-
tion was continuously monitored by TLC. After comple-
tion of the reaction, the mixture was cooled to room
temperature and the catalyst was magnetically separated.
After that, the solution was extracted using ethyl acetate
(5 ml). The combined organic layer was diluted with hot
ethanol to give the crude product. The diluted solution
was purified by recrystallization using ethanol to afford
pure benzofurans.
2.8 | General procedure for synthesis of
Propargylamine
A catalytic amount of nanomagnetic h‐Fe2O3@SiO2‐IL/
Ag (25 mg) was added to a mixture of amine (1.0 equiv.),
acetylene (1.1 equiv.) and aldehyde or ketone (1.0 equiv.)
in water (10 ml). The reaction mixture was then
ultrasonicated at 100 W for 10 min (the progress of the
reaction was monitored by TLC). At the end of the reac-
tion, the mixture was cooled to room temperature and
the mixture was diluted with hot ethanol (10 ml). The sep-
aration of the catalyst was easily performed using an
external magnet. Notably, the recovered catalyst could
be washed with ethanol and reused after dying for subse-
quent reaction runs. The purification of propargylamine
was accomplished by recrystallization from hot ethanol.
3 | RESULTS AND DISCUSSION
3.1 | Catalyst characterization
Initially, the morphology of h‐Fe2O3@SiO2 was studied
using SEM. It can be clearly seen from Figure 2(a) that
h‐Fe2O3@SiO2 particles exhibited spherical morphology.
Interestingly, h‐Fe2O3@SiO2‐IL/Ag also possessed spheri-
cal morphology indicating that combining IL and Ag(0)
nanoparticles did not induce considerable morphology
change and the spherical morphology of h‐Fe2O3@SiO2
was preserved. Notably, in h‐Fe2O3@SiO2‐IL/Ag small
2.9 | General procedure for synthesis of
2,3‐Disubstituted Benzofurans
To a solution of salicylaldehyde (2 equiv.), acetylene (1.5
equiv.) and amine (1 equiv.) in 5 ml of water, NaOH (1.0
equiv.) and h‐Fe2O3@SiO2‐IL/Ag (25 mg) were added.
FIGURE 2 (a) SEM image of h‐Fe2O3@SiO2 and (b) SEM image of h‐Fe2O3@SiO2‐IL/ag. (c) EDX analysis of h‐Fe2O3@SiO2‐IL/Ag

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non‐spherical aggregates can also be observed, which can
be attributed to the unattached IL and the organic com-
pounds of the flower extract (Figure 2b).
The elemental mapping analysis of the catalyst is
depicted in Figure 3. The good dispersion of Si species
can confirm the formation of the silica shell. Moreover,
the abundance of silver species indicated the efficiency
of IL for anchoring the silver species. Notably, Ag is dis-
tributed almost uniformly on the surface of the catalyst.
The FT‐IR spectrum of h‐Fe2O3@SiO2‐CD/Ag is
depicted in Figure 4. This spectrum clearly exhibited the
characteristic bands of silica shell, i.e. the bands at
1089 cm−1, which can be assigned to Si─O stretching,
and the bands at 980 and 810 cm−1, which can be
attributed to the bending vibrations of the Si─O─Si
bond.[1] Moreover, Fe─O stretching vibration can be
confirmed by observing strong absorption bands at
The h‐Fe2O3@SiO2‐IL/Ag catalyst was also investi-
gated using EDX analysis (Figure 2c). The formation of
magnetic nanoparticles can be confirmed by observation
of signals of Fe and O atoms. Notably, the Fe2O3 magnetic
nanoparticles were also confirmed using more precise
techniques such as XRD. The presence of Si and O atoms
can be indicative of the formation of SiO2 shell. The
appearance of N, Si and C signals in EDX analysis can
be assigned to the presence of IL. Finally, observation of
Ag signal can establish the immobilization of Ag(0)
nanoparticles.
FIGURE 3 Elemental mapping analysis of the catalyst

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FIGURE 4 FT‐IR spectrum of h‐Fe2O3@SiO2‐IL/Ag
FIGURE 6 TGA analysis of h‐Fe2O3@SiO2‐IL/Ag
470–590 cm
.
−1 [6] The band at 3463 cm−1 is representative
(1.4%), occurring below 200 °C, can be assigned to the loss
of surface hydroxyl groups and adsorbed water molecules.
The weight loss of about 3.5% can be due to the
degradation of IL. Hence, the content of organic motif in
h‐Fe2O3@SiO2‐IL/Ag was calculated to be about 3.5 wt%.
ICP‐AES analysis was exploited for measuring the
content of silver in the catalyst. To prepare a sample for
analysis, a known amount of h‐Fe2O3@SiO2‐IL/Ag was
digested in concentrated hydrochloric and nitric acids
solution. Then, the obtained extract was analysed using
ICP‐AES. The silver content was estimated to be 5 wt%.
To elucidate whether decoration of the surface of
h‐Fe2O3 with SiO2 shell and with IL and Ag(0) nanoparti-
cles can alter the magnetic property, h‐Fe2O3@SiO2‐IL/Ag
was studied at room temperature using VSM, and its mag-
netic features compared with those of h‐Fe2O3 (Figure 7).
As can be seen, the maximum saturation magnetiza-
tion (Ms) values of h‐Fe2O3 and h‐Fe2O3@SiO2‐IL/Ag
are about 45 and 22 emu g−1, respectively. These
results indicated that incorporation of non‐magnetic
component can markedly reduce the magnetic property
of h‐Fe2O3. However, the hysteresis loops of both
of surface hydroxyl groups. Moreover, the bands at
2976 cm−1 can be assigned to ─CH2 stretching and is
indicative of the presence of IL in the structure of the
catalyst. The observed band at 1654 cm−1 is assigned to
the C═N (imine) functionality and can confirm the conju-
gation of IL.
The formation of Ag(0) as well as h‐Fe2O3 was clearly
confirmed from the XRD pattern (Figure 5). The peaks at
30.3°, 35.6°, 43.2°, 54.0°, 57.3°, 63.0° and 74.6° (labelled as
‘F’) are indicative of the {220}, {311}, {400}, {422}, {511},
{440} and {533} planes of the typical cubic structure of
hematite (JCPDS card no. 39–1346).[6] The peaks labelled
as ‘A’ are the characteristic peaks of Ag(0) nanoparticles
(JCPDS card no. 04–0783). It is worth noting that accord-
ing to a previous report,[41] the broad halo detected at
2θ = 5–20° (labelled as *) can be due to the formation of
amorphous silica and IL. The Debye–Scherrer equation
was employed for calculating the average particle size of
Ag(0) nanoparticles. This value was determined to be
35 nm.
The thermal stability of h‐Fe2O3@SiO2‐IL/Ag
was investigated using TGA. As shown in
Figure 6, h‐Fe2O3@SiO2‐IL/Ag exhibited two degradation
steps over the range 30–800 °C. The initial weight loss
h‐Fe2O3 and h‐Fe2O3@SiO2‐IL/Ag exhibited
a
superparamagnetic behaviour with their re‐dispersion
FIGURE 7 VSM analysis of (a) h‐Fe2O3 and (b) h‐Fe2O3@SiO2‐
IL/Ag
FIGURE 5 XRD pattern of h‐Fe2O3@SiO2‐IL/Ag

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SADJADI ET AL.
stability in solution, without aggregation. Moreover, no
obvious changes in the coercivity from the enlarged
view of the central hysteresis loop for h‐Fe2O3 and
h‐Fe2O3@SiO2‐IL/Ag were observed.
Using BET analysis, the textural features of
h‐Fe2O3@SiO2‐IL/Ag were determined. Figure 8 illus-
trates the nitrogen adsorption–desorption isotherm of
the catalyst. This isotherm, which is of type II with H3
hysteresis loops, clearly confirms the porous structure of
the catalyst.[42] The calculated average pore diameter, spe-
cific surface area and total pore volume of h‐Fe2O3@SiO2‐
IL/Ag are presented in Table 1.
were selected to study the necessity of the catalyst and for
optimizing the reaction conditions. First, the model reac-
tions were carried out in the absence of the catalyst. The
results established that no desired products were obtained
in the absence of the catalyst, indicating that the utiliza-
tion of the catalyst was essential for promoting the reac-
tion and generation of the desired products. Notably,
ultrasonic irradiation was selected as an efficient, green
and rapid procedure for performing the reactions. A com-
parison of the yields of the model products under conven-
tional reflux and stirring conditions with those of
ultrasonic irradiation clearly established that using ultra-
sonic irradiation could markedly accelerate the rate of
the reaction and improve the yield of the desired products.
Interestingly, no by‐products were observed under this
unconventional condition.
The high efficiency of ultrasonic irradiation was
attributed to the cavitation phenomenon.[31,43] This phe-
nomenon includes generation, growth and collapse of
cavities. This can cause high local temperatures and pres-
sures and focus vert large amounts of energy from the
conversion of kinetic energy of liquid motion into heating
of the contents of the cavities.[43]
Then, the reaction conditions were optimized for both
model reactions. For this purpose, the yields of the model
products on altering the reaction variables such as sol-
vent, power of ultrasonic irradiation and catalyst amount
were compared. In Figure 9, the results for optimization
of the model synthesis of propargylamine are depicted.
As shown, the best results were obtained using water as
a green solvent. In this solvent, increasing the amount of
the catalyst from 15 to 25 mg had a positive effect on the
yield of the product. However, further increase in this
value had no significant effect on the yield of the product.
Moreover, increasing the power of ultrasonic irradiation
from 50 to 100 W improved the yield of the reaction. How-
ever, this trend was not steady and a further increase in
power did not alter the yield of the product. Hence,
performing the reaction in water in the presence of
3.2 | Catalytic activity
Considering the importance of propargylamines and
benzo[b]furans from the synthetic and biological points
of view, the synthesis of propargylamine derivatives from
reaction of amines, acetylenes and aldehydes and the syn-
thesis of benzo[b]furans through reaction of amines, acet-
ylenes and salicylaldehydes were selected to investigate
the catalytic performance of h‐Fe2O3@SiO2‐IL/Ag. Ini-
tially, two model reactions, i.e. reaction of
phenylacetylene, benzaldehyde and morpholine and reac-
tion of salicylaldehyde, phenylacetylene and morpholine,
FIGURE 8 Nitrogen adsorption–desorption isotherms of h‐
Fe2O3@SiO2‐IL/Ag
TABLE 1 Textural properties of h‐Fe2O3@SiO2‐IL/Ag
SBET
Total pore
Average pore
Catalyst
(m2 g−1) volume (cm3 g−1) diameter (nm)
h‐Fe2O3@SiO2‐ 21
IL/Ag
0.18
35
FIGURE 9 Effects of loading of catalyst, duration of reaction and
solvent for the synthesis of propargylamine

SADJADI ET AL.
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25 mg of the catalyst and using an ultrasonic irradiation of
power 100 W were found to be the optimum reaction con-
ditions. Similarly, the reaction conditions for the synthesis
of benzo[b]furan were optimized. The optimum reaction
variables for this reaction were using 25 mg of the cata-
lyst, an ultrasonic irradiation of power of 100 W and water
as solvent.
Armed with the optimum reaction conditions, the
generality of these two protocols was investigated using
various aromatic and aliphatic aldehydes, acetylenes and
amines with various electron densities and steric features
(Tables 2 and 3). Gratifyingly, all amines, acetylenes and
aldehydes could be successfully used in these protocols
to furnish the corresponding products in excellent yields
in very short reaction times.
Next, to elucidate the merit of h‐Fe2O3@SiO2‐IL/Ag
catalyst and ultrasonic irradiation, the performance of
h‐Fe2O3@SiO2‐IL/Ag for the model synthesis of
propargylamine was compared with that of some of previ-
ously reported catalysts (Table 4). As is evident, using
ultrasonic irradiation could markedly accelerate the reac-
tion rate. Notably, bare h‐Fe2O3 exhibited a catalytic
activity to some extent. However, the performance of
h‐Fe2O3@SiO2‐IL/Ag is superior compared to h‐Fe2O3,
indicating the role of silver nanoparticles in the catalytic
cycle. The h‐Fe2O3@SiO2‐IL/Ag catalyst exhibited cata-
lytic performance comparable to our previously reported
magnetic catalyst,[6] h‐Fe2O3@DA/Ag, implying the effi-
ciency of hybrid magnetic catalysts based on a combina-
tion of h‐Fe2O3 and silver nanoparticles. Compared to
other catalysts presented in Table 4, h‐Fe2O3@SiO2‐IL/
Ag showed higher or comparable catalytic activity. More-
over, this catalyst could promote the reaction at room
temperature in water with no need for inert conditions.
Hence, this protocol can be considered as a mild, green
and rapid strategy. Although Table 4 does not include
all the catalysts used for the synthesis of model
propargylamine, this comparison can demonstrate the
advantageous catalytic activity of h‐Fe2O3@SiO2‐IL/Ag.
Regarding the reaction mechanism for the formation
of benzofurans,[28] it is speculated that the catalyst
induces generation of silver acetylide intermediate which
then undergoes reaction with iminium ion that is pro-
duced in situ through the reaction of salicylaldehyde and
amine. h‐Fe2O3@SiO2‐IL/Ag can also act as a Lewis acid
and catalyse a cyclization reaction via nucleophilic attack
by hydroxyl group to furnish the desired product and the
catalyst.
3.4 | Catalyst reusability
Considering the importance of simple recovery and
reusability of heterogeneous catalysts, the reusability of
h‐Fe2O3@SiO2‐IL/Ag for the model synthesis of
propargylamine and benzo[b]furan was investigated. For
this purpose, the catalyst was recovered after the first
reaction run using an external magnet. The recovered cat-
alyst was washed with EtOH, dried and subjected to the
next reaction run. The reusability of the catalyst was stud-
ied for seven successive runs and the yields of the prod-
ucts obtained using fresh and recycled catalysis were
compared (Figure 10). As is obvious, for both reactions,
the catalyst could be successfully reused with only
slight loss of catalytic activity. Next, to establish the
stability of the reused catalyst, the FT‐IR spectrum of
fresh h‐Fe2O3@SiO2‐IL/Ag was compared with that of
the reused one (Figure 11). Both fresh and reused catalyst
exhibited similar bands in their FT‐IR spectra, implying
that the catalyst preserved its structure upon reuse.
Finally, to study the nature of the catalysis and the
leaching of Ag(0) nanoparticles, ICP‐AES analysis of the
reused catalyst was performed. Interestingly, the results
established almost zero leaching of Ag(0) nanoparticles,
indicating the heterogeneous nature of the catalysis and
the efficiency of immobilized IL for anchoring Ag(0)
nanoparticles on h‐Fe2O3@SiO2.
3.5 | Spectral data for some selected
compounds, Supporting information
3.3 | Reaction mechanism
1‐(1,3‐Diphenylprop‐2‐ynyl)piperidine (Table 2, 6a). Pale
1
Based on previous reports,[44,45] a possible reaction mech-
anism for the synthesis of propargylamines includes ini-
tial activation of the terminal C─H bond of acetylene by
h‐Fe2O3@SiO2‐IL/Ag and subsequent generation of silver
acetylide intermediate. The catalyst can also promote the
formation of imnium ion through the reaction of amine
and aldehyde. Then, the generated imnium ion undergoes
reaction with silver acetylide to afford the corresponding
propargylamine as well as h‐Fe2O3@SiO2‐IL/Ag
(Scheme 2).
yellow oily liquid. H NMR (400 MHz, CDCl3, δ, ppm):
1.45–1.49 (m, 2H), 1.58–1.65 (m, 4H), 2.59 (t, 4H), 4.81
(s, 1H), 7.31–7.40 (m, 6H), 7.53–7.55 (m, 2H), 7.65–7.67
(d, J = 7.6 Hz, 2H).
1‐(3‐Phenyl‐1‐(4‐(3‐phenyl‐1‐(piperidin‐1‐yl)prop‐2‐
ynyl)phenyl)prop‐2‐ynyl)piperidine (Table 2,
6 h).
White solid; m.p. 157–159 °C (lit.[46] 158–160 °C). H
NMR (400 MHz, CDCl3, δ, ppm): 1.47 (m, 2H), 1.59–
1.63 (m, 4H), 2.59 (m, 4H), 4.81 (s, 1H), 7.33–7.35 (m,
3H), 7.52–7.55 (m, 2H), 7.63 (s, 2H).
1

10 of 14
SADJADI ET AL.
TABLE 2 Synthesis of three‐component reaction of aldehyde or cyclic ketone, secondary amine and terminal alkyne catalysed by h‐
Fe2O3@SiO2‐IL/Aga[9,28,44–48]
R1
R2
R3
R4
R5
Product
6a
Time (min)
Yield (%)b
1a: C6H5
H
4a: ─(CH2)5─
5a: C6H5
10
92
1b: p‐cl‐C6H4
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
5a
6b
6c
6d
6e
6f
10
15
18
10
8
92
95
92
90
94
80
90
92
90
88
96
85
82
90
90
90
91
92
90
93
82
92
86
91
90
82
92
85
90
83
79
91
85
82
80
88
90
91
92
1c: p‐NO2‐C6H4
5a
1d: p‐me‐C6H4
5a
1e: p‐MeO‐C6H4
5a
1f: o‐OH‐C6H4
5a
1g: Furfuryl
5a
6g
6h
6i
15
10
15
18
20
10
15
15
15
10
17
25
30
15
15
13
8
1h: p‐OHCC6H4
5a
1i: o‐Naphthyl
5a
1a
5b: p‐CH3−C6H4
6j
1a
5c: p‐F‐C6H4
6k
6l
1a
4b: ─(CH2)2O(CH2)2─
5a
5a
5a
5a
5a
5a
5a
5a
5b
5a
5a
5a
5b
5a
5a
5a
5a
5b
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
1b
4b
6m
6n
6o
6p
6q
6r
6s
6t
1c
4b
1d
4b
1e
4b
1f
4b
1g
4b
1j: m‐NO2‐C6H4
4b
1a
4b
1a
4c: ─(CH2)4─
6u
6v
7a
7b
7c
7d
7e
7f
1a
4d: C2H5
4a
C2H5
2ac: H
2a
4a
10
10
10
15
15
17
13
15
19
15
10
19
20
20
22
22
25
2a
4b
2a
4c
2a
4d
2b: C6H11
4a
2b
4b
7g
7h
7i
2b
4b
2b
4c
2b
4d
7j
2c: ─(CH2)2─me
4a
7l
2c
4b
7m
7n
7o
8a
8b
8c
8d
2c
4c
2c
4d
3a: ─(CH2)4─
4a
3a
4b
3a
4c
3b: ─(CH2)5─
4a
(Continues)

SADJADI ET AL.
11 of 14
TABLE 2 (Continued)
R1
3b
R2
R3
4a
R4
R5
5b
Product
8e
Time (min)
30
Yield (%)b
89
3b
3b
3b
3b
4b
4b
4b
4c
5a
5b
5c
5a
8f
33
35
28
23
88
85
90
92
8g
8h
8i
aReaction conditions: arylaldehydes 1a–j (1.0 equiv.) or aliphatic aldehyde 2a–c (1.0 equiv.) or aliphatic ketone 3a, b (1.0 equiv.),amines 4a–d (1.0 equiv.),
alkynes 5a–c (1.1 equiv.), H2O (20 ml) and h‐Fe2O3@SiO2‐IL/Ag (0.025 g) under ultrasonic irradiation (100 W) at room temperature.
bIsolated yield.
cAqueous formaldehyde (37%, 0.4 ml).
TABLE 3 Synthesis of three‐component reaction of salicylaldehyde, secondary amine and terminal alkyne catalysed by h‐Fe2O3@SiO2‐
IL/Aga
R6
R3
R4
R5
5a
Product
10a
Time (min)
Yield (%)b
Ref.
[28]
9a: H
3a: ─(CH2)5─
40
90
[28]
[30]
[28]
[30]
[28]
[30]
[30]
9b: Br
9c: NO2
9a
3a
3a
5a
5a
5a
5c
5a
5a
5b
10b
10c
10d
10e
10f
35
30
30
30
25
20
30
92
93
85
88
88
90
91
3b: ─(CH2)2O(CH2)2─
9a
3b
3b
3b
3b
9b
9c
10 g
10 h
9c
aReaction conditions: arylaldehydes 1a (1.0 equiv.) or aliphatic ketone 2a (1.0 equiv.), amines 3a (1.0 equiv.), alkynes (1.1 equiv.), H2O (20 ml) and h‐
Fe2O3@SiO2‐IL/Ag(0.025 g) under ultrasonic irradiation (100 W) at room temperature.
bIsolated yield.
TABLE 4 Comparison of h‐Fe2O3@SiO2‐IL/ag with other recently reported acid catalysts for synthesis of propargylamines (Scheme 1)
Reaction
conditions
Time
(min)
Catalyst
amount
Yield
(%)
Catalyst
Ref.
h‐Fe2O3@SiO2‐IL/Ag
H2O/ r.t./ultrasound
Sf/90 °C
12
25 mg
96
96
75
89
89
65
59
91
89
87
95
93
95
83
This work
[6]
h‐Fe2O3@DA/Ag
60
10 mg
h‐Fe2O3
H2O/r.t./ultrasound
Stirrer/90 °C
12
25 mg
This work
[13]
ZnO nanoparticles
120
240
720
20
10 mol%
10 mol%
5 mg
[52]
[49]
[50]
[10]
[51]
[17]
[20]
[18]
[21]
[19]
Immobilized silver on surface‐modified ZnO nanoparticles
Ag‐CIN‐1a
AgI‐pc‐Lb
Reflux/H2O
H2O/40 °C
Toluene/MW/150 °C
Neat/70 °C
3 mol%
0.5 mol%
10 mol%
20 mg
CuNPs/TiO2
420
270
1440
90
ZnS
Reflux/CH3CN
Reflux/EtOH, 90 °C
Solvent‐free, 70 °C
Solvent‐free, 90 °C
THF, 60 °C
Sulfonate‐based cu(I) metal–organic frameworks
CuI catalysts supported on protonated trititanate nanotubes
Cu2O/nano‐CuFe2O4
20 mg
40
10 mg
Copper nanoparticles supported on starch microparticles
Cu(II) Schiff base complex immobilized on graphene oxide
1200
900
0.3 mol%
20 mg
Water, reflux, N2
aAg‐grafted covalent imine network material.
bAg(I)–(pyridine‐containing ligand) complexes.

12 of 14
SADJADI ET AL.
SCHEME 2 Plausible mechanism for synthesis of propargylamines and benzo[b]furans catalysed by h‐Fe2O3@SiO2‐IL/Ag
(m, 2H), 7.58–7.61 (m, 2H), 7.79 (dd, J1 = J2 = 8.4 Hz,
1H), 7.85–7.91 (m, 3H), 8.11 (s, 1H). 13C NMR
(100 MHz, CDCl3, δ, ppm): 24.4, 26.2, 50.8, 62.5, 86,
88.1, 123.3, 125.8, 125.9, 126.7, 127.2, 127.5, 127.7,
128.1, 128.12, 131.8, 132.9, 133.1, 136.3.
N,N‐Diethyl‐1,3‐diphenylprop‐2‐yn‐1‐amine (Table 2,
1
6v). Pale yellow oily liquid. H NMR (400 MHz, CDCl3,
δ, ppm): 1.04 (m, 6H), 2.36–2.62 (m, 4H), 5.19 (s, 1H),
7.15–7.27 (m, 4H), 7.29–7.38 (m, 3H), 7.39–7.41 (m, 2H).
4‐(3‐Phenylprop‐2‐ynyl)morpholine (Table 2, 7c). Yel-
low oil. 1H NMR (400 MHz, CDCl3, δ, ppm): 2.64–2.67 (m,
6H), 3.52 (s, 3H), 3.69–3.71 (m, 1H), 3.77–3.79 (m, 6H),
7.28–7.31 (m, 4H), 7.43–7.46 (m, 2H).
FIGURE 10 Reusability of h‐Fe2O3@SiO2‐IL/Ag catalyst for
synthesis of (a) propargylamine and (b) benzofuran
1‐(1‐Cyclohexyl‐3‐phenylprop‐2‐ynyl)pyrrolidine (Table 2,
1
7i), Colourless liquid. H NMR (400 MHz, CDCl3, δ, ppm):
1.05–1.36 (m, 5H), 1.56–1.63 (m, 2H), 1.75–1.79 (m, 6H),
1.82–2.10 (m, 4H), 2.5–2.98 (m, 4H), 3.36–3.38 (d,
J = 7.6 Hz, 1H), 7.14–7.33 (m, 3H), 7.50–7.63 (m, 2H).
13C NMR (100 MHz, CDCl3, δ, ppm): 24.9, 26.9, 27.1,
28.3, 32.7, 33, 42.9, 51.1, 61.1, 86.1, 88.9, 125.9, 128.9,
129.8, 132.6.
4‐(1‐Phenylhex‐1‐yn‐3‐yl)morpholine (Table 2, 7 m).
1
Yellow oil. H NMR (400 MHz, DMSO‐d6, δ, ppm): 0.97
(m, 3H), 1.45–1.75 (m, 4H), 2.67–2.70 (m, 2H), 2.79–2.83
(m, 2H), 3.82–4.13 (m, 1H), 4.15–4.17 (m, 4H), 7.46–7.50
(m, 3H), 7.62–7.64 (m, 2H).
4‐(1‐(2‐Phenylethynyl)cyclohexyl)morpholine(Table 2,
8f ). Pale yellow oily liquid. 1H NMR (400 MHz, CDCl3, δ,
ppm): 1.28–1.30 (m, 1H), 1.52 (m, 2H), 1.63–1.67 (m, 3H),
1.73 (br.s, 2H), 2.03–2.05 (m, 2H), 2.74 (br.s, 4H), 3.78 (br.
s, 4H), 7.27 (m, 3H), 7.44–7.45 (m, 2H). 13C NMR
(100 MHz, CDCl3, δ, ppm): 22.7, 25.7, 35.4, 46.6, 58.8,
67.4, 86.4, 89.8, 123.4, 127.7, 128.1, 131.7.
FIGURE 11 Comparison of FT‐IR spectra of fresh h‐
Fe2O3@SiO2‐IL/Ag and after seven runs
1‐(1‐(Naphthalen‐3‐yl)‐3‐phenylprop‐2‐ynyl)piper-
idine (Table 2, 6i). Yellow oil. 1H NMR (400 MHz,
CDCl3, δ, ppm): 1.47–1.51 (m, 2H), 1.60–1.67 (m, 4H),
2.64 (t, 4H), 4.97 (s, 1H), 7.36–7.40 (m, 3H), 7.48–7.52

SADJADI ET AL.
13 of 14
4‐(1‐((4‐Fluorophenyl)ethynyl)cyclohexyl)morpholine
(Table 2, 8 h). Yellow oil. H NMR (400 MHz, DMSO‐d6,
studies confirmed that the magnetic catalyst could be eas-
ily separated from the reaction mixture and reused for
seven reaction runs with only slight loss of catalytic activ-
ity. ICP‐AES analysis confirmed suppressed silver
leaching and proved the heterogeneous nature of the
catalysis. High yields, short reaction times, broad sub-
strate scope and low amount of catalyst are other advan-
tages of this methodology. Moreover, using aqueous
media and ultrasonic irradiation rendered this protocol
green and environmentally friendly.
1
δ, ppm): 1.26–1.34 (m, 1H), 1.57–1.62 (m, 2H), 1.69–1.78
(m, 3H), 1.80–1.86 (m, 2H), 2.00–2.02 (m, 2H), 2.78 (s,
4H), 3.70 (br.t, J = 4.2 Hz, 4H), 6.97–7.00 (t, J = 8.6 Hz,
2H), 7.32–7.40 (m, 2H).
4‐(2‐Benzylbenzofuran‐3‐yl)morpholine (Table 3,
10d). Yellow solid, m.p. 107–109 °C (lit.[28] 106–108 °C).
1H NMR (400 MHz, CDCl3, δ, ppm): 3.19 (t, J = 4.5 Hz,
4H, 2 CH2‐N), 3.87 (t, J = 4.5 Hz, 4H, 2CH2‐O), 4.20 (s,
2H, CH2), 7.19–7.34 (m, 7H, ArH), 7.40–7.42 (d,
J = 8 Hz, 1H, ArH), 7.69–7.71 (d, J = 8 Hz, 1H, ArH).
13C NMR (100 MHz, CDCl3, δ, ppm): 31.4, 51.7, 67.0,
112.7, 114.7, 121.5, 125.6, 126.3, 127.6, 127.8, 128.0,
128.2, 137.1, 150.8, 152.1.
4‐(2‐Benzyl‐5‐bromobenzofuran‐3‐yl)morpholine(Table3,
10f).Yellowsolid,m.p.110–112°C(lit.[28] 110–111°C).1HNMR
(400 MHz, CDCl3, δ, ppm):3.14 (t, J = 5 Hz, 4H, 2 CH2‐N), 3.85
(t, J = 5 Hz, 4H, 2CH2‐O), 4.16 (s, 2H, CH2), 7.21–7.53 (m, 8H,
ArH), 7.79 (s, 1H, ArH). 13C NMR (100 MHz, CDCl3, δ, ppm):
32.3, 52.4, 67.6, 113.1, 115.2, 122.4, 126.3, 126.6, 128.0, 128.2,
128.5, 128.6, 137.3, 151.7, 152.2.
ACKNOWLEDGEMENTS
The authors are grateful for partial financial support from
Alzahra University and Iran Polymer and Petrochemical
Institute. M.M.H. is also grateful to Iran National Science
Foundation for an individual grant.
ORCID
Samahe Sadjadi http://orcid.org/0000-0002-6884-4328
Majid M. Heravi http://orcid.org/0000-0003-2978-1157
4‐(2‐Benzyl‐5‐nitrobenzofuran‐3‐yl)morpholine (Table 3,
10 g). Yellow solid, m.p. 118–120 °C (lit.[30] 118–120 °C). 1H
NMR (400 MHz, CDCl3, δ, ppm): 3.19 (t, J = 4.8 Hz, 4H, 2
CH2‐N), 3.87 (t, J = 4.8 Hz, 4H, 2CH2‐O), 4.21 (s, 2H, CH2),
7.27–7.35 (m, 5H, ArH), 7.43–7.45 (d, J = 10 Hz, 1H, ArH),
8.14–8.17 (d, J = 10 Hz, 1H, ArH), 8.57 (s, 1H, ArH). 13C
NMR (100 MHz, CDCl3, δ, ppm): 32.5, 53.1, 68.5, 113.1,
114.6, 122.7, 125.1, 126.5, 127.1, 127.3, 128.1, 128.3, 138.8,
150.7, 151.1.
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How to cite this article: Sadjadi S, Heravi MM,
Malmir M. Green bio‐based synthesis of
Fe2O3@SiO2‐IL/Ag hollow spheres and their
catalytic utility for ultrasonic‐assisted synthesis of
propargylamines and benzo[b]furans. Appl
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