Synthesis, characterization and spectroscopic properties of some new azo disperse dyes derived from 4-hydroxybenzo[h]quinolin-2-(1H)-one as a new synthesized enol type coupling component

Article abstract of DOI:10.1016/j.dyepig.2012.06.008

4-Hydroxybenzo[h]quinolin-2-(1H)-one (IV) was synthesized from the cyclocondensation of 3-(naphthalen-1-ylamino)-3-oxopropanoic acid (I) or N,N′-di(naphthalen-1-yl)malonamide (II) and subsequently coupled with diazotized p-substituted aniline derivatives.

Full text of DOI:10.1016/j.dyepig.2012.06.008

Dyes and Pigments 95 (2012) 632e638
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, characterization and spectroscopic properties of some new azo
disperse dyes derived from 4-hydroxybenzo[h]quinolin-2-(1H)-one as a new
synthesized enol type coupling component
,
b
E.O. Moradi Rufchahi a , A. Ghanadzadeh Gilani
*
a Department of Chemistry, Faculty of Science, Lahijan Branch, Islamic Azad University, Lahijan, Iran
b Department of Chemistry, Faculty of Science, University of Guilan, Rasht, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
4-Hydroxybenzo[h]quinolin-2-(1H)-one (IV) was synthesized from the cyclocondensation of 3-(naph-
thalen-1-ylamino)-3-oxopropanoic acid (I) or N,N0-di(naphthalen-1-yl)malonamide (II) and subse-
quently coupled with diazotized p-substituted aniline derivatives. The structures of the synthesized dyes
were determined by spectroscopic and analytical methods. Solvent effects on the ultravioletevisible
absorption spectra of these novel azo dyes were studied in six pure organic solvents with different
polarities. The color of the dyes is discussed with respect to the nature of substituents on the benzene
ring. The tautomeric structures of the azo compounds were studied by 1H NMR spectroscopy in DMSO-d6
and CDCl3. The effects of acid and base on the visible absorption spectra of the dyes were also reported.
Ionization constants, pKa, for these dyes were determined in 80 vol. % ethanolewater medium at room
Received 30 April 2012
Received in revised form
7 June 2012
Accepted 18 June 2012
Available online 26 June 2012
Keywords:
Azobenzoquinolone dyes
Coupling components
Tautomerism
temperature and correlated with the substituent constant, sp
.
Ó 2012 Elsevier Ltd. All rights reserved.
Solvatochromism
Acidic dissociation constant
Azo-hydrazone
1. Introduction
studies dedicated to synthesis and spectroscopic characterization
of these dyes for evaluating and improving their physical and
chemical features [18e22]. Some important investigations have
been carried out on the synthesis and spectroscopic behavior of
arylazo dyes based on 4-hydroxy coumarin as an enol type coupling
component by Shawali and coworkers [23,24]. In particular, the
synthesis and tautomerism of heteroaryl azo dyes derived from 4-
hydroxyquinolone and its derivatives have been explored by
several authors [25e27].
In view of these encouraging reports, in this study we report the
synthesis of 4-hydroxybenzo[h]quinolin-2-(1H)-one (IV) (Scheme 1)
and using it as coupling component in reaction with some diazotized
aromatic amines as diazo components (Scheme 2). The effects of
solvents,substituents,acidandbaseonthevisibleabsorptionmaxima
of the dyes are also reported along with the acid dissociation
constants of the dyes.
Azo dyes and pigments constitute by far the most important
chemical class of organic colorant owing to their versatile appli-
cation in various fields of dye and organic chemistry [1,2]. Azo dyes
synthesized from heterocyclic compounds have attracted much
attention for their bright and strong color shades ranging from
yellow to greenish blue on synthetic and natural fabrics [3,4]. In the
last fifty years a number of studies have been carried out on
synthesis, spectroscopic properties and dyeing performance of
these compounds [5e10].
Enol type coupling components are among the most useful
precursors for a wide variety of heterocyclic azo dyes [11]. The azo
dyes derived from enol type coupling components constitute an
interesting type of compound since they potentially have several
tautomeric forms (enol-azo, keto-azo, hydrazo) in solution and
solid state [12e15]. Azo-hydrazone tautomerism in azo dyes
synthesized from enol type coupling components has been known
for many years and has been reviewed several times [16,17]. Many
2. Experimental
2.1. General
All chemicals used for the synthesis of the studied compounds
were obtained from Merck and Aldrich chemical companies and
used without any purification process. Solvents used were of
* Corresponding author. Tel.: þ98 1315515849; fax: þ98 1412229081.
E-mail addresses: moradierufchahi1350@gmail.com, moradierufchahi@liau.ac.ir,
ena_moradi@yahoo.com (E.O.M. Rufchahi).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.06.008

E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
633
O
O
O
O
NH2
HN
OCH3
HN
OH
1)NaOH
2)HCl
CH3SO3H
P2O5
I
OH
II
O
O
O
O
NH2
CH3O
OCH3
N
H
O
HN
NH
IV
2
PPA
III
Scheme 1. Procedures used for synthesis of the 4-hydroxybenzo[h]quinolin-2-(1H)-one (IV).
spectroscopic grade. Melting points were determined with a Barn-
stead Electrothermal 9100 melting point apparatus in open capil-
lary tubes and uncorrected. 1H and 13C NMR spectra measured on
a Bruker 400 MHz spectrometer in DMSO-d6 and CDCl3 using TMS
as an internal reference. The absorption spectra of the compounds
were scanned on a Cary UVevis Double-beam spectrophotometer
(Model 100). Infrared spectra (in KBr pellets) were recorded on
a Shimadzu-8400 FT-IR spectrometer. Microanalyses for C, H and N
were performed on a PerkineElmer 2400(II) elemental analyzer.
washed well with water and dried. Recrystallization from chloro-
form giving the acid (II) (1.65 g, 72%) as white crystals: mp
138e139.5 ꢀC, FT-IR (KBr):
n
3500 (OH), 3414 (NH), 3050 (Aro-H),
2962 (Aliph-H), 1720 (C]O), 1641 (C]O) cmꢁ1 1H NMR (CDCl3):
9.01 (1H, b, NH), 7.92e8.00 (3H, m, overlapped, Ar-H), 7.79 (1H, d,
;
d
J ¼ 6.5 Hz), 7.46e7.68 (3H, m, overlapped), 3.72 (2H, s, eCH2e) ppm.
2.4. Preparation of N,N0-di(1-naphthyl)malonamide (III)
A mixture of 1-naphthyl amine (100 mmol, 14.32 g) with die-
mthyl malonate (50 mmol, 5.75 ml) was refluxed for 4 h in an oil
bath. After cooling, the mixture was digested with diethylether,
filtered by suction and recrystallized from ethanol giving the
malonamide (III) (14.23 g, 81%) as creamy solid: mp 229e230 ꢀC, FT-
2.2. Preparation of methyl 3-(1-naphthylamino)-3-oxopropanoate (I)
2-Naphthyl amine (10.0 mmol, 1.432 g) was dissolved in
dimethyl malonate (100.0 mmol, 11.5 ml) and the mixture was
refluxed in a 100 ml round bottom flask equipped with an air
condenser for 1 h so that the methanol evolved and escaped from
the top of the condenser. The solution was cooled and the volume
was reduced to one third. On cooling in an ice bath a white solid
product was obtained. Recrystallization from dibutylether afforded
the white solid of methyl 3-(naphthalen-1-ylamino)-3-
oxopropanoate (I) (1.71 g, 71%): mp 103e105 ꢀC; FT-IR (KBr):
IR (KBr):
n 3414 (NH), 3053 (Aro-H), 2965 (Aliph-H), 1640 (C]O)
cmꢁ1; 1H NMR (CDCl3):
d
10.31 (2H, b, NH), 8.00 (2H, d, J ¼ 9.0 Hz),
7.90 (2H, d, J ¼ 7.6 Hz), 7.77 (2H, d, J ¼ 9.0 Hz), 7.63 (2H, d, J ¼ 8.0 Hz),
7.43e7.37 (3H, m, overlapped), 3.79 (2H, s, eCH2e) ppm.
2.5. Synthesis of 4-hydroxybenzo[h]quinolin-2-(1H)-one (IV)
n
3415 (NH), 3050 (Aro-H), 2965 (Aliph-H), 1745 (C]O), 1644 (C]
O) 1110 (CeO) cmꢁ1; 1H NMR (CDCl3):
d
9.94 (1H, b, NH), 8.15 (1H, d,
2.5.1. Method A: from 3-(1-naphthylamino)-3-oxopropanoic acid
(II)
J ¼ 7.5 Hz), 8.04 (1H, d, J ¼ 8.5 Hz), 7.90 (1H, d, J ¼ 8.0 Hz), 7.72 (1H,
d, J ¼ 8.2 Hz), 7.62e7.50 (3H, m, overlapped), 3.91 (3H, s, eOCH3),
3.67 (2H, s, eCH2e) ppm.
A mixture of (II) (10 mmol, 2.3 g) was dissolved in 18.0 ml
methanesulfonic acid, which contains 10% of phosphorus pent-
oxide, and then heated at 120 ꢀC for 30 min. The dark viscous
solution was allowed to cool, water was added and the resultant
gum solidified on prolonged standing. The solid was filtered, and
then dissolved in 100 ml 10% sodium hydroxide. The aqueous
solution was filtered to remove insoluble material and slowly
acidified to pH < 4 with 20% hydrochloric acid. The resulting crude
precipitates were collected, washed with water and dried to afford
2.3. Preparation of 3-(1-naphthylamino)-3-oxopropanoic acid (II)
Compound (I) (10.0 mmol, 2.43 g) was stirred with a 1.0 mol Lꢁ1
NaOH (100 ml) at room temperature for 2.0 h, after which time the
entire solid had dissolved. The solution was filtered and acidified
with 10% HCl to yield a white precipitate which was filtered and
OH
OH
-
N2+Cl
N
N
X
1) OH-(pH=9-10)
2)H+(pH=4-5)
+
O
N
N
H
O
H
X
(1):X=-NO2
(6):X= -Br
(2):X= -CN
(7):X= - I
(3):X= -CF3
(8): X= -H
(4):X= -F
(5):X= -Cl
(9):X= -CH3 (10):X= -OCH2CH3
Scheme 2. Synthesis of azo dyes 1e10.

634
E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
4-hydroxybenzo[h]quinolin-2-(1H)-one (IV) (1.4 g, 66%) as a deep
pink powder.
method A malonamide ester (I) was converted to half malonic acid
(II) which subsequently was treated with phosphorous pentoxide
in methanesulfonic acid to give compound (IV). In method B,
malonamide (III) was prepared by refluxing 2-naphthyl amine with
dimethyl malonate (2:1 molar ratio) in good yield. Heating N,N0-
di(1-naphthyl)malonamide (III) in polyphosphoric acid (PPA) at
140e150 ꢀC afforded the 4-hydroxybenzo[h]quinolin-2-(1H)-one
(IV). All of the compounds were characterized by the FT-IR and
NMR spectral analysis. 1H NMR spectra recorded for the prepared
compounds clearly supported the proposed structures. The protons
belonging to the aromatic system were observed at the expected
chemical shifts and integral values. The peak at 5.89 ppm (]CH)
also confirmed the formation of the desired quinolone ring in
compound (IV).
The arylazoquinololin-2-one dyes 1e10 were prepared by
coupling reaction of 4-hydroxybenzo[h]quinolin-2-(1H)-one with
diazotized p-substituted aniline derivatives in basic solution
(Scheme 2). The chemical structures of these dyes were confirmed
by some spectroscopic methods and elemental analysis. The phys-
ical and spectral data of the dyes are summarized in Tables 1 and 2.
As shown in Scheme 3, the four possible tautomeric forms enol-azo-
keto (EAK), twoketo-hydrazo-keto(KHK1 and KHK2) and keto-azo-
enol (KAE) can be written for the synthesized azo dyes.
2.5.2. Method B: from N,N0-di(1-naphthyl)malonamide (III)
N,N0-di(1-naphthyl)malonamide (III) (3.540 g, 10.0 mmol) was
thoroughly mixedwith11.5gpolyphosphoricacid(PPA, sp. gr. 2.08)in
80 ꢀC and was then heated in an oil bath for 5 h at 150 ꢀC. The dark
viscous solution was allowed to cool, water was added and the
precipitated compound was filtered off, washed with water and dried
in air. The crude product was dissolved in 100 ml of sodium hydroxide
solution 0.1 mol Lꢁ1 and undissolved material wasfiltered. The filtrate
was neutralized with concentrated hydrochloric acid and the
precipitate was recrystallized from ethanol to afford 4-hydroxybenzo
[h]quinolin-2-(1H)-one (IV) (1.65 g, 78%) as deep pink powder: mp
318e320 ꢀC, FT-IR (KBr):
n
3500 (OH), 3402 (NH), 3050 (Aro-H), 1637
11.58 (1H, b, OH), 11.42 (1H, b,
1
(C]O) cmꢁ1; H NMR (DMSO-d6):
d
NH), 8.83 (1H, d, J ¼ 8.2 Hz), 7.96 (1H, d, J ¼ 8.7 Hz), 7.66e7.59 (3H, m,
overlapped), 5.89 (1H, s), 13C NMR (DMSO-d6):
d
164.8, 164.1, 135.0,
129.7, 129.3, 128.7, 127.2, 123.41, 122.4, 122.2, 120.5, 111.5, 99.1 ppm.
2.6. Preparation of arylazobenzoquinolone dyes 1e10
A cold solution of aryldiazonium salt (2.0 mmol) was prepared by
adding a solution of NaNO2 (2.2 mmol, 0.15 g into 1.0 mL H2O) to
a cold solution ofarylamine hydrochloride (2.0 mmolof arylamine in
1.5 mL conc. HCl). The resulting solution of aryldiazonium salt was
added drop wise to a mixture of compound (IV) (2.0 mmol, 0.42 g) in
water (15 mL) containing NaOH (25 mmol, 1.0 g) at 0e5 ꢀC. The
reaction mixture was stirred for 2 h at the same temperature and the
precipitate was filtered off and the resulting solid was washed with
cold ethanol and dried. The crude product was purified using the
recrystallization method as mentioned in Table 1. Under the same
reaction conditions, a series substituted arylazobenzoquinolone
dyes were obtained in satisfactory yields (Table 1, Scheme 2). When
aryldiazonium salts bearing an electron-withdrawing group such as
nitro and trifluoromethyl or halogen atom were employed, corre-
sponding arylazobenzoquinolone dyes were obtained with satisfied
yields from 60 to 75% (Table 1, entries 1e6). However, when
substrates borean electrondonating groupsuchas methyl orethoxy,
the corresponding diazonium salts were very unstable in the reac-
tion mixture and evolution of nitrogen gas was observed during the
reaction process, thus only a small quantity of products were iso-
lated in 30e42% yields (Table 1, entries 8e10).
Spectral investigations of the new synthesized azo dyes showed
good agreement with proposed structures. FT-IR spectrum of
compounds 1e10 showed broad OH and NH bands at
3434e3176 cmꢁ1 and carbonyl group peaks at 1670e1640 cmꢁ1
.
The 1H NMR spectra measured in DMSO-d6 at 25 ꢀC revealed
a multiplet from 8.88 to 7.01 ppm for aromatic protons, a singlet at
2.37 ppm (CH3, 9), a quartet at 4.12 ppm (eOCH2e, 10) and a triplet
at 1.36 ppm (eCH3, 10). The results also showed that in DMSO-d6
such dyes exist as a mixture of keto-hydrazo-keto forms KHK1 and
KHK2 with nearly equal integration ratio. The spectra showed in
each case two hydrazone proton signals (]NeNHe) at
16.85e14.97 ppm. These signals undoubtedly correspond to the
hydrazone NH proton resonance related to hydrazone-keto forms
KHK1 and KHK2 [19e22]. Further evidence for this assignment is
provided by the observation that the 1H NMR spectrum of the 15N-
phenylhydrazone derivatives of some azo heterocycles were re-
ported to show two doublets centered at similar regions with
J ¼ 93e100 Hz indicating that the proton is attached to nitrogen
atom [20]. It was reported that the hydroxyazo OH proton reso-
nance comes 3e5 ppm higher than NH proton resonance; hence,
the OH proton resonance signal of enol forms is expected to be in
region 9e12 ppm [20,21]. The possibility of tautomers involving
ring NH rearrangement can be eliminated by studying the 1H NMR
spectrum of the compounds in DMSO-d6 and CDCl3. The 1H NMR
spectrum of all the dyes showed two singlets at 11.34e11.53 and
11.45e11.60 ppm. The presence of these two broad singlets
provides firm evidence for presence of the amide NeH bonds and is
3. Results and discussion
3.1. Synthesis and characterization
As depicted in Scheme 1, 4-hydroxybenzo[h]quinolin-2-(1H)-
one (IV) was prepared via two different methods A and B. In
Table 1
The physical properties of the dyes used in this study.
Dye
Color
Mp (ꢀC)
Recrystalization
%C
%H
%N
Yield (%)
Calcd.
Found
Calcd.
Found
Calcd.
Found
1
2
3
4
5
6
7
8
9
Dark red
Dark red
Bright red
Orange
Dark red
Clear red
Dark brown
Brown
>370
>370
DMF
DMF
DMF
DMF
63.33
70.58
62.67
68.46
65.24
57.89
51.72
72.37
72.94
70.18
64.02
70.81
61.98
68.01
64.80
56.91
50.91
72.96
72.11
69.94
3.36
3.55
3.16
3.63
3.46
3.07
2.74
4.16
4.59
4.77
3.29
3.59
3.11
3.69
3.51
3.14
2.78
4.21
4.64
4.84
15.55
16.46
10.96
12.61
12.01
10.66
9.52
13.33
12.76
11.69
15.19
16.92
10.02
12.74
12.25
10.02
9.23
13.01
12.16
11.62
60
65
64
68
69
75
73
70
52
46
354e357
365e368
340e342
356e358
307e308
310e312
325e327
297e299
DMF
DMF/H2O
DMF/H2O
DMF/H2O
DMF/H2O
DMF/H2O
Dark red
Clear red
10

E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
635
Table 2
Spectral data for dyes 1e10.
Dye
IR (KBr, cmꢁ1
)
1H NMR (
Other
d, ppm)
vOeH
vNeH
vC]O
vC]N
Aro-H
Alip.-H
NeH
functional groups
Hydrazo
Amide
1
2
3
3419
3416
3434
3200
3155
3188
1658
1641
1670
1590
1596
1600
1520 and 1261 (NO2)
8.85 (1H, d, J ¼ 6.4 Hz), 8.39 (2H,
e
e
e
14.97
15.77
15.76
16.85
15.08
15.94
11.53
11.60
11.50
11.55
11.49
11.54
d, J ¼ 6.8 Hz) 7.99e7.69 (7H, m, overlapped)
8.83 (1H, d, J ¼ 8.4 Hz), 8.01e7.88 (6H, m,
overlapped), 7.75 (1H, t, J ¼ 6.8 Hz), 7.67 (2H, d, J ¼ 8 Hz)
8.85 (1H, d, J ¼ 8.4 Hz), 8.01 (2H, d, J ¼ 8.0 Hz),
7.94e7.88 (3H, m, overlapped), 7.75 (2H, t, J ¼ 7.2 Hz),
7.68 (2H, d, J ¼ 8.4 Hz)
2254 (CN)
1320 (CeF)
4
5
3405
3415
3186
3180
1654
1648
1600
1596
1325 (CeF)
765 (CeCl)
8.84 (1H, d, J ¼ 8.4 Hz), 8.00 (2H, d, J ¼ 7.6 Hz), 7.83e7.67
(5H, m, overlapped), 7.40 (2H, t, J ¼ 8.5 Hz)
8.83 (1H, d, J ¼ 8.4 Hz), 7.94 (2H, d, J ¼ 8.4 Hz), 7.80
(1H, d, J ¼ 8.8 Hz), 7.74 (2H, t, J ¼ 7.6 Hz), 7.67
(2H, d, J ¼ 8.0 Hz), 7.60 (2H, d, J ¼ 8.4 Hz)
8.84 (1H, d, J ¼ 8.8 Hz), 8.01e7.66 (9H, m, overlapped)
e
e
15.24
16.30
15.16
16.14
11.45
11.56
11.48
11.54
6
7
3411
3417
3187
3176
1644
1644
1602
1601
654 (CeBr)
534 (CeI)
e
e
15.15
16.10
15.12
16.08
11.34
11.45
11.43
11.49
8.83 (1H, d, J ¼ 8.4 Hz), 7.99 (2H, d, J ¼ 8.4 Hz), 7.88
(2H, d, J ¼ 8.4 Hz), 7.74 (1H, t, J ¼ 7.2 Hz), 7.66
(2H, d, J ¼ 8.4 Hz), 7.58 (2H, d, J ¼ 8.4 Hz)
8
3422
3212
1640
1600
e
8.85 (1H, d, J ¼ 7.9 Hz), 8.01 (2H, t, J ¼ 8.2 Hz),
7.77e7.56 (7H, m, overlapped), 7.37 (1H, t, J ¼ 8.5 Hz)
a8.16 (1H, d, J ¼ 8.4 Hz), 8.05 (1H, d, J ¼ 7.6 Hz),
7.95 (1H, d, J ¼ 7.6 Hz), 7.78e7.50 (8H, m, overlapped))
8.83 (1H, d, J ¼ 8.4 Hz), 8.00 (2H, t, J ¼ 6.8 Hz), 7.76e7.61
(5H, m, overlapped), 7.36 (2H, d, J ¼ 8.4 Hz)
8.85 (1H, d, J ¼ 8.8 Hz), 8.02 (2H, t, J ¼ 8.8 Hz), 7.76e7.66
(5H, m, overlapped), 7.11 (2H, d, J ¼ 9.2 Hz)
a8.16 (1H, d, J ¼ 8.8 Hz), 8.08 (1H, d, J ¼ 7.6 Hz),
7.94 (1H, d, J ¼ 7.6 Hz), 7.74e7.55 (5H, m, overlapped),
7.02 (2H, d, J ¼ 8.8 Hz)
e
15.27
16.33
15.33
16.90
15.34
16.46
15.49
16.72
15.55
17.30
11.45
11.50
8.55
e
8.87
9
3424
3422
3210
3196
1645
1642
1600
1600
2966 (CeH)
1266 (CeO)
2.37 (3H, s)
11.43
11.48
11.43
11.51
8.99
10
4.11 (2H, q),
1.37 (3H, t)
4.12 (2H, q),
1.48 (3H, t)
9.05
a
1H NMR recorded in CDCl3.
related to amide protons of two types of tautomeric forms KHK1
and KHK2. The quinolone ring NH was extremely affected by
solvent species, but the hydrazone NH was not affected so much.
For example, in the 1H NMR spectra of dyes 8 and 10, the quinolone
ring NH peak was observed at higher field in chloroform than in
DMSO. The quinolone rings NHs of dye 10 were observed at 8.98
and 9.05 ppm in CDCl3. whereas the corresponding protons were
observed at 11.43 and 11.51 ppm in DMSO. The downfield chemical
shift of the NH proton signal in DMSO-d6 is larger than in CDCl3,
because of the intermolecular hydrogen bonding between the NH
and DMSO (Table 1, entries 8 and 10).
3.2. UVevisible study of the prepared azo dyes
The absorption spectra of arylazobenzoquinolone dyes 1e10
were measured in six organic solvents with different polarities
(chloroform, ethanol, acetic acid, acetonitrile, dimethyl formamide
and dimethyl sulfoxide) in the wavelength rang 300e600 nm at
a concentration w10ꢁ5 mol Lꢁ1. The results are given in Table 3. The
dyes are hardly soluble in some of the used solvents but are
completely soluble in DMSO. Therefore, stock solutions of each dye
with a concentration of w10ꢁ3 mol Lꢁ1 were accurately prepared in
DMSO and dilutions of these stocks were used for absorption
measurements.
The electronic absorption spectra of the dyes in all used solvents
(Table 3) revealed, in each case, two bands in the regions of
396e417 and 418e476 nm (e.g. Fig. 1 for dye 7). It can be suggested
that the dyes may exist as a mixture of two tautomeric forms in
various solvents. The visible absorption spectra of the dyes didn’t
show regular variation with the polarity of solvents, therefore, it
can be considered as a result of several solvent characteristics such
as polarity, basicity and H-bond-accepting or -donating ability.
Furthermore the spectra of unsubstituted derivatives 8 in different
solvents showed small changes in maximum absorption wave-
length (lmax). The little absorption changes in lmax strongly suggest
the intramolecular hydrogen bonding in the compound. These
results seem to be compatible with the hydrazone forms KHK1 and
KHK2 rather than azo forms EAK and KAE, as they are similar to
that of related hydrazone compounds [20e22]. The small shifts in
lmax of 8 in different solvents are due to solventesolute interactions
and are consistent with the assigned tautomeric structures. In
agreement with this conclusion is the observation that the spectra
of arylazo dyes derived from the reaction of similar enol type
coupling components with diazotized aniline derivatives are
largely independent of the solvent polarity [28e30].
Ar
H
Ar
H
O
N
N
O
N
N
N
H
O
N
H
O
KHK1
EAK
O
O
Ar
Ar
N
N
N
N
H
H
N
H
O
N
H
O
KAE
KHK2
Scheme 3. Tautomeric forms for the prepared azo dyes.

636
E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
Table 3
Absorption maxima (in nm) of dyes 1e10 in different solvents.
Dye DMSO DMF CH3CN CHCl3 EtOH
CH3COOH
1
2
3
4
5
6
7
8
9
10
438, 417s 426, 415s 420, 410s 429, 406s 422, 413s 430, 411s
413s, 422 407, 427s 403, 425s 410s, 422 408, 426s 411s, 426
410, 422s 401, 432s 396, 428s 402s, 417 400, 427s 402s, 418
409s, 431 399, 461s 401s, 425 400s, 434 399, 436s 404s, 432
433, 412s 462s, 399 427, 404s 438, 402s 419, 404s 436, 403s
414s, 432 409s, 424 409s, 428 411s, 439 405s, 434 407s, 437
414s, 440 408, 476s 408s, 432 409s, 443 405s, 438 405s, 441
412s, 431 410s, 427 406s, 424 407s, 434 408s, 429 404s, 431
440, 410s 437, 411s 434, 406s 443, 411s 437, 406s 441, 407s
412s, 459 406s, 467 409s, 453 412s, 462 409s, 459 404s, 461
s ¼ shoulder.
The difference in the lmax values for the dye solutions can be
Fig. 2. Absorption spectra of the arylazobenzoquinolone dyes with different substit-
uents on the benzenoid system.
assessed in terms of the electronic power of the substituents in the
benzenoid system. Details of the visible absorption spectra of ary-
lazobenzoquinolone dyes containing electron-accepting and
electron-donating substituents are shown in Table 3. As it is
apparent in Table 3, the introduction of electron donating ethoxy
group in the benzene ring resulted in bathochromic shifts in all
solvents with respect to electron-accepting nitro, cyano, tri-
fluoromethyl and fluoro groups (e.g. for dye 10 Dl ¼ 37 nm relative
to dye 1, Dl ¼ 51 nm relative to dye 2, Dl ¼ 59 nm relative to dye 3,
Dl ¼ 60 nm relative to dye 4 in ethanol). The introduction of
electron-donating methyl and iodo (p-) groups in the benzene rings
resulted in bathochromic shifts in all solvents in comparison with
unsubstituted dye 8. Similar significant changes were not observed
for the dyes with p-Cl and p-Br substituents on diazo components
(e.g. for dye 6 Dl ¼ 1 nm in DMSO, Dl ¼ 3 nm in DMF, Dl ¼ 4 nm in
CH3CN, Dl ¼ 5 nm in CHCl3, Dl ¼ 5 nm in EtOH and Dl ¼ 6 nm in
CH3COOH relative to dye 8). Fig. 2 compares the absorption spectra
of some of the dyes with different substituents in chloroform.
Absorption maxima of the prepared dyes 1e10 were also
measured in acidic and basic media. It was observed that the
absorption curves of the dyes were not sensitive to acid but is very
sensitive to base. There was no significant change in the spectra of
all the synthesized dyes when a small amount of 0.1 mol Lꢁ1 HCl
was added to their ethanolic solutions and the absorption curves
are resembled those in high proton donating solvents such as
ethanol and acetic acid. When 0.1 mol Lꢁ1 KOH was added to
ethanolic solution of the dyes, both a shoulder and a maximum in
the longer wavelength region were decreased and a new maximum
O
OH
N
O
Ar
N
O
Ar
N
N
H
KT
N
N
H
H
Ka
O
-
O
N
Ar
N
Ar
N
-
N
+ H+
N
H
O
N
O
+H +
H
Scheme 4. Acidic dissociation equilibrium of the prepared azo compounds.
at short wavelength region was observed. These hypsochromic
shifts in basic solvents are due to deprotonation of dye molecules,
which lead to anionic forms of dyes (Scheme 4). This indicates that
arylazobenzoquinolone dyes 1e10 exist partly in a dissociated form
and there is equilibrium between neutral and anionic forms. A
typical example is shown in Fig. 3.
3.3. Determination of pKa values of the azo dyes
The ionization constants (pKa) of 1 to 10 were determined in 80
vo1% ethanolewater medium at room temperature and a
m of 0.1
Fig. 1. Absorption spectra of 7 in different solvents.
Fig. 3. Absorption spectra of dye 5 in acidic and basic solutions.

E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
637
Table 4
Acidic dissociation constants (pKa) and absorption maxima (lmax) of prepared azo
dyes in different pH values.
a
Dye
X
sp
pH
pKa
1.77 6.43 6.78 7.50 8.03 9.53 10.40 12.15 13.19
lmax
1
2
3
4
5
6
7
8
9
p-NO2
p-CN
p-CF3
p-F
p-Cl
p-Br
p-I
0.81 426 427 427 427 426 425 426 425 427 4.98
0.70 420 415 420 422 403 401 400 401 400 6.66
0.53 414 413 414 412 392 391 388 388 388 6.78
0.15 431 431 431 431 429 395 378 377 378 7.53
0.24 434 434 434 434 390 396 385 384 384 7.94
0.26 435 430 434 435 406 396 387 387 385 7.66
0.28 439 438 440 439 427 400 389 387 388 8.16
0.0 431 432 431 431 431 431 387 380 380 8.61
p-H
p-CH3 ꢁ0.14 440 440 440 441 440 441 391 380 379 8.78
10 p-OCH2 ꢁ0.28 461 461 460 460 461 448 383 382 382 9.02
CH3
a
Taken from Ref. [28].
Fig. 5. AbsorbanceepH curve for dye 8 at
l
¼ 431 nm.
5 ꢂ 10ꢁ5 M in the azo dye, 0.1 M in HCl, and contained 80% volume
ethanol. The test solution (50 ml) was then transferred to a 100 ml
Erlenmeyer flask and the pH of the solution was measured and the
spectrum was recorded using either the ionic medium or the cor-
responding aqueous ethanol as a blank. In both cases identical
absorbance values in the employed wavelength range were ob-
tained. The pH of the test solution was increased by addition of
small volume of concentrated carbonate-free sodium hydroxide
made up from the same solvent. Since the total change in volume
did not exceed 1.0% no correction was made for dilution. After each
spectral measurement, the pH was checked, and in all cases, the
two values before and after the spectral measurement were found
to be the same within the limits of the accuracy of the pH meter. In
each run10e15 pH readings were taken and the value of pKa was
calculated from each reading using the equation:
using a spectrophotometric titration method and given in Table 4.
Each compound exhibited two bands in region of 379e427 nm for
anionic and 412e462 nm for the molecular species. In all cases, as
the pH value of the solution increased, the height of the former
band increased and simultaneously that of the latter decreased.
From the optical spectra (Fig. 4), in each case, the isobestic points
indicate that anionic and neutral species are in equilibrium. Typical
absorbanceepH curve is also showed in Fig. 5.
A digital pH meter Genway model 3505 was employed for
determination of pH. It was calibrated using two standard Genway
buffer solutions at pH 4.01 and 7.00. The pH meter readings (B)
recorded in ethanolewater solutions were converted to hydrogen
ion concentration [Hþ] by means of the widely used relation of Van
Uitert and Haas [31], namely where log UH, is the correction factor
for the solvent composition and ionic strength for which B is read.
For this purpose, readings were made on a series of solutions
containing known amounts of hydrochloric acid and sodium
chloride in a way that the ionic strength was equal to 0.1 in 80 vol.%
ethanolewater at room temperature. The value of log UH, was
found to be ꢁ0.235.
pKa ¼ pHi þ logðAb ꢁ AiÞ=ðAi ꢁ AaÞ
where Ai is the absorbance of the solution at pHi and Aa and Ab are the
absorbance values of the strong acidic and alkaline solutions of each
compound. Each compound was subjected to three pKa determi-
nations, and the averagevalues, given inTable 4 arewithin ꢃ0.05 pKa
units. Plotting pKa values against Hammet constants (sp) yields the
graph shown in Fig. 6. The equation of such a correlation is:
Â
Ã
ꢁlog Hþ ¼ B þ log UH
The acid dissociation constants of 1 to 10 were evaluated
spectrophotometrically. An aliquot of a stock solution of the
appropriate dye in dimethyl sulfoxide was diluted with aqueous
hydrochloric acid and ethanol so that the final solution was
pKa ¼ 8:4377 ꢁ 3:2381 sp
Fig. 4. Absorption spectra of dye 4 in different pH values.
Fig. 6. Relation between Hammet constant (sp) and pKa values for the prepared dyes.

638
E.O.M. Rufchahi, A.G. Gilani / Dyes and Pigments 95 (2012) 632e638
properties, and theoretical studies of novel thienylpyrrole azo dyes bearing
Since the electron density on the aromatic rings can be reduced by
benzothiazole acceptor groups. Tetrahedron 2011;67:5189e98.
[10] Raposo MMM, Castro MCR, Belsley M, Fonseca AMC. Pushepull bithiophene
azo-chromophores bearing thiazole and benzothiazole acceptor moieties:
synthesis and evaluation of their redox and nonlinear optical properties. Dyes
Pigm 2011;91:454e65.
the electron withdrawing groups such as eNO2, eCN and eCF3, the
pKa values show that the acidity of the hydroxyl group increases.
While eOEt and eCH3 groups attached to the compounds 9 and 10
decrease the acidic character, due to their electron donating ability
which destabilizes anionic forms of the azo dyes (Scheme 4).
[11] Schwander HR. Heterocyclic azo coupling components. Dyes Pigm 1982;3:
133e60.
[12] Ertan N. Synthesis of some hetarylazopyrazolone dyes and solvent effects on
their absorption spectra. Dyes Pigm 2000;44:41e8.
[13] Karcı F, Ertan N. Hetarylazo disperse dyes derived from 3-methyl-1-(3,5-
dipiperidino-s-triazinyl)-5-pyrazolone as coupling component. Dyes Pigm
2002;55:99e108.
[14] Sener I, Karcı F, Ertan N, Kılıc E. Synthesis and investigations of the absorption
spectra of hetarylazo disperse dyes derived from 2,4-quinolinediol. Dyes Pigm
2006;70:143e8.
[15] Karcı F, Ertan N. Synthesis of some novel hetarylazo disperse dyes derived
from 4-hydroxy-2H-1-benzopyran-2-one (4-hydroxycoumarin) as coupling
component and investigation of their absorption spectra. Dyes Pigm 2005;64:
243e9.
[16] Ball P, Nichol CH. Azo-hydrazone tautomerism of hydroxy-azo compounds-
a review. Dyes Pigm 1882;3:5e26.
[17] Peng Q, Li M, Gao K, Cheng L. Hydrazone-azo tautomerism of pyridone azo
dyes: part II: relationship between structure and pH values. Dyes Pigm 1991;
15:263e74.
4. Conclusions
In this study, the enol type coupling component 4-hydroxybenzo
[h]quinolin-2-(1H)-one was synthesized by cyclocondensation
reaction in good yield via two different methods. This compound
was coupled with diazotized aniline derivatives to give the corre-
sponding arylazo-benzoquinolone dyes 1e10 in moderate to good
yields. The dyes exhibited orange to red hues. All synthesized
compounds were characterized by IR,1H NMR, UVevis spectroscopy
and elemental analysis.
All the azo dyes displayed two bands in their electronic
absorption spectra in various organic solvents. The absorption
spectra of these dyes were in consistent with 1H NMR results and
revealed that these compounds do exist in forming hydrazone-keto
form species. The absorption curves of the dyes were very sensitive
to small amounts sodium hydroxide solution, leading to new bands
appearing at shorter wavelengths.
[18] Peng Q, Li M, Gao K, Cheng L. Hydrazone-azo tautomerism of pyridone azo
dyes: part 1: NMR spectra of tautomers. Dyes Pigm 1990;14:89e99.
[19] Lestina GJ, Regan TH. Determination of the azo-hydrazono tautomerism of
some 2-pyrazolin-5-onedyes by means of nuclear magnetic resonance spec-
troscopy and
15N-labeled compounds. J Org Chem 1969;34:1685e6.
[20] Snavely FA, Yoder CH. A study of tautomerism in arylazopyrazolones and
related heterocycles with nuclear magnetic resonance spectroscopy. J Org
Chem 1968;33:513e5.
The acid dissociation constants (pKa) of these azo dyes were also
measured and showed a good correlation with Hammet
constants of substituents on diazo components.
s-
[21] Yoder CH, Barth RC, Richter WM, Snavely FA. A nuclear magnetic resonance
study of some nitrogen-15 substituted azo heterocycles. J Org Chem 1972;37:
4121e3.
[22] Shawali AS, Harb NMS, Badahdah KO. A study of tautomerism in diazonium
Acknowledgment
coupling products of 4-hydroxy coumarin.
J Heterocycl Chem 1985;22:
1397e403.
[23] Kurasawa Y, Hosaka T, Takada A. Substituent effects on the tautomer rations
between the hydrazone imine and diazenyl enamine forms in 3-(arylhy-
drazonomethyl-2-oxo-1,2-dihydroquinoxalines). Correlation of the Hammett
constants sp with the tautomeric equilibrium constants KT. J Heterocycl Chem
1994;31:1661e5.
The authors are very grateful to Islamic Azad University of
Lahijan Branch for providing financial support for this project.
References
[24] Yazdanbakhsh MR, Ghanadzadeh A, Moradi E. Synthesis of some new azo
dyes derived from 4-hydroxy coumarin and spectrometric determination of
their acidic dissociation constants. J Mol Liq 2007;136:165e8.
[25] Buhler U. Hydroxy quinolone monoazo dyestuffs, their preparation and use.
US Patent no. 5760197, 1998.
[1] Zollinger H. Color chemistry: syntheses, properties and application of organic
dyes and pigments. 2nd ed. Weinheim: VCH; 1991.
[2] Christie RM. Colour chemistry. Cambridge CB4 0WF, UK: Royal Society of
Chemistry; 2001.
[26] Moradi-e-Rufchahi EO. Synthesis of 6-chloro and 6-fluoro-4-hydroxyl-2-
quinolone and their azo disperse dyes. Chin Chem Lett 2010;21:542e6.
[27] Moradi-e-Rufchahi EO, Ghanadzadeh A. A study of solvatochromism in dia-
zonium coupling products of 6-flouro 4-hydroxyl-2-quinolone. J Mol Liq
2011;160:160e5.
[3] Herbst W, Hunger K. Industrial organic pigments: production, properties,
applications. 3rd ed. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA; 2004.
[4] Bamfield P, Hutchings MG. Chromic phenomena technological applications of
colour chemistry. 2nd ed. The Royal Society of Chemistry; 2010.
[5] Towns AD. Developments in azo disperse dyes derived from heterocyclic
diazo components. Dyes Pigm 1999;42:3e28.
[6] Funar-Timofei S, Fabian WMF, Kurunczi L, Goodarzi M. Modelling heterocyclic
azo dye affinities for cellulose fibres by computational approaches. Dyes Pigm
2012;94:278e89.
[7] Choi J-H, Hong S-H, Towns AD. High fastness heterocyclic azo disperse dyes
bearing ester functions. Color Technol 1999;115:32e7.
[8] Shawali AS. Synthesis and tautomerism of aryl- and hetaryl-azo derivatives of
bi- and tri-heterocycles. J Adv Res 2010;1:255e90.
[28] March J, Smith MB. March’s advanced organic chemistry: reactions, mecha-
nisms, and structures. 6th ed. Wiley and Sons; 2007.
[29] Shawali SA, Zeid IF, Abdelkader HM, Elsherbini AA, Altalbawy FMA. Synthesis,
acidity constants and tautomeric structure of 7-arylhydrazono[1,2,4][1,3,4]
thiadiazines in ground and exited states. J Chin Chem Soc 2001;48:65e72.
[30] Seferoglu Z, Aktan E, Ertan N. Spectral characterization and computational
studies of some novel phenylazoindol-2-one dyes. Color Techol 2009;123:
342e53.
[31] Van Uitert LG, Haas CG. A method for determining thermodynamic equilib-
rium constants in mixed solvents. J Am Chem Soc 1953;75:451e5.
[9] Raposo MMM, Castro CR, Fonseca AMC, Schellenberg P, Belsley M. Design,
synthesis, and characterization of the electrochemical, nonlinear optical