α-Fe2O3 nanoparticles: An efficient, inexpensive catalyst for the one-pot preparation of 3,4-dihydropyrano[c] chromenes

Article abstract of DOI:10.1016/j.cclet.2010.09.020

This paper describes the combustion synthesis of α-Fe ₂O₃ nanopowder at much lower temperature and its catalytic activity for the one-pot preparation of 3,4-dihydropyrano[c]chromenes. The combustion derived α-Fe₂O₃

Full text of DOI:10.1016/j.cclet.2010.09.020

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Chinese Chemical Letters 22 (2011) 143–146
www.elsevier.com/locate/cclet
a-Fe2O3 nanoparticles: An efficient, inexpensive catalyst for the
one-pot preparation of 3,4-dihydropyrano[c]chromenes
H. Nagabhushana a, S. Sandeep Saundalkar b, L. Muralidhar b, B.M. Nagabhushana c,
*
,
C.R. Girija b, D. Nagaraja d, M.A. Pasha e, V.P. Jayashankara b,
*
a Department of PG Studies in Physics and Research, University Science College, Tumkur University, Tumkur 572103, India
b Department of Chemistry, SSMRV College, Chemistry Research Center, Bangalore 560041, India
c Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560054, India
d Department of PG Studies in Chemistry and Research, University Science College, Tumkur University, Tumkur 572103, India
e Department of Chemistry, Central College Campus, Bangalore University, Bangalore 560001, India
Received 16 April 2010
Abstract
This paper describes the combustion synthesis of a-Fe2O3 nanopowder at much lower temperature and its catalytic activity for the
one-pot preparation of 3,4-dihydropyrano[c]chromenes. The combustion derived a-Fe2O3 nanopowder was characterized by powder
X-ray diffraction (PXRD), Braunauer, Emmett and Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier
transform infrared spectroscopy (FTIR). Highly efficient, three-component condensation of aromatic aldehyde, malanonitrile and 4-
hydroxycoumarin catalyzed by a-Fe2O3 nanoparticles at room temperature is described. The method offers an excellent alternative to
the synthesis of 3,4-dihydropyrano[c]chromenes. The reactions are rapid, clean, and the products with good yield and high purity.
# 2010 Published by Elsevier B.V. on behalf of Chinese Chemical Society.
Keywords: a-Fe2O3 nanopowder; One pot three-component condensation; Aromatic aldehyde; Malanonitrile; 4-Hydroxycoumarin
3,4-Dihydropyrano[c]chromenes and its derivatives are very useful compounds in various fields of chemistry,
biology and pharmacology. Some of these compounds exhibit spasmolytic, diuretic, anticoagulant, anti-cancer, and
anti-anaphylactic activity [1]. In addition, they can be used as cognitive enhancers for the treatment of
neurodegenerative diseases, including Alzheimer’s disease, amyotrophic lateral sclerosis, Parkinson’s disease,
Huntington’s disease, AIDS associated dementia and Down’s syndrome for the treatment of schizophrenia and
myoclonus [2]. Recently, one-pot procedures for the synthesis of 2-amino-4-aryl-5-oxo-4H,5H-pyrano[3,2-
c]chromene-3-carbonitrile from aromatic aldehyde, malononitrile and 4-hydroxycoumarin have been developed in
the presence of a variety of catalysts such as diammonium hydrogen phosphate [3], H6P2W18O62ꢀ18H2O [4], TBABr
[5], and K2CO3 under microwave irradiation [6]. However, many of these methods are associated with several
disadvantages such as long reaction time, drastic reaction conditions, very expensive reagents, low yields and tedious
work-up procedures. The main disadvantage is that the catalyst is destroyed during the work-up procedure and cannot
be recovered and reused. Therefore, it is important to find a simple, inexpense, recoverable and reusable catalyst for
the synthesis of 3,4-dihydropyrano[c]chromenes. Iron oxide nanoparticles are of considerable interest because of the
* Corresponding authors.
E-mail addresses: bmnshan@yahoo.com (B.M. Nagabhushana), jayashankarvp@gmail.com (V.P. Jayashankara).
1001-8417/$ – see front matter # 2010 Published by Elsevier B.V. on behalf of Chinese Chemical Society.
doi:10.1016/j.cclet.2010.09.020

144
H. Nagabhushana et al. / Chinese Chemical Letters 22 (2011) 143–146
valuable applications such as magnetic storage, medicine, and as catalyst [7,8]. Over the years researchers have
employed in synthesis of iron oxide nanoparticles using different synthesis techniques such as sol–gel processes [9],
chemical precipitation [10,11] forced hydrolysis [12] and other methods [13–16]. In the present work, an attempt has
been made to study catalytic activity of a-Fe2O3 on synthesis of 3,4-dihydropyrano[c]-chromenes, to the best of our
knowledge is concerned the use of a-Fe2O3 nanoparticles as a catalyst in the synthesis of 3,4-dihydropyrano[c]-
chromenes has not been reported yet. Instantaneous combustion synthesis is an important powder processing
technique generally used to prepare oxide ceramics [17]. It involves several advantages like fast heating rates, short
reaction time, besides producing foamy, homogeneous and high surface area nanocrystalline products. It has also the
advantage of doping desired amounts of dopant ions in solution medium and ‘low processing temperature’ leading to
uniform crystallite size at superfine dimensions. High purity and homogeneity can be achieved at temperature as low
as 300 8C as against 1470 8C needed to synthesize these materials via combustion route.
1. Experimental
The initial ingredients used for the preparation of a-Fe2O3 nanoparticles were of analar grade ferric nitrite
(Fe(NO3)3ꢀ9H2O) and oxalyl dihydrazide fuel (ODH; C2H6N4O2). The ODH fuel was prepared in our laboratory by
the reaction of diethyl oxalate and hydrazine hydrate as described in the literature [18]. An aqueous solution
containing stoichiometric amounts of ferric nitrite Fe(NO3)3ꢀ9H2O and ODH; C2H6N4O2 were taken in a Petri dish of
approximately 300 mL capacity. The excess water is allowed to evaporate by heating over a hot plate until a wet
powder is left out. Then the Petri dish is introduced into a pre heated muffle furnace maintained at 300 ꢁ 10 8C. The
reaction mixture undergoes thermal dehydration and ignites at one spot with liberation of gaseous products such as
oxides of nitrogen and carbon. The combustion propagates throughout the reaction mixture without further need of any
external heating, as the heat of the reaction is sufficient for the decomposition of the redox mixture. Finally, a
voluminous and foamy reddish product has been obtained. Assuming complete combustion, the theoretical equation
for the formation a-Fe2O3 with ODH can be written as follows:
2FeðNO3Þ3 þC2H6N4O2 þ5O2 ! Fe2O3 þ2CO2 þ3H2O þ 5N2 10:0molofgasesliberated=molofFe2O3
(1)
The phase of the as-formed a-Fe2O3 nanopowder has been characterized by PXRD in a Philips diffractometer
˚
operating with Cu-Ka radiation (l = 1.54056 A). In Fig. 1, all the PXRD peaks can be indexed as hexagonal phase of
a-Fe2O3 which are consistent with the values in the literature (Joint Committee on Powder Diffraction Standards
(JCPDS card No.: 33-0664)). The average crystallite size of the product was estimated from the Debye–Scherrer’s
equation and found in the range 30–40 nm. The surface morphology of the powders is examined by scanning electron
microscope (SEM), using a JEOL (JSM-840A). The circular shaped primary particles are agglomerated and size in the
order 0.2–1.0 mm (Fig. 2). The surface area of the powder sample was 35.0 m2/g, determined by a Quanta Chrome
Corporation, NOVA1000 Gas Sorption Analyzer. The infrared spectroscopy of the as prepared nanocrystalline a-
Fe2O3 was examined using a Perkin-Elmer spectrometer (spectrum 1000) with KBr pellets, the band at 450 and
537 cmꢂ1 were ascribed to Fe–O stretching vibrations.
[()TD$FIG]
70
60
50
40
30
20
10
0
20
30
40
50
60
70
2 θ (degrees)
Fig. 1. PXRD of as-formed a-Fe2O3.

[()TD$FIG]
H. Nagabhushana et al. / Chinese Chemical Letters 22 (2011) 143–146
145
Fig. 2. SEM picture of as-formed a-Fe2O3.
Table 1
Optimization of reaction conditions for the synthesis of 4a.a,b
Entry
Catalyst
Quantity (wt%)
Solvent
Time (min)
Yields (%)c
1
2
3
4
5
6
7
Fe2O3
Fe2O3
Fe2O3
Fe2O3
Fe2O3
Fe2O3
Fe2O3
5
10
15
10
10
10
10
C2H5OH
C2H5OH
C2H5OH
CH3OH
CH3CN
DCM
60
30
30
60
60
60
60
62
93
90
60
55
40
35
THF
a
Reagents: 1a (1 mmol), 2 (1.2 mmol), 3 (1 mmol), solvent (20 volume).
All reactions were carried out at room temperature condition.
Yield refers to isolated product.
b
c
2. Results and discussion
Initially, the reaction of benzaldehyde (1, 1 mmol) malanonitrile (2, 1.2 mmol) and 4-hydroxycoumarin (3, 1 mmol)
was chosen as a model reaction for the optimization of solvent effect and catalyst amount (Table 1, entries 1–7). Reaction
in acetonitrile, dichloromethane (DCM) and tetrahydrofuran (THF) solvent gave low product yields even after 60 min
(Table 1, entries 5–7). Although the yields were moderate in case of ethanol and methanol (Table 1, entries 1 and 4). We
found ethanol and 10 wt% of a-Fe2O3 catalyst an efficient reaction medium in terms of reaction time as well as yield
under room temperature (Table 1, entry 2). It is noteworthy to mention that in the absence of catalyst, no product was
found even after 5 h. These results indicate that the catalyst exhibits a high catalytic activity in this transformation.
Encouraged by these results and to explore the catalytic activity of nano catalyst, a variety of aldehyde with electron
donating and withdrawing substituent was used for the highly selective synthesis of 3,4-dihydropyrano[c]chromenes in
the presence of a-Fe2O3 under similar experimental conditions. However, the variations in the yields were very little and
both substituted aromatic aldehydes such as 4-nitro and 2-nitro as well as heterocyclic aldehydes like 2-pyridine
carboxaldehyde and gave the desired products in excellent yields (Scheme 1 and Table 2).
Reusability of the catalyst was examined employing the reaction between 1a, 2 and 3 to obtain 4a under identical
reaction conditions. The catalyst was easily recovered from the mixture by filtration. The catalyst was washed with
distilled water and ethanol repeatedly, and dried for 2–3 h under vacuum before re-use. The recycled catalyst was used
five times to obtain 2-amino-4-aryl-5-oxo-4H,5H-pyrano[3,2-c]chromenes without appreciable decrease in the yield 93,
90, 89, 85 and 82% respectively for 1–5 cycles. After every reaction, the catalyst was recovered from the reaction mixture
[()TD$FIG]
NH2
CN
Ar
OH
O
O
O
CN
X
X
Nano-Fe2O3
+
+
Ar
H
CN
RT, EtOH
O
O
O
1
2
3
4
X = H, CH3
Scheme 1.

146
H. Nagabhushana et al. / Chinese Chemical Letters 22 (2011) 143–146
Table 2
Synthesis of 2-amino-4-aryl-5-oxo-4H,5H-pyrano[3,2-c]chromenes in the presence of a-Fe2O3 [19].
Entry
Ar
X
Product
Time (min)
Yield (%)a
Mp (8C)
1
2
3
4
5
4-Pyridyle
H
4a
4b
4c
4d
4e
30
30
30
30
30
87
83
86
84
94
182–184b
218–220b
266–268b
225–227b
152–153b
8-Quinoline
3-CH3OC6H4
2,4-(CH3O)2C6H3
4-O2NC6H4
H
CH3
CH3
CH3
a
Yields are related to isolated pure products.
Novel compounds.
b
by filtration and regenerated as described above. In conclusion this procedure offers several advantages including mild
reaction conditions, cleaner reaction, and satisfactory yields of products, as well as simple experimental and isolating
procedure, which makes it a useful and attractive protocol for the synthesis of these compounds.
Acknowledgment
The authors thank Dr. S.C. Sharma, Vice chancellor, Tumkur University, Tumkur for his constant encouragement.
The authors thank VTU (VTU/Aca./2009-10/A-9/11714) for the financial support and Chemistry-TEQIP Laboratory
of MSRIT and SSMRV College, Chemistry Research Center.
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[19] General procedure for the synthesis of of dihydropyrano[c]chromenes: a mixture of aldehyde (1, 1 mmol), malanonitrile (2, 1.2 mmol), 4-
hydroxycoumarin (3, 1 mmol) and a-Fe2O3 (10 wt%) in (20 vol.) absolute ethanol was stirred at room temperature for 30 min, the progress of the
reactionwas monitored by TLCanalysis. After the completion of reaction, the reaction mass was filtered, then washed with THF, the mother liquor
containing the product was reduced to one fourth thevolume and the pure product precipitated was filtered and dried to afford title compound good
toexcellent yield. Products {using 4-methoxy, 4-nitro, 3-nitro, 4-chloro, 2,4 and 2,3-dichlorobenzaldehydes(yields86–93%)[Lit. 3,4]} areknown
compounds and their physical data, IR, and 1H NMR spectra were essentially identical with those of authentic samples. Other products (4a–4e),
which are new, were characterized by IR, 1H NMR and LCMS analysis. Compound 4a: brown solid, IR (KBr): y max = 3386, 3132, 1728, 1685,
1645, 1586, 1438, 1246, 817 cmꢂ1; 1H NMR: (400MHz, DMSO-d6):d 4.96 (s, 1H), 7.22–7.23 (d, 1H), 7.48–7.52 (t, 2H), 7.72–7.77 (m, 3H), 7.87–
7.89(d, 1H), 8.01ꢂ8.02(d, 1H);MS: m/z = 318(M+). Compound4b:Cremishsolid, IR(KBr):y max = 3402, 3224, 1665, 1519, 1434, 1338, 1234,
1068, 813 cmꢂ1; 1H NMR: (400 MHz, DMSO-d6): d 4.52 (s, 1H), 7.31–7.33 (t, 2H), 7.48–7.54 (m, 4H), 7.72–7.77 (m, 1H), 7.90–7.92 (m, 1H),
8.51ꢂ8.52 (m, 1H); MS: m/z = 368 (M+). Compound 4c: White solid, IR (KBr): y max = 3479, 3321, 3197, 2923, 2198, 1704, 1665, 1585, 1377,
1257, 821 cmꢂ1; 1H NMR: (400 MHz, DMSO-d6): d 2.43 (s, 3H), 3.72 (s, 3H), 4.41 (s, 1H), 6.78–6.83 (m, 3H), 7.21–7.25 (t, 1H), 7.35–7.38 (d,
3H), 7.52–7.55 (m, 1H), 7.71 (s, 1H); MS: m/z = 361 (M+). Compound 4d: Cream solid, IR (KBr): y max = 3460, 3325, 3213, 2927, 2194, 1697,
1670, 1380, 1130, 779 cmꢂ1. 1H NMR: (400 MHz, DMSO-d6): d 2.43 (s, 3H), 3.69(s, 3H), 3.73 (s, 3H), 4.58(s, 1H), 6.42–6.45 (m, 1H), 6.52–6.53
(d, 1H), 6.97–6.99 (d, 1H), 7.17 (s, 2H) 7.34–7.36 (d, 3H), 7.50–7.53 (m, 1H), 7.71 (s, 1H); MS: m/z = 390 (M+). Compound 4e: Yellow solid, IR
(KBr): y max = 3477, 3336, 2198, 1758, 1685, 1586, 1410, 1190, 1185, 1058, 817 cmꢂ1; 1H NMR: (400 MHz, DMSO-d6): d 2.43 (s, 3H), 4.66 (s,
1H), 7.36–7.38 (d, 1H), 7.53–7.59 (t, 4H), 7.72 (s, 1H), 8.17–8.19 (d, 2H); MS: m/z = 375 (M+).