Zinc oxide as a regioselective and heterogeneous catalyst for the synthesis of chalcones at room temperature

Article abstract of DOI:10.1016/j.catcom.2012.06.012

Zinc oxide catalyzed synthesis of chalcones has been carried out under solvent-free conditions at room temperature. Activated as well as unactivated aromatics smoothly underwent Friedel-Crafts acylation with α, β-unsaturated acid chlorides furnishing excellent yields of the corresponding chalcones. The zinc oxide can be recovered and reused at least three times without any appreciable loss in activity.

Full text of DOI:10.1016/j.catcom.2012.06.012

Catalysis Communications 27 (2012) 30–32
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Zinc oxide as a regioselective and heterogeneous catalyst for the synthesis of
chalcones at room temperature
b
c
Parmeshwar E. More a, , Babasaheb P. Bandgar , Vinod T. Kamble
⁎
a
Department of Chemistry, Shardabai Pawar Mahila Mahavidyalaya Shardanagar, Baramati, Dist. Pune 413115, India
Organic Chemistry Research Laboratory, School of Chemical Sciences, Solapur University Solapur 413255, India
Organic Chemistry Research Laboratory, School of Chemical Sciences, S.R.T.M. University Nanded 431606, India
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Zinc oxide catalyzed synthesis of chalcones has been carried out under solvent-free conditions at room temperature.
Activated as well as unactivated aromatics smoothly underwent Friedel–Crafts acylation with α, β-unsaturated acid
chlorides furnishing excellent yields of the corresponding chalcones. The zinc oxide can be recovered and reused at
least three times without any appreciable loss in activity.
Received 6 March 2012
Received in revised form 8 June 2012
Accepted 11 June 2012
Available online 23 June 2012
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Chalcone
α,β-unsaturated acid chloride
Zinc oxide
Solvent-free condition
1. Introduction
transformations [17–22]. Herein, we report a new, simple, and
regioselective synthesis of chalcones using ZnO as a catalyst under
Chalcones (1,3-diaryl-2-propene-1-ones) constitute an important
group of natural products found in a number of plants or synthetically
prepared. They display many biological activities such as anti-cancer
[1], anti-inflammatory [2], antimitotic [3], anti-tubercular [4], cardio-
vascular [5], cell differentiation inducing [6], nitric oxide regulation
modulatory [7] and anti-hyperglycemic agents [8].
solvent-free conditions at room temperature (Scheme 1).
2. Experimental
2.1. General remarks
The straightforward route leading to the synthesis of chalcones is
Friedel–Crafts acylation of arenes with α,β-unsaturated aryl acid ha-
lides [9,10]. These methods have several limitations such as limited
regioselectivity, need of stoichiometric amount of AlCl3 and are not ap-
plicable to the synthesis of acid-sensitive chalcones. Recently, some
solid material has been employed as a heterogeneous catalyst to syn-
thesize chalcones, in particular NaNO3/natural phosphates [11] LiNO3/
natural phosphates [12], acidic clay [13] and ZnO supported metal ox-
ides [14]. However, these methods are limited because special efforts
are needed for the preparation of catalyst using harsh conditions or a
high reaction time. The microwave irradiation in presence of solid cata-
lysts has been also used for the synthesis of these compounds [15,16];
furthermore the recycling of catalyst is difficult due to structural modi-
fication by microwave. In order to overcome these limitations, synthetic
chemists continue to develop new catalysts which carry out selective
reactions under mild conditions.
Zinc oxide was purchased from Sigma-Aldrich as bright blue-white
color and odorless powder and used without any further purification.
Melting points were determined in a capillary Electro-thermal melting
point apparatus and are given uncorrected. 1H NMR spectra were
recorded using Varian Mercury YH-300 MHz spectrometer with TMS
as an internal standard. Infrared spectra were taken with a Perkin Elmer
1310 spectrometer. Elemental analysis was recorded on ELEMENTAR
(Vario EL, Germany).
2.2. General procedure
A mixture of α,β-unsaturated acid chloride (501 mg, 3 mmol), an ar-
omatic compound (324 mg, 3 mmol) and zinc oxide (120 mg, 1.5 mmol)
was stirred at room temperature (25–30 °C) for the specified time
(Table 2). The progress of the reaction was monitored by TLC.
After completion of the reaction, the product was extracted with
dichloromethane (3×5 mL), and extract was washed with aq. NaHCO3.
The organic layer was dried over anhydrous Na2SO4 and removal of
the solvent under reduced pressure furnished analytically pure product
with 92% yield (219 mg).
Zinc oxide (ZnO) is an inexpensive and commercially available
inorganic solid has been used as a catalyst in number of chemical
⁎
Corresponding author. Fax: +91 2112 254576.
E-mail address: morepe_2007@yahoo.co.in (P.E. More).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.06.012

P.E. More et al. / Catalysis Communications 27 (2012) 30–32
31
O
Table 2 (continued)
Entry \R
Substrate
Product Time
(min.) (%)
Yielda
O
R
ZnO
+
Cl
25-30 oC
R
g
3 g
3 h
10
10
90
87
X
X
3 a-q
1
2
Scheme 1.
h
Table 1
Evaluation of catalytic activity of zinc oxide in the synthesis of 1-(4′-Methoxyphenyl)-
3-phenylpropenone.
i
3i
10
89
Entry
Amount of zinc oxide
(mg)
Time
(min)
Yielda
(%)
1
2
3
4
5
6
7
0
45
45
30
25
10
10
05
ND
45
65
80
92
90
55
10
20
30
40
50
40
j
3j
09
92
89
86
86
83
92
89
89
k
l
3 k
3 l
3 m
3n
3o
3p
3q
10
Reaction conditions: cinnamoyl chloride (167 mg, 1 mmol), 4-methoxy benzene (108 mg,
1 mmol) and zinc oxide.
130
120
130
60
3. Result and discussion
m
n
o
p
In search of the best experimental conditions, the reaction of
cinnamoyl chloride (167 mg, 1 mmol) and methoxy benzene (108 mg,
1 mmol) in the presence of zinc oxide under solvent-free conditions
was considered as a standard and model reaction. When the reaction
was carried out in the absence of any catalyst the product was not
Table 2
ZnO catalyzed synthesis of chalcones.
Entry \R
Substrate
Product Time
(min.) (%)
Yielda
60
a
3a
10
92
q
45
b
c
3b
15
89
a
Yield of pure isolated products.
detected (Table 1, entry 1). In the presence of zinc oxide the reaction
was possible, and in order to determine the appropriate quantity of cat-
alyst used, we investigated the model reaction at different concentra-
tions of zinc oxide such as 10, 20, 30, 40, and 50 mg. The product yield
was 45, 65, 80, 92 and 90%, respectively. This indicates that 40 mg of
zinc oxide is sufficient to carry out the reaction smoothly. When the
model reaction was run with 40 mg of zinc oxide and stopped at half
time, 55% yield of product was obtained.
Various activated as well as unactivated aromatic compounds with
α,β-unsaturated aromatic acid chlorides underwent smooth Friedel–
Crafts acylation furnishing excellent yields of the chalcones with a short
reaction time. Results are presented in Table 2. All activated aromatic
compounds reacted very rapidly to furnish corresponding chalcones
(Table 2, entries a–i) and no chromatographic separation is required to
get pure products except in a few cases (Table 2, entries h, i and p). The
regioselectivity is impressive as acylation occurred exclusively at the po-
sition para to OMe, Me, Cl and Br. Obviously time required for Friedel–
Crafts reaction of unactivated/deactivated aromatic compounds is more
as compared to that of activated aromatics. However, in the cases where
the para positions are blocked the acylation proceeded in the ortho posi-
tion (Table 2, entry c). This protocol is very well applicable to heterocyclic
3c
10
85
d
e
f
3d
3e
3f
10
05
07
83
97
96

32
P.E. More et al. / Catalysis Communications 27 (2012) 30–32
Table 3
Appendix A. Supplementary data
Reuse of recovered catalyst (ZnO).
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.06.012.
No. of uses
Yield (%)
Recovery of ZnO (%)
1
2
3
97
93
90
95
92
90
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4. Conclusion
In conclusion, we have developed a simple, clean and efficient pro-
cedure for the synthesis of chalcones using commerciality available in-
expensive and non-toxic zinc oxide powder as a new catalyst. Without
any activation, ZnO is directly used as a catalyst and not a supporting
metal oxide. The effectiveness of this protocol is manifested in its
regioselectivity and recyclability of the catalyst.
Acknowledgment
P. E. More is thankful to BCUD University of Pune for sanctioning
Research Project Proposal No.11SCI001203.