PVA/Fe(NO3)3 nanofiber mats: An efficient, heterogeneous and recyclable catalyst for the synthesis of quinolines via Friedl?nder annulations

Article abstract of DOI:10.1039/c4ra07643e

PVA/Fe(NO₃)₃ nanofiber mats are found to be a heterogeneous recyclable catalyst for the efficient synthesis of quinoline derivatives in the Friedl?nder condensation of 2-aminoarylketones with carbonyl compounds and β-keto esters. The

Full text of DOI:10.1039/c4ra07643e

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PVA/Fe(NO3)3nanofiber mats: an efficient, heterogeneous and
recyclable catalyst for the synthesis of quinolines via Friedländer
annulations
5
Hakimeh Ziyadi and Akbar Heydari*
Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Poly(vinyl alcohol) (PVA) is a water soluble and biodegradable
synthetic polymer.Polymerizationof vinyl acetate, followed by
55 hydrolysis ofthe product, leads toproduction of PVA. It is white
(colourless), odourless and granular in the commercial form. The
poly hydroxy structure of this polymer is shown below.
PVA/Fe(NO3)3nanofiber mats is found to be a heterogeneous
recyclable catalyst for the efficient synthesis of quinoline
10 derivatives in the Friedländer condensation of 2ꢀ
aminoarylketones with carbonyl compounds and βꢀketo
esters. The novel catalytic system could be recovered and
reused at least 5 times without any loss of catalytic activity.
60
Quinoline derivatives are an important class of heterocycles,
15 structural unit in alkaloids, therapeutics and synthetic analogues.1
These compounds have interesting biological activities such as
antimycobacterial,2 antimalarial,3 antiꢀinflammatory4 and
anticancer.5Quinolines are also valuable reagents for the synthesis
of nano and meso structures with enhanced electronic and
20 photonic properties.6 Due to their importance in a wide range of
synthetic and natural products, significant efforts continue to be
directed in to the development of novel procedures and catalysts
for preparation of quinoline derivatives including Skraup,7
Pfitzinger,8 Friedländer9 and Combes reactions.10 Among them,
25 Friedländer reaction is one of the most straightforward and
excellent methods. This procedure usually involves acid or base
catalyzed condensation between a 2ꢀaminoarylketone or aldehyde
and a carbonyl compound possessing a reactive αꢀmethylene
PVAis usedinvariousindustries such as membrane, coatings,
textile sizing, adhesive and medical devises because of
65 biocompatibility,
physicalproperties.22
good
chemical
resistance
and
This Inexpensive and nonꢀtoxic polymeris a good candidate as
the supported matrix to immobilize Lewis acid catalyst.
Transition metal species can be chelated with numeroussurface
70 hydroxyl functional groups of PVA to prepare heterogen solid
support which are insoluble in most organic solvents and can also
be functionalized.But semi crystalline structure, high melting
point and low active site of bulk PVA make it difficult to
fabricate in to suitable solid matrix for catalytic
75 application.23Electrospinning is a versatile method for preparation
of ultraꢀlong oneꢀdimensional PVA nanofibers. This method uses
an electromagnetic field with a voltage sufficient to overcome the
surface tension of a polymer solution and to draw ultrafine
nanofiber.The electrospunnanofibers exhibit a number of unique
80 features and properties such as 1D morphology, extraordinary
length, high surface area, and hierarchically porous structure.24
Against the nanoparticles, electrospunnanofibers can be easily
prepared as membranes (supported or freeꢀstanding, and
nonwoven or woven) that can be conveniently handled and
85 manipulated during an application.25Few studieshave been
reported on thecatalytic activity of PVA nanofibers. L. Shao used
Pd/PVA nanofiber mates as catalyst in coupling
reaction.26However, to our best knowledge, no study has been
conducted on the use of electrospun PVA nanofiber mats as a
90 heterogeneous Iron salt catalyst. We herein report the use of
PVA/Fe(NO3)3nanofiber mats as an effective heterogeneous
catalyst in quinolines synthesis via Friedländer annulations. This
catalyst showed good catalytic activity and high selectivity under
mild conditions. Besides it can be separated easily by forceps or
95 simple filtration and reused at least 5times without any catalytic
activity loose.
group.11Lewis
acid
catalysts
such
as
Zr(NO3)4,12
30 Y(OTf)3,13AgOTf,14 ZnCl2 and PdCl2 have been used in the
Friedländer reaction. However, many of these procedures have
some limitations such as low yield, low selectivity, long reaction
time, harsh reaction conditions and need to excess amount of
15
16
catalysts. Recently FeCl3,17 FeCl2 and Fe(NO3)319have been
18
35 reported for the effective synthesis of quinolinesas Iron based
Lewis acids catalyst. In spite of their high yield and short reaction
time, homogeneity of catalyst, tedious workꢀup, nonꢀreusability,
deactivation (due to aggregation of particles) and product
contamination by residual transition metal are main problems in
40 the use of these catalysts. A general scope in catalysis is
conversion of a homogeneous catalyst into a heterogeneous
catalytic system.19The immobilization of homogeneous catalysts
on solid supports opens up new route for design and engineering
of novel catalysts. These structures are easily separable from the
45 reaction mixture, allowing the recovery of the solid and
eventually its reuse. But the heterogenization of a homogeneous
catalysis decreases catalytic activity because it reduces the
accessible catalytic center and make it difficult to diffuse the
reactants to the catalyst site.20To enhance the availability of the
50 active site, materials with porous structure and different smaller
size structure such as nanoparticles and nanofibers have been
utilized.21
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Results and Discussion
Preparation and characterization of PVA/Fe(NO3)3nanofiber
mats
25 diameter distribution for 50 observed nanofibers. The diameter of
PVA/Fe(NO3)3 nanofibers is between 80ꢀ200 nm. Figure 2
provides the FTꢀIR spectra of PVA, Fe(NO3)3.9H2O and
PVA/Fe(NO3)3nanofibers. The FTꢀIR spectra of PVA/Fe(NO3)3
nanofiber mates are similar to those of the PVA with only slight
30 increasing the transmittance.Also thethe peaks corresponds to
Fe(NO3)3 stretch were eliminatedindicating that the Fe(NO3)3
were well retained in the PVA matrix. The Xꢀray diffraction
analysis (Fig. 3) has indicated that the nanofibershave
approximately amorphous structure andthe crystallites of PVA
35 powder diminished during the solution preparation followed
byelectrospining. As well asthere is no characteristic diffraction
peak for the ferric nitrate, suggesting that the metal salt dispersed
on the PVA nanofiber mats has amorphous structure and chelated
to PVA successfully.29 Previously, groups of researchers have
40 studied the binding energy of O1s and Fe2pduring the formation
of the PVA—Fe(Ⅲ) complex in nanofibers. These results
indicated the bonding of hydroxyl in PVA with metal ion through
the FeꢀOꢀC bond.30
Herein aguesPVA/Fe(NO3)3 solution was electrospun to produce
nanofiber mates that are insoluble in the most solventunlike the
Fe(NO3)3. This Freestanding membraneꢀlike structure was used
as a novel reusable Iron catalyst in Friedlander reaction.
Uniform and beadꢀfree structure of the nanofiber mats could be
achieved when the PVA weight concentration was at 6.0 ꢀ 8.0%
5
10 in water.27 The PVA weight (8.0 wt %) was chosen for
preparation of PVA solution and was mixed with ferric nitrate.28
Then electrospinning of solution producedPVA/Fe(NO3)3
nanofiber mats (scheme 1).The SEM images in Fig.1 (aꢀb) show
the morphologies of the PVA/Fe(NO3)3nanofibers with different
15 magnifications. As this figure shows the nanofibers appear
uniform in size, smooth surfaces and no significant bead in the
samples. The resultantnanofiber mats offer unique properties like
high surface area to volume ratio, porousmembrane structure,
good interconnectivity of pores and potential to functionality
20 onnanoscale. The obtained histograms (Fig. 1c) confirm the
narrow
45
Scheme 1 Preparation of PVA/Fe(NO3)3nanofiber mats
50
Fig. 1 a,b) SEM image of electrospunPVA/Fe(NO3)3fiber with different magnification, c) Fiber diameter distribution of electrospun PVA/Fe(NO3)3fibers
2
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Fig.3 XRD pattern of a) PVA b) Fe(NO3)3.9H2O c) PVA/Fe(NO3)3 nanofibers
Fig. 2 FTꢀIR spectra of a) PVA b) Fe(NO3)3.9H2O c) PVA/Fe(NO3)3
nanofibers
45 PVA/Fe(NO3)3nanofiber containing 3 mol% of Fe3+ at 80oC.
5
Table 1Optimization of the reaction conditions using the model systema
Synthesis of quinolines catalyzed by PVA/Fe(NO3)3 nanofiber
mats
Temp.
.(°C)
60
Time Yield
(h)
2
Entry
Catalyst(mol%)b
Fe(NO3)3.9H2O (1)
(%)c
84
After catalyst preparation, we investigated the reaction of 2ꢀ
aminobenzophenone with ethyl acetoacetate in the presence of
10 PVA/Fe(NO3)3 nanofibers as a model reaction to check catalyst
activity in Friedländer reaction (Scheme 2).
1
2
PVA/Fe(NO3)3nanofiber (1)
60
80
100
80
80
80
80
10
10
5
70
78
80
85
96
0
PVA/Fe(NO3)3nanofiber (1)
PVA/Fe(NO3)3nanofiber (1)
PVA/Fe(NO3)3nanofiber (2)
PVA/Fe(NO3)3nanofiber (3)
No catalyst
3
4
4
5
15
4
6
24
12
7
Scheme 2 Synthesis of ethyl 2ꢀmethylꢀ4ꢀphenylquinolineꢀ3ꢀ
8d
PVA nanofiber (0)
trace
carboxylate
aReaction conditions: 2ꢀaminobenzophenone (2mmole), ethyl
acetoacetate(2mmol), toluene (5mlit).
50 bmol % Fe 3+ in catalyst.
20
The reaction normally was done in toluene as solvent that is
the normal solvent for Friedlander reaction.31 As wellꢀknown,
Fe(NO3)3 in homogenous form was effective for synthesis of
quinoline (Table 1, entry1). This reaction proceeded in lower
time and good yieldbecause of the accessibility of catalytic
c Isolated yields.
d Reaction completed after 18 h.
We extended this condition to a variety of 2ꢀaminoarylketones
55 with carbonyl compounds. As shown in Table 2, this method is
equally effective for substituted 2ꢀaminoarylketones such as 2ꢀ
aminobenzophenone or 2ꢀamino5ꢀcholorobenzophenone and 2ꢀ
aminoacetophenone. Various 1,3ꢀdiketone and βꢀketoesters
25 Fe3+center in solution, but the salt was soluble and homogenous
in the solvent resulting to contamination of product by salt and
difficult work up without catalyst reuse. In the presence
ofheterogeneousPVA/Fe(NO3)3nanofibers, the reaction proceeded
clean and simple and the condensation product precipitated in
30 excellent isolated yield (Table 1, entry 2). Our result showed that
this catalyst was insoluble in toluene after 1 weeks reflux. To
optimize the reaction conditions and improve the yield, our
attention was drawn to the role of temperature. It was noticed
that increasing the temperature to 80 °C considerablyenhancesthe
35 yield amount. By elevating the temperature up to 80 °C, the yield
remained unchanged (Table 1, entries 3 and 4). In the next steps,
different amounts of catalyst were used for this transformation
(Table 1, entry 5 and 6). Increasing the amount of catalyst
increased the yield of quinolines. In the absence of the catalyst
40 the reaction takesmore than 24 h to complete (Table 1, entry 7).
The PVA nanofibers catalysts react with very low yield during
long time (Table 1, entry 8). Using catalyst containing 3
reacted
with
2ꢀaminoarylketones
to
give
the
60 correspondingquinolines. Under the same conditions cyclohexane
as a simple cyclic ketone gave the tricyclic quinoline, however,
the reaction needed excess amount of ketone and proceeded
slower than other reactants (Table 2, entry I).
The reusability of the nanofibers was also examined. After
65 completing the first run of model reaction, the catalyst was
washed with CH2Cl2 three times then was dried in a vacuum and
reused in the subsequent reaction. Large structure of nanofiber
mats catalyst leads to easy separation process using forceps. No
significant loss of catalyst activity was observed even after 5
70 times of reuse (Fig. 4).Negligible decrease of the catalyst activity,
rule out the deactivation of catalyst in fridlander reaction.
mol % of Fe3+ is most effective in term of both time and yield.
Therefore, the optimum conditions for this reaction are asfollows:
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Table 2: Preparation of quinoline derivatives in the presence of PVA/Fe(NO3)3 nanofibera
Entry
Compound 1
Compound 2
Product 3
Melting point (oC)
Time (h)
Yield (%)b TONc TOF(hꢀ1) d
60
107
32
8
a
4
95
96
90
80
5
65
100
32
30
8
b
4
4
6
10
108
7.5
c
70
108
27
32
4
8
d
15
75
131
e
4
96
20
80
100
33
8
f
4
4
6
8
4
5
98
90
75
70
78
85
25
135
30
25
8
4
g
85
156
h
30
90
Ie
163
23
26
3
35
215
6.5
j
95
100
28
6
k
40
100
oil
l
5
5
85
78
28
26
6
5
45
105
oil
m
50
105
23
4
110
n
6
70
a
3+
55
Reaction conditions: compound 1 (2mmole), compound 2 (2 mmole.), PVA/Fe(NO3)3nanofibers(3 mol% Fe ), toluene (5mlit), 80°C.
b Isolated yields. c Turnover number (total number of product moles per mole of the catalyst).d Turnover frequency (turnover number per hour).
115
e2 eq of compound 2 was used.
4
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electrospinning parameters such as injection rate, drum rotating
speed, working distance, needle scanning rate and temperature of
the electrospinning media. Electroris has also the industrial size
60 for preparation of nanofibers in large amounts.SEM images were
observed using SEM (Philips XL 30 and Sꢀ4160) with gold
coating equipped. Powder XRD spectrum was recorded at room
temperature by a Philips X’pert 1710 diffractometer using Co Kα
(α = 1.54056 Å) in BraggꢀBrentano geometry (θꢀ2θ). FTꢀIR
65 spectra were obtained over the region 400ꢀ4000 cmꢀ1 with
NICOLET IR100 FTꢀIR and spectroscopic grade KBr.NMR
spectra were recorded in CDCl3 (Bruker, 250 MHz, Switzerland)
and the proton chemical shifts are reportedin ppm relative to
TMS as the internal reference.
5
10
Fig. 4 Reusability of PVA/Fe(NO3)3nanofibers in reaction between 2ꢀ
amino benzophenone with ethyl acetoacetate
70 Catalyst preparation
15
0.800 g of PVA powder was added to 10.0 ml of deionized water
(8.0 wt %).Then 0.400 g ferric nitrate (Fe(NO3)3.9H2O) was
added to the above PVA aqueous solution with stirring for 6 h.
The electrospinning process was carried out using Electroris as an
L
eaching of Fe(NO3)3 from nanofiberto solvent was analysed by
ICP.
We
analysed
concentration
of
Fe3+
in
PVA/Fe(NO3)3nanofibers catalyst before and after the reaction.
75 electrospinner. The obtained solution was loaded into
a
20 The Fe3+ contents have been determined to be 0.055 and 0.052
mg for each mg of fresh and used catalyst respectively. After
completion of
plasticsyringe with 0.8 mm inner diameter of pinhead. In
ourexperiment,
electrospinning.
a
voltage of 20 kV was applied for
the reaction (monitored by TLC), catalyst and product were
separated from the solvent. Having evaporated the solvent, water
25 added as the new solvent. The resultant aqua solution
wasanalysed by ICP. The content of Fe in solutionwas 0.0002 mg
for each mg of catalyst, indicating that the Fe leaching is less than
1%. These results show that the Fe leaching from
PVA/Fe(NO3)3nanofiber mats is not significant during the
30 reaction. The SEM analysis of nanofibers after reaction(Fig. 5)
showed that this catalyst is stable in reaction condition and was
insoluble in toluene. Also the SEM of nanofibers after using for 5
run showed no distinct change in morphology.
The rate of flow was 1.0 ml/h and aluminum foil served as the
80 counter electrode. The distance between the capillary and the
substrate electrode was 12 cm while all parameters were
controlled
by
the
device.
The
electrospun
PVA/Fe(NO3)3nanofibers were placed in a vacuum oven for 12 h
at room temperature in order to remove the solvent residuals, then
85 peeled off from foil and used as catalyst.
General procedure for synthesis of quinolines
PVA/Fe(NO3)3nanofiber mates (61 mgr, 3 mol% Fe3+ ) was
added to a mixture of 2ꢀaminoaryl ketones (2 mmol) and βꢀ
ketoester / 1,3ꢀdiketone / cyclic ketone (2 mmol) in toluene (5
o
Experimental
90 mL) at 80 C. The mixture was stirred until completion of the
reaction, as indicated by TLC. The nanofiber mats were separated
from the reaction mixture by forceps. The precipitated product
was separated by filtration and vacuum dried. Then product was
recrystallized in CH2Cl2.All the products were known
95 compoundsand were characterized by IR, Mass, 1H NMR
spectroscopic data and respective melting points and were
compared with those reported in the literature.21,32Some selected
spectral data are given in supplementary data.
35 Instrumental and characterization
All chemicals were purchased from Merck chemicals Co.
(Germany). Reagents were used without further purification and
deionized water was used as solvent.
The electrospinning process was carried out using Electroris
40 (FNM Ltd., Iran, www.fnm.ir) as an electrospinner device having
a high voltage and a syringe pump controllable in range of 1–35
kV and 0.1– 100 mL/h, respectively. This device can control the
100
45
105
50
110
Fig. 5 SEM of electrospun PVA/Fe(NO3)3fibers (a) after reaction (b) after 5 times reusing
55
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25. L.M. Bellan, H.G. Craighead,Polym. Adv. Technol.
Conclusions
2011,22,304.
65
70
75
80
26. L. Shao, W. Ji, P. Dong, M. Zeng, Ch. Qi, X.M. Zhang, Appl.
Catal. A: General, 2012,413– 414, 267.
27. M.G. McKee, G.L. Wilkes, R.H. Colby, T.E.
Long,Macromolecules 2004,37,1760.
28. H. Ziyadi, A. Heydari, S.M. Rezayat,Ceram. Int. 2014, 40,
5913.
29. T.N. Glasnov, S. Findenig, C.O. Kappe, J. Eur. Chem.2009,
15, 1001.
30. N. Mahanta, S. Valivaveettil, RSC Adv., 2013, 3, 2776; Tao,
Zh. Wu, X. Wang, M. Li, J. Zhang. ActaPolymericasinica,
2006, 1, 387.
In summary the PVA/Fe(NO3)3nanofiber mates were prepared
by electrospinning of solution of poly(vinylalcohol) (PVA) and
Fe(NO3)3. The prepared nanofiber mates have been demonstrated
as a novel, effective, heterogeneous and biodegredable catalyst
for the synthesis of quinoline derivatives in the Friedländer
condensation of 2ꢀaminoarylketones with carbonyl compounds
and βꢀketo esters. Recovery of the catalyst was simple, allowing
its reuse without significant loss of its catalytic activity. The
10 simple and fast catalyst preparation, mild reaction conditions,
excellent yields, operational simplicity, product purity and
therefore cost efficiency are the advantages of this protocol. In
addition to this, environmentally benign membraneꢀlike catalyst
can be produced in large scales by industrial electrospinner.
5
31. J. MarcoꢀContelles, E. Perezꢀmayoral, A. Samadi,
M.Carreiras, E. Soriano,Chem. Rev. 2009,109,2652.
32. J. Akbari, A. Heydari, H.R. Kalhor, S.A. Kohan,J. Comb.
Chem.2010, 12,137.
Chemistry Department, TarbiatModares University, P. O. Box 14155-
4838 Tehran, Iran Fax: (+98)-21-82883455; Tel: (+98)-21-82883444,
email: heydar_a@modares.ac.ir
15 Acknowledgement
We are grateful to the University of TarbiatModares for
funding the project. We would also like to appreciate Dr Ali
Ziyaeemehr for reading up the paper and providing language
assistance
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