Industrial resin "INDION 130" modified with vanadyl cations as highly efficient heterogeneous catalyst for epoxidation of fatty compounds with TBHP as oxidant

Article abstract of DOI:10.1039/c5nj00744e

Industrial grade cation-exchange resin "INDION 130" was modified with vanadyl cations by an ion-exchange method and then used for the epoxidation of unsaturated fatty materials including acids, esters and vegetable oils using tert-butyl hydroperoxide (TBHP) in decane as oxidant. The effect of oxidant/double bond ratio, catalyst concentration, recycling of the catalyst and temperature on the conversion to epoxides was studied. After the epoxidation, the catalyst could easily be recovered by filtration and successfully reused for at least seven runs without any loss in catalytic activity.

Full text of DOI:10.1039/c5nj00744e

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Industrial resin ‘‘INDION 130’’ modified with
vanadyl cations as highly efficient heterogeneous
catalyst for epoxidation of fatty compounds with
TBHP as oxidant†
Cite this:DOI: 10.1039/c5nj00744e
a
b
b
b
a
Praveen K. Khatri, Mounika Aila, Jyoti Porwal, Savita Kaul* and Suman L. Jain*
Industrial grade cation-exchange resin ‘‘INDION 130’’ was modified with vanadyl cations by an ion-
exchange method and then used for the epoxidation of unsaturated fatty materials including acids,
esters and vegetable oils using tert-butyl hydroperoxide (TBHP) in decane as oxidant. The effect of
oxidant/double bond ratio, catalyst concentration, recycling of the catalyst and temperature on the
conversion to epoxides was studied. After the epoxidation, the catalyst could easily be recovered by
filtration and successfully reused for at least seven runs without any loss in catalytic activity.
Received (in Montpellier, France)
2
5th March 2015,
Accepted 19th May 2015
DOI: 10.1039/c5nj00744e
www.rsc.org/njc
equipment corrosion, more byproducts and environmental
problems. The introduction of acidic ionic exchange resins as
Introduction
Renewable raw materials are known to be environmentally heterogeneous catalysts is an important technical improvement
friendly, biodegradable, of low cost and readily available, and in the production of epoxidized oils, which improves the yield
10–13
they have received considerable interest in recent decades due and/or selectivity.
Nevertheless, there are some disadvantages
to their potential to serve as feedstock to substitute petroleum- such as lower thermal stability, long reaction time and in some
1
derived materials. Fats and oils are the most widely used instances higher cost, limiting their applications in large-scale
renewable raw materials in the chemical industry as they provide commodity manufacture. Immobilization of metal ions to the ion
widespread possibilities of different applications. They are the exchange resins is a promising and cost-effective approach to
cheapest and most abundant biological feedstocks which are transform homogeneous metal catalysts to heterogeneous forms
available in large quantities and can be used as starting materials with the added benefits of facile recovery/recycling and higher
2
for various transformations. Epoxidation of vegetable oils, i.e. of stability of the catalyst. In this context, ion exchange resins such
their unsaturated triglycerides, is a commercially important reac- as perfluorinated sulfonic acid polymer (i.e. Nafion-H and Nafion
tion as these epoxides can be used as precursors for synthesizing SAC-13) have been modified with metal ions and successfully used
numerous value-added chemicals including alcohols (polyols), as superior heterogeneous catalysts for a wide range of applications
3
–5
glycols, olefin compounds and polymers.
Furthermore, they in organic transformations. For example, Nafion-immobilized
) has been used for the synthesis
paint and coating components and as lubricants. The Prileshajev of nitrones via oxidation/condensation of aldehydes with primary
can directly be used as plasticizers and polymer stabilizers, as molybdenum oxychloride (MoOCl
4
6,7
1
4
15
reaction, i.e. the epoxidation of alkenes with peracids usually amines and oxo-vanadium-modified Nafion has been used
obtained in situ through the acid-catalyzed peroxidation of the for the hydrophosphonylation of aldehydes. However, the expen-
corresponding organic acid with hydrogen peroxide, is the most sive nature, super-acidic character and less functional group
applied method in industry for the epoxidation of unsaturated compatibility of Nafion resins make their synthetic utility limited
8
–9
fatty acids and triacylglycerols.
Soluble mineral acids, most for practical applications.
INDION 130 is an inexpensive, easily available, macroporous,
commonly sulfuric acid, are used as catalysts for this reaction.
However, there are some disadvantages to be dealt with, such as strongly acidic, industrial grade, sulfonic acid-containing cation
À1
exchange resin with an exchange capacity of 4.9 meq g . Owing
to its high thermal stability and superior catalytic activity, it has
a
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun-248005,
been successfully used as an acid catalyst for numerous organic
India. E-mail: suman@iip.res.in; Fax: +91-135-2660202; Tel: +91-135-2525788
Biofuel Division, CSIR-Indian Institute of Petroleum, Dehradun-248005, India.
E-mail: skaul@iip.res.in
16–18
transformations including multicomponent coupling,
ester-
However, to the best of
our knowledge, it has never been modified with metal ions to be
b
1
9,20
21,22
ification
and alkylation reactions.
†
Electronic supplementary information (ESI) available: EDX spectra of INDION-
1
VO catalyst and FTIR and H NMR of epoxidized oil. See DOI: 10.1039/c5nj00744e used as a heterogeneous catalyst for organic transformations.
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with vanadyl sulfate (VOSO
2 h (Scheme 2).
The functionalization of INDION resin with oxo-vanadium
4
Á5H
2
O) in refluxing ethanol for
1
2
+
(
VO ) ions was confirmed by XPS, FTIR and ICP-AES analyses.
The XPS spectra (Fig. 1) of INDION-VO exhibited a character-
istic band at 523 eV (V 2p3/2), which confirmed the presence of
vanadyl cation in the synthesized material.
Scheme 1 Epoxidation of fatty acids, esters and acid oils.
Vanadium compounds such as oxides, alkoxides, acetyl-
acetonate and other coordination compounds containing oxo-
vanadium(IV) ions are well known to react with alkylperoxides,
e.g. tert-butyl hydroperoxide (TBHP), to give reactive oxo-peroxo-
vanadium(V) species and have widely been used as effective catalysts
In addition, the FTIR spectrum of the INDION-VO catalyst
À1
(
Fig. 2) exhibited absorption bands at 994 and 998 cm , which
15
are assigned to the n(VQO) vibration. The presence of sulfonate
SO3 ) group in the synthesized catalyst was confirmed by the
appearance of two bands: one at around 1126 cm and another
at 1176 cm due to asymmetric and symmetric stretching of
À
(
À1
23
À1
for oxidation reactions including epoxidation of olefins. In this
24
3
1
regard Sen et al. reported the use of oxo-vanadium(IV) dihydrogen
SQO vibrations, respectively.
phosphate as a heterogeneous catalyst for olefin epoxidation
using TBHP as oxidant. Hsiao et al. reported polymer-supported
The thermal stability of the synthesized catalyst was deter-
mined by thermogravimetric analysis (TGA) in the presence of
nitrogen. As shown in Fig. 3(a and b), the vanadyl-modified
resin catalyst exhibited higher thermal stability as compared to
INDION resin (Fig. 3(a)).
25
vanadium complexes as catalysts for the oxidation of alkenes with
26
TBHP in water. Grivani and coworkers demonstrated novel oxo-
vanadium Schiff base complexes as homogeneous catalysts for
epoxidation of cyclooctene in different solvents using TBHP as
Furthermore, the vanadium content in the synthesized
catalyst was determined by ICP-AES analysis and it was found
27
oxidant. Nunes et al. reported mononuclear oxo-vanadium(IV)
complexes for olefin epoxidation using TBHP as well as hydrogen
28
2 2
peroxide (H O ) as oxidants. Belaidi et al. reported vanadium-
chromium-bentonite as a green heterogeneous catalyst for
epoxidation of cyclohexene with TBHP as an oxidant. Very
recently we have described an oxo-vanadium Schiff base covalently
immobilized to chemically functionalized graphene oxide (GO)
as an efficient heterogeneous catalyst for the epoxidation of fatty
2
9
acids and esters using TBHP as oxidant. However, a multistep
synthetic procedure involving modification of GO surface by
Scheme 2 Synthesis of INDION-VO catalyst.
3-aminopropyltrimethoxysilane and then immobilization of
oxo-vanadium complex makes the developed procedure tedious
and expensive.
3
0
Cordelle and coworkers demonstrated dinuclear vanadium
complexes with tridentate Schiff base ligand for epoxidation of
cyclooctene using aqueous TBHP as oxidant under solvent-less
conditions with moderate selectivity. However, these methods
have certain drawbacks such as multi-step tedious synthetic
procedures for oxo-vanadium catalysts, use of additional organic
solvents such as acetonitrile for the epoxidation reactions and
moderate product yields.
Fig. 1 XPS spectra of INDION-VO: (a) survey scan; (b) vanadium ion.
Herein, we report for the first time an easily accessible, cost-
effective and highly efficient heterogeneous vanadyl cation-
modified industrial grade INDION 130 resin (INDION-VO) as
heterogeneous catalyst for the epoxidation of fatty compounds
such as acids, esters and vegetable oils with TBHP as oxidant
under mild reaction conditions (Scheme 1). The developed hetero-
geneous oxo-vanadium catalyst exhibited higher catalytic activity
than the homogeneous catalyst with the added benefits of facile
recovery and recycling of the catalyst.
Results and discussion
Synthesis and characterization of the INDION-VO catalyst
INDION 130 acidic ion exchange resin was modified with
vanadyl cations (V(IV )Q O) by using the ion exchange method Fig. 2 FTIR spectrum of INDION-VO.
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Table 1 Epoxidation of fatty acids, esters and oils using INDION-VO
a
catalyst
b
b
c
Retention
time (min) (%)
Conv. Selec. Yield
b
Entry Reactant
1
(%)
(%)
9
9.2
99.1d
97.2
98.6
86.5
—
d
90.4
e, f
e, f
18.47
—
—
g
g
80.2
62.8
76
2
3
4
Acid oil (C18:1,C18:2,C18:3
)
26.52
27.11
26.89
99.0
98.4
98
99.4
99.1
99.1
98
97
Fig. 3 TGA of INDION-VO (b) and INDION 130 (a).
Methyl ester of acid oil
97.7
to be 0.8 mmol per gram. Elemental analysis data based on EDAX
indicated 1.3 wt% of elemental vanadium on the surface of the
catalyst (see Fig. S1, ESI†) confirming the successful modification
of the ion exchange resin with vanadyl cations.
‡
5
6
28.65
29.42
98
99.2
99.2
97.6
98
‡
98.8
Catalytic activity
With the vanadyl-modified INDION (INDION-VO) catalyst in
hand, we aimed to explore its catalytic activity for the epoxida-
tion of oleic acid with TBHP in 1 : 1.5 molar ratio at room
temperature in the presence of 5 wt% catalyst. Homogeneous
oxo-vanadium benzene sulfonate and unmodified INDION
‡
7
29.26
30.10
99.1
98.6
99.2
99.0
98.4
98.2
130 resin were also tested for comparison (Table 1, entry 1).
The results as shown in Table 1 revealed that the oxo-vanadium-
modified resin catalyst exhibited higher activity than homo-
geneous vanadium catalyst. The superior catalytic activity of
the heterogeneous catalyst can be attributed to the promoting
effect of the polymeric backbone of the ion exchange resin which
may interact with substrate and TBHP on the surface. However,
unmodified INDION 130 ion exchange resin did not exhibit
any catalytic activity under the described reaction conditions
8
9
1
30.85
29.71
96.4
94.1
99.0
99.1
95.8
93.5
0
a
Reaction conditions: fatty material (1 mmol), TBHP (1.5 mmol;
3
‡
‡
.0 mmol), catalyst (5 wt%; 10 wt%), room temperature, reaction time
b
(Table 1, entry 1). Blank experiments, in the absence of catalyst, 7 h. Conversion and selectivity for epoxide were determined by GC
(
8
Varian CP-3800, column: CP Sil 24, oven temp. program: 2 min at
did not produce the epoxidized product even after a prolonged
reaction time (12 h). Furthermore, to establish the superiority
À1
À1
0 1C, 10 min to 250 1C at 25 1C min , 10 min to 300 1C at 5 1C min ,
c
d
2
carrier gas N ). Isolated yield. Using homogeneous oxo-vanadium
e f
of the INDION-VO catalyst, we synthesized VO-Amberlyst-15 benzene sulfonate as catalyst. Using INDION 130. Blank experiment
g
without catalyst. Using VO-Amberlyst-15 resin catalyst.
resin catalyst by following a similar strategy and used it for
the epoxidation of oleic acid under identical experimental
conditions (Table 1, entry 1). The poor product yield in the case
of VO-Amberlyst-15 established the superiority of the INDION-VO and selectivity for epoxide formation to any significant extent.
catalyst over the other sulfonic polystyrene resin-based catalysts.
Further, to obtain the optimum reaction conditions, various selective for epoxide formation over CQC bond cleavage.
parameters (reaction time, molar ratio of TBHP to substrate Further we studied the effect of catalyst amount on the
These findings established that the developed method is highly
and catalyst concentration) were studied using oleic acid as the reaction. Initially the reaction conversion was found to increase
representative substrate. As shown in Fig. 4, the reaction conver- with increasing catalyst amount from 1 to 5 wt% with respect to
sion was found to increase with time and gave maximum conver- oleic acid (Fig. 6). A further increase in the catalyst amount did
sion of oleic acid to corresponding epoxide (99.2%) in 7 h.
not influence the reaction and the epoxide yield remained
The effect of molar ratio of ethylene unsaturation/TBHP on almost the same. Hence, 5 wt% catalyst was considered as
the conversion to epoxide was studied by varying the ratio from the optimum amount for further studies.
1
: 1 to 1 : 2.5 (Fig. 5). The conversion of oleic acid to corres-
After having optimized the reaction conditions, we explored
ponding epoxide was found to increase with the concentration the potential of the developed system for the epoxidation
of the oxidant and the maximum conversion was achieved when of various fatty compounds including acids, esters and acid
the molar ratio of oleic acid and TBHP was 1 : 1.5. A further oil, which is a waste product from the vegetable oil industry,
increase in TBHP concentration did not affect the conversion under optimized reaction conditions. The results of these
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Fig. 7 Results of recycling experiments.
Fig. 4 Effect of reaction time on the epoxidation of oleic acid [oleic
acid : TBHP (1 : 1.5), room temperature, catalyst 5 wt%].
attached to –CQC– are absent, confirming the successful
formation of epoxides. In addition, the appearance of a multi-
plet in the range of 3.1–3.2 ppm, assigned to epoxide protons,
confirmed the formation of respective epoxidized products
(Fig. S3, ESI†).
Furthermore, we performed recyclability experiments to
check the recycling of the developed heterogeneous catalyst
by considering the oxidation of oleic acid as a representative
example. After the reaction, the catalyst was recovered from the
reaction mixture by filtration, washed with methanol and dried
at 110 1C before reuse. The recovered catalyst was used for six
consecutive runs by using the same experimental conditions
(Fig. 7). The reused catalyst exhibited almost similar activity and
afforded almost similar conversion and selectivity of the epoxide.
To check the leaching of active vanadium species, we stopped
the reaction after one hour and isolated the catalyst by filtration
from the hot reaction mixture. After isolating the catalyst, the
reaction was continued for subsequent 6 h under the described
reaction conditions. The conversion of oleic acid remained very
similar to that obtained after 1 h. This study suggested that there
was no leaching and the reaction did not proceed in the absence
of the catalyst. Furthermore, the vanadium content as deter-
mined by ICP-AES analysis in the recovered catalyst after six runs
Fig. 5 Effect of TBHP concentration on the epoxidation of oleic acid
[oleic acid (1 mmol), room temperature, catalyst 5 wt%, time 7 h].
À1
was found to be very similar (0.78 mmol g ) to that of the fresh
À1
one (0.8 mmol g ). These results confirmed that the developed
catalyst was highly stable and truly heterogeneous in nature and
exhibited consistent catalytic activity for several runs.
The developed INDION-VO catalyst is more advantageous
2
8
than the reported heterogeneous oxo-vanadium catalyst in
terms of its facile synthetic methodology, easy accessibility of
INDION resin and comparable activity.
Fig. 6 Effect of catalyst concentration on the epoxidation of oleic acid
oleic acid : TBHP (1 : 1.5), room temperature, time 7 h].
[
experiments are summarized in Table 1. All the substrates were
efficiently converted to corresponding epoxides with excellent
Conclusions
selectivity under the described experimental conditions. The We have demonstrated an easily accessible, cost-effective and
formation of the epoxide product was initially characterized by highly efficient vanadyl-modified industrial grade ion exchange
the FTIR technique (Fig. S2, ESI†). The disappearance of the resin, INDION 130, as a heterogeneous catalyst for epoxidation
À1
band at 3005 cm , attributed to the –CQC– double bond, in the of fatty materials including fatty acids, esters and vegetable
FTIR spectra of epoxidized products supports the consumption oils using TBHP as oxidant under mild reaction conditions.
of double bonds and formation of epoxides during the reaction. The heterogeneous catalyst exhibited higher catalytic activity
1
Further, in H NMR spectra of the epoxidized oil (Fig. S3, than the homogeneous oxo-vanadium catalyst with the added
ESI†), the peaks between 5.3 and 5.5 ppm due to the protons benefits of facile recovery and recycling of the catalyst.
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Furthermore, low cost, high activity/selectivity and efficient (s, OQSQO; SO
recycling make the developed system more attractive for prac- by ICP-AES analysis and was found to be 0.8 mmol g catalyst.
3
), 998 (s, VQO). Metal loading was determined
À1
tical applications.
Typical experimental procedure for epoxidation
The epoxidation experiments were carried out in a 25 ml round-
bottomed flask equipped with a magnetic stirrer and a reflux
condenser. The flask was charged sequentially with oleic acid
Experimental
Material
(1 mmol), TBHP (5–6 M in decane, 1.5 mmol) and INDION-VO
Industrial grade INDION 130 (styrene-divinylbenzene copolymer) catalyst (5 wt% with respect to oleic acid). The resulting mixture
was purchased from Ion Exchange India Limited in the form of was stirred at room temperature for 7 h. The progress of the
light-colored spherical beads and dried at 110 1C before use. This reaction was monitored by thin-layer chromatography (silica gel)
is a macroporous strongly acidic material having sulfonic acid at regular intervals of time. After completion of reaction, the
À1
functional groups with acid site concentration of 4.8 meq g
.
catalyst was separated by filtration, washed with methanol and
These functional groups throughout the entire structure are dried for reuse for recycling experiments. The filtrate thus
readily accessible and provide efficient performance. The com- obtained was diluted with dichloromethane and washed with
mercially available INDION 130 ion exchange resin was found lukewarm water and ethanol successively to remove free acid. The
to be stable up to 150 1C. Fatty acids and sodium acetate were resulting organic layer was concentrated under reduced pressure
purchased from Alfa Aesar and used as received. Vanadyl sulfate and dried over anhydrous Na SO . The selectivity of the epoxides
2
4
and TBHP solution, 5.0–6.0 M in decane, were procured from was determined by GC (Agilent 6890 Series; HP-5 column, 30 m
Sigma-Aldrich and used without further purification. Acid oil 0.25 mm; FID detector) using mesitylene (Sigma, 99%) as an
used was the refinery waste which was used as received.
internal standard. GC peaks were identified by comparison
with peaks of authentic samples of reference standards and
by means of GC-MS analysis.
Techniques used
Fourier transform infrared spectroscopy (FTIR) was conducted
with a Perkin Elmer Spectrum RX-1 IR spectrophotometer.
XPS measurements were obtained using a KRATOS-AXIS 165
Acknowledgements
instrument equipped with dual aluminum–magnesium anodes We are grateful to director IIP for his kind permission to
using Mg Ka radiation (hn = 1253.6 eV) operated at 5 kV and publish these results. MA is grateful to CSIR, New Delhi for
15 mA with pass energy of 80 eV and an increment of 0.1 eV. The working as Technical HR in XII Five Year project.
conversions and selectivity of the products were determined by
1
high resolution GC-FID (Varian CP-3800). H-NMR spectra of the
products were obtained at 500 MHz by using a Bruker Avance-II
Notes and references
500 MHz instrument. Inductively coupled plasma atomic emission
1
U. Biermann, W. Friedt, S. Lang, W. Luhs, G. Machmuller,
J. O. Metzger, M. R. Klaas, H. J. Schafer and M. P. Schneider,
Angew. Chem., Int. Ed., 2000, 39, 2206–2224.
spectroscopy (ICP-AES) analysis was carried out with an ICP-AES
spectrometer (DRE, PS-3000UV, Leeman Labs Inc., USA). Samples
for ICP-AES were prepared by leaching out 0.01 g of sample with
2
3
F. D. Gunstone and F. B. Padley, Lipid Technologies and
Applications, Marcel Dekker, New York, 1997, pp. 759–769.
G. Lligadas, J. C. Ronda, M. Galia, U. Biermann and
J. O. Metzger, J. Polym. Sci., Part A: Polym. Chem., 2006, 44,
conc. HNO , and then heated for 30 min and the volume made up
3
to 10 ml. TGA of the samples was carried out using a thermal
analyzer (TA-SDT Q-600). All samples were analyzed in the tempera-
À1
ture range of 40 to 900 1C at a heating rate of 10 1C min under
6
34–645.
S. Warwel, F. Bruse and M. Kunz, Fresenius Environ. Bull.,
003, 12, 534–539.
nitrogen flow.
4
5
2
Synthesis of INDION-VO
P. Daute, R. Picard, J. D. Klamann, P. Wedl and A. Peters,
The required INDION-VO catalyst was synthesized by refluxing
a mixture of INDION 130 ion exchange resin (styrene-divinylbenzene
copolymer) (1 g), sodium acetate (0.398 g, 4.85 mmol) and vanadyl
sulfate pentahydrate (0.6 g, 2.37 mmol) in 50 ml of ethanol for 12 h
under nitrogen atmosphere. The light blue colored heterogeneous
INDION-VO was separated by filtration and washed with plenty
of distilled water and methanol in order to remove the
unreacted or excess amount of vanadyl sulfate. Filtered catalyst
was dried under vacuum at 60 1C for 5 h. The successful
synthesis of the catalyst was confirmed by comparing the XPS
US Pat., 7071343 B2, 2006.
6 B. K. Sharma, K. M. Doll and S. Z. Erhan, Green Chem., 2007,
9, 469–474.
7 B. R. Moser and S. Z. Erhan, Eur. J. Lipid Sci. Technol., 2007,
109, 206–213.
8 Recent developments in the synthesis of fatty acid derivatives,
ed. G. Knothe and J. T. P. Derksen, AOCS press, Champaign,
IL, 1999.
9 Z. S. Petrovic, A. Zlatanic, C. C. Lava and S. Sinadinovic-Fiser,
Eur. J. Lipid Sci. Technol., 2002, 104, 293–299.
1
5
and FTIR analysis with an existing report. XPS (V2p): 523 eV; 10 R. L. Musante, R. J. Grau and M. A. Ba1tan ´a s, Appl. Catal., A,
À1
FTIR (cm ): 3420 (s, broad, OH), 1628 (s, H
2
O), 1176, 1126
2000, 197, 165–173.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015
New J. Chem.

View Article Online
Paper
NJC
11 R. E. Kirk, D. F. Othmer, H. F. Mark and A. Standen, Kirk- 22 K. G. Chandra and M. M. Sharma, Catal. Lett., 1993, 19,
Othmer Encyclopedia of Chemical Technology, Wiley-VCH,
New York, 1965.
2 V. V. Goud, A. V. Patwardhan, S. Dinda and N. C. Pradhan,
309–317.
23 (a) J. A. L. da Silva, J. J. R. Fra u´ sto da Silva and A. J. L.
Pombeiro, Coord. Chem. Rev., 2011, 255, 2232–2248;
(b) H. Toshikazu, Chem. Rev., 1997, 97, 2707–2724.
1
1
1
1
1
1
1
Chem. Eng. Sci., 2007, 62, 4065–4076.
3 V. V. Goud, A. V. Patwardhan and N. C. Pradhan, Ind. Eng. 24 R. Sen, R. Bera, A. Bhattacharjee, P. G u¨ tlich, S. Ghosh, A. K.
Chem. Res., 2007, 46, 3078–3085. Mukherjee and S. Koner, Langmuir, 2008, 24, 5970–5975.
4 B. Singh, S. L. Jain, P. K. Khatri and B. Sain, Green Chem., 25 M.-C. Hsiao and S.-T. Liu, Catal. Lett., 2010, 139, 61–66.
2009, 11, 1941.
26 G. Grivani, G. Bruno, H. A. Rudbari, A. D. Khalaji and
5 S.-S. Weng, G.-Y. Lin, H.-C. Li, K.-C. Yang, T.-M. Yang, H.-C.
P. Pourteimouri, Inorg. Chem. Commun., 2012, 18, 15–20.
Liu and S.-H. Sie, Appl. Organomet. Chem., 2012, 26, 455–460. 27 C. D. Nunes, P. D. Vaz, V. F ´e lix, L. F. Veiros, T. Moniz,
6 A. M. Pansuriya, M. M. Savant, C. V. Bhuva, N. Kapuriya,
M. Rangel, S. Realista, A. C. Mouratoa and M. J. Calhorda,
J. Singh and Y. T. Naliapara, Lett. Org. Chem., 2009, 6, 619–623.
Dalton Trans., 2015, 44, 5125–5138.
7 S. B. Patil, P. R. Singh, M. P. Surpur and S. Samant, Synth. 28 N. Belaidi, S. Bedrane, A. Choukchou-Braham and
Commun., 2007, 37, 1659–1664. R. Bachir, Appl. Clay Sci., 2015, 107, 14–20.
8 S. B. Patil, P. R. Singh, M. P. Surpur and S. Samant, Synth. 29 S. Verma, M. Aila, S. Kaul and S. L. Jain, RSC Adv., 2014, 4,
Commun., 2006, 36, 2163–2168. 30598–30604.
9 G. D. Yadav and H. B. Kulkarni, Polymers, 2000, 44, 153–165. 30 C. Cordelle, D. Agustin, J.-C. Daran and R. Poli, Inorg. Chim.
1
2
0 G. D. Yadav and M. S. Krishnan, Org. Process Res. Dev., 1998,
, 86–95.
Acta, 2010, 364, 144–149.
2
31 P. P. Upare, J.-W. Yoon, M.-Y. Kim, H.-Y. Kang, D. W.
Hwang, Y. K. Hwang, H. H. Kung and J.-S. Chang, Green
Chem., 2013, 15, 2935–2943.
21 J. Gangadwala, S. Mankar, S. Mahajani, A. Kienle and
E. Stein, Ind. Eng. Chem. Res., 2003, 42, 2146–2155.
New J. Chem.
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