Sonochemically synthesis of pyrazolones using reusable catalyst CuI nanoparticles that was prepared by sonication

Article abstract of DOI:10.1016/j.ultsonch.2013.01.005

A simple and green process to prepare copper iodide in nano scale via sonication was carried out. Subsequently, this nanoparticles was used as an efficient catalyst for the synthesis of 2-aryl-5-methyl-2,3-dihydro-1H-3- pyrazolones via four-component reaction of hydrazine, ethyl acetoacetate, aldehyde and β-naphthol in water under ultrasound irradiation. The combinatorial synthesis was attained for this procedure with applying ultrasound irradiation while making use of water as green ambient. Simple work-up, excellent yield of products and short reaction times are some of the important features of this protocol. Notably, this catalyst could be recycled and reused for five times without noticeably decreasing the catalytic activity.

Full text of DOI:10.1016/j.ultsonch.2013.01.005

Ultrasonics Sonochemistry 20 (2013) 1069–1075
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Sonochemically synthesis of pyrazolones using reusable catalyst CuI
nanoparticles that was prepared by sonication
⇑
Abolfazl Ziarati, Javad Safaei-Ghomi , Sahar Rohani
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan 51167, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple and green process to prepare copper iodide in nano scale via sonication was carried out.
Subsequently, this nanoparticles was used as an efficient catalyst for the synthesis of 2-aryl-5-methyl-
2,3-dihydro-1H-3-pyrazolones via four-component reaction of hydrazine, ethyl acetoacetate, aldehyde
and b-naphthol in water under ultrasound irradiation. The combinatorial synthesis was attained for this
procedure with applying ultrasound irradiation while making use of water as green ambient. Simple
work-up, excellent yield of products and short reaction times are some of the important features of this
protocol. Notably, this catalyst could be recycled and reused for five times without noticeably decreasing
the catalytic activity.
Received 4 November 2012
Received in revised form 14 January 2013
Accepted 17 January 2013
Available online 26 January 2013
Keywords:
Ultrasonic irradiation
CuI nanoparticles
Pyrazolones
Ó 2013 Elsevier B.V. All rights reserved.
Four-component reactions
Green chemistry
1. Introduction
aration of different heterocyclic molecules and in drug discovery
procedures [13]. Although MCRs are efficient, environmentally
Ultrasound irradiation has progressively been considered as a
simple, clean and convenient method in chemical synthesis in
the last 30 years [1]. Ultrasonic activation, found on cavitation ef-
fects leading to mass transfer development, is extensively used
nowadays to promote nano structure synthesis and also organic
reactions [2]. An investigation of literature shows that the synthe-
sis of nano crystalline and organic compounds has been improved
by sonochemistry [3,4].
During the last decades, nano crystalline compounds has inter-
ested significant attention as efficient catalysts in many organic
reactions due to their high surface-to-volume ratio and coordina-
tion parts which provides a large number of active sites per unit
area compared to their heterogeneous counter parts [5,6]. In recent
years, copper iodide has concerned much interest because of the
uncommon characters such as negative spin–orbit splitting,
unusually large temperature dependency, abnormal diamagnetism
behavior, large direct band gap [7,8]. Also it has potential applica-
tions in solid-state solar cells, super ionic conductor and catalysis
for synthesis of organic compounds [9,10]. CuI nanoparticles has
indicated a significant level of performance as catalysts in terms
of reactivity, selectivity, and better yields of products particularly
in multi-component reactions [11,12].
friendly, fast, atom economic and time saving style. They supply
an effective tool for the preparation of various compounds with
pharmaceutical and biological properties [14]. One type of these
reactions is the synthesis of pyrazolones which display biological
and pharmacological properties. The pyrazolone skeleton is exist
in many antimicrobial [15], antifungal [16,17], antibacterial
[18,19], anti-inflammatory [20,21] and antitumor [22] agents. They
are also function as gastric secretion stimulatory [23], as antifilarial
activities [24] and are important in depressant disease [25]. Among
pyrazolones, there are also examples of drug-resistance antipy-
retic, analgesic [26] and a drug for the treating brain [26,27]. For
example some of known drugs that have pyrazolone skeleton were
shown in Fig. 1.
In continuous to progress the synthetic approach for the pro-
duction of various medicinally compounds using reusable nano
catalysts [28–31], herein we combined the advantages of ultra-
sonic irradiation and nanotechnology to design a new and efficient
method for synthesis of pyrazolone derivatives using CuI nanopar-
ticles under ultrasonic irradiation (Scheme 1).
2. Experimental
The research in multi-component reactions (MCRs) is a hot to-
pic of organic chemistry because of their advantageous in the prep-
2.1. Materials and apparatus
All the chemicals reagents used in our experiments were ana-
lytical grade and were used as received without further purifica-
tion. A multiwave ultrasonic generator (Sonicator 3200; Bandelin,
⇑
Corresponding author. Tel.: +98 361 5912385; fax: +98 361 5552935.
E-mail address: safaei@kashanu.ac.ir (J. Safaei-Ghomi).
1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2013.01.005

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A. Ziarati et al. / Ultrasonics Sonochemistry 20 (2013) 1069–1075
in the synthesis of pyrazolones. Then the catalyst was recycled
for five times.
2.3. General procedure for the synthesis of 2-aryl-5-methyl-
2,3-dihydro-1H-3-pyrazolones
2.3.1. Typical heating method (method A)
A
solution of hydrazine (1 mmol) and ethyl acetoacetate
(1 mmol) in water (3 ml) was stirred at room temperature for
60 min. Then aromatic aldehyde (1 mmol), b-naphthol (1 mmol)
and CuI nanoparticles (3 mol%) were added and heated to reflux
for the appropriate times (monitored by TLC). After completed
reaction the solid was filtered off and washed with chloroform.
The residue was dissolved in hot ethanol and then filtered until
heterogeneous catalyst was recovered. The filtrate was evaporated
to afford the pure product in 67–74% yield.
Fig. 1. Examples of drugs contain pyrazolone skeleton.
MS 73, Germany), equipped with a converter/transducer and tita-
nium oscillator (horn), 12.5 mm in diameter, operating at 20 kHz
with a maximum power output of 200 W, was used for the ultra-
sonic irradiation. The ultrasonic generator automatically adjusted
the power level. 1H NMR and 13C NMR spectra were recorded on
Bruker Avance-400 MHz spectrometers in the presence of tetra-
methylsilane as internal standard. The IR spectra were recorded
on FT-IR Magna 550 apparatus using with KBr plates. The elemen-
tal analyses (C, H, N) were obtained from a Carlo ERBA Model EA
1108 analyzer. Melting points were determined on Electro thermal
9200, and are not corrected. Microscopic morphology of products
was visualized by SEM (LEO 1455VP). The N2 adsorption/desorp-
tion analysis (BET) was performed at À196 °C using an automated
gas adsorption analyzer (Tristar 3000, Micromeritics). Powder
X-ray diffraction (XRD) was carried out on a Philips diffractometer
2.3.2. Ultrasound irradiation method (method B)
In a two-necked flask, a solution of hydrazine (1 mmol) and
ethyl acetoacetate (1 mmol) in water (3 ml) was sonicated at
20 kHz frequency and 50 W power, for 10 min in room tempera-
ture. Then aromatic aldehyde (1 mmol), b-naphthol (1 mmol) and
CuI nanoparticles (3 mol%) were added and sonicated for appropri-
ate times (monitored by TLC). After completed reaction the solid
was filtered off and washed with chloroform. The residue was dis-
solved in hot ethanol and then filtered until heterogeneous catalyst
was recovered. The filtrate was evaporated to afford the pure prod-
uct in 86–93% yield. The spectral data for some selected com-
pounds were given below.
of X’pert company with mono chromatized Cu K
a radiation
(k = 1.5406 Å). Transmission electron microscopy (TEM) images
were obtained on a Philips EM208 transmission electron micro-
scope with an accelerating voltage of 100 kV.
2.4. Representative spectral data
2.4.1. 4-[(2-Hydroxy-1-naphthyl)(phenyl)methyl]-5-methyl-2-
phenyl-2,3-dihydro-1H-3-pyrazolone (5a)
White solid; m.p = 205–206 °C; FT-IR (KBr): 3418, 3161, 3084,
2.2. Preparation of copper iodide nanoparticles under ultrasound
irradiation
2911, 1613, 1593, 1492, 1412, 1279, 1211, 730 and 694 cmÀ1 1H
;
NMR (400 MHz, DMSO-d6): d(ppm) 2.11 (s, 3H, CH3), 6.21 (s, 1H,
CH), 7.08 (m, 4H, ArH), 7.13 (m, 2H, ArH), 7.18 (m, 3H, ArH), 7.29
(m, 3H, ArH), 7.31 (s, 1H, NH), 7.71 (m, 3H, ArH), 8.23 (s, 1H,
ArH), 10.83 (brs, 1H, OH); 13C NMR (100 MHz, DMSO-d6): d
(ppm) 16.6, 40.9, 124.6, 125.3, 126.1, 127.4, 128.2, 130.5, 130.9,
131.6, 132.2, 133.0, 133.8, 133.9, 134.2, 138.9, 141.6, 146.8,
153.4, 159.1; Anal. Calcd. for C27H22N2O2: C, 79.77%; H, 5.46%; N,
6.90%; Found: C, 79.73%; H, 5.49%; N, 6.87%.
The catalyst was prepared via sonochemical method (worked at
20 kHz frequency and 90 W power). CuSO4 was used as the Cu
source. Firstly the copper substrate (1 mmol) is ultrasonically
cleaned for 20 s in acetone, followed by repeated rinsing with dis-
tilled water. After drying, the substrate is dipped slowly into a
solution of KI (1 mmol) in 40 mL of distilled water and sonicated
to react for 30 min. When the reaction was completed, disperse
gray precipitate was obtained. The solid was filtered and washed
with distilled water and ethanol several times and dried in vacuum
in less than 40 °C.
2.4.2. 4-[(2-Hydroxy-1-naphthyl)(4-methoxyphenyl)methyl]-5-
methyl-2-phenyl-2,3-dihydro-1H-3-pyrazolone (5d)
White solid; m.p = 180–181 °C; FT-IR (KBr): 3421, 3151, 3091,
2942, 1618, 1591, 1486, 1416, 1292, 814, 731, 688 cmÀ1 1H
;
2.2.1. Reusability of catalyst
NMR (400 MHz, DMSO-d6): d(ppm) 2.13 (s, 3H, CH3), 3.59 (s, 3H,
OCH3), 6.12 (s, 1H, CH), 6.77 (m, 2H, ArH), 6.95 (m, 2H, ArH),
7.08 (m, 1H, ArH), 7.23 (m, 2H, ArH),7.35 (s, 1H, NH), 7.46 (m,
The recovered catalyst from the experiment was washed by
acetone and hot ethanol (3 Â 5 mL). Then, it was dried and used
R1
H
O
O
N
NH2
R2
Me
OEt
(1)
(2)
CuI nanoparticles, H2O
HN
N
O
OH
OHC
I) reflux conditions
HO
or
(5a-5o)
II) U.S., rt
R1
R2
(3)
(4)
Scheme 1. Synthesis of pyrazolones in the presence of CuI nanoparticles under reflux and sonication conditions.

A. Ziarati et al. / Ultrasonics Sonochemistry 20 (2013) 1069–1075
1071
694 cmÀ1 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.14 (s, 3H,
;
CH3), 6.12 (s, 1H, CH), 7.04 (m, 5H, ArH), 7.09 (s, 1H, NH),7.21
(m, 2H, ArH), 7.29 (m, 2H, ArH), 7.36 (t, 1H, ArH), 7.56 (t, 1H,
ArH), 7.71 (d, 1H, ArH), 7.83 (d, 1H, ArH), 8.03 (d, 1H, ArH), 10.78
(brs, 1H, OH); 13C NMR (100 MHz, DMSO-d6): d (ppm) 14.7, 36.4,
106.4, 120.2, 121.5, 122.2, 123.4, 126.7, 127.2, 127.6,128.4, 128.7,
128.9, 129.1, 129.2, 129.6, 131.4, 131.9, 133.5, 134.9,138.6, 146.2,
153.9; Anal. Calcd. for C27H20BrClN2O2: C, 62.39%; H, 3.88%; N,
5.39%; Found: C, 62.37%; H, 3.69%; N, 5.46%.
3. Results and discussion
3.1. Structural analysis of CuI nanoparticles
Fig. 2. The XRD pattern of CuI nanoparticles.
The XRD pattern of the CuI nanoparticles was shown in
Fig. 2. All reflection peaks can be readily indexed to pure cubic
crystal phase of nano crystalline copper iodide. Also no specific
peaks due to any impurities were observed. The pattern agrees
well with the reported pattern for copper iodide (JCPDS No.
75-0832). The crystallite size diameter (D) of the CuI nanopar-
ticles has been calculated by Debye–Scherrer equation (D = Kk/
bcosh), where FWHM (full-width at half-maximum or half-
width) is in radians and h is the position of the maximum
of diffraction peak (b = 0.4723 [°2h]), K is the so-called shape
factor, which usually takes a value about 0.9, and k is the
X-ray wavelength. Crystallite size of CuI has been found to
be 20 nm.
The chemical purity of the sample as well as their stoichiometry
was tested by EDAX studies. The EDAX spectrum given in Fig. 3 was
shown the presence of copper and iodine as the only elementary
components.
In order to investigate the morphology and particle size of CuI
nanoparticles, SEM image of copper iodide nanoparticles was pre-
sented in Fig. 4. By SEM image some data about the morphology
and size of catalyst particles were obtained. Particle size of the
nano CuI was found to be small size till 20 nm.
3H, ArH), 7.68 (m, 3H, ArH), 7.79 (m, 1H, ArH), 8.19 (s, 1H, ArH),
10.86 (brs, 1H, OH); 13C NMR (100 MHz, DMSO-d6): d (ppm) 14.7,
34.4, 54.8, 106.6, 112.8, 119.1, 120.6, 121.8, 122.4, 124.9, 125.7,
128.2, 128.4, 128.5, 128.6, 132.6, 133.4, 136.1, 147.5, 148.6,
153.2, 156.7; Anal. Calcd. for C28H24N2O3: C, 77.04%; H, 5.54%; N,
6.42%; Found: C, 76.95%; H, 5.49%; N, 6.47%.
2.4.3. (2-(4-Clorophenyl)-4-[(2-hydroxy-1-naphthyl)
(4-nitrophenyl)methyl]-5-methyl-2,3-dihydro-1H-3-pyrazolone (5l)
White solid; m.p = 183–184 °C; FT-IR (KBr): 3431, 3087, 2916,
1616, 1595, 1493, 1342, 812,758, 735, 692, 598 cmÀ1 1H NMR
;
(400 MHz, DMSO-d6): d(ppm) 2.19 (s, 3H, CH3), 6.31 (s,1H, CH),
7.14 (m, 1H, ArH), 7.29 (s, 1H, NH), 7.33 (m, 3H, ArH), 7.46 (m,
1H, ArH),7.56 (m, 2H, ArH), 7.71 (m, 5H, ArH), 8.14 (m, 1H, ArH),
8.26 (m, 1H, ArH), 10.73 (brs, 1H, OH); 13C NMR (100 MHz,
DMSO-d6): d (ppm) 16.9, 40.8, 120.7, 121.4, 124.6, 125.9, 127.0,
127.2, 127.7, 128.3, 131.6, 133.5, 133.8, 134.2, 134.8, 138.2,
139.9, 149.6, 152.5, 153.7, 158.5, 163.1, 159.2; Anal. Calcd. for
C
27H20ClN3O4: C, 66.74%; H, 4.15%; N, 8.65%; Found: C, 67.01%; H,
4.13%; N, 8.78%.
The specific surface area was measured by nitrogen physisorp-
tion (the BET method), the specific surface area was approximately
1.94 m2/g.
For more investigation of the influence of ultrasound irradiation
in this reaction, the synthesis of nano copper iodide was compared
with previously method such as pulse laser deposition technique,
2.4.4. (2-(4-Clorophenyl)-4-[(4-Bromophenyl)(2-hydroxy-1-
naphthyl)methyl]-5-methyl-2,3dihydro-1H-3-pyrazolone (5o)
Yellowish solid; m.p = 157–158 °C; FT-IR (KBr): 3419, 3146,
3086, 2959, 1626, 1588, 1471, 1412, 1275, 816, 807, 736,
Fig. 3. The EDAX pattern of CuI nanoparticles.

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A. Ziarati et al. / Ultrasonics Sonochemistry 20 (2013) 1069–1075
Table 2
Optimization of the model reaction using various solvents.
Entry
Solvent
Time (min)
Yielda (%)
1
2
3
4
5
6
CH3CN
Toluene
H2O
EtOH
EtOH/H2O
Solvent-free
80
80
50
60
60
200
72
70
91
85
87
14
a
Isolated yield.
posed to ultrasound irradiation, extremely-high pressures and
temperatures are produced during acoustic cavitation, providing
energy to generate CuI nuclei. Also, the produced high temperature
and the adsorbed bubbling gasses on nuclei surface reduce the
interfacial free energy between nuclei and solution, consequently
inhibiting the growth of particles. Thus, a much more rapid nucle-
ation followed with a slower grain growth leads to smaller particle
sizes with high specific surface area in the process [37,38]. The in-
creased surface area due to small particle size added benefit for its
reactivity. This factor is responsible for the upward accessibility of
the substrate molecules on the catalyst surface.
Fig. 4. SEM image of the CuI nanoparticles.
Surface-Etching Route, hydrothermal treatment, and coprecipita-
tion [32–35] (Table 1).
As shown in Table 1, particle sizes of nano CuI prepared in the
absence of ultrasound were ranging from 70 nm to 1 lm, and spe-
cific surface area was 2.08 m2 gÀ1 [36]. However, size of CuI nano-
particles prepared in the presence of ultrasound was reduced until
3.2. Catalytic behaviors of CuI nanoparticles
20 nm, and specific surface area was increased about 2.96 m2 gÀ1
.
This observation is described by the effect of sonication. It is
known that size control must be done within a very short nucle-
ation period and the final particle number does not change during
the particle growth. When the solution contain precursor is ex-
In order to consider the effects of this nano catalyst under ultra-
sound irradiation; catalytic behaviors of same types of catalyst
such as MgO, ZnO, AgI, CuI were compared in the reaction of phe-
nyl hydrazine, ethyl acetoacetate, b-naphthol and benzaldehyde
Table 1
Comparison of ultrasonic method with other methods.
Method
Ultrasonica
20–40 nm
Pulse laser deposition
about 1
Surface-Etching
about 500 nm
Hydrothermal
70–110 nm
Coprecipitation
300–600 nm
Particle size
lm
a
Reaction condition: reaction of CuSO4 and KI at room temperature under ultrasonic irradiation.
75%
79%
HN
HN
N
N
O
O
73%
HO
HO
87%
HN
HN
5
N
N
O
O
0
n
HO
i
HO
m
m
i
n
0
5
64%
6
0
n
i
m
91%
m
i
n
5
3
HN
HN
H
N
OHC
N
N
O
O
NH2
HO
HO
O
O
HO
91%
nano CuI (4 mol%)
35 min
without catalyst
80 min
Me
OEt
trace
HN
HN
N
N
O
O
HO
HO
U. S.
Scheme 2. Optimization of the model reaction using various catalysts under ultrasonic irradiation.

A. Ziarati et al. / Ultrasonics Sonochemistry 20 (2013) 1069–1075
1073
Table 3
Synthesis of pyrazolone derivatives under reflux conditions and sonication (method A and B).
Entry
R1
R2
Product
Method Aa
Time (min)
Method Bb
Time (min)
M.P. (°C)
Yieldc (%)
Yieldc (%)
Found
Reported
1
2
3
4
5
6
7
8
H
4-Cl
H
H
H
H
H
H
H
H
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
360
330
330
420
420
360
360
360
390
330
330
360
390
420
330
72
73
74
69
67
71
73
72
70
71
70
70
71
68
70
35
30
30
40
45
35
35
35
40
40
40
40
40
45
40
91
93
93
88
86
90
92
91
89
92
91
92
90
87
92
205–206
176–177
209–210
180–181
141–142
133–134
179–180
156–157
184–185
161–162
153–154
183–184
122–123
173–174
157–158
205 [32]
176 [32]
207 [32]
179 [32]
–
–
–
157 [32]
184 [32]
–
4-NO2
4-Me
2-Me
2-Cl
4-Br
2-NO2
4-OMe
H
4-Cl
4-NO2
2-Cl
4-Me
4-Br
9
H
10
11
12
13
14
15
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
153 [32]
–
–
–
–
a
b
c
Reaction condition: reaction of hydrazine, ethylacetoacetate, b-naphthol and aldehyde in water at reflux.
Reaction condition: reaction of hydrazine, ethyl acetoacetate, b-naphthol and aldehyde at room temperature under ultrasonic irradiation.
Isolated yields.
O
O
nano CuI
nano CuI
R2NHNH2
+
O
CuI
O
H3C
OEt
N
NR2
6a
N
NR2
1
6b
2
H
O
CuI
N
NR2
6c
CuI
O
R1
CuI
O
CuI
O
OH
NR2
N
nano CuI
+
R1
H
3
4
7
6d
R1
O
R1
H
HN
N
N
N
O
R2
R2
HO
HO
8
5
Scheme 3. Possible mechanism for the formation of pyrazolones in the presence of CuI nanoparticles.
(Scheme 2). Obtain results were indicated that in absence of cata-
lyst, trace amount of product was generated but in presence of CuI
nanoparticles the reaction proceeds in high yield. Also the resulting
of Scheme 2 shows the optimum amount of the catalyst was
(3 mol%) of CuI nanoparticles which increasing of this amount
did not show any significant change in yield and time of reaction.
Expectedly, the catalytic system should be influenced by vari-
ous reaction factors, such as solvent system. To establish the opti-
mal reaction conditions, we have screened the effect of different
solvents with varying polarity and protic nature. It was observed
that water proved to be the best choice for this reaction over any
solvents such as toluene, acetonitrile and ethanol. Also the consid-
erable results were not observed in solvent free conditions
(Table 2).
Fig. 5. Reusability study of nano CuI for model reaction.

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A. Ziarati et al. / Ultrasonics Sonochemistry 20 (2013) 1069–1075
Fig. 6. TEM images of nano CuI before use (a) and after five times reuse (b).
The study was extended to prepare various 2-aryl-5-methyl-
and supply additional activation through efficient mixing and en-
hanced mass transport [43–46]. Furthermore, ultrasound irradia-
tion activates the reaction mixture by inducing high local
pressure and temperature generated inside the cavitation bubble
and its interfaces when it collapses and accelerates the reaction
rate and shortens the reaction time [41]. Therefore, it is reasonable
to assume that these effects should accelerate this four-component
reaction.
Consequently,the same reaction was carried out many times to
check the reusability of catalyst. The catalyst could be reused for
five times with a minimal loss of activity (Fig. 5).
The characterization of the nano CuI before use and after five
times reuse showed the same particle size by TEM (Fig. 6). Interest-
ingly, the shape and size of the nanoparticles remained unchanged
before and after reaction. We believe that, this isalso the possible
reason for the extreme stability of the CuI nanoparticles presented
herein.
2,3-dihydro-1H-3-pyrazolones using CuI nanoparticles. For explain
the efficiency and scope of the present process and to delineate the
role of ultrasound, reactions were compared at reflux conditions
(method A) and ultrasonic irradiation (method B) in water in the
presence of nano copper iodide 3 mol% (Table 3). When the reac-
tion was carried out under reflux conditions it gave comparatively
low yields of products and took longer reaction times, while the
same reaction was carried under ultrasonic irradiation gave excel-
lent yields of products in short reaction times. Also, compared with
conventional approach [39], this method is more environmentally
friendly, particularly when considering the basic green chemistry
concepts.
The reason may be the phenomenon of cavitation formed by
ultrasound. Cavitation is the origin of sonochemistry, a physical
process that builds, enlarges, and collapses gaseous and vaporous
cavities in an irradiated liquid, hence enhancing the mass transfer
and allowing chemical reactions to occur. Applying ultrasound,
compression of the liquid is followed by rarefaction, in which a
sudden pressure drop forms small, oscillating bubbles of gaseous
substances. These bubbles are small and rapidly collapse, they
can be seen as microreactors that offer the opportunity of speeding
up certain reactions and also allow mechanistically novel reactions
to take place in an absolutely safe manner [40–42].
4. Conclusions
To summary, we offer an efficient method to prepare copper io-
dide in nano scale via sonication and report this nanoparticles as a
highly efficient catalyst for the synthesis of 2-aryl-5-methyl-
2,3-dihydro-1H-3-pyrazolones by means of a multi-component
condensation of hydrazine, ethyl acetoacetate, aldehyde and
b-naphthol in water under ultrasound irradiation. This method is
applicable to a wide range of substrates, including aromatic alde-
hydes, and hydrazines to provide the corresponding pyrazolones
in good to excellent yields. The present method indicates some
advantages of sonication such as using green procedure, reducing
reaction times, high yields, operational simplicity, and assist to
prepare the lowest size and highest surface of CuI nanoparticles
as catalyst.
A proposed mechanism for this four-component reaction was
outlined in Scheme 3. The first step of this reaction can be visual-
ized by activation of ethyl acetoacetate 1 with nano CuI, following
by nucleophilic attack of hydrazine 2 to give 6a. On the other hand,
nano CuI allowing compound 6a was adsorbed on its surface to
provide 6d. In another reaction, b-naphthol 4 undergoes condensa-
tion with aldehyde 3 in presence of nano CuI to afford a, b-unsat-
urated carbonyl compound 7. Michael addition reaction between
compounds 7 and 6d gives intermediate 8 following by tautomer-
ization to afford products 5. The reaction mechanism involves a po-
lar transition state starting from a neutral ground state, that under
ultrasonic irradiation ionic reactions are accelerated by physical ef-
fects. Typically, in a heterogeneous solid/liquid system, the col-
lapse of the cavitation bubble results in significant structural and
mechanical defects. Collapse near the surface produces an asym-
metrical inrush of the fluid to fill the void forming a liquid jet
targeted at the surface. This effect is equal to high-pressure/
high-velocity liquid jets. These jets activate the nano catalyst and
increase the mass transfer to the surface by the disruption of the
interfacial boundary layers as well as dislodging the material occu-
pying the inactive positions. Collapse on the surface, produces an
adequate amount of energy to cause fragmentation. Thus, in this
situation, ultrasound can increase the surface area for a reaction
Acknowledgement
The authors are grateful to University of Kashan for supporting
this work by Grant NO: 159196/XX.
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