Fe3O4 nanoparticles: A powerful and magnetically recoverable catalyst for the synthesis of novel calix[4]resorcinarenes

Article abstract of DOI:10.1016/j.cclet.2011.11.005

A simple synthesis of novel and known calix[4]resorcinarenes derivatives has been achieved by the condensation of resorcinol and different aromatic aldehydes in the presence of catalytic amounts of Fe₃O₄ nanoparticles under solvent-f

Full text of DOI:10.1016/j.cclet.2011.11.005

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Chinese Chemical Letters 23 (2012) 173–176
www.elsevier.com/locate/cclet
Fe3O4 nanoparticles: A powerful and magnetically recoverable
catalyst for the synthesis of novel calix[4]resorcinarenes
a
b
b
Bahador Karami a, , S. Jafar Hoseini , Shaghayegh Nikoseresht , Saeed Khodabakhshi
*
a Department of Chemistry, Yasouj University, Yasouj 75918-74831, P.O. Box 353, Iran
b Department of Chemistry, Gachsaran Branch, Islamic Azad University, Gachsaran 75817, Iran
Received 25 August 2011
Available online 21 December 2011
Abstract
A simple synthesis of novel and known calix[4]resorcinarenes derivatives has been achieved by the condensation of resorcinol
and different aromatic aldehydes in the presence of catalytic amounts of Fe3O4 nanoparticles under solvent-free conditions. The
experimental conditions have been thoroughly optimized and established, allowing significant rate enhancements and good to
excellent yields. The reactions can be run safely without using any toxic organic solvents under mild reaction conditions. The Fe3O4
nanoparticles were characterized by powdered X-ray diffraction (XRD), transmission electron microscopy (TEM) and FT-IR
spectroscopy.
# 2011 Published by Elsevier B.V. on behalf of Chinese Chemical Society.
Keywords: Fe3O4 nanoparticles; Calix[4]resorcinarenes; Resorcinol; Arylaldehyde
The challenge in chemistry to develop the practical methods, reaction media, conditions and/or the use of materials
based on the idea of green chemistry is one of the important issues in the scientific community. However, in recent
years, the concept of ‘‘Green Chemistry’’ has emerged as one of the guiding principles of the environmentally organic
synthesis. Recently, preparing and employing the nanoparticles (NPs) in organic synthesis has been the subject of
intense interests. Using nanoparticles (NPs) offers advantages in ‘‘clean’’ chemistry since, in addition to being readily
recovered; they are non-toxic and widely accessible [1]. The NP surface can be functionalized to allow the attachment
of catalytically active groups [2]. Among the organic macrocyclic compounds, calix[4]resorcinarenes, a subclass of
calixarenes, are large cyclic tetramers which have found application [3] as macrocyclic receptors and dendrimers in
biological systems [4], nanoparticles [5], nano-capsule [6], supramolecular tectons [7], optical chemosensors [8], host
molecules [9], as components in liquid crystals [10], photoresists [11], selective membranes [12], HPLC stationary
phases [13], surface reforming agents [14], as ion channel mimics [15], and metal ion extraction agents [16]. Besides,
some calix[4]arene show metal ions recognition properties [17,18].
It should be noted that the synthesis of calix[4]resorcinarenes was first reported in the late 19th century by Bayer
based on the concentrated sulfuric acid catalyzed cyclocondensation of benzaldehyde and resorcinol [19]. Although
different synthetic routes have been used for the synthesis of calix[4]resorcinarene derivatives by employing some.
* Corresponding author.
E-mail address: karami@mail.yu.ac.ir (B. Karami).
1001-8417/$ – see front matter # 2011 Published by Elsevier B.V. on behalf of Chinese Chemical Society.
doi:10.1016/j.cclet.2011.11.005

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B. Karami et al. / Chinese Chemical Letters 23 (2012) 173–176
HO
OH
OH
OH
HO
OH
O
HO
HO
Fe O nanoparticles
R
R
3
4
(5 mol%)
+
R
R
R
H
o
Solvent-free, 120
C
1
2
OH HO
3
Scheme 1. General procedure for the synthesis of phenyl calix[4]resorcinarenes.
Lewis acid catalyst, however, some of the strategies suffer from the drawbacks such as low product yield, cumbersome
isolation of the product and long reaction time. In the past few years, we have been involved in a program directed
towards developing simple, novel, and facile methods for the preparation of organic compounds using various
catalysts and readily available starting materials [20]. This stimulated our interest for further studies on the chemistry
of catalysts.
In this work, we describe a new and green strategy based on the condensation of resorcinol 1 with arylaldehyde 2
using Fe3O4 nanoparticle as a powerful, safe and recyclable catalyst under solvent-free conditions for the preparation
of novel and known calix[4]resorcinarene derivatives 3 (Scheme 1). It should be mentioned that in a previous study,
Huanwang Jing and Dongsheng Bai et al. reported the synthesis of cyclic carbonate from epoxide and CO2 catalyzed
by magnetic nanoparticle-supported porphyrin [21].
To investigate the suitable reaction conditions, the reaction of benzaldehyde with resorcinol was taken as a model
reaction. At first, we found that in the absence of Fe3O4 nanoparticles, the reaction did not proceed even at high
temperature. After examining the various amounts of Fe3O4 nanoparticles at 120 8C, it was found that the reaction can
be efficiently carried out by adding 5 mol% of the catalyst under solvent-free conditions in a short time span of 15 min.
The use of excessive amounts of the catalyst does not increase the yield and reaction rate. According to Table 1, under
the optimized reaction conditions, a number of aromatic aldehydes were allowed to undergo reaction with resorcinol in
a molar ratio of 1:1 with catalyst affording calix[4]resorcinarenes 3a–3i in good to excellent yields.
In another variation, in order to comparison of catalytic activity of Fe3O4 powder with Fe3O4 nanoparticles, two
parallel reactions, one through the employing the Fe3O4 powder and another by employing the Fe3O4 nanoparticles
were designed. The Fe3O4 nanoparticles catalyst plays an important role in the completion of this process. As shown in
Table 2, the product yields were moderate (58–77%) after 43–70 min, when the reactions were carried out with Fe3O4
powder whereas the same reactions in the presence of Fe3O4 nanoparticles gave good to excellent yields (78–92%)
after 15–43 min under solvent less conditions.
It should be reminded that the solids with a smaller particle size (e.g. nano chips) react more quickly than solids
with a larger particle size (e.g. powders). In fact, this is due to the number of sites available for a reaction to occur. So
more collisions can occur and therefore more ‘‘Effective Collision’’ can happen.
Table 1
Synthesis of calix[4]resorcinarene derivatives catalyzed with Fe3O4 nanoparticles under solvent-free conditions at 120 8C.
Entry
Product
R
Time (min)
Yield (%)a
M.p., 8C (decompose)
1
2
3a
3b
C6H5
15
80
92
85
297
298
O
H
3
4
5
6
7
8
9
3c
3d
3e
3f
2-OH–3-MeO–C6H5
2-Cl–C6H5
60
17
40
33
30
60
43
82
90
84
90
95
89
78
264
270
262
264
269
225
240
4-MeO–C6H5
4-Cl–C6H5
3g
3h
3i
3-Br–C6H5
2-NO2–C6H5
4-Me–C6H5
a
Isolated yields.

B. Karami et al. / Chinese Chemical Letters 23 (2012) 173–176
175
Table 2
Comparison of catalytic activity of Fe3O4 powder and Fe3O4 nanoparticles in the synthesis of phenyl calix[4]resorcinarene 3a.
Entry
Product
Fe3O4
Fe3O4 nanoparticles
Yield (%)a
Yield (%)a
Time (min)
Time (min)
1
2
3
3a
3g
3i
77
60
58
43
56
70
92
95
78
15
30
43
a
Isolated yields.
Fig. 1. (a) The powder X-ray diffraction pattern of the Fe3O4 nanoparticles; (b) TEM image shows spherical Fe3O4 nanoparticles with 10 nm; (c)
SEM image of Fe3O4 nanoparticles; and (d) FT-IR spectra of Fe3O4 nanoparticles.
Fig. 1a shows the XRD patterns of Fe3O4 nanoparticles. A number of prominent Bragg reflections by their indices
((2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0)) reveal that the resultant nanoparticles were Fe3O4 with a spinel
structure [22]. The size of the Fe3O4 nanoparticles was also determined from X-ray line broading using the Debye–
˚
Scherrer formula given as D = 0.9l/b cos u, where D is the average crystalline size (A), l the X-ray wavelength used
(nm), b the angular line width at half maximum intensity (radians) and u the Bragg’s angle (8). For (3 1 1) reflection at
˚
2u ꢀ 368, for b = 0.011 radians (0.648), l = 1.54 A and u ꢀ 188, the average size of the Fe3O4 nanoparticles is
estimated to be around 13 nm. Transmission electron microscopy (TEM) analyses were used for characterization
(Fig. 1b). The TEM image reveals the spherical Fe3O4 nanoparticles with average size 10 nm. In characterization of
Fe3O4 nanoparticles, in order to observe the morphology of the Fe3O4 nanoparticles in larger area, SEM images were
also provided (Fig. 1c). The FT-IR spectra of Fe3O4 nanoparticles are shown in Fig. 1d. The absorbance bands at
584.3 cmÀ1 ascribed to Fe2+–O2À which are consistent with the reported IR spectra for spinel Fe3O4 [23,24].
Although the exact mechanism for this reaction over Fe3O4 nanoparticles is not so clear, a feasible pathway might
involve the complexation of iron NPs with the carbonyl, thereby acting as a Lewis acid, and also playing a complex
role in promoting the dehydration and cyclization steps.
The need to implement green chemistry principles is a driving force towards the development of recoverable and
reusable catalysts and avoidance of the use of toxic and inexpensive organic solvents. It should be mentioned that the
main disadvantage of many of the reported methods for the synthesis of calix[4]resorcinarenes is that the catalysts are
destroyed in the work-up procedure and cannot be recovered or reused. However, we found that magnetic nano
particles Fe3O4 showed high catalytic activity with short reaction time and can be recovered and reused for five cycles
without significant loss of activity.
1. General procedure for the preparation of Fe3O4 nanoparticles
To prepare Fe3O4 nanoparticles, 5.2 g of FeCl3 and 2.0 g of FeCl2 were successively dissolved in 25 mL of distilled
water containing 0.85 mL of 12.1 mol/L HCl. The resulting solution was added dropwise into 250 mL of 1.5 mol/L
NaOH solution under vigorous stirring. The last step generated an instant black precipitate. The precipitate was
isolated in the magnetic field, and the supernatant was removed from the precipitate by decantation [25].

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B. Karami et al. / Chinese Chemical Letters 23 (2012) 173–176
2. General procedure for the rapid synthesis of calix[4]resorcinarene derivatives
A mixture of resorcinol 1 (1 mmol), aryl aldehyde 2 (1 mmol), and Fe3O4 nanoparticles (5 mol%) was stirred and
heated at 120 8C in a preheated oil bath for appropriate time (Table 2). After completion of the reaction as indicated by
TLC (ethyl acetate/n-hexane 7:3), the reaction mixture was cooled down to room temperature and dissolved in
methanol to separate the catalyst through the magnetic absorption by a magnet. After separating the catalyst, the
solution was heated and filtered to afford the pure product 3. At the end of the reaction, the separated catalyst was
washed with diethyl ether, dried at 130 8C for 1 h, and reused in another reaction.
To conclude, a green synthetic route to novel and known calix[4]resorcinarene derivatives using Fe3O4
nanoparticles under solvent-free conditions was presented. Using this method not only gives high yield and purity but
also is a cheap, speedy, facile, and eco-friendly method throughout the course of the reaction.
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