Solvent-free synthesis of some1-acetyl pyrazoles

Article abstract of DOI:10.5012/jkcs.2013.57.5.599

Some N-acetyl pyrazoles including 1-(3-(3,4-dichlorophenyl)-5-(substituted phenyl)-4,5-dihydro-¹H-pyrazole-1-yl) ethanones have been synthesised by solvent free cyclization cum acetylation of chalcones like substituted styryl 3,4-dichlorophenyl

Full text of DOI:10.5012/jkcs.2013.57.5.599

Journal of the Korean Chemical Society
2013, Vol. 57, No. 5
Printed in the Republic of Korea
http://dx.doi.org/10.5012/jkcs.2013.57.5.599
Solvent-Free Synthesis of Some1-Acetyl Pyrazoles
†,
*
Ganesamoorthy Thirunarayanan and Krishnamoorthy Guna Sekar
‡
†
Department of Chemistry, Annamalai University, Annamalainagar-608 002, India.
*
E-mail: drgtnarayanan@gmail.com
‡
Department of Chemistry, National College, Tiruchirappalli-620 001, India.
(Received June 11, 2013; Accepted August 28, 2013)
1
ABSTRACT. Some N-acetyl pyrazoles including 1-(3-(3,4-dichlorophenyl)-5-(substituted phenyl)-4,5-dihydro- H-pyrazole-
1-yl) ethanones have been synthesised by solvent free cyclization cum acetylation of chalcones like substituted styryl 3,4-
dichlorophenyl ketones using hydrazine hydrate and acetic anhydride in presence of catalytic amount of fly-ash: H2SO4 catalyst. The
yield of these N-acetyl pyrazole derivatives are more than 75%. The synthesised N-acetyl pyrazoline derivatives were charac-
terized by their physical constants and spectral data
Key words: Solvent-free cyclization cum acetylation, N-acetyl pyrazoles, IR, NMR spectra
(substitutedphenyl)-4,5-dihydro-pyrazol-3-ylphenyl}-4-(4-
INTRODUCTION
15
hydroxyphenyl) azetidin-2-one in acetic acid. N-acetyl-3-
N-acetyl pyrazole is one of the derivatives of 4, 5-dihy-
(2-naphthyl)-5-aryl pyrazoline derivatives were synthe-
sised and studied their FTIR, NMR and HRMS data by
1
dro- H-pyrazoles. These N-acetyl pyrazole derivatives are
16
Ethiraj et al. Many N-acetyl pyrazole derivatives such as
important precursor for the synthesis of some other pyra-
1
zoline based heterocycles such as cyanopyridine indoxacarb
2
17
N-acetyl-3,5-diphenyl pyrazolines, 1-acetyl-4-5-(3-chloro-
3
4
carbohydrazide hydrazine, pyrimidine. There are numerous
solvent-free or solvent assisted acetylation methods avail-
able for the synthesis of N-acetylated pyrazoline deriva-
4-fluorophenyl)-2-furyl-3-substituted phenyl-4,5-dihydro-
18
1H-pyrazoles, 2,4-bis-(tetrahydro-1,4-oxazine)-6-4''-
{1''-acetyl-5''-(4'''-methoxyphenyl)-2''-pyrazoline-3''-yl}
5−8
tives in literature. Glacial acetic acid and acetic anhydride
19
phenylamino-s-triazine , fluorine containing arylfuryl N-
were employed with solvent assisted conventional heat-
ing, solvent-free microwave and ultrasound wave irradi-
acetylpyrazolines 7 and 4,6-dimethoxy-5-(1-acetyl-5-aryl-2-
20
pyrazolin-3-yl)benzobfurans were synthesised by syn-
5,6
ation for acetylation of pyrazolines. The sulfated solid
thetic organic chemists using conventional heating method
and studied their spectral data. These 1-acetyl pyrazoline
derivatives possess important biological activities such as
9
catalysts such as sulphated titania, sulphated zirconia,
10
11
sulphated tinoxide , sulphated and molybdated iron oxide
12
13
and sulphated and phosphate zirconia were employed for
6,7,15,18
antibacterial,
17
endogenous proteolysis, cytotoxic-
16
8
14
solvent assisted and solvent-free synthesis of organics.
ity, EGFR kinase and anti-inflammatory activities. The
literature survey reveals that there is no information avail-
able for solvent-free synthesis of some N-acetyl pyrazolines
including 3-(3,4-dichlorophenyl)-5-(substitutedphenyl)-
1
Osman et al., have synthesised 75% yield of 4,7-dimethoxy-
5-(5-aryl-N-acetylpyrazolin-3-yl)benzofuran-6-ols by reflux-
ing of Khellinone chalcones, hydrazine hydrate and glacial
acetic acid. The 5-(p-tolyl)-4,5-dihydro-1-acetyl-pyrazol-
3-yl-phenyl}-3H-quinazolin-4-ones were synthesised using
refluxation method of corresponding chalcones with hydra-
1
4,5-dihydro- H-pyrazole) derivatives by cyclization of the
respective chalcones and acetic anhydride in the presence
of solid fly-ash:H2SO4 catalyst. Therefore the authors
have taken efforts to synthesis some N-acetyl pyrazolines
including 3-(3,4-dichlorophenyl)-5-(substitutedphenyl)-
14
zine acetic acid in ethanol by Mosaad et al. More than
1
84% yield of some series of new N -cinnamoyl-3,5-diaryl-
1
4,5-dihydro- H-pyrazole) derivatives by solvent free
2-pyrazolines have been synthesised using microwave as
6
well as conventional heating by Srivastava et al. Shah et
microwave assisted cyclization of chalcones with hydra-
zine hydrate and acetic anhydride in presence of catalytic
quantity of fly-ash:H2SO4. The purities of these pyrazo-
lines were checked by their physical constants and spec-
tral data with reference published earlier in literature.
1
al., have synthesised 75% yield and studied the IR and H
NMR spectra of some new series of 4-(4-hydroxyphenyl)-
3-chloro-1-{4-5-(substituted phenyl)-1-acetyl-4,5-dihydro-
pyrazol-3-ylphenyl} azetidin-2-one with 3-chloro-1-{4-5-
-599-

600
Ganesamoorthy Thirunarayanan and Krishnamoorthy Guna Sekar
Figs. 1a and 1b depicted that the crystallinity is found to
EXPERIMENTAL
be more in pure fly ash. The spherical shaped particles are
clearly seen at both magnifications in Figs. 1a and 1b. Fig.
1a reveals that the globular structure of pure fly ash (round
shaped particle). This also seen from Figs. 1c and 1d that
some of the particles are slightly corroded by H2SO4 (indi-
cated by arrow mark) and this may be due to dissolution of
Fly-ash by H2SO4. This will further confirmed by Fig. 1d,
the well-shaped particles of pure Fly-ash. Fig. 1b is aggre-
gated to Fig. 1d due to presence of H2SO4.
Materials and Methods
All chemicals used were procured from Sigma-Aldrich
and E-Merck. Melting points of all pyrazoles have been
determined in open glass capillaries on Mettler FP51 melting
point apparatus and are uncorrected. Infrared spectra
−1
(KBr, 4000−400 cm ) have been recorded on BRUKER
(Thermo Nicolet) Fourier transform spectrophotometer.
The NMR spectra of all pyrazolines have been recorded
on Bruker AV400 spectrometer operating at 400 MHz for
1
13
21
recording H and 100 MHz for C spectra in CDCl3 sol-
vent using TMS as internal standard. Mass spectra have
been recorded on SHIMADZU spectrometer using chem-
ical ionization technique.
Synthesis of 3,4-Dichlorophenyl Chalcones
The substituted styryl 3,4-dichlorophenyl ketones were
synthesized by literature method. An appropriate equi-molar
quantities of 3,4-dichloro acetophenone (2 mmol), substi-
tuted benzaldehydes (2 mmol) and Fly-ash:H2SO4 (0.5 g)
were taken in Borosil tube and tightly capped. The mix-
ture was subjected to microwave heated for 5−6 minutes
(Scheme S1; See supplementary data) in a microwave
oven at 480 W (Samsung Grill, GW73BD Microwave oven,
230V A/c, 50 Hz, 2450 Hz, 100−750 W (IEC-705), and then
cooled to room temperature. The organic layer was sep-
arated with dichloromethane and the solid product was
obtained on evaporation. The solid, on recrystallization
with benzene-hexane mixture gave glittering pale yellow
solid. The insoluble catalyst was recycled by washing the
solid reagent remained on the filter by ethyl acetate (8 mL)
Preparation and Characterization of Fly-ash:H2SO4
Catalyst
The fly-ash:H2SO4 catalyst was prepared by the proce-
21
dure published in literature. In a 50 mL Borosil beaker,
1 g of Fly-ash and 0.8 mL (0.5 mol) of sulphuric acid were
taken and mixed thoroughly with glass rod. This mixture
o
was heated on a hot air oven at 85 C for 1 h, cooled to
room temperature, stored in a Borosil bottle and tightly
capped. This was characterized by infrared spectra and
SEM analysis.
−1
Infrared spectral data of fly-ash:H2SO4 is ν(cm ): 3456
o
followed by drying in an oven at 100 C for 1h and it was
(OH); 3010 (C−H); 1495, 1390 (C−S); 1336, 1154 (S=O);
and op modes: 1136, 1090, 976, 890, 850, 820, 667, 658,
620, 580, 498, 425.
made reusable for further reactions. The purities of the
synthesized chalcones were checked by their physical
constants. The analytical, physical constants and mass frag-
ments of the chalcones were presented in Table S1 (See
supplementary data).
The SEM images of pure Fly-ash and Fly-ash:H2SO4 at
two different magnifications are shown in Fig. 1(a−d).
Synthesis of N-Acetyl Substituted Pyrazole Derivatives
An appropriate equi-molar quantities of chalcones (2
mmol), hydrazine hydrate (2 mmol), acetic anhydride (1
mmol) and fly-ash:H2SO4 (0.4 g) were taken in a 50 mL
borosil beaker and closed with lid. The mixture was sub-
jected to microwave irradiation for 4−6 minutes in a micro-
wave oven at 550 watts, 2540 MHz frequency (Scheme 1)
(Samsung Grill, GW73BD Microwave oven, 230V A/c,
50Hz, 2450Hz, 100−750W (IEC-705), and then cooled to
room temperature. After separating the organic layer with
dichloromethane, the solid product was separated by evapo-
ration. The solid, on recrystallization from benzene-hex-
ane mixture afforded glittering product. The insoluble catalyst
was recovered by washing with ethyl acetate (8 mL) fol-
o
lowed by drying in an oven at 100 C for 1h and reused for
Figure 1. SEM images of fly-ash:H2SO4 catalyst.
Journal of the Korean Chemical Society

Solvent-Free Synthesis of Some1-Acetyl Pyrazoles
601
further reaction runs.
the authors have synthesized the N-acetyl substituted pyrazo-
line derivatives by the cyclization of 2 mmol of chalcone,
2 mmol of hydrazine hydrate and 1mmol of acetic anhy-
dride under microwave irradiation with 0.4 g of fly-ash:H2SO4
catalyst at 550W for 4−6 minutes (Samsung Grill, GW73BD
Microwave oven, 230V A/c, 50Hz, 2450Hz, 100−750W (IEC-
705), (Scheme 1). During the course of this reaction fly-
ash:H2SO4 catalyses cyclization cum acetylation between
chalcones, hydrazine hydrate and acetic anhydride through
elimination of water followed by proton transfer gave the
RESULTS AND DISCUSSION
In our organic chemistryresearch laboratory, we attempt to
synthesize N-acetyl substituted pyrazoline derivatives by
cyclization of chalcones possess electron with-drawing as
well as electron donating group as substituents, hydrazine
hydrate and acetic anhydride in the presence of acidic cat-
alyst fly-ash:H2SO4 using microwave irradiation. Hence
Scheme 1. Synthesis of 1-acetyl pyrazoline derivatives synthesised by solvent-free cyclization cum acetylation of aryl chalcones with hydra-
zine hydrate and acetic anhydride in the presence of fly-ash:H2SO4 catalyst.
Scheme 2. The proposed general mechanism for the synthesis of 1-acetyl pyrazoline derivatives by solvent-free cyclization cum acety-
lation of aryl chalcones with hydrazine hydrate and acetic anhydride in the presence of fly-ash:H2SO4 catalyst.
2013, Vol. 57, No. 5

602
Ganesamoorthy Thirunarayanan and Krishnamoorthy Guna Sekar
1-acetyl pyrazolines. The yield of the N-acetyl pyrazolines
in this reaction is more than 75%. The proposed general
mechanism of this reaction is shown in Scheme 2. In this
cyclization and acetylation, first the amine nucleophilic
attack of carbonyl carbon of the chalcone bynitrogen atom of
hydrazine hydrate and the carbonyl oxygen gets hydrox-
ylation. Another end of the nitrogen atom of hydrazine
hydrate bonded with β-carbon of chalcone leads to cycliza-
tion, the unsaturation was shifted between carbonyl and α
carbon of the chalcones. The hydroxylated group was elimi-
nated as water molecule. Migration of proton of cyclic N-
th
2 to 4 C of azole ring and the π-bond was shifted to N-2
and C-3 of the azole ring. The acetylation process was fea-
sible by n-acetylation method. The chalcone containing
electron donating substituent (OCH3) gave higher yields
than electron-withdrawing (halogens, NO2) substituents.
Further we have investigated this cyclization reaction with
equimolar quantities of the styryl 3,4-dichlorophenyl ketone
(entry 13), hydrazine hydrate and 1mole of acetic anhydride
under the same condition as above. In this reaction the
Figure 2. The effect of catalyst loading.
obtained yield was 90%. The effect of catalyst on this reac-
tion was studied by varying the catalyst quantity from 0.1 to
1 g. As the catalyst quantity is increased from 0.1 to 0.4 g, the
percentage of yield of product is increased from 82 to
Table 1. The Analytical, physical constants and mass fragments (m/z) data of 1-acetyl pyrazoline derivatives synthesised by solvent-free
cyclization cum acetylation of aryl chalcones with hydrazine hydrate and acetic anhydride in the presence of fly-ash:H2SO4 for the following
reaction
Entry
R
R'
M.W.
264
Yield (%)
m.p. (°C)
Mass (m/z)
17
+
1
77
123−124 (120−122)
264M
17
+
298M , 300M
2+
2
3
4
5
6
7
8
9
298
278
309
382
418
398
402
398
89
89
85
85
85
88
86
86
111−112 (108−110)
17
+
109−110 (107−108)
163−164 (164−165)
278M
17
+
309M
18
+
2+
4+
4+
4+
4+
4+
167−168 (167)
382M , 384M , 386M
18
+
2+
177−178 (177)
418M , 420M , 422M
18
+
2+
172−173 (175)
398M , 400M , 402M
18
+
2+
173−174 (172)
402M , 404M , 406M
18
+ 2+
398M , 400M , 402M
163−134 (163)
Journal of the Korean Chemical Society

Solvent-Free Synthesis of Some1-Acetyl Pyrazoles
603
Table 1. Continued
Entry
R
R'
M.W.
360
Yield (%)
m.p. (°C)
Mass (m/z)
7
+
360M , 362M , 364M
2+
4+
10
11
12
13
14
15
16
17
18
19
20
21
22
23
87
180−181 (178−180)
6
+
280
404
334
412
368
368
350
364
348
348
378
378
394
85
89
90
85
85
86
87
91
90
89
85
85
89
136−137 (136)
280M
16
+
154−155 (152−155)
121−122
135−36
404M
+
2+
4+
4+
4+
4+
4+
4+
4+
4+
4+
4+
4+
334M , 336M , 338M
+
2+
412M , 414M , 416M
+
2+
119−120
131−132
147−148
112−113
368M , 370M , 372M
+
2+
368M , 370M , 372M
+
2+
350M , 352M , 354M
+
2+
364M , 366M , 368M
+
2+
125−126
116−117
348M , 350M , 352M
+
2+
348M , 350M , 352M
+
2+
152−153
147−148
121−122
378M , 380M , 382M
+
2+
378M , 380M , 382M
+ 2+
394M , 396M , 398M
90%. Further increase in the catalyst amount beyond 0.4 g,
there is no significant increase in the percentage of the
product. The effect of catalyst loading is shown in Fig. 2.
The optimum quantity of catalyst loading was found to be
0.4 g. The results, analytical and mass spectral data are
summarized in Table 1. The mass spectra and the possible
fragments of the selective 1-acetyl pyrazolines are presented in
Table 2. Reusability of fly-ash:H2SO4 catalyst on cyclization cum
acetylation of styryl 3,4-dichlorophenyl ketone (2 mmol) with
hydrazine hydrate (2 mmol) and acetic anhydride (1 mmol) under
microwave irradiation (entry 13)
Run
Yield
1
2
3
4
5
90
90
89.5
89.5
89
2013, Vol. 57, No. 5

604
Ganesamoorthy Thirunarayanan and Krishnamoorthy Guna Sekar
Table 3. The effect of solvents in conventional heating and without solvent in microwave irradiation on yield of 1-acetyl pyrazoline (entry 13)
Solvents
Microwave irradiation
MeOH
SA
EtOH
SA
DCM
SA
THF
SA
16
FA
72
FASA
78
FA
70
FASA
85
FA
74
FASA
85
FA
75
FAPA
87
FA
80
SA
23
FASA
90
13
15
12
MeOH=Methanol; EtOH=Ethanol; DCM= Dichloromethane; THF=Tetrahydrofuran; FA=fly-ash; SA=Sulphuric acid; FASA=fly-ash:H2SO4
1
Table 4. The infrared, NMR spectral data of 1-(3-(3,4-dichlorophenyl)-5-(substitutedphenyl)-4,5-dihydro- H-pyrazole-1-yl) ethanones (entries
13−23)
1
13
IR
H NMR
C
Entry
X
C=N
C=O
Ha
Hb
Hc
CH3
X
C=N
C=O
CH3
X
13
14
15
16
17
18
19
20
21
22
23
H
1574.18 1641.20 3.297
1578.21 1644.65 3.197
1576.84 1643.82 3.195
1577.71 1647.41 3.851
1576.21 1644.17 3.201
1570.07 1638.74 3.117
1571.19 1640.94 3.153
1570.27 1639.71 3.167
1575.16 1644.97 3.208
1575.97 1645.08 3.217
3.819
3.857
3.879
2.996
3.846
3.701
3.794
3.807
3.943
3.997
3.671
5.568
5.565
5.594
5.671
6.071
5.457
5.497
5.943
5.973
5.997
5.471
2.934
2.401
2.295
2.265
2.401
2.249
2.310
2.287
2.441
2.531
2.031
−
159.06 168.67
159.66 173.56
158.97 172.96
158.67 169.80
159.71 168.12
158.58 168.80
157.67 172.05
158.09 171.94
159.87 174.91
159.97 174.96
158.08 173.17
24.46
24.61
25.87
25.81
24.16
22.74
24.77
23.79
26.97
26.87
26.71
−
4-Br
−
−
2-Cl
−
−
−
−
4-Cl
4-F
−
−
4-OCH3
3-CH3
4-CH3
3-NO2
4-NO2
3.845
2.401
2.316
−
58.45
24.68
24.35
−
−
−
3,5-(OCH3)2 1572.61 1640.40 3.071
−
−
supplementary data (See supplementary data). The reus-
ability of this catalyst was studied for the cyclization of
styryl 3,4-dichlorophenyl ketone, hydrazine hydrate and
acetic anhydride (entry 13) and is presented in Table 2.
From the Table 2, first two runs gave 90% product. The
third, fourth and fifth runs of reactions gave respectively
the yields 89.5%, 89.5% and 89% of 1-acetyl pyrazolines.
There was no appreciable loss in its effect of catalytic activity
observed up to fifth run. The effect of solvents on the yield
was also studied with methanol, ethanol, dichloromethane
and tetrahydrofuran from each component of the catalyst
(entry 13). Similarly the effect of microwave irradiation
was studied on each component of the catalyst. The effect
of solvents on the yield of 1-acetyl pyrazolines was pre-
sented in Table 3. From the table highest yield of 1-acetyl
pyrazolines obtained from the cyclization cum acetyla-
tion of chalcone, hydrazine hydrate and acetic anhydride
with the catalyst fly-ash:H2SO4 in microwave irradiation.
The infrared and nmr spectroscopic data of these 1-acetyl
pyrazolines are summarized in Table 4.
of chalcones cum acetylation of pyrazole and acetic anhy-
dride. The yield of the synthesized 1-acetyl pyrazolines
are more than 75%. This methodology offers efficient,
solvent free cum acetylation of chalcones and non-haz-
ardousness to the environment.
Acknowledgments. The publication cost of this paper
was supported by the Korean Chemical Society.
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