Synthesis of 1-amidoalkyl 2-naphthols using ionic liquid with metal complex as an efficient and reusable catalyst under solvent free conditions

Article abstract of DOI:10.1016/j.molliq.2015.09.041

Pyridinium dicationic salt containing transition metal complex anion (1,1′-hexane-1,6-diylbis (3-methylpyridinium) tetrachlorocobaltate (II) (C₆(Mpy)₂] [CoCl₄]^{2 -})) was used as a catalyst for the synthesis of 1-

Full text of DOI:10.1016/j.molliq.2015.09.041

Journal of Molecular Liquids 212 (2015) 413–417
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Synthesis of 1-amidoalkyl 2-naphthols using ionic liquid with metal
complex as an efficient and reusable catalyst under solvent
free conditions
⁎
Amutha Chinnappan, Arvind H. Jadhav, Wook-Jin Chung, Hern Kim
Energy and Environment Fusion Technology Center, Department of Energy Science and Technology, Myongji University, Yongin, Gyeonggi-do 17058, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 June 2015
Received in revised form 24 September 2015
Accepted 25 September 2015
Available online xxxx
Pyridinium dicationic salt containing transition metal complex anion (1,1′-hexane-1,6-diylbis (3-methyl-
pyridinium) tetrachlorocobaltate (II) (C6(Mpy)2] [CoCl4]2−)) was used as a catalyst for the synthesis of 1-
amidoalkyl-2-naphthols under solvent free conditions. The ionic liquid showed excellent catalytic performance.
They could be recycled and reused for five times without much loss in its activity.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Aromatic aldehydes
[C6(Mpy)2] [CoCl4]2−
Multicomponent reaction
Amidoalkyl naphthols
Solvent free
1. Introduction
1,3-amino oxygenated functional groups with the compounds are
more found in biologically important natural products and potent
Transformations of starting materials into desired final products
usually require a number of chemical operations in which additional re-
agents, catalysts, solvents, etc. are used. Thus, in the course of synthesis,
besides the desired products, many waste materials (chemical toxins)
are produced because these transformations are not quantitative and
selective processes, particularly due to the use of these additional com-
ponents. The wastes should be regenerated, destroyed or disposed, but
it consumes much energy and damage the environment. It is of great
importance to develop and use synthetic methodologies that minimize
such problems. Therefore, one of the thrust areas for achieving this tar-
get is to explore alternative expeditious reaction conditions and eco-
friendly reaction media to accomplish the desired chemical transforma-
tions with minimized by-products or waste as well as eliminating the
use of conventional organic solvents wherever possible [1–3]. Multi-
component reactions (MCRs) are fundamentally different from two-
component reactions in several aspects. Besides the multistep, sequen-
tial synthesis of a target molecule, the desired product can also be
obtained in one-pot reactions of three or more starting compounds,
the multicompoent reactions (MCRs), in many cases [4–9]. They are at-
tractive and play an essential role in the elegant art of organic synthesis
due to formation of the desired products in a single synthetic process
without many difficulties in separating the intermediates.
drugs such as nucleoside antibiotics and HIV protease inhibitors
[10–12]. Numerous methods have been reported in the literature
for the synthesis of 1-amidoalkyl-2-naphthols such as Al(H2PO4)3 [13],
p-TSA [14], montmorillonite K10 [15], Fe(HSO4)3 [16], cation-
exchange resins [17], K5CoW12O40.3H2O [18], Ce(SO4)2 [19], sulfamic
acid [20,21], iodine [22]. These reactions, however, suffer from a num-
ber of drawbacks such as catalyst loss into the product, catalyst decom-
position and poor reagent solubilities. We postulated that these
problems might be resolved by the use of ionic liquids.
Ionic liquids (ILs) are neither completely nonvolatile nor non-
flammable; the use of ILs omits the risk of combustion by replacement
of volatile organic compounds widely used as solvents in organic reac-
tions. The intense interest in the ILs field raised in the last decade has
been universal and interdisciplinary, and it has led to advances both in
fundamental knowledge and in technological applications. The perfor-
mance of an IL will strongly depend on the technology in which it is im-
plemented [23–26]. Ionic liquids are potential candidates to replace
volatile organic solvents in a variety of different processes, from reactions
to extractions to materials processing. They can be utilized in very differ-
ent ways: homogeneous, heterogeneous, as multifunctional compounds
like solvents and ligands, solvents and catalysts, stabilizing agents for the
catalysts or intermediates, in bio transformations or in organo-catalysis.
They play a specific role in all these approaches [27–30].
Ionic liquid containing metal chlorides are designed to replace some
expensive metal halide catalysts such as Pd, Pt in chemical reactions.
⁎
Corresponding author.
E-mail address: hernkim@mju.ac.kr (H. Kim).
http://dx.doi.org/10.1016/j.molliq.2015.09.041
0167-7322/© 2015 Elsevier B.V. All rights reserved.

414
A. Chinnappan et al. / Journal of Molecular Liquids 212 (2015) 413–417
Scheme 1. Synthesis of amidoalkyl naphthols.
The advantages of using IL with metal complexes have organic cation
and inorganic anion can be used as solvent and catalyst. We have al-
ready tested these ILs in aromatic nitro compounds reduction [31],
NBoc protection and biomass conversion [32,33]. They have shown ex-
cellent performance. In a continuation of our investigations on the de-
velopment of new synthetic methodologies, herein we report a new
and convenient synthesis of amidoalkyl naphthols by multicomponent
reaction of aldehydes, 2-naphthols and amides using ionic liquid con-
taining metal chlorides (Scheme 1) under solvent free conditions.
completion (confirmed by TLC), the reaction mixture was brought
down to room temperature and then hot water (10 mL) was added
and stirred. It was repeated for several times to remove the unreacted
starting materials. The product was filtered off and then the filtrate con-
taining IL was evaporated under reduced pressure. The separated cata-
lyst IL was washed with ethyl acetate, and finally dried in an oven at
80 °C. The obtained product was recrystallized by ethanol. The analytical
data of this product are in good accord with the reported data. This pro-
cedure was followed for all of the products listed in Table 2.
2. Experimental
3. Results and discussion
2.1. Materials
Initially to optimize the reaction condition, the reaction of 3-
nitrobenzaldehyde, 2-naphthol and acetamide in the presence of differ-
ent amounts of IL [C6(mpy)2][CoCl4]2− as a model was performed under
solvent free condition at 120 °C. The results are summarized in Table 1.
The reaction was carried out in the absence of IL with similar condition,
but no reaction was observed. This indicated the requirement of a cata-
lyst for this multicomponent reaction. In order to check the catalytic ef-
ficiency of IL, increased the amounts of IL from 0.0002–0.0018 mol.
When the amount of IL was increased from 0.0002 to 0.0004 mol, the
yield was found to increase from 80 to 91% (Table 1, entries 1 and 2).
Further increase in the amount of catalyst upto 0.0018 mol resulted in
lower yields (Table 1, entries 3–5). These results confirm that
0.0004 mol of IL is adequate enough to push the reaction forward. We
also checked the effects of solvents in the reaction (Table 1, entries 6
and 7). The reactions were sluggish and gave poor yield with longer re-
action time. A variety of aromatic aldehyde derivatives with electron-
donating and electron-withdrawing groups were tested with naphthol
and acetamide/benzamide/urea under standardized condition, and
gave excellent yields. The results are listed in Table 2. So far there was
no report using IL with metal complexes for such kind of reactions. It
reacted efficiently with naphthol and acetamide/benzamide/urea and
gave the desired product in excellent yields.
All chemicals were purchased from Sigma Aldrich and used as re-
ceived. The ionic liquid used in this study was synthesized according
to the previous reported work [34,35]. The spectral data of the com-
pounds were in good agreement with those reported in the literature
[5,7,10].
2.2. Preparation of 1,1′-hexane-1,6-diylbis (3-methylpyridinium)
tetrachlorocobaltate (II) ([C6(MPy)2] [CoCl4]2−
)
3-methyl pyridine (0.04 mol, 3.89 mL) is dissolved in 25 mL toluene
at RT. 1, 6-dibromohexane (0.02 mol, 3.07 mL) was added slowly into
the flask within 30 min in an ice bath. The stirring was continued at
this temperature for 30 min before elevating the temperature to 110
°C for 12 h. An off-white solid was formed. Upon completion of the reac-
tion, the toluene layer was removed by decanting. Then, the impure
ionic liquid, off-white solid, was washed with ethyl acetate
(3 × 30 mL) followed by filtration. Then the resulting white solid was
dried under vacuum oven at 70 °C for 5 h to get the pure product.
1,1′-hexane-1,6-diylbis (3-methylpyridinium) dibromide [C6(mpy)2]
(Br)2: 1H NMR (400 MHz, DMSO-d6, δ/ppm relative to TMS) 9.09 (s, 2 H),
8.98 (d, 2 H, J = 8 Hz), 8.43 (d, 2 H, J = 8 Hz), 8.01 (dd, 2 H, J = 6 Hz), 4.57
(t, 4 H, J = 7.9 Hz), 3.49 (s, 6 H), 1.91 (m, 4 H), 1.30 (m, 4 H). 13C NMR
(400 MHz, DMSO): δH (ppm) 146.20, 144.76, 142.44, 139.08, 127.71,
60.55, 30.66, 25.04, 18.29.
1,1′-hexane-1,6-diylbis (3-methylpyridinium) dibromide ([C6(Mpy)2]
(Br)2) (0.007 mol) and CoCl2. 6H2O (0.017 mol) were dissolved in eth-
anol and stirred at room temperature for four days. After completion of
the reaction the solvent evaporated in rotary evaporator to give the blue
color solid. The obtained product was washed with ethyl acetate several
times and dried in vacuum at 80 °C for 5 h. LRMS (FAB+) calcd for
C18H26N2Cl4Co (M − [CoCl4])+ 135.10 found 135.14.
The proposed mechanism for the synthesis of 1-amidoalkyl 2-
naphthols is not clear, but based on the literature [5], we shown in
Scheme 2. The reaction of 2-naphthol with aromatic aldehydes to
ortho-quinone methides formed by the nucleophilic addition was
accelerated by ionic liquid containing transition metal complex
Table 1
The effect of different amounts of [C6(MPy)2][CoCl4]2− on the reaction of 3 nitro-
benzaldehyde, acetamide and 2-naphthol.
Entry
[C6(MPy)2][CoCl4]2− (mol)
Time
Yield (%)a
1
2
3
4
5
6
7
8
0.0002
0.0004
0.0008
0.001
0.0018
None
0.0004/DCM (5 ml)
0.0004/MeOH (5 ml)
20 min
15 min
15 min
15 min
15 min
3 h
80
91
87
85
81
NRb
45
30
2.3. Typical procedure for synthesis of amidoalkyl
A 1:1:1.2:0.05 mixture of benzaldehyde (1 mL, 0.009 mol), 2-
naphthol (1 g, 0.009 mol), acetamide (0.5 g, 0.011 mol), and
[C6(MPy)2][CoCl4]2− (0.2 g, 0.0004 mol) was taken in a round bottom
flask 100 mL and placed in a preheated oil bath at 120 °C under solvent
free condition by stirring for the required time. The progress of the
reaction was monitored by thin layer chromatography (TLC). After
10 h
8 h
a
Isolated yield.
b
No reaction was observed.

A. Chinnappan et al. / Journal of Molecular Liquids 212 (2015) 413–417
415
Table 2
[C6(MPy)2][CoCl4]2− catalyzed synthesis of amidoalkyl naphthols.a
Entry
1
R1
R2
Time (min)
25
Yield (%)b
CH3
75
2
CH3
30
91
3
4
CH3
CH3
20
30
77
75
5
6
CH3
CH3
30
15
81
91
7
CH3
15
93
8
9
CH3
NH2
45
6
92
80
10
C6H5
30
71
a
Reaction conditions: molar ratio: aldehyde (1): naphthol (1): acetamide/benzamide/urea (1.2): IL (0.05), temperature (120 °C).
Isolated yield.
b
([C6(MPy)2][CoCl4]2−). Then the o-QMs reacted with amides or urea to
produce 1-amidoalkyl-2 naphthol derivatives.
In view of the economy of the reaction, the recovery as well as
recycling of the catalyst is mandatory. The recycling experiment was
carried out with benzaldehyde, 2-naphthol and acetamide under the
same condition described in Table 2, entry 1. After completion of the re-
action, hot water was added to the reaction mixture. The product was
separated by filtration and then the filtrate containing IL was evaporat-
ed under reduced pressure. The separated catalyst IL was washed with
ethyl acetate, and finally dried in an oven at 80 °C. The IL was recovered
and reused without further activation up to five cycles. Table 4 shows
In comparison with other catalysts employed for the synthesis of N-
[(3-nitro-phenyl)-(2-hydroxy-naphthalen-1-yl)-methyl] acetamide
from 3-nitrobenzaldehyde, 2-naphthol and acetamide, IL containing
transition metal halide showed a much better performance in terms
of catalyst loading, short reaction time and yield (Table 3). SO3H
functionalised IL (entry 1) shows a bit superior to our IL in terms of
time and yield, but catalyst loading was huge.
Scheme 2. The proposed mechanism.

416
A. Chinnappan et al. / Journal of Molecular Liquids 212 (2015) 413–417
Table 3
Comparison of different catalysts for the reaction of 3-nitrobenzaldehyde, acetamide and 2-naphthol.
Entry
Catalyst
Catalyst amount
Solvent
Temp (°C)
Time
Yield (%)
References
1
2
3
4
5
6
7
8
SO3H functionalised IL
Nano-S
[TEBSA][HSO4]
Montmorillonite K10
K5CoW12O40·3H2O
Thiamine HCl
10 mol%
3.5 mol%
5 mol%
0.1 g
1 mol%
10 mol%
5 mol%
0.0004 mol
–
–
–
–
120
50
120
125
125
80
3 min
10 min
10 min
30 min
3 h
4 h
10 h
15 min
96
90
89
96
78
88
85
91
[36]
[7]
[10]
[15]
[18]
[11]
[22]
Present study
–
DCE
–
Iodine
rt
120
[C6(MPy)2][CoCl4]2−
that the catalyst maintains the consistency up to three cycles, but a
slight decrease in the activity of the catalyst was found in the last
cycle. This may be due to the decrease in the amounts of IL during
recycling time.
N-[(2-hydroxynaphthalen-1-yl)-(4-methylphenyl)]-acetamide
(Table 2, entry 8): mp 212 ( 1) °C; IR νmax (cm−1) 3399, 3008, 2970,
1637; 1H NMR (400 MHz, DMSO-d6): 9.95 (s, 1 H), 8.38–8.36 (d, 1 H),
7.80–7.29 (m, 4 H), 7.23–7.16 (m, 3 H), 7.05–7.00 (m, 4 H), 2.19
(s, 3 H), 1.93 (s, 3 H); 13C NMR (400 MHz, DMSO-d6) δ 169.5, 153.5,
140.0, 135.4, 132.7, 129.5, 128.8, 126.4, 123.7, 119.4, 48.0, 23.1, 20.9.
N-[(2-hydroxynaphthalen-1-yl)-(3-nitrophenyl)methyl]-urea
(Table 2, entry 9): mp 187 ( 1)°C; IR νmax (cm−1) 3420, 3367, 3256,
2971, 1628; 1H NMR (400 MHz, DMSO-d6): 10.07 (s, 1 H), 8.13–7.82
(m, 6 H), 7.57–7.35 (m, 4 H), 7.23 (s, 1 H), 6.95 (s, 1 H), 5.74 (s, 2 H);
13C NMR (400 MHz, DMSO-d6) δ 158.9, 153.4, 147.3, 135.0, 133.0,
132.4, 130.1, 129.2, 128.9, 127.3, 123.1, 119.0, 48.3, 18.9.
N-[(2-hydroxynaphthalen-1-yl)-(4-methylphenyl)]-benzamide
(Table 2, entry 10): mp 209 ( 1) °C; IR νmax (cm−1) 3414, 3013, 2970,
1627; 1H NMR (400 MHz, DMSO-d6): 10.28 (s, 1 H), 8.98–8.96 (d, 1 H),
8.04–7.03 (m, 16 H), 2.20 (s, 3 H); 13C NMR (400 MHz, DMSO-d6)
δ 166.0, 153.5, 139.4, 134.8, 132.7, 129.7, 128.9, `128.1, 126.4, 126.2,
123.2, 122.4, 119.1, 118.8, 49.5, 20.9.
4. Conclusion
In conclusion, we established a simple, convenient and prac-
tical method for the synthesis of 1-amidoalkyl 2-naphthols using
[C6(MPy)2][CoCl4]2−. The IL was recovered and reused without further
activation up to five cycles. These transition based metal ionic liquids
play an important role as catalyst in organic reactions.
Spectral data of 1-amidoalkyl-2 naphthol derivatives (Table 2, en-
tries 1, 2, 6–10).
N-[(2-hydroxynaphthalen-1-yl)-phenylmethyl]-acetamide (Table 2,
entry 1): mp 206 ( 1) °C; IR νmax (cm−1) 3397, 3246, 2982, 1631; 1H
NMR (400 MHz, DMSO-d6): 9.99 (s, 1 H), 8.43–8.41 (d, 1 H), 7.83–7.81
(m, 1 H), 7.78–7.70 (m, 3 H), 7.24–7.06 (m, 8 H), 1.96 (s, 3 H); 13C
NMR (400 MHz, DMSO-d6) δ 169.6, 153.6, 143.0, 132.7, 128.8, 128.4,
128.1, 127.9, 126.4, 123.0, 119.2, 118.8, 48.2, 23.0.
Acknowledgments
N-[(2-hydroxynaphthalen-1-yl)-(3-chlorophenyl)methyl]-acetamide
(Table 2, entry 2): mp 245 ( 1) °C; IR νmax (cm−1) 3408, 3026, 2970,
1646; 1H NMR (400 MHz, DMSO-d6): 10.06 (s, 1 H), 8.47–8.45 (d, 1 H),
7.79–7.40 (m, 3 H), 7.38–7.34 (m, 3 H), 7.26–7.02 (m, 7 H), 1.95
(s, 3 H); 13C NMR (400 MHz, DMSO-d6) δ 169.8, 153.6, 145.9, 133.2,
130.0, 129.7, 128.8, 127.0, 123.0, 119.0, 118.6, 47.9, 23.0.
N-[(2-hydroxynaphthalen-1-yl)-(3-nitrophenyl)methyl]-acetamide
(Table 2, entry 6): mp 253 ( 1) °C; IR νmax (cm−1) 3371, 3192, 2970,
1645; 1H NMR (400 MHz, DMSO-d6): 10.10 (s, 1 H), 8.59 (d, 1 H),
8.02–8.00 (m, 2 H), 7.99–7.76 (m, 3 H), 7.53–7.49 (m, 2 H), 7.39–7.27
(m, 1 H), 7.19–7.15 (m, 3 H), 1.98 (s, 3 H); 13C NMR (400 MHz,
DMSO-d6) δ 170.1, 153.7, 148.11, 145.8, 132.5, 130.0, 129.1, 128.8,
127.2, 123.3, 121.6, 118.8, 48.0, 22.9.
N-[(2-hydroxynaphthalen-1-yl)-(4-nitrophenyl)methyl]-acetamide
(Table 2, entry 7): mp 223 ( 1) °C; IR νmax (cm−1) 3390, 3066, 2954,
1636; 1H NMR (400 MHz, DMSO-d6): 10.12 (s, 1 H), 8.58 (d, 1 H),
8.13–8.10 (m, 2 H), 8.00–7.97 (m, 2 H), 7.26–7.19 (m, 3 H), 7.10–7.05
(m, 4 H), 2.00 (s, 3 H); 13C NMR (400 MHz, DMSO-d6) δ 170.2, 154.2,
132.6, 130.3, 129.4, 128.8, 128.1, 127.1, 126.4, 123.3, 122.8, 120.9,
118.2, 56.8, 48.3, 18.9.
This study was supported by National Research Foundation of Korea
(NRF) — Grants funded by the Ministry of Science, ICT and Future Plan-
ning (2014R1A2A2A01004352) and the Ministry of Education (2009-
0093816), Republic of Korea.
References
[1] P.T. Anastas, M.M. Kirchhoff, Acc. Chem. Res. 35 (2002) 686.
[2] J.H. Clark, S.J. Tavener, Org. Process. Res. Dev. 11 (2007) 149.
[3] A. Domling, I. Ugi, Angew. Chem. Int. Ed. 39 (2000) 3168.
[4] Y. Gu, Green Chem. 14 (2012) 2091.
[5] Q. Zhang, J. Luo, Y. Wei, Green Chem. 12 (2010) 2246.
[6] A. Hasaninejad, A. Zare, M. Shekouhy, J.A. Rad, J. Comb. Chem. 12 (2010) 844.
[7] V.K. Das, M. Borah, A.J. Thakur, J. Organomet. Chem. 78 (2013) 3361.
[8] R. Tayebee, M.M. Amini, H. Rostamian, A. Aliakbari, Dalton Trans. (2014), http://dx.
doi.org/10.1039/c3dt51594j.
[9] J. Safari, Z. Zarnegar, J. Mol. Catal. A Chem. 379 (2013) 269.
[10] A.R. Hajipour, Y. Ghayeb, N. Sheikhan, A.E. Ruoho, Tetrahedron Lett. 50 (2009) 5649.
[11] M. Lei, L. Maa, L. Hu, Tetrahedron Lett. 50 (2009) 6393.
[12] A. Domling, Chem. Rev. 106 (2006) 17.
[13] H.R. Shaterian, A. Amirzadeh, F. Khorami, M. Ghashang, Synth. Commun. 38 (2008)
2983.
[14] M.M. Khodaei, A.R. Khosropour, H. Moghanian, Synlett (2006) 916.
[15] S. Kantevari, S.V.N. Vuppalapati, L. Nagarapu, Catal. Commun. 8 (2007) 1857.
[16] H.R. Shaterian, H. Yarahmadi, M. Ghashang, Bioorg. Med. Chem. Lett. 18 (2008) 788.
[17] S.B. Patil, P.R. Singh, M.P. Surpur, S.D. Samant, Synth. Commun. 37 (2007) 1659.
[18] L. Nagarapu, M. Baseeruddin, S. Apuri, S. Kantevari, Catal. Commun. 8 (2007) 1729.
[19] N.P. Selvam, P.T. Perumal, A new synthesis of acetamido phenols promoted by
Ce(SO4)2, Tetrahedron Lett. 47 (2006) 7481.
[20] R.R. Nagawade, D.B. Shinde, Chin. J. Chem. 25 (2007) 1710.
[21] S.B. Patil, P.R. Singh, M.P. Surpur, S.D. Samant, Ultrason. Sonochem. 14 (2007) 515.
[22] B. Das, K. Laxminarayana, B. Ravikanth, R. Rao, J. Mol. Catal. A Chem. 261 (2007) 180.
[23] J.S. Wilkes, J. Mol. Catal. A Chem. 214 (2004) 11.
[24] M.D. Bermúdez, A.E. Jiménez, J. Sanes, F.J. Carrión, Molecules 14 (2009) 2888.
[25] J.L. Anderson, R. Ding, A. Ellern, D.W. Armstrong, J. Am. Chem. Soc. 127 (2005) 593.
[26] H. Olivier-Bourbigou, L. Magna, D. Morvan, Appl. Catal. A Gen. 373 (2010) 1.
[27] A. Zare, T. Yousofia, A.R. Moosavi-Zare, RSC Adv. 2 (2012) 7988.
[28] M.J. Earle, S.P. Katdare, K.R. Seddon, Org. Lett. 6 (2004) 707.
[29] A.C. Cole, J.L. Jensen, I. Ntai, K.L.T. Tran, K.J. Weaver, D.C. Forbes, J.H. Davis Jr., J. Am.
Chem. Soc. 124 (2002) 5962.
Table 4
Reusability of [C6(MPy)2][CoCl4]2−.a
Entry
Number of cycles
Yield (%)b
1
2
3
4
5
6
Fresh
75
75
75
75
70
70
1st run
2nd run
3rd run
4th run
5th run
a
Reaction conditions: Similar to Table 2, entry 1.
Isolated yield.
b

A. Chinnappan et al. / Journal of Molecular Liquids 212 (2015) 413–417
417
[30] A.H. Jadhav, A. Chinnappan, R.H. Patil, W.J. Chung, H. Kim, Chem. Eng. J. 236 (2014)
300.
[35] J.-C. Chang, W.-Y. Ho, I.-W. Sun, Y.-K. Chou, H.-H. Hsieh, T.-Y. Wua, Polyhedron 30
(2011) 497–507.
[31] A. Chinnappan, H. Kim, RSC Adv. 3 (2013) 3399.
[36] M.A. Zolfigola, A. Khazaeia, A.R. Moosavi-Zarea, A. Zareb, V. Khakyzadeha, Appl.
Catal. A Gen. 400 (2011) 70.
[32] A. Chinnappan, D. La, H. Kim, RSC Adv. 3 (2013) 13324.
[33] A. Chinnappan, A.H. Jadhav, H. Kim, W.J. Chung, Chem. Eng. J. 237 (2014) 95.
[34] A. Chinnappan, H. Kim, C. Baskar, I.T. Hwang, Int. J. Hydrog. Energy 37 (2012) 10240.