Development of Br?nsted-Lewis acidic solid catalytic system of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides for the preparation of bis(indolyl)methanes

Article abstract of DOI:10.1016/j.apcata.2014.12.013

Three new heterogeneous catalysts of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides [Msim][X] (where X = [FeCl₄]^-, [ZnCl₃]^-, [CuCl₂]^-) were synthesized containing both Lewi

Full text of DOI:10.1016/j.apcata.2014.12.013

Accepted Manuscript
Title: Development of Br o¨ nsted-Lewis Acidic Solid Catalytic
System of 3-Methyl-1-Sulfonic Acid Imidazolium Transition
Metal Chlorides for the Preparation of Bis(indolyl)methanes
Author: Pinky Gogoi Arup Kumar Dutta Parishmita Sarma
Ruli Borah
PII:
S0926-860X(14)00764-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2014.12.013
APCATA 15151
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
4-8-2014
3-12-2014
5-12-2014
Please cite this article as: P. Gogoi, A.K. Dutta, P. Sarma, R. Borah, Development
of Br o¨ nsted-Lewis Acidic Solid Catalytic System of 3-Methyl-1-Sulfonic Acid
Imidazolium Transition Metal Chlorides for the Preparation of Bis(indolyl)methanes,
Applied Catalysis A, General (2014), http://dx.doi.org/10.1016/j.apcata.2014.12.013
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Highlights


 Brönsted and Lewis acidic three heterogeneous 3-methyl-1-sulfonic acid imidazolium
transition metal chlorides were synthesized.
 All compounds were characterized by NMR, FT-IR, RAMAN, XRD, SEM-EDX, BET,
AAS, powder XRD and elemental analysis techniques.



Acidity of these compounds was measured by Hammett function.
 Higher catalytic activity were observed in solution for the preparation of bis(indolyl)methane
at room temperature.

 All compounds were recycled for three consecutive runs without reactivation.
1
Page 1 of 30

Development of Brönsted-Lewis Acidic Solid Catalytic System of 3-Methyl-1-
Sulfonic Acid Imidazolium Transition Metal Chlorides for the Preparation of
Bis(indolyl)methanes
Pinky Gogoi, Arup Kumar Dutta, Parishmita Sarma and Ruli Borah*
Department of Chemical Sciences, Tezpur University,
Napaam-784028, Tezpur-Assam, India
*
To whom the correspondence should be addressed:
Tel.: +91 3712 267007/8/9
Fax: +91 3712 267005/6
E-mail: ruli@tezu.ernet.in
Addresses:
Dr Ruli Borah
Department of Chemical Sciences
Tezpur University (A Central University)
Napaam, Tezpur 784028
Assam, India
2
Page 2 of 30

Development of Brönsted-Lewis Acidic Solid Catalytic System of 3-Methyl-1-
Sulfonic Acid Imidazolium Transition Metal Chlorides for the Preparation of
Bis(indolyl)methanes
Pinky Gogoi, Arup Kumar Dutta, Parishmita Sarma and Ruli Borah*
Department of Chemical Sciences, Tezpur University,
Napaam-784028, Tezpur-Assam, India
Abstract
Three new heterogeneous catalysts of 3-methyl-1-sulfonic acid imidazolium transition metal
-
-
-
chlorides [Msim][X] (where X= [FeCl
4 3 2
] , [ZnCl ] , [CuCl ] ) were synthesized containing both
Lewis and Brönsted acidic sites. These solid acids were fully characterized by various analytical
1
13
tools such as FT-IR, Raman, HNMR, CNMR, SEM-EDX, TGA, Powder XRD, AAS, BET,
Uv-vis and elemental analysis. All of them were efficiently utilized as reusable catalysts (5 -10
mol %) for the selective synthesis of bis(indolyl)methane derivatives in ethylacetate at room
temperature within short time with excellent yields.
Key words: Lewis acid, Brönsted acid, heterogeneity, recyclability, 3-methyl-1-sulfonic acid
imidazolium transition metal chlorides, bis(indolyl)methane
1. Introduction
Acid catalysts are vital in various organic transformations [1-4]. Although, traditional Brønsted
or Lewis acid catalysed reactions are highly efficient but separation of them from the reaction
mixture in homogeneous phases posses a limitation to their use thus resulting as non-recyclable
acid waste. In these contexts, a number of solid acids have shown great potential to replace them
as they offer attractive recyclability and environmental acceptability [5-12]. The design of a
3
Page 3 of 30

catalyst with high activity and selectivity, which is benign to the environment and easily
recovered, is an interesting and rapidly developing area in chemistry [13-16, 4]. In recent years,
many reports have been spotted utilizing ionic liquids both as catalysts and medium in numerous
organic conversions. They can be designed as homogeneous, heterogeneous or multiphase
catalytic frameworks as per required reactivity to run a reaction in combination with various
metals salts, Lewis acids, Brønsted acids, and polymers etc [13-24]. Development of prospective
heterogeneous catalytic systems is our best interest. As we know, both Lewis and Brönsted acids
play important roles in acid catalysed processes [19-20]. These considerations incited us to
construct three new catalytic frameworks of 3-methyl-1-sulfonic acid imidazolium transition
metal chlorides [Msim][X] ionic compounds as solid acids with dual acid sites, where X=
-
-
-
[
4 3 2
FeCl ] , [ZnCl ] , [CuCl ] : a series of 3-methyl-1-sulfonic acid imidazolium transition metal
chlorides. The catalytic performance of these solid acids was examined for the preparation of
various bis(indolyl)methane derivatives at ambient conditions using the reaction of indole with
different aromatic aldehydes. Bis(indolyl)methanes, indole and their derivatives are known as
important intermediates in organic synthesis and pharmaceutical chemistry [25-27]. A large
number of synthetic methods have been reported in the literature with various limitations for the
preparation of bis(indolyl)methanes in presence of Lewis or protic acids [28-30]. Some modified
methodologies described the dual applications of ionic liquids for this synthesis [31-34]. Herein,
we are interested to report the preparation, characterization of 3-methyl-1-sulfonic imidazolium
metal chlorides as solid acid catalysts and their applications in the efficient and rapid synthesis of
bis(indolyl)methanes (5).
2
. Experimental
.1. General remarks
2
4
Page 4 of 30

All chemicals were purchased from different chemical suppliers and used as received without
1
13
any further treatment. The HNMR and CNMR were recorded on a JEOL 400 MHz
spectrometer (δ in ppm) in DMSO-d and CDCl solvents. Nicolet Impact-410 spectrometer was
used to record FT-IR spectra. The Hammett plot of the solid acids was determined on an UV
550 spectrophotometer using 4-nitroaniline as the basic indicator. The thermogravimetric
6
3
2
analysis of the three solid acids was performed on Shimadzu TGA 50. All elemental analyses
were obtained from Perkin Elmer 20 analyzer. The scanning electron microscopy (SEM)
analyses were carried out using a JEOL JSM-6390LV SEM, equipped with an Energy-
Dispersive X-ray analyzer. The powder X-ray diffraction patterns were recorded on a Rigaku
Multiflex instrument using a nickel-filtered CuKα (0.15418 nm) radiation source and
scintillation counter detector. Melting points were recorded on a Buchi-545 apparatus. The laser
micro-Raman spectroscopic measurement was conducted in a Horiba LabRAM HR spectrometer
equipped with a He−Ne laser that has an excitation wavelength of 514.5 nm. The BET surface
area of 2a was measured in Quantachrome NovaWin apparatus. Atomic absorption analyses of
the solid acids were performed on an AAS, model Analyst 200, Thermo iCE 3000 series. The
spectral data of known bis(indolyl)methanes (5) were compared with the literature data [35-36] .
2
.2.
Preparation of 3-Methyl-1-Sulfonic Acid Imidazolium Metal Chlorides
-
-
-
-
[
Msim][X], where X = [FeCl ] , [ZnCl ] , [CuCl ]
4 3 2
2 2
To a stirred solution of 1-methyl imidazole (10 mmol) in dry CH Cl (30 mL), chlorosulfonic
acid (10 mmol) was added drop wise over a period of 5 minutes at ice bath. The reaction mixture
was stirred for another 45 minutes to make certain completion. After the reaction was over
2 2 2 2
CH Cl layer was decanted, the residue was washed with dry CH Cl (3×20 mL) and dried under
powerful vacuum to give 3-methyl-1-sulfonic acid imidazolium chloride [Msim]Cl as viscous
5
Page 5 of 30

pale yellow oil in 98% yield. Then the solid [Msim][X] acids were prepared by stirring
equimolar amounts of 3-methyl-1-sulfonic acid imidazolium chloride and the respective metal
3 2
chlorides(FeCl , ZnCl and CuCl ) in an oil bath at 50°C under nitrogen atmosphere for 1
hour. The reaction mixture was stirred for an extra one hour to ensure complete impregnation of
the metal halides over the basic moiety [Msim]Cl. The resultant solid residues were dried under
powerful vacuum to get the respective [Msim][X] in 97-99 % yields and stored in vacuum
desicator.
2
.3.
Characterisation data for [Msim][X](2):
[
Msim][FeCl ]2a:Green Solid, 98% yield ; Mp. 130.2°C ; FT-IR (KBr): 3354, 3283 ,2894,
4
-
1
1
2
848, 1629, 1444, 1222, 1075, 1000, 810,752, 618 cm ; H NMR(DMSO-d
6
, 400 MHz):
SN FeCl
δ14.5(s, 1H) , 8.91(s, 1H), 7.56-7.53(s, 2H), 3.74(s, 3H); CHN analysis(%): C
4
H
7
O
3
2
4
:
Cal. C 13.30 , H 1.93, N 7.76 ; Found C 13.27, H 2.08, N 7.74.
[
Msim][ZnCl ]2b:Off White Solid, 97 % yield; Mp. 132 °C; FT-IR(KBr): 3427, 3327, 2894,
3
-
1 1
1
1
1
1
729, 1623, 1429, 1218, 1070, 1006, 855, 764, 592 cm ; HNMR(DMSO-d
6
, 400 MHz):14.2(s,
, 100 MHz): 136.3,
4 7 3 2 3
H O SN ZnCl : Cal. C 14.3, H 2.08, N 8.36; Found C
1
3
H), 8.97(s, 1H), 7.62(s, 1H), 7.58(s, 1H), 3.99 (s, 3H); C NMR (DMSO-d
6
23.7, 120.2, 39.7; CHN analysis(%): C
4. 26, H 2.50, N 8.30.
[
Msim][CuCl ] 2c:Dark brown Solid, 99 % yield ; Mp. 110 °C ; FT-IR (KBr): 3430, 3368,
2
-
1
1
2
1
1
989, 1628, 1447, 1198, 1068, 1007, 877, 754, 580cm ; H NMR(DMSO-d
6
, 400 MHz): δ
,100 MHz): δ 136.2, 123.7,
2
: Cal. C 16.14, H 2.35, N 9.41 ; Found C 16.10
1
3
4.1(s, 1H), 8.84(s,1H), 7.49(s, 2H), 3.88(s,3H); C NMR (DMSO-d
6
20.2, 36.1 ;CHN analysis(%): C SN CuCl
4
H
7
O
3
2
,
H 3.28 ,N 9.38.
.4.
2
General Procedure for the Synthesis of Bis(indolyl)methanes (5) :
6
Page 6 of 30

A mixture of aromatic aldehyde (1 mmol), indole (2 mmol) and the solid acid (5 or 10 mol%)
in 1 mL of ethylacetate was magnetically stirred in a 50 mL round bottomed flask at room
temperature fitted with a calcium chloride guard tube. The progress of the reaction was
monitored by thin layer chromatography using petroleum ether and ethylacetate as solvent
system. After completion of the reaction, the product was dissolved in ethylacetate and then
filtered to collect the solid catalysts for recycling. The product was isolated from the solution by
evaporation of the solvent. The crude product was recrystallized from aqueous ethanol to get
analytically pure product.
3
. Results and discussion
In context with the development of environmentally benign methodologies [37-38], we
synthesized three new compounds of 3-methyl-1-sulfonic acid imidazolium metal chlorides (2a,
2
b & 2c) from the 1:1 mixture of 3-methyl-1-sulfonic acid imidazolium chloride (1) and three
3 2
transition metal chlorides as Lewis acids (FeCl , ZnCl and CuCl) at 60°C in an inert atmosphere
for two hour stirring (Scheme 1).
<
Scheme 1>
Characterization of catalysts(2a-c)
.1.1. Preliminary spectral analysis
3
3
.1.
The corresponding FT-IR spectral data of the catalysts are presented in Fig.1. The presence of
SO H groups were identified from the characteristic strong FT-IR absorptions at 1198-1222,
068-1075 and 580-618 cm corresponding to S-O symmetric and antisymmetric stretching and
-
3
-1
1
-1
bending vibrations respectively. A peak at 1623-1629 cm is due to –C=N- stretching vibrations.
-1
The band near 1429-1447cm expressed the out of phase bending vibrations of C-H bonds of
methyl group [ 39].We also observed the N-S stretching and in plane ring bending vibrations in
7
Page 7 of 30

-1
-1
the same region at 810-877 cm . The peak around 752-764cm is vibrations of out-of- plane
-1
1
ring C-H bending [40]. The broad –OH stretching vibrations appeared at 3000-3450 cm .The H
3
NMR spectra of these acids showed the acidic -SO H protons in the range of 14.1-14.5 ppm as
1
singlet. We got the H NMR spectra of 2a in dilute solution of DMSO-d6 solvent where the
1
3
13
concentration of 2a may be insufficient to produce C NMR spectra of the solid acid. The C
NMR spectra of 2b and 2c confirmed the existence of 3-methyl imidazolium moiety in these
acids. The elemental analyses further supported the formation of the catalysts.
<
Fig. 1>
3
.1.2. Raman Analysis
-1
In Fig. 2, the Raman spectrum of 2a displayed a strong peak at 339 cm which coincides very
-
closely to the literature value for [FeCl
4
] species [41]. The Raman spectra of [Msim][ZnCl
3
](2b)
-1
-1
indicated two broad shoulder at 265 cm and 323 cm which can be assigned to a doubly
2-
charged [Zn
2
Cl
6
] anion as supported by literature data [42-45]. Since there is no experimental
-
evidence for the existence of [ZnCl
3
] in either the solid or liquid state. In case of
-1
-1
[Msim][CuCl
2
](2c) catalyst, we got two absorption in the region 266-295 cm and at 423 cm
-
-
which can be assigned for the mixtures of [CuCl
2
] along with minor amount of [Cu
2
Cl
3
]
anions according to the supportive information of Yoke et al [46]. In literature, the existence of
-
-1
-
[
CuCl
2
] anions was evidenced by the presence of strong peaks at300 cm and 412 cm
corresponding to symmetric and antisymmetric stretching [47]. The formation of [Cu Cl
with the starting CuCl.
1
-
2
3
]
anions may be possible in presence of small amount of CuCl
Fig. 2>
2
<
3
.1.3. Surface morphology
To study the surface morphology, SEM measurements were carried out and the images are
8
Page 8 of 30

provided in Fig. 3. SEM results showed that catalyst particles have no definite morphology and
size on their surfaces. These showed different structural arrangements of the 3-methyl 1- sulfonic
acid imidazolium transition metal chlorides in solid state. The SEM images of (a) points the
surface to be a rough one. The SEM image of (b) depicts the surface to be formed of some
aggregates rather than detached particles and not by a continuous film. In case of (c) the surface
is more even than (a) and (b). In some parts, these solid acids form some spherical clotting like
structure.
<
Fig. 3>
3
.1.4. EDX analysis
Energy dispersion X-ray (EDX) analyses of the catalysts confirmed the existence of respective
metal halides on the surface of the basic moiety [Msim]Cl (Fig.3) devoid of any other impurities.
3
.1.5. TGA analysis
TGA analysis of the three catalysts was carried out to check for the thermal stability. The TGA
curve for 2a suggested three weight loss steps (Fig. 4). Initial 13 % weight loss below 100 °C
nd
rd
may be attributed to the physical evaporation of absorbed moisture. The 2 and 3 steps
observed in the temperature regions of 115-150 °C and 150-346 °C respectively. The TGA
curves of 2b and 2c represented negligible amount of absorbed moisture in the compounds. 2c
displayed thermal stability up to 376 °C. The highest thermal stability among the three acids was
observed up to 444 °C for 2b.
<
Fig. 4>
3
.1.6. Powder X-ray Diffraction analysis
Fig. 5 displayed the XRD pattern for 2b and 2c. In XRD analysis of (2b) [Msim][ZnCl3]
9
Page 9 of 30

diffraction peaks centred at 2θ= 26.1°, 29.1°, 35.6° & 41.2 characteristic of ZnCl
which matches well with XRD database (JCPDS card no. 74-0517) and they could be assigned to
101), (102), (103), (104) reflections respectively. The observed broadening of the peaks may be
due to loss of some percent crystallinity of ZnCl
during the impregnation process. For (2c)
Msim][CuCl ] solid acid , diffraction peaks at 2θ= 28.5°, 47.4° were displayed which may be
attributed to (111) & (220) reflections respectively and they are characteristic of crystalline CuCl
JCPDS 06-0334). Two additional diffraction peaks at 2θ= 25.1° & 26.8° were obtained which
may be attributed to the presence of considerable amount of CuCl in the starting CuCl. By
comparing the diffraction peaks with the standard chart for CuCl, no significant loss in
2
are obtained,
(
2
[
2
(
2
crystallinity were observed. The higher hygroscopic nature of (2a)[Msim][FeCl
TGA curve (Fig. 4) may limited this acid to generate accurate XRD data.
] as shown by
4
<
Fig. 5>
3
.1.7. Atomic Absorption Spectroscopy analysis
AAS analysis of the solid acids was performed to quantify the metal contents (Table 1). For
each of the three acids, 10 ppm solution of the compounds in water was prepared. The obtained
results were found to be well equipped with the original metal content in the respective
imidazolium metal chlorides and ensures the 1:1 ratio for the basic moiety [Msim]Cl and the
respective metal halides.
<
Table 1>
3
.1.8. BET Analysis
The nitrogen adsorption-desorption isotherm was measured only for 2a at the temperature of
2
liquid N with a Quantachrome Nova Win apparatus. The surface area of ferric chloride
containing compound was found to be negligible as determined by the BET method which may
1
0
Page 10 of 30

be attributed to non-porous nature of 2a.
3
.2. Acidity Measurement by Hammett function
The Hammett plots of the three solid acid catalysts were determined on an UV-Vis
spectrophotometer (Fig. 6) using p-nitroaniline as the basic indicator to determine the brönsted
acidity of the catalysts [48-49].The absorbance of the indicator [I] in ionic salts solutions were
+
reduced as the acidity of catalysts increases. The protonated form [HI] of the indicator didn’t
o
appear due to low molar absorptivity. The Hammett function H for the solid acid catalysts was
+
measured from the absorption differences [I]/[IH] using equation-1[50].
o
＋
H ＝pK(I)aq＋log[I]/[IH] (1)
Where pK(I)aq is the pKa value of the p-nitroaniline indicator in aqueous solution. The
procedure required the mixing of equal concentration of 4-nitroaniline (5 mg/L, pKa＝0.99) and
catalyst (5 mmol/L) in ethanol solution. The indicator displayed maximum absorbance at 378nm
in ethanol. The Hammett plot expressed the following decreasing Brönsted acidity order of the
0
three
catalysts
against
their
observed
H
values
as:
4
[Msim][FeCl ]>
[
Msim][ZnCl
3
]>[Msim][CuCl ].
2
<
Fig. 6>
The presence of both Lewis and Brönsted acidic sites in these solid acids make them more
suitable to perform as reactive heterogeneous catalysts in organic synthesis.
3
.3.
Catalytic Performance
1
1
Page 11 of 30

After full characterization of the these acids, we investigated the activity of these compounds as
reusable heterogeneous acid catalysts for the synthesis of bis(indolyl)methanes in a typical
reaction procedure utilizing indole (1 mmol) and aromatic aldehyde(0.5 mmol) in
dichloromethane (1 mL) at room temperature stirring. The relative acidity order among the three
solid catalysts for the model reaction under optimized conditions were identical with the order of
Hammett plot. The catalysts can be recovered as solid residue after dissolving the mixture in
dichloromethane and then filtration.
<
Table 2>
From Table 2, it was observed that only 5 mol % of the more acidic [Msim][FeCl
was sufficient to produce 98 % of product 5a in 15 mins under mild condition (table 3, entry
). For the less acidic [Msim][ZnCl ] and [Msim][CuCl ] 10 mol % of catalysts was required to
] catalyst
4
1
3
2
give excellent yields during 60 - 75 mins reaction time (Table 2, entries 2-3). The higher
TON/TOF of 2a under optimized conditions distinctly expressed the superior catalytic
behaviour of 2a for the synthesis of bis(indolyl)methane derivative 5a (Table 2, entry 1).
We also studied the effect of solvents on the activity of [Msim][FeCl
reaction in different polar (EtOH,CH CN,EtOAc) and non-polar solvents (CHCl
ambient temperature using 5 mol % of the catalyst. The reactions proceeded well with 97-98 %
yields in CH Cl , CH CN, CHCl and EtOAc within 10 -15 minutes. In EtOH, only 60% yield
4
] for the above model
3
3
, CH Cl ) at
2
2
2
2
3
3
was obtained. By considering the environmental risk, disposal issues and time frame we selected
ethylacetate as the best solvent for carrying out the reactions with the optimized amount of
catalysts. The above optimized conditions were extended with various types of aromatic
aldehydes using the three acid catalysts for the synthesis of other bis(indolyl)methane
1
2
Page 12 of 30

derivatives. (Table 3).
<
Table 3>
The results of Table 3 clearly represented the higher catalytic activity of these Brönsted -Lewis
acidic sites containing solid acids. The reusability of the solid acids were expressed by the bar
diagram (Fig.7) for three consecutive runs for the reactions of indole (1 mmol) and benzaldehyde
in ethylacetate solution. Reclyclabilty study indicated the high catalytic activity of the three
catalysts even after the third run without reactivation.
<
Fig. 7>
4
.
Conclusion
In summary, we have developed a new class of solid acids of 3-methyl-1-sulfonic acid
imidazolium transition metal chlorides as heterogeneous catalysts containing both Lewis and
Brönsted acidic sites from the reaction of transition metal chlorides with 3-methyl-1-sulfonic
acid imidazolium chloride ILs. The resulting catalysts were characterized in terms of
composition, structure, thermal stability, and morphology. The efficiency of the newly
synthesized catalysts was evaluated for the selective synthesis of bis(indolyl)methane derivatives
in ethylacetate at ambient temperature within short time with excellent yields. The obvious
advantages of these catalytic systems are high thermal stability, high catalytic activity, simple
operation coupled with easy work up procedure, recyclability, and low cost. We believe that
these green features will award supremacy to these Brönsted-Lewis acidic catalysts over the
traditional ones in organic synthesis and will find extensive application in the catalysis field.
1
3
Page 13 of 30

Acknowledgement
The authors are thankful to Sophisticated Analytical Instrumentation Centre, T.U. and Central
Instrument Facility, IIT-Guwahati for analyses of various samples for this work and also to
CSIR, New Delhi, India for granting a research project no. 02(0067)/12/EMR-II to R. B.
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27]T. Doroshenko, S. Samsoniya, L. Chikvaidze, Bisindole Derivatives: Synthesis of Bis(1H–
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29] M.A. Zolfigol, P. Salehi, M. Shiri, Z.Tanbakouchian, Catal. Commun. 8 (2007) 173–178.
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31] S.J. Ji, M.F. Zhou, D.G. Gu, S.Y. Wang, T.P. Loh, Synlett 13 (2003) 2077–2079;
32] X. Mi, S. Luo, J. He, J.P. Cheng, Tetra. Lett. 45 (2004) 4567–4570.
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92.
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[
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50] The calculation of Hammett functions were observed using the equation – (1) and all the
[
values were supplied as table in the supporting file.
1
7
Page 17 of 30

Legends
Scheme 1: Synthesis of 3-methyl-1-sulfonic acid imidazolium metal chlorides
Fig. 1: FT-IR spectra of 3-methyl-1-sulfonic acid imidazolium metal chlorides
Fig. 2: Raman spectra of [Msim][FeCl ](2a),[Msim][ZnCl ](2b)and[Msim][CuCl ](2c)
4
3
2
Fig. 3: SEM photographs [ (a), (b) & (c)] and EDX analysis [(d), (e) & (f)] of [Msim][FeCl4],
Msim][ZnCl ] and [Msim][CuCl
[
3
2
]
Fig. 4: TGA patterns of 3-methyl-1-sulfonic acid imidazolium metal chlorides
Fig. 5: Powder XRD patterns of (2b) [Msim][ZnCl ] and (2c) [Msim][CuCl ]
3
2
Table 1: Atomic absorption analysis data of the three solid acids
Fig. 6: Hammett plot of the three solid acids
Table 2:Optimization of the amount of solid acid catalysts for the preparation of
bis(indolyl)methane derivatives at room temperature
Table 3: Synthesis of bis(indolyl)methane derivatives 5 using the solid acid catalysts
Fig. 7: Bar diagram for reusability of the solid acids
1
8
Page 18 of 30

N
N
N
H C
3
ClSO H
3
r.t., 30 mins
N SO H
3
CuCl2-
N
CuCl
N SO H
3
FeCl -
4
N SO H
Cl-
3
FeCl3
N
H C
3
00C, 2 h
H C
3
5
H C
3
0
50 C, 2 h
1
2
c
2a
Msim][FeCl4]
ZnCl2
[
[
Msim][CuCl2]
00C, 2 h
5
N SO H
ZnCl -
3
3
N
H C
3
2
b
[Msim][ZnCl3]
Scheme 1: Synthesis of 3-methyl-1-sulfonic acid imidazolium metal chlorides
1
9
Page 19 of 30

Fig. 1: FT-IR spectra of 3-methyl-1-sulfonic acid imidazolium metal chlorides
2
0
Page 20 of 30

Fig. 2: Raman spectra of [Msim][FeCl ](2a),[Msim][ZnCl ](2b)and[Msim][CuCl ](2c)
4
3
2
2
1
Page 21 of 30

(a)
(b)
(c)
(d)
(e)
(f)
Fig. 3: SEM photographs [ (a), (b) & (c)] and EDX analysis [(d), (e) & (f)] of [Msim][FeCl4],
Msim][ZnCl ] and [Msim][CuCl
[
3
2
]
2
2
Page 22 of 30

Fig. 4: TGA patterns of 3-methyl-1-sulfonic acid imidazolium metal chlorides
2
3
Page 23 of 30

Fig. 5: Powder XRD patterns of (2b) [Msim][ZnCl ] and (2c) [Msim][CuCl ]
3
2
2
4
Page 24 of 30

Table 1: Atomic absorption analysis data of the three solid acids
Entry
Sample
Molecular
weight
Atomic weight of
the metal
Amount of the metal (mg/L)
Experimental Calculated
(g/mol)
(g/mol)
1
2
3
[Msim][FeCl
4
]
360.98
296.50
335.01
55.85
63.50
65.38
1.56
2.18
1.96
1.54
2.14
1.95
[Msim][CuCl
2
]
[Msim][ZnCl
3
]
2
5
Page 25 of 30

Fig. 6: Hammett plot of the three solid acids
2
6
Page 26 of 30

Table 2: Optimization of the amount of solid acid catalysts for the preparation of
bis(indolyl)methane derivatives at room temperature
PhCHO
2
2a (5mol%) /2b /2c (10mol%)
N
H
HN
NH
5a
3
4a
a
-
Entry
ILs
Amount
mol%)
Time(mins)
Yield(%)
TON/TOF(h
1
b
)
(
5a
1
2
3
[Msim][FeCl
[Msim][ZnCl
[Msim][CuCl
4
]
50/25/10/5
50/25/10/5
50/25/10
3/5/10/15
15/30/60/75
30/45/75
98
97
97
19.6/78.4
9.7/9.7
3
]
2
]
9.7/7.8
a
b
Using 2 mmol of indole and 1mmol of benzaldehyde in dichloromethane; Turnover number (TON) = (molar
amount of product)/(molar amount of catalyst). Turnover frequency (TOF) = TON/ (time in h) which were
calculated only for the optimized conditions.
2
7
Page 27 of 30

Table 3: Synthesis of bis(indolyl)methane derivatives 5 using the solid acid catalysts
CHO
2
2a (5mol%) /2b /2c (10mol%)
r.t. stirring, CH Cl (1mL)
N
H
2
2
X
HN
NH
3
4a
5
a
Where X = electron withdrawing or donating groups
a
a
Entry
X
Time(method)
mins
Yield(%)
Mp(°C)
Found
Mp(°C)
reported
1
2
3
4
5
6
7
C
6
H
5
4a
4-OMe 4b
4-NO
4c
4-Cl 4d
-CH=CH-4e
15[A]/60[B]/75[C] 98/97/97 5a
10[A]/20[B]/40[C] 97/97/96 5b
20[A]/30[B]/45[C] 97/96/96 5c
20[A]/30[B]/50[C] 98/97/97 5d
10[A]/15[B]/40[C] 97/96/95 5e
120.3
185.2
242.4
90
124–126[35]
195[36]
2
245–246[35]
87–89[36]
94–96[35]
227-229[36]
96–98[35]
C
6
H
5
95
2-naphthaldehyde 4f 30[A]/60[B]/90[C] 98/97/95 5f
4-CH
4g 10[A]/15[B]/30[C] 97/96/94 5g
228
99
3
a
Methods : [A] Using 5 mol % of 2a as catalyst ; [B] Using 10 mol % of 2b as catalyst ; [C] Using 10 mol% of
c as catalyst
2
2
8
Page 28 of 30

Fig. 7: Bar diagram for reusability of the solid acids
2
9
Page 29 of 30