One dimensional CdS nanostructures: Heterogeneous catalyst for synthesis of aryl-3,3′-bis(indol-3-yl)methanes

Article abstract of DOI:10.1039/c4ra03419h

Herein, we have developed a novel heterogeneous catalytic system for synthesis of bis(indol-3-yl)methanes using one dimensional (1D) CdS nanorods. CdS nanorods were synthesized by a solvothermal reaction technique at 200 °C over 12 h in the presence of et

Full text of DOI:10.1039/c4ra03419h

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One dimensional CdS nanostructures:
heterogeneous catalyst for synthesis of aryl-3,30-
Cite this: RSC Adv., 2014, 4, 28623
bis(indol-3-yl)methanes†
Prakash K. Chhattise,ab Sudhir S. Arbuj,c Kakasaheb C. Mohite,b Sanjay V. Bhavsar,a
a
a
a
*
Amit S. Horne, Kalpana N. Handore and Vasant V. Chabukswar
Herein, we have developed a novel heterogeneous catalytic system for synthesis of bis(indol-3-yl)methanes
using one dimensional (1D) CdS nanorods. CdS nanorods were synthesized by a solvothermal reaction
technique at 200 ꢀC over 12 h in the presence of ethylenediamine as a solvent. The prepared 1D CdS
was characterized using various spectroscopic methods. X-ray diffraction (XRD) revealed the formation
of highly crystalline CdS having a wurtzite structure. FESEM analysis confirms the formation of a rod like
morphology with length around 150 to 200 nm and diameter ꢁ15 nm. TEM also validates the formation
of uniform size one dimensional (1D) CdS nanostructures. The catalytic activity of 1D CdS as a Lewis acid
was investigated for the synthesis of bis(indol-3-yl)methanes (BIMs) with various substituted aldehydes
and indoles within shorter reaction time affording the corresponding product in excellent yield.
Received 15th April 2014
Accepted 16th June 2014
DOI: 10.1039/c4ra03419h
www.rsc.org/advances
ions and tedious work-up procedures, lack of reusability and
loss of expensive metals/ligands.27 All the above reaction
1. Introduction
provides high reaction rate with good selectivity and yield. But
majority of these reactions are carried out using homogeneous
catalysis. Recently, the use of heterogeneous catalysis in organic
synthesis has augmented appreciable interest due to higher
reaction yield, recyclability and milder reaction conditions.28,29
Several researchers have reported the use of oxide based catalyst
for the synthesis of bis(indol-3-yl)methanes. Moreover, carbon–
carbon coupling reactions have been reported using noble
metal loaded on graphene oxide,30 carbon nanotubes,31 cellu-
lose32 etc. Of late the use of metal sulphide nanostructures for
organic transformation have been reported in presence of
light.33 In this regards here in, we have synthesized one
dimensional cadmium sulde (CdS) nanostructures and per-
formed the synthesis of bis(indol-3-yl)methanes under ambient
reaction conditions. To the best of our knowledge this is the
rst report exploring the activity of CdS nanorods as heteroge-
neous catalyst for synthesis of bis(indolyl)methanes having
excellent yield under mild reaction conditions. In the present
work we have reported inexpensive and effective use of hetero-
geneous catalyst for the synthesis of bis(indol-3-yl)methanes
avoiding use of toxic reagents or solvents.
Indole and its derivatives have received signicant attention
from organic chemists and researchers due to its wide range of
biological activities1 such as antibacterial, cytotoxic, antioxi-
dant, insecticidal,2,3 antimicrobial, and antifungal.4 Bis(indol-3-
yl)methanes (BIMs) are used as bioactive intermediates in
pharmaceuticals,5 agrochemicals6 and material science.7 They
are also used as tranquilizers8 in the treatment of cancer, AIDS,
bromyalgia, chronic fatigue, and irritable bowel syndrome.
Various methods have been reported for the synthesis of these
derivatives which involves condensation of indole with various
aldehydes or ketones employing Lewis acids9 or protic acids10 as
a catalyst. The synthesis of bis(indol-3-yl)methanes has been
also reported using diverse range of catalysts like, Ln(OTf)3,11
FeCl3,12 KHSO4,13 In(OTf)3,14 Dy(OTf)3,15 LiClO4,16 I2,17 NBS,18
CAN,19 NaHSO4$SiO2,20 H–Y zeolite,21 ion exchange resin,22
H3PMo12O
40$xH2O,23 clay24 or using different ionic liquids in
association with In(OTf)3 or FeCl3$6H2O.25 Recently, Mulla et al.
reported synthesis of bis(indol-3-yl)methanes using ionic liquid
(EAN) as a catalyst.26 Most of the reported methods suffer from
various disadvantages such as prolonged reaction time, harsh
reaction conditions, use of expensive Lewis acids, toxic metal
aDepartment of Chemistry, Nowrosjee Wadia College, 19, Joag Path, Pune – 411001,
India. E-mail: vvchabukswar@gmail.com; Fax: +912026169108; Tel: +912026162944
bDepartment of Chemistry, Haribhai V. Desai College, Pune – 411002, India
cCentre for Materials for Electronics Technology, Off Pashan Road, Panchwati, Pune –
411008, India
2. Experimental section
2.1. Materials and reagent
Cadmium nitrate (Cd(NO3)2$4H2O), thiourea, ethylenediamine
(EDA, C2H4(NH2)2), of Sisco Research Laboratory (SRL) make
were used for the synthesis of CdS nanostructures. All other
† Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
of selected compounds are shown. See DOI: 10.1039/c4ra03419h
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chemicals solvents were of analytical grade and used as received
without further purication.
3. Results and discussion
3.1. X-ray diffraction analysis
The synthesized CdS nanostructure was analyzed by powder X-
ray diffractometry to identify the crystalline phase. XRD pattern
of CdS prepared at 12 h is depicted in Fig. 1. The diffraction
peaks at 2q ¼ 24.8, 26.5, 28.1, 36.6, 43.6, 47.8 and 51.8ꢀ can be
indexed to (100), (002), (101), (102), (110), (103) and (112) crystal
planes of hexagonal CdS (PDF card 41-1049 JCPDS) respectively.
The intensity of (002) peak is higher than the other diffraction
peaks of (100) and (101), this revealed the high crystalline order
along c-axis and poor crystalline order along x–y plane resulting
one dimensional growth. Additional peaks due to other impu-
rities were not observed indicating formation of highly pure CdS
nanostructure.
2.2. Synthesis of CdS nanorods
The cadmium sulde (CdS) nanorods were synthesized using
solvothermal technique by dissolving Cd(NO3)2$4H2O
(10 mmol) and thiourea (20 mmol) separately in 30 mL of
ethylenediamine (EDA) respectively and mixed together with
constant stirring. The resultant mixture was stirred for 10 min,
transferred into Teon lined stainless steel autoclave and was
further heated at 200 ꢀC for 12 h. The resultant mass was
centrifuged, washed with distilled water several times and
nally with ethanol. It was subsequently, dried at 80 ꢀC for 4 h
in an oven, well grinded in mortar and pestle and used for
further physico-chemical analysis and catalytic study.
3.2. FE-SEM analysis
2.3. Characterisation techniques
The surface morphology of CdS sample was examined by
FESEM, high and low resolution FESEM images are reproduced
in Fig. 2. CdS prepared at 12 h of reaction time reveals the
formation of rod like morphology with uniform size and
smooth surface, the observed thickness of the rods are ꢁ15 nm
and length in the range of 150 to 200 nm (Fig. 2a and b).
X-ray diffraction (XRD) analysis of the synthesized material was
carried out using Bruker AXS model D-8, (10 to 70ꢀ range, scan
rate ¼ 1ꢀ minꢂ1) equipped with a monochromator and Ni-
ltered Cu Ka radiation. UV-Visible absorbance spectrum was
recorded using Shimadzu UV-Vis-NIR spectrophotometer
(Model UV-3600) over a wavelength range of 300 to 900 nm. The
morphological characterization of the samples was accom-
plished using HITACHI S-4800. Microstructure analysis was
carried out using transmission electron microscopy performed
by Technai 20 G2 (FEI, Netherlands) microscope operating at
200 kV.
3.3. TEM analysis
The microstructure of synthesized CdS was investigated by TEM
analysis. TEM images along with selected area electron
2.4. General procedure for synthesis of bis(indol-3-yl)
methanes
In a 25 mL round bottom ask, aldehyde (1.0 mmol), indole (2.0
mmol), cadmium sulphide (5 mol%, catalytic amount) and
methanol (5 mL) was added, reaction mixture was reuxed for
15 min. The progress of the reaction was monitored by TLC
(30% hexane–ethyl acetate). Aer completion of the reaction,
the catalyst was ltered and resulting crude product was
extracted with ethyl acetate, dried over anhydrous sodium
sulfate and the solvent was evaporated under reduced pressure.
The crude product was puried by silica column chromatog-
raphy using hexane–ethyl acetate (90 : 10 v/v) as eluent. 1H NMR
spectra were recorded at Varian 400 MHz NMR spectropho-
tometer with CDCl3 or DMSO-d6 as a solvent. Proton chemical
shis (d) are relative to TMS (d ¼ 0) as internal standard and
expressed in ppm. Coupling constants (J) are given in Hertz.
FTIR spectra were recorded using Perkin-Elmer 1600 A in the
range of 400–4000 cmꢂ1. UV-Visible absorption spectrum of
BIMs was recorded by double beam spectrophotometer (Shi-
madzu, UV-3600) in the range of 300–900 nm. Melting points
were determined on Buchi M-560. Mass spectral data was
obtained from LC-MS (Shimadzu 2010). Reaction was moni-
tored by thin layer chromatography (TLC) on Merck's silica gel
plates (60 F254). The characterization data MP, NMR, IR of
these compounds were found to be identical with those repor-
ted in the literature.
Fig. 1 X-ray diffraction pattern of CdS nanostructures.
Fig. 2 FESEM micrographs of CdS nanostructures with (a) high and (b)
low resolution.
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diffraction (SAED) pattern are depicted in Fig. 3. TEM images of aer prolonged reaction time; the lower yield was due to the
CdS nanostructure indicate the formation of uniform size nano inhomogeneity of reactants. Yield of BIMs in methanol was
rods having diameter 10 to 15 nm and length 100 to 150 nm almost more than 95% whereas, in ethanol it was 65%. Other
(Fig. 3a). SAED pattern revealed the formation of polycrystalline polar aprotic solvents (CH3CN, CH2Cl2, THF, CHCl3, DMF)
CdS and conrm the hexagonal phase of CdS (inset of Fig. 3b). affords moderate yield (Table 2 entry 4 to 7 and 9), while in non-
TEM analysis supports the XRD observations and conrms the polar solvents (1,4-dioxane, toluene) the yield of corresponding
formation of nanorods.
product is low which require longer reaction time (Table 2 entry
8 and 10). Among the studied solvents methanol gave the
excellent yield of bis(indol-3-yl)methanes within 15 min under
reux reaction condition. For further investigation we employed
5 mol% catalyst and methanol as a solvent. To explore the
further applicability of this reaction, we extended the method-
ology for the synthesis of variety of bis(indol-3-yl)methanes
using various aromatic aldehydes with either electron-releasing
or electron-withdrawing substituent's in the ortho, meta and
para positions (Scheme 1), the results are summarized in Table
3. The benzaldehyde and halogenated benzaldehydes gave
almost more than 87% yield (Table 3, entries 1–4).
Triuorobenzaldehyde afforded 93% yield of corresponding
BIM (Table 3, entry 3). Di substituted halogenated benzalde-
hyde under similar reaction condition leads to ꢁ92% yield of
BIM (Table 3, entry 6 and 7). It was observed that the reaction
proceeds at faster rate with all the aldehydes possessing elec-
tron-withdrawing groups on the aromatic ring (Table 3, entry 8)
than aldehydes possessing electron-donating substituent's
(Table 3, entries 9–13) giving good to excellent yield of corre-
sponding products. Additionally, the methodology was further
extended for heterocyclic aldehydes, affording more than 90%
yield (Table 3 entries 16–18). The reusability of catalyst was
studied by the reaction of 4-nitrobenzaldehyde with indole in
3.4. Synthesis of bis(indol-3-yl)methanes using CdS
nanorods as a catalyst
To establish the general reaction conditions for the synthesis of
bis(indol-3-yl)methanes a model reaction was carried out with
p-nitrobenzaldehyde and indole using CdS nanorods as a
catalyst.
In order to nd the appropriate concentration of CdS for BIM
synthesis, the catalyst amount varied from 0.5 mol% to 10
mol%, the results are depicted in Table 1.
With increase in catalyst amount the yield of the reaction
increases from 72% to 96% respectively. Based on these results
for further study the 5 mol% catalyst was used.
With higher catalyst amount (>5 mol%) the yield of the
product was around 96% this indicates that further increase in
catalyst amount did not show any appreciable enhancement in
the yield of desired product. Hence, for further study 5 mol%
catalyst was found to be effective. The inuence of various
protic, polar aprotic and non polar solvents on the yield of BIMs
was also investigated using 5 mol% CdS nanorods and results
are shown in Table 2. The reaction in water gave only 10% yield
Table 2 Influence of solvent on bis(indol-3-yl)methanes synthesisc
Entry
Solvent
Time
Yieldb
1
H2O
4.5 h
>10%
95%
7%
2
MeOH
MeOH
EtOH
Acetonitrile
DCM
15 min
120 min
15 min
40 min
55 min
50 min
45 min
60 min
90 min
40 min
2a
3
65%
89%
82%
80%
88%
76%
60%
40%
4
5
6
7
8
9
10
THF
Fig. 3 (a and b) TEM analysis of CdS nanostructure, inset of (b) is SAED
pattern and high resolution TEM image.
CHCl3
1,4-dioxane
DMF
Toluene
Table 1 Optimization of amount of catalystb
a
Reaction at room temperature. b Isolated yield aer chromatographic
separation. c Reaction conditions: aldehyde (1 mmol), indole (2 mmol),
catalyst (5 mol%) were stirred in 5 mL methanol at reux temperature.
Entry
CdS (x mmol)
Yielda
1
2
3
4
5
6
0.5
1.0
2.5
5.0
7.5
72%
83%
90%
95%
96%
96%
10.0
a
b
Isolated yield aer chromatographic separation.
Reaction
conditions: aldehyde (1 mmol), indole (0.117 g, 2 mmol), catalyst
(x mol%) were stirred in 5 mL methanol at reux temperature, time
15 min.
Scheme 1
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Table 3 Synthesis of bis(indol-3-yl)methanes using CdS nanorodsb
Entry
Aldehye
Product yielda (%)
1
2
3
4
5
6
7
8
Benzaldehye
4-Fluorobenzaldehye
4-Triuorobenzaldehye
4-Bromobenzaldehye
4-Chlorobenzaldehye
5-Bromo-2-uorobenzaldehye
4-Chloro-2-uorobenzaldehye
4-Nitrobenzaldehye
4-Methoxybenzaldehye
4-Hydroxybenzaldehye
3-Hydroxybenzaldehye
4-Methoxy-3-hydroxybenzaldehye
3,4-Dimethoxybenzaldehye
4-N,N-Dimethylbenzaldehye
4-Formylbenzoic acid
87
89
93
92
90
93
92
95
90
90
95
90
90
85
87
92
92
94
9
10
11
12
13
14
15
16
17
18
Scheme 2
5-Bromo-piconilaldehyde
2-Bromoisonicotinaldehyde
2-Bromonicotinaldehyde
a
b
Further, another molecule of indole reacts with intermediate
(ii) followed by subsequent loss of H2O and CdS to give corre-
sponding bis(indol-3-yl)methane (iii).
Isolated yield aer chromatographic separation.
Reaction
conditions: aldehyde (1 mmol), indole (2 mmol), catalyst (5 mol%)
were stirred in 5 mL methanol at reux temperature for 15 min.
We compared our data with the reported results in the
literature and details are given in Table 5. In comparison with
these reagents our approach gives higher yield under ambient
reaction conditions.
presence of CdS as a catalyst for desired time under reux
reaction condition. Aer completion of reaction the catalyst was
recovered, ltered, washed repeatedly with ethyl acetate and
dried. It was reused under optimized reaction conditions and
was found that yield of bis(indol-3-yl)methanes was almost
comparable. The reusability of catalyst checked for four cycles
and the corresponding yields obtained in each cycle is
summarized in (Table 4). The decrease in the catalytic activity of
CdS was might be due to the deactivation of active sites of
catalyst. To conrm the deactivation of catalyst we heated the
CdS recovered aer fourth run at 150 ꢀC in N2 atmosphere for 60
min and again reused for the reaction which gave 94% yield.
This conrmed reusability of the catalyst without loss in
activity.
Overall, the synthesis of BIMs using CdS nanorods with
higher yield was the rst report. In this reaction CdS acts as
Lewis acid, the plausible mechanism is shown in Scheme 2. The
electrophilic condensation reaction most likely proceeds
through activation of a carbonyl group (intermediate i) followed
by attack of indole to give azafulvenium salt (intermediate ii).
3.5. Characterization data
3,30-((4-Fluorophenyl) methylene bis(1H indole)). (Table 3,
1
entry 2); H NMR d (400 Hz, CDCl3, Me4Si) 5.8 (1H, s, CH), 6.6
(2H, s, Ph), 6.93–7.02 (4H, m, Ph), 7.15–7.2 (2H, m, Ph), 7.27–
7.30 (3H, m, Ph), 7.36 (4H, dd, J ¼ 2 and 7.60 Hz, Ph), 7.9(2H, br
ꢀ
s, NH) mp 160–162 C.
3,30-((4-Bromophenyl) methylene bis(1H indole)). (Table 3,
entry 4);1H NMR d (400 Hz, CDCl3, Me4Si) 5.8 (s, 1H, CH), 6.67
(4H, d, Ph), 6.82 (2H, m, Ph), 7.1–7.21 (4H, m, Ph), 7.3 (4H, d, J ¼
8.3 Hz, Ph), 7.8 (2H, bs, NH) mp 120–125 ꢀC.
3,30-((4-Nitrophenyl) methylene bis(1H indole)). (Table 3,
entry 8); d (400 Hz, DMSO-d6, Me4Si) 6 (1H, s, CH), 6.8 (2H, d, J ¼
8.4, CH), 6.7 (2H, d), 6.84 (2H, t, J ¼ 8.0 and 15.2 Hz, Ph), 7.01
(2H, t, J ¼ 7.60 and 14.8 Hz, Ph), 7.1 (2H, d, J ¼ 8.4 Hz, Ph), 7.2
(2H, d, J ¼ 8.0 Hz, Ph), 7.3 (2H, d, J ¼ 8.4 Hz, Ph), 10.8 (1H, bs,
ꢀ
NH); mp 170–174 C.
Table 4 Recyclability of catalystc
Table 5 Comparison between CdS nanorods and other catalysts used
to synthesis bis(indol-3-yl)methanes
Entry
Number of cycles
Yielda
1
2
3
4
Fresh
First
Second
Third
Fourth
Fih
95%
92%
89%
85%
80%
94%
Sr. no. Reagent and solvent
Time
Yield (%) Ref.
1
2
3
4
In(OTf)3/CH3CN
[bmim]BF4
25 min 71
4.5 h 87
40 min 92
5.5 h 97
14
16b
34
5
AlPW12O40/CH3CN
Acidic ionic liquid
immobilized on silica
(ILIS)/CH3CN, rt
CdS nanostructure/
MeOH, reux
6b
35
a
b
Isolated yield aer chromatographic separation. Used CdS catalyst
from fourth recycle, heated at 150 ꢀC for 60 min in N2 atmosphere.
c
5
15 min 95
Present work
Reaction conditions: aldehyde (1 mmol), indole (2 mmol), catalyst (5
mol%) were stirred in 5 mL methanol at reux temperature, time 15
min.
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3,30-((3-Hydroxyphenyl) methylene bis(1H indole)). (Table 3,
RSC Advances
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entry 11); brown solid (from 20% EtOAc–hexane); 1H NMR d
(400 Hz, DMSO-d6, Me4Si) 5.69 (1H, s, CH), 6.5 (2H, d, Ph), 6.78
(2H, m, Ph), 6.86 (2H, t, J ¼ 7.6 and 15.2 Hz, Ph), 7.0 (4H, t, J ¼
8.0 and 16 Hz, Ph), 7.2 (2H, d, J ¼ 8.0 Hz, Ph), 7.3 (2H, d, J ¼ 8.4
ꢀ
Hz, Ph), 9.1 (1H, bs, OH), 10.7 (2H, bs, NH), mp 158–162 C.
3,30-((3,4-Dimethoxyphenyl) methylene bis(1H indole)).
(Table 3, entry 13); 1H NMR d (400 Hz, CDCl3, Me4Si) 3.7 (3H, s,
OMe), 3.8 (3H, s, OMe), 5.8 (1H, s, CH), 6.6 (2H, s, Ph), 6.77 (1H,
d, J ¼ 8.4 Hz, Ph), 6.83 (1H, m, Ph), 6.9 (1H, s, Ph), 7.0 (2H, t, J ¼
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3,30-((4-N,N-Dimethylphenyl) methylene bis(1H indole)).
1
(Table 3, entry 14); brown solid (from 20% EtOAc–hexane); H
NMR d (400 Hz, CDCl3, Me4Si) 2.9 (6H, s), 5.8 (s, 1H, CH), 6.67 (4H,
d, Ph), 6.9 (2H, m, Ph), 7.2–1.12 (4H, m, Ph), 7.3 (2H, d, J ¼ 8.4 Hz,
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A simple methodology for an efficient synthesis of a variety of
biologically active bis(indol-3-yl)methanes using one dimen-
sional CdS nanostructures as a heterogeneous catalyst is
reported. It offers short reaction time, high conversions and
simple and easy workup procedure compared to the traditional
methods of synthesis.
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Acknowledgements
Authors sincerely acknowledge University Grants Commission,
New Delhi, ISRO University of Pune for nancial assistance and
C-MET, Pune for characterization. We also thank Nowrosjee
Wadia College Pune for providing lab facility.
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