Efficient one-pot three-component synthesis of N-(4-arylthiazol-2-yl) hydrazones in water under ultrasound irradiation

Article abstract of DOI:10.1016/j.ultsonch.2011.10.017

A highly efficient and facile one-pot three-component synthesis of N-(4-arylthiazol-2-yl) hydrazones was carried out in excellent yield without any catalyst in water under ultrasound irradiation.

Full text of DOI:10.1016/j.ultsonch.2011.10.017

Ultrasonics Sonochemistry 19 (2012) 475–478
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Efficient one-pot three-component synthesis of N-(4-arylthiazol-2-yl) hydrazones
in water under ultrasound irradiation
c,
b
d
Dong-Nuan Zhang a,b, Ji-Tai Li a, , Ya-Li Song , Hui-Min Liu , Hong-Ya Li
⇑
⇑
a College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China
b College of Science, Agricultural University of Hebei, Baoding 071001, China
c Pharmaceutical Sciences College, Hebei University, Baoding 071002, China
d College of Life Science, Agricultural University of Hebei, Baoding 071001, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 June 2011
Received in revised form 15 October 2011
Accepted 15 October 2011
Available online 10 November 2011
A highly efficient and facile one-pot three-component synthesis of N-(4-arylthiazol-2-yl) hydrazones was
carried out in excellent yield without any catalyst in water under ultrasound irradiation.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
One-pot synthesis
Hydrazothiazole
Condensation
Ultrasound irradiation
Aqueous media
1. Introduction
of a-halo ketones, thiosemicarbazide, and 2-hydroxybenzaldehyde
in PEG-400 to give good results [10].
Schiff bases are well known for their pharmacological properties
as anti-bacterial, anti-fungal, anti-cancer and anti-viral agents [1].
Similarly, thiazole derivatives possess activities such as anti-bacte-
rial [2], anti-fungal [3], anti-inflammatory [4], anti-hypertensive
[5], anti-HIV [6], anti-tumor [7], and anti-filarial [7c,d]. The poten-
tial possibility of hydrazothiazole derivatives for better therapeutic
results has attracted extensive interest in last decade. Generally,
N-(4-arylthiazol-2-yl) hydrazones are synthesised through two
steps in conventional methods. Aromatic aldehydes or ketones react
with thiosemicarbazide to yield thiosemicarbazones, which then
Organic reactions in aqueous media have currently attracted
increasing interest because of environmental issues and the under-
standing of biochemical processes. Water offers many practical and
economic advantages as a reaction solvent, including low cost, safe
handing and environmental compatibility. Recently, many organic
reactions in aqueous media have been described in the literatures
[11]. On the other hand, a large number of organic reactions can be
carried out in higher yield, shorter reaction time and milder condi-
tions under ultrasonic irradiation than at classical conditions [12].
To the best of our knowledge, there is no report on one-pot three-
component reaction in water for the synthesis of N-(4-arylthiazol-
2-yl) hydrazones under ultrasound irradiation. Herein, we wish to
report an efficient one-pot procedure for the synthesis of N-(4-aryl-
thiazol-2-yl) hydrazones in water under ultrasound irradiation
(Scheme 1).
react with
x-bromoacetophenone to obtain N-(4-arylthiazol-2-yl)
hydrazones by the cyclization [8]. In spite of their potential utility,
some of the reported two-step methods suffer from drawbacks such
as long reaction time, use of organic solvents, and moderate yields.
Compared with two-steps strategy, one-pot reaction provides
useful products without isolation of any intermediate, and thus
reduces time, saves both energy and raw materials [9]. Kamble
et al. described the synthesis of 2-{2-[N-(2-hydroxybenzylid-
ene)hydrazino]thiazol-4-yl}phenols by the one-pot condensation
2. Methods
2.1. Apparatus and analysis
Melting points were uncorrected. Sonication was performed in
Tianjin AS 20500AT Ultrasonic Cleaner (with a frequency of
25 kHz and a nominal power 250 W). NMR spectra were measured
on a Bruker AVANCE 600 (600 MHz) spectrometer using TMS as the
⇑
Corresponding authors. Address: College of Chemistry and Environmental
Science, Hebei University, Wusi East Road No. 180, Baoding 071002, China. Fax: +86
312 5079628 (J.-T. Li).
E-mail address: lijitai@hbu.cn (J.-T. Li).
1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2011.10.017

476
D.-N. Zhang et al. / Ultrasonics Sonochemistry 19 (2012) 475–478
O
3052, 1618, 1538; Anal. Calcd for C16H13N3OS: C 65.06, H 4.44, N
14.23%; Found: C 65.40, H 4.32, N 14.35%.
O
R1
R
S
S
water
NNH
NH2NHCNH2 BrH2C
R1
R
R2
N
r.t., u.s.
R2
2
3
1
2.2.4. Compound 3d
2-[2-(2-Chlorobenzylidene)hydrazinyl]-4-phenyl-1,3-thiazole,
solid, mp 174–175 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm):
12.40 (s, 1H, NH), 8.40 (s, 1H, N@CH), 7.93 (dd, J = 7.8 Hz, 1.8 Hz,
1H, ArH), 7.84–7.88(m, 2H, ArH), 7.51 (dd, J = 7.8 Hz, 1.2 Hz, 1H,
ArH), 7.38–7.44 (m, 4H, ArH), 7.36 (s, 1H, thiazole H), 7.31 (t,
J = 7.2 Hz, 1H, ArH); 13C NMR (150 MHz, DMSO-d6) d (ppm):
168.4, 138.7, 132.6, 132.0, 131.7, 131.1, 130.4, 130.2, 129.1,
Scheme 1. One-pot three-component synthesis of N-(4-arylthiazol-2-yl) hydra-
zones under ultrasound irradiation.
internal standards and DMSO as a solvent. HRMS spectra were
determined on a Bruker apex ultra 7.0 T Fourier transform mass
spectrometer. IR spectra were recorded on a Rayleigh WQF-510
FTIR spectrometer. Elemental analyzes were taken with an Exeter
Analytical CE-440 elemental analyzer.
128.1, 127.9, 126.7, 126.0, 104.6; IR (KBr, m
, cmꢀ1): 3415, 3249,
3151, 1573; Anal. Calcd for C16H12ClN3S: C 61.24, H 3.85, N
13.39%; Found: C 61.54, H 3.77, N 13.71%.
2.2. General procedure for the condensation of N-(4-arylthiazol-2-yl)
hydrazones
2.2.5. Compound 3e
2-[2-(3-Chlorobenzylidene)hydrazinyl]-4-phenyl-1,3-thiazole,
solid, mp 163–164 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm):
12.36 (s, 1H, NH), 8.03 (s, 1H, N@CH), 7.89–7.84 (m, 2H, ArH),
7.71 (s, 1H, ArH), 7.64–7.61(m, 1H, ArH), 7.48–7.39 (m, 4H, ArH),
7.36 (s, 1H, thiazole H), 7.31 (dt, J = 7.2 Hz, 1.2 Hz, 1H, ArH); 13C
NMR (150 MHz, DMSO-d6) d (ppm): 168.5, 151.0, 140.0, 137.1,
135.0, 134.1, 131.2, 129.3, 129.1, 128.1, 126.0, 125.9, 125.4,
Aromatic aldehydes or ketones (1, 0.5 mmol), thiosemicarba-
zide (0.5 mmol), substituted phenacyl bromide (2, 0.5 mmol) and
water (8 mL) were mixed in a 25 mL round-bottomed flask. The
reaction mixture was either stirred, or irradiated in the water bath
of an ultrasonic cleaner, at room temperature for the period (the
reaction was monitored by TLC, silica gel; petroleum ether:ethyl
acetate = 3:1 V/V) as indicated in Table 2. After completion of the
reaction, the reaction mixture was filtered, and the precipitate
was washed with EtOH, affording the crude product, which was
purified by column chromatography on basic alumina column
(200–300 mesh) eluted with petroleum ether (b.p. 60–90 °C) or a
mixture of petroleum ether and ethyl acetate (10:1 V/V). The
authenticity of the products (3a–3l) was established by their 1H
NMR, 13C NMR, IR, HRMS data or elemental analyzes.
104.4; IR (KBr,
16H12ClN3S: C 61.24, H 3.85, N 13.39%; Found: C 61.25, H 4.00,
N 13.11%.
m
, cmꢀ1): 3415, 3155, 3072, 1581; Anal. Calcd for
C
2.2.6. Compound 3f
2-[2-(4-Chlorobenzylidene)hydrazinyl]-4-phenyl-1,3-thiazole,
solid, mp 178–179 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm):
12.07 (s, 1H, NH), 8.03 (s, 1H, N@CH), 7.85 (d, J = 7.2 Hz, 2H,
ArH), 7.66 (d, J = 8.4 Hz, 2H, ArH), 7.48 (d, J = 7.8 Hz, 2H, ArH),
7.40 (t, J = 7.8 Hz, 2H, ArH), 7.34–7.27 (m, 2H, ArH + thiazole H);
13C NMR (150 MHz, DMSO-d6) d (ppm): 168.6, 151.0, 140.4,
135.1, 134.1, 133.8, 129.4, 129.1, 128.3, 128.0, 126.0, 104.2; IR
2.2.1. Compound 3a
2-(2-Benzylidenehydrazinyl)-4-phenyl-1,3-thiazole, solid, m.p.
174–175 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm): 12.18 (s, 1H,
NH), 8.05 (s, 1H, N@CH), 7.87 (d, J = 7.2 Hz, 2H, ArH), 7.67 (d,
J = 7.2 Hz, 2H, ArH), 7.37–7.47 (m, 5H, ArH), 7.33 (s, 1H, thiazole
H), 7.31 (t, J = 7.2 Hz, 1H, ArH); 13C NMR (150 MHz, DMSO-d6) d
(ppm): 168.7, 141.6, 135.1, 134.8, 129.7, 129.3, 129.1, 128.0,
(KBr,
16H12ClN3S: C 61.24, H 3.85, N 13.39%; Found: C 61.00, H 3.76,
m
, cmꢀ1): 3434, 3286, 3160, 1581, 1502; Anal. Calcd for
C
N 13.87%.
126.7, 125.9, 104.1; IR (KBr,
m
, cmꢀ1): 3394, 3305, 3151, 1560,
2.2.7. Compound 3g
1535; Anal. Calcd for C16H13N3S: C 68.79, H 4.69, N 15.04%; Found:
C 68.72, H 4.64, N 14.88%.
5-Methoxy-2-{[2-(4-phenyl-1,3-thiazol-2-yl)hydrazinylid-
ene]methyl}phenol, solid, mp 181–182 °C; 1H NMR (600 MHz,
DMSO-d6) d (ppm): 12.17 (s, 1H, NH), 9.51 (s, 1H, OH), 8.36 (s,
1H, N@CH), 7.86 (d, J = 7.8 Hz, 2H, ArH), 7.45–7.38 (m, 2H, ArH),
7.34–7.28 (m, 2H, ArH + thiazole H), 7.26 (d, J = 7.8 Hz, 1H, ArH),
6.97 (d, J = 8.4 Hz, 1H, ArH), 6.97 (td, J = 7.8 Hz, 1.2 Hz, 1H, ArH),
3.83 (s, 3H, CH3); 13C NMR (150 MHz, DMSO-d6) d (ppm): 168.4,
148.5, 145.9, 140.0, 135.1, 129.1, 128.0, 126.0, 121.0, 119.7,
2.2.2. Compound 3b
2-[2-(4-Methoxybenzylidene)hydrazinyl]-4-phenyl-1,3-thia-
zole, solid, m.p. 169–170 °C; 1H NMR (600 MHz, DMSO-d6) d
(ppm): 12.01 (s, 1H, NH), 8.00 (s, 1H, N@CH), 7.86 (d, J = 7.8 Hz,
2H, ArH), 7.61 (d, J = 9.0 Hz, 2H, ArH), 7.41 (t, J = 7.8 Hz, 2H, ArH),
7.27–7.32 (m, 2H, ArH + thiazole H), 7.00 (d, J = 9.0 Hz, 2H, ArH),
3.80 (s, 3H, CH3); 13C NMR (150 MHz, DMSO-d6) d (ppm): 168.3,
160.2, 150.6, 141.3, 134.7, 128.5, 127.8, 127.4, 127.0, 125.5,
118.4, 113.0, 103.8, 56,3; IR (KBr,
m
, cmꢀ1): 3459, 3342, 3162,
3031, 1621, 1596, 1540; Anal. Calcd for C17H15N3O2S: C 62.75, H
4.65, N 12.91%; Found: C 62.32, H 4.67, N 12.56%.
114.3, 103.3, 55.2; IR (KBr,
m
, cmꢀ1): 3290, 3112, 2962, 2846,
1612, 1565, 1511; Anal. Calcd for C17H15N3OS: C 66.00, H 4.89, N
13.58%; Found: C 65.73, H 4.84, N 13.68%.
2.2.8. Compound 3h
N,N-Dimethyl-4-{[2-(4-phenyl-1,3-thiazol-2-yl)hydrazinylid-
ene]methyl}aniline, solid, mp 183–184 °C; 1H NMR (600 MHz,
DMSO-d6) d (ppm): 11.79 (s, 1H, NH), 7.92 (s, 1H, N@CH), 7.87–
7.82 (m, 2H, ArH), 7.47 (d, J = 9.0 Hz, 1H, ArH), 7.40 (t, J = 7.8 Hz,
2H, ArH), 7.29 (t, J = 7.2 Hz, 1H, ArH), 7.23 (s, 1H, thiazole H),
6.74 (d, J = 8.4 Hz, 2H, ArH), 2.95 (s, 6H, 2CH3); 13C NMR
(150 MHz, DMSO-d6) d (ppm): 168.9, 151.5, 150.9, 142.9, 140.0,
2.2.3. Compound 3c
2-{[2-(4-Phenyl-1,3-thiazol-2-yl)hydrazinylidene]methyl}phe-
nol, solid, mp 195–196 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm):
12.15 (s, 1H, NH), 10.13 (s, 1H, OH), 8.33 (s, 1H, N@CH), 7.86 (d,
J = 7.2 Hz, 2H, ArH), 7.62–7.65 (m, 1H, ArH), 7.41 (t, J = 7.8 Hz,
2H, ArH), 7.29–7.33 (m, 2H, ArH + thiazole H), 7.21–7.25 (m, 1H,
ArH), 6.87–6.93 (m, 2H, ArH); 13C NMR (150 MHz, DMSO-d6) d
(ppm): 168.4, 156.4, 151.3, 139.9, 135.2, 130.0, 129.1, 128.1,
135.3, 129.1, 128.0, 126.0, 122.3, 112.4, 103.4, 40.3; IR (KBr,
cmꢀ1): 3372, 3290, 3104, 2798, 1606, 1565, 1523; Anal. Calcd for
18H18N4S: C 67.05, H 5.63, N 17.38%; Found: C 66.82, H 5.55, N
17.10%.
m,
C
127.0, 126.0, 120.0, 116.6, 114.3, 103.9; IR (KBr, m
, cmꢀ1): 3317,

D.-N. Zhang et al. / Ultrasonics Sonochemistry 19 (2012) 475–478
477
2.2.9. Compound 3i
CH3); 13C NMR (150 MHz, DMSO-d6) d (ppm): 170.5, 147.2, 138.7,
2-(2-Cyclopentylidenehydrazinyl)-4-phenyl-1,3-thiazole, solid,
mp 156–157 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm): 10.55 (s,
1H, NH), 7.86–7.82 (m, 2H, ArH), 7.36 (dd, J = 10.6 Hz, 4.9 Hz, 2H,
ArH), 7.30–7.26 (m, 1H, ArH), 7.22 (s, 1H, thiazole H), 2.36 (dd,
J = 11.2 Hz, 7.0 Hz, 4H, 2CH2), 1.82–1.75 (m, 2H, CH2), 1.73–1.66
(m, 2H, CH2); 13C NMR (150 MHz, DMSO-d6) d (ppm): 170.2,
162.1, 151.0, 135.4, 129.0, 127.8, 126.0, 103.6, 33.3, 29.1, 25.1; IR
135.6, 134.1, 132.4, 129.5, 129.3, 127.7, 127.0, 126.1, 105.3, 21.3,
14.5; IR (KBr, m
, cmꢀ1): 3332, 1697, 1683, 1670, 1560, 1510; HRMS:
m/z Calcd for C18H17ClN3S: [M+H]+, 342.0826; Found: 342.0829.
2.2.12. Compound 3l
2-(2-Cyclohexylidenehydrazinyl)-4-p-tolyl-1,3-thiazole, solid,
mp 132–133 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm): 10.84 (s,
1H, NH), 7.71 (d, J = 8.1 Hz, 2H, ArH), 7.22 (d, J = 8.0 Hz, 2H, ArH),
7.18 (s, 1H, thiazole H), 2.39 (t, J = 6.9 Hz, 4H, 2CH2), 2.32 (s, 3H,
CH3), 1.80–1.69 (m, 6H, 3CH2); 13C NMR (150 MHz, DMSO-d6) d
(ppm): 170.6, 155.6, 135.5, 129.0, 127.8, 126.0, 103.6, 35.2, 27.6,
(KBr,
m
, cmꢀ1): 3145, 2917, 2856, 1560; HRMS: m/z Calcd for
C
14H15N3NaS: [M+Na]+, 280.0879; Found: 280.0895.
2.2.10. Compound 3j
27.3, 26.0, 25.6; IR (KBr, m
, cmꢀ1): 3062, 2948, 1558; HRMS: m/z
2-(2-Cyclohexylidenehydrazinyl)-4-phenyl-1,3-thiazole, solid,
mp 148–149 °C; 1H NMR (600 MHz, DMSO-d6) d (ppm): 10.79 (s,
1H, NH), 7.86–7.82 (m, 2H, ArH), 7.39 (dd, J = 10.7 Hz, 4.8 Hz, 2H,
ArH), 7.28 (t, J = 7.8 Hz, 1H, ArH), 7.21 (s, 1H, thiazole H), 2.44 (t,
J = 5.8 Hz, 2H, CH2), 2.23–2.27 (m, 2H, CH2), 1.56–1.66 (m, 6H,
3CH2); 13C NMR (150 MHz, DMSO-d6) d (ppm): 170.6, 155.6,
135.5, 129.0, 127.8, 126.0, 103.6, 35.2, 27.6, 27.3, 26.0, 25.6; IR
Calcd for C15H18N3S: [M+H]+, 272.1216; Found: 272.1216.
3. Results and discussion
In order to verify the effect of solvents on the condensation un-
der ultrasound, the condensation of benzaldehyde (1a), thiosemi-
carbazide and phenacyl bromide to form 3a in different solvents
was accomplished at room temperature under ultrasound irradia-
tion. The results are summarized in Table 1. As shown, the reaction
in water completed in 50 min with yield of 90%, water was more
effective than organic solvents.
The effect of temperature on the yield of 3a was also observed.
As shown in Table 2, the condensation of benzaldehyde (1a), thio-
semicarbazide and phenacyl bromide was carried out in 90% yield
within 50 min at 25 °C in water under ultrasound (Table 2, entry
1). So the reaction temperature was chosen at 25 °C.
We also did the experiment for synthesis of 2-benzylidenhyd-
razo-4-phenylthiazole using two-steps method by stirring alone
without ultrasound. The benzaldehyde reacted with thiosemicar-
bazide in water at room temperature to form benzaldehyde thio-
semicarbazone, which then reacted with phenacyl bromide to
give the corresponding 2-benzylidenhydrazo-4-phenylthiazole
(3a), the invert yield and reaction time for reaction to give 3a were
54.6% and 130 min, respectively. Under ultrasound, one-pot reac-
tion in water at room temperature was completed within 50 min
to obtain 3a in 90% yield. It is apparent that one-pot reaction under
ultrasound was more efficient than the classical two-steps
approach.
(KBr,
C
m,
cmꢀ1): 3062, 2948, 1558; HRMS: m/z Calcd for
15H18N3S: [M+H]+, 272.1216; Found: 272.1216.
2.2.11. Compound 3k
4-(4-Chlorophenyl)-2-[2-(1-p-tolylethylidene)hydrazinyl]-1,3-
thiazole, solid, mp 240–241 °C; 1H NMR (600 MHz, DMSO-d6) d
(ppm): 11.22 (s, 1H, NH), 7.89 (d, J = 8.5 Hz, 2H, ArH), 7.68 (d,
J = 8.1 Hz, 2H, ArH), 7.47 (d, J = 8.5 Hz, 2H, ArH), 7.37 (s, 1H, thia-
zole H), 7.22 (d, J = 8.2 Hz, 2H, ArH), 2.33 (s, 3H, CH3), 2.31 (s, 3H,
Table 1
The effect of solvents on reaction of benzaldehyde, thiosemicarbazide and phenacyl
bromide under ultrasound irradiation.a
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
EtOH
50
50
50
50
50
63
65
45
56
90
2-Propanol
CH3CN
CH2Cl2
H2O
a
Reaction condition: benzaldehyde, 0.5 mmol; thiosemicarbazide, 0.5 mmol;
phenyacyl bromide, 0.5 mmol; solvent: 8 mL; reaction temperature: 25 °C.
Table 2
Encouraged by this result, we extended the reaction to other aro-
maticaldehydesorketonesandsubstitutedphenacylbromideunder
ultrasound irradiation or conventional stirring respectively. The re-
sults are summarized in Table 3. As shown in Table 3, the aromatic
aldehyde with electron-rich functionality as well as electron-poor
functionality condensed with thiosemicarbazide and phenacyl bro-
mide to afford the corresponding N-(4-arylthiazol-2-yl) hydrazones
The effect of reaction temperature on the yield of 3a under ultrasound irradiation.
Entry
Temperature (°C)
Time (min)
Yield (%)
1
2
3
25
35
45
50
40
40
90
82
78
Table 3
Reaction of aromatic aldehydes or ketones, thiosemicarbazide and phenacyl bromide with and without ultrasound irradiation.
Entry
R/R1
R2
3
Conventional stirring
Time (min)
Ultrasonic irradiation
Time (min)
Yield (%)
Yield (%)
1
2
3
4
5
6
7
8
C6H5/H
H
H
H
H
H
H
H
H
H
H
4-Cl
4-CH3
3a
3b
3c
3d
3e
3f
3g
3h
3i
90
180
240
240
240
180
180
210
180
180
240
240
80
76
82
78
89
72
92
65
60
80
62
87
50
60
100
70
120
100
70
100
90
90
95
90
89
89
88
92
86
88
89
92
93
4-CH3OC6H5/H
2-OHC6H5/H
2-ClC6H5/H
3-ClC6H5/H
4-ClC6H5/H
2-OH,4-CH3OC6H5/H
4-N(CH3)2C6H5/H
(CH2)4
9
10
11
12
(CH2)5
4-CH3C6H5/CH3
(CH2)5
3j
3k
3l
80
120
100

478
D.-N. Zhang et al. / Ultrasonics Sonochemistry 19 (2012) 475–478
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in excellent yields (89–95%). Furthermore, substituted phenacyl
bromide smoothly reacted with thiosemicarbazide and aromatic
aldehyde or ketones affording the corresponding products 3k, 3l in
excellent yields of 92%, 93% (Table 2, entries 11 and 12). Compared
with conventionalstirring, the reaction underultrasoundirradiation
was completed in shorter time to give the title compounds in higher
yields. According to the two-step method in the literature [8a], the
total yield of compound 3a, 3c and 3h was 64.2%, 83.4% and 55.8%,
respectively. Whereas, the present procedure gave 3a, 3c and 3h in
90%, 90% and 86% yield (Table 2, entries 1, 3 and 8), respectively.
Compared with the one-pot reaction in PEG-400 [10], the
advantage of the present procedure is the use of water instead of
PEG-400, the reaction temperature is also reduced from 40 to
25 °C. However, the disadvantages include the longer reaction time
and a little lower yield.
It can be observed that almost all reactions were complete in 1–
2 h in water under ultrasound irradiation without any added cata-
lyst or organic solvents at r.t. The reaction time was shorter and the
yield was higher under ultrasound than under conventional
stirring.
Cavitation is the origin of sonochemistry. In the heterogeneous
reactions involving immiscible liquid, the reaction between these
species can only occur in the interfacial region between the liquids.
Sonication can be used to produce very fine emulsions and en-
hances mass transfer from immiscible liquids. This is possible be-
cause cavitational collapse at or near the interface disrupts it and
implies jets of one liquid into the other to form the emulsion
[12a,b]. These can cause the reaction to take place rapidly.
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In conclusion, we have described a simple and highly efficient
protocol for the synthesis of N-(4-arylthiazol-2-yl) hydrazones in
water as reaction medium at room temperature. Ultrasound irradi-
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use of organic solvents and catalyst. Furthermore, the procedure
offers several advantages including improved yields, simple exper-
imental procedure, cleaner reactions, and low cost, which makes it
a useful and attractive strategy in view of economic and environ-
mental advantages.
(1-arylethylidene)-N0-(4-arylthiazol-2-yl)hydrazones
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