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http://http://www.chemistrymag.org//cji/2006/083017ne.htm |
Mar. 12, 2006 Vol.8 No.3 P.17 Copyright |
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Condensation of aryl aldehydes with rhodanine in water media catalyzed by Tween 80
Luo Jinju, Li Yiqun, Zhou
Meiyun
(Department
of Chemistry, Jinan University, Guangzhou 510632, China)
Received on Dec.26, 2005; The project was supported by the National Natural Science Foundation of China (20272018) and the Guangdong Natural Science Foundation (04010458, 021166)
Abstract Condensation
reactions of various aryl aldehydes with rhodanine proceeded smoothly in
water without any organic solvents to afford the corresponding products at
room temperature in excellent yields. The procedure presented has the
merits of environmentally benign, simple operation, convenient work-up and
moderate to good yields.
Keywords aldehyde, rhodanine, Tween 80,
water media, condensation
The rhodanine derivatives have
attracted considerable pharmaceutical interest. The compounds with
rhodanine moiety are reported to have anticonvulsant[1],
antibacterial[2], antiviral[3] and
anti-diabetic[4] properties. Therefore, the preparation of this
heterocyclic core unit has attracted the attention of many organic
chemists. The simple and direct method involves the Knoevenagel
condensation of a variety of aryl aldehydes and rhodanine in refluxing
glacial acetic acid[5], ethanol[6], and
toluene[7] in the presence of catalyst. Recently, many other
methods including microwave irradiation[8], dry
reaction[9] with high temperature, and solid phase
synthesis[10] also have been employed for this transformation.
However, many of these methods suffer from one or other limitations such
as requiring harsh conditions, low to moderate yields, relatively long
reaction time and cumbersome experimental process. So it is necessary to
find a new catalyst for this important preparation.
Reactions performed in water media have gained much interest in synthetic
chemistry over the past decade, not only for the advantages accorded by
avoiding using and disposal of harmful organic solvents, but also for the
unique patterns of reactivity and selectivity in certain cases compared to
the convenient organic solvents[11].
However, the use of water in organic reaction processes is rather
limited because many organic compounds are hydrophobic and many reagents
are sensitive to water, therefore, there
is need for the use of surfactants or water stable catalysts to overcome
the barriers. The common used surfactants are quaternary ammonium cationic
compounds such as cetyltrimethylammonium chloride (CTAC),
cetyltrimethylammonium bromide (CTAB) etc.
Unlike
the quaternary ammonium salt surfactants, which have significant toxic
effects on a variety of bacteria and fungi[12], Tween 80, (also
known as Polysorbate 80), is safe, biodegradable and found extensive use
as a surfactant and solubilizing agent, not only in chemical, biochemical,
pharmacological, and medicine research, but also in food, cosmetics, and
pharmaceutical industries.
In the course of our
investigations to develop new synthetic reactions in water media, we
herein report the use of Tween 80 as a catalyst for the condensation of
aryl aldehydes with rhodanine in water media at ambient temperature
(Scheme 1).
Various aryl aldehydes reacted well with rhodanine
in the presence of a catalytic amount of Tween 80 in potassium carbonate
solution to give the corresponding products in 60-95% yields at room
temperature. The results were summarized in Table
1.
Table 1
Condensation of aryl aldehydes and rhodanine using Tween 80 as catalyst in
water media
|
entry |
aldehyde (1) |
product (3) |
time (h) |
yielda (%) |
mp (¡ãC) | |
|
found |
reported | |||||
|
1 |
4-NO2-C6H4CHO |
3a |
3 |
95 |
250.5-253 |
249-250[13] |
|
2 |
3-NO2-C6H4CHO |
3b |
5 |
87 |
264-265.5 |
263-264.5[8] |
|
3 |
2, 4-2Cl-C6H3CHO |
3c |
26 |
80 |
234-235.5 |
231.5-232.5[6] |
|
4 |
2-Cl-C6H4CHO |
3d |
15 |
85 |
189-190 |
192[5a] |
|
5 |
4-Cl-C6H4CHO |
3e |
30 |
85 |
228.5-229.5 |
231-232[5a] |
|
6 |
4-MeO-C6H4CHO |
3g |
66 |
60 |
250-252 |
250-251[14] |
|
7 |
4-Me-C6H4CHO |
3h |
57 |
67 |
221-223 |
219-220[6] |
|
8 |
C6H5CHO |
3i |
50 |
71 |
204-205.5 |
204.5-206[8] |
|
9 |
|
3j |
30 |
90 |
231-232 |
228-229[8] |
a
Isolated yield.As shown in Table 1,
both the aryl aldehydes with electron donor groups or withdrawing groups
gave the desired products in moderate to excellent yields in the reaction
time ranging from 3 to 66h. The nature of both electron-withdrawing groups
and electron-donating groups on the aromatic ring of the aldehydes has
significant effect on the reaction time and yields. Aryl aldehydes such as
p-nitrobenzaldehyde and m-nitrobenzaldehyde required
relatively short reaction time (Table 1, entries 1-2). Aryl aldehydes with
electron-donating groups such as p-anisaldehyde and
p-methylaldehyde required much longer reaction time (Table 1,
entries 6-7).
In summary, we have described an
efficient and eco-friendly procedure for the condensation reaction of
various aryl aldehydes with rhodanine using Tween 80 as catalyst in water
media at ambient temperature with moderate to excellent yields. The
procedure offers several advantages including mild reaction condition,
expeditious work-up condition, simple isolation procedure, cleaner
reaction profiles.
Experimental
Melting
points were measured by X6 micro-melting point apparatus and
were uncorrected. Infrared spectra were recorded using KBr pellet on a
Bruker Equinox 55 spectrometer. 1H NMR spectra were recorded in
DMSO-d6 on a Bruker AVANCE 300£¨300 MHz£©instrument with the residue DMSO as an internal
standard at d 2.54 ppm. Furyl aldehyde and benzaldehyde were purified by
distillation. All other chemicals used were of commercial grade without
further purification.
General procedure for the condensation of aryl
aldehyde and rhodanine: A mixture of the aryl aldehyde (3
mmol), rhodanine (3 mmol) and K2CO3 (6 mmol) was
stirred at ambient temperature in water (10 mL) for the specified time in
Table 1. After completion of the reaction monitored by TLC, the mixture
was poured into water and neutralized with 5% HCl. The precipitant was
filtered off and treated with saturated NaHSO3 and brine to
afford the products. Although the products were found practically pure,
further purification was carried out by recrystallization with aqueous
ethanol. All compounds are characterized by melting point, IR,
1H NMR and also compared with the data reported in the
literature.
4-Nitrobenzylidene rhodanine 3a: 1H NMR
(DMSO-d6, 300MHz) d : 7.76 (s, 1H, CH=), 7.88 (d, J =
8.82 Hz, 2H, Ar-H), 8.36 (d, J = 8.82 Hz, 2H, Ar-H)£»IR (KBr) n : 3437, 1722, 1640, 1609, 1530, 1446,
1345, 1192 cm-1.
3-Nitrobenzylidene rhodanine
3b: 1H NMR (DMSO-d6, 300MHz) d : 7.79 (s,
1H, Ar-H), 7.81-7.86 (m, 1H, Ar-H), 8.00 (d, J = 7.65 Hz, 1H,
Ar-H), 8.32 (d, J = 8.13 Hz, 1H, Ar-H), 8.44 (s, 1H,
CH=)£»IR (KBr) n : 3437, 1702, 1640,
1532, 1407, 1350, 1193 cm-1.
2, 4-Dichlorobenzylidene
rhodanine 3c: 1H NMR (DMSO-d6, 300MHz) d :
7.56-7.67 (m, 2H, Ar-H), 7.71 (s, 1H, Ar-H), 7.89 (s, 1H,
CH=)£»IR (KBr) n : 3436, 1702, 1639,
1584, 1436, 1196 cm-1.
2-Chlorobenzylidene rhodanine
3d: 1H NMR (DMSO-d6, 300MHz) d : 7.54-7.58 (m,
3H, Ar-H), 7.66 (m, 2H, Ar-H), 7.46 (s, 1H, CH=)£»IR (KBr) n : 3437, 3074, 1701, 1591, 1435, 1195
cm-1.
4-Chlorobenzylidene rhodanine 3e:
1H NMR (DMSO-d6, 300MHz) d : 7.65 (s, 4H, Ar-H),
7.68 (s, 1H, CH=)£»IR (KBr) n : 3438,
3085, 1709, 1597, 1442, 1183
cm-1.
4-Methoxylbenzylidene rhodanine 3f:
1H NMR (DMSO-d6, 300MHz) d : 3.04 (s, 3H,
CH3), 7.15 (d, J = 8.71 Hz, 2H, Ar-H), 7.60 (d, J
= 8.72 Hz, 2H, Ar-H), 7.65 (s, 1H, CH=)£»IR (KBr) n : 3437, 1687, 1640, 1586, 1261, 1172
cm-1.
4-Methylbenzylidene rhodanine
3g: 1H NMR (DMSO-d6, 300MHz) d : 2.40 (s,
3H, CH3), 7.40 (d, J = 8.09 Hz, 2H, Ar-H), 7.53 (d, J
= 8.16 Hz, 2H, Ar-H), 7.65 (s, 1H, CH=)£»IR (KBr) n : 3437, 1693, 1592, 1432, 1235, 1179
cm-1.
4-Benzylidene rhodanine 3h: 1H NMR
(DMSO-d6, 300MHz) d : 7.51-7.85 (m, 5H, Ar-H), 7.68 (s, 1H,
CH=)£»IR (KBr) n : 3437, 1702, 1674,
1593, 1438, 1236, 1194 cm-1.
2-Furylidene rhodanine 3i:
1H NMR (DMSO-d6, 300MHz) d : 6.80 (s, 1H, Ar-H),
7.20 (d, J = 3.22 Hz, 1H, Ar-H), 7.51 (s, 1H , Ar-H), 8.13 (s, 1H,
CH=)£»IR (KBr) n : 3438, 3142, 3035,
1690, 1601, 1443, 1319, 1226, 1178 cm-1.
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