Polyaniline-Anchored Metal Salts for Michael Reaction of ,-Unsaturated Ketones

Article abstract of DOI:10.1080/00397910802664277

A catalyst consisting of polyaniline-anchored metal salts is used as a Lewis acid to promote the Michael reaction of ,-unsaturated ketones. The reaction is performed efficiently with imidazole, acetyl acetone, and ethyl acetate as Michel donors and chalcones as the acceptors under ultrasound irradiation.

Full text of DOI:10.1080/00397910802664277

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Polyaniline-Anchored Metal
Salts for Michael Reaction of
α,β-Unsaturated Ketones
Arun L. Patel a , Harish R. Talele a , H. S. Rama a &
Ashutosh V. Bedekar a
a Department of Chemistry, Faculty of Science,
Maharaja Sayajirao University of Baroda, Vadodara,
India
Published online: 03 Aug 2009.
To cite this article: Arun L. Patel , Harish R. Talele , H. S. Rama & Ashutosh V.
Bedekar (2009): Polyaniline-Anchored Metal Salts for Michael Reaction of α,β-
Unsaturated Ketones, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 39:17, 3016-3023
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Synthetic Communications1, 39: 3016–3023, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802664277
Polyaniline-Anchored Metal Salts for Michael
Reaction of a,b-Unsaturated Ketones
Arun L. Patel, Harish R. Talele, H. S. Rama, and
Ashutosh V. Bedekar
Department of Chemistry, Faculty of Science,
Maharaja Sayajirao University of Baroda, Vadodara, India
Abstract: A catalyst consisting of polyaniline-anchored metal salts is used as
a Lewis acid to promote the Michael reaction of a,b-unsaturated ketones. The
reaction is performed efficiently with imidazole, acetyl acetone, and ethyl acetate
as Michel donors and chalcones as the acceptors under ultrasound irradiation.
Keywords: Metal salts, Michael reaction, polyaniline, ultrasound
INTRODUCTION
Michael reaction of a,b-unsaturated ketones is an important process
extensively used in synthetic organic chemistry.[1] The reaction works
very well with different types of nucleophiles such as nitrogen,[2] sulfur,[3]
oxygen,[4] and carbon,[5] leading to molecules with new bonds to
b-carbon. When an amine is the nucleophile and a,b-unsaturated ester
is the Michael acceptor, the product is a precursor of b-amino acid.[6]
Polyaniline and other polyamines are widely studied for their
electrical conducting properties.[7] Polyaniline–hydrochloride can be
easily polymerized to polyamine with ammonium peroxydisulfate to get
solid polyaniline (PANI).
Received October 23, 2008.
Address correspondence to Ashutosh V. Bedekar, Department of Chemistry,
Faculty of Science, Maharaja Sayajirao University of Baroda, Vadodara 390
002, India. E-mail: avbedekar@yahoo.co.in
3016

Polyaniline-Anchored Metal Salts
3017
The solid PANI, which has very low solubility in most of the organic
solvents, is an ideal candidate for use as a solid support for the making
heterogenous catalysts. The presence of several nitrogen atoms in PANI
provide a perfect handle for the complexation with transition-metal ions,
a prerequisite for a suitable catalyst support. There are a few reports of
the use of polyaniline-anchored metal catalysts for catalytic reactions.[8]
There are other applications such as polyaniline-supported MnO2, which
is used to decolorize dyes in industrial waste.[9]
RESULTS AND DISCUSSION
In this communication, we report our results in the use of PANI-
supported metal catalysts for the Michael reaction on chalcones.[10] To
test this reaction, a simple chalcone 1 was reacted with imidazole under
different conditions. Polyaniline and its metal salts with Co(OAc)2,
Cu(OAc)2, FeCl3, and MnCl2 were prepared by the reported method[8d]
and tried as catalysts for this reaction. The results of the reaction run
in an ultrasonic bath are summarized in Table 1. For this reaction,
Cu–PANI as well as Montmorillonite K-10 clay[2b] were effective for this
reaction.
A stronger Lewis acid, ferric chloride, was less effective for this
reaction, probably because it binds too well with imidazole and does
not smoothly effect the addition reaction.
The same reaction was then studied for reaction of 1 with acetyl
acetone 4 and ethyl acetoacetate 5, and results are summarized in Table 2.
The reactions of 4 or 5, which possess acidic protons to give a stabi-
lized carbon nucleophile for the catalytic Michael reaction with chalcone
1, gave the products 6 or 7 respectively. The sample of only PANI
without any metal ions does not give the reaction (entry 1, Table 2),
and similarly the reaction without any catalyst in ultrasound did not
work (entry 2). In this reaction, Fe–PANI was effective, whereas Cu–
PANI did not work at all. The effect of ultrasound to enhance the reac-
tion is clearly seen by comparison with the reaction conducted at room
temperature at much longer time (entries 3 and 4).[11] Reaction of 3 with
ethyl acetoacetate gave a nonseparable mixture of two isomers of 7; its
ratio was determined to be 88:12 based on H NMR (entry 6).

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A. L. Patel et al.
Table 1. Michael reaction of chalcone with imidazole
Entry
Catalyst=conditions
Isolated yield (%)
1
2
3
4
5
CoꢀPANI
No reaction
CuꢀPANI
68
26
18
60
FeꢀPANI
MnꢀPANI
Montmorillonite
K-10 (25% w=w)
Note. All the reactions were run in an ultrasonic bath for 2 h in 1,2-
dichloroethane.
Table 2. Michael reaction of chalcone with diketone
Entry Michael donor
Catalyst=conditions
Isolated yield (%)
1
2
3
4
5
6
Acetylacetone
Acetylacetone
Acetylacetone
Acetylacetone
Acetylacetone
PANI, ultrasound, 2 h
No reaction
No reaction
60
24
No reaction
53
No catalyst, ultrasound, 2 h
FeꢀPANI, ultrasound, 2 h
FeꢀPANI, room temperature, 24 h
CuꢀPANI, ultrasound, 2 h
Ethyl acetoacetate FeꢀPANI, ultrasound, 2 h

Polyaniline-Anchored Metal Salts
3019
Figure 1. H NMR of 10a, major (73), and 10b, minor (27).
The Michael reaction of 4 and 5 was next studied with a bis-chalcone
8 with an aim to prepare a bis-Michael addition product. However, a
large excess of 4 or 5 with Fe–PANI under ultrasound irradiation did
not give the expected bis product; only single Michael addition took
place, and products 9 and 10 were isolated in good yields.
The proton NMR of the product 10 indicated the presence of two
isomers in the ratio of 73:27, which could not be purified by column
chromatography. From the NMR pattern, the tentative assignment of
the two isomers is shown in Figure 1.
The reaction of 1,5-diphenyl-1,4-pentadien-3-one 8 with 1,3-dicarbonyl
compound in the presence of basic catalyst is reported[12] to give 1,1-
disubstituted-2,6-diphenylcyclohexane-4-one, which was not observed in
our reaction conditions.
EXPERIMENTAL
Polyaniline was prepared in aqueous acidic solution in the presence of
ammonium persulfate with proper washing and drying.[8d] Its metal
complexes were prepared by stirring the PANI with appropriate metal
salt in acetic acid–acetonitrile (1:1) at room temperature for 36 h,

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A. L. Patel et al.
following by proper washing with acetic acid, acetonitrile, and diethyl
ether and drying at 80ꢁC for 2 h. The chalcones were prepared from
benzaldehyde–acetophenone for 1 and from acetone–acetophenone for
8 with NaOH solution.[13]
Standard Reaction Conditions
3-Acetyl-4,8-diphenyloct-7-en-2,6-dione (9)
A solution of 1,5-diphenyl-1,4-pentadien-3-one (0.2 g, 0.85 mmol),
2,4-pentadione (0.42 g, 4.0 mmol) , and catalyst Fe–PANI (0.1 g) was
irradiated in an ultrasonic bath for 2 h. After the reaction was complete
(as monitored by thin-layer chromatography), the mixture was diluted
with diethyl ether and the catalyst was filtered. The solution was concen-
trated and purified by column chromatography over silica gel to afford
pure product (0.27 g, 81%) as a white solid, mp ¼ 139–41ꢁC.
H NMR (CDCl3, 400 MHz): d 1.88 (s, 3H), 2.29 (s, 3H), 2.86–2.91
(dd, J ¼ 15.6 & 4.4 Hz, 1H), 2.96–3.02 (dd, J ¼ 16.0 & 8.8 Hz, 1H),
4.10–4.16 (m, 1H), 4.28–4.31 (d, J ¼ 10.8 Hz, 1H), 6.54–6.58 (d,
J ¼ 16.4 Hz, 1H), 7.16–7.28 (m, 7H), 7.35–7.39 (m, 2H), 7.43–7.47 (m, 2H).
Data
3-Imidazol-1-Yl-1,3-diphenylpropan-1-one (2)
H NMR (CDCl3, 400 MHz): d 3.76–3.82 (dd, J ¼ 17.4 & 5.8 Hz, 1H),
3.92–3.98 (dd, J ¼ 17.4 & 7.9 Hz, 1H), 6.05–6.09 (dd, J ¼ 7.9 & 5.8 Hz,
1H), 6.96 (m, 1H), 7.04 (m, 1H), 7.24–7.29 (m, 2H), 7.30–7.40 (m, 3H),
7.45–7.52 (m, 2H), 7.57–7.64 (m, 2H), 7.92–7.95 (m, 2H).
4-Acetyl-1,3-diphenylhexane-1,5-dione (6)
Mp¼ 146–47ꢁC. H NMR (CDCl3, 400 MHz): d 1.88 (s, 3H), 2.28 (s, 3H),
3.16–3.21 (dd, J ¼ 16.3 & 4.1 Hz, 1H), 3.29–3.35 (dd, J ¼ 16.3 & 8.9 Hz,
1H), 4.21–4.25 (m, 1H), 4.31–4.33 (d, J ¼ 10.9 Hz, 1H), 7.16–7.18 (m, 1H),
7.21–7.24 (m, 4H), 7.38–7.42 (m, 2H), 7.49–7.53 (m, 1H), 7.80–7.82 (m, 2H).
Ethyl(2-acetyl-5-oxo-3,5-diphenyl)pentanoate (7)
Mp 116–18ꢁC. H NMR (CDCl3, 400 MHz): d 0.96 (t, J ¼ 7.05 Hz, 3H of
7a), 1.27 (t, J ¼ 7.05 Hz, 3H of 7b), 2.00 (s, 3H, of 7b), 2.30 (s, 3H, of 7a),

Polyaniline-Anchored Metal Salts
3021
3.30–3.55 (m, 2H of 7a & 7b), 3.91 (overlapping q, 2H, 7a & 7b), 4.00–4.03
(m, 1H, of 7a & 7b), 4.14–4.19 (m, 1H, of 7a & 7b), 7.15–7.18 (m, 1H, of
7a & 7b), 7.21–7.24 (m, 4H, of 7a & 7b), 7.39–7.43 (m, 2H, of 7a & 7b),
7.50–7.54 (m, 1H, of 7a & 7b), 7.84–7.90 (m, 2H, of 7a & 7b).
Ethyl(2-acetyl-5-oxo-3,7-diphenyl)hept-6-enoate (10)
Mp ¼ 125–28ꢁC H NMR (CDCl3, 400 MHz): d 0.97 (t, J ¼ 7.1 Hz, 3H,
for 10a), 1.27 (t, J ¼ 7.1, 3H, for 10b), 2.00 (s, 3H, for 10b), 2.31 (s,
3H, for 10a), 3.00–3.20 (m, 2H, for 10a & 10b), 3.91 (q, J ¼ 7.1, 2H,
for 10a), 3.95–4.03 (m, 1H, for 10a & 10b), 4.05–4.16 (m, 1H, for 10a
& 10b), 4.21 (q, J ¼ 7.1 Hz, 2H, for 10b), 6.60 (d, J ¼ 16.2 Hz, 1H, for
10a), 6.62 (d, J ¼ 16.2 Hz, 1H, for 10b), 7.14–7.21 (m, 1H, for 10a &
10b), 7.22–7.29 (m, 4H, for 10a & 10b), 7.34–7.41 (m, 3H, for 10a &
10b), 7.42–7.52 (m, 3H, for 10a & 10b).
CONCLUSION
In this short communication, we report the application of PANI-
supported metal salts for the Michael reactions on chalcones. These reac-
tions are promoted by ultrasound irradiation to give good conversions in
short and straightforward reaction conditions.
ACKNOWLEDGMENTS
We thank Prof. S. Devi and Prof. B. V. Kamath for providing laboratory
facilities and for suggestions and encouragement.
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