Facile pathway for synthesis of two efficient catalysts for preparation of 2-aminothiophenes and tetrahydrobenzo[b]pyrans

Article abstract of DOI:10.1007/s11164-017-3223-x

Abstract: We report here a new magnetically recyclable catalyst consisting of iron-substituted Keggin-type heteropolyacid (HPA) grafted on modified Fe₃O₄ nanoparticles. The synthesized hybrid nanomaterial exhibited the excellent catalytic efficiency in condensation reaction for the preparation of tetrahydrobenzo[b]pyrans under solvent-free conditions as well as in the synthesis of 2-aminothiophenes via Gewald reaction. It must be noted that, HPA supported magnetite nanoparticles catalyzed the preparation of tetrahydrobenzo[b]pyrans, whereas for Gewald reaction amine-functionalized magnetite nanoparticles acted as a catalyst. Different characterization techniques such as Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used to characterize the hybrid nanomaterial. The reusability of catalyst was affirmed by using in consecutive runs for five times. Performance of prepared catalyst was compared with the various previously reported catalysts; the newly synthesized catalysts found to be most efficient with regard to reaction time, yield and ease of catalyst separation. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-017-3223-x

Res Chem Intermed
https://doi.org/10.1007/s11164-017-3223-x
Facile pathway for synthesis of two efcient
catalysts for preparation of 2‑aminothiophenes
and tetrahydrobenzo[b]pyrans
Hamid Reza Saadati‑Moshtaghin1 · Farrokhzad Mohammadi Zonoz1
Received: 12 August 2017 / Accepted: 4 December 2017
© Springer Science+Business Media B.V., part of Springer Nature 2017
Abstract We report here a new magnetically recyclable catalyst consisting of iron-
substituted Keggin-type heteropolyacid (HPA) grafted on modifed Fe3O4 nanoparti-
cles. The synthesized hybrid nanomaterial exhibited the excellent catalytic efciency
in condensation reaction for the preparation of tetrahydrobenzo[b]pyrans under sol-
vent-free conditions as well as in the synthesis of 2-aminothiophenes via Gewald
reaction. It must be noted that, HPA supported magnetite nanoparticles catalyzed
the preparation of tetrahydrobenzo[b]pyrans, whereas for Gewald reaction amine-
functionalized magnetite nanoparticles acted as a catalyst. Diferent characteriza-
tion techniques such as Fourier transform infrared (FT-IR), X-ray powder difrac-
tion (XRD), feld emission scanning electron microscopy (FESEM), transmission
electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used
to characterize the hybrid nanomaterial. The reusability of catalyst was afrmed by
using in consecutive runs for fve times. Performance of prepared catalyst was com-
pared with the various previously reported catalysts; the newly synthesized catalysts
found to be most efcient with regard to reaction time, yield and ease of catalyst
separation.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/
s11164-017-3223-x) contains supplementary material, which is available to authorized users.
*
Farrokhzad Mohammadi Zonoz
fzmohamadi@yahoo.com
Hamid Reza Saadati-Moshtaghin
h_r_saadati@yahoo.com
1
Department of Chemistry, Faculty of Science, Hakim Sabzevari University,
Sabzevar 96179-76487, Iran
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
Graphical Abstract
Keywords Magnetite nanoparticles · Heteropolyacid · Solvent-free conditions ·
Tetrahydrobenzo[b]pyran · 2-Aminothiophene
Introduction
Choice of an efcient catalyst with appropriate support was one of the early princi-
ples of green chemistry. Based on the nature of the reaction and the catalyst, there
are three classes of catalytic reactions: class 1, in which acid and base catalysts pro-
mote the reaction; class 2, in which the reaction is catalyzed by redox catalysts; and
class 3, hydrogenation reactions.
With increasing environmental concerns, research on multipurpose catalysts and
identifcation of novel catalysts or procedures which could catalyze acidic, basic,
and oxidative reactions would be highly desirable. Therefore, we report herein prep-
aration of two catalysts by one procedure, which possesses all mentioned properties.
Heteropolyacids (HPAs) are a large, fundamental, and interesting class of inor-
ganic compounds which have attracted considerable attention due to their acidic and
redox properties, being studied as homogeneous and heterogeneous catalysts as well
as sorbents [1–7]. HPAs are highly soluble in water and polar solvents and have low
surface area (≤ 10 m2 g−1), hindering their recycling and reuse in catalytic reactions
[1]. Increased surface area can be achieved by dispersing HPAs on solid supports
with high surface area. Therefore, many attempts have been focused on immobi-
lizing HPAs on various solid supports, including MCM-41, montmorillonite, active
1 3

Facile pathway for synthesis of two efcient catalysts for…
R1
CN
O
CN
CN
APSCMNPs
S8
+
+
R2
Solvent-free conditions
R1
R2
NH2
S
Scheme 1 Synthesis of 2-aminothiophenes
O
Ar
O
O
CN
CN
SiW11Fe-APSCMNPs
Solvent-free conditions
O
+
+
Ar
H
CN
O
NH2
Scheme 2 Synthesis of tetrahydrobenzo[b]pyrans
carbon, SiO2, TiO2, zeolites, functionalized polymers, and resins [8–15]. However,
the time required to fltrate such solid catalysts from the reaction mixture is another
problem in this regard.
During the past decade, signifcant considerations have been given to magnetic
nanoparticle (MNPs) as attractive solid supports for immobilization of homogene-
ous catalysts [16–19]. Superparamagnetism is clearly the most important property
making magnetic nanoparticles superior to other solid supports, as they exhibit mag-
netic properties in the presence of an external magnetic feld and can be isolated
from the product solution, but do not retain residual magnetization after removal of
the external feld [20].
There are some reports about polyoxometalates supported on MNPs. In 2011,
Luo et al. reported using surface-modifed Fe3O4 with H3PW12O40 heteropolyacid
as supported catalyst for Friedel–Crafts reactions of indoles [21]. In 2011, Ding and
coworkers studied oxidation of dibenzothiophene with H2O2 by using magnetite-
polyoxometalate nanomaterial [22]. In another report, Kooti et al. studied synthesis
of α-aminophosphonates under solvent-free condition at room temperature using a
nanocatalyst formed of H3PW12O40 heteropolyacid immobilized on surface-modi-
fed CoFe2O4 magnetic nanoparticles [23].
We report herein a procedure for preparation and characterization of iron-substi-
tuted HPA grafted on aminopropyl-functionalized Fe3O4 nanoparticles as a novel
catalyst. In this regard, Fe3O4 nanoparticles were treated with (3-aminopropyl)tri-
ethoxysilane to obtain aminopropyl-functionalized Fe3O4 nanoparticles, as a basic
catalyst. We demonstrated its catalytic efciency in synthesis of 2-aminothiophenes
(Scheme 1). Subsequently, the interaction between amine groups with heteropoly-
acid aforded HPA supported on magnetite nanoparticles as an acidic catalyst, exhib-
iting catalytic performance for preparation of tetrahydrobenzo[b]pyrans via one-pot
three-component reaction under solvent-free condition (Scheme 2).
Tetrahydrobenzo[b]pyrans and 2-aminothiophenes are heterocyclic compounds
that play a central role in drug design. They can be used as efective tools to improve
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
the pharmacological properties of drugs by manipulating their polarity, hydrogen
bonding, and lipophilicity. Tetrahydrobenzo[b]pyrans also serve as anticancer, anti-
coagulant, diuretic, spasmolytic, and antianaphylactic agents [24, 25].
Several methods and diferent catalysts have been reported in literature for syn-
thesis of tetrahydrobenzo[b]pyrans, such as use of microwave [26] or ultrasonic irra-
diation [27], molecular iodine [28], potassium phosphate [29], phenylboronic acid
[30], and tetrabutylammonium bromide [31]. Each of these methods ofers advan-
tages, but most of them sufer from drawbacks such as poor yield, toxicity, and dif-
fcult workup.
To the best of the authors’ knowledge, there are no reports on preparation and
utilization of H5[SiW11FeIII(H2O)O39] (abbreviated H5SiW11Fe) supported on the
surface of aminopropyl-modifed magnetite nanoparticles.
Experimental
Materials and methods
All reagents and solvents were obtained from Merck and Aldrich chemical com-
panies and used without purifcation. Reported yields refer to purifed products.
The obtained products were characterized by comparison of spectral and physi-
cal data with literature values. A Shimadzu 8400S spectrophotometer was used to
record Fourier-transform infrared (FT-IR) spectra from KBr pellets. X-ray difrac-
tion (XRD) patterns were recorded using a Philips PW1730 difractometer. The
magnetic properties of the nanoparticles were measured using a vibrating-sample
magnetometer (VSM, BHV-55; Riken, Japan) in the magnetic feld range of – 8500
to 8500 Oe at room temperature. Field-emission scanning electron microscopy
(FESEM) images of the samples were taken using a Hitachi S-4160. Transmission
electron microscopy (TEM) images of nanoparticles were recorded using a Philips
CM30. The melting point of catalytic reaction products was measured by capillary
tube method using a Barnstead Electrothermal 9200 melting point apparatus. Thin-
layer chromatography (TLC) was used to monitor the progress of catalytic reactions.
Synthesis of iron‑substituted heteropolyacid
Synthesis of K5[SiW11FeIII(H2O)O39]·14H2O
K5[SiW11FeIII(H2O)O39]·14H2O was prepared according to literature procedure
[32]. A sample containing 64.0 g (0.02 mol) K8SiWl1O39·13H2O was dissolved in
125 mL hot (95 °C) water, and 8.15 g (0.0202 mol) solid Fe(NO3)3·9H2O was added
to this solution in small portions. After complete dissolution, the excess precipitate
of iron as hydrated iron(III) hydroxide was fltered. To the cooled fltrate was added
twice its volume of 1:1 (v/v) methanol/ethanol mixture. The precipitated light-yel-
low salt was fltered of and recrystallized thrice from warm (45 °C) water, to which
1 3

Facile pathway for synthesis of two efcient catalysts for…
methanol was added until precipitation began, followed by cooling to 2 °C. The
purifed salt was dried in air.
Preparation of H5[SiW11FeIII(H2O)O39]
Keggin-type H5SiW11Fe acid catalyst was prepared according to previously reported
method [33]. The iron-substituted heteropolyanion K5[SiW11Fe(H2O)O39]·14H2O
was converted to the corresponding acid by passing it through a column of Dowex-
50 W-X8 ion-exchange resin. A sample of K5[SiW11Fe(H2O)O39]·14H2O (3 g) was
dissolved in 60 mL water, then the solution was passed through the resin column in
H+ form. This process was repeated two times. Slow evaporation of the fnal solu-
tion gave pure H5SiW11Fe heteropolyacid.
Preparation of aminopropyl‑modifed silica‑coated magnetite nanoparticles
(APSCMNPs)
Chemical coprecipitation of Fe3+ and Fe2+ ions at molar ratio of 2:1 was applied for
preparation of magnetite (Fe3O4) nanoparticles [34]. The obtained magnetite nano-
particles (MNPs) were silica coated to aford silica-coated magnetite nanoparticles
(SCMNPs) by reported method [35]. (3-Aminopropyl)triethoxysilane (3 ml) was
added to the suspension of obtained SCMNPs (2 g) dispersed in ethanol (100 mL)
under dry nitrogen atmosphere and refuxed for 12 h. The resulting solid was then
magnetically separated, washed three times with ethanol to remove unreacted resid-
ual silylating reagent, then dried at 60 °C.
Supporting iron‑substituted heteropolyacid on APSCMNPs
H5SiW11Fe (1 mmol) was dissolved in 30 mL deionized water then added dropwise
to suspension of obtained APSCMNPs (1 g) in 50 mL deionized water and stirred
for 12 h at room temperature. Finally, H5SiW11Fe-APSCMNPs were magnetically
separated and washed twice with deionized water, then dried at 60 °C.
General procedure for preparation of 2‑aminothiophenes
APSCMNPs (0.05 g) were added to a mixture of aldehyde or ketone (10 mmol),
malononitrile (10 mmol), and sulfur powder (10 mmol). Then, the mixture was
stirred in 60 °C in an oil bath under solvent-free condition for adequate time. After
reaction completion, 10 mL ethanol was added to the mixture, and the catalyst was
easily separated using a magnet. Thereafter, the reaction mixture cooled to room
temperature and was poured into 100 mL ice-water. The fltered crude product was
washed with cold water, dried, and purifed by silica gel column chromatography
with hexane:ethyl acetate (10:1) as eluent.
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
General procedure for preparation of tetrahydrobenzo[b]pyrans
To a mixture of aromatic aldehyde (1.0 mmol), malononitrile (1.0 mmol), and dime-
done (1.0 mmol) was added 0.03 g H5SiW11Fe-APSCMNPs. Then, the mixture was
stirred at 80 °C in an oil bath under solvent-free condition for appropriate time.
After reaction completion as monitored by TLC, the mass was cooled to 25 °C, and
the mixture was dissolved in boiling ethanol; fnally, catalyst was separated using an
external magnet. Afterward, the liquor was poured into ice. The mixture was fltered
to separate the product. The crude product was purifed by recrystallization from
ethanol to obtain pure tetrahydrobenzo[b]pyran derivatives. The purity of the prod-
ucts was determined by comparison of their physical data, viz. melting point, FT-IR,
and 1H and 13C nuclear magnetic resonance (NMR) spectra, with known compounds
in literature [36–38].
Results and discussion
Catalyst preparation and characterization
The procedure used for preparation and characterization of magnetite nanocatalyst is
illustrated in Scheme 3.
In the frst step, Fe3O4 nanoparticles were prepared by chemical coprecipitation of
Fe2+ and Fe3+ in basic solution [34]. Then, to avoid possible oxidation and decom-
position induced by the surrounding environment and prevent further aggregation,
the external surface of the MNPs was coated with a layer of SiO2 to obtain SCMNPs
[35]. Treatment of silanol group of SCMNPs with (3-aminopropyl)triethoxysilane
Scheme 3 Procedure for preparation of H5SiW11Fe-APSCMNPs
1 3

Facile pathway for synthesis of two efcient catalysts for…
Fig. 1 FT-IR spectra of a SCMNPs, b APSCMNPs, and c H5SiW11Fe-APSCMNPs
Table 1 Chemical analysis of
Material
N (mmol/g)
W (mmol/g)
prepared nanomaterial
APSCMNPs
H5SiW11Fe-APSCMNPs
0.68
0.46
-
1.595
aforded APSCMNPs. In the last step, interaction between amine groups of APSC-
MNPs with H5SiW11Fe heteropolyacid gave H5SiW11Fe-APSCMNPs. Protonation
of amine groups gives positively charge ammonium cations, which bind electrostati-
cally to the produced heteropolyanion. It has been shown that heteropolyanion salts
of organic cations are generally insoluble in water [39]. Therefore, excess HPA can
be simply removed by washing the resulting material with water.
FT-IR spectra of the prepared SCMNPs (a), APSCMNPs (b), and
H5SiW11Fe-APSCMNPs (c) are shown in Fig. 1. Two peaks at around 457–590 cm−1
confrm the presence of a magnetite core in all the prepared nanomaterials [40]. The
broad peak at about 1100 cm−1, assigned to Si–O–Si and Si–OH stretching vibra-
tions, demonstrates survival of the SiO2 layer around the magnetite nanoparticles
[41]. The stretching vibrations at about 2935 cm−1 in the spectrum of APSCM-
NPs confrm the anchored propyl groups. The peak attributed to N–H stretching
at 3400 cm−1 exhibits interference from O–H stretching absorbance. In addition,
the peak for N–H bending appears at 1529 cm−1. Keggin-type HPAs showed four
characteristic peaks in the wavenumber region of 800–1100 cm−1, appearing in
the H5SiW11Fe-APSCMNPs spectra (Fig. 1c) at 946 cm−1 (stretching vibration of
W=O), 900, and 815 cm−1 (corner- and edge-sharing W–O–W vibrations) [42]. The
increase in the frequencies of the W–O–W and W=O stretching vibrations of the
prepared nanomaterial in comparison with neat HPAs is due to the strong interaction
between the heteropolyanion and organic cation [43]. These FT-IR spectroscopy
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
results confrm the surface modifcation of the magnetite nanoparticles and prepara-
tion of H5SiW11Fe-APSCMNPs.
The chemical analysis of the prepared nanomaterial is presented in Table 1,
including the loading amount of HPA, which is related to the W content of the pre-
pared nanomaterial. Considering the molar ratio of HPA to W (1:11), the nitrogen to
HPA ratio is approximately 3:1.
Figure 2 shows the X-ray difraction patterns of (a) standard XRD data for mag-
netite [Joint Committee on Powder Difraction Standards (JCPDS) no. 19-0629], (b)
Fe3O4 nanoparticles, and (c) H5SiW11Fe-APSCMNPs. The XRD difractions from
the Fe3O4 nanoparticles are comparable to those of the standard. The series of dif-
fractions at 2θ = 18.36°, 30.29°, 35.69°, 36.82°, 43.30°, 53.69°, 57.38°, 62.98°, and
74.5° correspond to (111), (220), (311), (222), (400), (422), (511), (440), and (533)
refections, respectively.
The difractions can be assigned to the planes of inverse cubic spinel-structured
Fe3O4. As seen in Fig. 2c, only common difractions of Fe3O4 nanoparticles can be
observed, with no characteristic difractions from Kegging-type HPA, demonstrat-
ing that the HPA species are well dispersed on the surface of the APSCMNPs [44].
According to the FESEM images (Fig. 3a), the prepared nanoparticles were
approximately spherical. Also, aggregation resulted in increased size of the
observed nanoparticles. The TEM image of H5SiW11Fe-APSCMNPs presented
in Fig. 3b shows that the average size of these nanoparticles lay in the range of
80–120 nm. Excitingly, the dark spot in the TEM image represents the magnetic
core while the bright sphere shows the thin SiO2 shell. The chemical identity of the
H5SiW11Fe-APSCMNPs was confrmed by EDX analysis (Fig. 3c), indicating coex-
istence of Fe, Si, O, C, N, and W; the presence of W reveals heteropolyacid sup-
ported on the surface of APSCMNPs.
Results of magnetic measurements on the MNPs, APSCMNPs, and
H5SiW11Fe-APSCMNPs are shown in Fig. 4. The magnetization curves of the
Fig. 2 X-ray difraction patterns
of a standard XRD data for
magnetite (JCPDS no. 19-0629),
b Fe3O4 nanoparticles, and c
H5SiW11Fe-APSCMNPs
1 3

Facile pathway for synthesis of two efcient catalysts for…
Fig. 3 a FESEM and b TEM images and c EDX analysis of H5SiW11Fe-APSCMNPs
Fig. 4 Magnetization curves of a MNPs, b APSCMNPs, and c H5SiW11Fe-APSCMNPs
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
nanomaterial show no remanence efect (demonstrating superparamagnetic prop-
erty) with saturation magnetization of about 72, 45, and 25 emu/g for MNPs, APSC-
MNPs, and H5SiW11Fe-APSCMNPs, respectively. The decrease in mass saturation
magnetization can be assigned to presence of the silica shell and functionalized
groups around the magnetite core. This superparamagnetic nature of the obtained
H5SiW11Fe-APSCMNPs is important for its applications, as it can prevent aggrega-
tion and enable rapid redispersion on removal of the magnetic feld [45].
Catalytic experiments
The synthesized APSCMNPs and H5SiW11Fe-APSCMNPs were used for prepara-
tion of 2-aminothiophenes and tetrahydrobenzo[b]pyrans under solvent-free condi-
tion, respectively. The best experimental condition was determined via optimization
of the catalyst amount, reaction time, and various catalysts.
Catalytic activity of APSCMNPs in synthesis of 2‑aminothiophenes
A simple and efcient procedure was applied for synthesis of 2-aminothiophene
derivatives in presence of APSCMNPs. To optimize the conditions, the condensa-
tion reaction of cyclohexanone (10 mmol), malononitrile (10 mmol), and elemental
sulfur (10 mmol) at 60 °C after 2 h under solvent-free condition was used as model
reaction to examine the efect of APSCMNPs catalyst amount (0–0.1 g).
Table 2 presents the efect of the catalyst amount on the synthesis of 2-aminothio-
phenes. According to the results, in absence of catalyst, only trace amount of the
desired product was obtained after 2 h. It was observed that the yield increased with
increasing catalyst amount, with 0.05 g catalyst being sufcient to achieve the maxi-
mum yield.
Then, the efect of time was studied in the reaction of cyclohexanone (10 mmol),
malononitrile (10 mmol), and elemental sulfur (10 mmol) in presence of 0.05 g cata-
lyst at 60 °C (Fig. 5), revealing that the yield increased on prolonging the reaction
time from 0.5 to 4 h. However, the yield decreased when increasing the reaction
time from 2 to 4 h. Therefore, reaction time of 2 h was selected as the best duration
for the reaction.
Table 2 Efect of amount of
Entry
Catalyst (g)
Yield (%)
APSCMNPs on preparation of
2-aminothiophene
1
2
3
4
5
0
8
42
63
88
78
0.01
0.02
0.05
0.1
Reaction conditions: cyclohexanone, malononitrile, and sulfur pow-
der (10, 10, and 10 mmol) were mixed at 60 °C for 2 h under sol-
vent-free condition
1 3

Facile pathway for synthesis of two efcient catalysts for…
Fig. 5 Efect of reaction time on preparation of 2-aminothiophene in presence of 0.05 g catalyst at 60 °C
The generality of the present methodology was examined by using a range of
ketones and aldehydes in the desired Gewald reaction under the optimum condi-
tion. The results are summarized in Table 3. In all cases, the intended product was
obtained in good yield.
To the best of the authors’ knowledge, several methods and catalysts have been
reported for preparation of 2-aminothiophene [46, 47]. However, it seems that the
present procedure is unique among them due to its shorter reaction time and higher
yield (Table 4). Furthermore, operational simplicity, cost-efectiveness, reusability
of catalyst, and avoidance of toxic organic solvents are other notable advantages of
the present procedure.
Reusability is a key factor to consider a solid material as a potent catalyst for
use in industry. To study its reusability, the catalyst was separated from the reaction
mixture using a magnet and washed with deionized water. Then, the catalyst was
dried in a vacuum oven at 60 °C for 5 h and reused for fve runs (Fig. 6).
Catalytic activity of H5SiW11Fe‑APSCMNPs in synthesis of tetrahydrobenzo[b]
pyrans
The appropriate amount of H5SiW11Fe-APSCMNPs as catalyst was investi-
gated for preparation of tetrahydrobenzo[b]pyrans by using 0–0.05 g catalyst in a
model reaction of benzaldehyde (1.0 mmol), malononitrile (1.0 mmol), and dime-
done (1.0 mmol) at 80 °C in an oil bath under solvent-free condition (Table 5). As
expected, in absence of nanocatalyst, no product was produced (Table 5, entry 1),
indicating that the nanocatalyst is essential for reaction progress. As expected, the
yield of tetrahydrobenzo[b]pyran increased with increasing amount of catalyst.
Therefore, 0.03 g catalyst was chosen as the optimal quantity.
Figure 7 shows the efect of reaction time on the synthesis of tetrahydrobenzo[b]
pyrans under the standard reaction condition (reaction temperature of 80 °C with
0.03 g catalyst), revealing that the best reaction duration was 20 min.
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
Table 3 Synthesis of diferent 2-aminothiophenes using APSCMNPs under solvent-free condition
Reaction conditions: Substituted ketone or aldehyde, malononitrile, and sulfur powder (10, 10, and
10 mmol) were mixed in presence of 0.05 g catalyst at 60 °C for 2 h under solvent-free condition
Table 4 Comparison of catalytic activity of APSCMNPs with some reported catalysts for synthesis of
2-aminothiophenes
Entry
Catalyst
Mol (%)
Yield (%)
Time (h)
Condition
References
1
2
3
4
5
6
APSCMNPs
Imidazole
Morpholine
ZnO
TiO2
SBA-15
0.05 g
88
75
49
65
74
20
2
10
11
10
10
10
Solvent-free
In DMF
In DMF
Solvent-free
Solvent-free
Solvent-free
This work
[46]
[46]
[47]
[47]
10
10
5
5
5
[47]
1 3

Facile pathway for synthesis of two efcient catalysts for…
Fig. 6 Reusability of APSCMNPs
Table 5 Efect of catalyst
Entry
H5SiW11Fe-APSC-
Time (min)
Yield (%)
amount on synthesis of
MNPs (g)
tetrahydrobenzo[b]pyrans
1
2
3
4
5
0
120
20
20
20
20
0
51
76
90
88
0.01
0.02
0.03
0.05
Reaction conditions: benzaldehyde, malononitrile, and dimedone
(1.0, 1.0, and 1.0 mmol) were mixed at 80 °C under solvent-free
condition
Fig. 7 Efect of time on synthesis of tetrahydrobenzo[b]pyrans in presence of 0.03 g catalyst at 80 °C
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
Table 6 Comparison of catalytic activity of H5SiW11Fe-APSCMNPs with some catalysts reported for
synthesis of tetrahydrobenzo[b]pyrans
Entry
Catalyst
Time
Yield (%)
References
1
2
3
4
5
6
7
8
9
Molecular iodine
Potassium phosphate
Phenylboronic acid
Tetrabutylammonium bromide
Fe3O4
SCMNPs
APSCMNPs
H3PW12O40
H5SiW12O40
3–4 h
85–90
94
88
90
35
Trace
Trace
83
87
90
[28]
[29]
[30]
[31]
45 min
30 min
40 min
60 min
60 min
60 min
20 min
20 min
20 min
[19]
This work
This work
This work
This work
This work
10
H5SiW11Fe-APSCMNPs
The catalytic performance of the prepared nanomaterial is compared with previ-
ously reported methods in Table 6. The superiority of the present catalyst in terms of
reaction time and yield is quite obvious. Furthermore, the reusability of the catalyst,
simple workup and reaction conditions, and economical aspects are other remark-
able advantages of the present methodology.
As seen in Table 6 (entries 6, 7), trace amount of product was obtained when
SCMNPs and APSCMNPs were used as catalyst. This demonstrates that supported
H5SiW11Fe is the active site for catalytic activity.
A series of substituted aromatic aldehydes with electron-withdrawing or elec-
tron-donating functional groups were reacted with malononitrile and dimedone in
presence of H5SiW11Fe-APSCMNPs using the optimal conditions (Table 7). We
observed that electron-withdrawing substituent resulted in higher yields than elec-
tron-donating substituent on the aromatic ring.
Catalyst reusability is very important for use in synthetic and practical applica-
tions. This property was confrmed for H5SiW11Fe-APSCMNPs by use in consecu-
tive runs. As shown in Fig. 8, the catalytic activity of the catalyst was restored dur-
ing fve successive runs.
Conclusions
We synthesized and characterized a novel magnetic hybrid nanomaterial consist-
ing of iron-substituted HPA supported on aminopropyl-functionalized magnetite
nanoparticles. The obtained aminopropyl-functionalized magnetite nanoparticles
were used for preparation of 2-aminothiophenes as a model base-catalyzed reac-
tion, while HPA-supported magnetite nanoparticles were used for preparation of
tetrahydrobenzo[b]pyrans as a model acid-catalyzed reaction. The results indicated
that the synthesized catalysts exhibited excellent catalytic activity in synthesis of
2-aminothiophenes and tetrahydrobenzo[b]pyrans under solvent-free condition. The
1 3

Facile pathway for synthesis of two efcient catalysts for…
Table 7 Synthesis of tetrahydrobenzo[b]pyran derivatives
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
Table 7 (continued)
1 3

Facile pathway for synthesis of two efcient catalysts for…
Table 7 (continued)
*There are no reported melting point on the articles for these entries
1 3

H. R. Saadati-Moshtaghin, F. M. Zonoz
Fig. 8 Reusability of H5SiW11Fe-APSCMNPs
advantages of this efcient catalyst include mild operation condition, excellent yield,
recyclability, and ease of catalyst separation.
Acknowledgements We are grateful to the University of Hakim Sabzevari Research Council for partial
support of this research.
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