Synthesis of cinnamic acids catalyzed by expansive graphite under ultrasound

Article abstract of DOI:10.1081/SCC-100103251

Knoevenagel condensation of malonic acid with aromatic aldehydes catalysed by expansive graphite results cinnamic acids in 65-98% yields under ultrasound irradiation.

Full text of DOI:10.1081/SCC-100103251

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SYNTHESIS OF CINNAMIC
ACIDS CATALYZED BY
EXPANSIVE GRAPHITE UNDER
ULTRASOUND
Ji-Tai Li a , Hong-Jun Zang a , Jian-Ying Feng a , Li-
Jun Li a & Tong-Shuang Li a
a Department of Chemistry, Hebei University,
Baoding, 071002, P.R. China
Published online: 16 Aug 2006.
To cite this article: Ji-Tai Li , Hong-Jun Zang , Jian-Ying Feng , Li-Jun Li & Tong-
Shuang Li (2001) SYNTHESIS OF CINNAMIC ACIDS CATALYZED BY EXPANSIVE GRAPHITE
UNDER ULTRASOUND, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 31:5, 653-656, DOI: 10.1081/
SCC-100103251
To link to this article: http://dx.doi.org/10.1081/SCC-100103251
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SYNTHETIC COMMUNICATIONS, 31(5), 653–656 (2001)
SYNTHESIS OF CINNAMIC ACIDS
CATALYZED BY EXPANSIVE GRAPHITE
UNDER ULTRASOUND
Ji-Tai Li,* Hong-Jun Zang, Jian-Ying Feng, Li-Jun Li,
and Tong-Shuang Li
Department of Chemistry, Hebei University, Baoding,
071002, P.R. China
ABSTRACT
Knoevenagel condensation of malonic acid with
aromatic aldehydes catalysed by expansive graphite results
cinnamic acids in 65–98% yields under ultrasound irradiation.
Reported applications for cinnamic acids and its derivatives include:
used as a light penetration inhibitor in sunscreen formulations;1 for the
preparation of herbicidal compositions;2 used as a substrate in the forma-
tion of photopolymers,3 used as a raw material in the synthesis of hetero-
cyclic color complexes4 and antitumor agents et al.5,6
The Knoevenagel condensation of various aromatic aldehydes with
malonic acid to give cinnamic acids has been extensively studied using
base catalysts like ammonia, primary and secondary amines, particularly
piperidine, pyridine, pyridine with a trace of piperidine and other secondary
and tertiary amine.7,8 It has been reported using acidic catalysts for the
condensation such as sulfuric acid,9,10 sulfuric acid–acetic acid.11
However, both bases and acids, as homogenous catalysts, are difficult to
be recovered and easily polluted the environment.
* Corresponding author. E-mail: orgsyn@mail.hbu.edu.cn
653
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

654
LI ET AL.
Ultrasound has been increasingly used in organic synthesis.12–15
Herein, we wish to report the efficient condensation between malonic
acid and various aromatic aldehydes catalysed by expansive graphite
under ultrasound.
Scheme
As shown in the Scheme and Table, the ultrasound technique rep-
resented a better procedure in terms of the higher yield, milder reaction
condition, easier workup. For example, 4-nitrocinnamic acid and 3-nitro-
cinnamic acid was previously prepared in yield 73% and 75% respectively,
catalysed by piperidine, after standing for 24 h at rt, continuous heating for
7 h at 90ꢀC.8 Whereas under ultrasonication, 4-nitrocinnamic acid and 3-
nitrocinnamic acid were obtained in a 98% and 89% yield at 43ꢀC for 6–7 h.
The catalyst, expansive graphite, can be easily removed by filtration and
can be reused only by dried. Meanwhile, the present procedure also got a
good result on molar scale for 1a. It is worth noting that a prolonged period
Table. Preparation of Cinnamic Acids Catalysed by Expansive Graphite Under
Ultrasound
Time (h)/
temp (ꢀC)
Yielda
(%)
m.p.
(ꢀC) (lit.)
Entry
Ar
a
2-furyl
3.5/41
3.5–5/43
3.5/43
77
84b
84
98
98
89
81
85
98
65
97
135–136(136)16
135–136
b
c
d
e
f
4-ClC6H4
248–249(249–250)18
162–163(162–163)18
284–286(283–286)8
199–200(198–201)8
170(170–172)8
214–215(216)17
168–169(169)16
196–197(198)16
238–239(240)16
3-ClC6H4
6.0/43
4-O2NC6H4
6.0/43
3-O2NC6H4
7.0/43
4-CH3OC6H4
4-(CH3)2NC6H4
4-OH-3-MeOC6H3
4-CH3C6H4
10.0/43
9.0/43
g
h
i
10.0/43
10.0/43
10.0/43
j
3,4-(OCH2O)C6H3
aIsolated yield based on aldehyde.
bThe reaction was done on molar scale.

CINNAMIC ACIDS
655
of ultrasonication did not increase the product yields. On the contrary,
the products were polymerized.
In conclusion, we have established a practical condensation procedure
for the synthesis of cinnamic acids catalysed by expansive graphite under
ultrasound irradiation. The operational simplicity, use of inexpensive, non-
corrosive and reusable catalyst, high yields and non-pollution can make this
procedure a useful and attractive alternative to the currently available
methods.
EXPERIMENTAL
Liquid aldehydes were purified by distillation prior to use. Melting
points were uncorrected. IR spectra were recorded on Bio-Rad FTS-40
1
spectrometer (KBr). H NMR spectra were measured on VXR-300S spec-
trometer, using TMS as internal standard and using CDCl3 as solvent.
Sonication was performed in Shanghai Branson-CQX ultrasonic cleaner
with a frequency of 25 kHz and a nominal power 500 W. The reaction
flask was located at the maximum energy area in the cleaner and the tem-
perature of water bath was controlled by addition or removal of water.
Preparation of Expansive Graphite
A mixture of concentrated sulfuric acid (98%, 20 g), nitric acid (65%,
10 g), natural flake graphite (10 g) and potassium permanganate (0.7 g) was
stirred at rt for 30 min. The expansive graphite was filtered, washed with
water until pH ¼ 6–7 and dried at 60ꢀC for 1 h.
General Procedure
To a 50 ml Pyrex flask was charged with substituted aromatic aldehyde
(1, 0.1 mol), malonic acid (2, 0.15 ml), expansive graphite (1.02 g), and ethyl
acetate (20 ml). The mixture was irradiated in the water bath of an ultra-
sonic cleaner at the temperature for the period as indicated in the Table
(sonication was continued until aldehyde disappeared, as indicated by
TLC). The catalyst was separated by filtration and washed with ethyl acet-
ate, the solvent was evaporated under reduced pressure until the crystal
appeared. After cooling in an ice water bath, the formed product was
collected by filtration and washed with water. The authenticity of the prod-
1
ucts was established by their melting points, IR and H NMR spectra.

656
LI ET AL.
The procedure on molar scale was followed with furfural (1.00 mol),
malonic acid (1.50 mol), expansive graphite (10.2 g), and ethyl acetate
(400 ml) in a 1000 ml Pyrex flask. The mixture was irradiated in the water
bath of an ultrasonic cleaner at 43ꢀC for 3.5 h (sonication was continued
until aldehyde disappeared, as indicated by TLC). The following procedure
was the same as stated in the general workup.
ACKNOWLEDGMENT
The project was supported by NSFC (29872011), Natural Science
Foundation of Hebei Province (299080), P.R. China.
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