Aldol condensations of a variety of different aldehydes and ketones under ultrasonic irradiation using poly(N-vinylimidazole) as a new heterogeneous base catalyst under solvent-free conditions in a liquid-solid system

Article abstract of DOI:10.1016/S1872-2067(12)60658-5

An ultrasound-assisted aldol condensation reaction has been developed for a range of ketones with a variety of aromatic aldehydes using poly(N-vinylimidazole) as a solid base catalyst in a liquid-solid system. The catalyst can be recovered by simple filtration and reused at least 10 times without any significant reduction in its activity. The reaction is also amenable to the large scale, making the procedure potentially useful for industrial applications.

Full text of DOI:10.1016/S1872-2067(12)60658-5

Chinese Journal of Catalysis 34 (2013) 2167–2173
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Aldol condensations of a variety of different aldehydes and ketones
under ultrasonic irradiation using poly(N‐vinylimidazole) as a new
heterogeneous base catalyst under solvent‐free conditions in a
liquid‐solid system
Nader Ghaffari Khaligha,*, Taraneh Mihankhahb
a House Research of Professor Reza. Education Guilan, Rasht, District 1, 41569‐17139, Iran
b Department of Civil Engineering, Noshirvani of University of Technology, Babol, 47148‐71167, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
An ultrasound‐assisted aldol condensation reaction has been developed for a range of ketones with
a variety of aromatic aldehydes using poly(N‐vinylimidazole) as a solid base catalyst in a liquid‐solid
system. The catalyst can be recovered by simple filtration and reused at least 10 times without any
significant reduction in its activity. The reaction is also amenable to the large scale, making the pro‐
cedure potentially useful for industrial applications.
Received 24 June 2013
Accepted 11 July 2013
Published 20 December 2013
© 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
Ultrasound‐assisted reaction
Liquid‐solid system
Poly(N‐vinylimidazole)
Aldol condensation
Solvent‐free
1. Introduction
tion [3–7].
Ultrasound‐assisted organic synthesis (UAOS) is a green
Heterogeneous catalysis has attracted considerable levels of
attention because of its potential advantages over homogene‐
ous systems [1]. A limited number of reactions in heterogene‐
ous systems have been reported as acid‐ or base‐catalyzed re‐
actions, with studies pertaining to base‐catalyzed reactions in
heterogeneous systems being particularly scarce. Heterogene‐
ous bases have been used as catalysts in a variety of different
synthetic procedures [2].
Solvents play a major role in defining the environmental
performance of industrial chemical processes and can also have
a significant impact on the associated costs and hazards. The
use of “green” solvents has become increasingly important in
industrial processes as a way of minimizing the environmental
impact resulting from the use of solvents in chemical produc‐
synthetic technique that has grown in popularity during the
past two decades and is applicable to a variety of practical syn‐
theses. There are several notable features to UAOS, including
enhanced reaction rates, improved levels of selectivity, higher
product yields and purity, and facile manipulation. Further‐
more, UAOS can be considered as a processing aid in terms of
energy conservation and waste minimization compared with
traditional methods, and represents a chemistry platform that
is much more amenable to the implementation of green chem‐
istry concepts [8–14]. We recently described a series of differ‐
ent syntheses that were catalyzed by new solid acid catalysts
under ultrasound irradiation conditions, including the synthe‐
sis of 14‐aryl‐14H‐dibenzo[a,j]xanthenes [15], a one‐pot syn‐
thesis of substituted coumarins [16], and the chemoselective
*Corresponding author. Tel: +98‐21‐66431738; Fax: +98‐21‐66934046; E‐mail: ngkhaligh@gmail.com, ngkhaligh@guilan.ac.ir
DOI: 10.1016/S1872‐2067(12)60658‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 34, No. 12, December 2013

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
1,1‐diacetate protection and deprotection of aldehydes [17].
The use of ultrasound in heterocyclic system, however, remains
relatively unexplored [18].
we report the use of PVIm as a catalyst for the aldol condensa‐
tion reaction of ketones with aldehydes under ultrasound irra‐
diation and solvent‐free conditions in liquid‐solid media
(Scheme 1). Pleasingly, this method provided access to the
corresponding α,β‐unsaturated ketones in high yields, and the
catalyst could be readily separated from the reaction mixture
and reused several times without any significant impact on its
activity.
The aldol condensation reaction is one of the most funda‐
mental and important C–C bond forming reactions in organic
synthesis [19–28]. Based on the importance of the methylene
moiety, which is found in many naturally occurring compounds
and antibiotics, and the use of α,α'‐bis(substituted benzylidene)
cycloalkanones as precursors for the synthesis of bioactive
pyrimidine derivatives [29], we were particularly interested in
the condensation of cycloalkanones with aldehydes and ke‐
tones, and the cross‐aldol condensation reactions represent an
effective way in which to access these materials. These reac‐
tions are usually catalyzed by strong acids or bases, and a vari‐
ety of different Lewis acids have been evaluated in this reaction
[30]. Although chalcones are traditionally prepared by the base
catalyzed Claisen‐Schmidt condensation [31] of arylaldehydes
and acetophenones, acid‐catalyzed [32,33], solid‐ [34] and res‐
in‐supported [35], and microwave‐assisted [36] versions of the
condensation reaction have also been reported in the literature.
There have also been reports in the literature involving con‐
densation reactions under ultrasound irradiation conditions
that were catalyzed by inorganic bases [37–40]. Unfortunately,
the presence of a strong acid or base promotes the reverse re‐
action [41], and this can lead to the self‐condensation of the
starting materials to give the corresponding byproducts in low
yields [42].
The practical applications of poly(N‐vinylimidazole) (PVIm)
are wide and varied, ranging from dyestuffs, catalysts, corro‐
sion inhibitors, and ion exchange resins to their application in
quenching media and metal ion complexation reactions [43].
N‐Methylimidazole has been used as a Lewis base catalyst for
the aldol condensation reactions of trimethylsilyl enolate with a
range of different aldehydes [44,45].
In a continuation of our ongoing research towards the de‐
velopment of new catalysts and methods for organic synthesis
[46–52], we recently used PVIm as an efficient solid Lewis base
catalyst for the N‐Boc protection of amines as well as the acet‐
ylation of alcohols, phenols, thiols, and amines under sol‐
vent‐free conditions [53,54]. To expand the application of ul‐
trasound for the synthesis of heterocyclic compounds, herein
2. Experimental
2.1. Materials
Unless specified otherwise, all of the chemicals used in the
current study were purchased as the analytical grades from
Merck, Aldrich, or Fluka and used without further purification.
The products were characterized on the basis of their physical
data and a comparison with authentic samples. The reactions
and substrate purity levels were monitored by TLC using silica
gel SIL G/UV 254 plates.
2.2. Instrumentation
The Fourier transform infrared (FT‐IR) spectra were rec‐
orded on a Perkin Elmer 781 spectrophotometer using KBr
pellets for solid samples in the range of 4000–400 cm–1. Liquid
samples were evaluated as neat samples by IR under the same
conditions. Mass spectra were recorded on a Finnigan MAT
8430 mass spectrometer operating at an ionization potential of
70 eV. In all the cases, the 1H NMR spectra were recorded on a
Bruker Avance 400 or 300 MHz instrument. All of the chemical
shifts have been quoted in parts per million (ppm) relative to
TMS in a deuterated solvent. Microanalyses were performed on
a Perkin‐Elmer 240‐B microanalyzer. Melting points were rec‐
orded on a Büchi B‐545 apparatus in open capillary tubes. A
Shanghai Branson‐CQX ultrasonic cleaner with a frequency of
25 kHz and a nominal power 250 W, and Bandelin Sonorex
ultrasonic bath with built‐in heating (30–80 °C), a frequency of
35 kHz, and a nominal power 200 W, were used for the ultra‐
sonic irradiation.
O
O
CH3
R
(Table 1, entries 1-6)
N
N
O
O
CH3
n
R
R
O
(Table 1, entries 7, 8)
PVIm
, )))))
H
+
O
O
R
O
O
Solvent-free, 30-80 min
2
(Table 1, entries 9-14)
R
R
R
(Table 1, entries 15-20)
1
3
Scheme 1. Aldol condensation of ketones with aldehydes.

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
2.3. Preparation of PVIm
8.13–7.27 (m, 13H); MS (EI) m/z = 272 [M+].
2,6‐Di(p‐methoxybenzylidene)cyclohexanone (Table 2, en‐
PVIm was synthesized using
a
standard free‐radical
try 12). mp 200–201 °C; IR (KBr) ν = 3020, 2922, 1655, 1600,
1147, 780 cm–1; H NMR (300 MHz, CDCl3) δ = 1.79–1.85 (m,
2H), 2.95 (t, J = 6.0 Hz, 4H), 3.82 (s, 6H), 6.91–7.40 (m, 8H), 7.77
(s, 2H); MS (EI) m/z = 334 [M+].
1
polymerization process as previously reported [55,56]. The
polymer was precipitated as a white powder and collected by
filtration before being dried at 40 °C. The PVIm was purified by
a process of dissolution in methanol and subsequent precipita‐
tion from acetone, with the process being performed twice. The
polymer was then dialyzed against distilled water using dialysis
tubing before being isolated by lyophilization and dried over
P4O10 in vacuo at ambient temperature. The molecular weight
of the PVIm sample was determined by viscometry using the
Mark‐Houwink‐Sakurada equation, as follows, using parame‐
ters taken from the literature [57]: [µ] = K(Mv)a, where K = 122
× 10–3 mL/g and a = 0.51 in 0.1 mol/L NaCl at 25 °C. The Mv
value of PVIm was found to be 305000 g/mol.
2,6‐Di(p‐nitrobenzylidene)cyclopentanone (Table 2, entry
19). mp 232–234 °C; IR (KBr) ν = 3105, 2852, 1705, 1602,
1
1525, 1344, 821 cm–1; H NMR (300 MHz, CDCl3) δ = 3.07 (s,
4H), 7.62–8.10 (m, 8H), 8.28 (s, 2H); MS (EI) m/z = 350 [M+].
2.6. General procedure for catalyst recycling in a liquid/solid
system
A mixture of the polymeric reagent (1.0 g) collected from
different experiments was washed several times with cold
ethanol and then dried at ambient temperature for 12 h under
vacuum. The resulting catalyst was then considered to be ready
for further runs. Experimental results revealed that the PVIm
could be effectively recovered from the reaction mixture during
the work‐up procedure. The recovery in most cases was 100%,
with no discernible changes detected in the catalytic activity of
the PVIm.
2.4. General procedure for aldol condensation in a liquid/solid
system under refluxing conditions
Benzaldehyde (10 mmol) was slowly added to a magneti‐
cally stirred suspension of acetophenone (12 mmol) and PVIm
(50 mg) in a round‐bottomed flask (25 mL) equipped with a
condenser, and the resulting mixture was stirred at reflux for 4
h. The reaction mixture was then cooled to ambient tempera‐
ture and diluted with CH2Cl2 (20 mL) before being filtered to
allow for the recovery of the catalyst. The filtrate was then col‐
lected and the solvent was removed under reduced pressure to
give the crude product as a residue, which was purified by silica
gel column chromatography using a mixture of ethyl acetate
(EtOAc) and petroleum ether (2:8, v/v) as the eluent to give the
α,β‐unsaturated ketone (Chalcone).
3. Results and discussion
Before evaluating the scope of the current ultrasonic irradi‐
ation reaction, we endeavored to optimize the reaction condi‐
tions in terms of the yield and reaction time by investigating
the impact of several different reaction parameters, including
the reaction solvent, temperature, and catalyst loading. Our
initial investigations focused on the PVIm catalyzed aldol con‐
densation of benzaldehyde with acetophenone as a model reac‐
tion. When the condensation reaction was conducted in differ‐
ent organic solvents, including ethanol, acetonitrile, dichloro‐
methane, and toluene, a mixture of products was obtained in
poor to moderate yields. The rate and yield of the condensation
reaction were determined to be dependent on the type of sol‐
vent with a preference for the use of polar solvents (Table 1).
Increases in the reaction temperature led to increases in the
rate of the condensation reaction and gave higher yields of the
desired products (Table 1). When the PVIm catalyzed reaction
was performed in refluxing solvents, however, no significant
improvements in the yield were observed. The use of different
solvents, with the exception of ethanol and acetonitrile, led to
lower yields of the product. These results suggested that the
lower yields observed in polar solvents were not necessarily
related to the polarity of the solvent. When a mixture of ben‐
zaldehyde and acetophenone was stirred in ethanol or acetoni‐
trile for 16 h at reflux in the presence of PVIm, chalcone was
produced in 96% or 88% yield, respectively.
2.5. General procedure for aldol condensation in a liquid/solid
system under ultrasound irradiation
A mixture of acetophenone (12 mmol), benzaldehyde (10
mmol), and PVIm (50 mg) in a round‐bottom flask was irradi‐
ated in a Shanghai Branson‐CQX ultrasonic apparatus (with a
frequency of 25 kHz and a nominal power 250 W) at ambient
temperature for 40 min. A portion of CH2Cl2 (20 mL) was then
added to the reaction and the resulting mixture was filtered to
allow for the recovery of the catalyst. The filtrate was then col‐
lected and the solvent removed in vacuo to give the crude
product as a residue, which was purified by silica gel column
chromatography using a mixture of EtOAc and petroleum ether
(2:8, v/v) as an eluent to give the desired chalcone. The chal‐
cones were then crystallized from hot methanol prior to their
analysis and the determination of their meting points [58–67].
Chalcone (Table 2, entry 1). mp 55–57 °C; IR (KBr) ν = 3230,
2931, 1830, 1730, 1655, 1287, 753, 682 cm–1; H NMR (300
1
MHz, CDCl3) δ = 6.12 (d, J = 16.0 Hz, 1H), 7.25 (d, J = 16.0 Hz,
1H), 7.09–7.30 (m, 5H), 7.39–7.93 (m, 5H); MS (EI) m/z = 208
[M+].
1‐Naphthalen‐2‐yl‐3‐tolyl‐propenone (Table 2, entry 8). mp
140–142 °C; IR (KBr) ν = 3011, 2910, 1649, 1600, 1554, 1174,
978, 805, 746 cm–1; 1H NMR (300 MHz, CDCl3) δ = 3.37 (s, 3H),
It is noteworthy that solvent‐free conditions were required
in several cases to allow for the desired products to be obtained
in practically useful yields, because the use of organic solvents
in these cases had a severe adverse impact on the rate of the
processes and made them practically unfeasible. The results of
these experiments revealed that the highest yield for the model

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
or mechanical stirring equipment. The failure of these different
Table 1
stirring methods is what prompted us to investigate the use of
sonication as a way in which to achieve more efficient levels of
mixing at higher reaction concentrations. Pleasingly, at a cata‐
lyst loading of 50 mg combined with sonication, the model re‐
action gave the desired chalcone in 94% of yield in 40 min.
Further increases in the sonication time did not lead to in‐
creases in the yield. In comparison, when the reaction was
conducted under solvent‐free conditions without ultrasonic
irradiation at ambient temperature, a reaction time of 4 h was
required to provide a yield of 94%. The use of ultrasound
therefore clearly accelerated the synthesis of the chalcone. The
chemical effects of ultrasounds have been attributed to the
implosive collapse of the cavitations produced by the sound
waves. The cavitation process itself is associated with the for‐
mation of bubbles having dynamic life under ultrasonic irradia‐
tion conditions. These bubbles are generated at localized sites
in the liquid mixture that contain small amounts of dissolved
gases. The bursting of these bubbles results in high tempera‐
tures and pressures that can facilitate intermolecular reactions.
When one of the phases is a solid, such as the catalyst or the
substrate, ultrasonic irradiation can have several additional
enhancing effects, and this can be especially useful when the
solid acts as a catalyst [68]. The cavitation effect can lead to the
formation of microjects of acetophenone that can bombard the
surface of the solid base (PVIm). This in turn can lead to an
increase in the number of exposed sites on the unreacted sur‐
face of the PVIm and enhance the overall reactivity of the in‐
terphase surface [69]. The ultrasound technique has been
shown to represent a more effective procedure than standard
stirring techniques in terms of providing higher yields and re‐
quiring milder reaction conditions and shorter reaction times.
The effect of different irradiation frequencies on the reac‐
tion was also investigated. When the frequency of ultrasound
irradiation was 25 kHz, the yield of the chalcone was 94%
within 40 min, whereas the use of a frequency of 35 kHz pro‐
vided a yield of 84% in the same time. The use of a lower fre‐
quency of ultrasound irradiation appeared to provide higher
yields of the chalcone, likely because the use of a higher ultra‐
sonic frequency would lead to a reduction in the production of
cavitations in the liquids [70,71].
Effect of different solvents on the reaction of acetophenone with ben‐
zaldehyde at ambient temperature and refluxing conditions in the
presence of catalytic PVIm.
Entry
1
Solvent
Dichloromethane
Condition
r.t.
Yield a (%)
35
reflux
r.t.
reflux
r.t.
reflux
r.t.
reflux
r.t.
reflux
r.t.
reflux
r.t.
42
33
37
12
20
11
14
30
44
32
40
69
2
3
4
5
6
7
Dichloroethane
Toluene
Methanol
Ethanol
Acetonitrile
Solvent‐free b
50 °C
71
Reaction conditions: PVIm 5 mg, benzaldehyde 1 mmol, acetophenone
1.2 mmol, different solvents 5 mL, 4 h.
a Isolated yield.
b Reaction conditions: PVIm 50 mg, benzaldehyde 10 mmol, acetophe‐
none 12 mmol, 4 h.
reaction was obtained under solvent‐free conditions (Table 1,
entry 7). When the amount of PVIm added to the reaction was 5
mg with respect to the charge of the benzaldehyde (10 mmol),
the yield of the chalcone was found to be 69% within 4 h at
ambient temperature under solvent‐free conditions. Further
increasing the reaction temperature to 50 °C provided no ob‐
vious improvement in the yield (Table 1, entry 7). Furthermore,
increases in the reaction temperature led to a deterioration in
the purity profile of the reaction, with more byproducts being
formed.
We then proceeded to investigate the loading of the catalyst
for the transformation using loadings in the range of 5 to 50 mg
of catalyst for 10 mmol of benzaldehyde. A control experiment
was also conducted in the absence of the PVIm catalyst at am‐
bient temperature and revealed that none of the desired prod‐
uct was formed under the solvent‐free conditions even when
the reaction time was extended to 24 h. This result therefore
highlighted the importance of the PVIm catalyst. Increasing the
amount of PVIm to 10, 25, and 50 mg/10 mmol benzaldehyde
led to increases in the yield of the chalcone to 77%, 85%, and
94% within 4 h, respectively. The results also revealed that the
catalytic activity of the PVIm catalyst increased when the load‐
ing was increased from 5 to 50 mg, with the yield of the chal‐
cone increasing from 69% to 94%. The activity of the catalyst
was found to be directly proportional to the number of active
basic sites available for the reactants. The basicity of the PVIm
is derived predominantly from the free imidazole moieties at‐
tached to the backbone of PVIm polymer. For the reactions
conducted over a range of different PVIm loadings (from low to
high), the number of active basic sites increased in a linear
manner, and this was directly reflected by increases in the yield
of the chalcone. To achieve efficient stirring, we found that the
loading of the catalyst could not exceed 30 mg (with respect to
10 mmol benzaldehyde). More concentrated reaction mixtures
were simply too viscous to be stirred effectively with magnetic
With the optimized reaction conditions in hand, we pro‐
ceeded to define the scope and limitations of this new method‐
ology by subjecting a variety of different aromatic aldehydes to
the aldol condensation with a range of different ketones under
the optimized conditions. The results are summarized in Table
2. Pleasingly, the results revealed that the current method was
quite general and particularly effective for the synthesis of
chalcones and α,α'‐bis(substituted benzylidene) cycloalka‐
nones. Furthermore, the reaction conditions were sufficiently
mild enough not to induce any damage to sensitive moieties
such as the methoxy group (Table 2, entries 4, 12, and 18),
which can often undergo cleavage in the presence of strong
acids or certain Lewis acids. Table 2 shows that significant dif‐
ferences were observed in the reaction times of different sub‐
strates. For example, aromatic aldehydes bearing elec‐
tron‐withdrawing substituents (Table 2, entries 5, 13 and 19)

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
Table 2
Synthesis of chalcone and α,α'‐bis(substituted) benzylidene cyclopentanone and cyclohexanones derivatives in the presence PVIm under ultrasonic
conditions.a
Melting point (C)
Entry
Ketone
R
Time (min)
Yield b (%)
Found
Reported
1
2
3
Acetophenone
H
4‐Cl
4‐Me
40
40
25
94
92
94
55–57
112–114
98–99
55–57 [58]
114–115 [58,59]
98–99 [58]
4
4‐MeO
60
90
75–76
75–76 [58]
5
6
7
8
4‐NO2
Cinnamaldehyde
20
40
60
40
40
40
40
55
25
40
40
40
25
40
94
92
93
96
93
92
91
92
90
95
93
92
96
91
154–156
105–106
164–167
140–142
115–117
143–145
172–174
200–201
156–157
176–178
190–191
230–232
216–218
208–210
158–159 [58,60]
103–104 [60]
162–164 [59]
2‐Acetonaphthone c
Cyclohexanone d
4‐Cl
4‐Me
H
4‐Cl
4‐Me
143–145 [59]
9
116–117 [61,62]
147–148 [63–65]
170 [64–66]
203–204 [61,62,64]
158–159 [61,62,64]
179 [61,62,64]
188–189 [61,62,64]
225 [59,61]
218–220 [59,61,67]
210–211 [61,62,64]
10
11
12
13
14
15
16
17
18
4‐MeO
4‐NO2
Cinnamaldehyde
H
Cyclopentanone d
4‐Cl
4‐Me
4‐MeO
19
20
4‐NO2
30
40
90
93
232–234
220–221
230–231 [61,62,64]
223 [61,62,64]
Cinnamaldehyde
a All of the products were characterized on the basis of their physical data and through a comparison with authentic samples [58–67].
b Isolated yields.
c 2‐Acetonaphthone is a solid at room temperature with a melting point in the range of 53–55 °C. Under ultrasonic conditions, however, this material
appeared to melt at ambient temperature.
d Reaction conditions: PVIm 50 mg, cyclohexanone or cyclopentanone 10 mmol, an aldehyde 20 mmol, under ultrasonic.
underwent the reaction at a much faster rate than aromatic
aldehydes bearing electron‐donating groups (Table 2, entries 4,
12, and 18).
the desired product was isolated in 85% yield within 40 min,
indicating that a large‐scale reaction was also feasible using an
efficient quantity of PVIm.
The reusability of solid Lewis base PVIm catalyst was evalu‐
ated using the aldol condensation of acetophenone with ben‐
zaldehyde in the presence of recycled PVIm. This reaction gave
isolated yields of the chalcone in the yield of 94%–91% follow‐
ing ten runs with the recycled catalyst, and clearly demon‐
strated the practical recyclability of the catalyst (Table 3).
Interestingly, we were able to conduct the synthesis of
chalcone on a larger scale without any difficulty by using only
50 mg of PVIm under ultrasound irradiation conditions. The
reaction of acetophenone (30 mmol) was investigated with
benzaldehyde (25 mmol) in the presence of PVIm (50 mg), and
We have proposed a mechanism for the current transfor‐
mation as shown in Scheme 2. In the first step, the microjects of
acetophenone (1) would be deprotonated on the surface of
solid base catalyst with the imidazole groups of the PVIm be‐
having as proton acceptors. The microjects of the resulting
enolate compound could then condensed with aldehyde (2) to
give an aldol, which would be dehydrated to give the chalcone
product (3).
Some previously reported data for the reaction conditions
and associated product yields for the preparation of
α,α'‐bis(substituted benzylidene)cyclopentanone (Table 2,
entry 15) were compared with our results (Table 4). The re‐
sults clearly show that our newly developed conditions provide
preferable results in nearly all cases in terms of the yield and
reaction time.
Table 3
Reusability of PVIm for the synthesis of chalcone.
Run
1
2
3
4
Time (min)
Isolated yield (%)
40
40
40
40
40
40
42
42
44
44
94
93
94
94
93
93
93
93
93
92
4. Conclusions
We have developed an efficient and much improved proce‐
dure for the coupling reaction of acetophenone with benzalde‐
hydes, and therefore provided facile access to a variety of dif‐
ferent chalcone derivatives in high yield. There are several ad‐
vantages to the current methodology, including: (1) the current
procedure is particularly simple because the use of PVIm as a
solid base catalyst does not require any inert or anhydrous
conditions; (2) the reaction represents a green process because
5
6
7
8
9
10
Reaction conditions: PVIm 50 mg, benzaldehyde 10 mmol, acetophe‐
none 12 mmole under ultrasonic irradiation at room temperature.

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
PVIm
PVImH+
N
N
N
N
N
N
N
N
N
N
O
N
N
N
N
N
N
N
NH
H
N
N
O
O
(2)
R
H
C
CH2
(1)
H2
Microjects of acetophenone and the resulting enolate
induced by ultrasound irradiation
O
O
OH
-H2O
R
R
(3)
Scheme 2. Proposed mechanism for the synthesis of the chalcone derivatives.
Table 4
Comparison of the current result with those reported previously for the synthesis of α,α'‐bis(benzylidene) cyclopentanone.
Entry
1
Catalyst
TiCl3(SO3CF3)
Conditions
r.t., neat
Time (h)
Yield (%)
96
Ref.
[65]
1.5
2
Yb(OTf)3
90 °C, neat
6
92
[72]
3
4
5
SmI3
FeCl3·6H2O
Cu(OTf)2
THF, N2 atm., r.t.
[bmim][BF4], TMSCl, 80 °C
80 °C, neat
3
6
8
95
92
92
[73]
[74]
[75]
6
7
8
SiO2‐R‐SO3H
NaOH‐Al2O3
90 °C, neat
80 °C, neat
Reflux, ethanol
1.3
1
5
85
85a
93
[76]
[77]
[78]
NH4Cl
9
10
11
Calcined NaNO3/HAP (hydroxyapatite)
r.t.; methanol
Ultrasound irradiation, neat, 75–80 °C
Ultrasound irradiation, neat, r.t.
12
0.6
40 min
98
88
93
[79]
[80]
this work
NH2SO3H
PVIm
a The synthesis of 1,3‐dDiphenyl prop‐2‐en‐1‐one.
S S, Pawar R P. J Iran Chem Soc, 2009, 6: 519
PVIm is environmentally benign; (3) the reaction is atom eco‐
nomical; (4) the current methodology avoids the occurrence of
adverse side reactions because PVIm can facilitate the aldol
condensation under mild and neutral conditions and therefore
eliminate any side‐reactions resulting from strong basic condi‐
tions; and (5) the catalyst can be conveniently recovered and
reused without any significant impact on its activity. The cur‐
rent method represents an attractive alternative for the prepa‐
ration of chalcones. Further work aimed at exploring this novel
catalyst in other organic transformations is currently underway
in our laboratory.
[8] Mason T J. Practical Sonochemistry. New York: Ellis Horwood, 1991
[9] Li J T, Wang S X, Chen G F, Li T S. Curr Org Synth, 2005, 2: 415
[10] Xu H, Liao W M, Li H F. Ultrason Sonochem, 2007, 14: 779
[11] Guzen K P, Guarezemini A S, Órfão A T G, Cella R, Pereira C M P,
Stefani H A. Tetrahedron Lett, 2007, 48: 1845
[12] Sinha A K, Joshi B P, Sharma A, Kumar V, Acharya R. Aust J Chem,
2007, 60: 124
[13] Sinha A K, Sharma A, Joshi B P. Tetrahedron, 2007, 63: 960
[14] Kumar V, Sharma A, Sharma M, Sharma U K, Sinha A K. Tetrahe‐
dron, 2007, 63: 9718
[15] Khaligh N G. Ultrason Sonochem, 2012, 19: 736
[16] Khaligh N G, Shirini F. Ultrason Sonochem, 2013, 20: 26
[17] Khaligh N G, Shirini F. Ultrason Sonochem, 2013, 20: 19
[18] Martins M A P, Pereira C M P, Cunico W, Moura S, Rosa F A, Peres R
L, Machado P, Zanatta N, Bonacorso H G. Ultrason Sonochem, 2006,
13: 364
[19] Ji S J, Wang S Y. Ultrason Sonochem, 2005, 12: 339
[20] Khosropour A R. Ultrason Sonochem, 2008, 15: 659
[21] Nagarapu L, Kantevari S, Mahankhali V C, Apuri S. Catal Commun,
2007, 8: 1173
[22] Das B, Ravikanth B, Ramu R, Laxminarayana K, Vittal‐Rao B. J Mol
Catal A, 2006, 255: 74
[23] Saini A, Kumar S, Sandhu J S. Synlett, 2006: 1928
[24] Ko S, Yao C F. Tetrahedron Lett, 2006, 47: 8827
[25] Madhav J V, Reddy V T, Reddy P N, Reddy M N, Kuarm S, Crooks P
A, Rajitha B. J Mol Catal A, 2009, 304: 85
References
[1] Smith K. Solid Supports and Catalysis in Organic Synthesis. New
York: Ellis Horwood and PTR Prentice Hall, 1992
[2] Hattori H. Chem Rev, 1995, 95: 537
[3] Curzons A, Constable C C, Cunningham V L. Clean Prod Process,
1999, 1: 82
[4] Gani R, Jiménez‐Gonzalez C, ten Kate A, Crafts P A, Powell M J,
Powell L, Atherton J H, Cordiner J L. Chem Eng, 2006, 113: 30
[5] Zare A, Hasaninejad A, Khalafi‐Nezhad A, Moosavi‐Zare A R, Beyza‐
vi M H, Khedri F, Asadi F, Hayati N, Asifi A. J Iran Chem Soc, 2010, 7:
461
[6] Shaabani A, Ghadari R, Rahmati A, Rezayan A H. J Iran Chem Soc,
2009, 6: 710
[26] Smith M B, March J. March's Advanced Organic Chemistry: Reac‐
[7] Bhosale R S, Sarda S R, Giram R P, Raut D S, Parwe S P, Ardhapure

Nader Ghaffari Khaligh et al. / Chinese Journal of Catalysis 34 (2013) 2167–2173
Graphical Abstract
Chin. J. Catal., 2013, 34: 2167–2173 doi: 10.1016/S1872‐2067(12)60658‐5
Aldol condensations of a variety of different aldehydes and ketones under ultrasonic irradiation using poly(N‐vinylimidazole)
as a new heterogeneous base catalyst under solvent‐free conditions in a liquid‐solid system
Nader Ghaffari Khaligh*, Tarane Mihankhah
House Research of Professor Reza. Education Guilan, Iran; Noshirvani of University of Technology, Iran
O
O
CH3
O
R
(Table 1, entries 1-6)
(Table 1, entries 7, 8)
(Table 1, entries 9-14)
(Table 1, entries 15-20)
N
N
O
CH3
n
R
O
PVIm
, )))))
H
+
O
O
R
O
O
Solvent-free, 30-80 min
2
R
R
R
R
1
3
The aldol condensation reaction of a variety of different ketones with a range of aromatic aldehydes can be efficiently catalyzed in the
presence of poly(N‐vinylimidazole) (PVIm) in a liquid‐solid system under ultrasonic irradiation conditions.
tions, Mechanisms, and Structure. New York: John Wiley & Sons,
2001. 1218
[52] Shirini F, Khaligh N G, Jolodar O G. J Iran Chem Soc, 2013, 10: 181
[53] Khaligh N G. RSC Adv, 2012, 2: 12364
[27] Norcross R D, Paterson I. Chem Rev, 1995, 95: 2041
[28] Trost B M, Fleming I. Comprehensive Organic Synthesis: 9‐Volume
Set. Oxford: Pergamon, 1991. Vol. 2, Parts 1.4–1.7
[29] Deli J, Lorand T, Szabo D, Foldesi A. Pharmazie, 1984, 39: 539
[30] Reeves R L. In: Patai S Ed. Chemistry of Carbonyl Group. New
York: Wiley, 1966. 580
[31] Vogel A I, Tatchell A R, Furnis B S, Hannaford A J, Smith P W G.
Vogel’s Textbook of Practical Organic Chemistry. 5th ed. Harlow,
Essex, UK: Addison Wesley Longman, 1989. 1034
[32] Deng G S, Ren T G. Synth Commun, 2003, 33: 2995
[33] Wang L M, Sheng J, Tian H, Han J W, Fan Z Y, Qian C T. Synthesis,
2004: 3060
[34] Tanaka K, Toda F. Chem Rev, 2000, 100: 1025
[35] Cao Y Q, Dai Z, Zhang R, Chen B H. Synth Commun, 2005, 35: 1045
[36] Huang D F, Wang J X, Hu Y L, Zhang Y M, Tang J. Synth Commun,
2002, 32: 971
[37] Fuentes A, Marinas J M, Sinisterra J V. Tetrahedron Lett, 1987, 28:
4541
[38] Li J T, Chen G F, Wang J X, Li T S. Synth Commun, 1999, 29: 965
[39] Li J T, Yang W Z, Wang S X, Li S H, Li T S. Ultrason Sonochem, 2002,
9: 237
[40] Perozo‐Rondón E, Martín‐Aranda R M, Casal B, Durán‐Valle C J,
Lau W N, Zhang X F, Yeung K L. Catal Today, 2006, 114: 183
[41] Hathaway B A. J Chem Educ, 1987, 64: 367
[42] Nakano T, Irifune S, Umano S, Inada A, Ishii Y, Ogawa M. J Org
Chem, 1987, 52: 2239
[54] Khaligh N G. RSC Adv, 2013, 3: 99
[55] Chapiro A, Mankowski Z. Eur Polym J, 1988, 24: 1019
[56] Cabot B, Deratani A, Foissy A. Colloids Surf A, 1998, 139: 287
[57] Brandrup J, Immergut E H, Grulke E. Polymer Handbook. 4th ed.
New York: Wiley, 1999. Sec VII
[58] Watanabe K, Imazawa A. Bull Chem Soc Jpn, 1982, 55: 3208
[59] Salehi P, Khodaei M M, Zolfigol M A, Keyvan A. Monatsh Chem,
2002, 133: 1291
[60] Irie K, Watanabe K. Bull Chem Soc Jpn, 1980, 53: 1366
[61] Zheng M, Wang L C, Shao J G, Zhong Q. Synth Commun, 1997, 27:
351
[62] Yadav J S, Reddy B V S, Nagaraju A, Sarma J A R P. Synth Commun,
2002, 32: 893
[63] Huitric A C, Kumler W D. J Am Chem Soc, 1956, 78: 614
[64] Iranpoor N, Kazemi F. Tetrahedron, 1998, 54: 9475
[65] Iranpoor N, Zeynizadeh B, Aghapour A. J Chem Res (S), 1999: 554
[66] Garland C E, Reid E E. J Am Chem Soc, 1925, 47: 2333
[67] Nakano T, Irifune S, Umano S, Inada A, Ishii Y, Ogawa M. J Org
Chem, 1987, 52: 2239
[68] Calvino‐Casilda V, López‐Peinado A J, Martín‐Aranda R M, Ferre‐
ra‐Escudero S, Durán‐Valle C J. Carbon, 2004, 42: 1363
[69] Mason T J, Lorimer J P, Mistry B P. Tetrahedron, 1985, 41: 5201
[70] Zeng X F, Ji S J, Wang S Y. Tetrahedron, 2005, 61: 10235
[71] Doktycz S J, Suslick K S. Science, 1990, 247: 1067
[72] Wang L M, Sheng J, Tian H, Han J W, Fan Z Y, Qian C T. Synthesis,
2004, 18: 3060
[43] Sutton R C, Thai L, Hewitt J M, Voycheck C L, Tan J S. Macromole‐
cules, 1988, 21: 2432
[44] Hagiwara H, Inoguchi H, Fukushima M, Hoshi T, Suzuki T. Tetra‐
hedron Lett, 2006, 47: 5371
[45] Srivastava R. J Mol Catal A, 2007, 264: 146
[46] Shirini F, Khaligh N G. J Iran Chem Soc, 2012, 9: 495
[47] Khaligh N G, Shirini F. J Mol Catal A, 2011, 348: 20
[48] Khaligh N G. Tetrahedron Lett, 2012, 53: 1637
[49] Khaligh N G. RSC Adv, 2012, 2: 3321
[73] Bao W L, Zhang Y M, Ying T K. Synth Commun, 1996, 26: 503
[74] Zhang X Y, Fan X S, Niu H Y, Wang J J. Green Chem, 2003, 5: 267
[75] Li J J, Su W K, Li N. Synth Commun, 2005, 35: 3037
[76] Habibi A, Sheikhhosseini E, Bigdeli M, Balalaie S, Farrokhi E. Int J
Org Chem, 2011, 1: 143
[77] Sarda S R, Jadhav W N, Bhusare S R, Wasmatkar S K, Dake S A,
Pawar R P. Int J ChemTech Res, 2009, 1: 265
[78] Teimouri F, Hadi Khezri S, Miri Z, Eftekhari‐Sis B, Azizian J. J Sci I A
U (JSIAU), 2009, 19: 103
[50] Khaligh N G. Catal Sci Technol, 2012, 2: 2211
[51] Khaligh N G. J Mol Catal A, 2012, 363‐364: 90
[79] Sebti S, Solhy A, Tahir R, Smahi A. Appl Catal A, 2002, 235: 273
[80] Zeng H Y, Yin S F, Li Y. Chin J Org Chem, 2007, 27: 528