Molecular interactions between carbon nanotubes and ammonium ionic liquids and their catalysis properties

Article abstract of DOI:10.1016/j.materresbull.2014.03.025

A new catalytic method has been developed for the synthesis of aza/thia-Michael addition reactions of amines/thiols, which provide higher product yields. This catalyst is a combination of multi-walled carbon nanotubes (MWCNT) with triethylammonium hydroge

Full text of DOI:10.1016/j.materresbull.2014.03.025

G Model
MRB 7357 1–4
Materials Research Bulletin xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
1
2
Molecular interactions between carbon nanotubes and ammonium
ionic liquids and their catalysis properties
b
c
a
a
Pankaj Attri a, , Rohit Bhatia , Bharti Arora , Naresh Kumar , Ji Hoon Park ,
3
Q1
*
Ku Youn Baik a, Geon Joon Lee a, In Tae Kim d, Je Huan Koo a, Eun Ha Choi a,
*
Plasma Bioscience Research Center/Department of Electrical and Biological Physics, Kwangwoon University, Seoul, 139-701, Republic of Korea
Department of Chemistry, University of Delhi, Delhi 110007, India
Department of Applied Sciences, ITM University, Sector-23(A), Gurgaon 122017, Haryana, India
4
5
6
7
8
a
b
c
d
Department of Chemistry, Kwangwoon University, Seoul, 139-701, 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 30 July 2013
Received in revised form 15 March 2014
Accepted 20 March 2014
Available online xxx
A new catalytic method has been developed for the synthesis of aza/thia-Michael addition reactions of
amines/thiols, which provide higher product yields. This catalyst is a combination of multi-walled carbon
nanotubes (MWCNT) with triethylammonium hydrogen phosphate (TEAP) ionic liquid (IL), commonly
referred to as bucky gel. In order to gain insight into the interactions involved between IL and MWCNT, we
utilised Raman spectroscopy for our analysis. The interactions between MWCNT with TEAP were clearly
evidenced by the increasing intensity ratios and spectral shift in the wavelength for the Raman D and G
bands of MWCNT. The morphological studies of the resulting composite materials of TEAP and MWCNT
(bucky gel) were carried out using scanning electron microscopy (SEM). The key advantage of using bucky
gel as a catalyst is that higher product yield is obtained in reduced reaction time for Michael reactions.
ã 2014 Published by Elsevier Ltd.
Keywords:
A. Organic compounds
A. Nanostructures
B. Chemical synthesis
C. Raman spectroscopy
D. Catalytic properties
9
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
1. Introduction
synthesis of pharmaceutical intermediates, peptide analogues,
antibiotics, and other biologically active molecules and drugs
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Ionic liquids (ILs) and carbon nanotubes (CNTs) represent very
interesting class materials due to their unique properties and wide
range of applications [1–16]. Recently, the interactions between
carbon nanotubes and active materials such as inorganic metal
oxides render the enhanced catalytic performance [17–20].
However, there has been significant curiosity to explore the
properties and interactions of ILs with CNTs [21–27]. These bucky
gels are found to be of great usage in chemical, physical and
biological applications [26]. Fukushima et al. [21] were the first to
report that imidazolium based ILs, such as 1-butyl-3-methylimi-
dazolium tetrafluoroborate can form a gel called “bucky gels” by
grinding them with single-walled carbon nanotubes (SWCNTs).
Later, Wang et al. [28] studied the dispersion mechanism of
SWCNTs in imidazolium-based ILs. In order to boost the
applicability of bucky gel in organic reactions, we explored the
Michael reactions. The Michael reaction has also been studied for
more than one century [29]. It has been used extensively in the
[29–33]. Unfortunately, the reaction is suffering from many
limitations, such as the use of expensive reagents, harsh
conditions, etc. All these limitations enforced us to explore a
new, more efficient catalyst with limited drawbacks. In light of the
above considerations, we have explored the combination of IL
(triethylammonium dihydrogen phosphate (TEAP)) and MWCNTas
a catalyst system for organic reactions commonly known as bucky
gel. We also examined the interactions between MWCNT and TEAP
using Raman spectroscopy. We were further motivated to carry out
morphological studies of the resulting composite materials of TEAP
and MWCNT using scanning electron microscopy (SEM). In
addition, the synthesis of aza/thia-Michael reaction products
was carried out using this bucky gel as a catalyst system.
42
43
2. Materials and methods
2.1. Materials
44
45
46
47
CNTs were obtained from Sigma-Aldrich (USA). All the reagents
used were of analytical grade. Melting points were determined
using a Thomas Hoover melting point apparatus.1H (400 MHz) and
13C (75 MHz) nuclear magnetic resonance (NMR) spectra were
* Corresponding authors. Tel.: +82 029405236; fax: +82 2 913 6187.
E-mail addresses: chem.pankaj@gmail.com (P. Attri), ehchoi@kw.ac.kr
(E.H. Choi).
http://dx.doi.org/10.1016/j.materresbull.2014.03.025
0025-5408/ã 2014 Published by Elsevier Ltd.
Please cite this article in press as: P. Attri, et al. Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.025

G Model
MRB 7357 1–4
2
P. Attri et al. / Materials Research Bulletin xxx (2014) xxx–xxx
Q2
Fig. 1. Raman spectra of (a) TEAP IL, and (b) pure MWCNT (black) and MWCNT–TEAP (red). (For interpretation of the references to color in this figure legend, the reader is
referred to the web version of the article.)
Fig. 2. SEM image of (a) pure MWCNT, (b) TEAP IL and (c) MWCNT–TEAP composite.
48
49
50
51
52
53
54
55
recorded on
a
Jeol 400 NMR spectrometer in CDCl3 (with
2.2. General procedure for the preparation for aza/thia-Michael
reaction
tetramethylsilane (TMS) for 1H and chloroform-d for 13C as
internal references).
56
57
58
59
60
61
62
63
64
65
66
CNTs could be easily dispersed in the TEAP based room
temperature IL by mechanical milling, forming a thermally stable
bucky gel as discussed below [21,27,28].
A
solution of 1 mmol amine/thiol and 1.2 mmol
a,b-unsaturated nitriles or carbonyl compounds was added to
bucky gel (0.1 mmol) and the mixture was stirred at 25 ꢀC for 1 min.
Likewise, the completion of the reaction was monitored using TLC.
The product formed in the one-phase system, was further
extracted with ether. In the same way as in the above preparation,
the resulting organic phase extract was washed with a saturated
solution of NaHCO3, water, and dried over Na2SO4. After removal of
the solvent, the residue was further purified by recrystallization or
silica gel chromatography. The reaction products were then
analyzed using 1H and 13C NMR spectroscopy.
CN
R
CN
R
X
R'
XH
Bucky gel
R'
1 min, 25oC
Bucky gel
1 min, 25oC
O
O
Table 1
R
The Michael reaction in entry 1, Table 2 in the presence of bucky gel.
XH
R
X
R'
Entry
Catalyst
Temperature
(ꢀC)
Time for complete
conversion
Yield (%)
1
2
No catalyst
MWCNT
25
25
24 hr
24 hr
No
product
No
product
80
89
X= N,S
R, R'=H, N-alkyl, N-arylpiperazines, aliphatic, aromatic,
heterocycles.
4
5
6
TEAP
TEAP
MWCNT–TEAP 25
25
25
1 min
24 hr
1 min
Scheme 1. The conjugate addition of amines and thiols to a,b-unsaturated nitriles
and carbonyl compounds using the bucky gel.
98
Please cite this article in press as: P. Attri, et al. Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.025

G Model
MRB 7357 1–4
P. Attri et al. / Materials Research Bulletin xxx (2014) xxx–xxx
3
Table 2
Q3
Michael reaction of products catalyzed by MWCNT–TEAP at room temperature as per Scheme 1.
Entry
Amine/thiols
Michael acceptor time (min)
1
Yield (%)a
98
1
O
N
NH
2
3
4
5
1
1
1
1
95
96
94
93
CN
CN
CN
CN
Cl
N
NH
O2N
H2N
N
N
NH
NH
NH
N
O
O
6
7
1
97
OMe
CN
HS
1
1
96
99
HS
CN
CN
Me
8
n-HS-(CH2)7CH3
a
Yields determined by GC analysis.
67
91
3. Results and discussion
images of pure MWCNT morphology, TEAP and MWCNT–TEAP
composite, was found to be quite distinct from each other (Fig. 2).
Fig. 2c clearly illustrates that MWCNT is buried inside the TEAP.
And, the SEM images strongly suggest that MWCNT–TEAP gel
composites produce more flat film morphology with a smoother
surface. We find these results to be in good agreement with the
reported results [25,27].
In order to investigate the applicability of bucky gel in organic
reactions, we have further explored Michael reactions. Further, to
gain more insight into the effectiveness of this environment
friendly catalyst (bucky gel) for CÀÀN and CÀÀS bond formation
reactions, herein we report the conjugate addition of amines and
92
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
93
Our present investigation has revealed a new catalyst system
(bucky gel) for the synthesis of Michael reaction products. We have
utilized the Raman spectroscopy to ascertain the interactions
between TEAP and CNTs during the formation of bucky gel. Raman
spectroscopy (Renishaw Raman spectroscopy, of 514 nm) proves to
be a powerful tool for the structural characterization of CNTs. The
Raman spectra of TEAP IL is as displayed in Fig. 1a and its
comparison with that of MWCNT (black curve) and MWCNT–TEAP
composite (red curve) is well exhibited in Fig. 1b. The curvature
and the graphene like sheet character in the MWCNTs is better
exemplified by the characteristic D and G bands of MWCNTs as
depicted by all the curves. The Raman spectra clearly depicts that
the D band shifts from 1357 to 1362 cmÀ1 and likewise the G band
shifts from 1585 to 1597 cmÀ1 in case of MWCNT–TEAP composite.
The significant shifts in the characteristic D and G bands in Raman
spectra of MWCNT may be assigned due to the modifications in the
surface characteristics of the MWCNT with the addition of TEAP.
The 12 cmÀ1 shift in the G-band of MWCNT–TEAP composite is
most likely due to the interaction of MWCNT with TEAP, which
correlates very well with the studies done in the past [34].
To quantify the morphologies of the resulting MWCNT–TEAP
composites, we used scanning electron microscopy (SEM) of Zeiss
EVO 40 Company for further analysis. On comparing the SEM
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
thiols to
a,b-unsaturated nitriles and carbonyl compounds using
the bucky gel catalyst (Scheme 1). The standardized results are as
represented in Table 1, which clearly indicate that the yield of the
desired product increases with the addition of MWCNT–TEAP
catalyst under solvent free conditions. However, it is hard to
predict the actual mechanism for the increase in yield in the
presence of MWCNT–TEAP, while this might be due to high surface
to volume ratio [35] that helps the MWCNT–TEAP to increase the
yield in short intervals of time. In the presence of TEAP after 24 h,
yield increases up to the 89%, while in the presence of
MWCNT–TEAP the yield increases up to 98% in 1 min. Similar
results were obtained by Zhang and coworkers [20] depicting that
CeO2 nanoparticles can convert the NO up to 50%, while the pure
Please cite this article in press as: P. Attri, et al. Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.025

G Model
MRB 7357 1–4
4
P. Attri et al. / Materials Research Bulletin xxx (2014) xxx–xxx
147
148
Research Foundation of Korea (NRF) grant funded by the Korea
government (MSIP) (No. 2012R1A1A3019866).
100
80
60
40
20
149
References
[1] S. Iijima, Nature 354 (1991) 56–58.
[2] R.H. Baughman, A.A. Zakhidov, W.A. de Heer, Science 297 (2002) 787–792.
[3] P. Attri, P. Venkatesu, A. Kumar, Physical Chemistry Chemical Physics 13 (2011)
2788–2796.
150
151
152
153
154
155
156
157
158
[4] P. Attri, P. Venkatesu, T. Hofman, The Journal of Physical Chemistry B 115 (2011)
10086–10097.
[5] C. Chen, J. Zhang, F. Peng, D. Su, Materials Research Bulletin 48 (2013)
3218–3222.
[6] R. Atchudan, J. Joo, A. Pandurangan, Materials Research Bulletin 48 (2013)
2205–2212.
[7] S.S. Bhoware, M.S. Maubane, A. Shaikjee, I. Beas, A. Ziegler, N.J. Coville,
Materials Research Bulletin 48 (2013) 2347–2350.
[8] C. Liu, H. Chen, K. Dai, A. Xue, H. Chen, Q. Huang, Materials Research Bulletin 48
(2013) 1499–1505.
[9] J. Luo, H.-J. Niu, H.-L. Wen, W.-J. Wu, P. Zhao, C. Wang, X.-D. Bai, W. Wang,
Materials Research Bulletin 48 (2013) 988–994.
[10] X. Fu, H. Yang, K. He, Y. Zhang, J. Wu, Materials Research Bulletin 48 (2013)
487–494.
0
1
2
3
4
5
6
Cycles
Fig. 3. Catalytic cycles versus yield for Michael reaction.
[11] D. Xue, K. Li, J. Liu, C. Sun, K. Chen, Materials Research Bulletin 47 (2012)
2838–2842.
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
[12] X. Li, Z. Xu, Materials Research Bulletin 47 (2012) 4383–4391.
[13] S.H. Kim, T.K. Lee, J.H. Jung, J.N. Park, J.B. Kim, S.H. Hur, Materials Research
Bulletin 47 (2012) 2760–2764.
CNT had very low conversion rate. Whereas, in the presence of
CeO2 supported CNT the conversion of NO was found to be very
high. Additionally, another group showed that the activity of the
CÀÀC bond coupling reaction in the presence of palladium
nanoparticle supported CNT was very high as compared to the
palladium supported activated carbon [36]. Therefore, we cata-
lyzed the rest of the Michael addition of various substituted
piperazines, aliphatic, aromatic amines, imidazoles, and thiols
159
160
161
[14] S. Saipanya, T. Sarakonsri, P. Wongtap, Materials Research Bulletin 47 (2012)
2765–2766.
[15] S. Santangelo, M. Lanza, E. Piperopoulos, S. Galvagno, C. Milone, Materials
Research Bulletin 47 (2012) 595–601.
[16] F.-J. Zhang, W.-C. Oh, K. Zhang, Materials Research Bulletin 47 (2012) 619–624.
[17] D. Zhang, L. Zhang, L. Shi, C. Fang, H. Li, R. Gao, L. Huang, J. Zhang, Nanoscale 5
(2013) 1127–1136.
162
163
164
165
166
[18] C. Fang, D. Zhang, S. Cai, L. Zhang, L. Huang, H. Li, P. Maitarad, L. Shi, R. Gao, J.
with
a,b-unsaturated nitriles or carbonyl compounds in the
Zhang, Nanoscale 5 (2013) 9199–9207.
[19] D. Zhang, L. Zhang, C. Fang, R. Gao, Y. Qian, L. Shi, J. Zhang, RSC Advances 3
(2013) 8811–8819.
[20] C. Fang, D. Zhang, L. Shi, R. Gao, H. Li, L. Ye, J. Zhang, Catalysis Science &
Technology 3 (2013) 803–811.
[21] T. Fukushima, A. Kosaka, Y. Ishimura, T. Yamamoto, T. Takigawa, N. Ishii, T. Aida,
Science 300 (2003) 2072–2207.
[22] T. Fukushima, T. Aida, Chemistry – A European Journal 13 (2007) 5048–5058.
[23] M. Mohammadi, M. Foroutan, Physical Chemistry Chemical Physics 15 (2013)
2482–2494.
[24] Y. Chen, L. Bai, C. Zhou, J.-M. Lee, Y. Yang, Chemical Communications 47 (2011)
6452–6454.
[25] S.H. Hong, T.T. Tung, L.K.H. Trang, T.Y. Kim, K.S. Suh, Colloid and Polymer
Science 288 (2010) 1013–1018.
[26] M.L. Polo-Luque, B.M. Simonet, M. Valcárcel, TrAC Trends in Analytical
presence of MWCNT–TEAP catalyst system. The results of the
above reactions are schematically summarized in Table 2. We also
observed the recyclability of bucky gel that shows that it will retain
its yield up to six cycles in high yield, as shown in Fig. 3.
In conclusion, the interaction between MWCNT and TEAP
results in a new catalyst system which is well documented as an
accomplished catalyst for the synthesis of Michael reactions under
solvent-free conditions. The use of this catalyst provides several
advantages; (i) MWCNT–TEAP is a cost effective and environmen-
tally benign reagent, (ii) green synthesis (avoiding hazardous and
toxic organic solvents for work-up), (iii) applicability to a wide
range of substituted aldehydes and (iv) mild temperature reaction
condition. So, basically the type of MWCNT governs the catalytic
efficiency of bucky gel. Hence, the MWCNT–TEAP catalyst provides
a better product yield, simple reaction conditions, shorter reaction
times, easy work-up and recyclability making it a green, easy and
superior method for the synthesis.
167
168
169
170
Chemistry 47 (2013) 99–110.
[27] M. Tunckol, J. Durand, P. Serp, Carbon 50 (2012) 4303–4334.
[28] J.Y. Wang, H.B. Chu, Y. Li, ACS Nano. 2 (2008) 2540–2546.
[29] Y.E. Ahmad, E. Laurent, P. Maillet, A. Talab, J.F. Teste, R. Dohkan, G. Tran, V.
Ollivier, Journal of Medicinal Chemistry 40 (1997) 952–960.
[30] N. Azizi, M.R. Saidi, Tetrahedron 60 (2004) 383–387.
[31] A.K. Verma, P. Attri, V. Chopra, R.K. Tiwari, R. Chandra, Monatshefte fur Chemie
139 (2008) 1041–1047.
171
172
173
[32] M.R. Saidi, Y. Pourshojaei, F. Aryanasab, Synthetic Communications 39 (2009)
1109–1119.
142
Acknowledgements
[33] V.R. Choudhary, D.K. Dumbre, S.K. Patil, RSC Advances 2 (2012) 7061–7065.
[34] L. Zhao, Y. Li, Z. Liu, H. Shimizu, Chemistry of Materials 22 (2010) 5949–5956.
[35] X.R. Ye, Y. Lin, C.M. Wai, Chemical Communications (2003) 642–643.
[36] A. Corma, H. Garcia, A. Leyva, Journal of Molecular Catalysis A: Chemical 230
(2005) 97–105.
143
144
145
146
We gratefully acknowledge the SRC program of the National
Research Foundation of Korea (NRF) grant funded by the Korea
government (MSIP) (No. 20100029418) and in part by Kwangwoon
University 2014. KY Baik gratefully acknowledges the National
174
Please cite this article in press as: P. Attri, et al. Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.025