F. Zamani, E. Izadi / Catalysis Communications 42 (2013) 104–108
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In the first step, phenylacetic acid coated Fe3O4 nanocomposite was
synthesized by the method as reported previously [24]. FeCl3.6H2O
(13 g) and FeCl2.4H2O (4.8 g) were dissolved in 100 mL deionized
water and stirred at 40 °C for 15 min under nitrogen atmosphere.
Then, 8 mL phenylacetic acid (PAA) was added to the above mixture
and PH was adjusted to 11 with NH4OH solution (25 wt.%). The suspen-
sion was then refluxed at 100 °C for 6 h under nitrogen atmosphere
with vigorous stirring. Finally, the obtained nanocomposite was sep-
arated from the aqueous solution by magnetic decantation, washed
several times with distilled water and then dried in a vacuum oven
overnight to yield Fe3O4/PAA.
In the second step, the Fe3O4/PAA was sulfonated using various
amounts of chlorosulfonic acid (10.5, 12.5, 14.5, 16.5, 18.5 and
20.5 mmol). The Fe3O4/PAA composite (1 g) was dispersed in 10 mL
of acetonitrile in a three-neck flask glass reactor. Chlorosulfonic acid
was added drop-wise into the mixture at room temperature. Upon
completion of the addition, the mixture was stirred for 6 h under N2 at-
mosphere at room temperature. The resulted magnetic nanocomposite
was separated from the suspension by an external magnet, washed
several times with acetonitrile and anhydrous ethanol and dried at
60 °C to give Fe3O4/PAA-SO3H.
The content of acid sites of Fe3O4/PAA-SO3H nanocomposite was
estimated by back titration using HCl (0.337 N). 10 mL of NaOH
(0.130 N) was added to 0.1 g of these composites and stirred for
30 min. The catalysts were separated and washed with deionized
water. The excess amount of NaOH was titrated with HCl (0.337 N)
in the presence of phenolphthalein as indicator. The acid site contents
were 2.14, 2.58, 2.93, 3.32, 3.71 and 3.76 mmol g−1 for 10.5, 12.5,
14.5, 16.5, 18.5 and 20.5 mmol of used chlorosulfonic acid, respectively.
Fig. 1. X-ray powder diffraction patterns of Fe3O4/PAA-SO3H nanocomposite, (a) uncalcined
and (b) calcined form (at 600 °C for 3 h).
spinel structure of Fe3O4 [25], which can be assigned to the diffrac-
tions of the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0)
faces of the crystals, respectively. In addition, the XRD patterns rep-
resent similar diffraction peaks which indicate that the coating agent
does not significantly affect the crystal structure of the magnetite
nanoparticles. The XRD results indicate that the Fe3O4 particles
were successfully coated with the phenylacetic acid.
2.2. Catalyst characterization
Fig. 2 depicts the FT-IR spectrum of Fe3O4/PAA-SO3H nanocompos-
ite. The adsorption peak at 592 cm−1 is the characteristic absorption
of Fe\O bond which confirms the presence of Fe3O4 nanoparticles.
The absorption peaks at 3000–3100 cm−1 and 1688–1850 cm−1 corre-
spond to C\H of the benzene ring. The absorption peaks at 1461 and
1605 cm−1 correspond to the C\C bonds in the benzene ring, and the
absorption peaks at 700 and 755 cm−1 are caused by the bending vibra-
tion of the C\H on the benzene ring [26]. It is also clear that the strong
The crystalline structures of the samples were evaluated by X-ray
diffraction (XRD) analysis on a Bruker D8 Advance diffractometer with
CuKα radiation at 40 kV and 20 mA. Fourier transform infrared (FT-IR)
spectra were recorded with a Perkin Elmer 65 spectrometer in the
range of 400–4000 cm−1. Transmission electron microscopy (TEM)
analysis was performed on a Phillips CM10 microscope at an acceler-
ating voltage of 200 kV. Magnetization measurements were carried
out on a BHV-55 vibrating sample magnetometer (VSM). Thermal
stability of the catalyst was investigated by Thermogravimetric analysis
(TGA, TSTA Type 503) at a heating rate of 10 °C/min under nitrogen
atmosphere.
C_O band of carboxyl group, which is generally present at 1650 cm−1
,
was absent in the spectrum of Fe3O4/PAA-SO3H. Instead, two charac-
teristic bands appeared at 1569 and 1512 cm−1, which were as-
cribed to COO− and COO− stretch of carboxyl group [24]. This
as
s
result can be indicated that the bonding pattern of the carboxylic
acids on the surface of Fe3O4 nanoparticles was a combination of
molecules bonded symmetrically and molecules bonded at an angle
to the surface [24]. The bands at 2800–3000 cm−1 were attributed
to the asymmetric and symmetric CH2 stretching vibrations. In addi-
tion, two bands at 1381 cm−1 and 1245 cm−1 can be seen which are
related to grafted sulfonic acid groups on rings [27]. Based on the
above observations, it can be concluded that the Fe3O4 nanoparticles
2.3. General procedure for Biginelli reaction catalyzed by Fe3O4/PAA-SO3H
In a typical procedure, a mixture of aldehyde (1 mmol), ethyl
acetoacetate (1 mmol), urea (or thiourea) (1.2 mmol) and Fe3O4/
PAA-SO3H (0.06 g) was placed in a round-bottom flask. The suspen-
sion was stirred at room temperature. Completion of the reaction
was monitored by Thin Layer Chromatography (TLC). After comple-
tion of the reaction, the catalyst was separated from the solid crude
product using an external magnet. The precipitated solid was then
collected and recrystallized from ethanol to afford the pure product.
The product was identified with 1H NMR, 13C NMR and FT-IR spec-
troscopy techniques.
3. Results and discussion
3.1. Catalyst characterization
Crystalline phases of the Fe3O4/PAA-SO3H nanocomposite before
calcination and after calcination (at 600 °C for 3 h) were identified
by XRD and the resultant patterns were shown in Fig. 1. The XRD pat-
terns indicate that for both products (Fig. 1a,b) the diffraction peaks
at 2θ of 30.1°, 35.4°, 43.1°, 53.4°, 56.9° and 62.5° correspond to the
Fig. 2. FT-IR spectrum of Fe3O4/PAA-SO3H nanocomposite.