SiO2?12WO3?24H2O: A highly efficient catalyst for the synthesis of 5-arylidene barbituric acid in the presence of water

Article abstract of DOI:10.1071/CH08320

The condensation of aromatic aldehydes and barbituric acid catalyzed by SiO₂12WO₃24H₂O in aqueous media at room temperature gave 5-arylidene barbituric acid in high yields with or without the use of ultrasound, providing a simple and efficient route to synthesis of these compounds.

Full text of DOI:10.1071/CH08320

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Aust. J. Chem. 2009, 62, 353–355
SiO ·12WO ·24H O: a Highly Efficient Catalyst
2
3
2
for the Synthesis of 5-Arylidene Barbituric Acid
in the Presence of Water
Ji-Tai LiA,B and Ming-Xuan SunA
ACollege of Chemistry and Environmental Science, Hebei University, Key Laboratory
of Analytical Science and Technology of Hebei Province, Baoding 071002, China.
B
Corresponding author. Email: lijitai@hbu.cn
The condensation of aromatic aldehydes and barbituric acid catalyzed by SiO2·12WO3·24H2O in aqueous media at room
temperature gave 5-arylidene barbituric acid in high yields with or without the use of ultrasound, providing a simple and
efficient route to synthesis of these compounds.
Manuscript received: 28 July 2008.
Final version: 16 January 2009.
O
Some barbituric acid derivatives have been widely used as
sedative, hypnotic, anticonvulsant, antispasmodic, and local
anaesthetic agents.[ Benzylidene barbituric acids are use-
ful as potential organic oxidizers, for the preparation of
oxadeazaflavines, and for the asymmetrical synthesis of
O
O
NH
NH
SiO ·12WO ·24H O
2 3 2
NH
NH
ArCHO ϩ
O
ArCH
O
1]
Stirring or u.s./r.t./H O
2
O
1
2
3
[
2]
disulfides. Some of them have been recently studied as
[3]
non-linear optical materials. Over the past few years many
Scheme 1. Synthesis of 5-arylidene barbituric acid.
[
3–10]
synthetic methods
for preparation of these compounds have
[3]
been reported, such as infrared irradiation and microwave
[
4]
irradiation. However, in spite of their potential utility, some
of these procedures involve expensive catalysts, a long reaction
time and lower yields.
Table 1. Effect of reaction conditions on the reaction of
4-CH3OC6H4CHO with barbituric acid
Barbituric acid, 1mmol; 4-CH3OC6H4CHO, 1 mmol; A: stirring without
ultrasound; B: ultrasound irradiation, 25 kHz
Heteropolyacids have been found to act as outstanding cat-
[11]
alysts in electrophilic transformations.
Silicotungstic acid is
Entry
Molar ratio of
1:2:catalyst
Time [min]
Yield [%]
a solid heteropolyacid which has been used for the synthesis of
[
12]
[13]
trioxanes,
alkylation of benzene with olefins,
preparation
A
B
A
B
[14]
of acrolein from glycerol,
synthesis of novel indolyl crown
1
2
3
4
5
1:1:0
20
20
20
20
30
5
5
5
5
10
40
86
98
98
99
50
88
99
99
99
ethers and di(indolyl)pyrazolyl methanes, and cyclodehydration
of 1,4-butanediol to tetrahydrofuran.[ It has been previously
reported that silicotungstic acid has high catalytic activity and
good stability, and is an environmentally friendly catalyst.
Organic reactions in aqueous media are attracting increasing
interest due to environmental issues and the understanding of
biochemical processes. Water offers many practical and eco-
nomic advantages as a reaction solvent including low cost,
safe handling, and environmental compatibility. Recently, many
organic reactions in aqueous media have been described in
1:1:0.0025
1:1:0.005
1:1:0.01
1:1:0.05
15]
can improve the reaction yields. For example, in the absence
of silicotungstic acid the yield of arylidene barbituric acid was
40%, whereas using 0.005 mmol silicotungstic acid with stirring
the yield was 98% (Table 1, entry 3) for the same period.
The effect of ultrasound irradiation on the reaction was
observed. As shown in Table 1 and Table 2, condensation
of 4-methoxybenzaldehyde with barbituric acid catalyzed by
silicotungstic acid in the absence of ultrasound offered 5-(4-
methoxybenzylidene)-barbituric acid (Table 2, 3a) at 98% yield
within 20 min. The use of ultrasound irradiation allowed a sim-
ilar yield to be obtained within 5 min. Additionally the reaction
of 4-methylbenzaldehyde (1g) with barbituric acid with stirring
for 25 min gave 3g at 88% yield, whereas the use of ultrasound
[
16]
the literature.
To the best of our knowledge, however, there
are no literature examples of the synthesis of 5-arylidene bar-
bituric acid in aqueous media using silicotungstic acids as
catalysts, especially at room temperature with stirring or the
use of ultrasound irradiation. Herein, we wish to report an effi-
cient and simple procedure for the room temperature synthesis
of 5-arylidene barbituric acid in the presence of water, cat-
alyzed by SiO2·12WO3·24H2O, both with and without the use
of ultrasound irradiation (Scheme 1).
We studied the influence of the amount of catalyst on the
reaction. As shown in Table 1, increasing the amount of catalyst
©
CSIRO 2009
10.1071/CH08320
0004-9425/09/040353

3
54
J.-T. Li and M.-X. Sun
Table 2. Condensation of barbituric acid with aromatic aldehydes with and without the use of ultrasound
A, stirring without ultrasound; B, ultrasound irradiation
◦
◦
Compound
Ar
Time [min]
Yield [%]
mp [ C]
mp [ C] (Lit.)
A
B
A
B
8]
3
3
3
3
3
3
3
3
3
3
3
3
a
b
c
d
e
f
g
h
i
4-CH3OC6H4
2-CH3OC6H4
4-HOC6H4
3-CH3O-4-HOC6H3
4-ClC6H4
3-ClC6H4
4-CH3C6H4
C6H5
4-(CH3)2NC6H4
2-HO-3-CH3OC6H3
3,4-(OCH2O)C6H3
4-NO2C6H4
20
25
25
20
40
40
25
30
30
20
20
40
5
5
5
98
98
97
93
96
41
88
62
92
91
96
15
99
97
98
98
94
68
95
61
98
99
97
20
296–298
266–268
>350
307–310
300–301
267–268
277–279
267–268
280–283
>350
298–300[
[
7]
270–272
>350[
9]
9]
6]
8]
8]
8]
9]
4
309–313[
301–302[
10
10
10
10
5
5
5
15
[
274–278
278–280[
270–272[
[
282–284
10]
j
k
l
>350[
[
3]
326
306–308
320
307–310[
8]
gave a 95% yield of the same product within 10 nm. It is clear
that ultrasound can accelerate the condensation of some aromatic
aldehydes with barbituric acid.
From the results above the optimum reaction conditions
were chosen: aromatic aldehyde (1, 1 mmol), barbituric acid
lower than the level of the water. Observation of the surface of
the reaction solution during vertical adjustment of vessel depth
will show the optimum position by the point at which maximum
surface disturbance occurs. The reaction temperature was con-
trolled by the addition or removal of water from the ultrasonic
bath.
(
2, 1 mmol), silicotungstic acid (0.005 mmol), and water (3 mL).
Under these reaction conditions, a series of experiments for the
synthesis of 5-arylidene barbituric acids was carried out. Good
yields were obtained for all systems, except for 3f and 3l, within
General Procedure
Aldehyde(1, 1 mmol), barbituricacid(2, 1 mmol), SiO2·12WO3·
2
0–40 min (Table 2).
24H2O (0.005 mmol), and water (3 mL) were mixed in a 25 mL
When 4-aminoacetophenone, 4-nitroacetophenone, or 4-
round-bottomed flask.The reaction mixture was either stirred, or
irradiated in the water bath of an ultrasonic cleaner, at room tem-
perature for the period as indicated in Table 2. After completion
of the reaction, the reaction mixture was filtered, washed with
boiling H2O and then washed with EtOH, affording the known
products (3a–3l). The authenticity of the products was estab-
lished by spectroscopic data and by comparing their melting
methoxyacetophenone was used as a substrate, no product was
obtained despite the use of stirring, ultrasonic irradiation or
extending the reaction time. This indicates that the method has
some limitations with respect to some aromatic ketones, pos-
sibly due to steric hindrance around the carbonyl group which
inhibits the condensation.
The condensation of barbituric acid with aliphatic (cyclic)
ketones such as acetone, butanone, and cyclohexanone was also
carried out using either ultrasound radiation or stirring. In both
cases no reaction product was obtained.
[3,5–10]
points with literature values.
Acknowledgement
The project was supported by Natural Science Foundation of Hebei Province
We have shown that the method presented here represents an
efficient procedure in terms of high yield, mild reaction condi-
tions, and easy workup. In addition, compared with the use of
stirring, ultrasonic irradiation can reduce the reaction time.
In conclusion, we have found a practical procedure for the
preparation of 5-arylidene barbituric acids from some aromatic
aldehydes and barbituric acid, catalyzed by silicotungstic acid
(
B2006000969), China.
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