Deep eutectic solvent-catalyzed arylation of benzoxazoles with aromatic aldehydes

Article abstract of DOI:10.1039/c8ra01094c

A novel and efficient methodology for the arylation of benzoxazoles with aromatic aldehydes catalyzed by deep eutectic solvent has been developed. The reaction smoothly proceeded with a wide range of substrates to give the desired products in high yields within short reaction time. Deep eutectic solvents are easily recovered and reused without significant loss of catalytic activity.

Full text of DOI:10.1039/c8ra01094c

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Deep eutectic solvent-catalyzed arylation of
benzoxazoles with aromatic aldehydes†
Cite this: RSC Adv., 2018, 8, 11127
*
Phuong Hoang Tran
and Anh-Hung Thi Hang
Received 4th February 2018
Accepted 13th March 2018
A novel and efficient methodology for the arylation of benzoxazoles with aromatic aldehydes catalyzed by
deep eutectic solvent has been developed. The reaction smoothly proceeded with a wide range of
substrates to give the desired products in high yields within short reaction time. Deep eutectic solvents
are easily recovered and reused without significant loss of catalytic activity.
DOI: 10.1039/c8ra01094c
rsc.li/rsc-advances
reaction between benzoxazoles and aromatic aldehydes can be
conducted in the presence of a suitable catalyst, e.g., molec-
ular I2 or FeSO4.30,31 Until now, there has been no further
report on the arylation of benzoxazoles using aldehydes as
reagents.
Introduction
2-Arylbenzoxazoles are important structural subunits in
natural products, pharmaceuticals, agrochemicals, and
dyes.1–4 Therefore, the development of efficient synthetic
methods for C2-arylation of benzoxazoles has received much
attention.5,6 Among them, palladium-catalyzed cross-coupling
is one of the most powerful and reliable tools to achieve aryl-
substituted benzoxazoles through direct C–H activation and
subsequent C–C bond formation.7–9 However, this protocol
still suffered from inherent drawbacks associated with the use
of uncommon, toxic, and expensive agents such as aryl-
trimethylammonium triates,7 aryl halides or triates,10–17 aryl
boronic acids,18 sodium arylsulnates,19 arylsulfonyl hydra-
zides,20 and 3-phenylpropionic acid.21 Additionally, the
requirement of high-cost palladium catalysts and other
expensive additives also prevents the palladium-catalyzed
cross-coupling procedure from being employed in large-scale
synthesis.22 Recently, the replacement of palladium by other
transition metals, such as bis(diisopropylphosphinomethyl)
amine nickel(II) and nickel(0) complexes,23 metal–organic
frameworks,24,25 Cu/Fe system,26 CeO2/Fe3O4,27 CuCN(PPh3)2,28
and Ni(COD)2,29 has been investigated. These direct arylation
methods have received much attention due to their advantage
of avoiding the use of stoichiometric amounts of expensive
organometallic reagents or additives. However, these proto-
cols still encounter several problems including low yields, long
reaction times, poor substrate scope, and high toxicity.
Therefore, the development of an effective alternative method
for the arylation of benzoxazoles remains highly desirable.
Aromatic aldehydes are considered as preferable reagents in
the arylation of benzoxazoles owing to their widespread
availability, non-toxicity, and low-cost production. The
In an attempt to develop a cost-effective and environmentally
benign protocol, we focus on exploring a new and affordable
catalyst for direct arylation of benzoxazoles under “greener”
conditions. Deep eutectic solvents (DESs) which were discov-
ered for the rst time by Abbott in 2001 have been known as
a new class of ionic liquids possessing many outstanding
characteristics.32–34 DESs have found many applications as
green solvents in diverse elds including nanotechnology,35
separation processes,36 transition metal catalyzed reactions,37
material chemistry,38 stabilization of DNA,39 and organic
synthesis.40 Besides, DESs have been known as preferable
alternative solvents/catalysts for organic synthesis due to their
non-hazardous, non-toxic, stable, non-ammable, and inex-
pensive nature.41–49 Recently, we have reported DESs-catalyzed
organic transformations such as Friedel–Cras acylation and
esterication of sterically hindered alcohols.50,51 As our ongoing
efforts to develop environmentally benign syntheses, it is the
aim of this communication to describe our preliminary results
in the arylation of benzoxazoles with aromatic aldehyde using
DES as a green catalyst. Notable features of our report include:
(i) straightforward and affordable preparation of catalyst, (ii)
simple work-up, (iii) removable additive agents, (iv) recyclable,
biodegradable, and low-toxic catalyst.
Results and discussion
Preparation and characterization of [ZnCl2][ethylene glycol]4
DESs were synthesized by mixing zinc chloride and ethylene
glycol (HBDs) at a dened molar ratio (1 : 4) and heating at
120 ꢀC for 1 h at atmospheric pressure under constant magnetic
stirring until a homogeneous liquid was formed. The charge
delocalization which occurs through hydrogen bonding
between the halide anion and ethylene glycol is responsible for
the decrease in the Tm of the mixture.52,53
Department of Organic Chemistry, Faculty of Chemistry, University of Science, Viet
Nam National University, Ho Chi Minh City 721337, Viet Nam. E-mail: thphuong@
hcmus.edu.vn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra01094c
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The NMR characterization are in good agreement with the
structure of [ZnCl2][ethylene glycol]4 and the NMR spectra
show that the catalyst is free of impurities. DESs with high
viscosity and the inter- as well as intra-dipolar interactions
can cause the broadening effect on the resonance signals of
NMR spectrum.54 The high viscosity of DES used in the
current work involves the formation of massive hydrogen
bond network between each component.55 Fig. 1 displays the
FT-IR spectra of ethylene glycol and [ZnCl2][ethylene glycol]4.
The spectrum of the [ZnCl2][ethylene glycol]4 is an overlap of
those of ethylene glycol. The result showed that the structure
of ethylene glycol was not destroyed in the [ZnCl2][ethylene
glycol]4. Particularly, the absorption bands of ethylene glycol
at 3390 cmÀ1 could be ascribed to stretch vibration of O–H
functional group. As observed in Fig. 1, the O–H stretching
vibration of [ZnCl2][ethylene glycol]4 shis to lower wave-
number, indicating that O–H of ethylene glycol takes part in
the formation of the hydrogen bond with the anion of zinc
chloride.47,53,55
Fig. 2 Raman spectra of ethylene glycol (a), zinc chloride (b), and
[ZnCl2][ethylene glycol]4 (c).
The Raman spectra of ethylene glycol, zinc chloride, and
[ZnCl2][ethylene glycol]4 are presented in Fig.
2 for
a comparative analysis in the region from 50 to 1500 cmÀ1. In
pure ZnCl2, we have observed a strong signal at 225 cmÀ1 and
another weak signal at 290 cmÀ1; however, at low ZnCl2 molar
fraction (in deep eutectic solvent) the feature at 290 cmÀ1
becomes strong and the signal at 225 cmÀ1 disappears.
Rubim et al. have also observed the same feature for ZnCl2 in
eutectic mixture with 1-butyl-3-methylimidazolium chlo-
ride.56 Thus, the Raman spectrum of [ZnCl2][ethylene glycol]4
does not change as compared with the signal of ethylene
glycol but additional peaks from ZnCl2 appear at 80 and
290 cmÀ1
.
Thermal gravimetric analysis (TGA) of [ZnCl2][ethylene
glycol]4 was performed in Fig. 3. The major weight loss occurs in
ꢀ
ꢀ
the temperature range from 200 C to 475 C, which make the
[ZnCl2][ethylene glycol]4 suitable for high-temperature reaction
conditions.
Fig. 3 TG analysis of [ZnCl2][ethylene glycol]4.
Optimization of reaction conditions
We initiated our studies by investigating various reaction
conditions for the C2-arylation of benzoxazole by benzaldehyde
(Tables 1 and 2). The optimized condition revealed that the air-
stable and environmentally benign [ZnCl2][ethylene glycol]4
proved to be an effective catalyst for the highly selective C2-
arylation of benzoxazole with benzaldehyde in 2 : 1 molar
ratio. The method provided the desired product in high yield in
the absence of other additives such as organic solvents or bases.
It is also noteworthy that this arylation of benzoxazole pro-
ceeded smoothly without the need of inert atmosphere.
With the optimized catalyst in hand, the scope of the ben-
zoxazoles and aromatic aldehydes in the arylation reaction was
studied (Table 3). The results demonstrated that the developed
pathway provided the C2-arylation products in high yields.
Generally, the robust DES between ethylene glycol and zinc
chloride allowed a variety of substituted benzoxazoles and
aldehydes to transform into the desired products in good to
Fig. 1 FT-IR spectra of ethylene glycol (a), and [ZnCl2][ethylene
glycol]4 (b).
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Table 1 Optimization of catalyst for the arylation of benzoxazolea
Table
3
The scope of arylation of benzoxazoles with aromatic
aldehydes
Entry
Catalyst
Yieldb (%)
Entry
Product
Condition
120 ꢀC, 6 h
120 ꢀC, 5 h
Yielda (%)
95 (94)b
93
1
2
3
4
5
6
7
8
9
ZrCl4
ZnCl2
FeCl3
HfCl4
70
20
75
73
95
0
80
85
5
1
2
[ZnCl2][ethylene glycol]4
[ChCl][ZnCl2]3
[ZnCl2]4[urea]
[ZnCl2][glycerol]4
[ZnCl2][acetamide]4
3
4
5
6
7
120 ꢀC, 5 h
120 ꢀC, 4 h
140 ꢀC, 6 h
120 ꢀC, 4 h
120 ꢀC, 4 h
94
95
75
80
92
a
Reaction conditions: benzoxazole (1 mmol), benzaldehyde (0.5 mmol),
solvent-free. b Isolated yield.
Table 2 Optimization of the reaction conditions for the synthesis of 2-
phenylbenzoxazolea
Catalytic amount
(mol%)
Time
(h)
Temperature
(ꢀC)
Yieldb
(%)
Entry
1
2
3
4
5
6
7
8
1
2
3
5
10
5
5
5
5
5
5
5
5
5
5
5
5
5
6.0
6.0
6.0
6.0
6.0
1.0
1.5
2.5
4.0
4.5
6.0
6.5
6.0
6.0
6.0
6.0
6.0
6.0
120
120
120
120
120
120
120
120
120
120
120
120
90
60
75
80
95
95
0
8
120 ꢀC, 5 h
120 ꢀC, 5 h
120 ꢀC, 5 h
120 ꢀC, 4 h
120 ꢀC, 6 h
70
90
72
90
93
9
0
0
9
30
75
95
97
40
45
80
95
95
95
10
11
12
13
14
15
16
17
18
10
11
12
100
110
120
130
140
a
Reaction conditions: benzoxazole (1 mmol), benzaldehyde (0.5 mmol),
solvent-free. b Isolated yield.
13
14
15
120 ꢀC, 6 h
120 ꢀC, 5 h
120 ꢀC, 4 h
80
94
90
excellent yields with 100% selectivity in C2-arylation. First,
a large number of aromatic aldehydes, regardless of containing
electron-donating substituents (methyl, t-butyl, hydroxy,
methoxy) or electron-withdrawing substituents (nitro, halide),
can react with benzoxazoles to produce the expected products
under the given reaction conditions (Table 3). However, low
yields of the desired products were observed for benzaldehydes
bearing severe electron-withdrawing groups such as nitro or
uoro substituents (Table 3, entries 5, 6, 8, 10, 18, 26, 35). Next,
the scope of various benzoxazoles was also evaluated. As our
expectation both 5-methylbenzoxazole and 5-chlorobenzoxazole
generally underwent the arylation to give the corresponding
16
17
120 ꢀC, 4 h
120 ꢀC, 4 h
90
95
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Table 3 (Contd.)
Table 3 (Contd.)
Entry
18
Product
Condition
Yielda (%) Entry
Product
Condition
Yielda (%)
80
120 ꢀC, 4.5 h
120 ꢀC, 4.5 h
120 ꢀC, 6.5 h
120 ꢀC, 6 h
120 ꢀC, 5 h
120 ꢀC, 4 h
75
85
70
82
95
95
36
140 ꢀC, 6 h
19
37
140 ꢀC, 6 h
85
a
Isolated yield. b On 10 mmol or 20 mmol scale.
20
21
products in very good yields ranging from 82 to 95% except the
case of 4-uorobenzaldehyde and 4-hydroxybenzaldehyde
whose resulting arylated products were only obtained in
signicantly diminished yields of 70–75% (Table 3, entries 14–
30). For the benzoxazole bearing a nitro substituent, the lower
yields of arylation products with various aldehydes were recor-
ded even though harsher conditions (higher temperature for
prolonged reaction time) were employed (Table 3, entries 31–
37). It is noteworthy that the condensation between benzoxazole
and benzaldehyde was successfully performed on a 10 mmol or
20 mmol scale, and the yield is virtually the same as on 1 mmol
scale (Table 3, entry 1).
22
23
24
120 ꢀC, 4 h
90
25
26
27
28
29
30
31
32
120 ꢀC, 4 h
120 ꢀC, 4 h
120 ꢀC, 4 h
120 ꢀC, 6 h
120 ꢀC, 6.5 h
120 ꢀC, 6 h
140 ꢀC, 6 h
140 ꢀC, 5 h
95
75
95
85
75
85
70
75
The versatility of benzothiazole and benzimidazole as
substrates in the replacement of benzoxazole was also reported.
The adducts resulted from the condensation of benzothiazole
with various aromatic aldehydes were isolated in comparative
yields with those derived from benzoxazole (Table 4, entries 1–
6). Meanwhile, a failure in the formation of the desired product
was noted for the case of benzimidazole (Table 4, entry 7),
probably due to the existence of intermolecular hydrogen bonds
between the NH of benzimidazole and DES.
A comparative study between the current method and
previous ones was presented in Table 5. Deep eutectic solvent-
catalyzed arylation of benzoxazole afforded the arylated ben-
zoxazole products in excellent yields under a mild and simple
condition without the demand for any additives as in preceding
reports (Table 5, entry 6). Remarkably, no loss of catalytic
activity in the recycling test of DES is the most prominent
artifact of this protocol.
33
34
35
140 ꢀC, 5 h
140 ꢀC, 5 h
140 ꢀC, 6 h
75
80
72
As asserted in previous literature through isotope-labeling
mechanistic studies, the arylation of benzoxazoles with
aromatic aldehydes underwent the ring-opening step assisted
by Lewis acids such as I2 or FeSO4 to afford the key intermediate
2-aminophenol. Its nucleophilic addition to aldehydes followed
by oxidative ring closure provided arylated benzoxazoles as nal
products.30,31 As an extra part in our research to check the
conformability of the proposed mechanism for the same reac-
tion catalyzed by [ZnCl2][ethylene glycol]4, we also carried out
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Table
4 The arylation of benzothiazole and benzimidazole with
result, the same arylated benzoxazole product was obtained in
a comparable yield of 85%. Additionally, in another control
experiment whereby benzoxazole reacted with [ZnCl2][ethylene
glycol]4 in the absence of benzaldehyde, 2-aminophenol was
obtained in 62% yield. Thus, it is not doubtful that the arylation
of benzoxazole studied herein must also undergo the ring-
opening step prior to the condensation step with aldehydes.
Although the mechanism is not clear now, the method
possesses attractive merits including cheap and recyclable
catalyst, non-toxicity, and wide scope of substrates.
The recyclability is an important feature for applying a cata-
lyst in industrial processes. The recyclability of deep eutectic
solvent of zinc chloride and ethylene glycol under study in this
work was investigated in the model reaction. Aer completion
of the reaction, the product was extracted with diethyl ether
(10 Â 5 mL), the catalyst was separated from the ethereal
solution and dried under vacuum. The recovered catalyst was
aromatic aldehydes under current method
Entry
Product
Condition
120 ꢀC, 6 h
120 ꢀC, 5 h
Yielda (%)
1
2
85
88
3
4
5
6
120 ꢀC, 5 h
120 ꢀC, 4 h
120 ꢀC, 4 h
120 ꢀC, 6.5 h
90
85
80
70
7
120–140 ꢀC, 4–8 h
0
a
Isolated yield.
the acylation–cyclization of 2-aminophenol with benzaldehyde
under the same optimized conditions which were previously
applied for the arylation of benzoxazole by benzaldehyde. As the
Fig. 4 Reuse of [ZnCl2][ethylene glycol]4 catalyst in the arylation of
benzoxazole with benzaldehyde.
Table 5 The comparison of the current method with previous reports in the arylation of benzoxazole
Entry
Catalyst
Reagent
Condition
Yield (%)
1
2
FeSO4 (0.2 equiv.), H2O/diglyme/O2
I2 (2 equiv.), PhCl, DMF
150 ꢀC, 20 h
130 ꢀC, 30 h
70 (ref. 31)
75 (ref. 30)
3
[Pd(p-allyl)Cl]2 (0.1 equiv.), PCy3, NaOtBu (2 equiv.), DMF
120 ꢀC, 12 h
43 (ref. 7)
4
5
CuCN(PPh3)2 (10 mol%), PPh3, Cs2CO3, pivalonitrile
Reux, 24 h
85 (ref. 28)
91 (ref. 29)
Ni(COD)2 (0.1 equiv.), dcype (0.2 equiv.), Cs2CO3 (1.5 equiv.), p-xylene
140 ꢀC, 22 h
6
Current work: [ZnCl2][ethylene glycol]4 (5 mol%), solvent-free
120 ꢀC, 6 h
95
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of deep eutectic solvent is requisite for the quantitative produc-
tion of various 2-arylbenzoxazoles through a simplistic, environ-
mentally benign, and low-cost synthetic procedure.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This research is funded by Viet Nam National University, Ho Chi
Minh City (VNU-HCM) under grant number 562-2018-18-03.
Notes and references
1 O. Daugulis, H.-Q. Do and D. Shabashov, Acc. Chem. Res.,
2009, 42, 1074–1086.
Fig. 5 FT-IR of fresh [ZnCl2][ethylene glycol]4 (a) and [ZnCl2][ethylene
glycol]4 after the fifth recovery (b).
2 K. Kuroda, S. Tsuyumine and T. Kodama, Org. Process Res.
Dev., 2016, 20, 1053–1058.
3 C. S. Demmer and L. Bunch, Eur. J. Med. Chem., 2015, 97,
778–785.
4 K. Seth, S. K. Garg, R. Kumar, P. Purohit, V. S. Meena,
R. Goyal, U. C. Banerjee and A. K. Chakraborti, ACS Med.
Chem. Lett., 2014, 5, 512–516.
5 C. L. Sun and Z. J. Shi, Chem. Rev., 2014, 114, 9219–9280.
6 L. Yang and H. Huang, Chem. Rev., 2015, 115, 3468–3517.
7 F. Zhu, J.-L. Tao and Z.-X. Wang, Org. Lett., 2015, 17, 4926–
4929.
8 F. Bellina and R. Rossi, Tetrahedron, 2009, 65, 10269–10310.
9 G. Wu, J. Zhou, M. Zhang, P. Hu and W. Su, Chem. Commun.,
2012, 48, 8964–8966.
reused in the model reaction to the next run. As illustrated in
Fig. 4, the efficiency of deep eutectic solvent was found to be
constantly excellent even aer ve consecutive recycles. IR
spectroscopy of fresh and recovered deep eutectic solvent
indicated that no detectable structural degradation can be seen
(Fig. 5). Aer each recycling test, a very small amount of DES
leaching to diethyl ether phase during the work-up step was
indirectly estimated by means of ICP-MS technique in which Zn
content of about 0.08 ppm in the ethereal phase was deter-
mined. A slight decrease of catalytic activity was observed due to
a little loss of deep eutectic solvent during the work-up process.
10 B. Sezen and D. Sames, Org. Lett., 2003, 5, 3607–3610.
´
11 R. S. Sanchez and F. A. Zhuravlev, J. Am. Chem. Soc., 2007,
129, 5824–5825.
Experimental
12 F. Derridj, S. Djebbar, O. Benali-Baitich and H. Doucet, J.
Organomet. Chem., 2008, 693, 135–144.
13 F. Yang, Y. Wu, Z. Zhu, J. Zhang and Y. Li, Tetrahedron, 2008,
64, 6782–6787.
14 J. Canivet, J. Yamaguchi, I. Ban and K. Itami, Org. Lett., 2009,
11, 1733–1736.
General procedure for catalytic arylation of benzoxazole
Benzoxazole (119 mg, 1.0 mmol) was treated with benzaldehyde
(53 mg, 0.5 mmol) in the presence of [ZnCl2][ethylene glycol]4
(5 mg, 0.01 mmol) at 120 ꢀC for 6 h under solvent-free magnetic
stirring. The completion of the reaction was checked by
TLC and GC. The mixture was then diluted with diethyl ether
(10 Â 5 mL). The solvent was removed on a rotary evaporator.
The crude product was puried by silica gel chromatography
using acetone/petroleum ether (1/19) to afford the desired
product (95% yield). The purity and identity of the product were
conrmed by FT-IR, 1H NMR, 13C NMR, and MS. The recovered
catalyst was activated by heating under reduced vacuum at 80 ꢀC
for 30 min and reused for next cycles.
´
15 J. Roger, S. Mom, M. Beauperin, S. Royer, P. Meunier,
V. V. Ivanov, H. Doucet and J.-C. Hierso, ChemCatChem,
2010, 2, 296–305.
16 J. J. Dong, J. Roger, C. Verrier, T. Martin, R. Le Goff,
C. Hoarau and H. Doucet, Green Chem., 2010, 12, 2053–2063.
17 X.-B. Shen, Y. Zhang, W.-X. Chen, Z.-K. Xiao, T.-T. Hu and
L.-X. Shao, Org. Lett., 2014, 16, 1984–1987.
18 S. Ranjit and X. Liu, Chem.–Eur. J., 2011, 17, 1105–1108.
19 M. Wang, D. Li, W. Zhou and L. Wang, Tetrahedron, 2012, 68,
1926–1930.
20 F. Kwong, O. Yuen, C. So and W. Wong, Synlett, 2012, 23,
2714–2718.
Conclusions
In conclusion, we have developed the rst DES-mediated arylation
of benzoxazoles with aromatic aldehydes at the C2 position under 21 D. Liu, B. Liu and J. Cheng, RSC Adv., 2013, 3, 9193–9196.
solvent-free condition. The most important highlight of the 22 K. E. Balsane, S. H. Gund and J. M. Nagarkar, Catal.
current method is the use of inexpensive, air- and water-stable,
Commun., 2017, 89, 29–33.
and recyclable deep eutectic solvent in the replacement of high- 23 A. Kruckenberg, H. Wadepohl and L. H. Gade,
cost palladium catalysts. Interestingly, only a catalytic amount
Organometallics, 2013, 32, 5153–5170.
11132 | RSC Adv., 2018, 8, 11127–11133
This journal is © The Royal Society of Chemistry 2018

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Paper
RSC Advances
24 N. T. S. Phan, C. K. Nguyen, T. T. Nguyen and T. Truong, 41 M. Starykevich, A. N. Salak, D. K. Ivanou, A. D. Lisenkov,
Catal. Sci. Technol., 2014, 4, 369–377.
M. L. Zheludkevich and M. G. S. Ferreira, Electrochim. Acta,
2015, 170, 284–291.
42 E. L. Smith, A. P. Abbott and K. S. Ryder, Chem. Rev., 2014,
114, 11060–11082.
25 H. T. N. Le, T. T. Nguyen, P. H. L. Vu, T. Truong and
N. T. S. Phan, J. Mol. Catal. A: Chem., 2014, 391, 74–82.
26 S.-L. Zhang, W.-Y. Hu and P.-P. Wang, Synthesis, 2014, 47,
42–48.
´
´
´
43 J. I. Garcıa, H. Garcıa-Marın and E. Pires, Green Chem., 2014,
27 R. S. Shelkar, K. E. Balsane and J. M. Nagarkar, Tetrahedron
Lett., 2015, 56, 693–699.
28 D. Kim, K. Yoo, S. E. Kim, H. J. Cho, J. Lee, Y. Kim and
M. Kim, J. Org. Chem., 2015, 80, 3670–3676.
29 D. F. Steinberg, M. C. Turk and D. Kalyani, Tetrahedron,
2017, 73, 2196–2209.
16, 1007–1033.
44 J. Cao, B. Qi, J. Liu, Y. Shang, H. Liu, W. Wang, J. Lv, Z. Chen,
H. Zhang and X. Zhou, RSC Adv., 2016, 6, 21612–21616.
45 C. Mukesh, R. Gupta, D. N. Srivastava, S. K. Nataraj and
K. Prasad, RSC Adv., 2016, 6, 28586–28592.
´
46 G. Garcıa, S. Aparicio, R. Ullah and M. Atilhan, Energy Fuels,
30 Y. C. Teo, S. N. Riduan and Y. Zhang, Green Chem., 2013, 15,
2365–2368.
31 S. Liu, R. Chen, X. Guo, H. Yang, G. Deng and C.-J. Li, Green
Chem., 2012, 14, 1577–1580.
32 Q. Zhang, K. De Oliveira Vigier, S. Royer and F. Jerome,
Chem. Soc. Rev., 2012, 41, 7108–7146.
33 B.-Y. Zhao, P. Xu, F.-X. Yang, H. Wu, M.-H. Zong and
2015, 29, 2616–2644.
47 Q. Wang, X. Yao, Y. Geng, Q. Zhou, X. Lu and S. Zhang, Green
Chem., 2015, 17, 2473–2479.
48 O. S. Hammond, K. J. Edler, D. T. Bowron and L. Torrente-
Murciano, Nat. Commun., 2017, 8, 14150–14157.
49 A. R. Hajipour, S. H. Nazemzadeh and F. Mohammadsaleh,
Tetrahedron Lett., 2014, 55, 654–656.
W.-Y. Lou, ACS Sustainable Chem. Eng., 2015, 3, 2746–2755. 50 P. H. Tran, H. T. Nguyen, P. E. Hansen and T. N. Le, RSC Adv.,
34 A. P. Abbott, G. Capper, D. L. Davies, H. L. Munro, 2016, 6, 37031–37038.
R. K. Rasheed and V. Tambyrajah, Chem. Commun., 2001, 51 H. T. Nguyen and P. H. Tran, RSC Adv., 2016, 6, 98365–98368.
2010–2011.
52 Y. Dai, J. van Spronsen, G. J. Witkamp, R. Verpoorte and
Y. H. Choi, J. Nat. Prod., 2013, 76, 2162–2173.
53 A. Pandey, Bhawna, D. Dhingra and S. Pandey, J. Phys. Chem.
B, 2017, 121, 4202–4212.
54 C. D'Agostino, R. C. Harris, A. P. Abbott, L. F. Gladden and
M. D. Mantle, Phys. Chem. Chem. Phys., 2011, 13, 21383–
21391.
35 A. Abo-Hamad, M. Hayyan, M. A. AlSaadi and M. A. Hashim,
Chem. Eng. J., 2015, 273, 551–567.
36 B. Tang, H. Zhang and K. H. Row, J. Sep. Sci., 2015, 38, 1053–
1064.
´
´
37 J. Garcıa-Alvarez, Eur. J. Inorg. Chem., 2015, 2015, 5147–5157.
38 F. del Monte, D. Carriazo, M. C. Serrano, M. C. Gutierrez and
M. L. Ferrer, ChemSusChem, 2014, 7, 999–1009.
55 J. Zhu, K. Yu, Y. Zhu, R. Zhu, F. Ye, N. Song and Y. Xu, J. Mol.
Liq., 2017, 232, 182–187.
39 H. Zhao, J. Chem. Technol. Biotechnol., 2015, 90, 19–25.
´
´
´
´
40 C. Vidal, J. Garcıa-Alvarez, A. Hernan-Gomez, A. R. Kennedy 56 M. B. Alves, V. O. Santos Jr, V. C. D. Soares, P. A. Z. Suarez
and E. Hevia, Angew. Chem., Int. Ed., 2016, 55, 16145–16148.
and J. C. Rubim, J. Raman Spectrosc., 2008, 39, 1388–1395.
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