'One-pot' ultrasound irradiation promoted synthesis and spectral characterization of an array of novel 1,1′-(5,5′-(1,4-phenylene) bis(3-aryl-1H-pyrazole-5,1(4H,5H)-diyl))diethanones, a bis acetylated pyrazoles derivatives

Article abstract of DOI:10.1016/j.saa.2010.11.038

An array of novel 1,1′-(5,5′-(1,4-phenylene)bis(3-aryl-1H- pyrazole-5,1(4H,5H)-diyl))diethanones, a bis acetylated pyrazoles derivatives are synthesized in 'one-pot' by ultrasound irradiation method and are characterized by melting point, elemental analys

Full text of DOI:10.1016/j.saa.2010.11.038

Spectrochimica Acta Part A 78 (2011) 635–639
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
‘One-pot’ ultrasound irradiation promoted synthesis and spectral
characterization of an array of novel 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)
bis(3-aryl-1H-pyrazole-5,1(4H,5H)-diyl))diethanones, a bis acetylated
pyrazoles derivatives
V. Kanagarajana,b, M.R. Ezhilarasib, M. Gopalakrishnanb,∗
a Energetics Research Institute, Nanyang Technological University, 50, Nanyang Avenue, Singapore 639 798, Republic of Singapore
b Synthetic Organic Chemistry Laboratory, Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
An array of novel 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-5,1(4H,5H)-diyl))diethanones, a bis
acetylated pyrazoles derivatives are synthesized in ‘one-pot’ by ultrasound irradiation method and are
characterized by melting point, elemental analysis, MS, FT-IR, one-dimensional NMR (1H and 13C) and
two-dimensional NOESY spectra. The methylene and methane protons of pyrazoles moiety splits signal as
ABX pattern in the proton NMR spectra and the key nOe correlations are confirmed by NOESY spectrum.
© 2010 Elsevier B.V. All rights reserved.
Article history:
Received 19 May 2010
Received in revised form 28 October 2010
Accepted 30 November 2010
Keywords:
Bis acetylated pyrazoles
In situ acetylation
Ultrasound irradiation
ABX splitting pattern
NOESY spectrum
1. Introduction
1H-pyrazole-1-carbaldehyde [18]. Several 1,3-diaryl-5-(cyano-,
aminocarbonyl- and ethoxycarbonyl-)-2-pyrazoline, pyrrolo[3,4-
Pyrazole derivatives with a phenyl group at the 5-position
exhibit excellent characteristics of blue photoluminescence and
electroluminescence [1]. Pyrazoles display various biological activ-
ities such as antimicrobial [2], antifungal [3], antidepressant [4],
immunosuppressive [5], anticonvulsant [6], anti-tumor [7], anti-
amoebic [8], antibacterial [9] and anti-inflammatory [10] activities.
In the structure of pyrazoline containing two nitrogen atoms, one
of which forms an electron-donating p-conjugated system, so it
is able to function as hole-transporting material used in organic
electroluminescent device [11]. Reaction of ␣,␤-unsaturated alde-
hydes and ketones with phenyl hydrazine in refluxing acetic acid
is the prime method for the synthesis of 2-pyrazolines, first dis-
covered by Fischer and Knoevenagel [12]. Syntheses of pyrazolines
by reaction of ␣,␤-unsaturated carbonyl compounds with dia-
zoalkanes [13] or with hydrazine hydrate [14,15] were reported in
literature. Utilization of p-sulfamylphenylhydrazine is mentioned
to prepare N-(p-sulfamylphenyl)-2-pyrazolines only in few cases
[16,17]. Reaction of dibenzalacetone with hydrazine hydrate and
formic acid yields 5-phenyl-3-[(E)-2-phenylvinyl]-4,5-dihydro-
c]pyrazole-4,6-dione and 1,3,4,5-tetraaryl-2-pyrazoline deriva-
tives were prepared by the reaction of nitrilimine with different
dipolarophilic reagents by Abunanda et al. [19]. One sustainable
strategy for green synthesis of organic compounds is ultrasonic
irradiation. It accelerates the chemical reaction and mass trans-
fer via the process of acoustic cavitation [20]. Compared to
traditional methods, the procedure is more convenient to syn-
thesis structurally diverse compounds [21] and can be carried
out in higher yields in short reaction times under mild reac-
tion conditions. In continuation of our interest in synthesizing
fascinating structurally diverse heterocycles using environmen-
tally friendly methodologies [22–26], we report now the ‘one-pot’
ultrasound irradiation synthesis of 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-
aryl-1H-pyrazole-5,1(4H,5H)-diyl))diethanones, a novel series of
bis acetylated pyrazole derivatives.
2. Results and discussion
1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-5,1(4H,5H)-
diyl))diethanones 7–12 are synthesized in excellent yields by the
reaction of bis chalcones 1–6 with hydrazine hydrate catalyzed by
anhydrous sodium acetate/acetic anhydride under ultrasonic irra-
diation method at 45 ◦C within 10–20 min. Cavitation is responsible
∗
Corresponding author. Tel.: +91 4144 228 233.
E-mail address: profmgk@yahoo.co.in (M. Gopalakrishnan).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.11.038

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V. Kanagarajan et al. / Spectrochimica Acta Part A 78 (2011) 635–639
Table 1
Physical and analytical data of 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-5,1(4H,5H)-diyl))diethanones 7–12.
Compounds
X
Time ꢀ (h)/
sonication
(min)
Yield (%) ꢀ/
sonication
m.p. (◦C)
Elemental
analysis (%)
m/z (M)+.
molecular
formula
C found (calculated)
H found (calculated)
N found (calculated)
7
8
9
10
11
12
H
F
Cl
Br
CH3
OCH3
7/15
7/15
8/20
7/15
5/10
5/10
65/95
70/94
55/88
60/95
65/98
65/95
261
233
260
262
258
202
74.55 (74.65)
69.02 (69.12)
64.52 (64.74)
55.13 (55.28)
75.13 (75.29)
70.43 (70.57)
5.69 (5.82)
4.77 (4.97)
4.52 (4.66)
3.82 (3.98)
6.22 (6.32)
5.86 (5.92)
12.31 (12.44)
11.41 (11.52)
10.66 (10.79)
9.11 (9.21)
11.60 (11.71)
10.85 (10.97)
450 C28H26N4O2
486 C28H24F2N4O2
518, 520 C28H24Cl2N4O2
606, 608 C28H24Br2N4O2
478 C30H30N4O2
510 C30H30N4O4
for acceleration of chemical reactions by ultrasound irradiation
[27]. It has been observed in the traditional classical method, the
reaction mixture of bis chalcones 1–6 with hydrazine hydrate cat-
alyzed by anhydrous sodium acetate in refluxing acetic anhydride
for 5–8 h yield compounds 7–12 in moderate yields. However
when this reaction is performed under sonication method, the
reaction takes place rapidly within 10–20 min with excellent yields
(Table 1). In our present study, acetic anhydride is the best solvent
for the facile synthesis of bis pyrazoles, 7–12 in excellent yields with
out any solubility problem. In addition, in situ acetylation occurs in
the course of the reaction due to solvent, acetic anhydride under
the reaction conditions. An array of six compounds namely, 1,1ꢀ-
(5,5ꢀ-(1,4-phenylene)bis(3-phenyl-1H-pyrazole-5,1(4H,5H)-diyl))
diethanone 7, 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-(4-fluorophenyl)-1
H-pyrazole-5,1(4H,5H)-diyl))diethanone 8, 1,1ꢀ-(5,5ꢀ-(1,4-pheny-
lene)bis(3-(4-chlorophenyl)-1H-pyrazole-5,1(4H,5H)-diyl))dieth-
anone 9, 1,1ꢀ-(5,5ꢀ-(1,4-phenylene) bis(3-(4-bromophenyl)-1H-
pyrazole-5,1(4H,5H)diyl))diethanone 10, 1,1ꢀ-(5,5ꢀ-(1,4-phen-
ylene)bis(3-p-tolyl-1H-pyrazole-5,1(4H,5H)-diyl))diethanone 11,
1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-(4-methoxyphenyl)-1H-pyrazole-
5,1(4H,5H)-diyl)) diethanone 12 are synthesized both under
classical thermal as well as sonication methods. The structures of
the synthesized 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-
5,1(4H,5H)-diyl))diethanones 7–12 are confirmed by FT-IR, MS, 1
H
NMR, 13C NMR and NOESY spectral studies and elemental analysis
(Scheme 1).
The formation of 7–12 can be rationalized on the basis of two
reaction pathways as shown in Scheme 2. The first route involves
the initial formation of a hydrazone followed by a subsequent 5-
endo trig. ring cyclization, which according to Baldwin’s rules is
an unfavourable reaction. The second reaction pathway involves a
Michael addition of hydrazine on the bis chalcones 1–6, followed
by a 5-exo-trig. ring cyclization and dehydration. This is an allowed
process according to Baldwin’s rules [28]. However, due to the tau-
tomerism of pyrazolines, the products obtained by either of the
mechanisms is the same 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-
pyrazole-5,1(4H,5H)-diyl))diethanones 7–12.
In order to determine the structure of the synthesized
compounds, 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-phenyl-1H-pyrazole-
5,1(4H,5H)-diyl))diethanone
7
is taken as the representative
X
X
X
O
NH2-NH2.H2O
Anhyd. CH3COONa
(CH3CO)2O
N
3
2
O
Δ , 8 h
4
1
N
O
CH3
5
+
Pathway-A
CHO
CH3
NaOH
EtOH
(O-5)0C
stirring, 1 h
H3C
Pathway-B
CHO
5
NH2-NH2.H2O
Anhyd. CH3COONa
N
1
4
O
2
3
+
O
H3C
(CH3CO)2O
(((((( , 45 Hz
N
O
450C, 10-15 min.
X
X
(1-6)
(7-12)
X
Scheme 1. Synthesis of novel bis acetylated pyrazoles by both classical thermal and sonication methods.

V. Kanagarajan et al. / Spectrochimica Acta Part A 78 (2011) 635–639
637
Table 2
FT-IR absorption frequencies (cm−1) for selected functional groups of compounds 7–12.
Compound
Aromatic CH
stretching
Aliphatic CH
stretching
Amide C
stretching
O
C
N stretching
Aromatic ring
stretching
7
8
9
10
11
12
3057, 3030
3046
3041
3035
3063, 3035
3063, 3008
2923, 2852
1659
1655
1655
1652
1659
1657
1441, 1419
1446, 1417
1441, 1420
1441, 1420
1446, 1421
1453, 1430
763, 690, 559
632, 579, 544
637, 565, 543
671, 561, 552
633, 585, 543
561, 580, 549
2958, 2923, 2852
2958, 2923, 2852
2958, 2922, 2852
2958, 2923, 2853
2923, 2852
Table 3
Proton NMR chemical shifts (ı, ppm) of compounds 7–12.
Compounds
H4a (dd)
H4e (dd)
H5a (dd)
Acetyl CH3 (s)
Ar-protons (m)
Others (s)
7
8
9
10
11
12
3.06
3.04
3.12
3.12
3.14
3.08
3.61
3.60
3.68
3.68
3.68
3.80
5.48
5.48
5.58
5.57
5.56
5.49
2.31
2.30
2.38
2.38
2.39
2.27
7.09–7.64
7.00–7.64
7.17–7.65
7.16–7.57
7.17–7.63
6.99–7.72
–
–
–
–
2.42 (CH3)
3.80 (OCH3)
Fig. 1. Key nOe correlations for 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-phenyl-1H-pyrazole-5,1(4H,5H)-diyl))diethanone 7.
compound. FT-IR spectrum of 7 shows characteristic absorption
frequencies around 3057–3030 cm−1 due to aromatic CH stretch-
ing vibration. The absorption bands at 2923 and 2852 cm−1 are
attributed to the aliphatic CH stretching vibration. The absorption
frequency at 1659 cm−1 is assigned to amide carbonyl stretching
vibration. The absorption band around 1441 and 1419 cm−1 are
assigned to C N stretching vibration. The absence of carbonyl band
clearly supported the formation of 7, besides the disappearance
of NH stretching vibration, which confirms the in situ acetylation
reaction due to acetic anhydride solvent. The FT-IR absorption fre-
quencies (cm−1) for selected functional groups of compounds 7–12
are given in Table 2.
Mass spectrum of compound 7 shows molecular ion peak at m/z
450 (M+•), which is consistent with the proposed molecular mass of
7. Elemental analysis of 7 (Ccal 74.65, Cobs 74.55; Hcal 5.82, Hobs 5.69;
Ncal 12.44, Nobs 12.31) are consistent with the proposed molecular
formula (C28H26N4O2) of 7.
signals are observed at 5.48 ppm (J5a,4a = 11.8 Hz and J5a,4e = 4.6 Hz).
Also, the acetyl methyl protons of pyrazoline moiety gives signal
as a singlet at 2.31 ppm. The aromatic protons appear as a multi-
plet in the range of 7.09–7.64 ppm. The 1H NMR chemical shifts
values and coupling constant (J, Hz) values of 7–12 are given in
Tables 3 and 4.
In the 13C NMR spectrum of 1-acetyl-4,5-dihydro-5(4-(1-acetyl-
4,5-dihydro-3-phenyl-pyrazol-5-yl)phenyl-3-phenylpyrazole, 13C
resonance at 59.60 ppm is assigned to C-5 of the pyrazole moiety.
The 13C resonance observed at 42.17 ppm is due to C-4 carbon of
the pyrazole moiety. The 13C resonance observed at 154.05 ppm is
assignedtoC-3carbon ofthe pyrazole moiety. Thearomatic carbons
are observed in the region of 126.15–128.74 ppm. The remaining
13C signals at 141.12, 131.28 and 130.36 ppm are due to ipso car-
bons. The 13C NMR chemical shifts of 7–12 are given in Table 5.
The key nOe correlations of 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-
phenyl-1H-pyrazole-5,1(4H,5H)-diyl))diethanone is shown in
Fig. 1. In the NOESY spectrum, the signal for H4a at 3.06 ppm
gives strong nOe correlation with the signal at 3.61 ppm, which
In the 1H NMR spectrum of 7, the methylene protons (H-4a and
H-4e) of the pyrazole moiety appeared as two doublets of dou-
blet due to multiple coupling involving both geminal and vicinal
protons. The signals for H-4a and H-4e are observed at 3.06 and
3.61 ppm. The doublet of doublet at 3.06 ppm (J4a,5a = 17.6 Hz and
J4a,4e = 4.4 Hz) is assigned to H-4a proton of the pyrazoline moi-
ety. Likewise, the doublet of doublet at 3.61 ppm (J4e,4a = 17.6 Hz
and J4e,5a = 12.0 Hz) is assigned to H-4e proton of the pyrazole moi-
ety. Similarly, the methine proton (H-5) of the pyrazoline moiety
is expected to give signal as a doublet of doublet due to vicinal
coupling with the two magnetically nonequivalent protons of the
methylene group (H-4a and H-4e) of the pyrazoline moiety and the
Table 4
Various coupling constant values (Hz) of compounds 7–12.
Compounds
J4a,5a
J4a,4e
J4e,4a
J4e,5a
J5a,4a
J5a,4e
7
8
9
10
11
12
17.6
13.6
17.6
13.4
17.1
17.5
4.4
4.2
4.1
4.2
4.4
5.0
17.6
17.6
17.2
17.4
17.6
–
12.0
12.0
12.0
11.8
12.0
–
11.8
11.8
11.2
11.8
11.8
11.5
4.6
4.6
4.8
5.0
4.6
4.5

638
V. Kanagarajan et al. / Spectrochimica Acta Part A 78 (2011) 635–639
corresponds to H-4e proton of pyrazoles moiety and gives weak
nOe correlation with the signal at 5.48 ppm, due to H-5a proton of
pyrazoles moiety. Likewise, H-4e proton of pyrazoles gives strong
nOe correlation with the signal at 3.06 ppm, which corresponds to
H-4a proton of pyrazoles moiety and gives weak nOe correlation
with the signal at 5.48 ppm, due to H-5a proton of pyrazoles
moiety. Similarly, the signal at 5.48 ppm, due to H-5a proton of
pyrazoles moiety gives strong nOe correlations with the signals
at 3.06 ppm as well as the signal at 3.61 ppm, which are due to
H-4a and H-4e protons of pyrazoles moiety. Also, the methyl
protons of acetyl group does not show any nOe correlations with
the methylene or methane protons of pyrazoles moiety. Therefore,
with reference to FT-IR, MS, 1H NMR, 13C NMR and NOESY spectral
studies in compound 7, the tentative assignments made for the
title compounds are confirmed.
3. Experimental
3.1. General
Sonication is performed on a Life Care - Fast Ultrasonic system
operating at a frequency of 45 kHz. The reaction flask is located
in the maximum energy area in the bath and the addition or
removal of water controlled the temperature of the water bath.
IR spectra are recorded in KBr (pellet forms) on a Thermo Nicolet-
Avatar–330 FT-IR spectrophotometer and note worthy absorption
values (cm−1) alone are listed. 1H and 13C NMR spectra are recorded
at 400 MHz and 100 MHz respectively on Bruker AMX 400 NMR
spectrometer using CDCl3 as solvent. Two-dimensional NOESY
spectra are recorded at 500 MHz on Bruker DRX 500 NMR spec-
trometer using CDCl3 as solvent. The ESI +ve MS spectra are
recorded on a Varian Saturn 2200 MS spectrometer. Satisfactory
microanalyses are obtained on Carlo Erba 1106 CHN analyzer. Per-
forming TLC assessed the reactions and the purity of the products.
All the reported melting points are taken in open capillaries and
are uncorrected. By adopting the literature precedent, bis chalcones
1–6 [26] are prepared.
3.2. Experimental procedure for the synthesis of novel
1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-5,1(4H,5H)-
diyl))diethanones 7–12 under classical thermal
method
Bis chalcones 1–6, (0.01 mol), hydrazine hydrate (0.01 mol),
anhydrous sodium acetate (0.01 mol) and acetic anhydride (20 mL)
are taken in a round bottomed flask and the reaction mixture
flask was refluxed until the products are formed. The reaction is
monitored by TLC. The time required for the formation of various
pyrazoles is shown in Table 1. The reaction mixture is poured into
crushed ice and left overnight. The precipitate is separated by fil-
tration, washed well with water, dried and the obtained solids are
purified by column chromatography using toluene and ethylacetate
(1:1) mixture as eluent which afford the title compounds 7–12 in
moderate yields.
3.3. Experimental procedure for the synthesis of novel
1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-pyrazole-5,1(4H,5H)-
diyl))diethanones 7–12 under ultrasound
irradiation
Scheme 2. Synthetic reaction pathways towards the synthesis of title compounds
7–12 via, Schiff base formation or Michael addition pathway.
Bis chalcones 1–6, (0.01 mol), hydrazine hydrate (0.01 mol),
anhydrous sodium acetate (0.01 mol) and acetic anhydride (20 mL)
are taken in a conical flask and the reaction mixture flask is sus-
pended at the centre of the ultrasonic bath to get the maximum
ultrasound energy and sonicated until the products are formed.

V. Kanagarajan et al. / Spectrochimica Acta Part A 78 (2011) 635–639
639
Table 5
Carbon NMR chemical shifts (ı, ppm) of compounds 7–12.
Compound
C-3
C-4
C-5
Acetyl CH3
Amide C
O
Aromatic carbons
Ipso carbons
Others
7
8
9
10
11
12
154.05
152.99
152.92
152.96
154.14
154.40
42.17
42.23
42.06
42.01
42.22
42.56
59.60
59.68
59.76
59.78
59.51
59.43
21.94
21.91
21.95
21.95
21.94
22.11
168.88
168.82
168.89
168.89
168.77
167.57
126.15–128.74
115.80–128.62
126.13–129.78
124.67–128.02
126.13v129.44
114.68–128.77
141.12, 131.28, 130.36
141.08, 141.04
136.31, 141.01, 141.05
130.22, 131.97, 141.01,
141.15, 140.68
–
–
–
–
21.52 (CH3)
55.82 (OCH3)
141.06, 161.41
The reaction is monitored by TLC. The time required for the for-
mation of various pyrazoles is shown in Table 1. The reaction
mixture is poured into crushed ice and left overnight. The pre-
cipitate is separated by filtration, washed well with water, dried
and recrystallized from acetic acid to afford pale yellow coloured
crystals.
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4. Conclusion
An array of novel 1,1ꢀ-(5,5ꢀ-(1,4-phenylene)bis(3-aryl-1H-
pyrazole-5,1(4H,5H)-diyl))diethanones, a bis acetylated pyrazoles
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sodium acetate/acetic anhydride and are characterized by melt-
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and 13C) and two-dimensional NOESY spectra. Spectral investiga-
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methane protons of pyrazoles moiety splits signal as ABX pattern in
the proton NMR spectra and the key nOe correlations are confirmed
by NOESY spectrum. Also, the present protocol is quite convenient
and environmentally friendly, since the reaction proceeds under
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Authors are thankful to NMR Research Centre, Indian Institute of
Science, Bangalore for recording spectra. One of the authors namely
V. Kanagarajan is grateful to Council of Scientific and Industrial
Research (CSIR), New Delhi, Republic of India for providing finan-
cial support in the form of CSIR-Senior Research Fellowship (SRF)
in Organic Chemistry. Another author, M.R. Ezhilarasi is thankful to
Cavin Kare Research Centre, Chennai for providing financial support
in the form of Junior Research Fellowship.
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