(Cu/NCNTs): A new high temperature technique to prepare a recyclable nanocatalyst for four component pyridine derivative synthesis and nitroarenes reduction

Article abstract of DOI:10.1039/c6nj01464j

N-Doped carbon nanotubes (NCNTs), which are further decorated with copper nanoparticles, have been prepared using a novel approach to the pre-existing methods. Their properties and characteristics have been studied using different techniques including UV-

Full text of DOI:10.1039/c6nj01464j

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(Cu/NCNTs): a new high temperature technique
to prepare a recyclable nanocatalyst for four
component pyridine derivative synthesis and
nitroarenes reduction†
Cite this:DOI: 10.1039/c6nj01464j
a
a
b
b
Gurpreet Kour, Monika Gupta,* B. Vishwanathan and K. Thirunavukkarasu
N-Doped carbon nanotubes (NCNTs), which are further decorated with copper nanoparticles, have been
prepared using a novel approach to the pre-existing methods. Their properties and characteristics have
been studied using different techniques including UV-vis, XPS, TGA, ICP-AES, VSM, CHN, XRD, SEM-EDAX
and TEM analysis. The Cu/NCNTs show nanocatalytic activity for the synthesis of four component pyridine
derivatives and selective reduction of nitroarenes to their corresponding amines at ambient temperature
Received (in Montpellier, France)
18th May 2016,
Accepted 12th August 2016
1
13
conditions.
transformations. We also report a new pyridine derivative, ethyl 6-(4,6-diamino-1,3,5-triazin-2-yl amino)-
-cyano-2-methyl-4-phenylpyridine-3-carboxylate (5j), via the use of melamine as the nitrogen source in
the pyridine synthesis.
H
NMR and
C NMR were employed to confirm the products of the synthetic
DOI: 10.1039/c6nj01464j
5
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be a mere physical modification which involves the forces of
attraction between the modifying species and the carbon
Introduction
Life revolves around carbon, which is an important natural material or chemical bond modification by changing the struc-
abundant element obtained from biomass to biofuel. Carbon ture of existing molecules or making new chemical bonds.
based materials are seen as compatible catalyst supports, Doping of carbon materials with heteroatoms, such as boron,
particularly carbon nanotubes, which have the advantages of phosphorous and nitrogen, is an interesting chemical modifi-
1
4
low cost, tunable carbon framework, mechanical as well as cation in the fabrication of nanomaterials. These doped
chemical stability, conducting properties, high surface area and materials have shown improved conducting properties when
1
,2
porous character. Manipulation of the structural parameters combined with transition metals for e.g. N-doped carbon
1
5
of carbon has given high performance electrochemical devices improves the conductivity of transition metals. Keeping all
which include sensing devices, lithium-ion batteries and super- these perspectives in mind our present work focuses on such
3
–5
capacitors. Carbon nanotubes have been recently recognised materials and their application as catalysts in organic synthesis.
6
as sensing materials in robotics and prosthetic devices, and as To date, the synthesis and doping of NCNTs have been observed
drug delivery vectors for e.g. PEG-modified SWNTs have been by special apparatus and methodologies, such as arc-discharge,
7
16,17
used for in vivo drug delivery of paclitaxel, PEI-g-MWNTs laser ablation, and chemical vapour deposition,
however,
combined with DNA have been internalized in human liver herein, we report a very simple approach for the preparation
8
carcinoma Hep G2 cells, and work on PEI-CNTS is still in of N-doped carbon nanotubes using furnace heating for the
9
progress for pancreatic cancer (highest mortality rate) therapy.
purpose of doping. Panchakarla et al. used the arc-discharge
The oxidation of carbon materials to different function- methodology for N-doping and the amount of nitrogen doped
4
1
alities, such as carbonyl, hydroxyl and carboxyl groups, was 1.2 at%, Shan et al. reported the N-doping of 4.26 wt%
4
2
increases their surface energy and also provides different using the CVD method, Jeon et al. obtained 14.84 at%
1
0–13
43
binding sites.
Modification of these carbon materials can N-doped graphene using the ball milling technique, thermal
4
4
treatment by Zhang et al. yielded 6–11 at% nitrogen,
Gopalakrishnan et al. obtained 13–15 at% N-doped carbon
using the microwave technique, and a hydrothermal treat-
a
45
Department of Chemistry, University of Jammu, Jammu-180006, India.
E-mail: monika.gupta77@rediffmail.com
ment resulted in the N-doping of 4–5.2 at%, as reported by
b
National Centre for Catalysis Research, Indian Institute of Technology-Madras,
Chennai-600036, India
4
6
Long et al. The present high temperature furnace heating
methodology has resulted in 26.95 at% [(28.12 wt%) as
observed from EDX] N-doping in less time.
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c6nj01464j
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Results and discussion
Preparation and characterisation of Cu/NCNTs
Preparation of oxidised CNTs. 10 g sugar was placed in a
1000 mL beaker and to this conc. sulphuric acid (20 mL) was
added in a fuming hood. A vigorous reaction takes place and
sulphur dioxide is evolved, and all the sugar is converted into
carbon nanotubes (charring of sugar) within 20–30 min. This
material was neutralized with approximately 500 mL distilled
water and was further treated with hydrogen peroxide (5 mL) in
distilled water at 80 1C on a magnetic stirrer. After 4 h, the
carboxyl modified nanotubes were filtered and dried in an oven
at 100 1C for 5 h.
Preparation of NCNTs. Equal amounts of CNTs and guanidine
carbonate (1 : 1), which was the nitrogen source, were placed
in a silica glass crucible and heated in a furnace at 300 1C for
Scheme 1 Preparation of Cu nps/NCNTs.
2
0 minutes under an air flow. A shiny grayish ash material was
surface is smooth, at 20 000Â the material shows a spongy
surface and at 100 000Â hexagonal shiny matter can be
observed on a distinct material. This hexagonal material corre-
sponds to the metallic nanoparticles doped in the N-doped
carbon nanotubes (ESI,† Fig. S1).
obtained, which showed complete mixing (Fig. 1).
At lower temperatures of 100 1C and 200 1C, complete mixing
of the two materials was not observed. An attempt to use half the
amount of guanidine carbonate to CNTs (1 : 2) gave a lower
N-doping content. This data has been added in the ESI,† Table S2.
Heating at the high temperature of 300 1C (pyrolysis) fractured the
prepared carbon nanotubes and thus led to the doping of nitrogen
evolved from guanidine carbonate. This fracturing of nanotubes can
be easily seen in the TEM image [ESI,† Fig. S3(f)].
The EDX spectrum shows carbon with the highest elemental
weight percentage of 63.85, nitrogen 28.12 and copper 8.02
(ESI,† Table S1 and Fig S2).
TEM. Nanotubular structures can be observed very clearly in
ESI,† Fig. S3(a) and (b). Smaller circular structures can be
assigned to copper nanoparticles of average size of about
Preparation of Cu doped NCNTs. Copper nanoparticles were
prepared by the chemical reduction of copper(II) acetylacetonate
12.8 nm which are present without any agglomeration and a
(0.2 g/g NCNTs) in 25 mL ethanol, using hydrazine hydrate as the
closer observation shows some copper nps glued to the nano-
tubes. These nanotubes are opened at their ends which suggest
the formation of multiwalled nanotubes (MWNTs). A dark field
image showing the presence of copper nanoparticles at different
distances has also been obtained [ESI,† Fig. S3(c)]. ESI,† Fig. S3(e)
shows a floral set up of tubes also. All these TEM images give
different observation patterns of the Cu/NCNTs from different views.
UV analysis. UV analysis of copper nanoparticles generally
reducing agent which was added dropwise under an inert
N-atmosphere in a three necked round bottom flask and magne-
tically stirred at 80 1C in an oil bath. To ensure copper(0) nps were
obtained, the pH was maintained between 5–7 using appropriate
drops of HCl (0.5–1 mL). After 6 h stirring, red coloured Cu(0) nps
were obtained. This colloidal suspension of Cu nps was added to
the NCNTs in a round bottom flask and magnetically stirred at
room temperature for 4 h. The Cu/NCNTs were filtered under
vacuum and dried in an oven at 50 1C for 5 h. They were then
soaked in ethanol for half an hour to remove any acidic impurities
and oven dried again for 5 h at 50 1C (Scheme 1).
18
shows a plasmon at around 570 nm, however, for the Cu/NCNTs
this is shown at approximately 500 nm (Fig. 2).
XPS. Taking C 1s as a reference at 285.6 eV (C–C), the
different binding energies observed include 287 eV for the
C–N bond and 290 eV for the N–CQO moiety in the C 1s
spectrum. In N 1s, the binding energies at 399.9 eV and 401 eV
correspond to the presence of pyridine N and pyrrolic N which
confirm the N-doping. In the case of Cu 2p, a peak at 934.6 eV
for Cu 2p3/2 and 954.4 eV for Cu 2p1/2 appears with no change
at 943 eV, which is generally a feature of oxidized carbon.
The used material (recycled catalyst) also shows no change,
which confirms the recyclability of the as-prepared material
and its potential application in catalysis. There is a shift of
Characterization
SEM-EDX. SEM images obtained at different magnifications
depict different structural topographies. For instance, at 5000Â the
1.6 eV in the reference value for C 1s which is 284 eV, and such
a shift is observed in all the values of binding energies of the
different bonds (ESI,† Fig. S4).
VSM analysis. VSM analysis clearly shows a non-magnetic
material, since copper in the zero oxidation state is a dia-
magnetic species, as can be observed in Fig. 3 which supports
the data.
Fig. 1 Photographs of the prepared NCNTs when taken out from the
furnace.
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Fig. 4 TGA of Cu/NCNTs.
Fig. 2 UV absorbance for Cu/NCNTs.
Fig. 5 XRD of Cu/NCNTs.
out and the results obtained are given in ESI,† Table S2.
The results confirm the best doping with the guanidine carbonate
and CNTs ratio of 1 : 1.
Resistance. The resistance of the prepared Cu/NCNTS was
studied using a multimeter device which gave a mild resistance
value of 50 mOhm and thus shows that the prepared material
is quite conductive in nature.
Fig. 3 VSM analysis of Cu/NCNTs.
TGA. TGA shows an initial weight loss of 5.9% at 122 1C
which is due to physically adsorbed water and then the catalyst
is stable up to 422 1C where the weight loss reaches 11% which
Application of Cu/NCNTs
Synthesis of pyridine derivatives. The synthetic approach
may be due to the loss of functionalities or disruption of for pyridine derivatives has thus far been studied using the
structural features and this weight loss further continues to three component Hantzsch type synthesis and four component
3
9% at 756 1C (Fig. 4).
approach. The work to date in this regard includes the use
1
9
20
21
22
XRD analysis. The XRD pattern of the Cu/NCNTs prepared of SnCl Á2H O, p-TsOH, piperidine, tri-ethylamine and
2
2
2
3
by high temperature furnace heating followed by room tem- FeCl
3
as catalysts. All the earlier methods assure a good
perature metal loading is observed in Fig. 5 which shows synthetic yield with a variety of starting materials but at the
diffraction peaks at 2y = 21.61 and 44.61 for carbon (002) and same time all involve homogeneous conditions and thus do not
(
100) planes. The peaks at 44.31 and 49.031 and the very weak meet the standards of sustainable technology. Herein, we study
peak at 68.61 are attributed to zerovalent copper (111), (200) an eco friendly recoverable nanocatalytic system for the synthesis
and (220) planes. of pyridines via a four component pathway (Scheme 2) with good
ICP analysis. The amount of copper nanoparticles loaded on yields in reasonable time.
the NCNTs was 4.9 wt%, as analysed by inductively coupled
plasma atomic emission spectroscopy.
Cu nps/N-doped CNTs were used to catalytically overcome
the energy barrier for a four component conversion to pyridine
CHN analysis. CHN analysis of the N-doping of CNTs using derivatives. Various control experiments were conducted to
different ratios of guanidine carbonate and CNTs was carried study the catalytic behaviour of the Cu nps/N-doped modified
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Scheme 2
Table 1 Optimization of reaction conditions using benzaldehyde as a
variable substrate
S.
Temp. Yield
No. Catalyst
Solvent
(1C)
(%)
1
2
3
4
5
6
—
Ethanol
Ethanol
Reflux
—
Cu nps/CNTs
Cu nps/N-modified CNTs Ethanol
Cu nps/N-modified CNTs Water
Cu nps/N-modified CNTs Ethanol : water (1 : 1) 70
Cu nps/N-modified CNTs Solvent-free 80
Reflux 50
Reflux 88
Reflux 60
72
58
Scheme 3 Proposed mechanism.
carbon material. Ethanol was the first choice as the solvent
since ethanol is an alcohol and it stabilises metallic nano-
particles from agglomeration as well as from oxidation. The
refluxing temperature gave good to excellent yields with different
variable substrates for e.g. with benzaldehyde, the yield was 88%
in ethanol at refluxing temperature (entry 3, Table 1).
Subsequent optimisation of solvents was carried out using
water (entry 4, Table 1), an ethanol–water blend (1 : 1) [entry 5,
Table 1], and solvent-free conditions (entry 6, Table 1). After
optimising the temperature and solvent parameters, we per-
formed comparatives with parallel analogs, such as without any
catalytic material (entry 1, Table 1) and supported Cu nps
directly onto carbon nanotubes without N-dope modification
reaction between malanonitrile and variable aldehydes. This
intermediate undergoes Michael addition with ethyl-
A
acetoacetate to give intermediate B which upon reaction with
aniline gives intermediate C. Intermediate C undergoes cycliza-
tion to give the final product along with the removal of a water
molecule (Scheme 3).
Role of solvent. Besides dissolving the reactants, ethanol is a
polar solvent and thus polarizes malanonitrile first to undergo
Knoevenagel condensation. Also it polarizes ethylacetoacetate
to undergo Michael addition since there is no base involved in
the reaction (Scheme 3).
(entry 2, Table 1). Among the reactivity of substrates (variable
analogs such as aldehydes or anilines), electron withdrawing
compounds, particularly nitro-variants and halogens, gave
excellent yields, unsubstituted compounds gave good results,
and electron releasing variants giving moderate results, as can
be seen from Table 2.
Reduction of nitroarenes. Aromatic amines present an
interesting scaffold for a spectrum of organic compounds of
2
4
importance, such as in dyes like indigo, as herbicides such as
2
5
metolachlor, in pharmaceuticals such as for the preparation
2
6
of paracetamol drug, as an antioxidant such as diphenyl-
2
7
28
Proposed mechanism. The proposed mechanism involves the amine and in the rubber industry. Recognizing the impor-
formation of an intermediate A by the Knoevenagel condensation tance of aromatic amines and their derivatives and also realising
the deficiencies from the previous literature, some of which
2
9
30
include graphene oxide, modified TiO
2
,
photocatalytic Ag
3
1
32
33
34
35
36a,b
clusters, copper nanoparticles, Fe–Cu, Ni, Pd, Pt,
Table 2 Synthesis of pyridine derivatives in ethanol media
3
7
and Au as catalysts for the reduction of nitroarenes, we have
performed and observed this reduction conversion in more
eco-friendly conditions than the pre-existing methods.
a
Time Yield
M. pt/
S. No.
R
Product (h)
(%)
lit. M. pt
1
8
1
2
3
4
5
6
7
8
9
H
4-OCH
3,4-OMe
4-Br
2-NO
3-NO
4-NO
5a
5b
5c
5d
5e
5f
2
3
88
83
89
85
78
90
89
82
95
203/205–2061
8
Subsequently, we studied the selectivity of the reduction
with respect to other groups present, in addition to the nitro
group. For this, we chose p-nitrobenzaldehyde as the first
substrate (1 mmol), ethanol (2 mL) as the solvent, Cu–NCNTs
3
179/179–180
2.40
1.45
2.20
1.45
2.10
3
222–224
1
8
8
8
8
177/176–1781
2
2
2
189/187–189
198/198–2001
1
(0.1 g) as the catalyst under hydrogen atmosphere, with the
5h
5i
220/220–221
204–206
182
2-OH
other parameters kept same and ran the reaction for seven
hours. Product conversion was observed but was never moved
to completion even after a 12 h run. The next attempt was to
increase the polarity and for this purpose acetic acid, which is a
mild organic acid, was added (0.5 mmol) as an additive, and
C
6
H
5
(melamine 5j
1.45
as NH source)
2
a
Reaction conditions: 0.1 g catalyst (0.11 mol% copper), aldehyde
1 mmol), aniline (1 mmol), malanonitrile (1 mmol), ethyl aceto acetate
1 mmol), solvent–ethanol and 80 1C.
(
(
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Table 3 Control experiments
Table 4 Reduction of nitroarenes to aromatic amines
a
b
S.
Time Yield TON
À1
No. Reactant
Product
(h)
(%)
[TOF (h )]
2
1
2
2.5
95
863 (3.45 Â 10 )
Conditions
Yield (%)
Cu/NCNTs, ethanol, R.T.
Acetic acid, ethanol, R.T.
Acetic acid, ethanol, R.T., H
Cu/NCNTs, ethanol, acetic acid, R.T., H
40
No reaction
No reaction
95
2
2
2
4
92
654 (2.09 Â 10 )
this time a good amount of product was observed through
TLC in 2.5 h.
To determine if acetic acid alone is enough to carry out the
reduction with and without a hydrogen atmosphere, the appro-
priate conditions were applied and no product initiation was even
observed (Table 3). This led to the conclusive thought that acetic
acid does not initiate the mechanism but gets involved some-
where in between the mechanistic pathway. Further selectivity was
observed for substrates, such as p-nitrobenzoic acid (92%), nitro-
benzene (97%), and dinitrobenzene (99%), which gave the difunc-
tional reduction products halogen substituted nitrobenzene (97%
and 98%) and p-nitroaniline (82%). p-Nitroanilines showed less
conversion and among the other substrates dinitrobenzene and
halogen substituted nitrobenzene gave products with maximum
selectivity and yields. The entire data are summed up in Table 4.
Moreover, the catalyst along with acetic acid as an additive is
highly selective in giving only the single corresponding amine
product and no intermediates have been trapped, which signify
the fast conversion of intermediates to selectively one product.
Table 5 shows a comparison of the present catalytic work with
some previous copper mediated reductions of nitroarenes and
it can be seen that all the previous works employ a strong
reducing agent, i.e. sodium borohydride, whereas our work
utilises milder conditions and better yields.
2
3
4
2
3
97
99
881 (4.40 Â 10 )
2
900 (3.00 Â 10 )
2
5
6
2.45 97
881 (3.20 Â 10 )
2
2.45 98
890 (3.23 Â 10 )
2
7
8
4
3
82
90
745 (1.86 Â 10 )
Proposed mechanism. Hydrogen adsorbs over the surface of
the Cu/NCNTs and this combination converts nitroarenes to
nitroso intermediates followed by hydroxylamine intermediates,
which finally get converted to the corresponding amine without
affecting the other functionalities (Scheme 4).
2
818 (2.72 Â 10 )
Role of acetic acid. We observed that reaction mixture has
a pH of 7 i.e. neutral. This observation follows that acetic
acid acts somewhat as a buffer and helps in enhancing the
reduction rate, which otherwise was lower when 0.5 mmol of acetic
acid was not added (control experiments). This action of acetic acid
signifies its importance in maintaining the oxidation state of Cu
2
9
3.45 94
854 (2.47 Â 10 )
+
metal besides the presence of H ions in the medium and supports
the regeneration condition in addition to the conductive nature of
NCNTs for maintaining the reusability of the Cu/NCNTs.
a
Reaction conditions: 0.1 g catalyst (0.11 mol% copper), nitro sub-
, solvent–ethanol,
strate (1 mmol), acetic acid (0.5 mmol, additive), H
2
b
and room-temp. TON = turn over number = number of moles of
product per mole of copper in Cu/NCNTs. TOF = turn over frequency =
TON per h.
Recyclability of Cu/NCNTs
In the case of pyridine derivatives. Cu/NCNTs were applied
for the synthetic preparation of different pyridine derivatives
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Table 5 Comparison of the catalytic performance of Cu/NCNTs with some of the previously reported copper catalytic systems for the reduction of
nitroarenes in the case of nitrobenzene as the starting substrate
Cu catalysts
CuBr - Cu nps
Amount of cat. used
Reducing agent
Time
Temp. (1C)
Yield
38
2
10 mol%
10 mg
1 mg
NaBH
NaBH
NaBH
4
4
4
5 h
R.T.
60
R.T.
R.T.
90
92
39
C/CuPd nps
1.5 h
4 min
2 h
40
Cu
2
O nps
Not mentioned
97
Cu/NCNTs
0.11 mol%
2
H , acetic acid (additive)
Fig. 7 Recyclability using 1,3-dinitrobenzene as the test substrate.
Conclusion
Scheme 4 Proposed mechanism for the reduction of nitroarenes to the
corresponding amines.
We attempted a new high temperature furnace heating meth-
odology for the N-doping of CNTs to give NCNTs which have
good electronic conduction properties. This modified carbon
material was combined with transition metal–copper nps and
the good conduction effects were studied using the prepared
Cu/NCNTs in the synthesis of pyridine derivatives (via a four
component pathway) and in the reduction of nitroarenes to
selective corresponding amines (with a high tolerance to other
functionalities) as a recyclable catalyst in eco-friendly hetero-
geneous conditions in shorter times in comparison to previous
attempts. Moreover, copper nps, which are not very stable, were
been stabilized using NCNTs as a supporting system. Also their
magnetic and electrical properties were studied, which demon-
strate that copper is in the zerovalent state (VSM study) and the
Fig. 6 Recyclability using 3,4-dimethoxybenzaldehyde as the test substrate. small amount of resistance shown by a multimeter shows good
conduction behavior.
via a four component reaction, and were also studied for their
recyclability. For this purpose, 3,4-dimethoxybenzaldehyde was
used as the variable substrate in the test reaction for recycl-
ability. The Cu/NCNTs were reused five times and the observed
Experimental
Materials
All the starting materials used for the synthetic application of
Cu/NCNTs were purchased from Sigma Aldrich.
results show good yields with slight variation for five consecu-
tive runs (Fig. 6).
In the case of the reduction of nitroarenes. Here, we have
checked the recyclability of the Cu/NCNTs in the case of
Instrumentation
1
,3-dinitrobenzene as a variant for five consecutive runs and The heating for the preparation of Cu/NCNTs was performed
determined the efficiency of the Cu/NCNTs as a recyclable in a PHOENIX microwave furnace by CEM innovators. TEM
catalytic entity (Fig. 7). images were recorded on a PHILIPS CM200, and SEM-EDAX
Each time the catalyst was washed thoroughly with hot was studied on a JSM-7600F JEOL. TGA-DTA was conducted on
ethanol (15 mL) and then oven dried at 50 1C for 5 h. As a a Linseis STA PT-1000 (Germany) Thermal Analyser with a heating
À1
consequence of manual error, each time there was a loss in rate of 10 1C min . XPS was conducted on a VG Microtech
catalyst amount. Thus for the recyclability study, each time the ESCA 3000 spectrometer using Al Ka X-ray at room tempera-
reactant concentration was adjusted accordingly.
ture. ICP-AES was recorded on an ARCOS (1.6 kW, 27.12 MHz)
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and the VSM analysis was done on a Lakeshore, Model: 7410 (d, J = 8 Hz, 2H), 6.8–6.9 (m, 4H), 6.8 (s, 1H), 6.7 (d, J = 8.0 Hz,
series.
2H), 4.0 (q, J = 8.0 Hz, 2H), 3.7 (s, 6H), 2.29 (s, 3H), 1.1 (t, J =
8
.0 Hz, 3H).
General procedure for the preparation of four component
pyridine derivatives
13
C NMR (100 MHz, DMSO): d 166.6, 149.0, 148.1, 145.8,
42.4, 139.4, 129.6, 121.1, 119.0, 117.3, 112.4, 111.0, 102.1, 71.4,
1
Aldehyde (1 mmol), aniline (1 mmol), malanonitrile (1 mmol), 59.8, 55.8, 18.6, 14.8.
ethyl acetoacetate (1 mmol), 0.1 g (0.11 mol% Cu) of Cu/NCNTs Ethyl-6-(3-nitrophenylamino)-5-cyano-2-methyl-4-phenyl
and 2 mL ethanol were placed in a 100 mL round bottom flask pyridine-3-carboxylate (5f). H NMR (400 MHz, CDCl
1
3
): d 8.1
and stirred for the appropriate time at reflux in an oil bath on a (d, J = 8 Hz, 1H), 8.0 (s, 1H), 7.62 (m, 4H), 7.6 (d, J = 8.0 Hz, 1H),
magnetic stirrer under condensing conditions for appropriate 7.5 (t, J = 8.0 Hz, 1H), 7.4 (t, J = 8.0 Hz, 1H) 7.0 (d, J = 8.0 Hz, 1H),
times. Monitoring of the reaction was done using the TLC 4.0 (q, J = 8.0 Hz, 2H), 2.43 (s, 3H), 1.1 (t, J = 8.0 Hz, 3H).
1
3
technique using petroleum ether : ethylacetate (8 mL : 2 mL)
C NMR (100 MHz, CDCl ): d 165.0, 158.0, 157.0, 148.3,
3
as the elutant. To obtain the products, the reaction mixture 146.1, 133.4, 133.2, 130.3, 129.0, 128.4, 122.4, 120.9, 120.5,
was worked up by adding 25 mL ethyl acetate to the reac- 118.6, 106.4, 60.7, 18.4, 13.6.
tion mixture and filtering the catalyst. The filtrate was washed
with cold and hot brine solutions. Sodium sulphate was added 4-phenylpyridine-3-carboxylate (5j). H NMR (400 MHz, DMSO, d):
to the washed product, which was kept overnight to remove any 7.29 (t, J = 8 Hz, 1H), 7.20 (t, J = 8 Hz, 2H), 7.13 (d, J = 8 Hz, 2H),
Ethyl 6-(4,6-diamino-1,3,5-triazin-2-yl amino)-5-cyano-2-methyl-
1
water molecules present. Sodium sulphate was separated by 6.90 (bs), 4.29 (bs), 3.94 (t, J = 8 Hz, 2H; CH
2
–CH
3
), 2.31 (s, 3H,
13
filtration and the filtrate was evaporated and concentrated. CH ), 1.00 (t, J = 8 Hz, CH –CH ); C NMR (100 MHz, DMSO, d):
3
2
3
The crude product obtained was recrystallised using ethanol. 165.94, 158.95, 157.07, 145.30, 128.91, 127.64, 127.31, 120.21,
1
13
The obtained product was analysed using the H NMR and
NMR techniques.
C
107.70, 60.65, 57.73, 18.57, 14.16.
1
4-Aminobenzaldehyde 2(a). H NMR (400 MHz, CD
3
COCD
3
,
d): 10.24 (s, 1H), 8.45 (d, J = 8 Hz, 2H), 8.22 (d, J = 8 Hz, 2H), 2.07
General procedure for nitroarene reduction
13
3 3
(s, 2H, NH); C NMR (100 MHz, CD COCD , d): 191.34, 140.54,
Nitroarene (1 mmol), ethanol 2 mL, acetic acid (0.5 mmol) 130.52, 126.86, 124.19.
acting as an additive and Cu–NCNTs (0.1 g) were placed in Benzene-1,3-diamine 2(d). H NMR (400 MHz, CD
00 mL round bottom flask fitted under a hydrogen atmosphere d): 8.98 (s, 1H), 8.70 (dd, J = 8 Hz, 2H), 8.05 (t, J = 8 Hz, 1H), 2.93
1
3 3
COCD ,
1
1
3
and stirred at room temperature (approx. 20 1C) on a magnetic (s, 4H, NH); C NMR (100 MHz, CD COCD , d): 131.42, 129.09,
3
3
stirrer for appropriate times. The reactions were worked up by 118.60.
diluting the reaction mixture with ethyl acetate (25 mL), remov- 3-Chlorobenzenamine 2(e). H NMR (400 MHz, CD
ing the catalyst by simple filtration under vacuum and washing d): 8.20 (d, J = 8 Hz, 2H), 7.86 (d, J = 8 Hz, 1H), 7.71 (t, J = 8 Hz,
1
3
COCD
COCD , d):
COCD
3
,
1
3
three times with brine solution. The washed filtrate was dried 1H), 3.52 (s, 2H, NH); C NMR (100 MHz, CD
3
3
overnight with sodium sulphate and the product was obtained 148.93, 134.82, 131.21, 123.37, 121.95.
1
by concentrating the filtrate. All the products have been con-
firmed using H NMR and C NMR analysis.
Benzene-1,4-diamine 2(g). H NMR (400 MHz, CD
3
3
,
1
13
d): 8.98 (s, 1H), 8.70 (dd, J = 8 Hz, 2H), 8.05 (t, J = 8 Hz, 1H), 2.93
s, 4H, NH); C NMR (100 MHz, CD COCD , d): 126.38, 113.39.
1
3
(
3 3
Spectral data of some compounds
Ethyl 5-cyano-2-methyl-4-phenyl-6-(phenylamino)pyridine-3-
1
Acknowledgements
carboxylate (5a). H NMR (400 MHz, CDCl
3
, d): 7.69 (d, J = 8 Hz,
1
(
H), 7.49 (d, J = 8 Hz, 2H), 7.39 (t, J = 8 Hz, 5H), 7.26 (s, 1H), 7.15
d, J = 8 Hz, 2H), 3.97 (q, J = 10 Hz, 2H; CH –CH ), 2.62 (s, 3H,
); C NMR (100 MHz, CDCl , d):
We are thankful to SAIF, Mumbai for conducting SEM-EDAX,
TEM and ICP-AES analysis; NCCR, Chennai for conducting XPS
analysis, IIT, Guwahati for conducting VSM study SAIF, Punjab
University for conducting CHN studies.
2
3
1
3
CH
3
), 0.88 (t, J = 6 Hz, CH
2
–CH
3
3
1
1
1
2
67.51, 167.28, 160.49, 160.35, 155.42, 155.20, 154.01, 153.86,
38.36, 137.90, 135.93, 135.57, 129.51, 128.99, 128.63, 127.95,
24.09, 120.77, 120.54, 115.91, 90.83, 77.34, 77.03, 76.71, 61.35,
3.89, 13.48.
References
Ethyl-5-cyano-2-methyl-4-(4-methoxyphenyl)-6-(phenylamino)-
1
pyridine-3-carboxylate (5b). H NMR (400 MHz, CDCl
3
): d 7.6
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