A study of Solvatochromism in diazonium coupling products of 6-flouro 4-hydroxyl-2-quinolone

Article abstract of DOI:10.1016/j.molliq.2011.03.011

6-flouro 4-hydroxyl-2-quinolone was synthesized from cyclocondensation of corresponding dianilide and subsequently used as a potent coupling component with some diazotized aromatic amines. The prepared azo dyes were characterized by UV-vis, FT-IR, ^1<

Full text of DOI:10.1016/j.molliq.2011.03.011

Journal of Molecular Liquids 160 (2011) 160–165
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
A study of Solvatochromism in diazonium coupling products of
6-flouro 4-hydroxyl-2-quinolone
b
Enayat O'llah Moradi-e-Rufchahi a, , A. Ghanadzadeh
⁎
a
Department of Chemistry, Faculty of Science, Islamic Azad University, Lahijan Branch, Lahijan, Iran
b
Department of Chemistry, Faculty of Sciences, Guilan University, Rasht, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
6-flouro 4-hydroxyl-2-quinolone was synthesized from cyclocondensation of corresponding dianilide and
subsequently used as a potent coupling component with some diazotized aromatic amines. The prepared azo
dyes were characterized by UV–vis, FT-IR, 1H NMR spectroscopic techniques and elemental analysis. The
solvatochromism of dyes was evaluated with respect to wavelength of maximum absorption (λmax) in six
solvents: acetic acid, methanol, chloroform, acetonitrile, dimethyl sulfoxide and dimethyl formamide. The
color of the dyes is discussed with respect to the nature of substituents on the benzene ring. 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.% ethanol–water medium at room temperature and correlated with the
substituent constant, σx.
Received 20 January 2011
Received in revised form 17 February 2011
Accepted 17 March 2011
Available online 23 March 2011
Keywords:
Azo dyes
Heterocyclic coupling components
Solvatochromism
Diazotization
Hydroxyl quinolone
Substituent effects
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
solutions was controlled to be 0.1 using a NaCl solution. The structures
of coupling component and prepared dyes are depicted in Schemes 1
Heterocyclic azo dyes have attracted considerable interest and
have played an important role in the development of the chemistry of
dyes and dyeing process [1–6]. In this regard, azo dyes based on
heterocyclic coupling components have been developed and reported
in many patents and papers [7–12]. The resultant dyes have higher
tinctorial strength and give brighter dyeing than those derived from
benzene based coupling components [13–17]. Of these compounds,
very few comparable investigations were carried out using hydroxyl
quinolone derivatives. These derivatives afford very electron rich
coupling components and consequently can provide a pronounced
bathochromic effect compared to the corresponding benzenoid
compounds. Izzet sener et al. by using some heterocyclic amine
derivatives as diazo components, investigated preparation and the
tautomerism in azo dyes synthesizes from 4-hydroxy-2-quinolone
[18]. According to the importance of these compounds, the present
work reports the synthesis of 6-flouro-4-hydroxyl-2-quinolone and
using it as coupling component in reaction with some diazotized
aromatic amines as diazo components. The effects of solvents,
substituents, acid and base on the visible absorption maxima of the
dyes were also reported. The acid dissociation constants of the dyes
were determined using electronic spectroscopic method in 80% (v/v)
ethanol–water mixtures at 25 2 °C. The ionic strength of the
and 2.
2. Results and discussion
2.1. Synthesis and characterizations
6-flouro-4-hydroxyl-2-quinolone (I) were prepared by refluxing 2
equiv of 4-flouro aniline with dimethyl malonate and cyclocondasa-
tion of resulting dianilide in methane sulfunic acid containing 10% of
phosphorus pentoxide (instead of AlCl3 used by Zeigler) [19]
(Scheme 1).
The IR spectra of compound (I) showed strong absorptions at 3500–
3150 cm−1 for the OH and amide (NH) groups, and at 1637 cm−1 for
the C=O group. The 1H NMR spectrum (DMSO-d6) of compound (I)
revealed a broad peak at 11.29 ppm (1 H, b, NH), a singlet at 5.77 ppm
(1H) for the C=C–H of pyridone ring, a dd at 7.27 ppm (1H, J=8.9,
4.7 Hz), a multiplet at 7.38–7.45 ppm (2H) for the aromatic protons
(Aro.-H). The proton decoupled 13C NMR of this compound exhibited 9
distinct resonances at 164.16 ppm (C=O), 162 ppm ( C–OH), 157 ppm
(C–F), 136 ppm (C), 119 ppm (CH), 117 ppm (CH), 116 ppm (C),
108 ppm (CH) and 99.5 ppm ( CH) in agreement with the quinolone
structure.
The phenylazoquinolone dyes 1–14 were prepared by coupling 6-
flouro-4-hydroxyl-2-quinolone with diazotized aniline derivatives
(Scheme 2). The dyes may exist in six possible tautomeric forms,
named as azo-enol-keto (T1), azo-enol (T2), azo-enol (T3), hydrazone-
⁎
Corresponding author. Tel./fax: +98 1312250309.
E-mail address: ena_moradi@yahoo.com (E.O. Moradi-e-Rufchahi).
0167-7322/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2011.03.011

E.O.' Moradi-e-Rufchahi, A. Ghanadzadeh / Journal of Molecular Liquids 160 (2011) 160–165
161
NH2
OH
given in Table 2. The visible absorption spectra of the dyes did not show
regular variation with the polarity of solvents.
F
The electronic absorption spectra of the compounds 1–14 in all
used solvents revealed a shoulder in the region 347–411 and a band in
396–458 nm (e.g. Fig. 1 for dye 13). It can be suggested that dyes may
exist as a mixture of two tautomeric forms which are in equilibrium.
These results seem to be compatible with the hydrazone rather than
the azo forms depicted in Scheme 3 and are consistent with the
findings on tautomerism from 1H NMR conclusions. It was also
observed that the λmax values of dyes didn't change significantly in
various solvents. This behavior of dyes suggests that the molecules are
involved in strong intramolecular hydrogen bond.
It was also observed that the absorption curves of the dyes were
not significantly sensitive to acid but is sensitive to base. The
absorption spectra of the dyes in methanol didn't change significantly
when 0.1 M HCl was added and the absorption curves of the dyes
resembled those in acetic acid. The λmax of the dyes showed
hypsochromic shifts when 0.1 M KOH was added to each of the dye
solutions in methanol. A typical example is shown in Fig. 2.
1) CH2(CO2Me)2, reflux
2
2) CH SO H P O
/
3
3
2
5
N
H
O
150oC
F
I
Scheme 1. Preparation of 6-flouro-4-hydroxyl-2-quinolone (I).
keto-enol (T4), hydrazone-keto (T5) and hydrazone-keto (T6) as
shown in Scheme 3.
As it can be seen in Table 1, the infrared spectra of all the dyes (in
KBr) showed broad intense amide (NH–C=O) and hydroxyl (OH)
bands at 3436–3288 cm−1. The IR spectra also showed an intense
band at 1680–1635 cm−1, which was assigned to amide carbonyl
group.
The 1H NMR spectrum of all the dyes measured in DMSO-d6 at
25 °C (Table 1) showed a multiplet from 7.18–8.50 ppm for aromatic
protons, a singlet at 2.50 ppm (–CH3, 3), a singlet at 2.43 ppm (–CH3,
12), 2.49 ppm (–CH3, 13) and 3.82 ppm (–CH3, 14). The broad peaks at
16.34–14.84 ppm were assigned to tautomeric hydrazone proton
(=N–NH–).The spectra of the studied compounds 1–14 provide
additional evidence that they have the Hydrazone-keto structures T5
and T6 rather than the enol structures T1–T4. For example 1H NMR
spectrum of 10 in deuterated dimethyl sulfuxide exhibits two
signals at 15.01 and 15.60 ppm with nearly equal integration ratio.
Other compounds in these series show similar patterns (Table 1).
These signals undoubtedly correspond to the hydrazone NH
proton resonance related to hydrazone-keto forms T5 and T6. Further
evidence for this assignment is provided by the observation that 1H
NMR spectrum of the 15N-phenylhydrazone derivatives of some azo
heterocycles were reported to show two doublets centered at similar
regions with J=93–100 Hz [20] indicating that the proton is attached
to nitrogen atom. It was reported that the hydroxyazo OH proton
resonance comes 3–5 ppm higher than NH proton resonance, hence,
the OH proton resonance signal of enol forms is expected to be in
region 9–12 ppm [21,22].Two attributed broad singlet peaks at 11.22–
11.36 and 11.40–11.56 ppm for amide (–NH) groups are related to
amide protons of two types of tautomeric forms T5 and T6.
2.3. Substituent effects
As far as absorption maxima are concerned, λmax values are
directly proportional to the electronic power of the substituents in the
benzenoid system. As Fig. 3 depicts, a reasonable linear correlation
exists between the difference in wavelength (Δλmax) relative to that
of unsubstituted dye 11 and the Hammett substituent constants (σm
and σp) for relevant groups.
As it is apparent in Table 2, the introduction of electron donating
methoxy group in the benzene ring resulted in bathochromic shifts in
all solvents with respect to electron-accepting nitro, cyano and flouro
groups ( e.g. for dye 14 Δλ=35 nm relative to dye 1, Δλ=41 nm
relative to dye 2 in methanol). The introduction of electron-donating
methyl (m-, p-) groups in the benzene rings resulted in bathochromic
shifts in all solvents. The iodo (p-) group in the benzene ring resulted
in bathochromic shifts in all solvents.
The introduction of electron-withdrawing nitro (m-) group in the
benzene ring resulted in hypsochromic shifts in all solvents. The nitro
(p-) group in the benzene ring resulted in bathochromic shifts in
acetic acid and chloroform but did not change significantly in the
other solvents. The position of all groups did not show a regular
variation in all solvents. Fig. 4 compares the absorption spectra of
some of the dyes with different substituents in chloroform.
2.2. Solvent effect
The absorption spectra of the prepared dyes were measured in various
solvents at a concentration of approximately10−5 to 10−6 Mol. L−1 and
were run at different concentrations. The dyes were completely soluble in
DMSO. Therefore, more dilute solutions were prepared, and it was found
in all cases that λmax was unaffected by the dye concentration. The stock
solutions of each dye were accurately prepared in DMSO and dilutions of
these stocks were used for absorption measurements. The results are
2.4. Determination of pKa values of the azo dyes
The ionization constants (pKa's) of 1 to 14 were determined in
80 vo1.% ethanol–water medium at 25 2 °C and a μ of 0.1 using
spectrophotometric titration method and are given in Table 3. Each
compound exhibits two bands in region of 347–411 nm for anionic
and 396–458 nm for the molecular species. As the pH value of the
N2+Cl-
OH
OH
X
F
F
1) pH= 10-11
2) H+
N N
O
+
N
O
H
X
N
H
I
1-14
1 X= p-NO2
6 X= p-Cl
11 X= -H
2 X= p-CN
7 X= p-Br
3 X= p-COCH3
4 X= p-F
5 X= m-NO2
10 X= p-I
8 X= m-Cl
9 X= m-CF3
12 X= m-CH3
13 X= p-CH3
14 X= p-OCH3
Scheme 2. Synthetic routes for the preparation of azo dyes 1–14.

162
E.O.' Moradi-e-Rufchahi, A. Ghanadzadeh / Journal of Molecular Liquids 160 (2011) 160–165
H
Ar
H
Ar
O
N
N
O
N
N
OH
F
F
F
N
O
Ar
N
H
N
H
O
N
OH
N
T3
T2
T1
H
Ar
O
O
N
O
H
F
N
O
F
N
Ar
F
N
N
Ar
N
H
H
N
H
N
H
O
N
O
T4
T5
T6
Scheme 3. Possible tautomeric forms for the synthesized azo dyes.
solution increased, the height of the former band increases and
simultaneously that of the latter decreased. From the optical spectra
(Fig. 5), in each case, the isobestic points indicate that two species are
in equilibrium (Scheme 4).
A digital pH meter Genway model 3505 was employed for
determination of pH. The instrument was accurate to 0.01pH unit. It
was calibrated using two standard Genway buffer solutions at pH 4.01
and 7.00. The pH meter readings (B) recorded in ethanol–water
solutions were converted to hydrogen ion concentration [H+] by
means of the widely used relation of Van Uitert and Haas [23], namely
where log U, 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.% ethanol–water at 25 2 °C. The value of log U, was found to be
−0.235.
−log ½Hꢀþ = B + log UH
The acid dissociation constants of 1 to 14 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 5×10−5 M in the azo dye,
0.1 M in HCI, and contained 80% volume ethanol. The test solution
(50 ml) was then transferred to a water-jacketed thermostatted cell.
The pH of the solution was measured and the spectrum was recorded
Table 1
Spectral data for dyes 1–14.
Dye no. FT-IR (cm−1, in KBr)
1H NMR (δ, ppm)
vO―H vN―H vC=O vAro.-H Aro.-H
N―H
Alip.-H
Hydrazone amide
1
3429 3191 1687 3033 8.34 (2H , d, J=5 Hz), 7.85 (1 H, d, J=5 Hz), 7.92 (1 H, d, J=5 Hz), 7.64–7.26 (3H, m, overlapped)
3467 3193 1680 3042 7.92 (2H , d, J=8.4 Hz), 7.82–7.22 (5H, m, overlapped)
–
14.48
15.30
14.88
15.38
11.36
11.57
11.28
11.47
11.28
11.49
11.23
11.42
11.30
11.41
11.25
11.45
11.23
11.43
11.26
11.45
11.29
11.48
11.23
11.44
11.23
11.42
11.20
11.38
11.21
11.40
11.24
11.44
2
–
3
3422 3188 1676 3031 8.10–7.21 (7H, m, overlapped)
2.50 (3H, s) 15.07
15.64
1720
4
3410 3188 1683 3056 7.75 (2H, dd,J=9, 11.5 Hz), 7.64–7.34 (4H, m, overlapped), 7.25(1H, m)
–
–
–
–
–
–
–
–
15.19
15.92
14.96
15.48
15.10
15.76
15.72
15.07
15.58
14.97
15.02
15.60
15.73
15.07
15.22
15.95
5
3405 3186 1692 3044 8.50 (1H, s), 8.08 (2H, m, overlapped), 7.75 (1H, t, J=8.2 Hz), 7.63–7.21 (3H, m, overlapped)
3411 3187 1688 3041 7.73 (2H, d,J=8.6 Hz), 7.64–7.52 (4H, m, overlapped), 7.27 (1H, m)
3407 3186 1689 3033 7.69–7.63 (5H, m, overlapped), 7.53(1H, dd, J=3, 11 Hz), 7.23(1H, m)
3435 3200 1670 3060 7.80–7.21(7H, m, overlapped)
6
7
8
9
3420 3190 1684 3056 8.09 (1H, s), 8.03–7.21 (6H, m, overlapped)
3422 3196 1674 3042 7.86–7.20 (7H, m, overlapped)
10
11
12
13
14
3423 3204 1678 3054 7.73–7.21(8H, m, overlapped)
3418 3211 1666 3020 7.70–7.22 (7H, m, overlapped)
2.43 (3H,s) 15.31
16.05
2.38 (3H, s) 15.30
16.08
3.80 (3H, s) 15.44
16.34
3422 3150 1680 3065 7.66–7.20 (7H, m, overlapped)
3417 3145 1665 3064 7.71–7.10 (7H, m, overlapped)

E.O.' Moradi-e-Rufchahi, A. Ghanadzadeh / Journal of Molecular Liquids 160 (2011) 160–165
163
Table 2
Influence of solvents on λmax(nm) of the prepared dyes.
Dye
X
DMSO
DMF
CH3CN
CH3OH
CH3COOH
CHCl3
1
2
3
4
5
6
7
8
p-NO2
p-CN
p-COCH3
p-F
m-NO2
p-Cl
p-Br
m-Cl
m-CF3
p-I
-H
408s, 424
410s, 419
390s, 409
396s, 416
383s, 404
391s, 424
391s, 427
398s, 424
398s, 416
396s, 436
389s, 419
405s, 431
397s, 438
398s, 452
411s, 422
407s, 426
401s, 416
397s, 424
380s, 400
403s, 425
394s, 428
395s, 402
398s, 420
399s, 432
391s, 424
404s, 429
392s, 435
401s, 452
405s, 419
397s , 403
397s, 418
393s, 419
374s, 393
391s, 423
394s, 425
392s, 407
395s, 419
395s, 431
393s, 421
392s, 427
392s, 433
391s, 450
406s, 421
397s, 415
402s, 427
397s, 426
390s, 395
396s,430
395s, 432
391s, 419
400s, 418
399s, 436
391s, 425
400s, 431
392s, 437
400s, 456
402s, 425
399s, 421
404s, 433
398s, 430
388s, 413
395s, 433
394s, 435
392s, 424
400s, 413
398s, 441
390s, 429
396s, 433
391s, 438
396s, 458
405s, 423
400s, 416
401s, 433
398s, 432
379s, 396
394s, 435
392s, 438
390s, 426
397s, 430
394s, 441
390s, 432
402s, 436
400s, 442
396s, 459
9
10
11
12
13
14
m-CH3
p-CH3
p-OCH3
s=shoulder.
1.4
1.2
1
40
30
20
10
Δλ(nm)
p-OCH3
1
2
DMSO
CHCl3
p-I
6
5
4
p-Cl
p-Br
3 CH3COOH
p-CH3
-0.1
σ-constant
m-CH3
0
0.8
0.6
0.4
0.2
0
4
5
6
CH3CN
DMF
CH3OH
-H
-0.3
0.1
0.3
0.5
0.7
m-Cl
-10
3
2
p-CN
-20
-30
-40
1
m-NO2
300
400
500
600
Fig. 3. Relation between Hammet constant (σm and σp) and Δλmax for the prepared azo
dyes in CHCl3.
Wavelength(nm)
Fig. 1. Absorption spectra of dye 13 in various solvents.
compound was subjected to three pKa determinations, and the average
values, given in Table 4 are within 0.05 pKa units.
using either the ionic medium or the corresponding aqueous ethanol as
a blank. In both cases identical absorbance values in the employed
wavelength range were obtained. 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 run 10–15
pH readings were taken and the value of pKa was calculated from each
reading using the equation: pKa=pHi+log(Ab−Ai)/(Ai−Aa); 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
Plotting pka values against Hammet constants (σm and σp) yields
the graph shown in Fig. 6. The equation of such a correlation is:
pKa = 8:00−1:95 σ
Since the electron density on the aromatic rings can be reduced by
the electron withdrawing groups such as ―NO2, ―CN and ―CF3, the
pKa values show that the acidity of the hydroxyl group increases.
While ―OMe and ―CH3 groups attached to the compounds 12–14
can decrease the acidic character, due to their electron donating
ability which destabilizes anionic form of the azo dyes.
1
1 MeOH
2 MeOH+HCl
3 AcOH
0.8
0.6
0.4
0.2
0
1
13
4 MeOH+ KOH
14
1
10
3
2
2
11
0.5
0
4
1
300
350
400
450
500
550
600
300
350
400
450
500
550
600
Wavelength(nm)
Wavelength(nm)
Fig. 2. Absorption spectra of dye 11 in acidic and basic solutions.
Fig. 4. Absorption spectra of dyes 1, 2, 10, 11, 13 and 14 in chloroform.

164
E.O.' Moradi-e-Rufchahi, A. Ghanadzadeh / Journal of Molecular Liquids 160 (2011) 160–165
Table 3
3.2. Preparation of N, N′-Di-(4-flourophenyl)malonamide
Acidic dissociation constant (pKa) and absorption maxima (λmax) of prepared azo dyes
in different pH values.
A mixture of 4-flouroaniline (100 mmol, 9.6 ml) with dimethyl-
malonate (50 mmol, 5.7 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. Yield 91%, white solid, m.p.
214–216 °C (reported 212 °C [19]).
Dye pH=1 pH=3 pH=5 pH=7 pH=9 pH=11 pH=13 pKa
no.
(
0.05)
1
2
3
4
5
6
7
8
425
419
430
431
404
433
434
420
412
438
430
437
440
456
425
419
429
428
408
432
434
423
412
436
429
432
439
458
425
419
429
430
410
433
433
423
416
439
431
434
438
457
425
420
430
431
412
433
434
423
416
435
429
433
440
457
420
401
405
484
385
390
433
387
386
393
431
433
439
457
412
399
399
375
382
382
391
380
379
386
426
433
438
380
399
400
399
376
383
381
384
376
380
386
374
377
376
380
6.75
7.21
7.80
6.79
6.99
6.86
7.49
6.93
6.83
7.03
7.68
7.86
8.85
9.54
3.3. Synthesis of 6-flouro-4-hydroxyquinoline-2-(1H)-one
N, N′-Di-(4-flourophenyl)malonamide (0.576 g, 2 mmol) was
dissolved in 3.5 ml methanesulfunic acid, which contains 10% of
phosphorus pentoxide, and was then heated in an oil bath for 90 min
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 20 ml of
sodium hydroxide solution 0.1 mol∙L−1 and undissolved material was
filtered. The filtrate neutralized with concentrated hydrochloric acid
and the precipitate was recrystallized from ethanol to afford 6-flouro-
4-hydroxyquinoline-2-(1H)-one as creamy crystals.
9
10
11
12
13
14
0.4
pH
0.35
0.3
1
2
3
4
5
6
7
3.0
4.0
5.0
7.0
9.0
11.0
13.0
3.4. Preparation of phenylazohydroxyquinolone dyes
1
2
3
0.25
0.2
To a suspension of the aromatic amine (5.0 mmol) in water
(10 mL) concentrated hydrochloric acid (24 mmol, 2 mL) was
added until the mixture was homogeneous. The solution was
cooled and kept at 0–5 °C in an ice bath and diazotized by addition
of a solution of sodium nitrite (5.2 mmol, 0.345 g) in water (3 mL),
followed by stirring for 30 min at 0–5 °C. To a solution of 6-flouro-
4-hydroxyquinoline-2-(1H)-one (0.895 g) in sodium hydroxide
(20 mmol) and water (15 mL) a solution of the diazonium salt at
0–5 °C was slowly added. The pH of the reaction mixture was
maintained at 10–11 by adding 2.5% sodium hydroxide solution.
The resulting mixture was stirred for 2 h at 0–5 °C. The progress of
the reaction are followed by TLC, using DMF as developing solvent
and silica gel TLC plates as the stationary phase. In the end of
procedure the pH of reaction mixture was regulated at 4–5 by
addition of 10% hydrochloric acid solution. The resulting solid was
filtered, washed with cold ethanol and dried. The crude product was
purified using the recrystallization method. The selected physical
properties of dyes were measured and listed in Table 4.
7
6
4
0.15
0.1
5
0.05
0
300
400
500
600
Wavelength(nm)
Fig. 5. Absorption spectra of the dye 4 (R=p-F) at different pH values.
3. Experimental
3.1. General
The chemicals used in the synthesis of all dyes were obtained from
Merck Chemical Company and Aldrich Chemical Company and were
used without further purification. The absorption spectra of the
compounds were scanned on a Cary UV–vis Double-beam spectropho-
tometer (Model 100). Infrared spectra (in KBr pellets) were recorded on
a Shimadzu-8400 FT-IR spectrometer. 1H and 13C NMR spectra were
recorded on a Bruker 500 MHz spectrometer in DMSO-d6 using TMS as
an internal reference. Microanalyses for C, H and N were performed on a
PerkinElmer 2400(II) elemental analyzer. Melting points were deter-
mined on a Barnstead Electrothermal 9100 melting point apparatus and
uncorrected.
4. Conclusion
In this research 6-flouro 4-hydroxyl-2-quinolone and its disperse
azo dyes have been synthesized. Characterization and absorption
ability of 14 novel phenylazoquinolone based dyes (1–14) were
studied. Absorption spectra results of these dyes revealed that these
compounds do exist in forming hydrazone-keto form species. The
dyes exhibited yellow to red hues. The spectrophotometric results
showed that in quinolone section, in spite of hydroxyl group as an
electron donor, the stronger electron withdrawing nature of lactame
O-
OH
N
F
Ka
F
N
O
N
X
H3O+
N
+
H2O
+
X
N
O
H
N
H
Scheme 4. Acidic dissociation equilibrium of the prepared compounds.

E.O.' Moradi-e-Rufchahi, A. Ghanadzadeh / Journal of Molecular Liquids 160 (2011) 160–165
165
Table 4
The physical properties of the dyes used in this study.
Dye
Color
mp (°C)
Recrystallization
% C
% H
% N
Yield (%)
Calcd.
Found
Calcd.
Found
Calcd.
Found
1
2
3
4
5
6
7
8
Orange
Reddish orange
Brown
Dark yellow
Clear yellow
Luster yellow
Luster yellow
yellow
Yellow
Brown
Dark brown
Brown
Brown
N350
DMF
DMF
DMF
DMF
54.89
62.34
62.77
59.80
54.89
56.72
49.75
56.72
54.71
44.0
54.82
62.61
61.98
60.01
54.80
56.91
49.61
56.96
54.11
44.52
64.74
64.52
64.18
60.98
2.74
2.92
3.72
3.01
2.74
2.85
2.50
2.85
2.58
2.22
3.56
4.07
4.07
3.86
2.69
2.99
3.61
2.91
2.71
2.74
2.42
2.76
2.64
2.09
3.47
4.12
4.11
3.78
17.07
18.18
12.92
13.95
17.07
13.23
11.60
13.23
11.96
10.27
14.84
14.14
14.14
13.41
17.19
17.92
13.02
13.74
17.25
13.02
11.43
13.01
11.76
10.05
14.22
14.22
14.22
13.11
70
75
77
88
79
75
80
70
90
72
73
74
68
66
327–328
294–296
296–297
314–316
N350
336–338
300 (dec.)
286–288
346–347
N350
DMF
DMF/H2O
DMF/H2O
DMF/H2O
DMF/H2O
DMF/H2O
Ethanol
Ethanol
Ethanol
Ethanol
9
10
11
12
13
14
63.60
64.64
64.64
61.34
260–262
270 (dec.)
N350
Red
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10
p-OMe
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p-CH3
m-CH3
9
pKa =8.0006 -1.9553 σ
8
-H
p-Br
p-Cl
p-CN
m-NO2
p-F
m-Cl
7
6
p-I
0.2
p-NO2
m-CF3
σ-constant
-0.4
-0.2
0
0.4
0.6
0.8
1
Fig. 6. Relation between Hammet constant (σm and σp) and pKa values for the prepared
dyes.
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groups on diazo component the push–pull effect is better than others.
The acid dissociation constants (pKa) of these azo dyes were also
measured and showed a good correlation with Hammet σ-constants
of substituents on diazo components.
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