Fe3O4 nanoparticles as an efficient and magnetically recoverable catalyst for friedel-crafts acylation reaction in solvent-free conditions

Article abstract of DOI:10.1080/00397911.2012.663048

Application of Fe₃O₄ nanoparticles (NPs) as a robust, very efficient, and magnetically recoverable catalyst was investigated in Friedel-Crafts acylation (FCA) of ferrocene and aromatic compounds. This reaction was performed with acid chlorides in solvent-free conditions at room temperature. The catalyst was easily separated by an external magnetic field from the reaction mixture. The separated catalyst was recycled for several consecutive runs without appreciable loss of its catalytic activity. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications1 to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2012.663048

This article was downloaded by: [North Carolina State University]
On: 14 March 2013, At: 09:44
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Fe3O4 Nanoparticles as an Efficient and
Magnetically Recoverable Catalyst for
Friedel–Crafts Acylation Reaction in
Solvent-Free Conditions
S. Jafar Hoseini a , Hasan Nasrabadi a , Mahboobeh Azizi a , Alireza
Salimi Beni a & Reza Khalifeh b
a Department of Chemistry, Faculty of Sciences, Yasouj University,
Yasouj, Iran
b Department of Chemistry, Shiraz Uuniversity of Technology, Shiraz,
Iran
Accepted author version posted online: 08 Aug 2012.Version of
record first published: 06 Mar 2013.
To cite this article: S. Jafar Hoseini , Hasan Nasrabadi , Mahboobeh Azizi , Alireza Salimi Beni &
Reza Khalifeh (2013): Fe3O4 Nanoparticles as an Efficient and Magnetically Recoverable Catalyst
for Friedel–Crafts Acylation Reaction in Solvent-Free Conditions, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 43:12, 1683-1691
To link to this article: http://dx.doi.org/10.1080/00397911.2012.663048
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,

demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 43: 1683–1691, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.663048
Fe3O4 NANOPARTICLES AS AN EFFICIENT AND
MAGNETICALLY RECOVERABLE CATALYST FOR
FRIEDEL–CRAFTS ACYLATION REACTION IN
SOLVENT-FREE CONDITIONS
S. Jafar Hoseini,1 Hasan Nasrabadi,1 Mahboobeh Azizi,1
Alireza Salimi Beni,1 and Reza Khalifeh2
1Department of Chemistry, Faculty of Sciences, Yasouj University,
Yasouj, Iran
2Department of Chemistry, Shiraz Uuniversity of Technology, Shiraz, Iran
GRAPHICAL ABSTRACT
Abstract Application of Fe3O4 nanoparticles (NPs) as a robust, very efficient, and magneti-
cally recoverable catalyst was investigated in Friedel–Crafts acylation (FCA) of ferrocene
and aromatic compounds. This reaction was performed with acid chlorides in solvent-free
conditions at room temperature. The catalyst was easily separated by an external magnetic
field from the reaction mixture. The separated catalyst was recycled for several consecutive
runs without appreciable loss of its catalytic activity.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Catalyst; Fe3O4 nanoparticles; Friedel–Crafts acylation; heterogenous
catalysts; solvent free
INTRODUCTION
The application of sustainable, more efficient, and green catalysts for the
production of high-quality products with minimum waste and energy demands is
a key challenge in the field of chemistry. In this respect, iron catalysts have emerged
as ready available, inexpensive, and environmentally friendly catalysts in organic
reactions.[1] Superparamagnetic Fe3O4 (NPs) have attracted worldwide attention
because of their many biological and technological applications.[2] Recently, there
is growing interest in using of Fe3O4 NPs as magnetically supports for catalysts in
Received October 23, 2011.
Address correspondence to S. Jafar Hoseini, Department of Chemistry, Faculty of Science, Yasouj
University, Yasouj 74831, Iran. E-mail: jhosseini@mail.yu.ac.ir; sjhoseini54@yahoo.com
1683

1684
S. J. HOSEINI ET AL.
organic synthesis.[3] This type of catalyst can be easily separated from the reaction
mixture by employing an external magnet. Magnetically recoverable catalysts have
been used in some reactions, for example, in asymmetric hydrogenation,[3a] Suzuki
coupling reaction,[3b] and addition of alkoxy diboron reagent to C-C double
bonds.[3c] Also, use of Fe3O4 NPs as a catalyst without any modification is in
progress because easy large-scale synthesis and facile separation of magnetic NPs
with external magnetic fields are promising for industrial applications.[4]
Friedel–Crafts acylation (FCA) is the main industrial route for the synthesis of
aromatic ketones. Typically catalyzed by the Lewis acid AlCl3, it requires more than a
stoichiometric amount of catalyst because of the complexation of the Lewis acid with
substrates and=or with the aryl ketone product.[5] The design and development of a
highly reactive catalyst has been an intriguing and challenging goal in FCA.[6] Most
attempts have been directed toward the use of solid acid catalysts.[7] Different heteroge-
nous catalysts including zeolite, clays, hetropolyacids, metal oxides, sulfated zirconia,
and nafion have been studied and utilized in FCA.[7] So far, metal oxides are particularly
useful as catalysts because they are readily available, inexpensive, and noncorrosive, and
they exhibit numerous edges and corners for adsorption and activation of the reactants.[8]
In recent years, many researchers have focused their effort on the application of
metal or metal oxide NPs as novel catalysts in various organic transformations. Nano-
scale catalysts as a novel family of heterogeneous catalysts have many advantages such
as high catalytic activity, good recyclability, and improved selectivity. However, appli-
cation of nanostructure catalysts in FCA is rare.[9] To the best of our knowledge, there
is no report of application of magnetically recoverable nanocatalyst in FCA. In this
article, we report the use of magnetic Fe3O4 NPs as an efficient catalyst in the FCA
of ferrocene and some aromatic compounds with acid chlorides in solvent-free con-
ditions at room temperature. This catalyst showed two main advantages in FCA reac-
tion: First, it has high surface area because of nanosize of the particles and so the
contact between reactants and catalyst increases considerably. Second, because of their
insolubility in the reaction mixture and paramagnetic properties of Fe3O4 NPs, they
can be separated easily from the reaction mixture by applying an external magnet.
RESULTS AND DISCUSSION
The Fe3O4 NPs can be easily synthesized by coprecipitation from different
chemical sources.[2] Herein, we prepare Fe3O4 NPs by an aging stoichiometric mixture
of ferrous and ferric chloride in aqueous solutions without surfactants.[10] Large-scale
synthesis and easy separation of Fe3O4 NPs by an external magnetic field from the
reaction mixture have encouraged us to investigate the application of Fe3O4 NPs as
catalyst in organic reactions.[4a] Figure 1a shows the x-ray diffraction (XRD) patterns
of Fe3O4 NPs. A number of prominent Bragg reflections by their indices [(220), (311),
(400), (422), (511), and (440)] reveal that the resultant NPs were Fe3O4 with a spinel
structure. The size of the Fe3O4 NPs was also determined from x-ray line broading
using the Debye–Scherrer formula given as D ¼ 0.9k=bcosh, where D is the average
crystalline size, k is the x-ray wavelength used, b is the angular line width at half
maximum intensity, and h is the Bragg’s angle. For (311) reflection, the average size
of the Fe3O4 NPs is estimated to be around 13 nm. Transmission electron microscopy
(TEM) analysis was used for characterization (Fig. 1b). The TEM image reveals the

FRIEDEL–CRAFTS ACYLATION
1685
Figure 1. (a) The powder x-ray diffraction patterns of the Fe3O4 NPs. (b) TEM image shows spherical
Fe3O4 NPs of 20–30 nm.
spherical Fe3O4 NPs with average sizes of 20–30 nm. The Fourier transform–infrared
(FT-IR) spectra of Fe3O4 NPs are shown in Fig. 2. The absorbance bands at
584.3 cmꢀ1 are ascribed to Feþ2-Oꢀ2, which are consistent with the reported IR
spectra for spinel Fe3O4.[11]
We used anisole as a standard substrate to search for a suitable condition for
the Fe3O4 NPs to catalyze FCA (Table 1). No desired product was obtained in the
absence of Fe3O4 NPs (Table 1, entries 1 and 2). Solvents having strong coordination
ability such as tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) gave no pro-
ducts (Table 1, entries 7 and 8). Dichloromethane (DCM) afforded the products in
better yield (Table 1, entry 12). A trace product was detected when the reaction was
carried out in N,N-dimethylformamide (DMF) (Table 1, entry 10). Among the
conditions tested, solvent-free was the most effective for this reaction.
Commercially available bulk powders of Fe2O3 and Fe3O4 were evaluated as cat-
alysts in the FCA of anisole with acetyl chloride (Table 1, entries 4 and 6). Fe3O4 was
found to be more active when compared to the other metal oxides tested (Table 1, entry
Figure 2. FT-IR spectra of Fe3O4 NPs.

1686
S. J. HOSEINI ET AL.
Table 1. FCA of anisole with acetyl chloride in various reaction conditions
Entry
Catalyst
None
Solvent
Temp.
Time (min)
Yield (%)a
1
2
Solvent free
CH2Cl2
rt
reflux
rt
120
120
120
120
5
0
0
None
Fe2O3
Fe2O3
b
b
3
Solvent free
Solvent free
Solvent free
Solvent free
THF
0
32
4
80 ꢁC
5
c-Fe2O3 NPsc
Fe3O4
rt
90
70
6
rt
20
7
Fe3O4 NPs
Fe3O4 NPs
Fe3O4 NPs
Fe3O4 NPs
Fe3O4 NPs
Fe3O4 NPs
Fe3O4 NPsd
Fe3O4 NPse
rt
120
120
120
120
120
120
10
0
8
DMSO
rt
0
30
9
n-Hexane
DMF
Acetone
rt
10
11
12
13
14
rt
Trace
Trace
75
rt
CH2Cl2
Solvent free
Solvent free
rt
rt
88
98
rt
<3
aIsolated yield.
bReported from Ref. 8c.
cSynthesized according to Ref. 10.
d0.05 mmol Fe3O4 NPs.
e0.1 mmol Fe3O4 NPs.
6). To establish the role of nanoparticles, we studied this reaction in the presence of
Fe3O4 and c-Fe2O3 NPs. Considering the good yield, short time, and easy separation
of NPs by an external magnetic field, we conclude that Fe3O4 NPs catalyzed the reaction
better than other studied catalysts (Table 1, entry 14). Lower yield was observed when
slightly decreasing the catalyst loading (0.05 mmol) (Table 1, entry 13). The optimized
reaction conditions include 1.0 mmol of aromatic compound, 1.0 mmol of acid chloride,
and 0.1 mmol of Fe3O4 NPs in solvent-free conditions at room temperature.
To investigate the generality and versatility of this method, the reaction was
extended to various aromatic compounds. The results of the FCA of aromatic com-
pounds are collected in Table 2. All of the aromatic compounds reacted very rapidly
within 1–30 min. The reactions were remarkably clean, and no chromatographic sep-
aration was necessary to get the pure compounds except in entry 7. Acylation
occured exclusively at the position para to ꢀOMe and ꢀMe for all of the compounds
studied in almost quantitative yields. Also, benzoyl chloride reacted with anisole
after vigorous stirring for 5 min and 95% yield of the product was obtained. The
acylation of benzene with acetyl chloride was performed in 5 min with good yield
(Table 2, entry 4). The FCA of anisole with acetyl chloride on a 100-mmol scale
(Table 2, entry 8) proceeded just as well as in the 1-mmol reaction. In general, both
aromatic and aliphatic acid chloride underwent the addition reaction smoothly to
provide the desired product in moderate to good yields (Table 2, entries 1–7).

FRIEDEL–CRAFTS ACYLATION
1687
Table 2. FCA of aromatic compounds
Time Yield Mp (ꢁC)
Entry
Substrate
Acid chloride
Product
(min)
%
ref.
Ref.
[12]
1
<3
98
36–39
2
<3
96
—
[12]
3
4
5
5
91
94
—
20
[13]
[14]
5
6
5
95
95
58–61
85–87
[15]
[15]
10
7
8
30
70
79–81
36–39
[16]
[12]
<3
98a
aThe reaction was carried out on a 100-mmol scale.

1688
S. J. HOSEINI ET AL.
A plausible mechanism for the action of Fe3O4 NPs in FCA is shown in Fig. 3.
The reaction may proceed through the Lewis acid (Fe2þ or Fe3þ ion)–catalyzed for-
mation of an acylium ion intermediate. The in situ–generated chloride is adsorbed on
the outer surface of Fe3O4 NPs. This layer is considered as the first electrical layer
providing negative electrical charge on the Fe3O4 NPs. Also, the attractive interac-
tion of the negatively charged catalyst with acylium ion (positively charged) then
results in the acylinum ion to form the secondary layer on the Fe3O4 NP surface.
Therefore, this phenomenon precedes the acylation process (Fig. 3).[8] Also, HCl
gas is liberated and may exit the reaction mixture.
The Fe3O4 NPs can also be separated easily by magnetic method and reused.
The NPs were washed with ethyl acetate, air dried, and used directly for the next
round of reactions without further purification. It was shown that the Fe3O4 NPs
catalyst could be recovered and reused six times without significant loss of catalytic
activity (Table 3). The FeCl3 and FeCl2 may be generated from the reaction of Fe3O4
NPs with hydrogen chloride. Because the formation of ferrous and ferric chloride in
the presence of HCl and Fe3O4 is an endothermic reaction, formation of these salts
under our conditions (room temperature) is low. Also, for further confidence about
the lack of responsibility of the FeCl3 in the acylation process, we have used pure
FeCl3 as catalyst in the FCA but long reaction times are often required. We consider
that hydrogen chloride gas is liberated and exit the reaction mixture. Therefore,
FeCl3 is not considered as a true catalyst in the synthesis of organic compounds
during the acylation processes.
A comparison of the present protocol employing Fe3O4 NPs with previously
known procedures shows that the present experiment is better than several known
Figure 3. Mechanism proposed for FCA in the presence of Fe3O4 NPs.

FRIEDEL–CRAFTS ACYLATION
1689
Table 3. Reusability of the catalyst for acylation of toluene
with acetyl chloride
Entry
Time (min)
Yield (%)
1
2
3
4
5
6
<3
<3
3
96
96
93
90
90
89
3
3
3
procedures.[5–7] According to Table 2, FCA of anisole and toluene is quickly com-
pleted at room temperature in 98% and 96% yields, respectively. Most of the other
published procedures[5–7] need long times, preparation of the catalyst support, and
toxic solvent with lower isolated yield.
In summary, magnetically recoverable Fe3O4 NPs catalyzed the FCA reaction
in solvent-free conditions at room temperature. A diverse range of aromatic ketones
were obtained in moderate to good yield under mild conditions at room temperature.
The separation and reuse of the magnetic Fe3O4 NPs were very simple, effective, and
economical. In addition, the use of iron oxides as catalysts is more environmentally
friendly and safer than other transition-metal catalysts.
EXPERIMENTAL
All of the reagents used in our experiments were of analytical purity from
commercial source (Merck). X-ray diffraction (XRD, D8, Advance, Bruker, axs)
patterns were obtained for characterization of the heterogeneous catalyst. IR spectra
were obtained using a Jasco FT=IR-680 plus spectrometer. NMR spectra were
recorded on a Bruker Avance DPX-250 (1H NMR 250 MHz) or a Bruker Avance
DRX 500-MHz spectrometer in CDCl3 solvent with tetramethylsilane (TMS) as
an internal standard. Transmission electron microscopy (TEM) was carried out with
a Philips CM-10 TEM instrument.
Synthesis of Fe3O4 NPs
To prepare Fe3O4 NPs, 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 N HCl. The resulting
solution was added dropwise to 250 ml of 1.5 M NaOH solution under vigorous stir-
ring. 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.[10]
General Experimental Procedure
Acid chloride (1 mmol) was added to a mixture of Fe3O4 NPs (0.1 mmol,
10 mol%) and aromatic compound (1 mmol) at room temperature. The reaction mix-
ture was stirred for the appropriate reaction times (monitored by TLC, Table 2).

1690
S. J. HOSEINI ET AL.
After completion of the reaction, the magnetic stirring was stopped and the Fe3O4
NPs were adsorbed on the magnetic stirring bar. Ethyl acetate and water were added,
and the organic phase was separated, dried over anhydrous MgSO4. Pure correspond-
ing product was obtained after evaporation of solvent. Characterization of these
1
compounds was estabilished by comparison of their H NMR and IR spectra with
those of authentic sample.
Representative Spectral Data
Table 2, entry 1: This compound was obtained as white solid in 98% yield, IR
(KBr) t (CO) (cmꢀ1) ¼ 1664 (Fig. S5, available online in the Supplementary Material).
Table 2, entry 2: This compound was obtained in 96% yield, IR (KBr) t (CO)
1
(cmꢀ1) ¼ 1677 (Fig. S6). H NMR (250 MHz, CDCl3): d ¼ 2.1 (s, 3H), 2.52 (s, 3H),
6.92(d, 2H, J ¼ 8.0 Hz), 7.85 (d, 2H, J ¼ 8.0 Hz) (Fig. S1).
Table 2, entry 3: This compound was obtained in 91% yield, IR (KBr) t (CO)
(cmꢀ1) ¼ 1673 (Fig. S7).
Table 2, entry 4: This compound was obtained in 94% yield, IR (KBr) t (CO)
(cmꢀ1) ¼ 1681 (Fig. S8).
Table 2, entry 5: This compound was obtained as white solid in 95% yield;
1
M.p ¼ 58–63 ꢁC, IR (KBr) t (CO) (cmꢀ1) ¼ 1650 (Fig. S9). H NMR (250 MHz,
CDCl3): d ¼ 3.79 (s, 3H), 6.89 (dd, 2H, J1 ¼ 6.8, J2 ¼ 2.0 Hz), 7.39–7.47 (m, 3H),
7.69 (dd, 2H, J1 ¼ 8.5, J2 ¼ 1.7 Hz), 7.76 (d, 2H, J ¼ 8.9 Hz) (Fig. S2).
Table 2, entry 6: This compound was obtained as white solid in 95% yield.
M.p ¼ 85–87 ꢁC, IR (KBr) t (CO) (cmꢀ1) ¼ 1654 (Figure S10). 1H NMR
(250 MHz, CDCl3): d ¼ 2.35 (s, 3H), 3.81 (s, 3H), 6.89 (d, 2H, J ¼ 8.8 Hz), 7.19 (d,
2H, J ¼ 7.8 Hz), 7.59 (d, 2H, J ¼ 8.3 Hz), 7.73 (d, 2H, J ¼ 6.8 Hz) (Fig. S3).
Table 2, entry 7: This compound was obtained as orange crystalline solid in
70% yield. M.p ¼ 79–81 ꢁC, IR (KBr) t (cmꢀ1): 3105, 1654 (CO), 1456, 1279
1
(Fig. S11). H NMR (500 MHz, CDCl3): d ¼ 2.39 (s, 3H), 4.20 (s, 5H), 4.50 (t,
2H, J ¼ 2.0 Hz), 4.77 (t, 2H, J ¼ 2.0 Hz) (Fig. S4).
ACKNOWLEDGMENTS
We thank the Yasouj University Research Council and the Iranian Nanotech-
nology Initiative Council for financial support.
REFERENCES
1. Plietker, B. Iron Catalysis in Organic Chemistry; Wiley-VCH: Weinheim, 2008.
2. (a) Laurent, S.; Forge, D.; Port, M.; Roch, A.; Robic, C.; Elst, L. V.; Muller, R. N.
Magnetic iron oxide nanoparticles: Synthesis, stabilization, vectorization, physico-
chemical characterizations, and biological applications. Chem. Rev. 2008, 108, 2064–
2110; (b) Gomathi, A.; Hoseini, S. J.; Rao, C. N. R. Functionalization and solubilization
of inorganic nanostructures and carbon nanotubes by employing organosilicon and
organotin reagents. J. Mater. Chem. 2009, 19, 988–995.
3. (a) Panella, B.; Vargas, A.; Baiker, A. Magnetically separable Pt catalyst for asymmetric
hydrogenation. J. Catal. 2009, 261, 88–93; (b) Taher, A.; Kim, J.-B.; Jung, J. Y.; Ahn, W.-S.;
Jin, M.-J. Highly active and magnetically recoverable Pd-NHC catalyst immobilized on

FRIEDEL–CRAFTS ACYLATION
1691
Fe3O4 nanoparticle–ionic liquid matrix for Suzuki reaction in water. Synlett 2009, 15,
2477–2482; (c) Cano, R.; Ramon, D. J.; Yus, M. Impregnated copper on magnetite as
recyclable catalyst for the addition of alkoxy diboron reagents to CꢀC double bonds.
J. Org. Chem. 2010, 75, 3458–3460.
4. (a) Firouzabadi, H.; Iranpoor, N.; Gholinejad, M.; Hoseini, J. Magnetite (Fe3O4) nano-
particle–catalyzed Sonogashira–Hagihara reactions in ethylene glycol under ligand-free
conditions. Adv. Synth. Catal. 2011, 353, 125–132; (b) Mojtahedi, M. M.; Abaee, M. S.;
Alishiri, T. Superparamagnetic iron oxide as an efficient catalyst for the one-pot,
solvent-free synthesis of a-aminonitriles. Tetrahedron Lett. 2009, 50, 2322–2325; (c) Zeng,
T.; Chen, W. W.; Cirtiu, C. M.; Moores, A.; Song, G.; Li, C. J. Fe3O4 nanoparticles: A
robust and magnetically recoverable catalyst for three-component coupling of aldehyde,
alkyne, and amine. Green Chem. 2010, 12, 570–573; (d) Karami, B.; Hoseini, S. J.;
Eskandari, K.; Ghasemi, A.; Nasrabadi, H. Synthesis of xanthene derivatives by
employing Fe3O4 nanoparticles as an effective and magnetically recoverable catalyst in
water. Catal. Sci. Technol. 2012, 2, 331–338.
5. Olah, G. A. Friedel–Crafts and Related Reactions; Wiley-Interscience: New York, 1964.
6. Sartori, G.; Maggi, R. Advances in Friedel–Crafts Acylation Reactions: Catalytic and
Green Processes; Taylor and Francis: New York, 2010.
7. Sartori, G.; Maggi, R. Use of solid catalysts in friedel–Crafts acylation reactions. Chem.
Rev. 2006, 106, 1077–1104.
8. (a) Niederberger, M.; Pinna, N. Metal Oxide Nanoparticles in Organic Solvents: Synthesis,
Formation, Assembly, and Application; Springer-Verlag: London, 2009; (b) Morley, J. O.
Aromatic acylations catalysed by metal oxides. J. Chem. Soc., Perkin. 2 1977, 601–605;
(c) Sarvari, M. H.; Sharghi, H. Reactions on a solid surface: A simple, economical, and
efficient Friedel–Crafts acylation reaction over zinc oxide (ZnO) as a new catalyst. J. Org.
Chem. 2004, 69, 6953–6956; (d) Sharghi, H.; Jokar, M.; Doroodmand, M. M.; Khalifeh,
R. Catalyzed Friedel–Crafts acylation and benzoylation of aromatic compounds using acti-
vated hematite as a novel heterogeneous catalyst. Adv. Synth. Catal. 2010, 352, 3031–3044.
9. (a) Ji, X.; Qin, Z.; Dong, M.; Wang, G.; Dou, T.; Wanga, J. Friedel–Crafts acylation of
anisole and toluene with acetic anhydride over nano-sized b zeolites. Catal. Lett. 2007,
117, 171–176; (b) Ashoka, S.; Chithaiah, P.; Thipperudraiah, K. V.; Chandrappa, G. T.
Nanostructural zinc oxide hollow spheres: A facile synthesis and catalytic properties.
Inorg. Chim. Acta 2010, 363, 3442–3447; (c) Kantam, M. L.; Laha, S.; Yadav, J.;
Sreedhar, B. Friedel–Crafts alkylation of indoles with epoxides catalyzed by nanocrystal-
line titanium(IV) oxide. Tetrahedron Lett. 2006, 47, 6213–6216.
10. Kang, Y. S.; Rishbud, S.; Rabolt, J. F.; Stroeve, P. Synthesis and characterization of
nanometer-size Fe3O4 and c-Fe2O3 particles. Chem. Mater. 1996, 8, 2209–2211.
11. Liu, Y.; Liu, P.; Su, Z.; Li, F.; Wen, F. Attapulgite–Fe3O4 magnetic nanoparticles via
co-precipitation technique. Appl. Surf. Sci. 2008, 255, 2020–2025.
12. Ruan, J.; Li, X.; Saidi, O.; Xiao, J. Oxygen and base-free oxidative heck reactions of
arylboronic acids with olefins. J. Am. Chem. Soc. 2008, 130, 2424–2425.
13. Kawada, A.; Mitamura, S.; Kobayashi, S. Ln(OTf)3–LiClO4 as reusable catalyst system
for Friedel–Crafts acylation. J. Chem. Soc., Chem. Commun. 1996, 183–184.
14. Huang, A.; Liu, X.; Li, L.; Wu, X.; Liu, W.; Liang, Y. Antimony(V) chloride–benzyl-
triethylammonium chloride complex as an efficient catalyst for Friedel–Crafts acylation
reactions. Adv. Synth. Catal. 2004, 346, 599–602.
15. Rao, M. L. N.; Venkatesh, V.; Banerjee, D. Atom-efficient cross-coupling reactions
of triarylbismuths with acyl chlorides under Pd(0) catalysis. Tetrahedron 2007, 63,
12917–12926.
16. Hauser, C. R.; Lindsay, J. K. Certain acylations of ferrocene and some condensations
involving the a-hydrogen of acetylferrocene. J. Org. Chem. 1957, 22, 482–485.