Green synthesis of primary, secondary, and tertiary amides through oxidative amidation of methyl groups with amine hydrochlorides over recyclable CoFe2O4 NPs

Article abstract of DOI:10.1039/c6ra20902e

A practical and efficient method is developed for efficient synthesis of a wide variety of 1°, 2°, and 3° amides through amidation of methylarenes with amine hydrochloride salts, over magnetic CoFe₂O₄ NPs as a recyclable nanocatalyst, and aqueous tert-butyl hydroperoxide as an oxidant. This economically sound amidation reaction is operationally straightforward and provides desired amides in good to excellent yields, under mild conditions.

Full text of DOI:10.1039/c6ra20902e

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Green synthesis of primary, secondary, and tertiary
amides through oxidative amidation of methyl
groups with amine hydrochlorides over recyclable
CoFe2O4 NPs†
Cite this: RSC Adv., 2016, 6, 106873
*
Esmaiel Eidi and Mohammad Zaman Kassaee
A practical and efficient method is developed for efficient synthesis of a wide variety of 1ꢀ, 2ꢀ, and 3ꢀ amides
through amidation of methylarenes with amine hydrochloride salts, over magnetic CoFe2O4 NPs as
a recyclable nanocatalyst, and aqueous tert-butyl hydroperoxide as an oxidant. This economically sound
amidation reaction is operationally straightforward and provides desired amides in good to excellent
yields, under mild conditions.
Received 19th August 2016
Accepted 19th October 2016
DOI: 10.1039/c6ra20902e
www.rsc.org/advances
Introduction
Developments in nanoscience and nanotechnology call for new
synthetic approaches to nal products with carefully tailored
physicochemical properties. In recent years, nanoparticles as
heterogeneous catalysts have attracted a great deal of attention
because of their interesting structures and high catalytic activ-
ities.1 From this aspect, bimetallic nanoparticles initiate better
selectivity, catalytic activity and higher deactivation resistance
compared to monometallic ones. Such improved properties can
stem from synergetic electronic interactions between two
different metal atoms in an individual nanoparticle. Catalytic
activity of these systems depends mainly on the nature of the
bimetallic, size and morphology of the particles.2–4 Among the
countless number of mixed metal oxides the nanostructured
magnetic spinel type compounds MFe2O4 (M: Mn2+, Fe2+, Co2+,
Ni2+) are attracting increasing attention due to their excellent
magnetic performance and chemical stability.5 In recent
scenario much attention has been paid in the application of
spinel and perovskite type metal oxides as catalysts for various
organic transformations.6–9 Cobalt ferrite (CoFe2O4) nano-
crystals as a main category of bimetallic nanoparticles have
properties, such as large surface area-to-volume ratio, high
saturation magnetization, and size and shape dependent
magnetic behavior.10–16 Amides are one of the most important
functional groups in contemporary chemistry and this motif
plays a signicant role in the synthesis of natural products,
polymers, pharmaceuticals, and ne chemicals. Furthermore, it
has been assessed that about 25% of all synthetic
Scheme 1 Oxidative amidation of methylarenes catalysed by CoFe2O4
NPs.
pharmaceutical drugs contain an amide unit. These properties
have encouraged great challenges towards development of an
efficient and practical protocol for the amide bond formation in
synthetic chemistry. Amides are typically synthesized through
condensation of carboxylic acids,17 and their derivatives with
amines.18 Other methods for the synthesis of amides include,
Staudinger reaction,19 Schmidt reaction,20 Beckmann rearrange-
ment,21 direct amide synthesis from amines and alcohols,22 ami-
dation of nitriles,23 oxidative amidation of aldehydes,24 and
rearrangement of oximes.25 However, most of these methods
generate a large amount of wasteful byproducts and suffer from
low atom efficiency. Thus, a more environmentally friendly, safe
and highly atom-efficient method for the synthesis of amides is
still needed. Direct oxidative amidation of methylarenes with
amines is an attractive and economical method for synthesis of
these compounds.26 Here we report application of CoFe2O4 NPs,
as a green, effective, clean, and recoverable magnetic nanocatalyst
for the synthesis of important amides (Scheme 1).
Results and discussion
In continuation of our previous work,27 we reported the use of
a heterogeneous cobalt ferrite nanocatalyst with high efficiency
for the oxidative amidation of methylarenes with amine
hydrochlorides. Cobalt ferrite was prepared and characterized
via Fourier transform infrared (FT-IR), vibrating sample
Department of Chemistry, Tarbiat Modares University, P. O. Box 14155-4838, Tehran,
Iran. E-mail: kassaeem@modares.ac.ir; drkassaee@yahoo.com; Fax: +98-21-
88006544; Tel: +98-912-1000392
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra20902e
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Fig. 3 Energy-dispersive spectrum (EDS) of CoFe2O4 NPs.
Fig. 1 FT-IR spectrum of CoFe2O4 NPs.
SEM
The size and morphology of CoFe2O4 NPs are estimated via SEM
(Fig. 4). Uniformly dispersed spherical particles are observed,
along with weak agglomerations.
magnetometry (VSM), energy-dispersive spectrum (EDS), scan-
ning electron microscopy (SEM), thermal gravimetric analysis
(TGA), and X-ray diffraction (XRD) analyses.
VSM
FT-IR spectroscopy
Field-dependent magnetic measurements are performed on
CoFe2O4 nanoparticles at room temperature, using VSM, in the
range from +1 T to ꢁ1 T (Fig. 5). Room temperature specic
magnetization (M) vs. applied magnetic eld (H) curve
measurements of the sample indicates a saturation magneti-
Among FT-IR peaks of CoFe2O4 are those at 597.14, 1628.29, and
3405.11 cmꢁ1 (Fig. 1). The one at 597.54 cmꢁ1 corresponds to
the M–O tetrahedral site of the spinel structure, and shows the
basic nature of the nanoparticles obtained. The broad bands at
3405.11 and 1628.29 cmꢁ1 are assigned to OH stretching and
bending vibrations of water, respectively.
zation value (Ms) of 17 emu gꢁ1
.
X-ray diffraction
Thermal analyses
International Center for Diffraction Data PDF cards 3-864 and In order to probe thermal stability, TGA analysis of CoFe2O4 NPs
22-1086, reveal that CoFe2O4 nanoparticles have cubic structure are carried out by heating NPs from room temperature to 900 ꢀC
(Fig. 2).28 The XRD pattern of the particles shows six different at a rate of 10 ꢀC minꢁ1 (Fig. 6). The TGA pattern shows an
peaks at 2q about 35.1ꢀ, 41.4ꢀ, 50.9ꢀ, 63.5ꢀ, 67.5ꢀ and 74.4ꢀ initial weight loss attributed tꢀo water desorption at 100 ꢀC. The
marked by their indices (220), (311), (400), (422), (511), and slight weight loss below 350 C may be due to dehydration of
(440), respectively.
water or hydroxyl groups present on the surface of spinel
structure, no further mass lose is detected up to 800 C, which
show the thermal stability of the catalyst.29
Aer characterization of CoFe2O4 nanocatalyst, its role as
a heterogeneous nanocatalyst was evaluated for synthesis of N-
benzylbenzamide through interaction of toluene with
ꢀ
EDX
The structural composition of the catalyst is examined by EDX
(Fig. 3). This analysis shows the elemental distribution of
CoFe2O4 including Co and Fe.
Fig. 2 XRD pattern of the catalyst CoFe2O4 NPs.
106874 | RSC Adv., 2016, 6, 106873–106879
Fig. 4 SEM analysis of the catalyst CoFe2O4 NPs.
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Table 1 Optimization of the reaction conditionsa
Entry Cat. (mg) Oxidant Base
Solvent Temp. (ꢀC) Yieldb [%]
1
2
3
4
5
6
7
8
25
25
25
20
25
20
25
20
15
20
20
20
20
20
20
20
20
20
20
—
20
t-BuOOH CaCO3 CH3CN 25
Trace
<10
37
58
74
90
90
77
73
55
32
24
20
64
59
50
32
14
28
—
t-BuOOH CaCO3 CH3CN 40
t-BuOOH CaCO3 CH3CN 60
t-BuOOH CaCO3 CH3CN 70
t-BuOOH CaCO3 CH3CN 70
t-BuOOH CaCO3 CH3CN 80
t-BuOOH CaCO3 CH3CN 80
t-BuOOH CaCO3 CH3CN 90
t-BuOOH CaCO3 CH3CN 80
t-BuOOH CaCO3 DMSO 80
Fig. 5 Vibrating sample magnetometer (VSM) curve for CoFe2O4 NPs.
9
10
11
12
13
14
15
16
17
18
19
20
21
t-BuOOH CaCO3 THF
t-BuOOH CaCO3 DMF
80
80
t-BuOOH CaCO3 CH2Cl2 80
t-BuOOH Na2CO3 CH3CN 80
t-BuOOH K2CO3 CH3CN 80
t-BuOOH Cs2CO3 CH3CN 80
t-BuOOH Et3N
m-CPBA CaCO3 CH3CN 80
H2O2 CaCO3 CH3CN 80
t-BuOOH CaCO3 CH3CN 80
CaCO3 CH3CN 80
CH3CN 80
—
—
a
Reaction conditions: toluene (1 mmol), benzyl amine hydrochloride
salt (1.5 mmol), oxidant (6 equiv.), base (3 equiv.), solvent (2 mL),
b
under Ar atmosphere, 9 h. Isolated yields.
Fig. 6 TGA/DTA/DTG analysis of CoFe2O4 NPs.
gave higher yields than their electron-withdrawing substituted
counterparts. Encouraged by these promising results for the
successful synthesis of primary and secondary amides, we
extended the scope of this protocol for the formation of tertiary
amides by carrying out reactions between methylarenes and
secondary amines.
benzylamine hydrochloride salt, and employed it as a model
reaction. Effects of solvents, oxidants, base, temperature, and
amounts of catalyst on the reaction rate were probed under
similar circumstances. At rst, the model reaction studied with
different amounts of catalyst (15, 20, 25 mg) in various
temperature. Aer screening different mounts of catalyst, best
result was obtained in the presence of 20 mg of catalyst. In order
to probe the role of the solvents, the reaction was examined in
various solvent such as, DMSO, THF, MeCN, CH2Cl2, and DMF.
Among them, MeCN appeared to be the solvent of choice. In
addition, we explored different oxidant sources and the best
result was obtained with tert-butyl hydroperoxide (TBHP), while
other oxidants were ineffective in giving the desired product. No
product was observed in the absence of an oxidant. Also,
experiments were carried out under similar conditions using
different bases such as Cs2CO3, K2CO3 and Na2CO3. The best
base among several others was CaCO3. It is important to note
that in the absence of the catalyst, only trace products were
detected. Optimum conditions for this reaction were employ-
ment of 20 mg CoFe2O4 at 80 ꢀC, in acetonitrile using CaCO3 as
the base and t-BuOOH as the oxidant (Table 1).
Based on these results and literature reports,30 we propose
a plausible free radical mechanism as shown in Scheme 2.
Initially, Co2+ metal center catalysis the heterolytic cleavage of
tert-butyl hydroperoxide to tert-butylperoxyl radical and
a proton. The tert-butylperoxyl radical abstract a hydrogen from
the toluene to give the benzyl radical intermediate (I). Subse-
quently, the benzaldehyde (II) is generated from the benzyl
radical (I) in the presence of tert-butyl hydroperoxide and tert-
butoxyl radical. The benzaldehyde can react with the free
amine, generated in situ from the reaction of the amine salt with
CaCO3, to form a hemiaminal intermediate (III). Finally, the
corresponding amide product is obtained by the same
CoFe2O4–TBHP catalytic system. In the presence of a radical
scavenger 2,6-di-tert-buty-4-methylphenol, completely stopped
the oxidation, and no product was detected. It seems that the
reactions proceed via the radical path. According to this, a free-
radical mechanism is conrmed for oxidative amidation.
Reusability of the catalyst is evaluated under the reaction
conditions described above for the model reaction. Aer
Subsequently, we investigated the substrate scope of this
reaction under the established optimal conditions, and
produced a wide range of primary, secondary and tertiary
amides (Table 2). Generally, electron-donating substituents
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Table 2 Oxidative amidation of methylarenes with amine hydro- Table 2 (Contd.)
chlorides in the presence of CoFe2O4 NPsa
Entry Methylarenes Amine
Product
Yieldb [%]
80
Entry Methylarenes Amine
Product
Yieldb [%]
78
14
1
15
16
17
78
75
77
2
3
4
82
76
60
5
6
7
8
90
91
82
84
18
19
71
70
20
68
21
22
53
55
9
73
64
10
23
46
11
12
13
70
72
77
a
Reaction conditions: methylarenes (1 mmol), amine hydrochloride
salt (1.5 mmol), CH3CN (2 mL), CaCO3 (3 equiv.), t-BuOOH (6 equiv.),
b
catalyst (20 mg), 80 ꢀC, under Ar atmosphere, 9 h. Isolated yields.
completion of the reaction, the catalyst was easily recovered by
applying a strong external permanent magnet, followed by
washing with ethanol to remove the residual product(s). Then
the recovered catalyst was dried under vacuum, and reused
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Scheme 4 Preparation of magnetic CoFe2O4 nanocatalyst.
microscopy using SEM (HITACHI S-4160) on gold coated
samples. Magnetic properties were obtained by a vibrating
magnetometer/Alternating Gradient Force Magnetometer
(VSM/AGFM, MDK Co., Iran).
Preparation of magnetic CoFe2O4 nanoparticles (MNPs)
Magnetic CoFe2O4 nanoparticles were prepared by chemical co-
precipitation chlorine salt of Fe3+ and Co2+ ions with a molar
ratio of 2 : 1. Typically, FeCl3$6H2O (5.8 g, 0.02 mol) and CoCl2
(1.3 g, 0.01 mol) were dissolved in 100 mL deionized water at
80 ꢀC under N2 atmosphere and vigorous stirring. Then, 10 mL
of 25% NH4OH was quickly injected into the reaction mixture in
one portion. The addition of the base to the Co2+/Fe3+ salt
solution resulted in immediate formation of a black precipitate
of MNPs. The reaction was continued for another 60 min and
the mixture was cooled to room temperature. The black
precipitate was washed with doubly warm distilled water
(Scheme 4).
Scheme 2 A plausible mechanism for catalytic oxidative amidation of
methylarenes with amine hydrochloride salts over CoFe2O4 NPs.
General procedure for direct amidation of methylarenes with
amine hydrochloride salts
A mixture was made that consisted of catalyst (20 mg), an amine
hydrochloride salt (1.5 mmol), CaCO3 (3 equiv.), methylarenes
(1 mmol), and t-BuOOH (70 wt% in H2O, 6 equiv.), in CH3CN
(2 mL), under an argon atmosphere for appropriate time at
80 ꢀC. Aer completion of the reaction (monitored by TLC), the
reaction mixture was cooled to room temperature and diluted
with EtOAc. The catalyst was separated using an external
magnet, washed several times with EtOAc and dried under
vacuum at room temperature to be ready for a later run. The
mixture was extracted with EtOAc, then the combined organic
phases were dried over anhydrous MgSO4 and the solvent was
evaporated under reduced pressure. The crude product was
puried by silica gel column chromatography to provide the
desired amides.
Scheme
benzylbenzamide.
3 Reusability of nanocatalyst in synthesis of N-
directly for the next cycle without further treatment. The catalyst
was used over ve runs, and no obvious loss in the catalytic
activity was observed (Scheme 3).
Experimental
General
All chemical reagents used in our experiments were purchased
from Merck or Aldrich Chemical Company with high purity. All
solvents were distilled, dried and puried using standard
procedures. Melting points were measured on an Electro-
thermal 9100 apparatus. 1H NMR and 13C NMR spectra were
Conclusions
recorded on a Bruker Avance (DPX 500 MHz and DPX 125 MHz) This work demonstrates a novel and highly efficient method-
in pure deuterated CDCl3 solvent using tetramethylsilane (TMS) ology for the formation of amides from reaction of methylar-
as an internal reference. FT-IR spectra were recorded using KBr enes with amine hydrochloride salts, and aqueous tert-butyl
pellets on a Nicolet IR-100 infrared spectrometer. The powder hydroperoxide as an oxidant using recyclable CoFe2O4 NPs. This
X-ray diffraction spectrum was recorded at room temperature protocol provides high yield, short reaction time, and opera-
using a Philips X-Pert 1710 diffractometer. The latter appeared tional simplicity, green and low cost procedure for the synthesis
˚
with Co Ka (a ¼ 1.79285 A) voltage: 40 kV, current: 40 mA and of all types of amides (primary, secondary and tertiary). The
was in the range of 20–80ꢀ (2q) with a scan speed of 0.02ꢀ per s. highlights of this work are the reusability and rather high effi-
The particle morphology was examined by scanning electron ciency of the synthesized nanocatalyst.
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20 (a) T. Ribelin, C. E. Katz, D. G. English, S. Smith,
Acknowledgements
A. K. Manukyan, V. W. Day, B. Neuenswander,
´
J. L. Poutsma and J. Aube, Angew. Chem., Int. Ed., 2008, 47,
We acknowledge Tarbiat Modares University for partial support
of this work.
6233–6235; (b) S. Lang and J. Murphy, Chem. Soc. Rev.,
2006, 35, 146–156.
21 (a) N. A. Owston, A. J. Parker and J. M. Williams, Org. Lett.,
2007, 9, 3599–3601; (b) M. Hashimoto, Y. Obora,
S. Sakaguchi and Y. Ishii, J. Org. Chem., 2008, 73, 2894–2897.
Notes and references
1 (a) N. R. Shiju and V. V. Guliants, Appl. Catal., A, 2009, 356, 1– 22 (a) C. Gunanathan, Y. B. David and D. Milstein, Science,
´
17; (b) L. D. Pachon and G. Rothenberg, Appl. Organomet.
2007, 317, 790–792; (b) P. C. Chiang, Y. Kim and
J. W. Bode, Chem. Commun., 2009, 4566–4568; (c)
L. U. NordstrØm, H. Vogt and R. Madsen, J. Am. Chem.
Soc., 2008, 130, 17672–17673; (d) M. Are, D. Saberi,
M. Karimi and A. Heydari, ACS Comb. Sci., 2015, 17, 341–
347; (e) S. C. Ghosh, J. S. Ngiam, A. M. Seayad, D. T. Tuan,
C. W. Johannes and A. Chen, Tetrahedron Lett., 2013, 54,
4922–4925; (f) X. Wu, M. Sharif, A. Pews-Davtyan,
P. Langer, K. Ayub and M. Beller, Eur. J. Org. Chem., 2013,
2013, 2783–2787.
Chem., 2008, 22, 288–299.
2 (a) I. Beletskaya and V. Tyurin, Molecules, 2010, 15, 4792–
4814; (b) B. P. S. Chauhan, R. Thekkathu, L. Prasanth,
K. M. Mandal and K. Lewis, Appl. Organomet. Chem., 2010,
24, 222–228; (c) B. P. S. Chauhan, R. Sardar, U. Latif,
M. Chauhan and W. Lamoreaux, Acta Chim. Slov., 2005, 52,
361–370.
3 N. Toshima and T. Yonezawa, New J. Chem., 1998, 22, 1179–
1201.
4 F. M. Moghaddam, G. Tavakoli and H. R. Rezvani, Appl. 23 (a) S.-I. Murahashi, T. Naota and E. Saito, J. Am. Chem. Soc.,
Organomet. Chem., 2014, 28, 750–755.
5 G. Bate, in Magnetic Oxides Part 2, ed. D. J. Craik, John Wiley
& Sons, New York, 1975, pp. 705–707.
6 A. S. Reddy, C. S. Gopinath and S. Chilukuri, J. Catal., 2006,
243, 278–291.
7 A. H. de Morais Batista, F. S. Ramos, T. P. Braga, C. L. Lima,
F. F. de Sousa, E. B. Barros, M. Josue Filho, A. S. de Oliveira,
J. R. de Sousa and A. Valentini, Appl. Catal., A, 2010, 382, 148–
157.
8 K. Sreekumar, T. Mathew, B. M. Devassy, R. Rajgopal,
R. Vetrivel and B. Rao, Appl. Catal., A, 2001, 205, 11–18.
9 (a) A. S. Kulkarni and R. V. Jayaram, Appl. Catal., A, 2003, 252,
225–230; (b) B. Baruwati, M. N. Nadagouda and R. S. Varma,
J. Phys. Chem. C, 2008, 112, 18399–18404.
1986, 108, 7846–7847; (b) C. L. Allen, A. A. Lapkin and
J. M. J. Williams, Tetrahedron Lett., 2009, 50, 4262–4264.
24 (a) J. W. W. Chang, T. M. U. Ton, S. Tania, P. C. Taylor and
P. W. H. Chan, Chem. Commun., 2010, 46, 922–924; (b)
T. M. U. Ton, C. Tejo, S. Tania, J. W. W. Chang and
P. W. H. Chan, J. Org. Chem., 2011, 76, 4894–4904; (c)
S. C. Ghosh, J. S. Ngiam, C. L. Chai, A. M. Seayad,
T. T. Dang and A. Chen, Adv. Synth. Catal., 2012, 354,
1407–1412; (d) S. C. Ghosh, J. S. Ngiam, A. M. Seayad,
D. T. Tuan, C. L. Chai and A. Chen, J. Org. Chem., 2012, 77,
8007–8015; (e) K. S. Goh and C.-H. Tan, RSC Adv., 2012, 2,
5536–5538; (f) X. Liu and K. F. Jensen, Green Chem., 2012,
14, 1471–1474; (g) G.-L. Li, K. K.-Y. Kung and M.-K. Wong,
Chem. Commun., 2012, 48, 4112–4114; (h) M. Zhu,
K.-i. Fujita and R. Yamaguchi, J. Org. Chem., 2012, 77,
9102–9109.
10 Y. Wang, J. Park, B. Sun, H. Ahn and G. X. Wang, Chem.–
Asian J., 2012, 7, 1940–1946.
11 D. Fritsch and C. Ederer, Phys. Rev. B: Condens. Matter Mater. 25 (a) S. Park, Y. Choi, H. Han, S. H. Yang and S. Chang, Chem.
Phys., 2012, 86, 014406–014416.
12 R. Comes, H. X. Liu, M. Kholchov, R. Kasica, J. W. Lu and
S. A. Wolf, Nano Lett., 2012, 12, 2367–2373.
Commun., 2003, 1936–1937; (b) N. A. Owston, A. J. Parker and
J. M. J. Williams, Org. Lett., 2007, 9, 73–75.
26 (a) J. B. Feng and X. F. Wu, Appl. Organomet. Chem., 2015, 29,
63–86; (b) T. Wang, L. Yuan, Z. Zhao, A. Shao, M. Gao,
Y. Huang, F. Xiong, H. Zhang and J. Zhao, Green Chem.,
2015, 17, 2741–2744; (c) Y. Huang, T. Chen, Q. Li, Y. Zhou
and S.-F. Yin, Org. Biomol. Chem., 2015, 13, 7289–7293.
¨
13 R. S. Turtelli, G. V. Duong, W. Nunes, R. Grossinger and
M. Knobel, J. Magn. Magn. Mater., 2008, 320, e339–e342.
14 B. Q. Liu, Q. F. Li, B. Zhang, Y. L. Cui, H. F. Chen, G. N. Chen
and D. P. Tang, Nanoscale, 2011, 3, 2220–2226.
15 H. X. Wu, G. Liu, X. Wang, J. M. Zhang, Y. Chen, J. L. Shi, 27 E. Eidi, M. Kassaee and Z. Nasresfahani, Appl. Organomet.
H. Yang, H. Hu and S. P. Yang, Acta Biomater., 2011, 7,
3496–3504.
16 Y. D. Yang, S. Priya, Y. U. Wang, J. F. Li and D. Viehland, J.
Mater. Chem., 2009, 19, 4998–5002.
17 (a) L. Perreux, A. Loupy and F. Volatron, Tetrahedron, 2002,
58, 2155–2162; (b) C. L. Allen, A. R. Chhatwal and
J. M. Williams, Chem. Commun., 2012, 48, 666–668.
18 E. Valeur and M. Bradley, Chem. Soc. Rev., 2009, 38, 606–631.
19 (a) E. Saxon and C. R. Bertozzi, Science, 2000, 287, 2007–2010;
Chem., 2016, 30, 561–565.
28 (a) X. B. Cao and L. Gu, Nanotechnology, 2005, 16, 180–185;
(b) T. Hyeon, Y. Chung, J. Park, S. S. Lee, Y. W. Kim and
B. H. Park, J. Phys. Chem. B, 2002, 106, 6831–6833; (c)
S. Sun, H. Zeng, D. B. Robinson, S. Raoux, P. M. Rice,
S. X. Wang and G. Li, J. Am. Chem. Soc., 2004, 126, 273–
279; (d) T. Prozorov, P. Palo, L. Wang, M. Nilsen-Hamilton,
D. Jones, D. Orr, S. K. Mallapragada, B. Narasimhan,
P. C. Caneld and R. Prozorov, ACS Nano, 2007, 1, 228–233.
(b) F. Damkaci and P. De Shong, J. Am. Chem. Soc., 2003, 125, 29 (a) J. K. Rajput and G. Kaur, Chin. J. Catal., 2013, 34, 1697–
4408–4409; (c) Y. G. Gololobov and L. F. Kasukhin,
Tetrahedron, 1992, 48, 1353–1406.
1704; (b) P. Sivakumar, R. Ramesh, A. Ramanand,
106878 | RSC Adv., 2016, 6, 106873–106879
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
S. Ponnusamy and C. Muthamizhchelvan, Mater. Res. Bull.,
RSC Advances
P. Rao, P. Nagaraju, P. S. Prasad and N. Lingaiah, J. Mol.
Catal. A: Chem., 2009, 303, 84–89; (d) T. C. Mac Leod,
M. V. Kirillova, A. J. Pombeiro, M. A. Schiavon and
M. D. Assis, Appl. Catal., A, 2010, 372, 191–198; (e)
P. K. Tandon, M. Srivastava, S. Kumar and S. Singh, J. Mol.
Catal. A: Chem., 2009, 304, 101–106.
2011, 46, 2204–2207.
30 (a) A. S. Kumar, B. Thulasiram, S. B. Laxmi, V. S. Rawat and
B. Sreedhar, Tetrahedron, 2014, 70, 6059–6067; (b) B. Ma,
Z. Zhang, W. Song, X. Xue, Y. Yu, Z. Zhao and Y. Ding, J.
Mol. Catal. A: Chem., 2013, 368, 152–158; (c) K. V. Rao,
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