Novel heterocyclic disazo dyes containing pyrazole and phenylpyrazole. part 1: Synthesis, characterization, solvent polarity and acid-base sensitive characteristics

Article abstract of DOI:10.1016/j.molstruc.2021.129960

A series of diazotised aniline and aniline derivative compounds were reacted with solution of malononitrile in pyridine at 0–5 °C were obtained 1a-1m compounds. Then 4-arylazo-3,5-diamino-1H-pyrazole (2a-2m) derivatives were synthesized by coupling arylazo malononitrile compounds with hydrazine. Finally, the synthesized pyrazole derivative 2a-2m compounds were again diazotised. By reacting these diazotised compounds with 3-amino-5?hydroxy-1-phenylpyrazole, the new thirteen heterocyclic disazo dyes (3a-3m) were joined the dye literature and the dye industry. The structures of these newly synthesized compounds were characterized using elemental analysis and spectroscopic methods such as Fourier transform infrared spectroscopy-Attenuated total reflectance (FT-IR-ATR), ¹H-Nuclear magnetic resonance (¹H NMR) spectroscopy and mass spectroscopy. Then solvatochromic properties and solvent effect in dimethyl sulfoxide, dimethyl formamide, acetonitrile, acetic acid, methanol and chloroform were investigated. In addition, the effects of organic and inorganic acids and bases on the absorption spectra of the compounds and the substituent effect of the phenyl ring-bound groups were investigated.

Full text of DOI:10.1016/j.molstruc.2021.129960

Journal of Molecular Structure 1231 (2021) 129960
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Novel heterocyclic disazo dyes containing pyrazole and
phenylpyrazole. part 1: Synthesis, characterization, solvent polarity
and acid-base sensitive characteristics
Aykut Demirçalı
Department of Chemistry, Faculty of Science and Art, Pamukkale University, 20160 Denizli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of diazotised aniline and aniline derivative compounds were reacted with solution of malonon-
itrile in pyridine at 0–5 °C were obtained 1a-1m compounds. Then 4-arylazo-3,5-diamino-1H-pyrazole
(2a-2m) derivatives were synthesized by coupling arylazo malononitrile compounds with hydrazine. Fi-
nally, the synthesized pyrazole derivative 2a-2m compounds were again diazotised. By reacting these
diazotised compounds with 3-amino-5–hydroxy-1-phenylpyrazole, the new thirteen heterocyclic disazo
dyes (3a-3m) were joined the dye literature and the dye industry. The structures of these newly synthe-
sized compounds were characterized using elemental analysis and spectroscopic methods such as Fourier
transform infrared spectroscopy-Attenuated total reflectance (FT-IR-ATR), 1H-Nuclear magnetic resonance
(1H NMR) spectroscopy and mass spectroscopy. Then solvatochromic properties and solvent effect in
dimethyl sulfoxide, dimethyl formamide, acetonitrile, acetic acid, methanol and chloroform were inves-
tigated. In addition, the effects of organic and inorganic acids and bases on the absorption spectra of the
compounds and the substituent effect of the phenyl ring-bound groups were investigated.
Received 2 November 2020
Revised 10 January 2021
Accepted 12 January 2021
Available online 19 January 2021
Keywords:
3-amino-5–hydroxy-1-phenylpyrazole
Heterocyclic disazo dyes
Diazotization
Diazo coupling reaction
Solvatochromism
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
Amino pyrazole derivatives are important compounds with a
wide range of interesting properties [15,16], including antihy-
The synthesis of azo dyestuffs have great importance nowadays
due to their many features such as having a wide color range from
greenish yellow to turquoise, showing good fastness properties, be-
ing easily obtained from cheap starting materials, high dyeing abil-
ity and chromophoric strength [1,2].
perglycemic [17], anti-inflammatory [18], antipyretic [19], anti-
bacterial [20] and anti-microbial [21]. Also these compounds are
used anti-fungal [22], anti-cancer [23,24], antiviral [25], antituber-
cular [26], antidiabetic [27] and antitumor agent [28]. Recently,
studies have been conducted stating that some amino pyrazoles
have anti-Alzheimer’s inhibitory activity [29]. Due to these fea-
tures, they have a widespread use in the field of biology, pharma-
cology and medicine due to their versatile biological activities.
In addition, the amino azo pyrazole derivative dyes are widely
used in various and current applications such as metallochromic
indicators [30], optical data storage tools [31], nonlinear optical
systems [32], dye-sensitized solar cells [33], organic light emitting
diodes [34], LCD color filters and coloring of plastics and polymer
[35,36]. These compounds are frequently used in organic advanced
synthesis applications.
In particularly, the presence of a heterocyclic atom such as ni-
trogen, oxygen, sulfur in the azo compounds allowed these dyes to
show better fastness properties, to obtain not only from yellow to
turquoise but also blue colors and to be used as a pH indicator in
the presence of conjugated acid and base [3–7].
The growing interest in amino pyrazole and amino phenyl pyra-
zole compounds today is due to the ability to re-diazotised of these
compounds, to obtain different heterocyclic dyes by reacted with
various active methylene compounds and there can be used in dif-
ferent areas [8,9]. In recent years, amino pyrazole derivatives are
preferred more in the textile and dyestuffs industry because they
have a wide range of colors, high dyeing properties and permanent
fastness properties [10–12]. Metal complexes of these compounds
are also included in the literature with their ion selective proper-
ties [13,14].
In the present study, firstly, 13 novels amino pyrazole deriva-
tives heterocyclic disazo dyestuffs (3a-3m) having industrial sig-
nificance in bright colors were synthesized by reacting diazotised
pyrazole derivative 2a-2m compounds with 3-amino-5–hydroxy-
1-phenylpyrazole. Then, characteristic features were clarified by
methods such as FT-IR spectroscopy, 1H NMR spectroscopy, mass
spectroscopy and elemental analysis. Lastly, tautomeric properties,
E-mail address: ademircali@pau.edu.tr
https://doi.org/10.1016/j.molstruc.2021.129960
0022-2860/© 2021 Elsevier B.V. All rights reserved.

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
H
N
CN
CN
NaNO2 + HCl
C4H2N2
N2H4.H2O
N
N
N
C
NH2
NH2
NH
X
X
X
2a-2m
1a-1m
X
N
H2N
m-NO2
m-OCH3
m-Cl
o-NO
1j:
1f:
1g:
1a: H
p-NO
2
1b:
1c: p-OCH3
o-OCH
2
1k:
1l:
3
1h:
o-Cl
p-Cl
1d:
1e:
1i: m-CH3
1m:o-CH3
p-CH
3
Scheme 1. General synthesis method of dyes 2a-2m.
absorbance properties and substituent effects of these compounds
in 6 different solvents and acid-base solutions were investigated
using UV–Vis. spectroscopy.
in water many times (60 ml). Later the dye was dried and crystal-
lized from the DMF-water (1:2, v:v) mixture. Color: red crystals,
yield: 80%, mp: 321–322 °C, mw: 388 g/mol, MS m/z: 388.51 (M+),
Elemental analysis: Calculated for C18 H16 N10O: C, 55.67; H, 4.12; N,
36.08%; Found: C, 55.68; H, 4.18; N, 36.21%.
2. Experimental
2.1. Materials and methods
ꢀ
ꢀ
ꢀ
ꢀ
2.3.2. 4-[3 -amino-4 -(p-nitrophenylazo)−1 H-pyrazole-5 -ylazo]−3-
amino-5–hydroxy-1-phenyl pyrazole
The chemicals used in the experiments were supplied from
Merck, Acros and Sigma-aldrich companies. These chemicals were
used in their original form with high purity.
(3b)
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(p-nitrophenylazo)−1 H-pyrazole-
Melting points of dyestuffs were determined using the Elec-
trothermal 9100 apparatus. Elemental analysis was calculated by
Costech ECS 4010 analyzer device. IR spectral data were mea-
sured using a Perkin Elmer UATR Two (FT-IR) Spectrophotome-
ter device. The mass spectrum values of the synthesized dyestuffs
were determined using the Thermo Scientific TSQ Quantum Ac-
cess MAX instrument. The data of the 1H NMR spectra were de-
termined by the Bruker-Spectrospin Avance DPX 400 Ultra-Shield
device in DMSO–d6 solvent utilizing the tetramethylsilane as the
referans compound, and chemical shifts (δ) were recorded as ppm.
UV–Vis. spectrums were procured by PG T80+ high performance
double beam spectrophotometer in six different solvents such as
dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetoni-
trile (CH3CN), methanol (CH3OH), acetic acid (CH3CO2H) and chlo-
roform (CHCl3) at concentration 1 × 10−6 M.
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3b) was obtained
from 4-(p-nitrophenylazo)−3,5-diamino-1H-pyrazole (2b) (1 g,
2.31 mmol). Color: brown crystals, yield: 92%, mp: 341–342 °C,
mw: 433 g/mol, MS m/z: 432.70 (M+), Elemental analysis: Cal-
culated for C18 H15N11 O3: C, 49.88; H, 3.46; N, 35.57%; Found: C,
49.95; H, 3.54; N, 35.48%.
ꢀ
ꢀ
ꢀ
ꢀ
2.3.3. 4-[3 -amino-4 -(p-methoxyphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3c)
Using the same procedure mentioned above for the synthe-
ꢀ
ꢀ
ꢀ
sis of dye 3a, 4-[3 -amino-4 -(p-methoxyphenylazo-1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3c) was obtained
from 4-(p-methoxyphenylazo)−3,5-diamino-1H-pyrazole (2c) (1 g,
2.39 mmol). Color: orange crystals, yield: 76%, mp: 327–328 °C,
mw: 418 g/mol, MS m/z: 418.02 (M+), Elemental analysis: Calcu-
lated for C19 H18 N10O2: C, 54.54; H, 4.30; N, 33.49%; Found: C,
54.50; H, 4.39; N, 33.48%.
2.2. Synthesis of 4-arylazo-3,5-diamino-1H-pyrazoles (2a-2m)
1a-1m and 2a-2m dyes were synthesized following the method
given in reference of [37]. The general synthesis method of 1a-1m
and 2a-2m were presented in Scheme 1.
ꢀ
ꢀ
ꢀ
ꢀ
2.3.4. 4-[3 -amino-4 -(p-chlorophenylazo)−1 H-pyrazole-5 -ylazo]−3-
amino-5–hydroxy-1-phenyl pyrazole
(3d)
2.3. Synthesis of new heterocyclic disazo dyestuffs (3a-3m)
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(p-chlorophenylazo)−1 H-pyrazole-
2.3.1. 4-(3 -amino-4 -phenylazo-1 H-pyrazole-5 -ylazo)−3-amino-5–
hydroxy-1-phenylpyrazole
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3d) was obtained
from 4-(p-chlorophenylazo)−3,5-diamino-1H-pyrazole (2d) (1 g,
2.37 mmol). Color: brown crystals, yield: 86%, mp: 331–332 °C,
mw: 422.5 g/mol, MS m/z: 421.98 (M+), Elemental analysis: Cal-
culated for C18 H15ClN10O: C, 51.12; H, 3.55; N, 33.14%; Found: C,
51.18; H, 3.61; N, 33.20%.
(3a)
4-phenylazo-3,5-diamino-1H-pyrazole compound (2a) (1.0 g,
2.58 mmol) was dissolved in a mixture of glacial acetic acid and
concentrated hydrochloric acid (30 ml, ratio 1: 1) and the solu-
tion was cooled to 0–5 °C. While the solution was stirring, NaNO2
(3.87 mmol) in water (10 ml) was slowly added to this solu-
tion. Stirring was continued until the diazonium salt was formed
(2 h). Then the basic mixed solution of 3-amino-5–hydroxy-1-
phenylpyrazole (0.45 g, 2.58 mmol) with potassium hydroxide
(0.14 g, 2.58 mmol) and water (20 ml) was added to the obtained
diazonium salt. The reaction was stirred for a further 4 h under
cold conditions (0–5 °C). At the end of the reaction, the synthe-
sized dye 3a was precipitated with 50 ml of water, filtered, washed
ꢀ
ꢀ
ꢀ
ꢀ
2.3.5. 4-[3 -amino-4 -(p-methylphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3e)
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(p-methylphenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3e) was obtained
from 4-(p-methylphenylazo)−3,5-diamino-1H-pyrazole (2e) (1 g,
2

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
-
+
N
N
NH2
N
N
N
N
N
N
N
NH2
NH
2 Cl
C9H9N3O
NaNO + HCl
2
X
X
X
CH3COOH
NH
NH
N
N
N
N
N
H2N
H2N
H2N
HO
2a-2m
3a-3m
Scheme 2. General synthesis method of dyes 3a-3m.
ꢀ
ꢀ
ꢀ
ꢀ
2.49 mmol). Color: orange crystals, yield: 79%, mp: 292–293 °C,
mw: 402 g/mol, MS m/z: 402.08 (M+), Elemental analysis: Calcu-
lated for C19 H18 N10O: C, 56.72; H, 4.48; N, 34.83%; Found: C, 56.78;
H, 4.55; N, 34.88%.
2.3.10. 4-[3 -amino-4 -(o-nitrophenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3j)
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(o-nitrophenylazo)−1 H-pyrazole-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3j) was obtained
2.3.6. 4-[3 -amino-4 -(m-nitrophenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3f)
from 4-(o-nitrophenylazo)−3,5-diamino-1H-pyrazole (2j) (1 g,
2.31 mmol). Color: brown crystals, yield: 88%, mp: 338–339 °C,
mw: 433 g/mol, MS m/z: 432.68 (M+), Elemental analysis: Calcu-
lated for C18 H15N11 O3: C, 49.88; H, 3.46; N, 35.57%; Founded: C,
49.81; H, 3.45; N, 35.53%.
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(m-nitrophenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3f) was obtained
from 4-(m-nitrophenylazo)−3,5-diamino-1H-pyrazole (2f) (1 g,
2.31 mmol). Color: brown crystals, yield: 89%, mp: 301–302 °C,
mw: 433 g/mol, MS m/z: 432.74 (M+), Elemental analysis: Cal-
culated for C18 H15N11 O3: C, 49.88; H, 3.46; N, 35.57%; Found: C,
49.90; H, 3.52; N, 35.49%.
ꢀ
ꢀ
ꢀ
ꢀ
2.3.11. 4-[3 -amino-4 -(o-methoxyphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3k)
Using the same procedure mentioned above for the synthe-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2.3.7. 4-[3 -amino-4 -(m-methoxyphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3g)
sis of dye 3a, 4-[3-amino-4 -(o-methoxyphenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3k) was obtained
from 4-(o-methoxyphenylazo)−3,5-diamino-1H-pyrazole (2k) (1 g,
2.39 mmol). Color: orange crystals, yield: 71%, mp: 319–320 °C,
mw: 418 g/mol, MS m/z: 418.06 (M+), Elemental analysis: Calcu-
lated for C19 H18 N10O2: C, 54.54; H, 4.30; N, 33.49%; Founded: C,
54.57; H, 4.37; N, 33.42%.
Using the same procedure mentioned above for the synthe-
ꢀ
ꢀ
ꢀ
sis of dye 3a, 4-[3 -amino-4 -(m-methoxyphenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3g) was obtained
from 4-(m-methoxyphenylazo)−3,5-diamino-1H-pyrazole (2g) (1 g,
2.39 mmol). Color: orange crystals, yield: 73%, mp: 305–306 °C,
mw: 418 g/mol, MS m/z: 418.10 (M+), Elemental analysis: Calcu-
lated for C19 H18 N10O2: C, 54.54; H, 4.30; N, 33.49%; Founded: C,
54.49; H, 4.33; N, 33.45%.
ꢀ
ꢀ
ꢀ
ꢀ
2.3.12. 4-[3 -amino-4 -(o-chlorophenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3l)
ꢀ
ꢀ
ꢀ
ꢀ
2.3.8. 4-[3 -amino-4 -(m-chlorophenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3h)
Using the same procedure mentioned above for the syn-
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(o-chlorophenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3l) was obtained
Using the same procedure mentioned above for the syn-
from 4-(o-chlorophenylazo)−3,5-diamino-1H-pyrazole (2l) (1 g,
2.37 mmol). Color: brown crystals, yield: 81%, mp: 328–329 °C,
mw: 422.5 g/mol, MS m/z: 422.09 (M+), Elemental analysis: Cal-
culated for C18 H15ClN10O: C, 51.12; H, 3.55; N, 33.14%; Founded: C,
51.15; H, 3.54; N, 33.18%.
ꢀ
ꢀ
ꢀ
thesis of dye 3a, 4-[3 -amino-4 -(m-chlorophenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3h) was obtained
from 4-(m-chlorophenylazo)−3,5-diamino-1H-pyrazole (2h) (1 g,
2.37 mmol). Color: brown crystals, yield: 84%, mp: 310–311 °C,
mw: 422.5 g/mol, MS m/z: 422.04 (M+), Elemental analysis: Cal-
culated for C18 H15ClN10O: C, 51.12; H, 3.55; N, 33.14%; Founded: C,
51.19; H, 3.54; N, 33.16%.
ꢀ
ꢀ
ꢀ
ꢀ
2.3.13. 4-[3 -amino-4 -(o-methylphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3m)
ꢀ
ꢀ
ꢀ
ꢀ
2.3.9. 4-[3 -amino-4 -(m-methylphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenyl pyrazole
(3i)
Using the same procedure mentioned above for the synthe-
ꢀ
ꢀ
ꢀ
ꢀ
Using the same procedure mentioned above for the synthe-
sis of dye 3a, 4-[3 -amino-4 -(o-methylphenylazo)−1 H-pyrazole-5 -
ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3m) was obtained
from 4-(o-methylphenylazo)−3,5-diamino-1H-pyrazole (2m) (1 g,
2.49 mmol). Color: red crystals, yield: 74%, mp: 313–314 °C, mw:
402 g/mol, MS m/z: 402.11 (M+), Elemental analysis: Calculated for
C19 H18 N10O: C, 56.72; H, 4.48; N, 34.83%; Founded: C, 56.71; H,
4.43; N, 34.84%. The general synthesis method of 3a-3m was pre-
sented in Scheme 2.
ꢀ
ꢀ
ꢀ
sis of dye 3a, 4-[3 -amino-4 -(m-methylphenylazo)−1 H-pyrazole-
ꢀ
5 -ylazo]−3-amino-5–hydroxy-1-phenylpyrazole (3i) was obtained
from 4-(m-methylphenylazo)−3,5-diamino-1H-pyrazole (2i) (1 g,
2.49 mmol). Color: red crystals, yield: 76%, mp: 317–318 °C, mw:
402 g/mol, MS m/z: 402.15 (M+), Elemental analysis: Calculated for
C19 H18 N10O: C, 56.72; H, 4.48; N, 34.83%; Founded: C, 56.81; H,
4.57; N, 34.84%.
3

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
N
N
NH2
N
N
NH2
N
N
N
N
X
X
KT
NH
NH
HO
N
N
N
N
N
N
H2N
H2N
O
T2
T1
(disazo-keto)
(disazo-enol)
KT
KT
- O
N
N
H
H
H
N
N
N
NH2
N
N
N
NH2
N
N
NH2
N
N
N
N
X
KT
X
KT
X
NH
N
N
N
NH
N
N
H2N
N
N
O
H2N
N
O
H2N
T3
A
T4
(azo-hydrazo-keto)
(anionic form)
(dishydrazo-keto)
KT
KT
H
H
N
N
NH2
N
N
NH2
N
N
N
N
KT
X
X
N
N
N
N
N
N
N
N
H2N
H2N
O
HO
T5
T6
(hydrazo-azo-keto)
(hydrazo-azo-enol)
Scheme 3. Possible tautomeric structures of 3a-3m dyes.
Table 1
3. Results and discussion
FT-IR spectral data of 3a-3m dyes.
3.1. FT-IR spectral evaluation and possible tautomeric structures of
new 3a-3m dyes
Dye No Vibratioanal frequencies (cm−1
)
νNH2
νNH
νAr-H
νAl-H
νC=O
νN=N
3a
3b
3c
3d
3e
3f
3442, 3317
3485, 3380
3418, 3296
3393, 3327
3414, 3309
3441, 3318
3438, 3385
3423, 3311
3443, 3312
3468, 3300
3409, 3302
3443, 3305
3441, 3314
3172
3174
3166
3173
3159
3158
3162
3184
3167
3170
3178
3167
3182
3061, 3021
3066, 3028
3069, 3024
3064, 3022
3058, 3016
3073, 3028
3071, 3031
3064, 3024
3062, 3026
3080, 3028
3066, 3025
3060, 3019
3066, 3022
–
1622
1622
1627
1630
1633
1624
1637
1643
1657
1650
1622
1627
1627
1537, 1497
1508, 1498
1539, 1497
1551, 1448
1556, 1497
1520, 1489
1533, 1498
1538, 1498
1538, 1495
1522, 1497
1538, 1497
1540, 1498
1557, 1497
3a-3m compounds could be found 6 possible tautomeric forms
such as T1 (disazo-enol), T2 (disazo-keto), T3 (azo-hydrazo-keto),
T4 (dishydrazo-keto), T5 (hydrazo-azo-keto) and T6 (hydrazo-azo-
enol). These tautomeric forms were shown in Scheme 3.
The FT-IR spectrum of compounds provides an important
gain in obtaining information about the presence or absence of
compound-specific functional groups, especially in organic com-
pounds. When comparing FT-IR samples, it gives specific results for
the fingerprint area, as well as the functional groups.
–
2966
–
2922
–
3g
3h
3i
2922
–
2917
–
3j
3k
3l
2923
–
FT-IR spectrum data of the synthesized dyestuffs were given in
Table 1. As an example, the FT-IR spectrum of dye 3j was given in
Fig. 1.
3m
2988
As seen in Table 1, it was thought that the peaks seen in the
range of 3393–3485 cm−1 belong to the amino (-NH2) group at-
tached to the phenyl pyrazole ring and the peaks seen at 3296–
3380 cm−1 belong to the amino (-NH2) group connected to the
pyrazole ring. It was observed that the peaks in the range of 3158–
3184 cm−1 belong to the imino (-NH) group attached to the pyra-
zole ring and the peaks between 1622 and 1657 cm−1 belong to
All of the IR spectra were taken while the dyes were solid. The
appearance of two different amino (-NH2) peaks, two different azo
=
=
(-N N) peaks and one carbonyl (-C O) peak in the FT-IR spectrum
results for all compounds showed that our dyes were in disazo-
keto (T2) tautomeric form in solid phase.
3.2. 1H NMR analysis and possible tautomeric structures of dyes
=
the carbonyl (-C O) group. The peaks observed between 1508 and
1557 and 1448–1498 cm−1 belong to the azo groups found in the
1H NMR results of compounds were taken in DMSO solvent uti-
lizing TMS as the internal reference. The measured values were
structure of our compound.
4

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
Fig. 1. FT-IR spectra of dye 3j.
Fig. 2. 1H NMR spectra of dye 3c.
5

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
Table 2
Spectral data for 1H NMR analyses of the synthesized dyes 3a-3m.
1H NMRa [(δ, ppm) (in DMSO–d6)]
Dye No
Phenylpyrazole-NH2
Pyrazole-NH2
Pyrazole-NH
Phenylpyrazole-OH
Aromatic-H
Aliphatic-H
3a
3b
3c
3d
3e
3f
14.17 (s, 2H)
14.09 (s, 2H)
14.14 (s, 2H)
14.17 (s, 2H)
14.06 (s, 2H)
14.31 (s, 2H)
14.11 (s, 2H)
14.12 (s, 2H)
14.09 (s, 2H)
14.25 (s, 2H)
14.29 (s, 2H)
14.21 (s, 2H)
14.19 (s, 2H)
13.99 (s, 2H)
13.45 (s, 2H)
13.90 (s, 2H)
13.80 (s, 2H)
13.93 (s, 2H)
13.74 (s, 2H)
13.82 (s, 2H)
13.62 (s, 2H)
13.60 (s, 2H)
13.42 (s, 2H)
13.64 (s, 2H)
13.56 (s, 2H)
13.62 (s, 2H)
12.76 (s, 1H)
12.78 (s, 1H)
12.67 (s, 1H)
12.77 (s, 1H)
12.69 (s, 1H)
12.78 (s, 1H)
12.76 (s, 1H)
12.79 (s, 1H)
12.71 (s, 1H)
12.69 (s, 1H)
12.72 (s, 1H)
12.84 (s, 1H)
12.76 (s, 1H)
11.86 (s, 1H)
12.03 (s, 1H)
11.81 (s, 1H)
11.86 (s, 1H)
11.82 (s, 1H)
11.94 (s, 1H)
11.86 (s, 1H)
11.89 (s, 1H)
11.84 (s, 1H)
11.89 (s, 1H)
11.93 (s, 1H)
11.73 (s, 1H)
11.80 (s, 1H)
6.30–8.10 (m, 10H)
6.22–8.32 (m, 9H)
6.28–8.05 (m, 9H)
6.29–8.10 (m, 9H)
6.15–7.94 (m, 9H)
6.14–8.05 (m, 9H)
6.31–7.94 (m, 9H)
6.27–7.98 (m, 9H)
6.30–7.97 (m, 9H)
6.31–8.10 (m, 9H)
6.35–7.92 (m, 9H)
6.40–7.93 (m, 9H)
6.40–8.37 (m, 9H)
–
–
3.85 (s, 3H)
–
2.33 (s, 3H)
–
3g
3h
3i
3.88 (s, 3H)
–
2.38 (s, 3H)
3j
–
3k
3l
3.93 (s, 3H)
–
3m
2.30 (s, 3H)
a
Abbreviations: s; singlet, m; multiplet.
Table 3
UV–Vis. wavelength parameters (λmax) of dyes 3a-3m in various solvents.
Dye No
DMSO
DMF
Acetonitrile
Acetic acid
Methanol
Chloroform
3a
3b
3c
3d
3e
3f
504, 410
538, 422
518, 424
538, 420
504, 412
526, 422
518, 412
532, 404
522, 414
534, 422
524, 408
534, 391
530, 396
500, 414
526, 422
506, 420
538, 424
500, 414
528, 420
512, 412
518, 404
520, 414
524, 424
520, 410
532, 396
526, 398
414
422
422
420
414
420
410
410
414
422
412
400
402
410
362
426
362
412
418
410
408
410
416
414
400
400
414
366
422
366
416
424
416
400
420
420
414
400
400
414
426
420
424
414
418
408
404
414
422
410
400
404
3g
3h
3i
3j
3k
3l
3m
recorded in Table 2. A sample 1H NMR spectrum of dye 3c was
given in Fig. 2.
According to Table 2, the peaks observed in the range of 14.06–
14.31 ppm was amino (-NH2) attached to the phenyl pyrazole ring,
the peaks observed in the range of 13.42–13.99 ppm was amino
(-NH2) attached to the pyrazole ring, the peaks in the range of
12.67–12.84 ppm was imino (-NH) attached to the pyrazole ring
and 11.73–12.03 the peaks in the ppm range were thought to be-
long to the hydroxyl (-OH) group attached to the phenyl pyrazole
ring. In addition, the peaks seen in the range of 3.85–3.93 ppm
belong to methoxy groups (3c, 3g, 3k) attached to the aromatic
phenyl ring, and the peaks seen at 2.30–2.38 ppm to methyl
groups (3e, 3i, 3m) attached to the aromatic phenyl ring.
As a result, the peaks of the hydroxyl group observed especially
in the range of 11.73–12.03 showed that our compounds could be
one of the tautomeric forms disazo-enol (T1) or hydrazo-azo-enol
(T6) in DMSO solvent.
3.3. Solvent effect on UV-visible absorption spectra of dyes
Fig. 3. Absorption spectra of dye 3m in various solvents.
UV-visible absorption spectra of dyes dissolved in 6 different
solvents such as DMSO, DMF, acetonitrile, methanol, acetic acid
length range for the other 11 dyes. It was observed hypsochromic
shift in 3b and 3d dyes in acetic acid and methanol which are
more acidic than other solvents. For these two dye compounds, the
hypochromic shift seen in acetic acid and methanol indicates that
these compounds transform into a different tautomeric structure
in these solvents as given in Scheme 3.
and chloroform were measured over the wavelengths range (λmax
)
between 350 nm and 700 nm in concentration 1 × 10−6 M. Analy-
sis results are given in Table 3. Absorption spectrum of the dye 3m
was showed in Fig. 3.
As seen in Table 3, two maximum absorption peaks were ob-
served in DMSO and DMF solvents for all dyestuffs, while a single
maximum absorption peak was observed in acetonitrile, methanol,
acetic acid and chloroform.
In addition, a second absorption peak was observed around
500 nm in DMSO and DMF solvents, whereas this second peak was
not observed in the other 4 solvents. This peak around 500 nm
indicates that the dyestuffs may be ionized in these two solvents
which have base properties compared to other solvents. As a re-
sult, this second absorption peak observed around 500 nm sug-
An absorption peak of about 400 nm was seen in all solvents.
Except for 3b and 3d compounds, there was no clear change in the
maximum absorption bands for each of the solvents in this wave-
6

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
Table 4
Organic and inorganic acid-base effect on 3a-3m dyes.
Dye No
Methanol
Methanol + HCl
Methanol + KOH
Chloroform
Acetic acid
Chloroform + Piperidine
3a
3b
3c
3d
3e
3f
414
366
422
366
416
424
416
400
420
420
414
400
400
412
366
424
364
416
422
416
406
424
426
418
406
406
456
478
456
476
458
464
456
456
456
490
490
482
470
414
426
420
424
414
418
408
404
414
422
410
400
404
410
362
426
362
412
418
410
408
410
416
414
400
400
460
462
462
450
466
446
460
462
470
518
476
502
474
3g
3h
3i
3j
3k
3l
3m
3.4. Organic and inorganic acid-base effect on UV-visible absorption
spectra of dyes
Inorganic acid and base solutions were prepared by adding
0.1 M KOH and 0.1 M HCl into 10−6 molar methanol solvent of the
dyes. The organic base solutions of the dyes were prepared by mix-
ing equal amounts of methanol and piperidine solvents (1:1, v:v).
The values measured on the instrument were reported in Table 4.
The UV-visible spectrum of a sample dye (3m) measured in the
presence of organic and inorganic acids and bases was given in
Fig. 4.
All dyes gave a single absorption peak in acidic and basic sol-
vents. These chemical shift values undergone bathochromic shift
in the presence of inorganic bases. For example, all of the com-
pounds showed bathochromic shift in alkaline methanol compared
to methanol. There was no visible change in the λmax values of
the solvents obtained by adding acid in methanol according to
methanol.
Likewise, with the addition of piperidine into chloroform,
chemical shift values of dyes showed bathochromic shift compared
to chloroform. There was no remarkable change in the UV-visible
results of the dyes in acetic acid solvent compared to the chlo-
roform solvent except for 3b and 3d Hypsochromic shifts were
recorded in the absorption data of 3b and 3d dyes in acetic acid
solvent. The common feature of these compounds is that both
3b and 3d dyes are bound to the para corner of the phenyl ring
and have electron-withdrawing properties from the ring. This sug-
gested that these two compounds transform into another tau-
tomeric form in acetic acid solvent, as given in Scheme 3.
4. Conclusion
In this study, 13 new heterocyclic disazo dyestuffs were synthe-
sized. The structures of the synthesized dyestuffs have been char-
acterized using elemental analysis, infrared spectroscopy, nuclear
magnetic resonance spectroscopy and mass spectroscopy methods.
The effects of electron withdrawing and electron donating groups
on the absorption ability of dyes in six different solvents were in-
vestigated. The synthesized dyes were found to have tautomeric
properties and these tautomers were given in Scheme 3. The data
obtained from the IR spectroscopy device were examined and it
was seen that the dyes were in solid disazo-keto (T2) tautomeric
form. According to the 1H NMR data, the dyes could be in disazo-
enol (T1) or (T6) tautomeric form, especially in DMSO solvent. In
addition, all dyes showed a single maximum absorption peak in
other solvents except DMSO and DMF, while two absorption peaks
were observed in these two solvents. In addition, the second peak
of these two solvents at around 500 nm showed that the dyes par-
tially ionized in these two solvents.
Fig. 4. Absorption spectra of dye 3m in acidic and basic solutions; a) Inorganic
acid-base, b) Organic acid-base.
gests that the dyestuffs dissolved in these two solvents transform
into the anionic form shown in Scheme 3.
Considering all these data, while some of our synthesized
dyestuffs showed hypsochromic shifts in acidic solvents, all of
them formed a second peak at higher wavelength in basic solvents.
This situation is a result we expect and target.
7

A. Demirçalı
Journal of Molecular Structure 1231 (2021) 129960
Concequently, the synthesis of 13 new amino pyrazole deriva-
[15] O.V. Kovalchukova, M.A. Ryabov, P.V. Dorovatovskii, Y.V. Zubavichus,
A.N. Utenyshev, D.N. Kuznetsov, O.V. Volyansky, V.K. Voronkova,
tive heterocyclic disazo dyestuff, which had many uses such as
the textile, medicine, food, cosmetics, and dye industry, and whose
popularity continues to increase day by day, was realized. With
the synthesis of these new compounds, it was aimed dyestuffs
have higher yield and brighter colors and to increase the variety
of amino pyrazole derivative azo dyestuffs in the dye literature.
V.N. Khrustalev, Synthesis and characterization of
a series of novel metal
complexes of N-heterocyclic azo-colorants derived from 4-azo-pyrazole-5-one,
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
[19] L.S. Athira, S. Balachandran, J. Annaraj, E.A. Noelson, Molecular structure, spec-
troscopic, solvatochromic, dyeing performance and biological evaluations of
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CRediT authorship contribution statement
[20] R.H. Wiley, P. Wiley, A. Weissberger (Ed.), Interscience Publishers, 1964.
[21] V.R. Mishra, C.W. Ghanavatkar, N. Sekar, UV protective heterocyclic disperse
azo dyes: spectral properties, dyeing, potent antibacterial activity on dyed fab-
ric and comparative computational study, Spectrochim. Acta A. 223 (2019)
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Aykut Demirçalı: Methodology, Conceptualization, Investiga-
tion, Data curation, Formal analysis, Writing - original draft.
[22] S. Ningaiah, U.K. Bhadraiah, S.D. Doddaramappa, S. Keshavamurthy,
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Acknowledgment
This study was supported by Pamukkale University Scien-
tific Research Project Coordination Unit as Beginner Level Project
(project number: 2013BSP003).
[23] M.F. El Shehry, M.M. Ghorab, S.Y. Abbas, E.A. Fayed, S.A. Shedid, Y.A. Ammar,
Quinoline derivatives bearing pyrazole moiety: synthesis and biological eval-
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8