Magnetically separable γ-Fe2O3 nanoparticles: An efficient catalyst for acylation of alcohols, phenols, and amines using sonication energy under solvent free condition

Article abstract of DOI:10.1016/j.molcata.2015.04.002

This paper reports a facile synthesis of magnetically separable iron oxide (γ-Fe₂O₃) nanoparticles using thermolysis method. The structural and morphological study of the synthesized γ-Fe₂O₃ nanoparticles was carried out using X-ray diffraction (XRD), field emission gun-scanning electron microscopy (FEG-SEM), energy dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) techniques. The electron microscopy reveals that the γ-Fe₂O₃ nanoparticles have spherical morphology with a particle size in the range of 40-100 nm. The XPS study confirmed the Fe is in +3 oxidation state. The synthesized γ-Fe₂O₃ nanoparticles have been used as an efficient heterogeneous catalyst for the organic transformation between phenols, alcohols, and amines with acetic anhydride under sonication using mild reaction conditions. Various electrons withdrawing and electrons donating substrates show an excellent yield of desired products with the advantage of magnetic separation and reusability of γ-Fe₂O₃ nanocatalyst.

Full text of DOI:10.1016/j.molcata.2015.04.002

Accepted Manuscript
Title: Magnetically separable ␥–Fe2O3 nanoparticles: An
efficient catalyst for acylation of alcohols, phenols and amines
using sonication energy under solvent free condition
Author: Manohar A. Bhosale Divya Ummineni Takehiko
Sasaki Daisuke Nishio-Hamane Bhalchandra M. Bhanage
PII:
S1381-1169(15)00141-7
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.04.002
MOLCAA 9465
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
12-2-2015
24-3-2015
6-4-2015
Please cite this article as: Manohar A.Bhosale, Divya Ummineni, Takehiko
Sasaki, Daisuke Nishio-Hamane, Bhalchandra M.Bhanage, Magnetically separable
rmgammandashFe2O3 nanoparticles: An efficient catalyst for acylation of alcohols,
phenols and amines using sonication energy under solvent free condition, Journal of
Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2015.04.002
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Magnetically separable γ–Fe2O3 nanoparticles: An efficient catalyst for acylation of
alcohols, phenols and amines using sonication energy under solvent free condition
Manohar A. Bhosale,a Divya Ummineni,b Takehiko Sasaki,c Daisuke Nishio-Hamaned and
Bhalchandra M. Bhanagea*
a Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400019,
India.
b Acharya Nagarjuna University, Guntur, Andhra Pradesh 522510, India.
c Department of Complexity Science and Engineering, Graduate School of Frontier Sciences,
The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
d Institute of Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba, 277-8581, Japan.
* Corresponding author- Tel.: +91 22 3361 2601; Fax: +91 22 3361 1020.
Email: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
Graphical abstract
An efficient synthesis of magnetically separable iron oxide nanoparticles and their
application as a recyclable catalyst for acylation of phenols, alcohols and amines by
sonication under solvent free condition at room temperature has been reported.
1

Research Highlights:
 Simple and efficient protocol for synthesis of magnetic separable γ-Fe2O3
nanoparticles.
 γ-Fe2O3 nanoparticles show excellent catalytic activity in acylation reaction at mild
reaction conditions.
 First time used sonication energy for acylation reaction of phenols, alcohols and
amines at room temperature.
 The γ-Fe2O3 catalyst was recycled by applying strong magnet and reused up to 4th run.
Abstract
This paper reports a facile synthesis of magnetically separable iron oxide (γ–Fe2O3)
nanoparticles using thermolysis method. The structural and morphological study of the
synthesized γ–Fe2O3 nanoparticles was carried out using X-ray diffraction (XRD), field
emission gun-scanning electron microscopy (FEG-SEM), energy dispersive X-ray spectrum
(EDS), transmission electron microscopy (TEM), fourier transform infrared spectroscopy
(FT-IR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS)
techniques. The electron microscopy reveals that the γ–Fe2O3 nanoparticles have spherical
morphology with a particle size in the range of 40 nm to 100 nm. The XPS study confirmed
the Fe is in +3 oxidation state. The synthesized γ–Fe2O3 nanoparticles have been used as an
efficient heterogeneous catalyst for the organic transformation between phenols, alcohols and
amines with acetic anhydride under sonication using mild reaction conditions. Various
electrons withdrawing and electrons donating substrates show an excellent yield of desired
products with the advantage of magnetic separation and reusability of γ–Fe2O3 nanocatalyst.
2

Keywords
γ–Fe2O3 nanoparticles; thermolysis; characterization; X-ray photoelectron spectroscopy;
coupling reaction.
1. Introduction
The synthesis of nanoparticles has been receiving increasing interest in the current
research due to their extraordinary physicochemical properties as compared to their bulk
counterparts. The fabrication of nanoparticles using green methodologies which can control
nucleation and propagation, to get size and shape selective nanoparticles is one of the
challenging tasks [1]. Iron oxide is an important inorganic material having magnetic
properties as well as good stability in aqueous dispersion [2]. Particularly, Fe2O3
nanoparticles find wide applications in gas sensing [3], Li-ion batteries [4,5], magnetizations
and water treatment [6,7], hydrogen production [8], cancer treatment [9], surface enhanced
Raman scattering and electrocatalysis [10], degradation of pharmaceutical compounds [11],
supercapacitor [12] and as a heterogeneous catalyst [13-15].
In literature, the functionalized iron oxide nanoparticles are synthesized using various
methods and are used in biodiesel production [16], photodegradation of
hexachlorocyclohexane [17], removal of fluoride in water [18], and catalysis [19,20]. Several
methods are reported to synthesize iron oxide nanoparticles, including hydrothermal [21],
solvothermal [22], co-precipitation [23], forced hydrolysis [24], electron beam irradiation
[25], microemulsion [26], sonochemical [27], and biosynthetic methods [28,29]. Recently,
Taniguchi and co-workers reported hydrothermal synthesis of iron oxide nanoparticles using
stainless steel autoclave [21], but the methodology has limitations such as use of high
3

temperature (up to 230 °C), longer reaction time and requirement of pressure. Almeida and
co-workers demonstrated the synthesis of iron oxide nanoparticles by hydrothermal method
in a Teflon-lined steel autoclave [30]. Nemati and groups synthesized iron oxide
nanoparticles by hydrothermal route [31]. These protocols achieve particles in nano region,
but they have one or more drawbacks as mentioned above. Therefore, there is a need to
develop an alternative method which can be simple, economical and greener for the synthesis
of iron oxide nanoparticles.
Nowadays, current research is not only focused on development of simple and greener
routes for the synthesis of morphology controlled nanoparticles, but is also focused on their
applications in various fields. Magnetic separable nanoparticles show good catalytic activity
in catalysis because of high surface area, high mechanical stability, increasing contacts
between catalyst and reactants and good dispersion in reaction mixture. The magnetic
separable nanoparticles have advantages such as insoluble in reaction mixture, paramagnetic
nature, and easy separation of nanocatalyst by using magnet which avoids the catalyst
filtration; it prevents the aggregation of nanocatalyst which increases the durability of the
catalysts, recycling and reusability of catalyst [32]. The researchers paid their efforts to
synthesis of magnetic s magnetic separable nanoparticles and their applications in catalysis
[33-35]. In our recent work, we have developed several facile and greener synthetic routes for
nanoparticles and developed their applications in catalysis [36-40]. In the present work, we
have developed an efficient method for the synthesis of γ–Fe2O3 nanoparticles by thermolysis
method. Herein, iron acetylacetonate is used as a starting material, oleic acid as surfactant
which prevents the agglomeration of particles, n-butylamine and 1,6-hexandiol acts as a
binding or capping agent as well as responsible to control the morphology of γ–Fe2O3
nanoparticles. Furthermore, we have shown the application of γ–Fe2O3 nanoparticles in
organic reaction for the coupling of phenols, alcohols and amines with acetic anhydride using
4

sonication energy. The synthesized γ–Fe2O3 nanoparticles exhibit good catalytic activity for
the reaction with an advantage of catalyst recyclability. The catalyst could be reused up to
fourth run without loss of catalytic activity. Notably the reaction works under low catalyst
o
loading, solvent free condition, at room temperature (28 C) and first time demonstrates the
use of simple sonication energy for this organic coupling reaction with catalyst recyclability.
This is a facile technique for synthesis of γ–Fe2O3 nanoparticles and it can also be further
extended for synthesis of other metal oxides.
2. Experimental Section
2.1 Materials
A.R. grade Iron acetylacetonate [Fe(acac)3] was procured from Spectrochem Pvt. Ltd.
India. n-butylamine, oleic acid and 1,6-hexandiol were procured from S. D. Fine chemicals
Pvt. Ltd. India. All chemicals were of high purity and were used without further purification.
2.2 Synthesis of γ–Fe2O3 nanoparticles
In a typical method for the synthesis of γ–Fe2O3 nanoparticles, a mixture of 200 mg
(0.57 mmol) of iron acetylacetonate with 6 mL of n-butylamine and 1 mL of oleic acid were
taken in a 100 mL round bottom flask. 1,6-hexandiol (492 mg, 4.16 mmol) was added under
stirring to the above mixture at room temperature. The reaction flask was sealed tightly with
lid using the Teflon tape around it. The reaction mixture was stirred vigorously with magnetic
stirrer at 100 °C for 2 h. A red colour precipitate was observed indicating the formation of γ–
Fe2O3 nanoparticles. After completion of reaction, the reaction mass was diluted with
distilled water and centrifuged at 8000 rpm for 10 min. The product was washed with
distilled water and absolute ethanol several times and dried at 70 °C in oven. The obtained
nanoparticles were characterized by different analytical techniques.
2.3 Method of characterization of γ–Fe2O3 nanoparticles
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As prepared γ–Fe2O3 nanoparticles were characterized by X-ray diffractometer
(Shimadzu XRD-6100 using CuKα radiations = 1.5405 Å) with scanning rate 2° per min and
2 theta (θ) angle ranging from 20° to 75° at current 30.0 mA and voltage 40.0 kW. The
morphology of the sample was examined by field emission gun-scanning electron
microscopy (FEG-SEM) analysis using Tescan MIRA 3 model and transmission electron
microscopy (TEM) using JEOL JEM-2100 in ISSP, operating voltage at 200 kV. The energy
dispersive X-ray spectrum (EDS) was recorded by using INCA x-act Oxford instrument
(Model 51-ADD0007). X-ray photoelectron spectra (XPS) were monitored by using PHI
5000 Versa Probe with a monochromatic focused (100 µm x 100 µm) Al Kα X-ray radiation
(15 kV, 30 mA) and duel beam neutralization using a combination of argon ion gun and
electron irradiation. Fourier transform infrared spectroscopy (FT-IR) was recorded on
JASCO-FTIR-400 spectrometer. Thermogravimetric analysis (TGA) was carried out using
Perkin Elmer STA 6000. Brunauer–Emmett–Teller (BET) surface area and pore size was
analyzed on ASAP 2010 (Micromeritics, USA) instrument.
2.4 General procedure for acylation reaction
A 25 mL sealed tube containing a magnetic stir bar was charged with
phenol/alcohol/amine (1 mmol) and acetic anhydride (1.5 mmol), nano γ–Fe2O3 (5 mol%, 8
mg) as catalyst. The reaction mixture was kept for sonication in sonication bath at room
o
temperature (28 C) for 1 h. The ultrasonic bath (Labman Scientific Instruments, Model –
LMUC 4) had a frequency of 33 kHz and electric power rating of 100 W. The reaction
progress was monitored on thin-layer chromatography (TLC) and gas chromatography
(Perkin–Elmer, GC Clarus 400) analysis. After completion of the reaction, the reaction
mixture was diluted with ethyl acetate and catalyst was separated from reaction mixture by
using a strong magnet. The separated catalyst was washed with distilled water and absolute
ethanol several times then dried in oven and reused for further reaction. The reaction mixture
6

was washed with sat. NaHCO3 solution (1 × 15 mL) and the product was extracted with ethyl
acetate (3 × 10 mL) and dried over Na2SO4 and evaporated under vacuum. All the obtained
products are well known in the literature and were confirmed by gas chromatography-mass
spectrometry (Shimadzu GCMS-QP 2010) analysis by comparison with literature data.
3. Results and Discussion
3.1 Characterization of synthesized Fe2O3 nanoparticles
The synthesized γ–Fe2O3 nanoparticles were characterized by FEG-SEM (Fig. 1),
which shows that particles are in nano region and spherical in shape along with some
aggregation of nanoparticles. Fig. 1 shows FEG-SEM images of the same sample with
different magnification. Fig. 1a and 1b are low magnification FEG-SEM images of γ–Fe2O3
nanoparticles whereas the Fig. 1c and 1d are high magnification FEG-SEM images of γ–
Fe2O3 nanoparticles, which indicates that the particle size of γ–Fe2O3 nanoparticles is in the
range of 40 nm to 100 nm which leads to the availability of high surface area for catalytic
activity (see ESI Fig. S2). The particle morphology was examined using TEM analysis. TEM
analysis was carried out by dispersing γ–Fe2O3 powder sample in ethanol and then it was
exposed to ultrasonication bath for 10 min. A drop from this slurry was deposited on a copper
grid. The TEM images Fig. 2a show the low magnification image of γ–Fe2O3 nanoparticles
whereas Fig. 2b, 2c and 2d are the high magnification images which show spherical
morphology with size range 40 nm to 100 nm. (see ESI Fig. S3). The morphology and
particle size of γ–Fe2O3 nanoparticles from TEM analysis is in good agreement with results
obtained by FEG-SEM analysis.
.
7

To check the effect of 1,6-hexanediol as a capping agent, we carried out the experiment
without 1,6-hexanediol. In surface morphological study, Fig. 3a and 3b are the high and low
magnification FEG-SEM images respectively, which reveals that there was no specific
morphology was observed for this reaction as compared to the reaction carried out in
presence 1,6-hexanediol (Fig. 1). This indicates that 1,6-hexanediol is essential to control the
crystal morphology of γ–Fe2O3 nanoparticles.
The phase identification of γ–Fe2O3 nanoparticles was carried out using XRD pattern (Fig. 4).
XRD indicates the (311), (400), (422), (511), (300) and (533) planes, confirm the formation
of γ–Fe2O3 nanoparticles. The obtained results from XRD are in good agreement with JCPDS
card No. 39-1346. EDS analysis clearly indicates presence of Fe and oxygen elements in the
material and confirms the purity of the prepared nanoparticles (Fig. 5a). In Fig. 5b, a strong
absorption band seen at 551 cm-1 in FT-IR spectrum of γ–Fe2O3 nanoparticles indicates the
presence of Fe–O bond. The band at 2846 and 2920 cm-1 can be attributed to C–H stretching
vibrations of alkyl chain, whereas the band at 1403 and 1532 cm-1 can be attributed to the
angular deformation of water δH−OH, it may also due to absorption peaks of n–butylamine,
acetylacetonate, oleic acid and 1,6-hexanediol. The energy dispersive X-ray elemental
mapping for γ–Fe2O3 nanoparticles shows that Fe (Fig. 6b, green) and oxygen (Fig. 6c, red)
species coexist in the material. The detailed analysis of the Fe (green) and oxygen (red)
mapping reveals that the concentration of oxygen is more than that of Fe.
Fig. 7a shows XPS survey spectrum of the synthesized γ–Fe2O3 nanoparticles, which shows
photoelectron peaks of iron (Fe2p), oxygen (O1s) and carbon (C1s) present on the surface.
The carbon peak comes from the carbon tape used as support in XPS analysis. The
corresponding high resolution XPS spectra at 530.4 eV indicates the O1s region (Fig. 7b) and
8

the high resolution XPS spectra of Fe2p region shown in Fig. 7c is attributed to presence of
Fe2O3. The peak observed at 710.9 eV is analogous to Fe2p3/2 and the peak at 725 eV is
analogous to Fe2p1/2. Additional peaks at 719 eV and 731.4 eV are the two shake-up satellite
peaks. The appearance of Fe3+ cations (710.9 eV) rather than Fe2+ cations (709 eV) indicates
the presence of the Fe2O3 phase [41].
The The Brunauer–Emmett–Teller (BET) specific surface area of the γ–Fe2O3 nanoparticles
is an important parameter for the high catalytic activity. Fig. 8a shows nitrogen adsorption
and desorption curve of γ–Fe2O3 nanoparticles. Analysis of the isotherms exhibits 23.8 m2/g
of the BET surface area. The pore volume and average pore diameter were found to be 0.20
cm3/g and 34.7 nm, respectively for the γ–Fe2O3 nanoparticles. TGA curve (Fig. 8b) indicates
weight loss in the range of 80 °C to 120 °C which is due to the evaporation of moisture
o
o
absorbed by γ–Fe2O3 material. Another weight loss between 250 C to 360 C is due to
o
decomposition of organic moieties such as 1,6-hexanediol (b.p. 208 C) and oleic acid (b.p.
o
360 C) which were used in the synthesis of γ–Fe2O3 nanoparticles. Vibrating sample
magnetometer (VSM) analysis gives idea about the magnetic properties of the materials. The
M–H hysteresis loop for γ–Fe2O3 nanoparticles was measured at room temperature (Fig. 9).
The detail analysis signifies that the magnetization becomes 0.17 emu/g. As the particle size
decreases, the magnetization also decreases.
3.2 Catalytic application of γ–Fe2O3 nanoparticles
Recently, catalysis research has been focused towards greener and environmentally
benign protocols which avoid the use of volatile organic solvents, toxic reagents, harsh
reaction conditions and time-consuming processes [42]. Nanocatalysis has several advantages
in research over conventional catalyst systems or bulk materials such as large surface-to-
volume ratio; easy separation; low catalyst loading and recyclability of catalyst [43]. The use
9

of magnetically separable nanoparticles in catalysis has promising and versatile role in
current research due to their insoluble and paramagnetic nature as it enables easy separation
of the catalysts from the reaction mixture using external magnet [35,44]. The catalytic
activity of synthesized magnetically recoverable γ–Fe2O3 nanoparticles was checked for the
acylation reaction using phenols, alcohols and amines with acetic anhydride under solvent
o
free condition using sonication energy at room temperature (28 C) (Scheme 1). The
sonication energy has several advantages such as high efficiency, low waste, less energy
requirement, it produces cavitation bubbles which increases the interaction between reactant
and catalyst, accelerates the reaction speed, provides better mass and heat transfer efficiency
compared to conventional heating, economic and easy operation [45,46].
Recently, the Azizi and Heydari reported acylation of phenols and alcohols using
vitamin B1 supported on silica-encapsulated γ-Fe2O3 nanoparticles (nano γ-
Fe2O3@SiO2@vitamin B1) [47]. The methodology shows random formation of nanoparticles
and does not get the specific shape and size of nanomaterials. It as well suffers from limited
substrate scope. Rajabi and Luque have reported Fe/SBA-15 catalyzed acylation of phenols
and alcohols [48]. The protocol uses some temperature and high catalyst loading for the
reaction. These protocols use support to increase the catalytic activity, but our protocol
provides good catalytic activity without using any support. It further uses sonication energy at
room temperature. Hoseini et al. have demonstrated the use of Fe3O4 nanoparticles for the
Friedel-Crafts acylation reaction of anisole to ortho- and para- directing acylated products
[49]. Our protocol uses a variety of different starting reagents and yields O– and N– acylated
o
products using γ–Fe2O3 nanoparticles under sonication at room temperature (28 C).
Literature survey reveals that acylation reactions of phenols, alcohols and amines have been
carried out using various catalysts such as modified Y zeolites [50], amorphous carbon-silica
composites bearing sulfonic acid [51], poly(N-vinylimidazole) [52], sulfonic acid [53],
10

titanocene bis(perfluorooctanesulfonate) [54], RuCl3 in [bmim][PF6] ionic liquid [55] 4-(N,N-
dimethylamino)pyridine hydrochloride [56], NaCo(CO)4 [57], Ac2O–Py/Al2O3 [58], FeCl2
[59], cobalt(II) salen complex [60], ZnAl2O4@SiO2 nanocomposite [61], BiFeO3 [62],
anhydrous NiCl2 [63], thallium(III) chloride [64], ErCl3 [65], Gd(OTf)2 [66], Cu(OTf)2 [67]
and nano CdO [68]. Most of these protocols have several disadvantages like use of additives
and surfactants, requirement of co-catalysts, longer reaction times, high catalyst loading and
use of homogenous catalysts. To overcome these drawbacks, we explored the catalytic
activity of magnetically recoverable γ–Fe2O3 nanoparticles for acylation of phenols, alcohols
and amines and found that it gives excellent yield of the corresponding products. Notably, the
reaction does not require any additives; reaction works with low catalyst loading, under
solvent free conditions with good to excellent yields of the desired products with catalyst
recyclability making the protocol attractive. This is one of the simple and ecological protocol
for acylation of phenols, alcohols and amines.
Initially, the reaction of phenol with acetic anhydride was chosen as a model reaction and
effects of various parameters such as catalyst loading, catalyst screening and time were
studied using sonication bath (Labman Scientific Instruments, Model – LMUC 4 had
frequency 33 kHz and electric power 100 W) under solvent free condition. At the beginning,
the reaction was carried out in absence of the catalyst, but reaction did not proceed (Table 1,
entry 1). Then we screened the catalyst loading using model reaction (Table 1, entries 2–5). It
was observed that 5 mol% of catalyst gives an excellent yield (92%) of the desired product
(Table 1, entry 4). We have checked the temperature after completion of reaction; it was
o
o
observed that temperature rises from 28 C to 36 C at the end of reaction. Along with nano
γ–Fe2O3, we also screened various catalysts such as Fe(OAc)2, FeCl3, FeCl2, Fe(NO3)3, Bulk
Fe2O3, Nano Cu/Cu2O [69] and Nano ZnO [70] to increase the reaction outcome (Table 1,
11

entries 4, 6–12). Among these, the synthesized nano γ–Fe2O3 shows good catalytic activity
for the model reaction (Table 1, entry 4). Furthermore, we also investigated the effect of
reaction time (Table 1, entries 4, 13 and 14) and it was found that the highest yield of the
desired product was obtained within 1 hour (Table 1, entry 4). The respective turnover
number (TON) for all optimized reaction conditions was included in Table 1. We have
investigated the yield of acylation product (42%) after prolong sonication for 2 h. In this case
reversible reaction was takes place and observed the formation of starting materials. We have
o
carried out reaction in absence of sonication i.e. room temperature (28 C) with nano γ–
Fe2O3, but reaction does not work. We also checked reaction in absence of nano γ–Fe2O3
under long sonication (3 h) and studied the effect of sonication on reaction. It was observed
that formation of 10% yield of acylation product.
Thus, the optimized reaction conditions for acylation reaction were; phenol (1 mmol),
acetic anhydride (1.5 mmol), nano γ–Fe2O3 (5 mol%) and sonication for 1 h at room
temperature. In order to broaden the substrate scope of the developed protocol various
derivatives of phenols and alcohols were examined for the acylation reaction (Table 2). The
reaction with phenols containing electron withdrawing (Table 2, entries 1–6) as well as
electron donating substituents (Table 2, entries 7–11) were compatible under the optimized
reaction conditions and provided good to excellent yields of the corresponding products. It
was observed that the electron withdrawing substituents of phenol gave a good yield as
compared to electron donating substituents of phenol. We also studied various substrates of
alcohol at optimized reaction conditions and it was observed that alcohols furnish moderate
yields of respective products (Table 2, entries 12–16).
Table 2 Substrate study for the coupling reaction of phenols/alcohols and acetic anhydridesa
12

By considering the above optimized reaction conditions of acylation reaction of
phenol we extended the scope of developed protocol for acylation of various derivatives of
amines (Table 3). The reactions with various derivatives of aromatic amines with electron
donating and electron withdrawing groups provided the acylation products in good yields
(Table 3, entries 1–4). It was observed that electron donating substituents of amines furnish
excellent yield of desired products as compared to electron withdrawing substituents. In
addition we examined aliphatic amines (Table 3, entries 5–8), cyclic amines (Table 3, entries
9 and 10) and heterocyclic amines (Table 3, entries 11 and 12) for the acylation reaction and
all amines provide moderate to excellent yield of desired products.
In mechanism, the acylation reaction is initiated by coordination of the carbonyl
group of acetic anhydride with Fe ion of γ–Fe2O3 nanoparticles and activation of carbonyl
group takes place. The carbonyl group reacts with substrate which acts as a nucleophile and
results in to the acetate product (Scheme 2).
The recyclability of catalyst is a great advantage in reducing the overall cost in
process chemistry and decreasing environmental pollution. It eliminates involvement in the
synthesis and resale process. We have investigated magnetic separation and reusability of the
γ–Fe2O3 nanoparticles for the acylation reaction using phenol and acetic anhydride as
substrates under solvent free conditions. The γ–Fe2O3 nanocatalyst was reused successfully
up to fourth run with excellent catalytic activity (Fig. 10). Inductively coupled plasma atomic
emission spectroscopy (ICP-AES) analysis determines the elemental concentration in the
sample. We have checked the leaching of Fe metal from γ–Fe2O3 nanocatalyst by ICP-AES
analysis after fourth run and the 1.95 wt% concentration of Fe was detected. As shown in the
13

Fig. 11, after completion of reaction, the reaction mixture was diluted with ethyl acetate and
the catalyst was recovered from the reaction mixture by applying strong magnet. The catalyst
was washed with distilled water and absolute alcohol several times to remove the organic
impurities. The obtained γ–Fe2O3 nanocatalyst was dried in the oven and used as a catalyst
for recyclability study (see ESI Fig. S1). The morphological study of fresh nanocatalyst and
after the fourth run was shown in Fig. 12. The Fig. 12a displays FEG-SEM analysis of fresh
γ–Fe2O3 nanoparticles whereas Fig. 12b displays FEG-SEM analysis of magnetically
recycled γ–Fe2O3 nanocatalyst after the fourth run. The detail analysis of recycled catalyst
reveals that nanoparticles are spherical in shape along with somewhat more aggregation of
particles (Fig. 12b) than that of fresh nanoparticles (Fig. 12a).
Conclusion
In summary, a simple and facile protocol for the synthesis of γ–Fe2O3 nanoparticles has been
developed using thermolysis method. The n-butylamine and 1,6-hexandiol act as structure
inducing agents in the reaction and give spherical morphology to the nanoparticles. It was
observed that the synthesis without using 1,6-hexandiol gives random size and shape of the
nanoparticles. The presence of 1,6-hexandiol significantly impacts the overall nucleation
growth process for the synthesis of γ–Fe2O3 nanoparticles. Furthermore, we have shown the
catalytic applicability of synthesized γ–Fe2O3 nanoparticles for coupling reaction of phenols,
alcohols and amines with acetic anhydride using sonication energy (sonication bath) at room
temperature. Under the optimized reaction conditions various derivatives of phenols, alcohols
and amines provided good to excellent yield of the respective products with an advantage of
catalyst recyclability up to fourth run.
14

Acknowledgement
Author MAB is obliged to Council of Scientific and Industrial Research (CSIR), New Delhi,
India for the financial support. We are thanking to Department of Science and Technology
(DST), India for financial support for this work under Nano Mission Project No. SR/NM/NS-
1097/2011. XPS measurements were conducted in Research Hub for Advanced Nano
Characterization, the University of Tokyo, supported by the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), Japan. This work is supported by DST and JSPS
under the India–Japan Science Cooperative Program (Project No. DST/INT/JSPS/P-
152/2013). We are also thankful to Prof. C. V. Tomy from Department of Physics, Indian
Institute of Technology (IIT), Bombay for providing VSM analysis facility.
Electronic Supplementary Information
Electronic supplementary information includes the general information, general reaction
scheme, experimental procedure for the reaction, catalyst recyclability, characterization of γ–
Fe2O3 nanocatalyst by FEG-SEM and TEM analysis, and GC-MS analysis data of products.
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Scheme 1 Acylation reactions of phenol, alcohol or amine using γ–Fe2O3 nanoparticles.
Scheme 2 Proposed mechanism of nano γ–Fe2O3 catalyzed acylation reaction.
Figure 1 FEG-SEM images of γ–Fe2O3 nanoparticles.
Figure 2 TEM images of γ–Fe2O3 nanoparticles.
Figure 3 FEG-SEM images of γ–Fe2O3 nanoparticles without using 1,6-hexanediol
Figure 4 XRD pattern of γ–Fe2O3 nanoparticles (JCPDS No. 39-1346).
Figure 5 (a) EDS spectrum and (b) FT-IR spectrum of γ–Fe2O3 nanoparticles.
Figure 6 EDS composition mapping (a) FEG-SEM image (b) iron (green) (c) oxygen (red) for
γ–Fe2O3 nanoparticles.
Figure 7 (a) XPS survey spectrum (b) O1s region (c) Fe2p region for γ–Fe2O3 nanoparticles.
Figure 8 (a) N2 adsorption–desorption isotherm and (b) TGA of γ–Fe2O3 nanoparticles.
Figure 9 Room temperature M-H curve (VSM) for γ–Fe2O3 nanoparticles.
Figure 10 Investigation of recyclability of the γ–Fe2O3 nanocatalyst.
Figure 11 Magnetic separations and recycling of the γ–Fe2O3 nanocatalyst.
Figure 12 FEG-SEM images of magnetic separable γ–Fe2O3 nanocatalyst after 4th run.
20

Table 1 Optimization of reaction conditionsa
Entry
Catalyst
Catalyst
(mol%)
Time
(h)
Yield [%]b
TON
Effect of catalyst loading
1
2
3
4
5
No catalyst
0
1
1
1
1
1
1
00
48
64
92
94
00
48
nano γ–Fe2O3
nano γ–Fe2O3
nano γ–Fe2O3
nano γ–Fe2O3
3
21.3
18.4
9.4
5
10
Effect of catalyst screening
6
Fe(OAc)2
FeCl3
5
5
5
5
5
5
5
1
1
1
1
1
1
1
34
78
80
20
48
28
56
6.8
15.6
16
7
8
FeCl2
9
Fe(NO3)3
Bulk Fe2O3
Nano Cu/Cu2Oc
Nano ZnOd
4
10
9.6
5.6
11.2
11
12
Effect of Time
13
nano γ–Fe2O3
nano γ–Fe2O3
5
5
0.5
1.5
60
90
12
18
14
a
Reaction condition: phenol (1 mmol), acetic anhydride (1.5 mmol), catalyst (5 mol%),
sonication for 1 h. b GC yield. c Synthesized according to Ref. 69. d Synthesized according to
Ref. 70.
21

Table 2 Substrate study for the coupling reaction of phenols/alcohols and acetic anhydridesa
Entry
1
phenol
Acetic anhydride
Product
Yield [%]b
92
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O2N
O
2
3
4
5
6
7
8
9
85
90
94
96
75
36
56
30
O
O
O
O
O
O
O
O
O
OH
O2N
O
O
O
O
10
11
12
44
65
64
O
O
O
O
O
O
O
O
O
O
O
13
14
15
66
58
53
O
O
O
22

O
O
16c
45
O
a Reaction condition: phenol (1 mmol), acetic anhydride (1.5 mmol), nano γ–Fe2O3 (5 mol%),
sonication for 1 h. b GC yield. c acetic anhydride (3 mmol).
Table 3 Substrate study for the coupling reaction of amines and acetic anhydridesa
Entry
1
amine
acetic anhydride
Product
Yield [%]b
95
O
O
O
O
O
O
O
2c
3
89
76
O
O
O
O
4
28
O
O
O
O
O
5
6
86
90
78
92
95
88
O
O
O
O
O
O
7
O
O
8
O
O
O
O
9
O
O
10
O
O
11
30
O
23

O
O
12
62
O
a Reaction condition: Amine (1 mmol), acetic anhydride (1.5 mmol), nano γ–Fe2O3 (5 mol%),
sonication for 1 h. b GC yield. c acetic anhydride (3 eq.)
Fig. 1
24

Fig. 2
Fig. 3
25

Fig. 4
Fig. 5
Fig. 6
26

Fig. 7
Fig. 8
27

Fig. 9
Fig. 10
Fig. 11
28

Fig. 12
Scheme 1
Scheme 2
29