Application of natural kaolin supported sulfuric acid as an ecofriendly catalyst for the efficient synthesis of bis(indolyl)methanes

Article abstract of DOI:10.1080/15533174.2011.615787

The acidified kaolin with sulfuric acid (2% w/w) is introduced as a novel, mild, highly efficient, easily prepared, very cheap, recyclable and ecofriendly catalyst in organic synthesis. This catalyst has been used successfully for the synthesis of bis(ind

Full text of DOI:10.1080/15533174.2011.615787

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:905–908, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.615787
Application of Natural Kaolin Supported Sulfuric Acid
as an Ecofriendly Catalyst for the Efficient Synthesis
of bis(indolyl)methanes
1
2
2
Zinat Gordi, Shaghayegh Eshghi, and Shohreh Eshghi
1
Department of Chemistry, Payame Noor University, Tehran, Iran
School of Medicine, Mashhad University of Medical Sciences, Mashhad 91775-1436, Iran
2
for the preparation of bis(indolyl)methanes through condensa-
The acidified kaolin with sulfuric acid (2% w/w) is introduced tion of aldehydes with indoles (Scheme 1).
as a novel, mild, highly efficient, easily prepared, very cheap, recy-
clable and ecofriendly catalyst in organic synthesis. This catalyst
has been used successfully for the synthesis of bis(indolyl)methanes
via the condensation of indoles with aldehydes at room tempera-
ture. The simplicity, efficiency, mild reaction condition, high yield
of product, easy work up procedure, and recyclability of the cata-
lyst are the advantages of this procedure.
R
O
2
Kaolin / H SO4
(2 % w/w)
+
X
R
H
CH Cl , rt
N
H
2
2
N
N
X
X
H
H
2
2
a) X = H
b) X = Me
3a-3m
Keywords kaolin, heterogeneous catalyst, bis(Indolyl)methanes,
SCH. 1.
Indoles, aldehydes
INTRODUCTION
Indole derivatives are present in many substances commonly EXPERIMENTAL
found in nature,[
1, 2]
as well as in many compounds with phar-
All materials and solvents were purchased from Merck
Bis(Indolyl)methane and Fluka. Melting points were determined in open capillary
[3–5]
macological and biological activities.
derivatives are very important compounds as they display tubes in an Electrothermal IA 9700 melting point apparatus.
[6, 7]
1
various biological and pharmaceutical activities.
There-
H-NMR spectra were recorded on a Bruker-100 MHz and
fore, a number of synthetic methods for preparation of 500 MHz instruments using tetramethylsilane (TMS) as an
bis(indolyl)alkane derivatives has been reported in the literature internal standard. IR spectra were recorded on a Shimadzu-IR
by reaction of indole with various aldehydes and ketones in the 470 spectrophotometer.
[
8]
[9, 10]
presence of protic acid, Lewis acid,
heterogeneous acidic
[
11, 12]
[13]
[14]
[15] Preparation of the Acidified Kaolin with Sulfuric Acid
catalysts,
and reagents such as I2,
NBS,
CAN,
ionic liquids,[
16–19]
[20]
(2% w/w)
and heteropolyacid.
However, there are
2
0 mL n-Hexane and (0.15 g, 0.08 mL) concentrated sulfuric
still some drawbacks to these catalytic systems, including the
requirement for large amounts of catalyst, long reaction times,
low yield of product, tedious workup leading to the generation
of large amount of toxic waste, highly expensive catalysts and
drastic reaction conditions for catalyst preparation. For these
reasons, a superior catalyst which is cheap, less toxic, and eas-
ily available and air stable is desirable. However, to the best
of our knowledge, there is no report on the use of kaolin as a
catalyst for this conversion. In this paper we will report natural
kaolin as an efficient, mild, inexpensive and recyclable catalyst
acid were added to natural kaolin (7.5 g) in a round bottomed
flask respectively and stirred for 1h. Then the mixture was fil-
tered and dried. The prepared acidified kaolin (2% w/w), was
stored for further applications.
General Procedure for the Synthesis of bis(Indolyl)
methanes
To a solution of indole (2 mmol) and aldehyde (1 mmol) in
dichloromethane (5 mL), the acidified kaolin (2% w/w) (75 mg),
was added and stirred vigorously at room temperature until the
disappearance of the starting materials (15–35 minutes). After
completion of the reaction as monitored by TLC, the precip-
itate was filtered and washed with cold mixture of n-hexane-
dichloromethane (1:1, 4 mL). The product was washed from
Received 24 June 2011; accepted 16 August 2011.
Address correspondence to Zinat Gordi, Department of Chemistry,
Payame Noor University, Tehran, Iran. E-mail: gordi z@yahoo.com
905

906
Z. GORDI ET AL.
TABLE 1
Synthesis of bis(indolyl)methanes in the presence of kaolin / sulfuric acid (2% w/w).
◦
Mp/ C
Reported [lit.]
Entry
1
Aldehyde
X
H
Producta
Time (min.)
25
Yield (%)b
92
Found
O
3a
140–141
140–142 [25]
H
O
H
2
3
4
H
H
H
3b
3c
3d
20
20
20
90
85
88
77–78
74–75
78–80 [26]
74–76 [19]
Cl
O
H
Cl
O
217–218
217–219 [19]
H
O N
2
O
O
5
H
3e
20
90
219–220
218–220 [25]
O N
2
H
H
6
7
H
H
H
3f
3g
3h
25
20
25
93
80
91
185–186
120–121
97–98
186–188 [18]
119–120 [26]
97–99 [27]
MeO
HO
O
H
O
8
9
H
Me
CH3-(CH2)4-CHO
H
H
3i
3j
25
35
91
69
71–72
65–66
71–73 [25]
66–68 [19]
1
0
1
CH3-(CH2)5-CHO
O
H
1
Me
3k
20
95
245–246
247–248 [21]
O
H
1
2
3
Me
Me
3l
15
20
92
90
240–241
176–177
240–242 [28]
174–177 [25]
O N
2
O
1
3m
H
Me
a
1
The products were characterized by IR and H-NMR spectroscopy and also their melting points are compared with authentic samples.
Isolated yields.
b

APPLICATION OF NATURAL KAOLIN
907
catalyst with ethyl acetate (3 × 10 mL). The organic extracts condensation of indoles with aldehydes at room temperature.
were combined and washed with saturated solution of NaHCO3 The simplicity, efficiency, mild reaction condition, high yield
(
2 × 15 mL) and then with water (15 mL). The organic layer of product, easy work up procedure, and recyclability of the
was separated and dried over Na2SO4. The solvent was evap- catalyst make it the preferred procedure for the preparation of
orated and the crude product was purified by recrystallization bis(indolyl)methanes.
from suitable solvent such as ethanol-water. The products were
characterized by comparison of their spectroscopic and physical
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