Synthesis of Symmetric Bridged Bis-Pyrazolone Based Metal Complex Acid Dyes and their Applications on Leather

Article abstract of DOI:10.1007/s10895-018-2282-8

Our present investigation aims at the synthesis and application of new, symmetric bridged bis-pyrazolone based acid dyes. The bis-pyrazolone compounds were accomplished from bis- hydrazine of 4,4′-Diaminostilbene-2,2′-disulfonic acid and ethyl acetoacetate. The bis-pyrazolones have been coupled with diazonium salts of o-hydroxyl aromatic amines which resulted in ligand dyes. The intermediate ligand dyes were treated with 3d transition metals to achieve the targeted metal complex acid dyes. The structures of investigated compounds were confirmed with the help of spectroscopic techniques. Dyes were applied on leather and their application parameters including their light fastness, wash fastness and rubbing fastness were determined. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10895-018-2282-8

Journal of Fluorescence
https://doi.org/10.1007/s10895-018-2282-8
ORIGINAL ARTICLE
Synthesis of Symmetric Bridged Bis-Pyrazolone Based Metal Complex
Acid Dyes and their Applications on Leather
Muhammad Ayaz1 & Muhammad Ayaz1 & Farman Ali1 & Aamer Saeed2 & Asma Khurshid3 & Ghulam Shabir2,4
Tanveer Ahmad4 & Syed Asad Raza Kazmi4 & Hassan Ali Khan4
&
Received: 17 April 2018 /Accepted: 20 August 2018
#
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Our present investigation aims at the synthesis and application of new, symmetric bridged bis-pyrazolone based acid dyes. The
bis-pyrazolone compounds were accomplished from bis- hydrazine of 4,4′-Diaminostilbene-2,2′-disulfonic acid and ethyl
acetoacetate. The bis-pyrazolones have been coupled with diazonium salts of o-hydroxyl aromatic amines which resulted in
ligand dyes. The intermediate ligand dyes were treated with 3d transition metals to achieve the targeted metal complex acid dyes.
The structures of investigated compounds were confirmed with the help of spectroscopic techniques. Dyes were applied on
leather and their application parameters including their light fastness, wash fastness and rubbing fastness were determined.
.
.
.
.
.
Keywords Bis-Pyrazolone Acid Dyes Diazotization Spectroscopic Techniques Leather Fastness
Introduction
properties in applications such as optical recording medium toner
ink-jet printing and oil-soluble light fast dyes [4, 5]. Azo dyes are
used in dyeing textile fibres, particularly cotton but also silk,
wool, viscose and synthetic fibres. They are considered to be
easy to use, relatively cheap and to provide clear, strong colors
[6, 7]. Recently, azo compounds as organic dyes have also
attracted attention due to their interesting electronic features in
Azo compounds and their metal complex dyes are continuously
gaining much attention in scientific research because of variety
of derivatives obtained by adopting a slight changing in dye
intermediate structure [1–3]. Furthermore, azo dyes have been
studied widely because of their excellent thermal and optical
Research Highlights
• Synthesis of symmetric bis-pyrazolones has been conducted.
• Bis-pyrazolones were employed to couples with diazonium salts of
ortho-hydroxy aromatic amines
• Ligand dyes have complexed with 3d metals and applied on leather.
* Farman Ali
Syed Asad Raza Kazmi
syedasadrazakazmi72@gmail.com
farmanqau@gmail.com
* Ghulam Shabir
Hassan Ali Khan
shabirg@yahoo.com
hassanalikhan@gmail.com
Muhammad Ayaz
mohammadayaz31@gmail.com
1
Department of Chemistry, Hazara University, KPK,
Mansehra 21300, Pakistan
Muhammad Ayaz
ayazanwar239@gmail.com
2
Department of Chemistry, Quaid-I-Azam University,
Islamabad 45320, Pakistan
Aamer Saeed
aamersaeed@yahoo.com
3
Department of Metallurgy and Material Engineering, PIEAS, PO
Nilore, Islamabad 45650, Pakistan
Asma Khurshid
asmakhurshid2000@hotmail.com
4
Tanveer Ahmad
Department of Chemistry, Govt. Gordon College Rawalpindi,
arslansaleem557@gmail.com
Punjab, Pakistan

J Fluoresc
connection with their application for molecular memory storage,
nonlinear optical elements and organic photoconductors [8].
Because of their interesting electronic properties in concern to
their application for molecular memory storage, wide variety of
hues ranging from blue to red in the visible region of the elec-
tromagnetic radiation (EMR) spectrum have been synthesized.
Above all the medicinal importance of azo compound is
well documented as antidiabetics, antiseptic, anti-neoplastic,
antibacterial and antitumor [9–11]. Besides these, a number of
biological reactions are there in which the azo compounds
exhibit their role such as in protein synthesis, RNA synthesis
and inhibition of DNA [12–17].
(a) Procedure for the Synthesis Bis-Hydrazine
from 4,4′-Diaminostilbene-2,2′-Disulfonic Acid
4,4′-Diaminostilbene-2,2′-disulfonic acid (7.4, 0.02 mol, 1)
was suspended in 100 ml of distilled water in a round bot-
tomed flask kept in ice bath and started stirring. It was added
HCl (14.6 ml) followed by addition of NaNO2 (2.8 g,
0.04 mol). Stirred the whole mixture for 1 h while keeping
the temperature constant (0-5 °C) until the diazotization was
completed which was observed by the paper chromatogram.
The diazonium salt of 4,4′-Diaminostilbene-2,2′-disulfonic
acid was filtered and precipitates were collected.
Keeping in view, the above mention facts, the main objec-
tive of this research is to develop and evaluate the bis-
symmetric bridged pyrazolone acid dyes having strong and
bright shade which should have ability to show exhaust dye-
ing when applied on leather. In order to cope with this pur-
pose, DASDA based bis-pyrazolone were prepared and their
acid dyes and metal complexes have been synthesized and
applied on leather.
The cooled and wet diazonium salt was subjected to reduc-
tion. A saturated solution of 12 g of Na2SO3.7H2O (5.02 g,
0.04 mol) was prepared in 50 ml water and cooled the solution
up to 0–5 °C. The diazonium salt was added slowly (within 1 h)
into the well stirred solution of sodium thiosulfate
Na2SO3.7H2O and further stirred the reaction mixture at 0-
5 °C for more one hour. Then removed the mixture from ice
jacket and heated up to 100 °C by gradual heating. It was
slowly added concentrated HCl (30 ml) at 100 °C with constant
stirring. The reaction mixture was then cooled to room temper-
ature and was added a pinch of Zn dust. The precipitates of (E)-
6,6′-(ethene-1,2-diyl) bis (3-hydrazinylbenzenesulfonic acid)
(3) were settled down by keeping the reaction mixture over-
night. The precipitates were filtered and dried in oven at 70 °C.
The above synthesized hydrazine (3, 4.0 g 0.01 mol) was
dissolved in 30 ml H2O in 100 ml beaker by adding Na2CO3
(2 g) and clear solution was obtained which was filtered to re-
move the undissolved materials. Few drops of HCl were added
to neutralize the hydrazine solution. The hydrazine solution was
poured in round bottomed flask and was refluxed at 100 °C with
ethyl acetoacetate (0.02 mol) for 1 h at constant stirring and
heating until completion of reaction was observed from TLC
(methanol: chloroform, 9:1). The reaction mixture was cooled
and added of HCl (10 ml) which resulted in the precipitation of
pyrazolone (4) which was filtered and dried in oven at 70 °C.
This synthesized pyrazolone (5.32 g, 0.01 mol) was coupled
with separately prepared diazonium salt of 4-Chloro-2-
aminophenol (2.86 g, 0.02 mol) at 0-5 °C in alkaline medium
(pH = 9.0). The synthesized ligand dye 7a was precipitated from
aqueous solution by adding HCl (15 ml), that was then filtered
and dried at 70 °C in oven. Similarly another dye 7b was syn-
thesized by coupling the pyrazolone (4) with diazonium salt of 4-
Nitro-2-aminophenol by employing the above conditions.
The ligand dye 7a (0.84 g 0.001 mol) was dissolved in meth-
anol and treated with CuSO4.5H2O (8a, 0.002 mol) in round
bottomed flask at reflux temperature. The reaction mixture was
then made basic by adding tri-ethylamine (pH = 9.5–10). The
reaction mixture was stirred for 4 h till complex formation was
completed. Methanolic solution of copper complex was kept at
room temperature for the slow evaporation of methanol and pre-
cipitates of metal complex dyes were obtained. In this way all
Experimental
Materials and Methods
All compounds were purchased from Sigma-Aldrich.
Analytical grade solvents were used and when necessary, were
redistilled and dried by the standard methods. Stuart melting
apparatus was used to determine the melting point of com-
pounds. The FT-IR spectra were conducted on the single beam
Nicolet IR 100 (Fourier-Transform); while UVof all the sam-
ples were taken in water using UV-Genesys spectrophotome-
1
ter. The H NMR and 13C NMR spectra were recorded in
DMSO-d6 using NMR Bruker DPX 300 spectrophotometer
operating at 300 MHz. TMS was used as internal standard
with the deuterium signal of the solvent as the lock and chem-
ical shifts δ were recorded in ppm. The elemental analysis (C,
H, N, S) of the compounds was performed using Flash EA
1112 elemental analyzer and the pH was measured employing
portable pH Meter PHB4. Compounds were routinely
checked by TLC on silica gel G plates using different eluting
solvents keeping in view the solvent polarities. The different
solvent systems which were employed in TLC separations are:
petroleum ether: chloroform (9:1, v/v), petroleum ether: chlo-
roform (6:4, v/v) and chloroform: methanol (9:1, v/v). The
developed TLC plates were visualized using UV lamp to de-
tect the presence of spots and Rf values were duly calculated.
All crude products were isolated as solids and purified by a
combination of column chromatography and re-crystalliza-
tion. Color fastness to light, rubbing and washing was deter-
mined as per standard test method of EN ISO 105-B02, ISO
11640 [18] and ISO 765–1979 [19] respectively.

J Fluoresc
metal complex dyes 9a-f and 10a-f were synthesized by treating
ligands 7a and 7b with different metal salts 8a-f. The character-
istic physical and spectroscopic data of synthesized ligand dyes
(7a-b) and their metal complexes (9a-f and 10a-f) is as follows.
1242 (S=O), 1176 (C-N Amines Aromatic), 1079 (C-O), 824
(C=C bending), 545 (N-Co). Anal. Calcd. For
C40H46Cl2Co2N8O16S2: C, 41.86; H, 4.04; N, 9.76; S, 5.59
Found: C, 41.75; H, 4.09; N, 9.63; S, 5.65.
5-(4-((E)-(5-Chloro-2-Hydroxyphenyl)Diazenyl)
-5-Hydroxy-3-Methyl-1H-Pyrazol-1-Yl)-2 ((E)-4-(4-((E)
-(5-Chloro-2-Hydroxyphenyl)Diazenyl)
-5-Hydroxy-3-Methyl-1H-Pyrazol-1-Yl) 2-Sulfostyryl)
Benzenesulfonic Acid (C34H26Cl2N8O10S2, 7a)
C40H46Cl2Cr2N8O16S2 (9e)
Dark brown (81%). λmax (nm, log ε): 497 (6.20). FTIR (KBr,
cm−1) νmax: 3155 (C-H), 1643, 1590, 1518 (C=C aromatic),
1447 (N=N), 1220 (S=O), 1060 (C-O), 1176 (C-N), 1090 (C-
O), 855 (C=C bending), 595 (O-Cr). Anal. Calcd. For
C40H46Cl2Cr2N8O16S2 C, 42.37; H, 4.09; N, 9.88; S, 5.66;
Found: C, 42.30; H, 4.15; N, 9.80; S, 5.71.
Brown crystal (76%) λmax (nm, log ε): 450 (5.80). FTIR (KBr,
cm−1) νmax: 3360 br (OH, NH), 3055 (C=C-H), 1731 (C=O),
1690 (C=O, amide), 1665, 1585, 1510 (C=C aromatic), 1270
1
(S=O), 1050 (C-O), 760 (C=C bend). H-NMR (300 MHz,
C40H46Cl2Zn2N8O16S2 (9f)
DMSO) δ: 2.32 (6H, s, CH3), 6.98 (1H, d), 7.04 (1H, d), 7.54
(1H, s), 7.74 (2H, d, J = 7.5), 7.95 (2H, d J = 7.5), 8.12 (1H, s),
Grey (78%). λmax (nm, log ε): 470 (6.01). FTIR (KBr, cm−1)
νmax: 3140 (N-H), 1578 (C=C Aromatic), 1389 (SO3H), 1335
8.44 (1H, s), 11.15 (2H, br, SO3H), 13.44 (1H, br, O-H). 13
C
NMR (75 MHz, DMSO) δ: 157.45, 148.95, 146.25, 145.53,
136.34, 131.97, 130.44, 129.30, 127.32, 126.72, 125.86,
124.40, 118.35, 117.61, 117.11, 114.05, 12.05. Anal. Calcd.
For C34H26Cl2N8O10S2; C, 48.52; H, 3.11; N, 13.31; S, 7.62;
Found: C, 48.30; H, 3.15; N, 12.80; S, 7.75.
(SO3H), 1285 (C-C stretch), 1177 (C-O stretch), 1079 (-CH-
OH), 1020 (S=O),507 (Zn). Anal. Calcd. For
C40H46Cl2Zn2N8O16S2: C, 41.39; H, 4.00; N, 9.65; S, 5.52;
Found: C, 41.32; H, 4.06; N, 9.63; S, 5.52.
5-(5-Hydroxy-4-((E)-(2-Hydroxy-5-Nitrophenyl)Diazenyl)
-3-Methyl-1H-Pyrazol-1-Yl)-2-((E)-4-(5-Hydroxy-4-((E)
-(2-Hydroxy-5-Nitrophenyl)Diazenyl)
C40H46Cl2Cu2N8O16S2 (9a)
Dark brown, (81%). λmax (nm, log ε): 505 (5.97). FTIR (KBr,
cm−1) νmax: 3047 (-C=C-H), 1635, 1558 (C=C benzene),
1417 (-CH2), 1339 (CH2 bend), 1274 (S=O), 1171 (C-N),
1074 (C-O), 812 (Ar-H), 560 (N-Cu). Anal. Calcd. For
C40H46Cl2Cu2N8O16S2 C, 41.53; H, 4.01; N, 9.69; S, 5.54;
Found: C, 41.44; H, 4.11; N, 9.54; S, 5.63.
-3-Methyl-1H-Pyrazol-1-Yl)-2-Sulfostyryl)Benzenesulfonic
Acid (C34H26N10O14S2 7b)
Yellowish brown crystal, (72%). λmax (nm, log ε): 460 (6.05). FTIR
(KBr, cm−1) νmax: 3365 br (OH), 3080 (C=C-H), 1720 (C=O),
1685 (C=O, amide), 1620, 1585, 1510 (C=C aromatic), 1484.7
(C-H scissoring), 1277 (S=O), 1070 (C-O), 780 (Ar-H). 1H-NMR
(300 MHz, DMSO) δ:2.25(6H, s, CH3), 6.98 (2H, d), 7.35 (2H, d),
7.71 (2H, s), 7.849–7.95 (4H, m), 8.11(2H, s), 8.29 (2H, s), 8.44
(2H, s), 11.15 (2H, br, SO3H), 13.67 (1H, br, O-H), 14.67 (1H, br,
O-H). 13C NMR (75 MHz, DMSO) δ: 161.87, 157.96, 148.82,
147.07, 146.47, 140.85, 136.61, 131.94, 128.57, 115.49, 112.96,
100.56, 12.30. Anal. Calcd. For C34H26N10O14S2; C, 47.33; H,
3.04; N, 16.24; S, 7.43; Found: C, 47.13; H, 3.14; N, 15.95; S, 7.48.
C40H46Cl2Fe2N8O16S2 (9b)
Reddish brown, (80%). λmax (nm, log ε): 455 (5.90). FTIR
(KBr, cm−1) νmax: 3190 (C-H), 1603, 1565 (C=C benzene),
1424 (-CH2), 1072 (C=O), 609 (C-Cl), 514 (O-Fe). Anal.
Calcd. For C40H46Cl2Fe2N8O16S2 C, 42.09; H, 4.06; N,
9.82; S, 5.62; Found: C, 42.02; H, 4.12; N, 9.74; S, 5.68.
C40H46Cl2Ni2N8O16S2 (9c)
C40Cu2H46N10O20S2 (10a)
Grey (80%). λmax (nm, log ε): 495 (6.10). FTIR (KBr, cm−1)
Pink violet (75%). λmax (nm, log ε): 515 (6.25). FTIR (KBr,
cm−1) νmax: 3080.5 (=C-H Stretch), 1610, 1570, 1515 (C=C
aromatic), 1484.7 (C-H scissoring), 1277.1 (S=O), 1161.2(C-O
Alcohol). Anal. Calcd. For C34H26N10O14S2; C, 40.78; H, 3.94;
N, 11.89; S, 5.44 Found: C, 40.70; H, 3.99; N, 11.89; S, 5.49.
νmax: 3154 (C-H, str), 1635, 1560 (C=C aromatic), 1453 (N=N,
str), 1320 (C-H, bend), 1240 (S=O str), 1056, C-O), 880 (C=C,
bend). Anal. Calcd. For C40H46Cl2Ni2N8O16S2 C, 41.88; H,
4.04; N, 9.77; S, 5.59 Found: C, 41.82; H, 4.14; N, 9.70; S, 5.65.
C40H46Cl2Co2N8O16S2 (9d)
C40Fe2H46N10O20S2 (10b)
Dark brown (81%). λmax (nm, log ε): 490 (6.16). FTIR (KBr,
cm−1) νmax: 3120 (C-H), 1643, 1590, 1518 (C=C aromatic),
Yellowish brown (76%). λmax (nm, log ε): 460 (6.14). FTIR
(KBr, cm−1) νmax: 3308.2(N-H), 2879.4(C-H Aliphatic),

J Fluoresc
1579.3(C=C benzene ring), 1474.8(N-H), 1277.1 (C-O
stretch), 1171.1(C-N amides), 1058.6(c-o), 828.2(C=C aro-
matic ring bending), 613.7(N-Fe), 505.4 (O-Fe). Anal.
Calcd. For C34H26N10O14S2; C, 41.32; H, 3.99; N, 12.05; S,
5.51; Found: C, 41.22; H, 4.06; N, 11.97; S, 5.59.
100 ml by adding required amount of water. The leather fabric
was introduced into the dye-bath with stirring. Dye bath con-
taining dye solution and leather pieces was stirred at 45-50 °C
for 1 h. The temperature was then gradually raised to 80 °C
over period of 1/2 h and adjusted at 80 °C for 3 h. The dye-
bath was kept rotating during the process of dyeing and was
added formic acid 2.0 ml to lower the pH value of dyeing
solution upto 2.0. After dyeing the leather, the dye liquor
was poured in volumetric flask. Then dyes leather piece was
washed with cold water and washing solution was stored and
the combined with dye liquor. The combined dye solution
was diluted to 250 ml with water. From this diluted solu-
tion, 1 ml was further diluted to 50 ml with water and the
absorbance of this solution was measured to observe the
dye exhaustion leather. The dyed leather piece was dried
and mounted on shade card. In order to measure the per-
centage fixation of dye, a weighed amount of dyed leather
was stirred in boiling acidified pyridine. The unfixed dye
was dissolved in pyridine and from the absorbance of this
pyridine solution percentage fixation was determined.
C40H46N10 Ni2O20S2 (10c)
Pink Violet (74%). λmax (nm, log ε): 407 (6.12). FTIR (KBr,
cm−1) νmax: 3188.5 (N-H), 1605, 1581.3(C=C benzene ring),
1478.3 (N-H bend), 1424.3(-CH2), 1285.7(C-O stretch),
1174.2(C-N Amines-Amides), 1072.0(C-O), 824.5(C=C
bending aromatic ring), 616.9(N-Ni), 509.5(O-Ni). Anal.
Calcd. For C34H26N10O14S2; C, 41.12; H, 3.97; N, 11.99; S,
5.49; Found: C, 41.02; H, 3.99; N, 11.82; S, 5.55.
C40Co2H46N10O20S2 (10d)
Pink Violet (70%). λmax (nm, log ε): 400 (6.18). FTIR (KBr,
cm−1) νmax: 3174.7(N-H), 1580.5(C=C benzene ring),
1478.4(N-H bend amides), 1427.3(-CH2), 1287.9 (C-O
stretch), 1177.4 (C-N Amines), 1072.2(-C=O), 1018.2(C-O),
825.0 (C=C bending), 516.3(N-Co). Anal. Calcd. For
C34H26N10O14S2; C, 41.10; H, 3.97; N, 11.98; S, 5.49;
Found: C, 41.00; H, 4.04; N, 11.76; S, 5.53.
Results and Discussion
Synthesis of Acid Dyes 7, 8 and their Metal Complexes
(10a-H, 11a-H)
C40Cr2H46N10O20S2 (10e)
The synthesis of acid dyes 7a-b based on bis pyrazolone (4) and
their Copper (II), Iron (II), Nickel (II), Cobalt (II), Chromium
(III) and Zinc (II) complexes (9a-f and 10a-f) were achieved by
following a multistep procedure which involved the diazotiza-
tion of 4,4′-Diaminostilbene-2,2′-disulfonic acid (DASDA) with
NaNO2 and HCl at low temperature 0-5 °C and its reduction
with Na2SO3.7H2O to produce its hydrazine (3). The synthe-
sized hydrazine (3) was condensed with ethylacetoacetate under
neutral conditions and reaction mixture was refluxes which pro-
duced pyrazolone nucleus on both sides of the hydrazine.
Reaction mixture on acidification with HCl provided the precip-
itates of the symmetric bis-pyrazolone (4). The symmetric
pyrazolone (4) were coupled with separately prepared diazoni-
um salt of 4-Chloro-2-aminophenol (6a) and achieved the ligand
acid dyes 7a-b. Coupling was conducted in alkaline medium to
do the reaction at active methylene centre and was accomplished
in 2.5 h with continuous stirring at 0-5 °C. By following the
same condition, the bis-pyrazolone was also coupled with dia-
zonium salt of 4-Nitro-2-aminophenol (6b) to obtain the dye 7b.
Synthesized dyes 7a-b were precipitated on completion of reac-
tion by changing the pH of solution to acidic at 4.0 with HCl.
Dyes were dried and purified by recrystallization in ethanol.
Metallization of above synthesized dyes was done by treating
the alkaline solution of dyes with FeSO4.7H2O, CuSO4.5H2O,
Ni(CH3COO)2.4H2O, Co(NO3)2.6H2O, Cr2(OOCCH3)2. 2H2O
and ZnCl2 with continuous stirring and heating the reaction
Reddish violet (74%). λmax (nm, log ε): 403 (6.20). FTIR
(KBr, cm−1) νmax: 3084(C=C-H Aromatic), 1594, 1536 (ben-
zene ring), 1487 (N-H bend), 1336 (C-H bending),
1294(S=O), 1072(C=O), 1015(C=O), 823 (C=C aromatic
bending), 616 (N-Co), 509(O-Co). Anal. Calcd. For
C40Cr2H46N10O20S2; C, 41.60; H, 4.01; N, 12.13; S, 5.55;
Found: C, 41.38; H, 4.12; N, 12.01; S, 5.62.
C40H46N10O20S2Zn2 (10f)
Yellowish brown (75%). λmax (nm, log ε): 405 (6.28). FTIR
(KBr, cm−1) νmax: 3323.5(N-H), 3202.1(O-H), 1590.8 (C=C
benzene ring), 1478.8 (N-H bend), 1403.2 (CH2), 1177.0 (C-
N, amines), 1072.6(C-O), 1018.2(C-O), 826.7(C=C bend),
6 2 7. 2 ( C - X ) , 5 0 9 . 4 ( O - Z n ) . A n al . C a l c d . F o r
C40H46N10O20S2Zn2; C, 40.66; H, 3.92; N, 11.85; S, 5.43;
Found: C, 40.32; H, 3.96; N, 11.56; S, 5.52.
Dyeing Method
Dyeing was conducted in dye bath containing 0.4% of dye
solution (10 ml, 0.4% w/v) in the presence of 20% sodium
sulfate solution (Na2SO4.7H2O, 7 ml. 20% w/v). Acetic acid
solution was used to set the pH of the dye-bath at 6.5 (1.0 ml.
10% w/v). The total volume of the dye-bath was adjusted to

J Fluoresc
mixture at 70-80 °C for 4-5 h in triethylamine at pH 9–10 until
the completion of reaction was observed by taking the TLC of
reaction mixture in 9:1 chloroform and methanol. Dyes 9a-f and
10a-f were precipitated with addition of HCl, filtered and dried
in oven at 70 °C. Dyes were again re-crystallized from ethanol,
dried, weighed and determined the percentage yield.

J Fluoresc
Table 1 Exhaustion and fixation
data of the dyes 7a-b and their
metal complexes (9a-f and 10a-f)
Dye
Shade on leather
λ
max (nm) in ethanol
Log ε
Exhaustion % (C)
Fixation % (C)
7a
Brown
450
505
455
495
490
497
470
460
510
460
407
400
403
405
5.80
5.97
5.90
6.10
6.16
6.20
6.01
6.05
6.25
6.14
6.12
6.18
6.20
6.28
72.80
74.46
75.42
76.76
74.45
73.28
75.77
75.55
76.88
77.64
78.43
77.79
78.32
77.91
83.38
84.23
92.35
79.63
82.23
81.25
82.54
87.18
78.40
80.49
80.54
85.15
80.57
86.34
9a
Dark brown
Reddish brown
Grey
9b
9c
9d
Dark brown
Dark brown
Grey
9e
9f
7b
Yellowish brown
Pink violet
Yellowish brown
Pink Violet
Pink Violet
Reddish violet
Yellowish brown
10a
10b
10c
10d
10e
10f
Spectral Properties of Dyes
two absorption maxima, one absorption maxima which is
common in all dyes fall in the UV range due to π-π* transi-
tion of C=C present in the aromatic moiety of the dyes, the
second one lies in visible region and is due to π-π* of azo
linkage because of N=N of dyes. The metal complex dyes
9a-f and 10a-f exhibited λmax in the range 455-505 nm and
405-515 nm respectively. From the Figs. 1 and 2, it is clear
that the λmax (absorption maxima) values have a direct rela-
tion to the nature, position and electronic power of the sub-
stituents on the aromatic rings of the diazo component and
the coupler as well. The copper complexes (9a and 10a) of
Dyes were synthesized and properly characterized by UV-
visible, FTIR and NMR spectroscopic techniques to con-
firm the structures of newly synthesized dyes. The UV vis-
ible studies of synthesized dyes 7a-b, 9a-f and 10a-f were
recorded in distilled water and are shown in Table 1 and
Figs. 1 and 2. UV-visible study provided us the presences
of chromophores and the conjugation framework of dyes.
The ligand dyes 7a and 7b showed λmax at 450 and 460 nm
respectively. The synthesized compounds (dyes) showed
1.4
2
1.2
7b
10a
1.0
7a
9a
9b
10b
10c
0.8
10d
9c
10e
1
0.6
10f
9d
9e
9f
0.4
0.2
0.0
0
-0.2
200
300
400
500
600
700
800
200
300
400
500
600
700
800
(Wavelength (nm)
Wavelength (nm)
Fig. 1 Combined UV spectrum of Ligand Acid Dye 7a and it complexes
Fig. 2 Combined UV spectrum of Ligand Acid Dye 7b and it complexes
9a-f
10a-f

J Fluoresc
Fig. 3 FTIR Spectrum of Ligand Acid Dye 7a
ligand dyes 7a-b exhibited largest bathochromic shift as
compared to ligand dyes. Change in λmax after metal com-
plex formation depends upon electron accepting or donating
ability of d-orbitals either they are in stable or unstable state
of electronic configuration and also on the geometry of mol-
ecule achieved after complex formation.
The FTIR spectra of the pyrazolones acid dyes deriva-
tives (7a-b) exhibited absorption due to O-H, Ar-H, C=O,
Fig. 4 FTIR Spectrum Cu (II) complex (9a) of Acid Dye 7a

J Fluoresc
Fig. 5 1H NMR spectrum of ligand acid dye 7a
C=C, N=N, S=O, C-O at 3365–3360, 3055–3080, 1731–
1720, 1690–1685, 1428–1450, 1277–1270, 1070–1050,
780–760. Specifically taking into consideration FTIR
spectrum of 7a it showed broad band in the range of
3000–3500 cm−1 due to H-bonding of O-H group present
in the molecule (Fig. 3). The absorption bands at 1665,
Fig. 6 13C NMR spectrum of ligand acid dye 7a

J Fluoresc
Fig. 7 1H NMR spectrum of ligand acid dye 7b
1585, 1510, 760 depicted the presence of C=C stretching
and bending vibrations of aromatic double bonds respec-
tively. Amide carbonyl peak was observed at 1690 cm−1. A
prominent peak at 1270 cm−1 is due to S=O bond of SO3H
present in dye 7a. Similarly the functional groups in dye 7b
have been correlated with the peaks in the FTIR spectrum.
The metal complexes (9a-f, 10a-f) of ligand dyes 7a
and 7b also have been correlated with spectra especially
for peaks of N-M and O-M which are present in the range
504–614 cm−1 (Fig. 4).
The 1H NMR spectrum of ligand acid dye 7a (Fig. 5) showed
signals down field at 13.47 and 11.15 ppm due to OH and SO3H
groups present in the coupling and azo components of dye and
are highly deshielded due to H-bonding. A set of doublet signals
at 6.98 and 7.04 ppm are due to two ortho protons present in the
coupling partner of ligand dye. A similar set of doublet signals at
7.74 and 7.95 ppm is exhibited by those ortho protons which are
present at the DASDA component of dye and these are
deshielded due to electron withdrawing nature of SO3H group.
A singlet signal for alkenic proton sandwiched between two
phenyl rings is present 7.54 ppm and is deshielded by two aro-
matic rings. The singlet signals at 8.11 and 8.41 ppm are due to
isolated protons present on the benzene rings of azo and cou-
pling component of dyes. A singlet signal at 2.35 ppm is
showed by methyl present at the pyrazolone moiety of
coupling component of ligand dye 7a. 13C NMR spectrum
of 7a (Fig. 6) showed twelve signals in the unsaturated
region at 157.45, 148.95, 146.25, 145.53, 136.34, 131.97,
130.44, 129.30, 127.32, 126.72, 125.86, 124.40, 118.35,
117.61, 117.11, 114.05 due to twelve non equivalent car-
bons and one signal at 12.05 ppm due to methyl carbon
Table 2 Fastness properties data of the dyes 7a-b and their metal
complexes (9a-f and 10a-f)
Dye
Light fastness
Wash fastness
Rubbing fastness
Dry
Wet
7a
6/7
6/7
6/7
5/6
5/6
5/6
5/6
5/6
5/6
5/6
5/6
5/6
5/6
5/6
4/5
4/5
4
4
3
9a
4
3
9b
5
4
9c
4/5
4/5
3/4
4
4/5
4/5
4/5
4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
9d
9e
9f
7b
4
4/5
4/5
4/5
4/5
4/5
4/5
4/5
10a
10b
10c
10d
10e
10f
5
4/5
4/5
4/5
4/5
4/5
1
attached at pyrazolone nucleus. Both H NMR and 13C
NMR spectra confirmed the structure of synthesized li-
gand dye 7a. Similarly the ligand acid dye 7b has also
1
been confirmed for its structure the respective H NMR

J Fluoresc
Fig. 8 13C NMR spectrum of ligand acid dye 7b
and 13C NMR spectra as presented in Figs. 7 and 8 re-
spectively. NMR structure study of metal complex dyes
was no conducted due to paramagnetic nature of metals in
complexes which caused the overlapping and broadness
of signals. The metal to ligand ratio in the metal complex
acid dyes was determined from UV visible studies.
An exhaustion deals with the amount of dye transferred from
dye bath to fiber and is articulated as percentage of the quantity
of dye originally placed in the dye bath. Fixation of a dye is
concerned with the amount of dye fixed with the fiber. Driving
force for exhaustion is concentration of dye in two phases and
for fixation is the physical as well as chemical interaction with
fiber. In order to acquire high degree of exhaustion, assisting
salt Na2SO4 was added in the dye bath to perk up exhaustion by
increasing the electrostatic interactions of dyes with fiber.
The percentage exhaustion and percentage fixation of 2%
dyeing on leather ranges from 72 to 78% and 78–92% respec-
tively as it is represented in the Table 1. All the dyes have good
exhaustion and fixation values which are probably due to the
rapid diffusion of the dye molecule within the fabric under
dyeing conditions and physical as well as chemical interac-
tions of polar groups present in diazo and coupling compo-
nents. From the applications of dyes on leather it appears that
metal complexes of the dyes have high exhaustion and
Dyeing Properties of Dyes
All the dyes 7a-b and their metal complexes 9a-f, 10a-f were
applied at 2% depth (Figs. 6 and 7) on leather according to the
standard procedure.
Exhaustion and Fixation Study
Exhaustion and fixation values are determined by the applica-
tion of dyes at 2% dyeing on leather fabric. Exhaustion and
fixation values are shown in Table 1.
Fig. 9 2% shade of dyes 7a-b and
their metal complexes 9a-f and
10a-f on leather

J Fluoresc
Table 3 TGA data of Ligand dyes 7a-b and their metal complexes 9a-f
and 10a-f
have very little susceptibility to phtochromisim, due to
involvement of electrons in complex formations. Wash
fastness is the resistance offered by dyed fabric to retain
color when washed by soaps and detergents. Wash fast-
ness of dyes was in range 4–5 and was high in case of
Copper and Chromium complexes.
Rubbing fastness is the most important test which is
always required for every colored fabric either it is printed
or dyed. Rubbing fastness was planned to determine the
degree of color which may transfer from the surface of a
colored fabric to a particular test cloth for abrasion.
Rubbing fastness of ligand acid dyes 7a-b and their metal
complexes was very high 4–5. Rubbing fastness gives
clue about other improved properties like wash fastness,
substantively and sturdiness in use of dyed fabric [20, 21].
It is obvious from rubbing fastness value that all these
dyes have high fixation on leather fabric (Fig. 9).
Compound
Temperature oC
TG Weight loss (%)
7a
0–100
13
9
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
51
10
23
25
10
12
24
9
9a
9b
9c
100–400
400–800
0–100
14
23
9
9d
100–400
400–800
0–100
16
43
7
9e
100–400
400–800
0–100
20
43
4
9f
Thermogravimetric Analysis of Acid Dye and its Metal
Complexes
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
0–100
100–400
400–800
24
31
12
9
49
7
12
24
5
13
23
6
14
25
5
16
29
9
15
37
8
16
34
7b
Thermogravimetric analysis is one of the most useful methods
for investigating the thermal degradation of dyes and polymer-
ic materials. The results obtained from thermal analysis can be
used to describe its thermal stability and to determine the
temperature range in which they can be used without chang-
es in its properties, colour and composition. Thermal deg-
radation of ligand acid dyes 7a-b and their metal complexes
was conducted in argon atmosphere using a Netzsch TG
209 thermogravimetric analyzer within temperature range
of 0-800 °C in flowing Argon atmosphere employing Al2O3
as reference material.
From the TGA profiles (Table 3) the onset temperature
(To) of ligand acid dyes was found at 80 °C and three
stages decomposition occurs and maximum weight loss
was observed in the range 400-800 °C. The total weight
loss in 7a was 73% and in 7b was 70% which indicates
that ligand dye 7a was less stable than 7b. Weight loss in
the range 0-100 °C was 12–13% which is most probably
due to H2O molecules trapped in dye molecules. The
weight loss in the rage 100-400 °C is 9% in both dyes
is due to loss of N2 gas formed by the decomposition of
azo linkages. The maximum weight loss in the range 400-
800 °C is due to breakage of intermediates formed after
the removal of azo linkage. In this range loss of SO2, CO
and CO2 gases occurs. Ligand dyes 7b is more stable
because it contains the coupling component which is 4-
Nitro-2-aminophenol which is more stable than 4-Chloro-
2-aminophenol because Cl2 is released more easily than
NO2 because of strong C-N and N-O bonds in 4-Nitro-2-
aminophenol. These bonds have character between single
and double bond. When metal complexes TGAs of Ligand
dyes 7a and 7b are considered it appears that Iron
10a
10b
10c
10d
10e
10f
fixation as compared to unmetallized dyes. Chromium (III)
complexes of dyes have high fixation as compared with iron
(II) and copper (II) complexes.
Fastness Properties
Fastness properties of dyes were assessed after application of
2% dye with respect to leather fabric as represented in Table 2.
These were light fastness, wash fastness and rubbing fastness
which provided the clear picture regarding quality of dye.
Light fastness is the property to which a dye resists
fading due to light exposure. Different dyes have different
degrees of resistance to fading by light. Light fastness of
ligand acid dyes 7a-b was in range 5–6 and their metal
complex showed have high light fastness 6–7. These dyes

J Fluoresc
Fig. 10 TGA Thermogram of metal complex acid dye 9c
complexes are more stable than other metals. Moreover,
the all metal complexes exhibit the less total weight loss
than ligand acid dyes and more residue is obtained at
800 °C (Figs. 10 and 11). This is due to M-N and M-O
Fig. 11 TGA Thermogram of metal complex acid dye 10c

J Fluoresc
9. Emel Y, Hamit B (2002) Synthesis of novel acidic mono Azo
and an investigation of their use in the textile industry. Turk J
Chem 26:897
10. Garg HG, Prakash C (1972) Preparation of 4-arylazo-3,5-disubsti-
tuted-(2H)-1,2,6-thiadiazine-1,1-dioxides. J Medic Chem 15:435
11. Browing CH, Cohen JB, Ellingworth S, Gulbransen R (1926) The
antiseptic properties of the amino derivatives of Styryl and Anil
Quinoline. J Storage 100:293
strong bonds formed during complex formation [22–24].
In all complexes weight loss during the temperature range
0-100 °C is comparatively less than ligand dyes and is 5–
10%.
Conclusions
12. Pagga U, Brown D (1986) The degradation of dyestuffs in aerobic
biodegradation tests. Chemosphere 15:479–491
A series of bis-symmetric acid dyes 7a-b and their metal
complexes 9a-f and 10a-f has been synthesized in high
yields from bis-pyrazolone 4. Copper complexes dyes 9a
and 10a showed more bathochromic shift in absorption
maximum as compared to other metal complexes of acid
dyes. Application of dyes was made on leather where they
showed high light fastness, rub fastness and wash fastness.
All metal complexes of dyes exhibited high exhaustion and
fixation on leather in comparison to ligand dyes. Metal
complex dyes showed more thermal stability than ligand
dyes due to strong metal to nitrogen and oxygen bonds.
13. Park C, Lim J, Lee Y, Lee B, Kim S, Lee J, Kim S (2007)
Optimization and morphologyfor decolorization of reactive black
5, by Funalia trogii. Enz Micro Technol 40:1758–1764
14. Rajendra GM, Madhu SV, Naveen KS (1998) Voltammetric inves-
tigations of the reduction of direct Orange-31 a bisazo dye. Croat
Chem Acta 71:715
15. Olayinka OA, Oluwabunmi EA, Alice OA, Abiola E, Winifred UA
(2013) Synthesis and spectroscopic study of Naphtholic and phe-
nolic Azo dyes. Phys. Res. Inter 3:28
16. Chandravadivelu G, Senniappan P (2011) In-vitro antimicrobial
activity of novel derivative of Azo dye from Cyano Ester. Inter. J.
Pharma. Chem Res 1:1082
17. Patel PS (2012) Studies on synthesis and dyeing performance of
disperse Azo dyes based on Schiff Base of Ninhydrin and 3-amino
phenol. Arch. Appl Sci Res 4:846
18. Berhanu T, Ratnapandian S (2017) Extraction and optimization of
natural dye from Hambo Hambo (Cassia singueana) plant used for
coloration of tanned leather materials. Adv Mater Sci Eng 2017:1–
5. https://doi.org/10.1155/2017/7516409
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