Oxidative Cyclization of Chalcones in the Presence of Sulfamic Acid as Catalyst. Synthesis, Biological Activity, and Thermal Properties of 1,3,5-Trisubstituted Pyrazoles

Article abstract of DOI:10.1134/S1070428020100243

Abstract: 1-Aroyl-3,5-diaryl-1H-pyrazoles weresynthesized by oxidative cyclization of chalcones with benzohydrazide and4-nitrobenzohydrazide using sulfamic acid as a catalyst. The correspondingchalcones were prepared by condensation of aromatic aldehydes with acetophenonesin PEG-400 in the presence of potassium hydroxide. Some representative featuresof the proposed procedure include exceptional regioselectivity, comparativelyshort reaction time, operational simplicity, and no need of external oxidant.The synthesized pyrazole derivatives were screened as antibacterial agentsagainst Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonellatyphi by the agar well diffusion method. Attempts were made tocompute specific heat capacity of the synthesized pyrazole derivatives as afunction of temperature using TGA–DSC in order to avail thermodynamic databasefor these biologically relevant heterocycles.

Full text of DOI:10.1134/S1070428020100243

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 10, pp. 1815–1822. © Pleiades Publishing, Ltd., 2020.
Oxidative Cyclization of Chalcones in the Presence
of Sulfamic Acid as Catalyst. Synthesis, Biological Activity,
and Thermal Properties of 1,3,5-Trisubstituted Pyrazoles
a
b,
c,
J. D. Bhirud , G. R. Gupta *, and H. P. Narkhede **
a
School of Chemical Sciences, Moolji Jaitha College, Jalgaon, 425002 India
b
Gajamal Tulshiram Patil College, Nandurbar, 425412 India
c
Smt. Padambai Kapurchandji Kotecha Mahila Mahavidyalaya, Bhusawal, 425201 India
e-mail: *grgupta83@gmail.com; **narkhede.hemant@rediffmail.com
Received May 29, 2020; revised June 16, 2020; accepted June 30, 2020
Abstract—1-Aroyl-3,5-diaryl-1H-pyrazoles were synthesized by oxidative cyclization of chalcones with
benzohydrazide and 4-nitrobenzohydrazide using sulfamic acid as a catalyst. The corresponding chalcones were
prepared by condensation of aromatic aldehydes with acetophenones in PEG-400 in the presence of potassium
hydroxide. Some representative features of the proposed procedure include exceptional regioselectivity,
comparatively short reaction time, operational simplicity, and no need of external oxidant. The synthesized
pyrazole derivatives were screened as antibacterial agents against Escherichia coli, Pseudomonas aeruginosa,
Staphylococcus aureus, and Salmonella typhi by the agar well diffusion method. Attempts were made to
compute specific heat capacity of the synthesized pyrazole derivatives as a function of temperature using TGA–
DSC in order to avail thermodynamic database for these biologically relevant heterocycles.
Keywords: sulfamic acid, pyrazoles, antibacterial activity, thermal analysis, specific heat capacity
DOI: 10.1134/S1070428020100243
INTRODUCTION
zines with wide variety of α,β-unsaturated ketones
gives rise to highly substituted pyrazole derivatives in
Nowadays, even a superficial glimpse into the
modern chemistry as well as biochemistry books
unveils the significance of heterocyclic compounds and
highlights their role in the life-governing processes
the presence of various catalyst such as I [25], (di-
2
3
acetoxy-λ -iodo)benzene [26], HBr/AcOH [27], zeolite
[
28], Zn(OTF) [29], copper trifluoromethanesulfonate
2
[
14], SiO /H SO [30], and Pd/C in acetic acid [31].
2
2
4
[
1–7]. Pyrazoles and their analogs are structural
Mixed anhydride method has also been utilized for the
synthesis of trisubstituted pyrazoles [8, 32]. The con-
densation between hydrazides and chalcones produces
motifs with limited access in nature. However, these
structural motifs have been extensively explored as
pesticides in agriculture, and they have found applica-
tions as antibacterial, antidepressant, anticonvulsant,
ulcerogenic, herbicidal, anticancer, insecticidal, anti-
hyperglycemic, analgesic, anti-inflammatory, sedative,
antipyretic, and antispasmodic agents [8–16]. Further-
more, these heterocycles are considered as versatile
ligands in coordination chemistry and are utilized as
optical brighteners, detergent additives, UV-stabilizers
for polystyrene, and highly selective fluorescence
sensors [17–24]. It is therefore of great interest for
synthetic organic chemists to explore several prospects
for the development of highly efficient synthetic
strategies to access these privileged frameworks. In
this context, the reaction of structurally diverse hydra-
1
,3,5-trisubstituted pyrazoles via oxidative cyclization
with high regioselectivity [26]. However, drawbacks
associated with the use of expensive catalysts, unavoid-
able simultaneous formation of by-products while
using organometallic catalysts, high catalyst loading
because of strong coordination with the metal, low
atom efficiency, and further purification of the product
are also obvious [33–35].
Herein we report an efficient and environmentally
benign protocol for the synthesis of biologically
relevant 1,3,5-trisubstituted pyrazoles via oxidative
cyclization of the corresponding chalcones with aro-
matic acid hydrazides using sulfamic acid as catalyst.
1
815

1816
BHIRUD et al.
Scheme 1.
O
O
CHO
KOH, PEG, 40°C
Me
+
R1
R2
R1
R2
1
a, 1b
2a–2c
3a–3c
1
2
1
2
1
2
1
, R = Br (a), F (b); 2, R = H (a), Me (b), Br (c); 3, R = Br, R = H (a), Me (b), R = F, R = Br (c).
Scheme 2.
O
Br
Me
O
H
2
NSO
H, EtOH/HCl
3
reflux, 3 h
+
NH
2
Ph
N
H
N
N
8
9%
Me
Br
Ph
O
3
b
4a
5a
The synthesized pyrazole derivatives were screened as
antibacterial agents, and their thermal stability profiles
were studied to determine specific heat capacity.
selected as a model system (Scheme 2). The reaction
conditions were optimized by varying the catalyst
loading, solvent, and temperature (Table 1). Initially,
several model reactions were performed in different
organic solvents, namely chloroform, acetonitrile, tolu-
ene, ethyl acetate, and acidified ethanol, and yields of
RESULTS AND DISCUSSION
Numerous selective organic transformations cata-
lyzed by sulfamic acid have already been reported in
the literature [36–40]. Notably, an excellent catalytic
potential with exceptional regio- and chemoselectivity
was addressed by sulfamic acid in organic synthesis.
Meanwhile, considering previous reports on the use of
sulfamic acid as a catalyst, we decided to design
oxidative cyclization of chalcones which were synthe-
sized as shown in Scheme 1. Chalcones 3a–3c were
allowed to react with benzohydrazide (4a) in the
presence of sulfamic acid. At the outset of our studies,
sulfamic acid-catalyzed oxidative cyclization of
4
2, 49, 28, 20, and 89%, respectively, were obtained.
Therefore, all further optimizations were carried out
using acidified ethanol as solvent (Table 1, entry no. 1).
The reaction temperature was found to significantly
affect the formation of pyrazole 5a. Continuous
increase in the yield (57, 69, 89, and 89%) as a function
of temperature (40, 60, 80, and 90°C, respectively) was
observed (Table 1, entry nos. 1–4), so that the tem-
perature 80°C was assumed to be optimal.
We then tried other commercially available catalysts
such as montmorillonite K-10, Fullerʼs earth, Fe3
montmorillonite, sulfamic acid, and BF ·Et O, which
+
(
E)-3-(4-bromophenyl)-1-(4-methylphenyl)prop-2-en-
-one (3b) with benzohydrazide (4a) in ethanol was
3
2
1
afforded 28, 19, 30, 89, and 40% yield of 5a, respec-
Table 1. Oxidative cyclization of (E)-3-(4-bromophenyl)-1-(4-methylphenyl)prop-2-en-1-one (3b) with benzohydrazide (4a)
to pyrazole 5a in EtOH/HCl in the presence of sulfamic acid
Entry no.
Catalyst concentration, mol %
Temperature, °C
Yield of 5a, %
1
2
3
4
5
6
7
8
9
20
20
20
20
5
80
40
60
90
80
80
80
80
80
89
57
69
89
54
65
80
90
–
10
15
25
–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 10 2020

OXIDATIVE CYCLIZATION OF CHALCONES
1817
Scheme 3.
R1
R2
O
O
H NSO H, EtOH/HCl
reflux, 3 h
2
3
NH2
N
H
+
N
N
8
9%
R3
R1
R2
R3
O
3
a–3c
4a, 4b
5a–5f
3
1
2
1
2
1
2
3
4
, R = H (a), NO (b); 5, R = Br, R = Me (a, d), R = H, R = Br (b, e), R = Br, R = F (c, f); R = H (a–c), NO (d–f).
2
2
tively. Thus, sulfamic acid was found to be superior to
the other catalysts used. Next, the concentration of
sulfamic acid was varied from 5 to 25 mol % (Table 1,
entry nos. 5–9). Increase of the catalyst loading to
therefore we turned our attention to explore their
thermal properties in order to calculate their specific
heat capacities as a function of temperature. Thermal
gravimetric analysis revealed that compounds 5a–5f
are thermally stable and are free from moisture (no
appropriate inflection near 100°C was observed;
Fig. 1a). The high thermal stability of these hetero-
cyclic frameworks was attributed to thermally induced
structural and isomorphic changes. On the other hand,
DSC analysis (Figs. 1b) showed mesophase transitions
below their melting temperature (~60°C). These meso-
phase transitions are very similar to the transitions
observed for triglycerides [41]. It should also be noted
that the push–pull effect exerted by electron-donating
and electron-withdrawing substituents is quite strong,
and the melting transition is clearly seen for compounds
2
5 mol % did not improve the yield of 5a to an ap-
preciable extent, whereas significant decrease of the
yield was observed when the amount of the catalyst
was lowered. In the absence of sulfamic acid, the yield
of 5a did not exceed 10% (Table 1, entry no. 9).
With the optimized conditions in hand, the scope of
the reaction was further extended by reacting differ-
ently substituted chalcones 3a–3c with hydrazides 4a
and 4b (Scheme 3). The corresponding 1,3,5-trisubsti-
tuted pyrazole derivatives 5a–5f were obtained in
7
2–92% yield.
Pyrazoles 5a–5f were evaluated for their in vitro
5
d–5f, while the melting transition of 5a–5c is difficult
to visualize.
Heat capacity is a significant thermodynamic prop-
antimicrobial activity against Escherichia coli ATCC
5922, Pseudomonas aeruginosa ATCC 19429,
2
Salmonella typhi ATCC 23564, and Staphylococcus
aureus ATCC 29737 by the agar well diffusion method.
The inhibition zone diameters are given in Table 2.
Compounds 5a and 5c showed a noticeable antibac-
terial activity against S. typhi, and compound 5c
showed a good activity against E. coli at a level com-
parable to that of streptomycin. All compounds showed
low activity against P. aeruginosa and S. aureus.
erty which is of fundamental importance since it
bridges quantum mechanics through enthalpy, entropy,
and Gibbs energy functions [42–45]. In recent years,
heat capacity data of biologically relevant molecules,
including carbohydrates, amino acids, and proteins,
have contributed much to the development of computa-
tional methods and molecular modeling [46]. Our
results encouraged us to calculate specific heat capac-
ities of the synthesized pyrazole derivatives. Figure 2
shows variation of the specific heat capacities of com-
To our delight, the synthesized pyrazole derivatives
can be regarded as effective antibacterial agents, and
Table 2. In vitro antimicrobial activity (inhibition zone diameter, mm) of compounds 5a–5f
Compound no.
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus aureus
Salmonella typhi
5
5
5
5
5
5
a
b
c
d
e
f
12
–
15
11
–
–
23
17
24
–
12
10
12
13
14
28
27
21
–
14
13
12
25
–
–
18
14
28
–
13
26
24
Streptomycin
Ampicillin
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 10 2020

1818
BHIRUD et al.
Weight loss, %
100
(a) Weight loss, %
5
5
5
a
b
c
5d
5e
5f
1
00
8
6
4
2
0
0
0
0
0
8
0
6
0
4
2
0
0
0
–
20
6
0
120 180 240 300 360 420 480
Temperature, °C
60 120 180 240 300 360 420 480 540
Temperature, °C
Heat flow, W/g
(b) Heat flow, W/g
5
a
5
5
d
e
5
b
5
5c
5
0
5f
0
–
5
–
5
–
10
–10
30
3
0
60
90
120
150
180
210
60
90
120
150
180
210
Temperature, °C
Temperature, °C
Fig. 1. (a) Thermogravimetry and (b) differential scanning calorimetry data for pyrazole derivatives 5a–5f; heating rate 10 deg/min.
Table 3. Specific heat capacities (C , J K g–1) for pyrazole derivatives 5a–5f at different temperatures
–
1
p
Temperature, °C
5a
5b
5c
5d
5e
5f
7
8
9
5
5
5
1.35
1.28
1.31
1.38
1.46
1.56
1.66
1.17
1.10
1.13
1.20
1.30
1.41
1.52
0.70
0.75
0.83
0.92
1.02
1.12
1.30
0.94
0.88
0.90
0.94
1.01
1.10
1.21
0.90
0.98
1.21
1.40
1.39
1.55
1.70
0.73
0.80
0.89
0.97
1.08
1.22
1.43
1
05
15
1
1
1
25
35
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 10 2020

OXIDATIVE CYCLIZATION OF CHALCONES
1819
C , J K g–1
–
1
(a)
C , J K–1 g–1
(b)
p
p
1
1
1
1
1
0
0
.8
.6
.4
.2
.0
.8
.6
1.8
1.6
1.4
1.2
1.0
0.8
5
5
5
a
b
c
5d
5e
5f
0.6
60
6
0
80
100
120
140
160
180
80
100
120
140
160
180
Temperature, °C
Temperature, °C
Fig. 2. Specific heat capacities of compounds (a) 5a–5c and (b) 5d–5f as a function of temperature.
pounds 5a–5f versus temperature (see also Table 3).
A closer scrutiny of Figs. 2a and 2b revealed smooth
temperature increments in the heat capacities of com-
pounds 5a–5c, whereas thermal kinks are observed for
compound 5d–5f.
range 298.15–773.15 K. The details regarding the
calculation of specific heat capacities were reported
previously [48–51].
Chalcones 3a–3c (general procedure). An equi-
molar mixture of acetophenone 1a or 1b and aldehyde
2
a–2c in PEG-400 (15 mL) containing 2 mmol of
EXPERIMENTAL
potassium hydroxide was stirred at 40°C for 1 h. The
progress of the reaction was monitored by TLC
Initial aldehydes, acetophenones, and hydrazides, as
well as sulfamic acid, were purchased from S.D. Fine
PVT. Ltd. (Mumbai). All solvents, including water,
were distilled before use. The IR spectra were recorded
in KBr on a Shimadzu Affinity FTIR spectrometer; the
instrument was calibrated against a polystyrene film.
(
hexane–ethyl acetate, 95:5). After completion of the
reaction, the mixture was poured into ice water
100 mL) [47], and the crystalline solid was filtered off
and recrystallized from ethanol.
,3,5-Trisubstituted pyrazoles 5a–5f (general
(
1
1
13
procedure). A 50-mL round-bottom flask was charged
with chalcone 3a–3c (5 mmol), benzohydrazide (4a) or
4-nitrobenzohydrazide (4b) (5 mmol), and 20 mol % of
sulfamic acid in acidified ethanol (15 mL). The mixture
was refluxed with stirring until the reaction was com-
plete (TLC, chloroform–diethyl ether, 80:20), cooled,
and poured into ice water, and the solid product was
filtered off and recrystallized from ethanol.
The H and C NMR spectra were recorded in
DMSO-d or CDCl using a Bruker Avance II 400
6
3
spectrometer at 400 and 100 MHz, respectively. The
mass spectra were run on a Waters Q-TOF Micromass
LC/MS instrument. The melting points were deter-
mined from the DSC data.
The TGA-DSC analyses were carried out on a TA
Instruments SDT Q 600 V20.9 thermal analyzer with
an accuracy of ±0.5 K under a nitrogen atmosphere,
which was placed in an air-conditioned lab with
a humidity of 5–10%. Samples with a weight of 4 to
[5-(4-Bromophenyl)-3-(4-methylphenyl)-1H-pyr-
azol-1-yl](phenyl)methanone (5a). Yield 0.370 g
(89%), pale yellow solid, mp 176–180 (open capillary),
178°C (DSC). IR spectrum, ν, cm : 1485 (C=C), 1598
(C=N), 1654 (C=O). H NMR spectrum (DMSO-d ), δ,
ppm: 8.03 d (2H, J = 8.2 Hz); 7.88 d (4H), 7.78 d.d
(3H), 7.70 s (1H, 4-H), 7.63 d.d (2H), 7.34 d (2H,
J = 8 Hz), 2.42 s (3H, CH ). C NMR spectrum
(DMSO-d ), δ , ppm: 188.3 (C=O), 143.4 (C ), 142.1
–
1
1
0 mg were used for the measurements. Heat flow
1
measurements were performed in the temperature
range of 313.15–1073.15 K (heating rate 5 deg/min)
at a nitrogen flow rate of 50 mL/min. The instrument
was calibrated using an empty pan, sapphire, and zinc.
The DSC data were obtained over the temperature
6
1
3
3
3
6
C
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 10 2020

1820
BHIRUD et al.
5
(
(
C ), 134.8, 133.8, 131.7, 130.4, 128.5, 123.8, 122.6
solution of 5a–5f or reference drug with a concentration
of 100 μg/mL was added into each well. The dishes
were incubated for 24 h at 37°C under aerobic
conditions, and the bacterial growth inhibition zone
diameter (mm) was measured; pure DMSO was used
as control.
4
+
C ), 21.2 (CH ). Mass spectrum: m/z 416/418 [M] .
3
[
3-(4-Bromophenyl)-5-phenyl-1H-pyrazol-1-yl]-
phenylmethanone (5b). Yield 0.349 g (87%), yel-
lowish white solid, mp 178–182 (open capillary),
84°C (DSC). H NMR spectrum (DMSO-d ), δ, ppm:
.75 d (2H), 7.18–7.82 m (6H),7.14 d (2H), 7.07 s (1H,
-H), 6.90 d.d (2H), 6.81 d.d (2H). Mass spectrum:
m/z 402/404 [M] .
1
1
8
4
6
ACKNOWLEDGMENTS
+
The authors are thankful to the central Instrumentation
Laboratory, Moolji Jaitha College (Jalgaon) for recording
the FT-IR spectra and evaluating biological activity. The
authors are also grateful to Punjab University, Chandigarh,
for providing the spectral data of the synthesized compounds
and to Nagpur University for TGA/DSC analysis.
[
5-(4-Bromophenyl)-3-(4-fluorophenyl)-1H-pyr-
azol-1-yl]phenylmethanone (5c). Yield 0.302 g
72%), pale yellow solid, mp 142–144 (open capillary),
39°C (DSC). IR spectrum, ν, cm : 1496 (C=C), 1600
C=N), 1656 (C=O). H NMR spectrum (DMSO-d ), δ,
ppm: 8.15 t (2H), 7.75 d (4H), 7.52 t.d (5H), 7.41 s
1H, 4-H), 7.22–7.39 m (2H). Mass spectrum:
(
1
(
–
1
1
6
(
CONFLICT OF INTEREST
The authors declare no conflict of interest.
SUPPLEMENTARY MATERIALS
+
m/z 420/422 [M] .
5-(4-Bromophenyl)-3-(4-methylphenyl)-1H-pyr-
azol-1-yl](4-nitrophenyl)methanone (5d). Yield
.410 g (89%), yellow solid, mp 148–151 (open capil-
[
0
–
1
lary), 145°C (DSC). IR spectrum, ν, cm : 1508 (C=C),
600 (C=N), 1656 (C=O). H NMR spectrum (CDCl ),
δ, ppm: 7.91 d (2H, J = 8.1 Hz), 7.70 d (2H), 7.52 d.d
6H), 7.47 s (1H, 4-H), 7.25 t (2H), 2.42 s (3H, CH ).
C NMR spectrum (CDCl ), δ , ppm: 189.6 (C=O),
43.8 (C ), 142.9 (C ), 135.4, 133.8, 132.1, 129.7,
29.3, 128.6, 124.6, 122.5 (C ), 21.69 (CH ).
1
1
Supplementary materials are available for this article at
https://doi.org/10.1134/S1070428020100243 and are acces-
sible for authorized users.
3
(
3
1
3
3
C
3
5
1
1
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3
1
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[
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