V2O5/SiO2 as an efficient catalyst in the synthesis of 5-amino-pyrazole derivatives under solvent free condition

Article abstract of DOI:10.4314/bcse.v33i1.13

An efficient and facile approach for the synthesis of 5-aminopyrazoles from ketene S,N-acetal and hydrazine hydrate via catalytic reaction under solvent free condition has been described. V2O5/SiO2 as a heterogeneous catalyst was prepared and characterize

Full text of DOI:10.4314/bcse.v33i1.13

Bull. Chem. Soc. Ethiop. 2019, 33(1), 135-142.
 2019 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v33i1.13
ISSN 1011-3924
Printed in Ethiopia
V2O5/SiO2 AS AN EFFICIENT CATALYST IN THE SYNTHESIS OF 5-AMINO-
PYRAZOLE DERIVATIVES UNDER SOLVENT FREE CONDITION
Tamer K. Khatab, Ashraf S. Hassan* and Taghrid S. Hafez
Organometallic and Organometalloid Chemistry Department, National Research Centre,
Dokki, 12622, Cairo, Egypt
(Received March 26, 2018; Revised November 30, 2018; Accepted December 4, 2018)
ABSTRACT. An efficient and facile approach for the synthesis of 5-aminopyrazoles from ketene S,N-acetal and
hydrazine hydrate via catalytic reaction under solvent free condition has been described. V2O5/SiO2 as a
heterogeneous catalyst was prepared and characterized using X-ray diffraction (XRD), Fourier transform infrared
spectroscopy (FTIR) and scanning electron microscope (SEM).
KEY WORDS: One-pot synthesis, 5-Amino-1H-pyrazole, Hydrazine hydrate, Vanadium oxide, Silica
INTRODUCTION
Pyrazoles and their derivatives have attracted considerable interest during the last two decades
due to their biological activities. For example, compound A, has been shown to exhibit
antifungal activity [1]. Compound B is a potent inhibitors of neutrophil chemotactic
responsiveness [2]. In addition, compound C showed antitumor activity by inhibition of cyclin-
dependent kinases (CDK) [3] (Figure 1). Furthermore, pyrazole compounds used as
intermediates in the synthesis of various bioactive compounds such as pyrazolopyrimidines,
pyrazolotriazines, pyrazoloquinazolines and Schiff bases [4-9].
O
S
NH
O
Cl
O
CH3
NH
NH
CN
N
N
N
O
Cl
O
N
N
N
O
B
N
H
H
C
A
inhibitors of neutrophil
chemotactic responsiveness
PHA-533533
antitumor activity
antifungal activity
Figure 1. Structures of the biological activities of pyrazole derivatives A-C.
A recent review of 5-aminopyrazoles described the miscellaneous synthetic methods [10] as
the condensation of β-ketonitriles [11] or malononitrile derivatives [12] with hydrazine hydrate.
The literature survey describe that, the general method for the synthesis of 5-aminopyrazole was
done by mixing the ketene S,N-acetal with hydrazine hydrate under reflux condition in ethanol
[13].
A green chemistry characterized by more than one advantage safe, facile and free solvent
reaction. Therefore, it is favorable for most researchers to use this technique. Basically for the
__________
*Corresponding author. E-mail: ashraf_salmoon@yahoo.com
This work is licensed under the Creative Commons Attribution 4.0 International License

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Tamer K. Khatab et al.
reactions under heterogeneous catalytic condition, it is preferable than other catalytic conditions
safe to store, insoluble in organic solvents, long lifetime, solid structure that avoids the
conjunction of active catalyst and good thermal stability. Nowadays, solid acid catalysts play a
significance role in organic synthesis under heterogeneous conditions [14]. Its constituents
based on clay and silica [15].
The literature survey explained that a silica-based catalyst was widely applicable as
presented in modern synthetic methods. In this work, we are trying to explore some significance
and commonly used silica-based catalyst in organic synthesis. In addition, green organic
reactions in solvent free conditions have attracted a great attention since it is eco-friendly, non-
toxic, and economic cost compared to classical reactions in organic solvents.
From previously explained facts, we reported in this paper the synthesis of 5-aminopyrazole
derivatives from the ketene acetal with hydrazine hydrate in solvent free condition by using
catalysis for simple procedure optimum results than previous methods.
EXPERIMENTAL
Catalyst preparation
To a suspension of SiO2 (for column chromatography, mesh 70-230, 0.06-0.2 mm, 2 g) in 50
mL CHCl3, V2O5 (1 g) was added. The mixture stirred at room temperature for 90 min. The
solvent was evaporated at room temperature to obtain a brown solid of 50% (w/w) V2O5/SiO2.
The catalyst was characterized by the following methods.
Catalyst characterization
X-Ray diffraction. X-Ray diffraction (XRD) pattern were recorded using PANalyticalX`Pert
PRO XRD system occupied with Cu Kα of wavelength  = 1.540 Å and tube operating voltage
of 30 kV. Measured Bragg’s angle (2θ) varied in between 5 to 60 degree.
Fourier transform infrared. Fourier transform infrared (FTIR) measurement was recorded on a
single beam spectrometer type Nicolet iS10 in the spectral range 4000-400 cm-1 at room
temperature. KBr technique was used for measurements, 1/100 sample/KBr ratio with
wavelength precision 0.01 cm-1 and spectral resolution 0.4 cm-1.
Scanning electron microscopy (SEM). The morphology of prepared catalyst was characterized
by scanning electron microscopy using (Jeol, Quanta FEG), operating at 200 V-30 kV
accelerating voltage magnification 14 xup to 5000 x. Surfaces of the samples were coated with a
thin layer of gold (3.5 nm) by the vacuum evaporation technique to minimize sample charging
effects due to the electron beam.
Chemicals and apparatus
Melting points are uncorrected. NMR spectra were scanned in DMSO-d6 on a Brucker NMR
1
spectrophotometer at 300 MHz for H NMR and 75 MHz for 13C NMR. Chemical shifts are
expressed in δ-values (parts per million) relative to an internal standard (TMS at 0.0 ppm) and
coupling constants (J) in Hz. Mass spectra were recorded on a Agilent LC-MS spectrometer
(pump quarter nary 1200 Series, quadruple MSD 6110); LC column into multimode
(ESI+APCI) ion source of MSD. Thin layer chromatography (TLC) was performed on Merck
silica gel F254 plates and visualized by UV-light (254 nm) and all chemicals were purchased
from Sigma-Aldrich.
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V2O5/SiO2 as an efficient catalyst in the synthesis of 5-aminopyrazole derivatives
137
General procedure and structure elucidation
The reaction was started by mixing ketene S,N-acetals (10 mmol) and hydrazine hydrate (20
mmol), the V2O5/SiO2 (0.2 g, 20 mol %) was added and the mixture was allowed to stir at 70-80
oC. The reaction was monitored by TLC until reaction completion. Ethyl acetate (20 mL) was
added to the reaction mixture. Then, the mixture was filtered off and the extract was vaporized.
The remaining residue was recrystallized to give pure product.
o
1
5-Amino-3-(phenylamino)-1H-pyrazole-4-carboxamide (1). White, m.p. 178-180 C. H NMR
(DMSO-d6, δ ppm) 5.79 (s, br, 2H, NH2), 6.70 (s, 2H, NH2), 7.13-7.31 (m, 5H, C6H5), 8.92 (s,
br, NH), 10.95 (s, br, 1H, NH). MS (m/z): 217 (M+) [16].
o
1
5-Amino-N-phenyl-3-(phenylamino)-1H-pyrazole-4-carboxamide (2). White, m.p. 247 C. H
NMR (DMSO-d6, δ ppm) 6.01 (s, 2H, NH2), 6.76-7.48 (m, 10H, 2C6H5), 8.52 (s, 1H, NH), 8.73
(s, 1H, NH), 11.32 (s, 1H, NH). MS (m/z): 293 (M+) [17].
5-Amino-3-(phenylamino)-N-(4-methylphenyl)-1H-pyrazole-4-carboxamide (3). White, m.p. 178
1
oC. H NMR (DMSO-d6, δ ppm) 2.23 (s, 3H, CH3), 5.98 (s, 2H, NH2), 7.05-7.37 (m, 9H, C6H4
and C6H5), 8.54 (s, 1H, NH), 8.64 (s, 1H, NH), 11.29 (s, 1H, NH). MS (m/z): 308 (M++1) [17].
5-Amino-N-(4-chlorophenyl)-3-(phenylamino)-1H-pyrazole-4-carboxamide (4). White, m.p. 115
1
oC. H NMR (DMSO-d6, δ ppm) 6.02 (s, 2H, NH2), 6.76-7.54 (m, 9H, C6H4 and C6H5), 8.51 (s,
1H, NH), 8.81 (s, 1H, NH), 11.29 (s, 1H, NH). MS (m/z): 327 (M+) [17].
5-Amino-3-[(4-methoxyphenyl)amino]-1H-pyrazole-4-carboxamide (5). White crystals, m.p.
200 oC. 1H NMR (DMSO-d6, δ ppm) 3.64 (s, 3H, OCH3), 5.74 (s, 2H, NH2, D2O exchangeable),
6.60 (s, 2H, NH2, D2O exchangeable), 6.75 (d, 2H, aromatic, AB-system, JHH=8.4 Hz), 7.24 (d,
2H, aromatic, AB-system, JHH=8.4 Hz), 8.68 (s, 1H, NH, D2O exchangeable), 10.82 (s, 1H, NH,
D2O exchangeable). 13C NMR (DMSO-d6, δ ppm) 55.6 (-OCH3), 86.2 (C4, pyrazole), 114.6 (2C,
aromatic), 117.4 (2C, aromatic), 137.0 (C, aromatic), 148.2 (C5, pyrazole), 152.2 (C3, pyrazole),
152.8 (C, aromatic), 167.2 (C=O, amide). MS (m/z): 247 (M+) [18].
5-Amino-3-[(4-methoxyphenyl)amino]-N-phenyl-1H-pyrazole-4-carboxamide
(6).
White
o
1
crystals, m.p. 175-177 C. H NMR (DMSO-d6, δ ppm) 3.63 (s, 3H, OCH3), 5.98 (s, 2H, NH2,
D2O exchangeable), 6.76 (d, 2H, aromatic, JHH=7.7 Hz), 6.98 (t, 1H, aromatic, JHH=7.7 Hz),
7.18 (t, 2H, aromatic, JHH=8.4 Hz), 7.25 (d, 2H, aromatic, JHH=7.7 Hz), 7.45 (d, 2H, aromatic,
JHH=7.7 Hz), 8.30 (s, 1H, NH, D2O exchangeable), 8.74 (s, 1H, NH, D2O exchangeable), 11.22
(s, 1H, NH, D2O exchangeable). 13C NMR (DMSO-d6, δ ppm) 55.6 (-OCH3), 88.3 (C4,
pyrazole), 114.7, 117.5, 120.3, 123.3, 129.1, 137.6, 139.4 (11C, aromatic), 149.1 (C5, pyrazole),
150.9 (C3, pyrazole), 153.1 (C, aromatic), 163.6 (C=O) [19].
5-Amino-3-[(4-methoxyphenyl)amino]-N-(4-methylphenyl)-1H-pyrazole-4-carboxamide
(7).
o
1
White crystals, m.p. 198-200 C. H-NMR (DMSO-d6, δ ppm) 2.21 (s, 3H, CH3), 3.64 (s, 3H,
OCH3), 5.95 (s, 2H, NH2, D2O exchangeable), 6.76 (d, 2H, aromatic, JHH=8.4 Hz), 7.04 (d, 2H,
aromatic, JHH=8.4 Hz), 7.16 (d, 2H, aromatic, JHH=8.4 Hz), 7.33 (d, 2H, aromatic, JHH=8.4 Hz),
8.30 (s, 1H, NH, D2O exchangeable), 8.66 (s, 1H, NH, D2O exchangeable), 11.21 (s, 1H, NH,
D2O exchangeable) [19].
5-Amino-N-(4-chlorophenyl)-3-[(4-methoxyphenyl)amino]-1H-pyrazole-4-carboxamide
(8).
1
White crystals, m.p. 190-192 oC. H NMR (DMSO-d6, δ ppm) 3.64 (s, 3H, OCH3), 6.00 (s, 2H,
NH2, D2O exchangeable), 6.77-7.51 (m, 8H, aromatic), 8.30 (s, 1H, NH, D2O exchangeable),
Bull. Chem. Soc. Ethiop. 2019, 33(1)

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Tamer K. Khatab et al.
8.82 (s, 1H, NH, D2O exchangeable), 11.20 (s, 1H, NH, D2O exchangeable). 13C NMR (DMSO-
d6, δ ppm) 55.7 (-OCH3), 87.9 (C4, pyrazole), 114.7, 117.7, 121.9, 126.8, 128.9, 137.4, 138.4
(11C, aromatic), 149.1 (C5, pyrazole), 151.1 (C3, pyrazole), 153.2 (C, aromatic), 163.6 (C=O).
MS (m/z): 358 (M+) [19]. X-ray crystal structure is shown in Figure 3.
RESULTS AND DISCUSSION
Catalyst preparation and characterization
Catalyst was prepared and characterized before using XRD, FTIR spectra and SEM [20]. X-Ray
diffraction pattern for SiO2 and prepared V2O5/SiO2. XRD of SiO2 show the amorphous nature
40
1.0
0.8
35
0.6
30
0.4
25
0.2
20
0.0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1
)
15
10
5
0
10
20
30
40
50
60
70
2 degree
70
1.0
Catalyst
0.8
0.6
0.4
0.2
0.0
60
50
40
30
20
10
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1
)
10
20
30
40
50
60
70
2 degree
Figure 2. XRD diffraction scans and collective FTIR spectra of received silica and vanadium
dioxide before the catalyst preparation and after interaction.
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V2O5/SiO2 as an efficient catalyst in the synthesis of 5-aminopyrazole derivatives
139
with no sharp peaks and the prepared V2O5/SiO2 explains sharp intense peaks at about (20.2,
26.1, 31.0 and 47.3o) and less intense sharp peaks at about (14.8, 24 and 53.5o) explaining the
formation of crystalline phase with orthorhombic geometry. The partially hydrated silanols
(Si–OH residue) and bonded hydrogen bands were reported in the range from 3500 to 3055 cm-1
band [21-23]. A detected band at 1030-1230 cm-1 overlapped with another broad band
recognized to Si–OH and Si–O–Si vibrations observed. The FTIR spectra of the catalyst band
presented at 990 cm-1 for V\O as a vibration-stretching band. Also, it was observed a various
functional groups at 3400 cm-1 for OH stretching and at 1571 cm-1 for bending OH vibration,
this result is due to wide specific surface area of silica and water molecules that trapped by the
obtained catalyst (Figure 2).
Organic synthesis
Catalysts contain silicon element attracted our attention and play an important role in our group
[24-26], and we forward are the aim of investigation new methods for design and synthesis of
heterocyclic compounds by efficient and simple reaction. This work presented the synthesis of
5-aminopyrazole derivatives using V2O5/SiO2 as a heterogeneous catalyst under solvent free
condition. The reaction was done via mixing one mol of ketene S,N-acetals and two moles of
hydrazine hydrate (80%) in the presence of selected catalyst under solvent free condition and in
the way to prove the effectiveness of our mixed catalyst (Scheme 1).
O
Ar1
O
HN
Ar
Ar1
KOH /
Ar1 NCS
HN
Ar CN
CH3I
SCH3
1
2
3
4
5
6
7
8
HN
Ar CN
H
C6H5
C6H5
C6H5
C6H5
4-CH3-C6H4
4-Cl-C6H4
H
C6H5
O
Ar
NH2
NH
4-CH3O-C6H4
4-CH3O-C6H4
N
NH2NH2 / catalyst
H
C6H5
solvent free / 70-80 o
C
N
HN
Ar1
4-CH3-C6H4 4-CH3O-C6H4
4-CH3O-C6H4
4-Cl-C6H4
1-8
Scheme 1. Synthesis of 5-aminopyrazole derivatives 1-8
The suggested mechanism for the V2O5/SiO2-catalyzed synthesis of 5-aminopyrazole is
presented in Scheme 2. The initial step involves improve the leaving power of (-SCH3) by the
catalyst and then nucleophilic substitution occurs by hydrazine hydrate and in the second step
the catalyst activate the nitrile group towards nucleophlic attack from (NH2). Ultimately, the
reaction ended by H-rearrangement to obtain more stable structure.
The proposed reaction mechanism was confirmed by the single crystal X-ray structure
analysis of compound 8 (Figure 3) [The crystallographic data was deposited to the Cambridge
Crystallographic Data Center (CCDC 1528985)].
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Tamer K. Khatab et al.
Ar
Ar
Ar
NH
N
NH
NH
N
N
C
C
C
O
O
O
NH2
NH2
H
H
N
-HSCH3
NH2
Ar1
N
H
SCH3
Ar1
N
H
N
H
N
Ar1
NH2
H
SCH3
V2O5/SiO2
V2O5/SiO2
V2O5/SiO2
Ar
Ar
Ar
V2O5/SiO2
NH
NH
NH2
NH
NH
Ar
N
NH
N
C
O
O
O
H
Shift
NH
NH
H
N
O
NHH2
Ar1
N
N
H
Ar1
N
N
Ar1
N
H
N
H
H
H
H
Ar1
N
N
H
H
Scheme 2. The proposed reaction mechanism.
Figure 3. X-ray structure of coompound 8.
These results prompted us to explore the potential of this protocol for the syntheesis of
various 5-aminopyrazole 1-8 in excellent yield. The results summarized in Table 1. Fr m the
data presented in the Table 1, we noticed that when (Ar1) equal (C6H5) the reaction gives more
yield and less reaction time. n addition, the presence of halogen in para position of aroomatic
oo
I
I
ring at (Ar) gives more yields and less reaction time rather than the presence of methyl group in
para position.
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V2O5/SiO2 as an efficient catalyst in the synthesis of 5-aminopyrazole derivatives
141
Table 1. Synthesis of 5-aminopyrazole 1-8 derivatives from ketene S,N-acetals and hydrazine hydrate.
Entry
Ar
Ar1
Traditional method
Yield (%) Time (min)
Ref.
Catalysis method
Yield (%) Time (min)
1
2
3
4
5
6
7
8
H
C6H5
4-CH3-C6H4-
4-Cl-C6H4-
H
C6H5
C6H5
C6H5
85
75
77
78
82
79
82
80
120
120-180
120-180
120-180
240
240
240
240
[16]
[17]
[17]
[17]
[18]
[19]
[19]
[19]
93
92
90
95
91
92
88
93
20
20
25
15
30
25
25
20
C6H5
4-CH3O-C6H4-
4-CH3O-C6H4-
C6H5
4-CH3-C6H4- 4-CH3O-C6H4-
4-Cl-C6H4- 4-CH3O-C6H4-
CONCLUSION
In conclusion, we have prepared and characterized V2O5/SiO2 as a heterogeneous catalyst,
which has been successful used as effective catalyst for the synthesis of various 5-
aminopyrazoles 1-8. This procedure has many advantages compared with common reported
methods in terms of high yield, mild reaction condition, simple procedure, green catalyst, low
cost, lack of toxicity and simplicity of workup.
ACKNOWLEDGEMENT
The authors wish to express their thanks to the National Research Centre, Dokki, Cairo, Egypt
for the facilities provided.
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