Polystyrene-supported 1-methylimidazolium tetrachloro ferrate: Synthesis, characterization, and application as an efficient and reusable heterogeneous catalyst for one-pot synthesis of 4H-chromene derivatives in aqueous media

Article abstract of DOI:10.4314/bcse.v32i3.12

Polystyrene-supported 1-methylimidazolium tetrachloroferrate (PS[mim][FeCl₄]) was prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The

Full text of DOI:10.4314/bcse.v32i3.12

Bull. Chem. Soc. Ethiop. 2018, 32(3), 531-540.
 2018 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v32i3.12
ISSN 1011-3924
Printed in Ethiopia
POLYSTYRENE-SUPPORTED 1-METHYLIMIDAZOLIUM TETRACHLORO
FERRATE: SYNTHESIS, CHARACTERIZATION, AND APPLICATION AS AN
EFFICIENT AND REUSABLE HETEROGENEOUS CATALYST FOR ONE-POT
SYNTHESIS OF 4H-CHROMENE DERIVATIVES IN AQUEOUS MEDIA
Narges Taheri1*, Mehdi Fallah-Mehrjardi2 ande Soheil Sayyahi1*
1Department of Chemistry, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
2Department of Chemistry, Payame Noor University (PNU), Tehran, Iran
(Received March 15, 2018; Revised September 22, 2018; Accepted October 10, 2018)
ABSTRACT. Polystyrene-supported 1-methylimidazolium tetrachloroferrate (PS[mim][FeCl4]) was prepared
and characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and
energy dispersive X-ray analysis (EDX). The catalytic activity of the heterogeneous catalyst was evaluated
through one-pot synthesis of 2-amino-4H-chromene-3-carbonitriles via the three-component condensation reaction
of aromatic aldehydes, malononitrile and dimedone or 2-naphthol in water. The heterogeneous catalyst could be
recovered easily and reused five times without significant loss of its catalytic activity.
KEY WORDS: Green chemistry, Heterogeneous catalyst, 4H-chromene derivatives, Multi-component reactions,
One-pot synthesis
INTRODUCTION
The use of water as solvent for organic reactions is one of the best solutions to the problem of
flammability, volatility, toxicity and disposal of organic solvents [1]. Since most organic
reactants do not dissolve in water, the use of phase-transfer catalysts can overcome this problem.
Both homogeneous and heterogeneous phase-transfer catalysts improve the intimate contact
between inorganic reagents and organic substrates, but one of the major problems associated
with the use of homogeneous catalysts is the recovery of the catalyst from the reaction medium.
Immobilization of the phase-transfer catalysts on an insoluble matrix can provide a simple
solution to this problem [2–5].
In this regard, polymer-supported reagents have become state-of-the-art tools, since the
pioneering work by Merrifield in the field of solid-phase chemistry. They offer advantages such
as reaction monitoring as well as increased safety, especially when the non-supported reagents
are toxic or hazardous as they can be easily removed from reaction media and recycled [6].
Among various 4H-chromenes derivatives, especially, 2-amino-4H-chromenes have a
potential applications in the treatment of rheumatoid, psoriasis, and cancer [7]. These
compounds have received considerable attention due to their various biological and
pharmacological activities such as antimicrobial [8], antibacterial [9], antitumoral [10],
antioxidant [11] and antibiotical [12].
Due to the important above-mentioned properties of 2-amino-4H-chromenes, remarkable
attention has been focused on the development of environmentally friendly methodologies to the
synthesis of this heterocyclic compounds by three-component tandem reaction of
aromatic/aliphatic aldehydes, malononitrile and diverse enolizable C-H activated acidic
compounds [13–23]. However, many reported methods for the synthesis of these compounds
suffer from disadvantages including relying on multi-step conditions, need for excessive
amounts of the reagents, the use of toxic organic solvents or catalysts, harsh reaction conditions,
tedious work-up procedure, long reaction times, low yields of products and non-recyclability of
the catalyst.
__________
*Corresponding author. E-mail: n.taheri91@yahoo.com; sayyahi.soheil@gmail.com
This work is licensed under the Creative Commons Attribution 4.0 International License

532
Narges Taheri et al.
Owing to the widespread applications of the described compounds, and in continuation of
our efforts on the synthesis of new heterogeneous catalysts [24–28], in this paper, we report our
study on synthesis, characterization, and catalytic properties of polystyrene-supported 1-
methylimidazolium tetrachloroferrate (PS[mim][FeCl4]). The catalyst was characterized with
several techniques, and its catalytic activity was investigated in the synthesis of 2-amino-4H-
chromene-3-carbonitrile derivatives through the one-pot condensation reaction of various aryl
aldehydes, malononitrile and dimedone or 2-naphthol under aqueous media (Scheme 1).
O
Ar
O
CN
O
NH2
O
CN
CN
PS[mim][FeCl4]
H2O, 80 oC
1a-1f
or
Ar
ArCHO
+
+
or
CN
OH
NH2
O
N
N
+
-
FeCl4
PS[mim][FeCl4]
2a-2f
Scheme 1. Synthesis of 4H-chromene derivatives in the presence of PS[mim][FeCl4].
EXPERIMENTAL
Materials and apparatus
Chemical reagents in high purity were purchased from Merck and Aldrich and were used
without further purification. Merrifield resin (Mesh 200-400, 2% cross-linked with
divinylbenzene, 2-4 mol capacity) was purchased from Alfa Aesar chemical company. Purity of
the synthesized compounds was monitored by TLC, visualizing with ultraviolet light and all
yields refer to isolated products. Melting points were determined using a Stuart scientific
apparatus in open capillary tubes. Scanning electron microscopy (SEM) and energy dispersive
X-ray (EDAX) analyses were carried out using a Philips XL30 instrument. FT-IR spectra of
synthesized compounds were recorded on KBr pellets on
a Bomem MB-1998
spectrophotometer. Raman measurements were performed on an Almega Thermo Nicolet
Dispersive Raman spectrometer at a wavelength of 532 nm of a Nd:YLF laser. Progress of the
reactions was observed by TLC on silica gel PolyGram SILG/UV 254 plates.
Synthesis of polystyrene-supported 1-methylimidazolium chloride (PS[mim][Cl])
Merrifield resin (2 g; 200-400 mesh, 2% cross-linked) and 1-methylimidazole (10 mL) were
placed in a round flask and stirred for 24 h at 90 ºC in an oil bath. The obtained yellow polymer-
support (PS[mim][Cl]) was filtered and washed with ethanol and acetone, and dried at room
temperature.
Synthesis of polystyrene-supported 1-methylimidazolium tetrachloroferrate (PS[mim][FeCl4])
The mixture of PS[mim][Cl] (2 g) and FeCl3.6H2O (0.54 g, 2 mmol) in methanol (5 mL) were
stirred for 15 min at room temperature. Afterwards, the resulted brown resins (PS[mim][FeCl4])
were filtered and washed with distilled water and dried under vacuum.
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Synthesis, characterization, and application of an efficient heterogeneous catalyst
533
General procedure for the synthesis of 2-amino-4H-chromenes catalyzed by PS[mim][FeCl4]
The heterogeneous catalyst, PS[mim][FeCl4], (0.1 g) was added to a mixture of aromatic
aldehydes (1 mmol), malononitrile (1 mmol), dimedone or 2-naphthol (1 mmol) in water (5
mL). The reaction mixture was stirred at 80 °C for the appropriate time shown in Table 2. After
completion of the reaction according to TLC analysis (n-hexane:ethyl acetate; 4:1), the reaction
mixture was filtered off and the filtrate was washed with cool ethanol to remove the excess
malononitrile. Eventually, separation of the catalyst from the obtained 2-amino-4H-chromenes,
and further purification of products were applied using methanol as solvent.
2-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile
(5a).
White solid; m.p. = 229-231 °C; IR (KBr, cm-1): vmax = 3394, 3325, 3209, 2962, 2199, 1678,
1661, 1600, 1369, 1250, 1215, 1161, 1138, 1033, 694; 1H NMR (400 MHz, DMSO-d6, ppm): δH
= 7.29 (t, J = 7.2 Hz, 2H), 7.11–7.22 (m, 3H), 6.99 (s, 2H), 4.15 (s, 1H), 2.48 (s, 2H), 2.28 (d, J
= 16.1 Hz, 1H), 2.11 (d, J = 16.1 Hz, 1H), 1.01 (s, 3H), 0.98 (s, 3H); 13C NMR (100 MHz,
DMSO-d6, ppm): δC = 195.45, 161.98, 159.12, 144.73, 128.18, 127.47, 126.50, 119.89, 111.96,
59.04, 50.03, 39.12, 34.86, 32.09, 29.63, 25.93.
RESULTS AND DISCUSSION
Synthesis and characterization of PS[mim][FeCl4]
Polystyrene-supported 1-methylimidazolium tetrachloroferrate was synthesized by the concise
route outlined in Scheme 2. First, the Merrifield resin was treated with 1-methylimidazole at 90
°C for 24 h to afford the polystyrene-supported 1-methylimidazolium chloride as a yellow solid.
Then, the stirring of the mixture of PS[mim][Cl] and ferric chloride in methanol at room
temperature lead to the brown PS[mim][FeCl4] resin.
N
N
+
-
FeCl4
Cl
Merrifield resin
PS[mim][FeCl4]
N
N
+
-
N
N
Cl
FeCl3.6H2O
90 oC, 24 h
MeOH
r.t., 15 min.
PS[mim][Cl]
Scheme 2. Synthesis of PS[mim][FeCl4] as a new heterogeneous catalyst.
The catalyst PS[mim][FeCl4] was characterized by the various techniques. The FT-IR
spectrum (Figure 1) showed a band vibration at 3200-3600 cm-1, which is probably related to the
absorbed water. The CH stretching and bending bands appeared at 2830-2950 cm-1 and 1400-
1500 cm-1, respectively. Two peaks at 1641 cm-1 and 1560 cm-1 assigned to C=C and C=N band
vibrations, respectively. Raman spectroscopy is a useful technique for the identification of
different types of ammonium tetrachloroferrate salts. The expanded Raman spectrum shows a
strong peak at approximately 330 cm-1 that is assigned to the totally symmetric Fe-Cl bond
stretch vibration (Figure 2). The SEM images of unsupported resin (PS), PS[mim]Cl and
PS[mim][FeCl4] clearly indicated that the PS has a smooth surface while the polymer-supports
have a rough surface and the changes in the morphology of polymers are remarkable (Figure 3).
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Narges Taheri et al.
Figure 1. The FT-IR of PS[mimm][FeCl4].
Figure 2. The Raman spectru
m
of PS[mim][FeCl4].
m
 
m
m
 
 
a
b
c
Figure 3. The SEM images of PS (a), PS[mim][Cl] (b) and PS[mim][FeCl4] (c).
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Synthesis, characterizaation, and application of an efficient heterogeneous catalyst
535
The data from EDX analyssis are consistent with our expectations and confirms the preesence
of carbon, nitrogen, iron and chlorine elements in PS[mim][FeCl4] (Figure 4).
Figure 4. The EDX spectroscopy of PS[mim][FeCl4].
Application of PS[mim][FeCll4] as heterogeneous catalyst for the synthesis of 4H-chromene
derivatives in water
After successful characterization of PS[mim][FeCl4], it was decided to evaluate its catalytic
activity as a heterogeneous p
carbonitriles. In order to optimize conditions the reaction of benzaldehyde with malon
and dimedone was selected as a model reaction. After preliminary experiments, it was found
hhase-transfer catalyst in the synthesis of 2-amino-4H-chromene-3-
onitrile
that the condensation react
PS[mim][FeCl4] in water
methylphenyl)-5-oxo-4H-5,6,7
reaction time (Table 1, entr
i
aa
on was efficiently carried out in the presence of 0.1 g of
t 80 °C and produced 2-amino-3-cyano-7,7-dimethy -4-(4-
,8-tetrahydrobenzo-pyran (1a) in excellent yield and in short
5). After optimizing the reaction conditions, we appli d this
ll
y
ee
catalyst for the synthesis of 2-amino-4H-chromene-3-carbonitrile derivatives using different aryl
aldehydes, malononitrile and imedone or 2-naphthol in water to establish the catalytic activity
d
d
of PS[mim][FeCl4] for this trannsformation (Table 2).
Table 1. Optimization of reaction conditions.
Entry
1
2
3
4
5
6
7
Catalyst (g)
Solvent
H2O
H2O
H2O
H2O
H2O
H2O
Neat
CHCl3
CH3CN
MeOH
H2O
Condition
reflux
reflux
r.t.
50 °C
80 °C
80 °C
80 °C
reflux
reflux
reflux
reflux
reflux
Time (min)
Yield (%)a
PS[mim][FeCl4] (0.2)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.05)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
PS[mim][FeCl4] (0.1)
18
20
90
90
20
90
90
90
90
90
90
90
91
93
35
65
92
88
65
35
55
8
9
10
11
12
60
40
trace
PS[mim][Cl] (
0
.1)
-
H2O
aIsolated yields.
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Narges Taheri et al.
Table 2. Synthesis of 4H-chromene derivatives catalyzed by PS[mim][FeCl4]a.
Time Yield
(h)
m.p. (°C)
[Ref.]
Entry
1
Aldehyde
Product
(%)b
CHO
O
229-231
[18]
20
92
CN
O
NH2
1a
Br
CHO
198-200
[19]
O
2
15
90
CN
Br
O
NH2
1b
Cl
CHO
212-214
[20]
O
O
O
3
4
5
15
90
60
88
91
85
CN
Cl
O
OH
NH2
1c
CHO
202-204
[19]
CN
HO
O
OCH3
NH2
1d
CHO
196-197
[18]
H3CO
CN
O
NH2
1e
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Synthesis, characterization, and application of an efficient heterogeneous catalyst
537
NO2
CHO
175-177
[18]
O
6
20
90
CN
O2N
O
NH2
1f
CN
NH2
CHO
286-288
[29]
7
30
90
O
2a
Br
Cl
CN
CHO
NH2
239-241
[21]
8
9
25
30
35
88
85
87
O
Br
Cl
2b
CN
CHO
CHO
NH2
206-208
[21]
O
2c
HO
CN
NH2
261-263
[22]
10
O
HO
2d
H3CO
CN
CHO
CHO
NH2
186-187
[21]
11
12
90
30
92
88
O
H3CO
2e
O2N
CN
NH2
187-188
[29]
O
O2N
2f
aReaction conditions: aryl aldehyde (1 mmol), malononitrile (1 mmol), dimedone or 2-naphthol (1 mmol),
PS[mim][FeCl4] (0.1 g), H2O (5 mL) at 80 °C. bIsolated yields.
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Narges Taheri et al.
Comparison of the catalytic efficiency of PS[mim][FeCl4] in the one-pot condennsation
between benzaldehyde, malononitrile and dimedone to produce the corresponding
tetrahydrobenzopyran with somme of methods reported in the literature is presented in Ta les 3.
The results showed that our p ocedure provided higher yield of product in shorter reactio time
and under milder reaction con itions.
b
b
rr
nn
dd
Table 3. Comparative synthesis of compound 1a using the reported methods versus the present method.
Time
(min)
30
25
5
25
15
20
20
Yield
(%)
97
77
70
94
95
92
92
Entry
Catalyst
Condition
Ref.
1
2
3
4
5
6
7
TBAF
MgO
H2O, reflux
Solvent-free, r.t.
Solvent-free, r.t.
EtOH, r.t.
PEG/H2O, r.t.
H2O, r.t.
[14]
[15]
[16]
[17]
[19]
[H3N+CH2CH2OH][HCO2 ]
-
SiO2 NPs
MNPs-Guanidine
[DiEG(mim)2][OH
PS[mim][FeCl4]
]
]
[22]
This work
2
H2O, 80 °C
To investigate the reusabillity of the catalyst, it was recovered from the reaction mixt
washed with acetone or methanol and dried in the air. It was then reused for subs
experiments (up to five cycless) under similar reaction conditions. It was observed that the yields
u
re and
eequent
of the product remained com
p
p
arable in these experiments (Figure 5, conversion decrease
s
s
from
100% to 95%), established the recyclability and the reusability of the catalyst witho
u
u
t any
significant loss of its activity.
100
80
60
40
20
0
1st run
2nd run 3rd run 4th run 5th run
Figure 5. Recovery and reusability of the catalyst.
CONCLUSION
In conclusion, a new heteroogeneous catalyst (PS[mim][FeCl4]) was successfully prepared,
characterized and applied for the one-pot three-component synthesis of 2-amino-4H-chrommenes
under aqueous media. This novel catalytic method offers several advantages inclluding
environmental friendliness, high yield, involving a simple work-up procedure, ease of
separation, and recyclability oof the catalyst. So we think that this procedure could be conssidered
a new and suitable addition to the present methodologies in this area.
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Synthesis, characterization, and application of an efficient heterogeneous catalyst
539
ACKNOWLEDGEMENT
The authors gratefully acknowledge financial support from the Mahshahr Branch, Islamic Azad
University, Iran.
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