La2O3/reduced graphene oxide nanocomposite: A highly efficient, reusable heterogeneous catalyst for the synthesis of biologically important bis(indolyl)methanes under solvent free conditions

Article abstract of DOI:10.1166/jnn.2017.13441

Synthesis and characterization of Lanthanum Oxide-reduced graphene oxide (La₂O₃/RGO) nanocomposite and its application as heterogeneous, reusable catalyst has been reported in this article. Biologically important molecules bis(indoly

Full text of DOI:10.1166/jnn.2017.13441

Article
Journal of
Nanoscience and Nanotechnology
Vol. 17, 2508–2514, 2017
Copyright © 2017 American Scientific Publishers
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Printed in the United States of America
La2O3/Reduced Graphene Oxide Nanocomposite:
A Highly Efficient, Reusable Heterogeneous Catalyst
for the Synthesis of Biologically Important
Bis(indolyl)methanes Under Solvent Free Conditions
Navin Kumar Mogha, Sugat Kirti, and Dhanraj T. Masram∗
Department of Chemistry, Faculty of Science, University of Delhi, Delhi 110007, India
Synthesis and characterization of Lanthanum Oxide-reduced graphene oxide (La2O3/RGO)
nanocomposite and its application as heterogeneous, reusable catalyst has been reported in this
article. Biologically important molecules bis(indolyl)methanes are synthesized in mild reaction con-
dition with excellent yield under solvent free condition. Catalyst was reused for four times without
any significant changes in the yields obtained. Reusability, green synthesis and environmentally
benign nature makes La2O3/RGO one of the best catalyst for the synthesis of biologically important
bis(indolyl)methanes.
Delivered by Ingenta to: State University of New York at Binghamton
Keywords: Bis(indolyl)methanes,
Catalysis,
Lanthanum
Oxide-Reduced
Graphene
IP: 185.13.32.70 On: Tue, 28 Feb 2017 20:06:05
Nanocomposite, Solvent Free Synthesis.
Copyright: American Scientific Publishers
1. INTRODUCTION
immobilized Graphene oxide for enhanced photocat-
alytic performance.11 Some more examples include NOx
reduction over TiO2/Graphene oxide nanocomposite,12
hydrodesulphurization using MoS2/Graphene oxide
composite13 and Palladium/Graphene composite for the
asymmetric hydrogenation.14 A very easy and efficient
method for graphene/metal NP composites preparations
is where both metal precursor and graphene oxide (GO)
sheets were mixed in aqueous solution and then reduced
simultaneously.15ꢀ16 Lanthanum oxide is a biocompat-
ible metal oxide17 and it is being extensively used in
sensing, environmental chemistry, and other catalytic
reactions.17–19 Various bioactive metabolites have indole
derivatives as their constituents and this is the reason
behind the importance of indole derivatives for synthetic
as well as biological chemists.10 Indole and its derivatives
possess broad spectrum of biological and pharmaceutical
activities21ꢀ22 and have been identified in over 3000 natural
isolates. Particularly bis(indolyl)methanes are known to
enhance estrogen metabolism in humans and is likely
to be drug of choice for breast cancer preventive and
antibacterial agent. Because of these interesting biological
activities andother uses, development of protocols for the
synthesis of bis(indolyl)methanes is of current interest.
Need for the development of new metal oxide catalysts is
progressing, albeit at a slower pace, the concurrent and
rapid development of high surface area catalyst supports
such as graphene and its functionalized derivatives has
provided unprecedented promise in the development of
multifunctional catalysts.1 Since its discovery,2 graphene
has been an excellent subject of research, as an attractive
material because of its very large theoretical surface area,
strong mechanical strength, high thermal conductivity,
and excellent electric conductivity.3ꢀ4 These properties
of graphene lead to the synthesis of Graphene-based
composite materials. Unique properties and structure of
these Graphene-based composite materials have shown
applications in electrocatalysis5ꢀ6 and sensing.7 A novel
way to develop catalysts is by dispersing metal nanopar-
ticles over the surface of graphene sheets.8ꢀ9 A facile
synthesis of graphene/metal NP composites with good
control of size and morphology is critical to the prac-
tical applications.10 Some novel catalyst based on the
graphene oxide metal nanocomposites has been reported
for carrying out different reaction like TiO2 nanorods
∗Author to whom correspondence should be addressed.
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J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 4
1533-4880/2017/17/2508/007
doi:10.1166/jnn.2017.13441

Mogha et al.
La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
Figure 1. Schematic representation of the catalytic synthesis of bis(indolyl)methanes.
The electrophilic substitution reaction of indoles with
carbonyl compounds to produce bis(indolyl)alkane is
an acid catalyzed reaction, and both protic (e.g., HCl,
Poly(ethylene glycol), both were ultrasonicated for about
one hour in 20 ml double distilled water than 200 mg
Graphene oxide is added followed by ultrasonication for
30 min. To the resulting suspension 200 ꢃL 0.1 M NaBH4
was added dropwise under ice cold conditions and left
for stirring for two hours. Afterwards solid was recovered
by centrifugation after multiple washing with water and
H2SO4ꢁ23ꢀ24 as well as Lewis acids like AlCl3 are known
25
to promote this reaction.
Here in this article we report the synthesis and charac-
terization of lanthanum oxide-reduced graphene nanocom-
posite (La2O3/RGO) and use it as reusable catalyst for the
synthesis of biologically important heterocyclic molecules
i.e., bis(indolyl)methanes under solvent free conditions
(Fig. 1).
ꢀ
ethanol, thus obtained solid was dried in air at 80 C for
1 h followed by the annealing at 300 C for 3 h.
ꢀ
2.2. Synthesis of Bis(indolyl)methanes
2 mM Indole and 1 mM benzaldehyde were mixed
together followed by addition of 5 wt%La2O3/RGO.
Resulting mixture was than stirred at 45 ꢀC for 35 minutes.
Completion of the reaction was monitored by thin layer
chromatography. After completion reaction mixture was
2. EXPERIMENTAL DETAILS
La(NO3ꢁ3 · 6H2O was obtained from Merck Millipore,
India; poly(ethylene glycol), MW∼35,000, was purchased
from Sigma-Aldrich, USA; Indole, carbonyl compounds
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diluted with chloroform (10 mL) and centrifuged to sepa-
IP: 185.13.32.70 On: Tue, 28 Feb 2017 20:06:05
were purchased from Aldrich and Merck. All the chem-
rate the catalyst. Supernatant was reduced under pressure
to afford the solid product, which is further purified by
recrystallization from petroleum ether.
Copyright: American Scientific Publishers
icals were of analytical grade and used without fur-
ther purification. X-ray diffraction pattern of La2O3/RGO
nanocomposite was recorded using X-ray diffractometer
(model no. D8 DISCOVER). Morphological character-
ization was carried out using TECNAI 200 Kv TEM
(Fei, Electron Optics) with digital imaging and 35 mm
photography system. Thin layer chromatography (Merck
Kiesel 60 F254, 0.2 mm thickness) was used to mon-
itor the progress of the reactions. The 1H-NMR and
13C-NMR spectrum were recorded on Jeol ECX spectrosp
in instrument at 400 and 100 MHz, respectively using
TMS as internal standard. The chemical shift values were
expressed on ꢂ scale and the coupling constant (J) in Hz.
FT-IR of all the synthesized bis(indolyl)methanes were
recorded on a spectrometer Perkin Elmer Spectrum BX
II from range 4000–400 cm−1 by making sample pallets
with KBr. The melting points of synthesized compounds
were determined on a Thomas Hoover Unimelt capillary
melting point apparatus.
3. RESULTS AND DISCUSSION
3.1. Catalyst Characterization
Raman spectra of La2O3/RGO and GO can be seen in
Figure 2(A), showing the characteristic D (j-point phonons
of A1g symmetry of sp3-bonded carbon atoms of dis-
ordered graphene) and G (scattering of E2g phonons of
sp2-bonded carbon atoms) bands of graphene. Raman
Spectra of GO shows D and G bands at 1354 cm−1 and
1600 cm−1 respectively. Similarly for La2O3/RGO Raman
spectra showing D band at 1317 cm−1 and G band at
1591 cm−1. ID/IG ratio for GO and La2O3/RGO found to
be 0.86 and 1.47 respectively, this increase in the inten-
sity ration is attributed to the increase in the disorderness
of the graphitic structure due to the binding of La3+ with
the free oxygen moieties on the graphene oxide surface to
form La2O3 nanoparticles.
2.1. Preparation of Graphene Oxide and Lanthanum
Oxide-Reduced Graphene Oxide
Figure 2(B) depicting the X-ray diffraction peaks pattern
of La2O3/RGO. In the spectrum of GO peak at 2ꢄ = 10ꢅ15ꢀ
and 2ꢄ = 42ꢅ40ꢀ represents the ꢁ001ꢂ plane and ꢁ100ꢂ
plane respectively. XRD pattern of La2O3/RGO shows
peaks at 2ꢄ = 25ꢅ18ꢀ, 2ꢄ = 42ꢅ85 represents the ꢁ002ꢂ and
ꢁ100ꢂ planes of RGO along with the 2ꢄ = 30ꢅ19 attributed
to ꢁ101ꢂ crystal plane of La2O3.
(La2O3/RGO) Nanocomposite
Graphene oxide was prepared by the Modified Hummers
method.26ꢀ27 Lanthanum oxide-reduced graphene oxide
nanocomposite (La2O3/RGO) was synthesized by
using 40 mg of La(NO3ꢁ3 · 6H2O and 0.2
g of
J. Nanosci. Nanotechnol. 17, 2508–2514, 2017
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La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
Mogha et al.
Figure 2. (A) Raman spectra of GO and La2O3/RGO showing D and G bands, (B) XRD pattern of GO and La2O3/RGO with different planes
labeled.
TEM images of the GO and La2O3/RGO nanocompos-
ite is shown in Figure 3. Figure 3(A) shows the sheet
like morphology of the graphene oxide with wrinkled
structures. Nanoclusters of Lanthanum oxide nanoparti-
cles can be seen attached to the wrinkled surface of the
RGO sheet in Figure 3(B). Nanoclusters of Lanthanum
oxide nanoparticles showing a porous morphology, and
Effect of different solvents on the reaction is moni-
tored with chloroform (1), methanol (2), N ,N -dimethyl
formamide (3), tetrahydrofuran (4) and water (5) and
solvent free (6) as reaction solvents conditions. Results
depicted in Figure 4(B), shows that under solvent free con-
ditions excellent yield is obtained in one fourth time as
compared to solvated conditions. It established the fact
this enhance catalytic property of La O /RGO nanocom-
that solvent free condition is best suitable for the synthesis
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posite in addition to the large surface area of RGO. Inset of bis(indolyl)methanes in the presence of La2O3/RGO as
Copyright: American Scientific Publishers
picture in Figure 3(A) is a HRTEM image of individ-
catalyst.
ual La2O3 nanoparticle in nanocluster over RGO surface
showing ꢁ101ꢂ crystal plane of La2O3.
After the model reaction we have tried various sub-
stituted aldehydes as summarized in Table I. Different
type of substituents i.e., electron withdrawing (entry 2–10)
and electron donating (entry 11–12) has shown differ-
ent trend in reaction time. Electron withdrawing groups
tends to stabilize the iminium ion formed during the reac-
tion, hence helping the reaction to complete in lesser
time. On the other hand electron donating groups destabi-
lize the iminium ion which causes increment in reaction
Catalytic activity for the synthesis bis(indolyl)
methanesis optimized using model reaction between
indole and benzaldehyde. First, effect of catalyst amount
is investigated, in which different amounts of catalysts are
used (Fig. 4(A)), and at 5, 10, and 20 wt.% yield obtained
found to be similar in same time but we selected 5 wt.%
for our further reactions for its being lesser amount.
Figure 3. (A) TEM image of GO with sheet like morphology, inset showing HRTEM image of La2O3/RGO showing La2O3 crystal plane of ꢁ101ꢂ,
(B) TEM image of La2O3/RGO showing La2O3 nanoclusters over the surface of RGO.
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Mogha et al.
La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
Figure 4. (A) Effect of the amount of catalyst for synthesis of bis(indolyl)methane for 25 minutes, (B) Effect of solvents on the synthesis of
bis(indolyl)methanes with different solvents as chloroform (1), methanol (2), N,N- dimethyl formamide (3), tetrahydrofuran (4) and water (5) and
solvent free (6).
completion time. Substituents with respect to their posi-
tions have also shown different behavior in terms of yields
and time. Para substituted aldehydes has taken less time in
reaction completion as compared to ortho, and meta sub-
stituted. This decrease in reaction completion time is due
to the greater stability provided by the substituent at para
position as compared to ortho and meta position.
attacks this intermediate to form another intermediate on
the catalyst surface and a final rearrange in intermediate
gives desired product.
For the comparison purpose we also used only graphene
oxide as catalyst for the same model reaction. Table II
summarize the comparision of La2O3/RGO with others
catalyst reported in literature and La2O3/RGO has been
found to be the best among these catalysts.
Reusability studies are also performed, where first cat-
alyst is recovered very easily by simple filtration, washed
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ꢀ
with chloroform, and dried in oven for 2 hours at 80 C.
3.2. Spectroscopic Data of the
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Afterwards it was reused for next run of reaction with ben-
Synthesized Compounds
Copyright: American Scientific Publishers
3,3ꢃ-Bis(indolyl)-phenylmethane (1): IR (KBr, cm−1):
3397, 3051, 1457, 1335, 1217, 1092, 1008, 745; 1H
NMR (CDCl3, 400 MHz) ꢂ: 5.87 (s, 1H), 6.64 (s, 2H),
6.96–7.00 (t, 2H, J = 8ꢅ05 Hz), 7.14–7.20 (m, 2H,), 7.25–
7.27 (m, 4H), 7.32–7.38 (m, 5H), 7.90 (br, 2H, NH). 13C
NMR (CDCl3, 100 MHz): 40.15, 110.97, 119.28, 119.97,
121.85, 123.56, 126.10, 127.19, 128.15, 128.68, 136.22,
144.25.
zaldehyde and indole. This process is repeated for three
more times to quantify the reusability of catalyst. A high
yield of 82, 80, 76 and 73% is obtained in four repeat
reactions for reusability studies.
We also proposed mechanism for the catalytic synthe-
sis of bis(indolyl)methane in the presence of La2O3/RGO
(Fig. 5), where iminium ion formation takes place from
aldehyde and first indole molecules in the presence of
active sites O2− and La3+ in La2O3/RGO, and an inter-
mediate gets stabilized on catalyst. Second indole atom
3,3ꢃ-Bis(indolyl)-3-flurophenylmethane
(2):
IR
(KBr, cm−1): 3402, 3051, 1606, 1459, 1338, 1220, 1095,
1011, 745; 1H NMR (CDCl3, 400 MHz) ꢂ: 5.82 (s, 1H),
6.61–6.63 (m, 2H), 6.97 (t, 2H, J = 8ꢅ05 Hz), 7.03 (t, 2H,
J = 8ꢅ05 Hz), 7.14–7.18 (m, 3H), 7.26–7.29 (m, 2H),
7.31–7.35 (m, 4H), 7.82 (br, 2H, NH); 13C NMR (CDCl3,
100 MHz): 39.41, 102.54, 111.15, 114.88, 119.29, 119.81,
122.06, 123.53, 124.82, 129.91, 130.16, 131.45, 135.89,
136.64, 139.56, 143.56.
Table I. Effect of different substituents on the rate of the reaction, in
the synthesis of bis(indolyl)methanes.
Mp (ꢀC)
Entry
R
Time (min) Yield (%) Experimental
Lit.
1
2
3
4
5
6
7
8
H
3-F
4-F
3-Cl
4-Cl
3-Br
4-Br
2-NO2
3-NO2
4-NO2
4-CH3
4-C2H5
35
40
25
35
25
30
25
40
35
25
45
60
96
89
93
94
93
92
94
96
95
97
89
88
122–124
81–84
78–79
77–79
80–82
112–114
107–111
137–140
217–219
210–223
94–98
125–126
82–83
80–82
78–80
77–81
115–117
110–112
140–141
218–220
220–221
95–97
3,3ꢃ-Bis(indolyl)-4-flurophenylmethane (3): IR (KBr,
cm−1): 3404, 3053, 1601, 1455, 1335, 1215, 1092, 1009,
741; 1H NMR (CDCl3, 400 MHz) ꢂ: 5.86 (s, 1H),
6.61–6.62 (m, 2H), 6.92 (t, 2H, J = 8ꢅ05 Hz), 6.99 (t, 2H,
J = 8ꢅ05 Hz), 7.14–7.19 (m, 2H), 7.26–7.29 (m, 2H),
7.33–7.37 (m, 4H), 7.80 (br, 2H, NH); 13C NMR (CDCl3
100 MHz): 39.42, 102.59, 111.05, 114.82, 119.27, 119.82,
122.00, 123.51, 129.99, 136.65, 139.64, 143.84.
9
10
11
12
3,3ꢃ-Bis(indolyl)-3-chlorophenylmethane (4): IR (KBr,
cm−1): 3406, 3020, 2927, 1687, 1582, 1419, 1215, 1194,
177–180
179–181
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La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
Mogha et al.
Figure 5. Proposed mechanism of catalytic synthesis of bis(indolyl)methane.
1093, 741; 1H NMR (CDCl3, 400 MHz) ꢂ: 5.86 (s, 1H),
6.65 (s, 2H), 7.01 (t, 2H, J = 8ꢅ05 Hz), 7.16–7.19 (m, 3H),
7.20–7.22 (m, 2H,) 7.34 (d, 2H, J = 7ꢅ32 Hz), 7.37 (d, 2H,
J = 7ꢅ32 Hz), 7.92 (br, 2H, NH); 13C NMR (CDCl3,
100 MHz): 39.92, 110.63, 114.49, 118.88, 119.27, 119.87,
7ꢅ32 Hz), 7.32–7.37 (m, 4H), 7.48–7.49 (m, 1H), 7.89 (br,
2H, NH); 13C NMR (CDCl3, 100 MHz): 39.90, 111.08,
118.89, 119.35, 119.71, 119.92, 122.36, 123.63, 124.34,
126.81, 127.34, 129.33, 129.80, 131.66, 136.62, 146.44.
3,3ꢃ-Bis(indolyl)-4-bromophenylmethane (7): IR (KBr,
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120.12, 122.90, 123.71, 124.32, 126.83, 130.57, 131.64,
cm ): 3408, 3055, 1490, 1455, 1335, 1216, 1092, 1009,
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133.61, 136.61, 146.14.
743; 1H NMR (CDCl3, 400 MHz) ꢂ: 5.87 (s, 1H),
6.63–6.64 (br, 2H), 6.98 (t, 2H, J = 8ꢅ05 Hz), 7.15 (t, 2H,
J = 8ꢅ05 Hz), 7.19 (d, 1H, J = 7ꢅ32 Hz), 7.27 (d, 1H,
J = 7ꢅ32 Hz), 7.33 (d, 4H, J = 7ꢅ32 Hz), 7.37 (d, 2H,
J = 7ꢅ32 Hz), 7.88 (br, 2H, NH); 13C NMR (CDCl3,
100 MHz): 40.01, 110.99, 119.19, 119.67, 119.90, 121.88,
123.57, 126.10, 127.03, 128.18, 128.68, 136.63, 143.95.
3,3ꢃ-Bis(indolyl)-2-nitrophenylmethane (8): IR (KBr,
cm−1): 3403, 3058, 1620, 1531, 1457, 1420, 1222, 1082,
1001, 746, 690. 1H NMR (CDCl3, 400 MHz) ꢂ: 5.94
(s, 1H), 6.61 (s, 2H), 7.02 (t, 2H, J = 8ꢅ05 Hz), 7.22
(t, 2H, J = 8ꢅ05 Hz), 7.41 (t, 4H, J = 8ꢅ05 Hz), 7.43
(t, 1H, J = 8ꢅ05 Hz), 7.68 (d, 1H, J = 7ꢅ32 Hz), 7.99 (br,
2H, NH), 8.04 (d, 1H, J = 7ꢅ32 Hz), 8.23 (s, 1H); 13C
NMR (CDCl3 100 MHz): 39.17, 110.23, 111.25, 118.29,
Copyright: American Scientific Publishers
3,3ꢃ-Bis(indolyl)-4-chlorophenylmethane (5): IR (KBr,
cm−1): 3404, 3052, 1594, 1455, 1215, 1089, 1011, 742;
1H NMR (CDCl3, 400 MHz) ꢂ: 5.87 (s, 1H), 6.66 (s, 2H),
7.02 (t, 2H, J = 8ꢅ05 Hz), 7.15 (t, 2H, J = 8ꢅ05 Hz),
7.22–7.24 (m, 2H), 7.26–7.29 (m, 2H), 7.34 (d, 2H, J =
7ꢅ32 Hz), 7.36 (d, 2H, J = 7ꢅ32 Hz), 7.92 (br, 2H, NH);
13C NMR (CDCl3, 100 MHz): 39.58, 102.59, 110.98,
111.08, 119.15, 119.32, 119.79, 122.05, 123.56, 126.84,
128.33, 130.04, 131.75, 136.64, 142.52.
3,3ꢃ-Bis(indolyl)-3-bromophenylmethane (6): IR (KBr,
cm−1): 3407, 3052, 1585, 1455, 1336, 1214, 1091, 1009,
741; 1H NMR (CDCl3, 400 MHz) ꢂ: 5.84 (s, 1H),
6.61–6.62 (br, 2H), 7.01 (t, 2H, J = 8ꢅ05 Hz), 7.12 (t, 2H,
J = 8ꢅ05 Hz), 7.17 (d, 2H, J = 7ꢅ32 Hz), 7.26 (d, 1H, J =
Table II. Comparison of bis(indolyl)methane preparation with different catalysts at various reaction conditions.
Entry
Catalyst (amount)
Conditions
Time (h)
Yield (%)
Reusable catalyst (Yes/No)
Ref.
1
2
3
4
5
6
7
8.
9
Polyindole salt (20 wt%)
[Et3NH][H2PO4] (0.4 g)
Al(HSO4)3 (0.636 g)
Ferric dodecyl sulfonate (1 mol%)
CuBr2 (10 mol%)
Methanol/r.t.
[Et3NH][H2PO4]/100 ꢀC
Ethanol/r.t.
3
98
97
92
90
94
98
52
36
96
Yes
No
No
No
No
Yes
Yes
Yes
Yes
[28]
[29]
[30]
[31]
[32]
10 min
2.5
6
30 min
1.5
24
H2O/r.t.
MeCN/r.t.
[omim][PF6]/r.t.
CCl4/70 ꢀC
Solvent free
FeCl3 ·6H2O (5 mol%)
SBA-15/SO3H (70%)
Graphene oxide
[33]
[34]
35 min
35 min
Present work
La2O3/RGO
Solvent free
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Mogha et al.
La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
119.67, 119.78, 121.49, 122.18, 123.67, 123.89, 124.14,
126.89, 129.18, 134.57, 136.78, 137.98, 146.79.
New Delhi, India for financial assistance. Authors are also
grateful to Head, Department of Chemistry, USIC, Uni-
versity of Delhi for providing instrumentation facilities
and Sophisticated Analytical Instrument Facility (SAIF)-
AIIMS, New Delhi, under the SAIF Program of DST for
providing TEM facility.
3,3ꢃ-Bis(indolyl)-3-nitrophenylmethane (9): IR (KBr,
cm−1): 3404, 3052, 1616, 1521, 1453, 1415, 1218, 1092,
1006, 741, 692. 1H NMR (CDCl3, 400 MHz) ꢂ: 5.93
(s, 1H), 6.61 (s, 2H), 7.05 (t, 2H, J = 8ꢅ05 Hz), 7.14
(t, 2H, J = 8ꢅ05 Hz), 7.31 (t, 4H, J = 8ꢅ05 Hz), 7.40
(t, 1H, J = 8ꢅ05 Hz), 7.60 (d, 1H, J = 7ꢅ32 Hz), 7.91 (br,
2H, NH), 8.04 (d, 1H, J = 7ꢅ32 Hz), 8.15 (s, 1H); 13C
NMR (CDCl3 100 MHz): 39.47, 111.11, 118.21, 119.56,
119.89, 121.22, 122.59, 123.60, 123.68, 124.71, 126.84,
129.34, 130.98, 134.93, 136.71, 146.33.
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3,3ꢃ-Bis(indolyl)-4-nitrophenylmethane (10): IR (KBr,
cm−1): 3404, 3052, 1521, 1346, 1212, 1093, 742; 1H NMR
(CDCl3, 400 MHz) ꢂ: 5.97 (s, 1H), 6.66–6.68 (m, 2H),
6.98–7.02 (t, 2H, J = 8ꢅ05 Hz), 7.16–7.20 (m, 2H),
7.30–7.38 (m, 4H), 7.42–7.49 (m, 2H), 7.99 (br, 2H, NH),
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3,3ꢃ-Bis(indolyl)-4-methylphenylmethane (11): IR (KBr,
cm−1): 3413, 3044, 1457, 1339, 1213, 1092, 1008, 738;
1H NMR (CDCl3, 400 MHz) ꢂ: 2.32 (s, 3H), 5.84 (s, 1H),
6.62–6.63 (s, 2H), 6.98 (t, 2H, J = 8ꢅ05 Hz), 7.08 (d, 2H,
J = 7ꢅ32 Hz), 7.16 (t, 2H, J = 8ꢅ05 Hz), 7.22 (d, 2H,
J = 7ꢅ32 Hz), 7.33 (d, 2H, J = 7ꢅ32 Hz), 7.40 (d, 2H,
J = 7ꢅ32 Hz), 7.84 (br, 2H, NH); 13C NMR (CDCl3,
Delivered by Ingenta to: State University of New York at Binghamton
100 MHz): 21.05, 39.71, 110.98, 119.13, 119.81, 119.91,
IP: 185.13.32.70 On: Tue, 28 Feb 2017 20:06:05
121.82, 123.51, 127.04, 128.52, 128.87, 135.45, 136.61,
140.93.
Copyright: American Scientific Publishers
3,3ꢃ-Bis(indolyl)-4-ethylphenylmethane (12): IR (KBr,
cm−1): 3404, 3051, 1480, 1453, 1211, 1095, 1010, 740;
1H NMR (CDCl3, 400 MHz) ꢂ: 1.30 (t, 3H), 2.39 (q, 2H),
5.82 (s, 1H), 6.61 (s, 2H), 7.01 (t, 2H, J = 8ꢅ05 Hz),
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119.84, 119.95, 121.86, 123.54, 127.08, 128.54, 128.88,
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4. CONCLUSION
A novel La2O3/RGO catalyst for the synthesis of
bis(indolyl)methanes under solvent free conditions at room
temperature has been reported. This procedure offerssev-
eral advantages such as easy catalyst separation from the
reaction medium, a simple workup procedure, catalyst
reusability, short reaction time, and good to excellent prod-
uct yields. In addition, the use of environmentally benign
catalysts and avoidance of hazardous organic solvents are
important features of this method.
Acknowledgments: The authors are grateful to Uni-
versity of Delhi for providing R&D Grant. Sugat Kirti
is Thankful to University Grants Commission (UGC),
J. Nanosci. Nanotechnol. 17, 2508–2514, 2017
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La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst
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Received: 31 March 2016. Accepted: 16 June 2016.
Delivered by Ingenta to: State University of New York at Binghamton
IP: 185.13.32.70 On: Tue, 28 Feb 2017 20:06:05
Copyright: American Scientific Publishers
2514
J. Nanosci. Nanotechnol. 17, 2508–2514, 2017