s-Triazinium-based ionic liquid immobilized on silica-coated Fe3O4 magnetic nanoparticles: an efficient and magnetically separable heterogeneous catalyst for synthesis of 2-amino-4,8-dihydropyrano[3,2-b]pyran-3-carbonitrile derivativ

Article abstract of DOI:10.1007/s13738-018-1521-x

We have described a new method to heterogenize s-triazine catalyst by easy preparation of ionic liquid-based s-triazine-immobilized silica-coated Fe₃O₄ magnetic nanoparticles [Fe₃O₄@SiO₂-s-triazinium

Full text of DOI:10.1007/s13738-018-1521-x

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1521-x
ORIGINAL PAPER
s-Triazinium-based ionic liquid immobilized on silica-coated
Fe3O4 magnetic nanoparticles: an efficient and magnetically
separable heterogeneous catalyst for synthesis of 2-amino-4,8-
dihydropyrano[3,2-b]pyran-3-carbonitrile derivatives for antioxidant
and antifungal evaluation studies
Davood Azarifar1 · Hakimeh Ebrahimiasl1 · Roya Karamian2 · Masoumeh Ahmadi‑Khoei2
Received: 16 June 2018 / Accepted: 8 October 2018
© Iranian Chemical Society 2018
Abstract
We have described a new method to heterogenize s-triazine catalyst by easy preparation of ionic liquid-based s-triazine-
immobilized silica-coated Fe3O4 magnetic nanoparticles [Fe3O4@SiO2-s-triazinium chloride]. The structure of the newly
prepared nanoparticles was characterized by Fourier transform infrared, X-ray powder diffraction, scanning electron micros-
copy, transmission electron microscopy, energy dispersive X-ray method, vibrating sample magnetometery and thermo-
gravimetric analysis. These nanoparticles were identified as an efficient catalyst for one-pot three-component synthesis of
4,8-dihydropyrano[3,2-b]pyran derivatives in excellent yields. The catalyst was easily separated by magnetic decantation, and
the recovered nanoparticles were reused for four fresh runs without any significant loss of catalytic activity. The synthesized
dihydropyrano[3,2-b]pyrans were evaluated for their antioxidant and antifungal activities and found they are relatively active.
Keywords Immobilized ionic liquid · s-Triazine-functionalized silica-coated Fe3O4 magnetic nanoparticles ·
4,8-Dihydropyrano[3,2-b]pyrans · One-pot three-component reaction · Magnetic catalyst · Antioxidant · Antifungal
Introduction
(1) high viscosity limiting the catalytic power of the ILs,
(2) homogeneous nature of ILs making the product separa-
tion and catalyst recovery difficult, and (3) high cost due
to the use of relatively large amounts of ILs [10–12]. The
most promising alternative solution to overcome these prob-
lems is the development of IL-based heterogeneous cata-
lysts [13–15]. In this context, the strategy of immobilizing
ILs onto solid supports such as carbon nanotubes,[16–18]
graphene oxide [19, 20], mesoporous silica [21–23], and
for the preparation of various IL-based heterogeneous cata-
lysts, amorphous silica [24, 25], has recently been deployed.
The aforementioned physical and chemical features of ILs
are not retained in these catalysts, but they offer the high
performance of recycling and easy separation making them
practically suitable in continuous industrial processes [26].
Recently, magnetic nanoparticles (MNPs), especially
magnetic nano-metal oxides [27], have found wide appli-
cations as excellent supports for various catalysts and ILs
[28–33], because of their high surface-area that provides
high catalyst loading capacity, magnetic susceptibility, cat-
alytic activity, and long-term stability [34–36]. Moreover,
In recent years, the enhanced environmental concerns have
prompted the development and application of ionic liquids
(ILs) as alternative reaction media and/or as task specific
catalysts in various organic syntheses [1–5]. The research
interest having been developed on ionic liquids is mainly
because of their favorable properties such as intrinsic ion
conductivity, non-volatility, high thermal stability, negligi-
ble vapor pressure, tunable acidity, and selective dissolv-
ability [6–9]. Despite these promising advantages, ILs are
still impeded in their widespread practical applications as
catalysts or reaction media for several drawbacks including:
* Davood Azarifar
azarifar@basu.ac.ir
1
Department of Chemistry, Bu-Ali Sina University,
65178 Hamedan, Iran
2
Department of Biology, Faculty of Science, Bu-Ali Sina
University, 65175/4161 Hamedan, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
these nonmagnetic catalysts can be easily separated and
recycled using an external magnet which prevents from the
tedious process of isolation and cyclization via filtration or
centrifugation [29, 37, 38].
Multi-component reactions (MCRs) have emerged as
efficient tools in the sustainable synthesis of organic and
biologically active compounds including heterocyclic prod-
ucts [39–41]. In organic synthesis, the MCRs have recently
received considerable interest because they offer versatile
and powerful strategy featured by high-synthetic efficiency
and atom-economical assembling of structurally divers and
complex molecules [42].
Scheme 1 Synthesis of 4H-pyrano[3,2-b]pyran-carbonitrilies cata-
lyzed by Fe3O4@SiO2-s-triazinium chloride MNPs
synthesized products was assessed against Fusarium oxyspo-
rum bacteria and the corresponding inhibitory zone values
were determined.
4H-Fused pyrans such as 2-amino-4H-pyrano[3,2-b]
pyran-carbonitrile derivatives belong to an important class
of biologically active heterocyclic compounds [43–45].
These compounds have been shown to exhibit a wide range
of biological and pharmaceutical properties such as anti-
microbial [46], antifungal [47], anti-HIV [48], anticancer
[49], calcium channel antagonist activity [50], antimalarial
[51], anti-diabetic [52], and anti-inflammatory activities
[53]. The methods recently reported for the synthesis of
2-amino-4H-pyrano[3,2-b]pyran-carbonitrile scaffolds are
mainly based on one-pot three-component reactions [46–48,
54]. However, most of these methods suffer from certain
drawbacks such as low yields, high temperature, high cost
of reagents and catalysts, and longer reaction times. There-
fore, the development of more convenient and efficient new
methods for preparation of these compounds appears to be
most challenging. In the last few years, 5-hydroxy-2-hydrox-
ymethyl-4H-pyran-4-one (kojic acid) has found considerable
interest as easily available and biologically active precursor
in the three-component reactions with malononitrile and
aldehydes for the preparation of pharmaceutically important
dihydropyrano[3,2-b]pyran-3-carbonitriles [55, 56].
As a continuation of our interest in developing environ-
mentally benign and efficient methodologies for the syn-
thesis of various heterocyclic compounds and other organic
transformations [57–61], we report, herein, the synthesis of
a new type of magnetically separable s-triazine-based ionic
liquid immobilized onto silica-coated Fe3O4 nanoparticles.
The synthesized Fe3O4@SiO2-s-triazinium chloride MNPs
were successfully examined as heterogeneous recyclable
catalyst for the synthesis of 2-amino-4H-pyrano[3,2-b]
pyran-carbonitrile scaffolds from one-pot three-compo-
nent reactions between aryl aldehydes, malononitrile and
5-hydroxy-2-hydroxymethyl-4H-pyran-4-one (kojic acid) in
water (Scheme 1).
Experimental details
General
Melting points were measured in open capillary tubes using
a BUCHI 510 apparatus. Fourier transform infrared (FT-IR)
spectra were recorded from KBr pellets on a Perkin Elmer
1
GX FT-IR spectrometer. H NMR and 13C NMR spectra
were recorded on 250 and 400 MHz BRUKER AVANCE
instruments at 400 MHz and 100 MHz, respectively, for
samples in DSMO-d6 as a solvent at ambient temperature
using tetramethylsilane (TMS) as internal standard. Scan-
ning electron microscopy (SEM) images were obtained on
an EM3200 instrument operated at 30 kV accelerating volt-
age. Energy-dispersive X-ray (EDX) analysis was carried
out using a FESEM-SIGM (German) instrument. The curves
obtained from thermo-gravimetric analysis (TGA) were
recorded in air using TGA/DTA PYRIS DIAMOND. Mag-
netic measurement of the catalyst was performed using a
vibrating sample magnetometer (VSM) instrument MDKFT.
In addition, high resolution transmission electron micros-
copy (TEM) was conducted on the nanoparticles using a
HRTEM Philips CM30, (300 kV) instrument.
Synthesis of IL‑based s‑triazine‑functionalized
Fe3O4@SiO2 magnetic nanoparticles
The sequential synthesis of the IL-based s-triazine-immo-
bilized silica-coated Fe3O4 nanoparticles is illustrated in
Scheme 2 as explained below.
In the following stage of the present research, we were
encouraged to evaluate the biological activities of the syn-
thesized 2-amino-4H-pyrano[3,2-b]pyran-carbonitriles
4a–j as potential antioxidants using 1,1-diphenyl-2-picryl-
hydrazyl (DPPH) radical scavenging assay as reported by
Mensor et al. [62]. Moreover, the antifungal activity of the
Preparation of magnetic Fe3O4 nanoparticles
The Fe3O4 nanoparticles were prepared by co-precipita-
tion according to the previously reported procedure [63].
In a typical procedure, a mixture of FeCl3·6H2O (5.84 g)
and FeCl2·4H2O (2.15 g) was dissolved in double distilled
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Immobilization of s-triazine onto the Fe3O4@SiO2–(CH2)3–Cl
nanoparticles
A suspension of the above-prepared Fe3O4@
SiO2–(CH2)3–Cl nanoparticles (0.5 g) in toluene (70 mL)
was placed in an ultrasonic bath and irradiated at room tem-
perature for 20 min. Then, to the resulted mixture was added
s-triazine (2 mmol) followed by stirring at 90 °C for 6 h
under N2 atmosphere. Eventually, the mixture was cooled
to room temperature to precipitate the s-triazine-functional-
ized nanoparticles Fe3O4@SiO2-s-triazinium chloride which
were separated by an external magnet, washed with ethanol,
and dried under vacuum at room temperature.
General procedure for synthesis
of 4H‑dihydropyrano[3,2‑b]pyran‑3‑carbonitrile
derivatives
Scheme 2 Sequential preparation of IL-based Fe3O4@SiO2-s-triazin-
ium chloride MNPs
To the mixture of aromatic aldehyde (1 mmol), malononi-
trile (1 mmol), 5-hydroxy-2-hydroxymethyl-4H-pyran-4-one
(kojic acid) (1 mmol) in H2O (5 mL), was added Fe3O4@
SiO2-s-triazinium chloride MNPs (0.02 g), and the resulted
mixture was refluxed at 100 °C for an appropriate time
(Table 4). After completion of the reaction as monitored by
TLC, the catalyst was magnetically separated using an exter-
nal magnet, dried under vacuum, and recrystallized from hot
ethanol to obtain the pure products 4a–k (Table 4).
water (60 mL). Then, to the mixture was quickly added 25%
NH4OH solution (15 mL) and the mixture was vigorously
stirred at 80 °C for 4 h. The precipitated Fe3O4 nanoparticles
were separated with an external magnet and washed with
distilled water and ethanol three times until the pH value
reached the neutral position. Then, the prepared nanoparti-
cles were dried in a vacuum oven at 60 °C.
Modification of the magnetic Fe3O4 nanoparticles
Characterization data
The silica-modification of the prepared Fe3O4 nanoparticles
was performed using the well-known Stӧber’s method with
little modification [64]. First, the as-prepared Fe3O4 nano-
particles (1 g) were dispersed in mixed ethanol (100 mL) and
deionized water (10 mL) containing 2.5 mL 25% ammonia
solution. To the rapidly stirred dispersion, was added tetra-
ethyl orthosilicate (TEOS) (2 mL) and stirring was contin-
ued for 2 h at 60 °C. The resulted Fe3O4@SiO2 magnetic
nanoparticles were separated magnetically, washed repeat-
edly with deionized water and ethanol, and then dried in air
for 4 h.
2-Amino-4-(2,6-dichlorophenyl)-6-(hydroxymethyl)-8-oxo-
4,8-dihydropyrano[3,2-b]pyran-3-carbonitrile (4c)
White solid; mp. 249–251 °C; IR (KBr, cm−1): 3313,
1
3273 (NH2), 3431 (OH), 2195 (CN), 1644 (C=O); H
NMR (400 MHz, DMSO-d6): δ 4.07–4.13 (ABq, 1H, 2J =
16 Hz, CHaliph), 4.15–4.21 (ABq, 2J = 16 Hz, 1H, CHaliph),
5.65–5.69 (t,1H, OH), 5.83 (s, 1H, CHvinyl), 6.35 (s, 1H,
CHaliph), 7.33 (s, 2H, NH2), 7.38–7.59 (m, 3H, CHarom) ppm;
13C NMR (400 MHz, DMSO-d6): 40.1, 52.2, 59.5, 111.6,
118.6, 129.0, 130.6, 132.8, 135.2, 137.6, 145.6, 160.0,
168.1, 169.2 ppm; MS: m/z=364 (M+).
Synthesis of 3-chloropropyl-bonded Fe3O4@SiO2 nanoparti-
cles (Fe3O4@SiO2–(CH2)3–Cl)
2-Amino-6-(hydroxymethyl)-4-(4-nitrophenyl)-8-oxo-4,
8-dihydropyrano[3,2-b]pyran-3-carbonitrile (4d)
Dark brown solid; mp. 243–245 °C; IR (KBr, cm−1): 3337,
3451 (NH2), 3326 (OH), 2194 (CN), 1649 (C=O), 190,
1351 (NO2); 1H NMR (400 MHz, DMSO-d6): δ 4.09–4.13
(ABq, 2J = 16 Hz, 1H, CHaliph), 4.17–4.21 (ABq, 2J =16 Hz,
1H,CHaliph), 5.07 (s, 1H, CHvinyl), 5.69 (s, 1H, OH), 6.35 (s,
1H, CHaliph), 7.38 (s, 2H, NH2), 7.60–7.63 (m, 4H, CHarom),
8.24–8.26 (m, 2H, CHarom) ppm; 13C NMR (400 MHz,
The Fe3O4@SiO2 nanoparticles (1 g) were added to a solu-
tion of 3-(chloropropyl)triethoxysilane (CPTES) (3 mL) in
dried toluene (100 mL) followed by stirring at 60 °C for 4 h
under nitrogen atmosphere. The precipitated chloropropyl-
bonded magnetic nanoparticles Fe3O4@SiO2–(CH2)3–Cl
were separated by a magnet, washed with toluene, and dried
under vacuum.
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Journal of the Iranian Chemical Society
DMSO-d6): δ 40.1, 54.6, 59.0, 110.5, 118.9, 124.1, 129.3,
136.7, 147.1, 147.7, 147.9, 159.3, 168.3, 169.5 ppm; MS:
m/z=341 (M+).
based on the method reported by Mensor et al. [62]. The stock
solutions (2.5 mL) of the samples at different concentrations
(0.2–1 mg mL−1) in methanol was prepared. Then, 1.0 mL of
each compound was mixed with 1 mL of 0.3 mM methanol
solution of DPPH radical with vigorously shaking. Then, the
samples were incubated in the dark at room temperature for
30 min. The absorbance was observed against a blank solution
at 517 nm using the UV/V spectrophotometer. The assay was
carried out in triplicate using ascorbic acid as a standard, and
the antioxidant activity, namely the percentage of inhibition,
was calculated according to the following formula (Table 4),
2-Amino-6-hydroxyme-
thyl-4-(4-hydroxyphenyl)-8-oxo-4,8-dihydropyrano[3,2-b]
pyran-3-carbonitrile (4 g)
Cream solid; mp. 240–242 °C; IR (KBr, cm−1): 3423, 3351
1
(NH2), 3233 (OH), 2200 (CN), 1657 (C=O); H NMR
(400 MHz, DMSO-d6): δ 4.09–4.15 (ABq, 2J = 16 Hz, 1H,
CHaliph), 4.18–4.23 (ABq, 2J = 16 Hz, 1H, CHaliph), 4.64 (s,
1H, CHvinyl), 5.67–5.70 (t, 1H, OH), 6.31 (s, 1H, CHaliph), 7.16
(s, 2H, NH2), 6.67–7.07 (m, 4H, CHarom), 9.49 (s,1H, OH)
ppm; 13C NMR (400 MHz, DMSO-d6): δ 56.0, 59.1, 111.2,
115.5, 115.6, 119.4, 128.8, 131.1, 136.0, 149.5, 157.0, 159.1,
168.1, 169.6 ppm; MS: m/z=312 (M+).
[
(
)
]
AA (%) = 1 − As − Ab /Ac × 100,
in which, As is the absorbance of the reaction mixture con-
taining samples and DPPH, Ab stands for the absorbance
of the mixture containing samples+methanol, and Ac rep-
resents the absorbance of the control sample containing
DPPH + methanol. Additionally, representing the sample
concentration causing 50% inhibition, IC50 value was deter-
mined (Fig. 8).
2-Amino-6-hydroxyme-
thyl-4-(naphthalen-1-yl)-8-oxo-4,8-dihydropyrano[3,2-b]
pyran-3-carbonitrile (4 h)
Antifungal activity
Light purple solid; mp. 252–254 °C; IR (KBr, cm−1): 3290,
3173 (NH2), 3395 (OH), 2204 (CN), 1668 (C=O); 1H NMR
(400 MHz, DMSO-d6): δ 3.89–3.95 (ABq, 2J = 16 Hz, 1H,
CHaliph), 4.08–4.12 (ABq, 2J = 16 Hz, 1H, CHaliph), 5.61–5.64
(t, 1H, OH), 5.76 (s, 1H, CHvinyl), 6.33 (s, 1H, CHaliph), 7.22
(s, 2H, NH2), 7.26–8.35 (m, 7H, CHarom) ppm; 13C NMR
(400 MHz, DMSO-d6): δ 40.1, 56.1, 59.0, 111.4, 119.3, 123.2,
126.0, 126.1, 126.6, 126.8, 128.5, 128.8, 131.1, 133.6, 136.7,
137.0, 149.8, 159.5, 168.3, 169.6 ppm; MS: m/z=346 (M+).
In vitro antifungal activities of the compounds 4a–j were
screened against Fusarium oxysporum cultivated in Potatoes
Dextrose Agar (PDA) medium. The samples were added to the
sterilized cultivation medium at a concentration of 200 ppm.
To make the control groups, double distilled water and DMSO
were added to the plates. After a 7-day incubation at the tem-
perature 27 °C of fungus on culture medium containing sam-
ples, radial growth of fungal mycelium was recorded. The
inhibition rate (%) was calculated using the following formula,
2-Amino-6-hydroxyme-
thyl-4-(naphthalen-2-yl)-8-oxo-4,8-dihydropyrano[3,2-b]
pyran-3-carbonitrile (4i)
Inhibition rate (%) = (R − r∕R) × 100,
where R is the radial growth of fungal mycelia on the con-
trol plate and r is the radial growth of fungal mycelia on the
plate treated with the new derivatives. All the resulting data
summarized in Table 5 are the average of triplicate assays.
Yellow solid; mp. 250–252 °C; IR (KBr, cm−1): 3385, 3190
1
(NH2), 3302 (OH), 2190 (CN), 1642 (C=O); H NMR
(400 MHz, DMSO-d6): δ 4.05–4.11 (ABq, 2J = 8 Hz, 1H,
CHaliph), 4.15–4.21 (ABq, 2J = 16 Hz, 1H, CHaliph), 4.98 (s,
1H, CHvinyl), 5.64–5.67 (t, 1H, OH), 6.34 (s, 1H, CHaliph),
7.85 (s, 2H, NH2), 7.90–7.97 (m, 7H, CHarom) ppm; 13C
NMR (400 MHz, DMSO-d6): δ 40.6, 55.8, 58.9, 59.1, 111.4,
119.3, 125.5, 126.3, 126.5, 126.7, 127.6, 127.9, 128.9,
132.7, 136.5, 138.3, 148.9, 159.2, 168.3, 169.6 ppm; MS:
m/z=346 (M+).
Statistical analysis
Statistical analysis of variance was performed using Student’s
t test by SPSS program and p value<0.05 was regarded to be
significant. Data are expressed as means standard deviation.
Results and discussion
Biological evaluation
Synthesis and characterization of the catalyst
Fe3O4@SiO2‑s‑triazinium chloride
Antioxidant activity
To prepare the Fe3O4@SiO2-supported s-triazinium chlo-
The radical scavenging activities of the synthesized com-
ride MNPs was initially prepared by the co-precipitation
pounds 4a–j were evaluated against the stable DPPH radical
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Journal of the Iranian Chemical Society
of ferrous (Fe2+) and ferric (Fe3+) ions in basic aqueous
solution of NH4OH under reflux condition in deionized
water according to the reported procedure [61]. Then, the
prepared Fe3O4 nanoparticles were coated with the silica
layer on their surface using the well-known Stӧber method
[64], by treatment of Fe3O4 suspension in alkaline ethanol/
water solution with tetraethyl orthosilicate (TEOS). In the
next step, the chloropropyl group as a linker was bonded
to the silicon atom to prepare the Fe3O4@SiO2–(CH2)3–Cl
nanoparticles by treatment of a suspension of Fe3O4@SiO2
nanoparticles in toluene with a solution of 3-(chloropro-
pyl)triethoxysilane (CPTES) in dried toluene. Finally, the
immobilization of s-triazine moiety onto the surface of
Fe3O4@SiO2–(CH2)3–Cl nanoparticles was achieved by
the addition of s-triazine to the suspension of the Fe3O4@
SiO2–(CH2)3–Cl nanoparticles in toluene under ultrasonic
irradiation condition at room temperature to obtain the
Fe3O4@SiO2-s-triazinium chloride MNPs (Scheme 2).
The FT-IR spectra of the bare Fe3O4, Fe3O4@SiO2,
Fe3O4@SiO2–(CH2)3–Cl, and Fe3O4@SiO2-s-triazinium
chloride MNPs shown in Fig. 1 clearly display the char-
acteristic bands around 3422, 1078 and 574 cm−1 ascribed
to the ν(O–H), ν(Si–O), and ν(Fe–O) characteristic bands,
respectively. The appearance of the stretching bands around
2345 and 1078 cm−1 due to the Si–O group indicated that
the nanoparticles were successfully coated with silica
groups on their surface. In addition, the stretching bands
shown at 2800–3000 cm−1 in the IR spectra of Fe3O4@
SiO2–(CH2)3–Cl (1c) and Fe3O4@SiO2-s-triazinium chlo-
ride (1d) nanoparticles are assigned to the aliphatic CH2
group confirming the successful loading of chloropropyl
linker onto the magnetic nanoparticles. Added to this, the
successful immobilization of s-triazine moiety onto the
surface of Fe3O4@SiO2–(CH2)3–Cl nanoparticles is clearly
verified by the appearance of the bands at 1728–1590 cm−1
attributed to the C–N stretching band of the s-triazine group
(Fig. 1d).
In Fig. 2, the X-ray powder diffraction patterns (XRD)
of Fe3O4 and Fe3O4@SiO2-s-triazinium chloride MNPs are
shown. The crystal planes at 2θ = 19.37°, 30.53°, 35.69°,
43.28°, 57.20°, 53.85°, 62.93° corresponding to their Miller
indices (111, 220, 311, 400, 422, 511, 440) respectively,
with including the diffraction peaks typical for amorphous
silica in the range 2θ=20–30°, are related to the pure crys-
talline Fe3O4 nanoparticles. As shown in Fig. 2b, the same
diffraction peaks are present in the XRD pattern obtained
for the Fe3O4@SiO2-s-triazinium chloride nanoparticles.
These diffraction peaks and indexed planes confirm excel-
lent crystallinity of these nanoparticles. The diffraction
peaks of pure Fe3O4 nanoparticles match well with highly
crystalline cubic spinel structure (JCPDS no. 65-3107) [65].
These results provided the evidence that the crystal struc-
ture of pure Fe3O4 did not change after immobilization with
s-triazine moiety. The crystal size of the Fe3O4@SiO2-s-tri-
azinium chloride can be determined from the XRD pattern
using Debye–Scherrer’sequation, which gives the relation-
ship between the peak broadening and the particle size. The
peak width, size and inter planar distance from the XRD
pattern of supported nanoparticles were investigated and
found to be ranging from 30.5° to 62.9° with the achieved
Fig. 1 FT-IR spectra of a Fe3O4, b Fe3O4@SiO2, c Fe3O4@SiO2–(CH2)3–Cl and d Fe3O4@SiO2–(CH2)3-s-triazinium chloride MNPs
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Journal of the Iranian Chemical Society
Fig. 2 XRD Diffraction patterns
of a bare Fe3O4 and b Fe3O4@
SiO2-s-triazinium chloride
MNPs
SiO2
b
(3 1 1)
(4 4 0)
(5 1 1)
(4 2 2)
(2 2 0)
30
(4 0 0)
a
10
20
40
50
2 (degree)
60
70
80
90
Table 1 X-ray diffraction (XRD) data for the Fe3O4@SiO2-s-triazin-
agreement with the SEM image presented in Fig. 3a, the
encapsulated particles of Fe3O4@SiO2-s-triazinium chloride
are well dispersed and exhibit approximately spherical mor-
phology made up of nano-sized particles with an average
diameter of 34 nm. In supporting analysis by transmission
electron microscopy (TEM) conducted on the synthesized
Fe3O4@SiO2-s-triazinium chloride nanoparticles (Fig. 3b),
it has been demonstrated that, these nanoparticles are quasi-
spherical in shape possessing almost a uniform distribution
of particle size. However, as inferred from the presence of
dark spots inside the bright spherical silica thin shell, these
magnetic nanoparticles can be considered to have core–shell
structure.
ium chloride MNPs
Entry
2θ
Peak width
[FWHM]
(degree)
Size (nm)
Inter planer
distance (nm)
1
2
3
4
5
6
30.50
35.60
43.20
53.80
57.20
62.90
0.15
0.90
0.23
0.20
0.35
0.40
58.11
9.34
34.65
45.62
26.15
23.49
0.292741
0.251885
0.209168
0.170190
0.160855
0.295258
The chemical identification of the elements contained in
the catalyst Fe3O4@SiO2-s-triazinium chloride was deter-
mined by energy dispersive X-ray (EDX) analysis. The
EDX spectral pattern shown in Fig. 4, clearly indicated the
chemical characterization of the typical catalyst sample
with the peaks for C, N, O, Si, Fe, Cl elements, confirming
results summarized in Table 1. The average core diameter of
the nanoparticles calculated from the XRD results using the
aforementioned equation was found to be 32 nm.
The morphological structure and particle distribution
of the Fe3O4@SiO2-s-triazinium chloride MNPs were ana-
lyzed by scanning electron microscopy (SEM) analysis. In
Fig. 3 a SEM and b TEM images of Fe3O4@SiO2-s-triazinium chloride MNPs
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Journal of the Iranian Chemical Society
the formation and dispersion of Fe3O4@SiO2-s-triazinium
chloride nanoparticles. Therefore, these results justify the
successful grafting of s-triazinium moiety onto the surface
of Fe3O4@SiO2 MNPs linked by propyl group.
on the surface of the particles, and also due to the function-
alization with triazine moiety. Despite this reduction in Ms
value of Fe3O4@SiO2-s-triazinium chloride nanoparticles,
they still have considerable paramagnetic property to be
magnetically separable from reaction mixture.
The magnetic properties of Fe3O4 and Fe3O4@SiO2-s-tri-
azinium chloride MNPs were studied by vibrating sample
magnetometer (VSM) at 300 K with the field sweeping range
from −9000 to +9000 Oersted (Fig. 5). According to the
magnetization curves shown in Fig. 5, these nanoparticles
perform reasonably high super paramagnetic properties. The
magnetization saturation (Ms) values of the bare Fe3O4 and
Fe3O4@SiO2-s-triazinium MNPs were found to be 56 and
38 emu g−1 respectively. The decrement in the Ms value of
Fe3O4@SiO2-s-triazinium chloride in comparison to the Ms
value of the bare Fe3O4 nanoparticles can be related to the
decrease in the particle size due to the silica layer coated
The thermal gravimetric analysis (TGA) was performed
on Fe3O4@SiO2-s-triazinium chloride nanoparticles to
obtain information about their thermal stability and behav-
ior. According to the TGA pattern shown in Fig. 6, the step-
wise decreasing in the weight percentage of the nanoparti-
cles take place in three consecutive steps from about 100
to 750 °C. It is likely that, the first weight loss of ca. 3% at
about 140 °C is due to the removal of physically adsorbed
solvents and moisture. The second weight loss of about 12%
occurring within the range 200–500 °C (centered at 430 °C)
possibly corresponds to decomposition of organic species
Fig. 4 EDX spectrum of
Fe3O4@SiO2-s-triazinium
chloride MNPs (presence of
signals for Au is allocated to the
sample grid)
Fig. 5 VSM patterns of a
uncoated Fe3O4 and b Fe3O4@
SiO2-s-triazinium chloride
MNPs
60
a
b
40
20
0
-9000
-7000
-5000
-3000
-1000
-20
1000
3000
5000
7000
9000
-40
-60
Applied Field (Oe)
1 3

Journal of the Iranian Chemical Society
Table 2 Screening the reaction parameters for the synthesis 2-amino-
6-hydroxymethyl-8-oxo-4-phenyl-4,8-dihydropyrano[3,2-b]pyran-
3-carbonitrile
and triazine group grafted to the surface of the nanoparticles.
In the final step, the complete decomposition of nanoparti-
cles happens beyond 500 °C. These results clearly verify the
successful grafting of triazine moiety to the silica-coated
Fe3O4 nanoparticles.
H
O
O
O
CN
CN
NH2
CN
O
H
O
+
+
H
O
H
O
O
O
Catalytic activity of Fe3O4@SiO2‑s‑triazinium chlo‑
ride MNPs
P
h
The catalytic activity of the prepared Fe3O4@SiO2-s-tri-
azinium chloride MNPs was examined as heterogeneous
recyclable ionic liquid-based magnetic nanocatalyst in
three-component synthesis of 4,8-dihydropyrano[3,2-b]
pyran-3-carbonitrile derivatives. In the initial step, to screen
the reaction parameters, the three-component condensa-
tion reaction between benzaldehyde, malononitrile, and
5-hydroxy-2-hydroxymethyl-4H-pyran-4-one (kojic acid)
was chosen as model reaction (Table 2). First, we studied
the effect of various solvents such as water, ethanol, and
acetonitrile on the reaction in the presence of Fe3O4@SiO2-
s-triazinium chloride (0.01 g) at room temperature. The best
result was observed when the reaction was performed using
water as the solvent in which the hydrogen bonding prevails
the solvent polarity (entry 1). Next, the temperature effect
was studied by conducting further experiments at 60 and
100 °C in water as the solvent of choice and the optimal
temperature was found to be 100 °C (entry 6). In further
studies, regarding the effect of catalyst loading, the optimal
Entry Catalyst (g) Solvent
Tem-
Time (min) Yield (%)b
perature
(°C)
1
2
3
4
5
6
7
8
0.01
0.01
0.01
0.01
0.01
0.01
0.02
0.02
0.02
0.03
0.02
–
H2O
EtOH
CH3CN
r.t
r.t
r.t
240
240
240
240
120
120
240
90
38
32
25
15
45
76
50
68
Solvent-free r.t
H2O
H2O
H2O
H2O
H2O
H2O
60
100
r.t
60
100
100
9
40
94
10
11
12
40
70
90
40
Solvent-free 100
H2O 100
240
Trace
Conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), Kojic
acid (1 mmol), solvent (5 mL)
aIsolated pure yield
Fig. 6 TGA diagram of Fe3O4@
SiO2-s-triazinium chloride
MNPs
1 3

Journal of the Iranian Chemical Society
O
O
Table 3 Three-component
synthesis of 2-amino-4-aryl-
6-hydroxymethyl-8-oxo-
O
O
NH2
O
A
CN
H
O
- -
.
t
)
e
F
s
SiO
2
r az n um c or
e
hl id
(
ca
t
O
@
4
i
i i
r
3
+
+
A CHO
H
O
H
O
C
N
100 o
C
4,8-dihydropyrano[3,2-b]
CN
H
2O /
r
-
-
pyran-3-carbonitriles catalyzed
by Fe3O4@SiO2-s-triazinium
chloride MNPs in H2O at 100°C
a
1
k
a
4
k
3
2
M.p (oC)
Product (4a–k)
Time Yieldb
(min) (%)
Entry
Ar
Reported
[56, 57, 67]
Found
O
NH2
O
H
O
1
2
C6H5
40
30
40
94 220–222 220–222
94 229–231 230–232
CN
O
4a
4b
4c
O
O
NH2
CN
O
H
O
2,3-Cl2C6H3
2,6-Cl2C6H3
Cl
Cl
O
O
NH2
O
O
3new
97 249–251
98 243–245
–
–
H
H
O
CN
Cl
Cl
O
O
NH2
CN
O
4new
4-NO2C6H4
3-NO2C6H4
20
NO2
O
4d
4e
O
O
NH2
CN
H
O
5
6
30
30
97 241–243 240–242
98 237–239 238–240
NO2
O
O
NH2
CN
O
H
O
4-Cl-3-NO2C6H3
NO2
Cl
O
4f
O
NH2
CN
H
O
O
7new
4-HOC6H4
45
85 240–242
–
H
O
4g
amount of the catalyst was achieved to be 0.02 g and the use
of higher amounts of catalyst (entry 10) did not have any
improving effect on the yield. The indispensable use of the
catalyst Fe3O4@SiO2-s-triazinium chloride in the reaction
was substantiated by conducting the reaction in the absence
of the catalyst which resulted in no detectable amount of the
respective product (entry 12).
1 3

Journal of the Iranian Chemical Society
M.p (oC)
Time Yieldb
Table 3 (continued)
Product (4a–k)
Entry
8new
Ar
Reported
(min) (%)
Found
[56, 57, 67]
O
NH2
O
H
O
1-Naphthyl
30
35
25
98 252–254
97 250–252
–
–
CN
O
4h
O
O
NH2
CN
O
HO
9new
2-Naphthyl
2-Thiophenyl
4-Pyridyl
4i
4j
O
O
NH2
CN
O
HO
10
95 238–240 238–240
93 250–252 251–253
S
O
O
O
NH2
CN
HO
11
25
N
4k
Conditions: aldehyde (1 mmol), malononitrile (1 mmol), kojic acid (1 mmol), catalyst (0.02 g), H2O
(5 mL), 100 °C
aIsolated yield
To establish the scope and generality of the reaction, a
divers series of aldehydes 4a–k bearing different substituents
were reacted in the presence of Fe3O4@SiO2-s-triazinium
chloride catalyst under the aforementioned optimized con-
ditions (Scheme 1). The experimental results summarized
in Table 3 clearly revealed that, all the reactions proceeded
smoothly and the relevant products 4a–k were produced in
excellent yields (85–98%) and relatively short reaction times
(20–45 min). In addition, the heteroaromatic aldehydes 1j
and 1k were also conveniently reacted under the optimal
condition to yield the corresponding products 4j and 4k in
excellent yields (entries 10, 11). As seen in Table 3, the
aldehydes containing electron-withdrawing groups generally
display higher reactivity in comparison to the aldehydes car-
rying electron-releasing groups. The products were charac-
terized on the basis of their physical and spectral (FT-IR, 1H
NMR, 13C NMR, MS) data and compared with the reported
data in the case of the known products.
Proposed reaction mechanism
A plausible mechanism similar to the previously reported
mechanism for other basic catalysts in the same reac-
tion [56, 66], has been suggested to describe the forma-
tion of 2-amino-4-aryl-6-(hydroxymethyl)-8-oxo-4,8-
dihydropyrano[3,2-b]pyran-3-carbonitriles from one-pot
three-component reaction between aromatic aldehydes,
malononitrile, and kojic acid under the catalytic effect of IL-
based Fe3O4@SiO2-s-triazinium chloride MNPs as depicted
in Scheme 3. Initially, deprotonation of malononitrile is
affected by the basic triazinium moiety of the catalyst to
generate the corresponding anion which undergoes dehydra-
tive addition to the aldehyde to furnish 2-arylidenemalononi-
trile intermediate (I). Similarly, the removal of proton from
5-hydroxy group of kojic acid under the same catalytic effect
results in the formation of the enolate ion (II). Subsequently,
nucleophilic addition of the enolate ion (II) to the interme-
diate (I) takes place to form the adduct (III) followed by
consecutive intramolecular cyclization and tautomerization
to yield the expected products.
1 3

Journal of the Iranian Chemical Society
Fig. 7 Recyclability test of Fe3O4@SiO2-s-triazinium chloride MNPs
scavengers, reducers and quenching agents to prevent the
biological systems from the free radical damages [69–71].
In the last few decades, there has been a great deal of
attention towards the production of new types of anti-
oxidant agents without posing any harmful side effects.
2,2-Diphenyl-1-picrylhydrazyl (DPPH) is a free radical,
showing hydrogen acceptor ability towards antioxidants.
Hence, it is commonly used in DPPH assay for measuring
the antioxidant activity of different natural and synthetic
samples [72]. With regard to the promising biological
properties of pyrano[3,2-b]pyran derivatives, we were
encouraged to study the free radical scavenging activity of
the synthesized dihydropyrano[3,2-b]pyran-3-carbonitriles
4a–j (C1–C10) using the DPPH assay. According to the
experimental results summarized in Table 4, and graphical
presentation in Fig. 8, many of these compounds perform
relatively high antiradical properties (16.40–81.54%) in
comparison with ascorbic acid as a standard antiradical
agent (80.16%). In general, the higher antioxidant activ-
ity is reflected in a lower IC50 value. Ascorbic acid, also
known as vitamin C, has been used as a standard with an
IC50 value of 0.127–0.006 mg mL−1 in the present study
exhibiting a lower IC50 value than most of the compounds
which are assessed in the present study (IC50; 0.96 0.09
to 2.43 0.07 mg mL−1) (Fig. 8). As shown in Fig. 8, the
radical scavenging efficiencies of the compounds C1–C10
against DPPH radicals range in descending order as: ascor-
bic acid > 4d > 4c > 4e > 4f > 4b > 4j > 4h > 4i˃4a˃4g.
Experiments were performed in triplicate and expressed
as mean SD. Values in each row with different super-
scripts are significantly different (p ≤ 0.05).
Scheme 3 A possible mechanism for the synthesis of
dihydropyrano[3,2-b]pyran-3-carbonitriles catalyzed by Fe3O4@
SiO2-s-triazinium chloride MNPs
Catalyst recyclability
The recyclability and reusability potentials of the catalyst
Fe3O4@SiO2-s-triazinium chloride were examined for the
model reaction. After the reaction completion, the catalyst
was recovered from the reaction mixture simply using an
external magnet. Then, the separated solid was washed
with hot ethanol and dried at room temperature. The
separated catalyst was reused under the same optimized
conditions for four consecutive fresh runs without any
noticeable drop in the yield of the product and catalytic
activity. The slight decrease in the yield of the product can
be attributed to the normal loss of the product and catalyst
during the work-up process (Fig. 7).
Biological assessment
Antioxidant activity
Antifungal activity
Antioxidants are recognized as an important class of bio-
logically active natural products and synthetic compounds
playing a key role in reducing the risk of chronic diseases
such as cancer and other diseases [68]. Antioxidants are
characterized by their high biological performance as
It is a well-known fact that, many types of fungal bacteria
species such as Fusarium species are hosted by different
kinds of plants and agricultural crops throughout the world
that cause soil-borne diseases of great economic concern.
1 3

Journal of the Iranian Chemical Society
Table 4 Antiradical activity
(%) of the compounds 4a–j
(C1–C10) and ascorbic acid as
standard
Sample
Concentration (mg mL−1
0.2 0.4
)
Average
0.6
0.8
1
C1 (4e)
C2 (4b)
C3 (4c)
C4 (4j)
C5 (4f)
C6 (4h)
C7 (4d)
C8 (4i)
C9 (4g)
C10 (4a)
67.20d 0.50 69.50c 0.78
62.46c 0.06 62.46c 0.06
69.19c 0.15 73.40b 0.81 75.21a 0.77 70.9
64.38b 0.42 66.00b 0.32 67.10a 0.70 65.33
67.27e 0.87 68.65d 0.07 73.79c 0.63 75.84b 0.51 77.96a 0.61 72.7
60.90c 0.21 60.6c 0.310
63.44b 0.24 64.56ab 0.21 65.56a 0.21 63.03
67.35d 0.13 68.45c 0.077 70.34b 0.65 71.05ab 0.21 71.07a 0.49 69.65
57.19b 0.80 58.35b 0.06 58.33b 0.07 60.04a 0.05 60.44a 1.18 58.87
72.43a 0.19 73.48a 0.36
53.68c 0.75 54.17c 0.36
77.46a 0.63 78.44a 0.70 81.54a 1.57 76.67
54.97bc 0.27 56.29a 0.04 54.97b 1.92 54.62
9.8b 1.47
12.1b 1.18
46.5d 3.05
12.68b 0.07 12.1b 0.6
51.17c 1.28 59.68b 0.6
16.4a 0.58
65.04a 0.5
12.62
51.84
36.7e 0.75
Ascorbic acid 80.84a 0.80 81.84a 1.70
81.21a 1.40 80.80a 2.30 80.16a 1.90 80.61
1.8
1.6
1.4
1.2
1
samples performed excellent antifungal activities (49–90%)
as shown in Table 5. Among these samples, the samples
C1 (4e), C8 (4i) and C10 (4a) performed highest antifun-
gal activities in this system at a concentration of 200 ppm.
Usually, most of the old synthetic fungicides are resistant
to environmental degradation through chemical, biological,
and photolytic processes and have human health impacts.
Therefore, our tested samples can be conveniently used as
alternative antifungal drugs to increase the resistance of a
wide variety of crop plants.
1.54
0.8
0.6
0.4
0.48
0.186
0.175
0.164
0.148
0.16
0.149
0.149
0.138
0.124
0.2
0
Experiments were carried out in triplicate and expressed
as mean SD. Values shown in the row with different super-
scripts are significantly different (p≤0.05).
Sample
Fig. 8 Comparison between antioxidant activities (IC50 values) of the
samples (C1–C10) and that of the ascorbic acid as a standard antioxi-
dant agent
Conclusion
In summary, we have successfully immobilized, for the
first time, s-triazine ring onto the magnetic Fe3O4@SiO2
nanoparticles to prepare the s-triazinium-based ionic liq-
uid Fe3O4@SiO2-s-triazinium chloride magnetic nanopar-
ticles. The structure of the synthesized catalyst was fully
characterized by FT-IR, EDX, SEM, XRD, TGA, and VSM
analytical techniques. This newly synthesized nanocatalyst
has been explored as an efficient, versatile and recyclable
heterogeneous nanocatalyst in three-component synthesis
of dihydropyrano[3,2-b]pyran-3-carbonitrile derivatives
in water in excellent yields. The catalyst can be easily
recovered simply by an external magnet and reused four
An area of media, where bacteria are unable to grow, owing
to the presence of a drug which impedes their growth, is
called inhibition zone. Fusarium oxysporum (F. oxysporum)
is one of the soil-borne pathogens that causes serious dam-
ages to the plants and harvests of great economic impor-
tance [73, 74]. Here, the potential antifungal activities of the
synthesized products were assessed and their corresponding
inhibitory zone values were assessed against F. oxysporum
bacteria (Table 5). Accordingly, it was observed that the
solvent dimethyl sulfoxide (DMSO) used as negative control
exhibited no activity against F. oxysporum, while the test
Table 5 Antifungal activities (%) of the synthesized compounds 4a–j
Concentration (ppm) Sample
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
200
90a 1.02 49e 0.86 74C 2.8 76c 2.8 62d 1.7 72c 1.5 61d 1.25 81.21b 1.4 74c 1.12 80b 0.14
1 3

Journal of the Iranian Chemical Society
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