Solvent-free selective cross-aldol condensation of ketones with aromatic aldehydes efficiently catalyzed by a reusable supported acidic ionic liquid

Article abstract of DOI:10.1016/S1872-2067(11)60470-1

A newly prepared catalyst consisting of acidic ionic liquid 1-(4-sulfonic acid) butylpyridinium hydrogen sulfate supported on silica was used to catalyze the cross-aldol condensation of ketones with aromatic aldehydes under solvent-free conditions. The highly active and selective catalyst gave good to excellent yields of the desired cross-aldol products without the occurrence of any self-condensation reactions. Reaction times were short, the procedure and work-up were simple, and no volatile or hazardous organic solvents were necessary. Moreover, the catalyst could be reused at least four times with only a slight reduction in activity.

Full text of DOI:10.1016/S1872-2067(11)60470-1

CHINESE JOURNAL OF CATALYSIS
Volume 33, Issue 12, 2012
Online English edition of the Chinese language journal
Cite this article as: Chin. J. Catal., 2012, 33: 1950–1957.
ARTICLE
Solvent-Free Selective Cross-Aldol Condensation of Ketones
with Aromatic Aldehydes Efficiently Catalyzed by a
Reusable Supported Acidic Ionic Liquid
Abolghasem DAVOODNIA*, Ghazaleh YASSAGHI
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Abstract: A newly prepared catalyst consisting of acidic ionic liquid 1-(4-sulfonic acid)butylpyridinium hydrogen sulfate supported on
silica was used to catalyze the cross-aldol condensation of ketones with aromatic aldehydes under solvent-free conditions. The highly ac-
tive and selective catalyst gave good to excellent yields of the desired cross-aldol products without the occurrence of any
self-condensation reactions. Reaction times were short, the procedure and work-up were simple, and no volatile or hazardous organic
solvents were necessary. Moreover, the catalyst could be reused at least four times with only a slight reduction in activity.
Key words: cross-aldol condensation, solvent-free condition, supported acidic ionic liquid; ketone; aromatic aldehyde
The aldol condensation, in which an enol or enolate ion re-
acts with a carbonyl compound and subsequent dehydration
forms a conjugated enone, is an important method for the
formation of carbon-carbon bonds. For example, cross-aldol
condensations between ketones and aromatic aldehydes (also
referred to as Claisen-Schmidt condensations) are useful for
the preparation of α,α'-bisarylidene cycloalkanones and chal-
cones.
compounds [13,14]. They also exhibit biological activities,
including antimitotic [15], antimalarial [16], anticancer [17],
and anti-inflammatory activity [18].
Aldol and cross-aldol condensations are traditionally cata-
lyzed by strong acids or bases such as HCl [19,20],
p-toluenesulfonic acid [21], and potassium or sodium hy-
droxide [22,23]. However, the presence of a strong acid or base
often induces the reverse reaction as well as self-condensation
reactions, and thus the yields of the desired products can be low.
Recently, researchers have performed the reaction in ionic
liquids [24,25]. However, the use of homogeneous catalysts
complicates product separation and catalyst recovery [26,27],
and thus there have been efforts to replace homogeneous
catalysts with easy-to-handle, noncorrosive, reusable, and
environmentally friendly heterogeneous catalysts. For example,
aldol condensations have been carried out with heterogeneous
catalysts such as BF -Et O [28], Mg(HSO ) [29], sulfamic
Arylidene cycloalkanones are important precursors for po-
tentially bioactive pyrimidine derivatives [1], 2,7-disubstituted
tropones [2], cytotoxic analogs [3], and monomers for liq-
uid-crystalline polymers [4]. Arylidene cycloalkanones have
also been reported to possess significant biological activities,
including antiangiogenic activity [5], quinine reduc-
tase-inducing activity [6], and cholesterol-lowering activity [7].
Furthermore, they have been used as key starting materials for
the synthesis of a new class of spiropyrrolidine antimicrobial
and antifungal agents [8], tetraazadispiro[4.1.4.3]tetradeca-
3
2
4 2
acid [30], Yb(OTf)3 [31], InCl3 [32], hydrotalcite [33], a
fluoroalkylated 1,4-disubstituted [1,2,3]triazole organocatalyst
[34], bis(p-methoxyphenyl)telluroxide [35], Cp ZrH in com-
2
,9-dien-6-ones [9], tricyclic thiazolo[3,2-a]thiapyrano[4,3-d]
pyrimidines (which are potential anti-inflammatory agents)
10], and other heterocyclic compounds [11]. Chalcone natural
2
2
[
bination with metal salts [36], NaOAc [37], silica chloride [38],
a sulfonated carbon nanocage [39], sulfated zirconia [40],
polystyrene-supported sulfonic acid [41], cetyl trimethyl am-
products are potentially important synthetic intermediates for
the preparation of flavonoids [12] and various heterocyclic
Received 15 August 2012. Accepted 23 Ocotober 2012.
*
Corresponding author. Tel: +98-511-8435000; Fax: +98-511-8424020; E-mail: adavoodnia@mshdiau.ac.ir; adavoodnia@yahoo.com
This work was supported by Islamic Azad University, Mashhad Branch.
Copyright © 2012, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(11)60470-1

Abolghasem DAVOODNIA et al. / Chinese Journal of Catalysis, 2012, 33: 1950–1957
monium bromide [42], and KF-Al
2
O
3
[43]. Although these
mmol for acetophenone and 2 mmol for cyclohexanone and
acetone), and [PYC SO H][HSO ]/ A300SiO (cat. 2, 0.07 g)
methods may be effective, some of them require long reaction
times and give low yields, are complicated by side reactions,
require hazardous solvents or catalysts or expensive catalysts,
or contribute to environmental pollution. These finding
prompted us to search for new species to cleanly and efficiently
catalyze the aldol condensation under environmentally friendly
conditions in high yields and short reaction times.
4
3
4
2
was heated in an oil bath at 130 °C for 25–40 min. After com-
pletion of the reaction, which was monitored by thin-layer
chromatography, the reaction mixture was cooled to room
temperature, and hot chloroform was added. The catalyst was
insoluble in hot chloroform and could therefore be collected by
a simple filtration. The filtrate was heated in vacuo to evapo-
rate the solvent. The solid residue was collected and recrystal-
lized from ethanol to give the desired product in high yield.
Melting points were recorded on a Stuart SMP3 melting
point apparatus. IR spectra were obtained with a Tensor 27
As part of our research on the development of reusable
catalysts for the synthesis of organic compounds [44–54], we
recently prepared a new solid acidic catalyst by impregnating
silica (Aerosil 300) with ionic liquid 1-(4-sulfonic acid)bu-
tylpyridinium hydrogen sulfate. This reusable heterogeneous
catalyst, designated [PYC SO H][HSO ]/A300SiO , showed
1
Bruker spectrophotometer on KBr disks. H NMR (400 MHz)
spectra were recorded with a Bruker 400 spectrometer.
4
3
4
2
1
high catalytic activity in the synthesis of 2,3-dihydroquina-
zolin-4(1H)-ones [55]. These results encouraged us to explore
the use of this catalyst for the cross-aldol condensation of
ketones with aromatic aldehydes.
3c (Ar = 4-ClC H ). H NMR (400 MHz, CDCl ):  7.39 (d,
6
4
3
2H, J = 8.3 Hz, arom-H), 7.457.65 (m, 6H, arom-H & CHvinyl),
7.76 (d, 1H, J = 15.7 Hz, CHvinyl), 8.03 (d, 2H, J = 7.7 Hz,
arom-H).
1
3
d (Ar = 4-FC H ). H NMR (400 MHz, CDCl ):  7.12 (t,
6
4
3
1
Experimental
2H, J = 8.6 Hz, arom-H), 7.46 (d, 1H, J = 15.7 Hz, CHvinyl),
.497.68 (m, 5H, arom-H), 7.78 (d, 1H, J = 15.7 Hz, CHvinyl),
8.02 (d, 2H, J = 7.2 Hz, arom-H).
7
1
.1 Preparation of [PYC
4
SO
3
H][HSO
4
]/A300SiO
2
1
3
e (Ar = 4-MeC H ). H NMR (400 MHz, CDCl ):  2.43 (s,
6
4
3
The catalyst [PYC SO H][HSO
4
3
4
]/A300SiO
2
(cat. 2) was
3H, CH ), 7.26 (d, 2H, J = 8.0 Hz, arom-H), 7.487.66 (m, 6H,
3
prepared by an impregnation method. Silica (Aerosil 300, 1.0 g)
was added to a solution of [PYC SO H][HSO ] (0.75 g) in
arom-H & CHvinyl), 7.83 (d, 1H, J = 15.6 Hz, CHvinyl), 8.05 (d,
2H, J = 7.6 Hz, arom-H).
4
3
4
1
methanol (20 ml). The mixture was stirred at room temperature
for 20 h to adsorb the ionic liquid on the surface of the support.
The methanol was removed with a rotary evaporator, and the
resulting solid powder was washed with cold chloroform and
3f (Ar = 2-O NC H ). H NMR (400 MHz, CDCl ):  7.35 (d,
2
6
4
3
1H, J = 15.6 Hz, CHvinyl), 7.507.85 (m, 6H, arom-H),
8.008.13 (m, 3H, arom-H), 8.17 (d, 1H, J = 15.6 Hz, CHvinyl).
1
4b (Ar = 4-BrC H ). H NMR (400 MHz, CDCl ):  1.83
6
4
3
+
dried in vacuo at 100 °C for 120 min [55]. The amount of H in
(quin, 2H, J = 6.0 Hz, CH ), 2.91 (t, 4H, J = 6.0 Hz, 2CH ),
2 2
the [PYC SO H][HSO ]/A300SiO was determined by
7.35 (d, 4H, J = 8.4 Hz, arom-H), 7.56 (d, 4H, J = 8.4 Hz,
4
3
4
2
acid-base titration to be 1.5 mmol/g.
arom-H), 7.74 (s, 2H, 2CHvinyl).
1
4
d (Ar = 4-ClC H ). H NMR (400 MHz, CDCl ):  1.80
6
4
3
1
.2 General procedure for cross-aldol condensation of
(quin, 2H, J = 6.1 Hz, CH
2
2
), 2.89 (t, 4H, J = 6.1 Hz, 2CH ),
ketones with aromatic aldehydes
7.357.43 (m, 8H, arom-H), 7.73 (s, 2H, 2CHvinyl).
1
4
e (Ar = 4-FC H ). H NMR (400 MHz, CDCl ):  1.81
6
4
3
In a round-bottomed flask equipped with a reflux condenser,
(quin, 2H, J = 6.2 Hz, CH
2
2
), 2.90 (t, 4H, J = 6.2 Hz, 2CH ),
a mixture of acetophenone (1a, 1 mmol) or cyclohexanone (1b,
7.10 (t, 4H, J = 8.6 Hz, arom-H), 7.45 (dd, 4H, J = 8.6, 5.5 Hz,
1
mmol) or acetone (1c, 1 mmol), an aromatic aldehyde 2 (1
arom-H), 7.75 (s, 2H, 2CHvinyl).
O
O
Ar
Ar
1
b
4a-4k
O
O
[
PYC SO H][HSO ]/A300SiO
4 3 4 2
or
O
or
+
ArCHO
Ph
CH3
solvent-free, 130 oC
Ph
Ar
1
a
2
3
a-3g
O
Ar
Ar
H3C
CH3
1
c
5a-5d
Scheme 1. Cross-aldol condensation of ketones with aromatic aldehydes catalyzed by [PYC
4
SO
3
4
H][HSO ]/A300SiO2.

Abolghasem DAVOODNIA et al. / Chinese Journal of Catalysis, 2012, 33: 1950–1957
1
4
k (Ar = 3-O
2
NC
6
H
4
). H NMR (400 MHz, CDCl
3
):  1.90
Table 1 Optimization of reaction conditions for synthesis of 3c cata-
lyzed by [PYC SO H][HSO ]/A300SiO
Catalyst
(
quin, 2H, J = 6.0 Hz, CH ), 3.00 (t, 4H, J = 6.0 Hz, 2CH ),
4
3
4
2
2
2
7
.64 (t, 2H, J = 8.0 Hz, arom-H), 7.79 (d, 2H, J = 7.6 Hz,
Time Isolated
(min) yield (%)
Entry
Catalyst
Solvent
T/°C
arom-H), 7.84 (s, 2H, 2CHvinyl), 8.24 (d, 2H, J = 8.0 Hz,
amount (g)
—
1
2
3
4
5
6
7
8
9
—
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent Free
solvent Free
solvent Free
solvent Free
solvent Free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
AcOEt
130
110
120
80
60
75
30
75
30
120
120
60
60
30
30
60
60
30
30
60
60
30
30
30
60
30
60
30
30
90
120
120
200
120
60
90
60
75
60
90
80
None
61
70
72
80
73
78
none
none
69
71
74
79
71
76
77
84
80
86
89
94
93
77
83
88
93
91
50
31
44
24
43
55
45
61
72
56
47
71
arom-H), 8.35 (s, 2H, arom-H).
1
cat. 1
cat. 1
cat. 1
cat. 1
cat. 1
cat. 1
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 3
cat. 3
cat. 3
cat. 3
cat. 3
cat. 1
cat. 1
cat. 1
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 2
cat. 3
cat. 3
cat. 3
0.05
0.05
0.07
0.07
0.10
0.10
0.05
0.07
0.02
0.02
0.02
0.02
0.05
0.05
0.05
0.05
0.07
0.07
0.07
0.07
0.10
0.05
0.05
0.07
0.07
0.10
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
5
b (Ar = 4-ClC H ). H NMR (400 MHz, CDCl ):  7.03 (d,
H, J = 15.9 Hz, CHvinyl), 7.39 (d, 4H, J = 8.1 Hz, arom-H),
.54 (d, 4H, J = 8.1 Hz, arom-H), 7.68 (d, 2H, J = 15.9 Hz,
6
4
3
130
2
7
110
130
CHvinyl).
110
130
1
.3 Reuse of the catalyst
r.t.
r.t.
The catalyst recovered by filtration was washed with cold
1
0
90
chloroform, dried in vacuo at 100 °C for 120 min, and reused.
The catalyst could be reused at least four times with only a
slight reduction in the catalytic activity.
11
12
13
110
120
130
1
1
1
1
1
1
2
2
2
2
4
5
6
7
8
9
0
1
2
3
90
110
2
Results and discussion
120
130
To optimize the aldol reaction conditions, we used the reac-
90
tion of acetophenone (1a, 1 mmol) and 4-chlorobenzaldehyde
1 mmol) as the model ketone and aromatic aldehyde, respec-
110
(
120
tively, to afford product 3c. We investigated the effect of the
ionic liquid loading on the silica support, the catalyst amount,
the solvent, and the temperature (Table 1). First, we confirmed
that the reaction did not proceed at all in the absence of catalyst
130
130
110
24
25
26
130
(
entry 1). Then we varied the ionic liquid loading on the cata-
110
lyst (0.5 (cat. 1), 0.75 (cat. 2), and 1.0 g (cat. 3) of ionic liquid
per gram of silica support in methanol). No self-condensation
reactions were observed with any of these three catalysts. The
fastest reaction and the highest yield were obtained with cat. 2
130
2
2
2
3
3
3
3
3
3
7
8
9
0
1
2
3
4
5
130
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
CHCl
3
CH
3
CN
O
(
entry 21), so we used it to study the effects of the other pa-
H
2
rameters on the model reaction.
EtOH
Using cat. 2, we evaluated the reaction in various solvents.
Refluxing EtOH, AcOEt, CHCl , or CH Cl gave moderate
AcOEt
3
2
2
CHCl
3
yields of the desired product (Table 1, entries 32–35). The
CH Cl
2
2
product yield in refluxing H O was low even after 200 min of
2
36
37
38
39
CH CN
3
reaction (entry 31), whereas a relatively good yield was ob-
AcOEt
tained in refluxing CH CN after 75 min (entry 36). To our
CHCl
3
3
surprise, when the reaction was performed under solvent-free
conditions, the product was obtained in excellent yield after
only 30 min at 130 °C (entry 21).
CH CN
3
Reaction conditions: substrates were acetophenone (1 mmol) and
-chlorobenzaldehyde (1 mmol) and cat. 1, cat. 2, and cat. 3 were pre-
pared by stirring 0.5, 0.75, and 1.0 g of [PYC SO H][HSO ], respectively,
4
4
3
4
The reaction temperature also strongly influenced the reac-
tion. No reaction occurred at room temperature in the presence
of cat. 2 (Table 1, entries 8 and 9). Increasing the reaction
temperature markedly enhanced both the yield and the reaction
rate: the reaction was complete within 30 min at 130 °C, and
the yield was 94% (entry 21).
with 1.0 g silica in methanol for 20 h as described in the experimental
section.
preparation method of cat. 2 had no effect on the rate or yield of
the aldol condensation.
We also investigated the effect of the solvent used to prepare
cat. 2. We prepared cat. 2 with acetonitrile or chloroform as the
solvent, instead of methanol, with stirring at room temperature
for 20 h. We then tested the performance of the resulting
catalysts in the synthesis of 3c and found that the solvent in the
To evaluate the substrate scope of the optimized reaction
conditions, we carried out cross-aldol condensations with
acetophenone, cyclohexanone, and acetone and a series of
aromatic aldehydes (Table 2). Aromatic aldehydes with elec-
tron-donating or -withdrawing substituents reacted efficiently

Abolghasem DAVOODNIA et al. / Chinese Journal of Catalysis, 2012, 33: 1950–1957
1
and relatively quickly with acetophenone, cyclohexanone, and
stereoisomer was produced, as indicated by H NMR spec-
troscopy. Large coupling constants between the two vinylic
protons in 3a–3g and 5a–5d indicated that the compounds were
acetone, to give condensation products 3a–3g, 4a–4k, and
5a–5d, respectively, in high yields. In all cases, only one
Table 2 Cross-aldol condensation of ketones with aromatic aldehydes catalyzed by [PYC
4
3 4 2
SO H][HSO ]/A300SiO
a
Entry
Ketone
O
Aldehyde
Product
Time (min) Isolated yield (%) m.p. (ºC)
O
O
Br
Br
1
2
H
H
Ph
Ph
3a
3b
30
35
89
85
8385
Ph
CH3
O
O
O
O
O
O
O
117120
Ph
Ph
Ph
Ph
CH3
CH3
CH3
CH3
Br
Cl
F
Br
Cl
F
O
3
4
5
H
Ph
Ph
Ph
3c
3d
3e
30
35
40
94
91
82
112115
8788
O
O
H
O
O
H
9092
Me
Me
NO2
O
O
NO2
O
O
6
7
8
H
Ph
3f
30
30
30
89
85
90
121122
141142
116118
Ph
Ph
CH3
CH3
O
H
O
O N
NO2
2
H
Ph
3g
4a
O
O
O
O
O
O
9
1
H
4b
25
92
164165
Br
Br
Br
O
O
Cl
O
Cl
O
O
Cl
0
H
4c
25
25
85
92
106108
145147
O
11
H
4d
Cl
F
Cl
F
Cl
F
O
O
O
O
O
O
O
1
1
1
2
3
4
H
4e
4f
25
30
35
93
89
88
157158
161163
O
H
MeO
MeO
MeO
MeO
OMe
OMe
O
H
4g
143145
MeO
MeO
OMe
(To be continued)

Abolghasem DAVOODNIA et al. / Chinese Journal of Catalysis, 2012, 33: 1950–1957
Table 2 (Continued)
a
Entry
Ketone
O
Aldehyde
Product
O
Time (min) Isolated yield (%) m.p. (ºC)
O
1
1
5
6
H
4h
4i
30
35
84
87
166167
252255
Me
Me
Me
O
O
O
H
Me N
Me N
NMe2
2
2
O
O
NO2
O
NO2
O
O
NO2
1
1
7
8
H
O
4j
25
35
92
85
158159
198199
O N
O N
NO2
2
2
H
4k
Cl
O
O
Cl
O
O
Cl
1
9
H
5a
35
85
117119
H C
3
CH3
O
O
O
O
2
2
2
0
1
2
H
5b
5c
5d
30
35
40
87
84
84
192193
175177
128129
H C
CH3
CH3
CH3
3
Cl
Cl
Me
Cl
O
O
O
H
H C
3
Me
Me
O
H
H C
3
MeO
MeO
OMe
Reaction conditions: acetophenone or cyclohexanone or acetone (1 mmol), aromatic aldehyde (1 mmol for acetophenone and 2 mmol for cyclohexanone and
acetone), and [PYC
4
SO
3
H][HSO
4
]/A300SiO
2
(cat. 2, 0.07 g) at 130 ºC under solvent-free conditions.
a
All the products were characterized by IR spectroscopy and by comparison of their melting points with those of authentic samples. The structures of some
1
products were confirmed by H NMR spectroscopy.
E stereoisomers. On the basis of previously reported results
24,29–31,37–43], however, we determined that 4a–4k also
[PYC SO H][HSO ]/A300SiO as a heterogeneous catalyst
4 3 4 2
[
with previously reported results for cross-aldol condensation
reactions in the presence of various homogeneous, heteroge-
neous, and supported catalysts (Table 3). Our reaction condi-
tions showed a shorter reaction time than all the other condi-
tions (except catalysis by KF-Al O with microwave irradia-
had the E configuration (as shown in Scheme 1). On the other
hand, we were unable to carry out selective monocondensation
from only one side of cyclohexanone and acetone, and
thin-layer chromatography indicated that the reactions pro-
duced mixtures of products, which we did not identify.
2
3
tion) and gave high yields of the desired products.
We compared the results we obtained using
We also used our optimized reaction conditions to evaluate
Table 3 Comparison of catalyst performance in cross-aldol condensations of ketones with aldehydes
Condition
Catalyst
Time (min)
Yield (%)
Ref.
Solvent
T/(ºC)
Other
—
Ionic liquid
Ionic liquid
— (for some cases: EtOH) r.t.
60180
9602880
120480
1501440
240720
6001200
8696
7896
8296
7794
8897
6696
24
25
29
30
31
34
—
—
r.t.
60
—
Mg(HSO
Sulfamic acid
Yb(OTf)
Fluoroalkylated 1,4-disubstituted
1,2,3]triazole organocatalyst
4
)
2
—
—
80
—
3
—
90
—
EtOH
reflux
—
[
(To be continued)

Abolghasem DAVOODNIA et al. / Chinese Journal of Catalysis, 2012, 33: 1950–1957
Table 3 (Continued)
Conditions
Time (min)
Catalyst
Yield (%)
Ref.
Solvent
T/ºC
120
Other
atmosphere
—
NaOAc
glacial AcOH
N
2
180480
120900
30120
8193
6595
7292
6396
7594
8098
7590
4055
8494
37
38
Silica chloride
—
—
—
100-110
70
Sulfonated carbon nanocage
Sulfated zirconia
—
39
170
—
240
40
Polystyrene-supported sulfonic acid
Cetyl trimethyl ammonium bromide
CHCl
3
reflux
60
—
240360
360480
25 min
480840
2540 min
41
H
2
O
NaOH
42
KF-Al
KF-Al
2
O
3
—
—
MW at 450 W
43
2
O
3
CH
3
CN
reflux
130
—
—
43
[
PYC
4
SO
3
H][HSO
4
]/A300SiO
2
(cat. 2)
—
this work
the reusability of cat. 2 (Fig. 1). After the reaction was com-
plete, the catalyst was recovered as described in the experi-
mental section and was then reused for a similar reaction. We
found that the catalyst could be used at least five times with
only a slight reduction in activity. Furthermore, the FT-IR
spectra of the recovered catalysts (Fig. 2(2)–(5)) were almost
identical to the spectrum of the fresh catalyst (Fig. 2(1)), in-
dicating that the structure of the catalyst was unchanged by the
reaction.
To confirm that the ionic liquid interacted strongly with the
silica support under the optimal reaction conditions, we added
hot chloroform to the reaction mixture 10 min after the first run
and then filtered the mixture. When the reaction was resumed
with the filtrate, in the absence of any externally added catalyst,
no increase in conversion was observed after 1 h, indicating
that the active catalyst was a heterogeneous solid catalyst.
3 Conclusions
100
4 3 4 2
We showed that [PYC SO H][HSO ]/A300SiO efficiently
catalyzed the cross-aldol condensation of ketones with aro-
matic aldehydes under solvent-free conditions. The method
was fast and high yielding, the work-up was easy, and only one
product was formed, as indicated by thin-layer chromatogra-
95
90
85
80
1
phy and H NMR spectroscopy. In addition, the reaction was
environmentally friendly because it was solvent free, and the
use of the solid acidic supported catalyst eliminated the need
for soluble inorganic acids and thus reduced waste. Moreover,
the catalyst could be easily recycled by filtration and reused at
least four times with only a slight reduction in activity.
1
2
3
4
5
Reaction cycle
Fig. 1.
PYC SO
Effect of recycling on catalytic performance of
H][HSO ]/A300SiO (cat. 2) in the synthesis of 3c.
Acknowledgements
[
4
3
4
2
The authors express their gratitude to the Islamic Azad
University, Mashhad Branch for its financial support.
(5)
(4)
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