The synthesis, characterization and investigation of absorption properties of disperse disazo dyes containing pyrazole and isoxazole

Article abstract of DOI:10.1016/j.molstruc.2018.12.033

In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro groups at their o-, m-, p- positions were synthesized (4a-4j). These newly synthesized ten disazo disperse dyes were characterized by elemental analysis and spectral techniques. Spectroscopic data for novel synthesized dyes, dissolved in six solvents, were procured. The influences of six different acidic and alkaline solutions were also reported. In addition, the absorption capability of these ten-novel heterocyclic disazo disperse dyes at their o-, m- and p- positions were explored in detail.

Full text of DOI:10.1016/j.molstruc.2018.12.033

Accepted Manuscript
The Synthesis, Characterization and Investigation of Absorption Properties of
Disperse Disazo Dyes Containing Pyrazole and Isoxazole
Aykut Demirçalı, Fikret Karcı, Ozan Avinc, Aylin Uğur Kahrıman, Görkem Gedik,
Emine Bakan
PII:
S0022-2860(18)31454-6
10.1016/j.molstruc.2018.12.033
MOLSTR 25970
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
23 August 2018
08 December 2018
Please cite this article as: Aykut Demirçalı, Fikret Karcı, Ozan Avinc, Aylin Uğur Kahrıman, Görkem
Gedik, Emine Bakan, The Synthesis, Characterization and Investigation of Absorption Properties of
Disperse Disazo Dyes Containing Pyrazole and Isoxazole, Journal of Molecular Structure (2018),
doi: 10.1016/j.molstruc.2018.12.033
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ACCEPTED MANUSCRIPT
The Synthesis, Characterization and Investigation of Absorption Properties
of Disperse Disazo Dyes Containing Pyrazole and Isoxazole
Aykut Demirçalı1, Fikret Karcı1, Ozan Avinc2, Aylin Uğur Kahrıman1, Görkem Gedik2, Emine
Bakan3*
1 Pamukkale University, Faculty of Science-Arts, Department of Chemistry, Denizli, Turkey
2Pamukkale University, Faculty of Engineering, Department of Textile Engineering, Denizli, Turkey
3 Uşak University, Higher Vocational School of Ulubey, Fashion Design Programme, Ulubey, Uşak, Turkey
*Corresponding Author: emine.tomruk@usak.edu.tr
Abstract
In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro
groups at their o-, m-, p- positions were synthesized (4a-4j). These newly synthesized ten disazo
disperse dyes were characterized by elemental analysis and spectral techniques. Spectroscopic
data for novel synthesized dyes, dissolved in six solvents, were procured. The influences of six
different acidic and alkaline solutions were also reported. In addition, the absorption capability
of these ten-novel heterocyclic disazo disperse dyes at their o-, m- and p- positions were
explored in detail.
Keywords: Disperse dye synthesis, Heterocyclic disazo disperse dye, Spectroscopic properties.
*Corresponding author. Phone: +90 276 7162739 Fax: +90 276 7162817
*E-mail address: emine.tomruk@usak.edu.tr
1

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1. Introduction
According to the chemical compound classification, most widely used and preferred
textile dyes are azo dyes due to their dyeing power, easy production of its cheap basic materials,
their wide color range and good fastness properties [1-10]. Main disadvantage of azo dyes is to
give dull shades on blue-violet color range [11-14]. However, this disadvantage was being
overcome with the use of heterocyclic compounds in this color range leading to brighter colors
[15-19]. Therefore, in the recent years, the usage of aromatic heterocyclic compound as a disazo
or coupling component has gained importance [20-26].
Pyrazoles are one of the important class of heterocyles according to their wide using
areas [27- 29]. On the other hand, pyrazole dyestuffs color and fastness properties on synthetic
fibers give good results.
Since commercial disperse dyes generally dye synthetic fibers, it is very important to
produce new disperse dyes which dye synthetics with high color yields along with good fastness
properties [13]. In this study, heterocyclic disazo disperse dyes substituted with methyl (-CH3),
nitro (-NO2) and chloro (-Cl) groups at their o-, m-, p-positions, for the first time in the literature,
were synthesized. The absorption capability of these synthesized dyes according to their
electron withdrawing and electron donating groups with o-, m- and p-positions was investigated
too.
2. Experimental
2.1. Materials and Methods
The chemicals utilized in the synthesis were supplied from Aldrich and Merck Chemical
Company without any purification. The spectroscopic grade of the used solvents was
appropriate.
Elemental analysis was implemented using a Costech ECS 4010 analyzer. UV-visible
spectrums were procured via a PG T80+ high performance double beam spectrophotometer in
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the range of varied solvents, i.e. acetonitrile, methanol, DMSO, DMF, acetic acid and
chloroform at different concentrations (1x10-6 - 10-8 M). IR spectra were measured via Perkin-
Elmer Spectrum Two (FT-IR) Spectrophotometer. Nuclear magnetic resonance (1H-NMR)
spectra were obtained on a Bruker-Spectrospin Avance DPX 400 Ultra-Shield in deuterated
dimethylsulphoxide (DMSO-d6) utilizing tetramethylsilane (TMS) as the internal reference and
chemical shifts () were reported in ppm. Molecular volume of ten synthesized disperse dyes
were calculated utilizing ACD / Chemsketch 12 software programme.
2.2. Synthesis of the novel heterocyclic disazo disperse dyes
Ten different heterocyclic disazo disperse dyes, one without auxochrome group and nine
with –NO2, –Cl, –CH3 auxochrome on para, meta and ortho positions, were synthesized. Dye
synthesis is explained in detail in the below section.
Insert Scheme 1 here
Aniline, o-, m-, p-nitroanilines, o-, m-, p-chloroanilines and o-, m-, p-methylanilines
were diazotized with 3-aminocrotononitrile and coupled to result in the corresponding 2-
arylhydrazono-3-ketiminobutyronitriles (1a-1j). After cyclization process of 2-arylhydrazono-
3-ketiminobutyronitriles (1a-1j) with hydrazine monohydrate, 5-amino-4-arylazo-3-methyl-
1H-pyrazoles (2a-2j) which were diazotised and coupled with ethyl acetoacetate afforded and
a series of ethyl pyrazolylhydrazonoacetoacetates (3a-3j) yielded. Cyclization of these ethyl
pyrazolylhydrazonoacetoacetates derivatives (3a-3j) with hydroxylamine afforded disazo dyes
4a-4j (Scheme 1). The precipitated dye was separated by dilution with water, was filtered off
and washed in water many times. Subsequently, the product is dried and crystallized from
DMF–H2O [30].
2.2.1. 4-(4'-phenylazo-3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-methylisoxazole (4a):
3

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o
Dark brown crystals; yield 80 %; mp. 265-266 C (DMF-H2O); IR (KBr):  (cm-1) = 3141 (-
1
NH), 3076 (Ar-H), 2923 (Al-H), 3430 (-OH); H-NMR (DMSO-d6): δ = 2.61 (3H, pyrazole-
CH3), 2.89 (3H, isoxazole-CH3), 7.36-8.01 (5H, Ar-H), 11.85 (-OH), 13.64 (-NH); Anal. Calcd.
for C14H13N7O2: C: 54.02, H: 4.21, N: 31.50. Found: C: 54.24, H: 4.13, N: 31.39. Molecular
weight: 311 g/mol.
2.2.2. 4-[4'-(p-nitrophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4b): Claret red crystals; yield 70 %; mp. 228-229 oC (DMF-H2O); IR (KBr):
 (cm-1) = 3151 (-NH), 3061 (Ar-H), 2925 (Al-H), 3428 (-OH) ; 1H-NMR (DMSO-d6): δ = 2.73
(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.47-9.26 (4H, ArH), 12.37 (-OH), 13.23 (-
NH); Anal. Calcd. for C14H12N8O4: C: 47.19, H: 3.39, N: 31.45. Found: C: 47.33, H: 3.42, N:
31.28. Molecular weight: 356 g/mol.
2.2.3. 4-[4'-(p-chlorophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4c) : Claret red crystals; yield 83 %; mp. 239-240 oC (DMF-H2O); IR (KBr):
 (cm-1) = 3168 (-NH), 3074 (Ar-H), 2925 (Al-H), 3414 (-OH); 1H-NMR (DMSO-d6): δ = 2.57
(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.38-8.37 (4H, ArH), 11.86 (-OH), 13.56 (-
NH); Anal. Calcd. for C14H12N7O2Cl: C: 48.63, H: 3.50, N: 28.36. Found: C: 48.56, H: 3.57,
N: 28.47. Molecular weight: 345.5 g/mol.
2.2.4. 4-[4'-(p-methylphenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
o
methylisoxazole (4d) : Red crystals; yield 74 %; mp. 258-259 C (DMF-H2O); IR (KBr): 
(cm-1) = 3133 (-NH), 3064 (Ar-H), 2924 (Al-H), 3451 (-OH); 1H-NMR (DMSO-d6): δ = 2.25
(3H, phenyl-CH3), 2.60 (3H, pyrazole-CH3), 2.90 (3H, isoxazole-CH3), 7.31-7.96 (4H, ArH),
11.95 (-OH), 13.64 (-NH); Anal. Calcd. for C15H15N7O2: C: 55.38, H: 4.65, N: 30.14. Found:
C: 55.51, H: 4.70, N: 30.05. Molecular weight: 325 g/mol.
2.2.5. 4-[4'-(m-nitrophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4e) : Claret red crystals; yield 86 %; mp. 260-261 oC (DMF-H2O); IR (KBr):
4

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 (cm-1) = 3133 (-NH), 3067 (Ar-H), 2926 (Al-H), 3405 (-OH); 1H-NMR (DMSO-d6): δ = 2.57
(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.40-8.11 (4H, ArH), 11.89 (-OH), 13.55 (-
NH); Anal. Calcd. for C14H12N8O4: C: 47.19, H: 3.39, N: 31.45. Found: C: 47.11, H: 3.42, N:
31.38. Molecular weight: 356 g/mol.
2.2.6. 4-[4'-(m-chlorophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4f) : Claret red crystals; yield 80 %; mp. 263-264 oC (DMF-H2O); IR (KBr):
 (cm-1) = 3142 (-NH), 3067 (Ar-H), 2926 (Al-H), 3360 (-OH); 1H-NMR (DMSO-d6): δ = 2.58
(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.45-8.94 (4H, ArH), 11.90 (-OH), 13.49 (-
NH); Anal. Calcd. for C14H12N7O2Cl: C: 48.63, H: 3.50, N: 28.36. Found: C: 48.45, H: 3.41,
N: 28.26. Molecular weight: 345.5 g/mol.
2.2.7. 4-[4'-(m-methylphenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4g) : Orange crystals; yield 90 %; mp. 175-176 oC (DMF-H2O); IR (KBr): 
(cm-1) = 3186 (-NH), 3073 (Ar-H), 2923 (Al-H), 3408 (-OH); 1H-NMR (DMSO-d6): δ = 2.18
(3H, phenyl-CH3), 2.58 (3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.01-7.60 (4H, ArH),
11.57 (-OH), 13.30 (-NH); Anal. Calcd. for C15H15N7O2: C: 55.38, H: 4.65, N: 30.14. Found:
C: 55.43, H: 4.72, N: 29.98. Molecular weight: 325 g/mol.
2.2.8. 4-[4'-(o-nitrophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4h) : Brown crystals; yield 60 %; mp. 233-234 oC (DMF-H2O); IR (KBr): 
(cm-1) = 3181 (-NH), 3091 (Ar-H), 2925 (Al-H), 3424 (-OH) ; 1H-NMR (DMSO-d6): δ = 2.56
(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.44-8.05 (4H, ArH), 11.89 (-OH), 13.51 (-
NH); Anal. Calcd. for C14H12N8O4: C: 47.19, H: 3.39, N: 31.45. Found: C: 47.07, H: 3.44, N:
31.52. Molecular weight: 356 g/mol.
2.2.9. 4-[4'-(o-chlorophenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4i) : Orange crystals; yield 76 %; mp. 254-255 oC (DMF-H2O); IR (KBr): 
(cm-1) = 3192 (-NH), 3059 (Ar-H), 2924 (Al-H), 3435 (-OH) ; 1H-NMR (DMSO-d6): δ = 2.61
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(3H, pyrazole-CH3), 2.89 (3H, isoxazole-CH3), 7.35-7.96 (4H, ArH), 11.40 (-OH), 13.40 (-
NH); Anal. Calcd. for C14H12N7O2Cl: C: 48.63, H: 3.50, N: 28.36. Found: C: 48.79, H: 3.54,
N: 28.17. Molecular weight: 345.5 g/mol.
2.2.10. 4-[4'-(o-methylphenylazo)-
3'-methyl-1'H-pyrazol-5'-ylazo)-5-hydroxy-3-
methylisoxazole (4j) : Red crystals; yield 84 %; mp. 223-224 oC (DMF-H2O); IR (KBr):  (cm-
1) = 3181 (-NH), 3055 (Ar-H), 2924 (Al-H), 3399 (-OH); ; 1H-NMR (DMSO-d6): δ = 2.10 (3H,
phenyl-CH3), 2.59 (3H, pyrazole-CH3), 2.94 (3H, isoxazole-CH3), 7.19-8.24 (4H, ArH), 11.81
(OH), 13.33 (NH); Anal. Calcd. for C15H15N7O2: C: 55.38, H: 4.65, N: 30.14. Found: C: 55.29,
H: 4.60, N: 30.26. Molecular weight: 325 g/mol.
3. Results and Discussion
3.1. Spectral characteristics and tautomerism
Synthesized pyrazole and isoxazole disperse dyes 4a-4j could exist in four possible
tautomeric forms, named as disazo-enol form T1, azo-hydrazo-keto form T2, hydrazo-azo-enol
form T3 and dishydrazo-keto form T4, displayed in Scheme 2. The FT-IR spectra of 4a-4j dyes
exhibited imino (NH) bands at 3133-3186 cm-1 and hydroxyl (O-H) bands at 3360-3451 cm-1.
The bands show that these compounds are overwhelmingly in the solid form as one of the
disazo-enol (T1) or hydrazo-azo-enol (T3) tautomeric forms. The FT-IR spectra of all dyes
prove that the compounds are generally in the enol form in solid state.
1H-NMR spectra of novel synthesized dyes 4a-4j exhibited one broad peak at 13.23-
13.64 ppm (NH) and one broad peak at 11.40-12.37 ppm (OH). Those outcomes advise that all
dyes (4a-4j) are in only one tautomeric form and these tautomeric forms might be disazo-enol
(T1) or hydrazo-azo-enol (T3) tautomeric forms in DMSO as shown in Scheme 2.
Insert Scheme 2 here
Insert Table 1 here
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3.2. Solvent effects on UV-vis. Spectra
UV-vis absorption spectra of dyes 4a-4j were obtained in the range of  between 300-
700 nm and summed up in Table 1. The visible absorption spectra of novel synthesized dyes
do not correlate with the solvent polarity. Synthesized dyes 4a-4j exhibited one maximum
absorption peaks in all utilized solvents, except for 4b and 4e. This means that all dyes except
4b and 4e are present in a single-tautomeric form in all utilized solvents. Dye 4b is present in
the mixture of tautomeric forms in solvents DMSO and DMF (Figure 1). Dye 4e is present in
the mixture of tautomeric forms in solvent DMF (Figure 2).
Insert Figure 1 here
Insert Figure 2 here
3.3. Acid and base influences on UV-visible spectra
Acid and base influences on the absorption of synthesized dye solutions were examined
and the outcomes were displayed in Table 2.
Insert Table 2 here
The absorption spectra of all dyes except 4g (m-CH3) in methanol and chloroform was
sensitive to alkali addition (KOH, piperidine, 0.1 M), with max of dyes 4a, 4b, 4c, 4d, 4e, 4f,
4h, 4i and 4j showing bathochromic shifts. These outcomes suggest that dyes 4a, 4b, 4c, 4d,
4e, 4f, 4h, 4i and 4j are present in the transition between tautomeric forms or can be explained
by equilibrium. The absorption spectra of dye 4g in alkali methanol and alkali chloroform
showed hypochromic shifts. This hypochromic shift can be explained that 4g compounds
undergoes tautomeric change in the alkaline medium by comparison in methanol and
chloroform solutions and in tautomeric structures given in Scheme 2, it shows that it transforms
7

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from one structure to another.
The absorption spectra of dye 4b in methanol changed significantly with alkali addition
(KOH, 0.1 M) (Figure 3). This result can be explained by the tautomeric structures turned into
anionic form with the addition of potassium hydroxide, 0.1 M.
The absorption spectra of all dyes except 4g and 4h in methanol were sensitive to acid
addition (HCl, 0.1 M), with max of all dyes displaying hypochromic shifts (Table 2). An
example of this result is given in Figure 4. These results can be explained by the transition
between short and long wavelength tautomeric forms.
Insert Figure 3 here
Insert Figure 3 here
3.4. Substituent effects on UV-vis. spectra
Compared to other dyes, as it is visible in Table 1, the compound 4b to which the p-NO2
group is substituted, that withdraws electron strongly from the ring, showed bathochromic shift
in DMSO and DMF in comparison with chloroform. The compound 4d, substituted with p-CH3
group, provides electron to the ring, showed also bathochromic shift in DMSO and DMF as
compound 4b.
The 4e and 4h compounds to which electron-providing m-NO2 and o-NO2 groups
substituted to the ring, showed bathochromic shift in DMSO and DMF, while there is no clear
change in the max of the 4g and 4j compounds to which electron-providing m-CH3 and o-CH3
groups substituted to the ring.
This indicates that there is no direct contribution to the substituent effect when the
substituents are dependent on the para position, but in particular, as the electron-donating
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groups approach to the phenyl substituted azo group showed that the compounds contribute to
tautomer exchange.
4. Conclusions
New heterocyclic disperse disazo dyes containing pyrazole and isoxazole groups were
synthesized by a series of synthesis processes. Acid-base, substituent and solvent influence have
been studied on the wavelength of maximum absorption. In this research, novel synthesized
some disperse disazo pyrazole and isoxazole dyes exhibited solvatochromic effects.
While all dyes are one of the single tautomeric forms shown in Scheme 2, 4b in DMSO
and DMF, 4e in DMF are thought to be in the form of a mixture of two tautomeric forms.
The absorption spectra of all synthesized dyes except 4g (m-CH3) in methanol and
chloroform was sensitive to alkali addition (KOH, piperidine, 0.1 M) and showed bathochromic
shifts. The absorption spectra of all dyes in acidic methanol (HCl, 0.1 M) showed hypochromic
shifts except 4g and 4h.
As it is specified in part 3.4, there isn’t any substitution effect seen when the substituents
are dependent on the para position when based on the meta and ortho group, it is thought that
the components change the structure.
Acknowledgements
This study is sponsored and supported by The Scientific and Technological Research Council
of Turkey (TUBITAK) with the TUBITAK project number of 109M578.
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11

ACCEPTED MANUSCRIPT
FIGURE LIST
Figure 1. Absorption spectra of synthesized dye 4b in varied solvents

ACCEPTED MANUSCRIPT
Figure 2. Absorption spectra of synthesized dye 4e in varied solvents

ACCEPTED MANUSCRIPT
Figure 3. Dye 4b’s absorption spectra in acidic and basic solvents

ACCEPTED MANUSCRIPT
Figure 4. Dye 4d’s absorption spectra in acidic and basic solvents

ACCEPTED MANUSCRIPT
SCHEME LIST
CN
NC
H
NH2
NH
_
H2NNH2H2O
+
C
C
N2 Cl
N
N
C
NH2
NH
N
H
N
C
+
CH3
CH3
X
X
X
(1a-1j)
H3C
N
(2a-2j)
h, X : o-NO2
e, X : m-NO2
a, X : H
i, X : o-Cl
j, X : o-CH3
b, X : p-NO2
c, X: p-Cl
f, X : m-Cl
g, X : m-CH3
d, X : p-CH3
O
HO
N
N
CH3
H
COCH3
N
N
N
C
N
N
N
N
NH2
N
N
X
COOC2H5
1) HCl/AcOH, NaNO2
2) CH3COCH2COOC2H5
NH
X
X
H2NOH
H3C
N
NH
NH
H3C
H3C
N
N
(4a-4j)
(3a-3j)
(2a-2j)
Scheme 1. Synthesis of heterocyclic disazo disperse dyestuffs

ACCEPTED MANUSCRIPT
O
O
N
O
HO
N
N
N
H
N
N
N
N
N
CH3
N
CH3
X
X
KT
NH
NH
H3C
H3C
N
N
_
O
O
N
azo-hydrazo-keto
(T2)
disazo-enol
(T1)
N
- H+
N
N
N
CH3
X
+ H+
KT
KT
O
O
NH
O
HO
N
N
H3C
N
N
H
H
N
H
N
anionic form
(A)
N
N
N
CH3
N
N
CH3
X
X
N
H3C
N
N
H3C
KT
N
dishydrazo-keto
(T4)
hydrazo-azo-enol
(T3)
Scheme 2. Tautomeric equilibrium of pyrazole and isoxazole dyes 4a-4j

ACCEPTED MANUSCRIPT
Highlights
- A series of novel pyrazole and isoxazole moieties disazo dyes were synthesized.
- The solvatochromic properties of these dyes in various solvents were evaluated.
- Acid and base effects on λmax of the dyes were also examined in detail.

ACCEPTED MANUSCRIPT
TABLE LIST
Table 1. Solvent effect on max (nm) of synthesized dyes 4a-4j
Dye
No.
4a
DMSO
454
DMF
459
Acetonitrile
416
Methanol
416
Acetic acid
413
Chloroform
431
4b
474, 574 (s)
450
471, 573 (s)
460
458
457
454
461
4c
422
428
416
436
4d
454
454
427
441
425
436
4e
448
466, 481 (s)
458
416
438
416
435
4f
442
429
449
426
441
4g
422
420
406
408
407
411
4h
444
496
430
344
424
431
4i
4j
459
460
434
446
432
446
435
437
404
412
405
436
s: shoulder

ACCEPTED MANUSCRIPT
Table 2. Absorption maximum values of synthesized dyes 4a-4j in acidic and basic solvents
Dye No.
max(nm)
Methanol
Methanol
+
Methanol Chloroform Chloroform + Acetic Acid
+
Piperidine
KOH
HCl
4a
4b
4c
4d
4e
4f
416
457
428
441
438
449
408
344
446
412
456
536
461
460
457
448
387
482
468
458
385
454
406
410
398
398
416
426
399
398
431
461
436
436
435
441
411
461
446
436
470
536
448
466
478
486
344
489
487
469
413
454
416
425
416
426
407
424
432
405
4g
4h
4i
4j