Ni0.5Zn0.5Fe2O4@Ha-PrS nanoparticle: A recoverable green catalyst for the synthesis of tetrahydrobenzo[b]pyrans in water

Article abstract of DOI:10.4314/bcse.v32i3.9

A green, efficient and simple technique for the synthesize of tetrahydrobenzo[b]pyrans through one-pot three-component reaction of dimedone, aromatic aldehydes and malonitrile as active methylene compound using immobilization of Preyssler heteropoly acid

Full text of DOI:10.4314/bcse.v32i3.9

Bull. Chem. Soc. Ethiop. 2018, 32(3), 501-511.
2018 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v32i3.9
ISSN 1011-3924
Printed in Ethiopia

Ni0.5Zn0.5Fe
2
O
4
@HA-PRS NANOPARTICLE: A RECOVERABLE GREEN CATALYST
FOR THE SYNTHESIS OF TETRAHYDROBENZO[b]PYRANS IN WATER
1
*
2
Ali Javid and Farid Moeinpour
1
Department of Chemistry, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Department of Chemistry, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran
2
(Received January 25, 2018; Revised October 21, 2018; Accepted October 23, 2018)
ABSTRACT. A green, efficient and simple technique for the synthesize of tetrahydrobenzo[b]pyrans through
one-pot three-component reaction of dimedone, aromatic aldehydes and malonitrile as active methylene
compound using immobilization of Preyssler heteropoly acid on Ni0.5Zn0.5Fe O magnetite nanoparticles (MNPs),
2 4
coated with hydroxyapatite (HA) as a catalyst is described. Comparing with the previous studies on preparation of
these compounds, the present methodology suggests some benefits which include high yields, short reaction times
2
and green reaction conditions (room teperature in H O). More importantly, the magnetic catalyst was isolated
from the reaction mixture using a simple magnet and efficiently reused at least five runs without any loss of
catalytic activity. Thus, the developed separable catalysts are potentially beneficial for the economic production of
organic compounds.
KEY WORDS: One-pot, Three-component, Tetrahydrobenzo[b]pyrans, Preyssler, Heteropoly acid, Magnetite
nanocatalyst
INTRODUCTION
Designing and preparation of reusable catalysts are of great economic and environmental
importance in the chemical and medicinal industries. Immobilization of homogeneous catalysts
on various insoluble supports can lead to simplify the catalyst recycling process via different
methods [1]. Recyclability and reusability are important features of heterogeneous catalysts,
compared with homogeneous catalysts [2, 3]. Therefore, design of new heterogeneous catalysts
is very important [4].
At present, nanoparticles (NPs) are used as solid supports for immobilizing homogeneous
catalysts [5]. Because of their large surface area, which can carry a high amount of catalytically
active species, these supported catalysts exhibit very high activity under mild conditions.
Among these NPs, much attention has been directed towards the production of magnetic
nanoparticles (MNPs), because these NPs can be well dispersed in the reaction mixtures without
the magnetic field providing a large surface for ready access of substrate molecules. This point
is important since at the end of the reactions, the MNP catalysts can be separated completely
from the mixture using an appropriate external magnet [6]. There are several MNP oxides, for
examples: Fe
3
O
4
, Fe
) is a type of MNP that has attracted attention because of its excellent thermal
stability, moderate saturation magnetization, remarkable chemical stability, and mechanical
hardness [7]. Coating of these nanoparticles with HA to obtain Ni0.5Zn0.5Fe @HA composite
2 3 2 4 2 4 2 4 2 4
O , MnFe O , CoFe O , NiFe O , CuFe O , etc. Nickel zinc ferrite
(
2 4
Ni0.5Zn0.5Fe O
2
O
4
can impart extra stabilization to such MNPs and retard their agglomeration in solutions [8]. The
outer layer of HA makes it suitable for multifunctional surface modification, including catalyst
immobilization [9, 10].
5 30
Preyssler (H14NaP W O120) is an important heteropoly acid (HPA) which has significant
advantages, such as 14 acidic protons, high thermal stability, high hydrolytic stability (0 < pH <
2
1
2) and safety [11, 12]. Due to the low surface area (7–10 m /g) and high solubility of HPAs in
polar solvents, it is usually preferred to use them in a supported form. These catalysts can be
_
*
_________
Corresponding author. E-mail: alijavids@yahoo.com
This work is licensed under the Creative Commons Attribution 4.0 International License

502
Ali Javid and Farid Moeinpour
supported on acid-neutral solids, such as silica and alumina, hydroxyapatite (HA), activated
carbons, zeolites and acidic ion-exchange resins [11-13].
4
H-pyrans belong to a main group of heterocyclic compounds with essential biological roles
[
14]. They are reported to have several pharmaceutical properties such as antibacterial [15],
antioxidant [16], antiallergic [17], potassium channel activator [18], and insulin-sensitizing
activities [19]. They are also reported to serve as an important regulator for potassium cation
channel [20] and photochemical activities [21].
Because of the intense interest in the biological activity of these compounds, several
improved procedures for the synthesis of pyrans were reported [22]. One of the main approaches
for synthesizing tetrahydrobenzo[b]pyrans is one-pot condensation of an aldehyde, dimedone
and malononitrile. Most of these methods employ various catalysts such as NH
magnetic Fe /phenylsulfonic acid [24], magnetite-dihydrogen phosphate [25], ionic liquid
26, 27], magnetite supported heteropoly acid [28], mixed metal nano-oxides [29], molecular
4 4 2
Al(SO ) [23],
3
O
4
[
iodine [30], Ru(II) complexes [31], copper oxide nanoparticles [32], lithium bromide [33],
sodium selenate [34], HPA-dendrimer functionalized magnetic nanoparticle [35], and nano α-
Al O supported ammonium dihydrogen phosphate [36]. However, despite these procedures are
2 3
relatively useful, most of the methods encounter some limitations, such as expensive catalysts,
long reaction times, toxic organic solvents and harsh reaction conditions. Thus, developing
simple, efficient, clean, high yielding, and environmentally friendly approaches using new
catalysts for synthesizing these compounds is a key role of organic chemists.
As a part of our program for investigating the use of reusable catalysts in organic reactions
[
37-42], the present article describes the results of an extended investigation into the activity of
the Preyssler HPA supported onto the hydroxyapatite (HA) coated Ni0.5Zn0.5Fe MNPs
@hydroxyapatite-Preyssler, abbreviated NZF@HA-PRS) as an effective
2
O
4
(
2 4
Ni0.5Zn0.5Fe O
catalyst for synthesizing tetrahydrobenzo[b]pyran derivatives. Facile isolation of the catalyst
using a magnetic field and the reusability of the catalyst (up to five cycles) is other main
advantages of this system. According to our knowledge, there is no report on the application of
NZF@HA-PRS as a novel nano magnetically-recoverable green catalyst for synthesizing
tetrahydrobenzo[b]pyrans from the condensation of dimedone, aromatic aldehydes and
malonitrile at ambient temperature in water. Therefore, we want to develop a simple, rapid and
an efficient synthetic technique for synthesizing these compounds using NZF@HA-PRS as a
heterogeneous nano acidic catalyst (Scheme 1).
Scheme 1. Synthesis of tetrahydrobenzo[b]pyran derivatives in the presence of NZF@HA-PRS
as a nano acidic catalyst.
EXPERIMENTAL
All materials and chemicals were obtained from companies of Merck and Aldrich and utilized
with no further purification. An Electrothermal model 9100 melting point apparatus was used to
determine melting points. A Thermo Nicolet AVATAR-370 FT-IR spectrophotometer and a
1
Bruker DRX400 spectrometer were used to provide FT-IR spectra and H NMR spectra.
NZF@HA-PRS was synthesized according to a previous report [42]. For synthesis of this
catalyst, the Preyssler HPA was immobilized on the NZF@HA (the core-shell NZF@HA was
synthesized based on our previous report [8]): To a suspension of NZF@HA (3 mmol; 1.0 g) in
Bull. Chem. Soc. Ethiop. 2018, 32(3)

Ni0.5Zn0.5Fe
2
O
4
@HA-PRS nanoparticle: a recoverable green catalyst
503
water (50 mL) was added a solution of the Preyssler HPA (0.1 mmol; 0.75 g) in water (5 mL)
dropwise. The mixture was stirred for 12 h at ambient temperature under N atmosphere. The
2
solvent was evaporated and the supported catalyst was collected, dried under vacuum overnight
o
and calcinated at 250 C for 2 h.
Synthesis of tetrahydrobenzo[b]pyran derivatives (4a-m)
A combination of dimedone (1.0 mmol), aromatic aldehydes (1.0 mmol) malonitrile (1.0 mmol),
–
3
and NZF@HA-PRS (2 × 10 mmol; 0.03 g) in water (10 mL) was stirred at room temperature
for 20-30 min. Upon completion (TLC monitoring using n-hexane/ethyl acetate, 1:1 as an
eluent), the nano-magnetic catalyst was isolated from the reaction mixture using a suitable
magnet placed on the outside wall of the reaction vessel, washed with acetone (50 mL) and
o
dried at 100 C for 2 h, to be reused in the next run. Finally, the preconcentration of reaction
mixture was performed under reduced pressure. The recrystallization of solid residue from
ethanol was performed to produce compounds 4a-m.
Spectral data for some selected tetrahydrobenzo[b]pyrans
2
-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile
(4a).
), 1.68 (s,
1
Yellow solid; H NMR (400 MHz, CDCl
H, CH ), 2.41 (s, 2H, CH ), 4.37 (s, 1H, CH), 4.73 (s, 2H, NH
KBr) : 3391, 3335, 2179, 1682, 1216 cm .
3
) δ ppm: 1.07 (s, 3H, CH
3
), 1.11 (s, 3H, CH
3
2
(
2
2
2
), 7.22-7.35 (m, 5H, Ph); IR
-
1
2
-Amino-7,7-dimethyl-4-(4-nitrophenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile
1
(
4c). Yellow solid; H NMR (400 MHz, CDCl ) δ ppm: 1.03 (s, 3H, CH ), 1.17 (s, 3H, CH ),
3 3 3
2
2
2 2 2
.24 (s, 2H, CH ), 2.51 (s, 2H, CH ), 4.57 (s, 1H, CH), 4.61 (s, 2H, NH ), 7.35 (d, J = 8.4 Hz,
H, Ph), 8.23 (d, J = 8.8 Hz, 2H, Ph); IR (KBr) : 3394, 3329, 2172, 1683, 1221 cm .
-
1
2
-Amino-4-(3-methoxyphenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboni-
1
trile (4d). White solid; H NMR (400 MHz, CDCl
2
6
3
) δ ppm: 1.06 (s, 3H, CH
), 3.82 (s, 3H, OCH ), 4.35 (s, 1H, CH), 4.61 (s, 2H, NH
.78-7.26 (m, 4H, Ph); IR (KBr) : 3390, 3328, 2177, 1685, 1213 cm .
3
), 1.14 (s, 3H, CH
3
),
),
.22 (s, 2H, CH
2
), 2.51 (s, 2H, CH
2
3
2
-
1
2
-Amino-4-(2-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitr-
1
ile (4f). Yellow solid; H NMR (400 MHz, CDCl
.19 (s, 2H, CH ), 2.47 (s, 2H, CH ), 4.60 (s, 2H, NH
Ph); IR (KBr) : 3395, 3326, 2187, 1684, 1215 cm .
3
) δ ppm: 1.09 (s, 3H, CH
3
), 1.17 (s, 3H, CH
3
),
2
2
2
2
), 4.89 (s, 1H, CH), 7.11-7.29 (m, 4H,
-
1
RESULTS AND DISCUSSION
2 4
In order to evaluate the catalytic activity of immobilized Preyssler HPA on Ni0.5Zn0.5Fe O
MNPs coated with HA, at first, three-component facile synthesis of tetrahydrobenzo[b]pyran
derivatives were performed in the presence of catalytic levels of NZF@HA-PRS. To establish
the possibility of the strategy and optimize the conditions, the reaction of dimedone,
benzaldehyde and malonitrile was chosen as a model reaction. The model reaction was
examined in the diverse solvents such as CH
solvent-free condition (Table 1). No product was achieved in the absence of the catalyst (entry
). The reaction yield in the polar solvents, especially in the polar protic solvents was more than
2 2 2
Cl , EtOH, MeOH and H O as well as under
1
when using non-polar solvents and solvent-free condition (entries 6-12). We believe that
because of the anionic structure generation and hydrogen bonding formation of HPAs in the
Bull. Chem. Soc. Ethiop. 2018, 32(3)

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Ali Javid and Farid Moeinpour
polar solvents, the reaction could produce better yields (entries 10-12). Also, among these polar
solvents, the use of water gave the best outcome (entry 12). Increasing the time of reaction and
temperature did not improve the yield (entries 13). In addition, the model reaction was
performed in the presence of Preyssler and others HPAs with Keggin structures, we observed
which performance of the reaction under the same time and reaction conditions was lower than
when we utilized NZF@HA-PRS as a catalyst (entries 14-16).
Table 1. Comparison of different catalysts and solvents in the preparation of tetrahydrobenzo[b]pyran
a
derivative of benzaldehyde
b
Entry
Catalyst
None
Solvent
Time (min)
Temperature
rt
Yield (%) [ref.]
No reaction
97 [34]
1
2
3
2
H O
120
60
30
Na
@SiO
NH
NH Al(SO
Fe @Ph-SO
2
SeO
4
H
2
O/EtOH
reflux
reflux
Fe
3
O
4
2
@NH-
2
H O
93 [28]
2
–PW
4
5
6
7
8
9
4
4
)
2
EtOH
120
30
30
30
30
30
30
30
20
60
30
30
30
reflux
rt
rt
100°C
rt
rt
rt
rt
rt
reflux
rt
rt
rt
92 [23]
95 [24]
3
O
4
3
H
2
H O
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
NZF@HA-PRS
solvent-free
solvent-free
41 (this work)
58 (this work)
Trace (this work)
23 (this work)
67 (this work)
75 (this work)
88 (this work)
89 (this work)
80 (this work)
74 (this work)
69 (this work)
CH
CH
2
Cl
CN
2
3
1
1
1
1
1
1
1
0
1
2
3
4
5
6
MeOH
EtOH
2
H O
2
H O
2
H O
2
H O
2
H O
H
14[NaP
[PW12
[SiW12
5
W
O
30
40
40
O
]
110
]
H
3
H
4
O
]
a
Dimedone (1 mmol), benzaldehyde (1 mmol) and malononitrile (1 mmol), in the present of different catalyst and
b
different conditions. Isolated yields.
To find the optimal amount of NZF@HA-PRS, the model reaction was performed under the
earlier mentioned conditions with various amounts of catalyst (Table 2). No product was
achieved without the presence of the catalyst (entry 1) demonstrating that the catalyst is
necessary for this reaction. Increasing the amount of the catalyst enhanced the efficiency of the
product 4a (entries 2-5). The use of 0.03 g of catalyst produced the maximum efficiency in 20
min (entry 5). Enhancing the amount of the catalyst beyond this value did not increase the
efficiency of the reaction noticeably (entries 6).
Table 2. Optimizing the level of NZF@HA-PRS in synthesis of tetrahydrobenzo[b]pyran derivative of
a
benzaldehyde
b
Entry
Catalyst amount (g)
Time (min)
Yield (%)
1
2
3
4
5
6
None
0.005
0.01
0.02
0.03
0.05
120
30
30
30
20
20
No reaction
Trace
41
70
88
89
a
Dimedone (1 mmol), benzaldehyde (1 mmol) malononitrile (1 mmol), and NZF@HA-PRS at room temperature
in water. Isolated yields.
b
Finally, under these optimal conditions, the scope and yield of the reaction were investigated
when an extensive range of substituted 2-amino-4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-
Bull. Chem. Soc. Ethiop. 2018, 32(3)

Ni0.5Zn0.5Fe
2
O
4
@HA-PRS nanoparticle: a recoverable green catalyst
505
4
H-chromene-3-carbonitriles were synthesized in the presence of NZF@HA-PRS. The results
are presented in Table 3. Interestingly, a range of aryl aldehydes with electron-withdrawing or
releasing substituents (ortho, meta, and para-substituted) participated well in this reaction and
gave the desired product, 2-amino-4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
3-carbonitriles in high yield (83-93%) confirming its efficiency.
a
Table 3. Synthesis of tetrahydrobenzo[b]pyrans using of NZF@HA-PRS as a catalyst .
Entry
Aldehyde
Product
Yield
Mp (°C)
Found
Mp (°C)
Reported [ref.]
b
(%)
1
C
6
H
5
CHO
88
90
226-228
231-233[23]
217-219[23]
2
4-ClC
6
4
H CHO
211-213
3
4
3-ClC
2-ClC
6
H
4
CHO
89
87
231-233
216-218
230-232[26]
213-215[26]
H
6 4
CHO
5
6
4-BrC
6
H
4
CHO
91
93
205-207
178-180
200-202[23]
182-184[25]
2 6 4
4-NO C H CHO
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Ali Javid and Farid Moeinpour
7
8
3-NO
2
C
6
H
4
CHO
90
204-206
212-214
210-212[25]
207-209[23]
4-OHC
6
H
4
CHO
86
9
4-
88
198-200
203-205[25]
MeOC
6
4
H CHO
1
0
1
3-
86
83
204-206
202-204
208-210[25]
200-202[25]
MeOC
6
H
4
CHO
1
1
2-
6 4
MeOC H
CHO
2
3
4-MeC
6
H
4
CHO
91
215-217
221-223[23]
220-223[26]
1
6 4
4-CNC H CHO
92
215-217
a
Conditions: dimedone (1 mmol), aldehyde (1 mmol), malononitrile (1 mmol), and NZF@HA-PRS catalyst (0.03
b
g) at room temperature in water, after 20-30 min. Isolated yields.
Bull. Chem. Soc. Ethiop. 2018, 32(3)

Ni0.5Zn0.5Fe
2
O
4
@HA-PRS nanoparticle: a recoverable green catalyst
507
Using literature [28], we proposed the following mechanism for synthesizing
tetrahydrobenzo[b]pyrans in the presence of nano acidic catalyst (Scheme 2). Initially, both
aldehyde and active methylene compound (malonitrile) are activated in the presence of Preyssler
HPA as a Bronsted acid. After Knoevenagel condensation and removal of a water molecule, the
product reacts with 1,3-dicabonyl compound (dimedone) via Michael addition. Finally, an
intramolecular cyclization and then, tautomerization of the intermediate afforded the desired
tetrahydrobenzo[b]pyran derivative.
Bull. Chem. Soc. Ethiop. 2018, 32(3)

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Ali Javid and Farid Moeinpour
O
Ar
OH
H
Ar
C
NH
CN
C
N
CN
O
O
O
Ar
O
O
Ar
H
CN
CN
NH
NH
O
2
Scheme 2. Suggested mecha nn ism for synthesis of tetrahydrobenzo[b]pyrans promot ee d by
NZF@HA-PRS.
In terms of green chemi
desirable. For this purpose, the similar model reaction was investigated under optimal con
s
s
try, high efficiency and recyclability of the catalyst are gg reatly
itions
dd
for a second time. At the end of the reaction, the nano-magnetic catalyst was isolated from the
o
mixture using a simple external magnet and then washed with acetone, dried at 100 C under
vacuum for 2 h, and reused for a similar reaction. As shown in Figure 1, the catalyst c oo uld be
reapplied at least five times ww ithout significant loss of its activity. In addition, there was no
difference between the weigh tt of the recovered catalyst and the fresh one that was used in the
first cycle.
8
8
86
86
84
1
00
80
60
40
20
80
0
Run1 Run2 Run3 Run4 Run5
Figure 1. Reusability of NZF
@
HA-PRS for the model reaction.
CONCLUSION
In summary, we have used N ZZ F@HA-PRS as an effective, and eco-friendly solid acid c aa talyst
to synthesize tetrahydrobenzo[b]pyran derivatives which were prepared via a one-pot three
component reaction system containing dimedone, aromatic aldehydes and malonitrile at a mm bient
temperature in water as a green solvent. The catalyst could be recycled after a very
workup (with the aid of an e ternal magnet), and reused at least five runs with no consi dd erable
change in its catalytic activit yy . Excellent yields (up to 93%), enhanced reaction rates and short
reaction times, simplicity of o pp erations, and easy workup are some benefits of this techni ue. In
uld be
ss imple
x
q
addition to the use of synthesi zz ing these products, the environmentally benign catalyst w
oo
potentially promising for a ra nn ge of other acid-catalyzed chemical reactions.
Bull. Chem. Soc. Ethiop. 2018, 32(3)

Ni0.5Zn0.5Fe
2
O
4
@HA-PRS nanoparticle: a recoverable green catalyst
509
ACKNOWLEDGEMENT
The authors are thankful to Ahvaz Branch of Islamic Azad University because of financial
support.
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