Hetarylazoindoles 1. Synthesis, characterization, and spectroscopic properties of new hetarylazoindole dyes

Article abstract of DOI:10.1080/10426500701637575

Synthesis of some new hetarylazoindole dyes have been carried out by diazotization of 5-substituted 2-aminothiazoles in nitrosylsulphuric acid and coupling with various 2- and 1,2-disubstituted indole derivatives. The structures of the dyes were confirmed by UV-VIS, FT-IR, and 1H NMR spectroscopy as well as by LC-MS or MS spectrometry and elemental analyses. The solvatochromism of the dyes was evaluated with respect to the absorption properties in various solvents. Absorption maxima of the dyes generally did not changed with the polarity of the solvent. The color of the dyes is discussed in relation to the substituents in the thiazole ring. The effects of an acid or a base on the visible absorption maxima of the dyes are also reported. In addition, the absorption spectra of the dyes were compared with those of corresponding model compounds, which do not exhibit azo-hydrazone tautomerism. Copyright Taylor & Francis Group, LLC.

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Hetarylazoindoles 1. Synthesis,
Characterization, and
Spectroscopic Properties of
New Hetarylazoindole Dyes
Zeynel Seferoĝlu a & Nermin Ertan a
a Gazi University, Faculty of Arts and Science,
Department of Chemistry , Ankara, Turkey
Published online: 09 May 2008.
To cite this article: Zeynel Seferoĝlu & Nermin Ertan (2008) Hetarylazoindoles 1.
Synthesis, Characterization, and Spectroscopic Properties of New Hetarylazoindole
Dyes, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:5, 1236-1251,
DOI: 10.1080/10426500701637575
To link to this article: http://dx.doi.org/10.1080/10426500701637575
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Phosphorus, Sulfur, and Silicon, 183:1236–1251, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701637575
Hetarylazoindoles 1. Synthesis, Characterization,
and Spectroscopic Properties of New Hetarylazoindole
Dyes
ˇ
Zeynel Seferoglu and Nermin Ertan
Gazi University, Faculty of Arts and Science, Department of Chemistry,
Ankara, Turkey
Synthesis of some new hetarylazoindole dyes have been carried out by diazotiza-
tion of 5-substituted 2-aminothiazoles in nitrosylsulphuric acid and coupling with
various 2- and 1,2-disubstituted indole derivatives. The structures of the dyes were
confirmed by UV-VIS, FT-IR, and 1 H NMR spectroscopy as well as by LC-MS or
MS spectrometry and elemental analyses. The solvatochromism of the dyes was
evaluated with respect to the absorption properties in various solvents. Absorption
maxima of the dyes generally did not changed with the polarity of the solvent.
The color of the dyes is discussed in relation to the substituents in the thiazole
ring. The effects of an acid or a base on the visible absorption maxima of the dyes
are also reported. In addition, the absorption spectra of the dyes were compared
with those of corresponding model compounds, which do not exhibit azo-hydrazone
tautomerism.
Keywords Hetarylazo indole dyes; heterocyclic disperse dyes; thiazolylazo dyes; solvent
effect; substituent effect
INTRODUCTION
Azo dyes with heterocyclic coupling components have been investigated
to produce bright and strong color shades ranging from yellow to green-
ish blue on synthetic fabrics. These results led to commercial prod-
ucts, which replaced the conventional azobenzene, disperse dyes.1–3
There are reports of some azo dyes derived from heterocycles, such
as pyridone, pyrazolone quinazoline-4-one, quinoxaline, and thiophene
derivatives.4–10 The visible absorption maxima of these dyes show
wavelength mostly in the range of yellow to orange, due to poorly
Received 5 May 2007; accepted 19 August 2007.
We are very grateful to Gazi University Research Fund for providing financial support
for this project (grant no. 05/2003-58).
Address correspondence to Nermin Ertan, Gazi University, Faculty of Arts and
Science, Department of Chemistry, 06500 Teknikokullar, Ankara, Turkey. E-mail:
nertan@gazi.edu.tr
1236

Hetarylazoindole Dyes
1237
delocalized electrons in the rings of the heterocycles. However, it has
also been observed that some of these dyes show deeper color strength
and shades such as red or violet.[4,9,11,12] On the other hand, the
use of heteroaromatic amines as diazo components in the genera-
tion of disperse dyes having essentially color deepening effect is well
established.[11,13,14]
Heterocyclic azo compounds tend to be more strongly affected by
solvents than those based on azobenzene; this is a consequence of
the increased polarity of the system, especially in the excited state.
We have previously reported the synthesis of some novel heterocyclic
systems such as hetarylazopyridones,15 hetarylazonaphto-quinones,16
hetarylazopyrazolones,17 and hetarylazoquinolines,18 which exhibited
the azo-hydrazone tautomerism and a strong solvent dependency in
their absorption spectra. Although many papers described the synthe-
sis and some properties of phenylazo indolecompounds,19–22 only a few
hetarylazo indole compounds and their alkyl cations were synthesized
and used in synthetic fibers in patent literature.22–35 These dyes have
not been characterized in these patents. In our previous papers on azo
indoles, we have described the synthesis and the structural and spectro-
scopic properties of some hetarylazo and phenylazo indole dyes obtained
by diazotization of some heterocyclic and carbocyclic amines using 2-
and 1,2-disubstituted indoles as coupling components.36–46 We observed
a marked difference in the absorption maxima of the dyes when the
polarity of the solvent was increased. In continuation of these investi-
gations, we report here the solvatochromic behaviour of bis-hetarylazo
compounds, which do not exhibit the azo-hydrazone tautomerism, and
on the evaluation of their absorption spectra in the visible range with
respect to the influence of the solvent. For this purpose we have pre-
pared three series of 3-thiazolylazo indole derivatives (1a–d, 2a–d, and
3a–d) using 2-methylindole, 1,2-dimethylindole, 2-phenylindole and 1-
methyl-2-phenylindole as coupling components. The dyes 1b, 1d, 2b,
2d, 3b, and 3d were used as model compounds. In this study, some of
the dyes prepared (1a, 1c, 1d, and 3a, Scheme 1) have been mentioned
in the patent literature, but have not been characterized. The visible ab-
sorption spectra of these compounds in various solvents are discussed.
The influences of the substituents at the 5-position of thiazole ring and
at the 2-position of the indole nucleus on the visible absorption maxima
of the dyes have been evaluated.
RESULTS AND DISCUSSION
The hetarylazoindole dyes (1a–d, 2a-d, and 3a–d) were pre-
pared by coupling of 2-methyl, 1,2-dimethyl, 2-phenyl and

ˇ
1238
Z. Seferoglu and N. Ertan
CH3
S
N
S
N
N
N
N
N
R2
R2
N
N
R1
R1
1a R1 = H, R2 = CH3
2a R1 = H, R2 = CH3
b R1 = CH3, R2 = CH3
c R1 = H, R2 = Ph
b R1 = CH3, R2 = CH3
c R1 = H, R2 = Ph
d R1= CH3, R2 = Ph
d R1 = CH3, R2 = Ph
NO2
S
N
N
N
R2
N
R1
3a R1 = H, R2 = CH3
b R1 = CH3, R2 = CH3
c R1 = H, R2 = Ph
d R1 = CH3, R2 = Ph
SCHEME 1 Structures of dyes 1–12.
1-methyl-2-phenylindole with diazotized 2-aminothiazole, 2-amino-5-
methylthiazole and 2-amino-5-nitrothiazole in nitrosyl sulphuric acid
(Scheme 1). The structures of the dyes were confirmed by UV-VIS,
FT-IR, and 1H NMR spectroscopy as well as by LC-MS or MS spectrom-
etry and elemental analyses. The dyes prepared from 2-methylindole
(1a, 2a, and 3a) and 2-phenylindole (1c, 2c, and 3c) may exist in two
possible tautomeric forms, namely the azo form A, and the hydrazone
form B (Scheme 2). The deprotonation of the two tautomers leads to
the common anion C.

Hetarylazoindole Dyes
1239
S
N
S
H
N
N
N
N
N
CH3
CH3
N
H
N
(B)
(hydrazone)
S
(A)
(azo)
N
N
N
CH3
N
..
-
(C)
(anion)
SCHEME 2 Azo-hydrazone tautomeric forms and anionic form of hetarylazo
indole dyes (1a and c, 2a and c, 3a and c).
The infrared spectra of the dyes prepared from 2-methylindole (1a,
2a, and 3a) and 2-phenylindole (1c, 2c, and 3c) showed a weak and
broad band within the range 3454-3278 cm−1 due to the -NH moi-
ety of the indole ring. The broadening of this band suggests that this
group is strongly involved in intermolecular hydrogen bonding in the
solid state.47 This band was not observed in the infrared spectra (in
KBr) of the dyes prepared from 1,2-dimethylindole and 1-methyl-2-
phenylindole. Characteristic bands at 3114–3031 cm−1 for aromatic –
1
CH and at 2972–2903 cm−1 for aliphatic CH were observed. The H
NMR spectra of the dyes prepared from 2-methylindole (1a, 2a, and
3a) and from 2-phenylindole (1c, 2c, and 3c) showed for the -NH group
a broad signal in the range 8.95–13.82 ppm, depending on the solvent
used. In the 1H NMR spectrum of 1c in CDCl3 the signal at 8.95 ppm can
be attributed to the -NH proton at 1-position of the indole ring. When
the 1H NMR spectrum of 1c was measured in DMSO-d6, the NH sig-
nal shifted to lower field by 3.88 ppm and appeared at 12.83 ppm.47 On
1
the other hand, the H NMR chemical shift of the -NH proton in 1a,
1c, 2a, 2c, 3a and 3c in DMSO-d6 and CDCl3/DMSO-d6 mixtures was
within the range of 11.64–13.82 ppm. This downfield shift in DMSO-d6
is probably due to intermolecular hydrogen bonding between the indole
NH and DMSO. Assignments for the signal of the NH proton of the
indole ring are in accord with data for analogous indole derivatives.48

ˇ
Z. Seferoglu and N. Ertan
1240
It was reported that the resonance of the hydrazone NH proton in
o- and p-hydroxyazo compounds appears at approximately 13.0–16.0
ppm.49–50 These results suggest that the dyes 1a, 1c, 2a, 2c, 3a, and
3c are predominantly in the azo form in the solid state and in solution
(Scheme 2).
Solvent Effect on the Absorption Spectra
The absorption spectra of the new dyes (1a–d, 2a–d, and 3a–d) were
recorded in various solvents at a concentration range of approximately
10−6–10−8 M and at different concentrations because of solubility prob-
lems. The results are given in Table I. Although many papers on azo-
hydrazone tautomerism of hydroxyazo dyes have been published, the
assignment of the tautomeric structure is difficult because the tau-
tomeric equilibrium strongly depends on the nature of the correspond-
ing medium. On the other hand, it was observed that the absorption
spectra of hetarylazo dyes exhibited a strong dependency on the sol-
vent. In order to settle this assignment problem, we prepared 1,2-
disubstituted indole derivatives of the dyes as model compounds and
compared their absorption spectra in various solvents with those of the
other dyes. The model compounds exist in the azo form and their absorp-
tion maxima in different solvents were found to show little dependency
on the solvent except in the case of acetic acid (Table I). For example,
λmax for 1b are 438 nm in chloroform, 455 nm in acetic acid, 444 nm in
methanol, 438 nm in acetonitrile, 443 nm in DMF, and 449 nm in DMSO.
Similar results were observed for λmax of the other model compounds.
The small shifts in λsmax of the model compounds in different solvents
TABLE I Influence of the Solvent on λmax (nm) of Dyes 1–12
Dye no
DMSO
DMF
Acetonitrile
Methanol Acetic acid
Chloroform
1a
1b
1c
1d
2a
2b
2c
2d
3a
”3b
3c
3d
441,421s
449,418s
465,432s
452,429s
448,417s
448,417s
469
460
525,399
531
438,418s
443,418s
467,432s
449,428s
443,416s
444,417s
471
456
586,393
527
411,435s
438,419s
442
431,449s
414,438s
438,420s
453
450
504,425
517
419,439s
444,419s
459
477
455,421s
488
487
491
456,420s
483
501
502
515
415,437s
438,419s
437,465s
431,454s
416,437s
442,420s
452
451
504,424s
514
444
444,418s
443,417s
464
453
509,429
522
605
538
603
532
593
525
539
522
527
514
526
524
S: shoulder

Hetarylazoindole Dyes
1241
are due to solute-solvent interactions.51 The absorption maxima of the
model compounds in acetic acid were observed in the range of 455–515
nm. The observed large bathochromic shifts are considered to be the
consequence of protonation of the nitrogen atom in the thiazole ring.
It has been reported that the protonation of the nitrogen atom of het-
eroaromatic rings in acidic media sometimes leads to a bathochromic
shift of the absorption bands.52
The absorption band of dye 1a and 1b shows a small bathochromic
shift, ꢀλmax = 1-8 nm, with the change of solvent except in the case of
acetic acid. This is attributed to substituent effect. The same shift was
observed for the other dyes except the nitro substituted compounds. It
was found, that the absorption maxima of the nitro substituted com-
pounds showed larger bathochromic shifts in DMSO and DMF as com-
pared to the shifts in other solvents (for 3a, λmax values are 525, 399
nm in DMSO, 586, 393 nm in DMF, 502 nm in acetic acid; for 3b, λmax
values are 531 in DMSO, 527 nm in DMF, 515 nm in acetic acid; for 3c,
λmax values are 605 in DMSO, 603 nm in DMF, 527 nm in acetic acid;
for 3d λmax values are 538 nm in DMSO, 532 nm in DMF, 514 nm in
acetic acid).
The absorption spectra of the dyes 2c, 2d, and 3c–d showed only one
absorption maximum in all of the solvents used, whereas the other dyes
prepared showed two absorption maxima or one absorption maximum
with a shoulder in all of the solvents used. The shifts of 2c in various
solvents are shown in Figure 1. It was observed that the λmax values
1.2
1. Acetic acid
2. Acetonitrile
1.0
0.8
0.6
0.4
0.2
0.0
3. DMF
4. DMSO
5. Chloroform
6. Methanol
2
3
1
6
4
5
350
400
450
500
550
Wavelength(nm)
FIGURE 1 Absorption spectra of dye 7 in various solvents.
600
650
700
750
800

ˇ
1242
Z. Seferoglu and N. Ertan
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
1. Acetic acid
2. Acetonitrile
3. DMF
6
5
4. DMSO
5. Chloroform
6. Methanol
1
2
3
4
350
400
450
500
550
Wavelength(nm)
FIGURE 2 Absorption spectra of dye 8 in various solvents.
600
650
700
750
800
of 2c and its model compound 2d have similar absorption maxima in
all of the solvents investigated (Figure 2). Therefore, dye 2c is present
in the azo form in all of the solvents used. In addition, compound 3a
showed two absorption maxima or shoulder in DMSO, DMF, acetoni-
trile, methanol and chloroform while dye 3b showed one absorption
maximum in all of the solvents used. Two absorption maxima may in-
dicate the presence of an azo-hydrazone tautomeric equilibrium or of
equilibrium between one of the tautomeric forms and an anionic form.
However, 3c showed one maximum in all of the solvents used, which
indicates that the compound is present in only one tautomeric form (azo
form) in these solvents. It was observed that λmax values of 3c and its
model compound 3d have similar absorption maxima in these solvents.
The effect of an acid or a base on the absorption maxima of the dyes
in solution was also investigated and the results are shown in Table II.
The absorption maxima of the dyes in DMSO and DMF were quite
sensitive to the addition of piperidine, with exception of the model com-
pounds (1b, 1d, 2b, 2d, 3b, and 3d). λmax of the dyes (except the model
compounds) showed large bathochromic shifts when a small amount of
piperidine was added to each of the solutions in DMSO and DMF. A typ-
ical example is shown in Figure 3. For 2c, ꢀλmax is 44 nm in DMSO +
piperidine relative to DMSO and 42 nm in DMF + piperidine relative
to DMF. There was no significant change in the spectra of the com-
pound 3c when a small amount of piperidine was added to its solutions

1243

ˇ
1244
Z. Seferoglu and N. Ertan
1,2
1,0
0,8
0,6
0,4
0,2
0,0
1. DMSO
2. DMSO+piperidine
3. Acetic acid
2
3
1
350
400
450
500
550
Wavelength(nm)
FIGURE 3 Absorption spectra of dye 7 in acidic and basic solution.
600
650
700
750
800
in DMSO. Similar effects were observed when a small amount of the
piperidine was added to the solution of 3c in DMF. This indicates that
compound 3c exist in its anionic form in DMSO and DMF. Same results
were observed for 3a in DMF. On the other hand, λmax of the dyes (ex-
cept the model compounds) showed small bathochromic shifts when a
small amount of piperidine was added to each of the dye solutions in
chloroform. For compound 2c ꢀλmax is 9 nm in chloroform + piperidine
relative to chloroform; similarly for 3c ꢀλmax is 11 nm in chloroform +
piperidine relative to chloroform.
When a small amount of 0.1 M KOH was added to the methano-
lic solutions of the dyes (except the model compounds), ꢀλmax values
showed bathochromic shifts and only one absorption maximum was
observed except for 2a and 3a. These dyes (2a and 3a) showed two ab-
sorption maxima or one absorption maximum with a shoulder in basic
methanolic solution. The dyes 1a–d and 2a–d may exist in the anionic
form in basic methanolic solution. For compound 1c ꢀλmax is 37 nm in
methanol + KOH relative to methanol; similarly for 3c ꢀλmax is 44 nm
in methanol + KOH relative to methanol. When a small amount of 0.1
M HCl was added to the methanolic solutions of dyes (except for com-
pounds 3a-d), the λmax values showed large bathochromic shifts and
also only one absorption maximum was observed. This indicates that
the dyes 1a–d and 2a–d exist in the cationic form in acidic methanolic
solution. For compound 2c ꢀλmax is 57 nm in methanol + HCl relative
to methanol; similarly for 2d ꢀλmax is 59 nm in methanol + HCl relative
to methanol (Figure 4).

Hetarylazoindole Dyes
1245
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
1. Methanol
1
2
2. Methanol+KOH
3. Methanol+HCl
3
350
400
450
500
550
Wavelength(nm)
FIGURE 4 Absorption spectra of dye 8 in acidic and basic solution.
600
650
700
750
800
The effects of dye concentration and temperature on the positions
of the absorption maxima were examined. The λmax values of the dyes
did not change with concentration in all solutions investigated. Since
in these experiments the dyes were not fully dissolved in acetonitrile,
methanol, acetic acid or chloroform (undissolved material was filtered
off), the actual concentration of dye in the solution was not precisely
known. More dilute solutions were therefore prepared, and it was found
in all cases, that λmax was unaffected by the dye concentration. When
solutions of the dyes 1a–d, 2a–d, and 3a–d in DMSO and DMF were
examined over the temperature range 25–70◦C , the λmax values did
not change significantly. These findings support the dissociation equi-
librium of hetarylazoindoles in proton-accepting solvents, which does
not involve a change in energy.
Substituent Effect on the Absorption Spectra
in Various Solvents
The effect of the substituents in the hetarylazoindole dyes was also
studied. As becomes apparent from Table II, introduction of an elec-
tron donating -CH3 group at 5-position of the thiazole ring results in
small bathochromic shifts in DMSO, DMF, acetonitrile and methanol.
For compound 2c ꢀλmax values are 4 nm in DMSO, 4 nm in DMF, 11 nm
in acetonitrile, and 5 nm in methanol relative to λmax of 1c in the same

ˇ
Z. Seferoglu and N. Ertan
1246
solvents. The introduction of the strong electron-withdrawing nitro
group at the 5-position of the thiazole ring results in large bathochromic
shifts in all of the solvents investigated. For compound 3c ꢀλmax values
are 140 nm in DMSO, 136 nm in DMF, 151 nm in acetonitrile, 80 nm
in methanol, 39 nm in acetic acid, and 89 nm in chloroform relative to
λmax of 1c in the same solvents. Similar shifts were observed for 3a and
3b in DMF (ꢀλmax = 59 nm) and for 3c and 3d in DMSO (ꢀλmax = 67
nm) and in DMF (ꢀλmax = 71 nm). These large bathochromic shifts sug-
gest that for the nitro substituted compounds 3a – 3d azo-hydrazone or
anionic equilibria are present in DMSO and DMF. The introduction of
an electron accepting nitro group in the 5-position of the thiazole ring
causes large bathochromic shifts of the absorption bands of the dyes.
This could be attributed to a more extensive π-conjugation in these
compounds. The absorption spectra of the dyes showed bathochromic
shifts in all solvents used when the phenyl group at the 2-position of
indole rings is replaced with the methyl group. For compound 1a ꢀλmax
values are 24 nm in DMSO, 29 nm in DMF, 31 nm in acetonitrile, 10 nm
in methanol, 11 nm in acetic acid and 22 nm in chloroform relative to
λmaxof 1c in the same solvents. In general the same results are observed
also for the model compounds. For compound 2b ꢀλmax values are 12
nm in DMSO, 12 nm in DMF, 12 nm in acetonitrile, 10 nm in methanol,
45 nm in acetic acid and 9 nm in chloroform relative to λmax of 2d in
the same solvents. These behaviors may be attributed to the π-donor
properties of the phenyl rings.
As a result, the dyes prepared (1a-d, 2a-d, and 3a-d) might be used
for polyester materials as disperse dyes. In addition, the dyes derived
from the model compounds could be used as cationic dyes.
EXPERIMENTAL
The chemicals used for the syntheses of all dyes were obtained from
Aldrich and were used without further purification. Solvents of spectro-
scopic grade purity were used. IR spectra were recorded with a Mattson
1000 FT-IR spectrophotometer in KBr. 1H NMR spectra were recorded
with a Bruker-Spectrospin Avance DPX 400 in DMSO-d6 and CDCl3
with TMS as internal reference. Chemical shifts are expressed in δ units
(ppm). Ultraviolet-visible (UV-VIS) absorption spectra were recorded
with a Analytik-Jena Specord 200 spectrophotometer at the wave-
length of maximum absorption (λmax) in dimethylsulphoxide (DMSO),
dimethylformamide (DMF), acetonitrile, methanol, acetic acid and chlo-
roform. Changes of λmax were investigated by adding of 0.1 mL of piperi-
dine to 1 mL of the dye solutions in chloroform, DMSO and DMF.
Similarly 0.1 mL of potassium hydroxide (0.1 M aqueous soln) or 0.1 mL

Hetarylazoindole Dyes
1247
of hydrochloric acid (0.1 M aqueous soln) was added to 1 mL of the dye
solutions in methanol. Mass spectra were recorded with a Agilent 5973
Network Mass Selective Detector instrument equipped with SIS (Direct
Insertion Probe) in electron impact mode at 70 and 100 eV and with an
AGILENT 1100 MSD instrument. Elemental analyses were obtained
with a LECO CHNS 932 instrument by the Turkish Research Council
Laboratories (Center of Science and Technology Research of Turkey).
All melting points are uncorrected and given in ◦C.
Preparation of the Hetarylazoindole Dyes
Diazotization of various heterocyclic amines was performed with ni-
trosylsulphuric acid. A typical procedure is described below for 2-
aminothiazole; all other dyes were prepared in a similar manner. The
yields of the dyes are in range of 65–90%.
2-Methyl-3-(thiazol-2-yldiazenyl)-1H-indole (1a)
2-Aminothiazole (0.2 g, 2 mmol) was dissolved in hot glacial acetic
acid—propionic acid mixture (2:1, 6.0 mL) and was rapidly cooled in an
salt/ice bath to −5◦C. The mixture was stirred for 1 h at 0–5◦C. Then the
resulting liquor was added in portions during 30 min to a cold solution
of nitrosylsulphuric acid, prepared from sodium nitrite (0.15 g) and
concentrated sulphuric acid (3 mL) at 50◦C . The mixture was stirred
for additional 2 h at 0◦C . The excess of nitrous acid was destroyed by
addition of urea. The resulting diazonium salt was cooled in an salt/ice
bath. 2-methylindole (0.26 g, 2 mmol) was dissolved in a mixture of
acetic acid and propionic acid (3:1, 8.0 mL) and cooled in a salt/ice bath.
To this cooled solution the cold diazonium solution was added dropwise
with stirring. The solution was stirred at 0–5◦C for 2 h and while the
pH of the reaction mixture was maintained at 4–6 by simultaneous
addition of saturated aqueous sodium carbonate solution. The mixture
was stirred for further 1 h at 5◦C . The resulting product was filtered,
washed with water, dried and crystallized from ethanol to give orange
crystals. Yield: 0.39 g, 81%; m.p: 212–213◦C ), FT–R (KBr) νmax: 3391
(indole NH), 3050, 3031 (aromatic C H), 2921, 2851 (aliphatic C H),
1503 (C C) cm−1; 1H NMR (DMSO-d6/CDCl3): δ = 12.78 (br, 1H, indole
-NH), 8.39 (m, 1H), 7.81 (d, 1H), 7.37 (d, 1H), 7.27 (d, 1H), 7.23-7.19 (m,
2H). Anal. Calcd. for C12H10N4S: C, 54.48; H, 4.16; N, 23.12; S, 13.23%.
Found: C, 54.59; H, 4.19; N, 22.96; S, 13.22%. MS (m/z, 70 eV): 242 (M+).
1,2-Dimethyl-3-(thiazol-2-yldiazenyl)-1H-indole (1b)
This compound was obtained from 2-aminothiazole and 1,2-
dimethylindole as orange crystals. Yield: 0.44 g, 86%%; m.p.:

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Z. Seferoglu and N. Ertan
1248
168–170◦C; FT–IR (KBr) νmax: 3051 (aromatic C H), 2941 (aliphatic
C H), 1527 (C C) cm−1; 1H NMR (DMSO-d6): δ = 8.31 (m, 1H), 7.87 (d,
1H), 7.63 (m, 1H), 7.56 (d, 1H), 7.39-7.31 (m, 2H), 3.83 (s, 3H, NCH3),
2.79 (s, 3H). Anal. Calcd. for C13H12N4S: C, 60.92; H, 4.72; N, 21.86; S,
12.51%. Found: C, 60.90; H, 4.66; N, 21.90; S, 12.48%. LC-MS (m/z, 100
eV): 257.1 (48.7%) (M+1)+, 172.1 (100%), 144.1 (58.0%).
2-Phenyl-3-(thiazol-2-yldiazenyl)-1H-indole (1c)
This compound was obtained from 2-aminothiazole and 2-
phenylindole as red crystals. Yield: 0.42 g, 69%; m.p.: 280◦C (dec.); FT–
IR (KBr) νmax: 3454 (indole NH), 3114, 3056 (aromatic C H), 1464
(C C) cm−1
;
1H NMR (CDCl3): δ = 8.95 (br, 1H, indole NH), 8.69
(m, 1H), 8.07 (m, 1H), 7.93 (d, 1H), 7.62–7.52 (m, 4H), 7.48–7.33 (m,
4H). Anal. Calcd. for C17H12N4S: C, 67.08; H, 3.97; N, 18.41; S, 10.53%.
Found: C, 67.19; H, 4.06; N, 18.59; S, 10.49%. MS (m/z, 70 eV): 304 (M+).
1-Methyl-2-phenyl-3-(thiazol-2-yldiazenyl)-1H-indole (1d)
This compound was obtained from 2-aminothiazole and 1-methyl-2-
phenylindole as orange crystals. Yield: 0.49 g, 77%; m.p.: 196–199◦C;
FT–IR (KBr) νmax: 3070 (aromatic C H), 2935 (aliphatic C H), 1464
(C C) cm−1; 1H NMR (DMSO-d6/CDCl3): δ = 8.34 (m, 1H), 7.58 (d, 1H),
7.50-7.10 (m, 8H), 6.92 (d, 1H), 3.68 (s, 3H, NCH3). Anal. Calcd. for
C18H14N4S: C, 67.90; H, 4.43; N, 17.60; S, 10.07%. Found: C, 67.98; H,
4.46; N, 17.59; S, 10.09%. MS (m/z, 70 eV): 318 (M+).
2-Methyl-3-(5-methylthiazol-2-yldiazenyl)-1H-indole (2a)
This compound was obtained from 2-amino-5-methylthiazole and 2-
methylindole as orange crystals. Yield: 0.41 g, 80%; m.p.: 243◦C (dec.);
FT-IR (KBr) νmax: 3442 (indole NH), 3050, 3034 (aromatic C H), 2954,
1
2928 (aliphatic C H), 1541 (C C) cm−1; H NMR (DMSO-d6/CDCl3):
δ = 11.64 (br, 1H, indole NH), 7.93 (m, 1H), 7.16 (s, 1H), 6.91 (m, 1H),
6.77 (m, 2H), 2.44 (s, 3H), 2.04 (s, 3H). Anal. Calcd. for C13H12N4S: C,
60.92; H, 4.72; N, 21.86; S, 12.51%. Found: C, 61.09; H, 4.80; N, 22.01;
S, 12.44%. MS (m/z, 70 eV): 256 (M+).
1,2-Dimethyl -3-(5-methylthiazol-2-yldiazenyl)-1H-indole (2b)
This compound was obtained from 2-amino-5-methylthiazole and
1,2-dimethylindole as orange crystals. Yield: 0.49 g, 90%; m.p.: 200–
202◦C ; FT–IR (KBr) νmax: 3067 (aromatic C H), 2910 (aliphatic C H),
1519 (C C) cm−1; 1H NMR (DMSO-d6): δ = 8.28 (m, 1H), 7.62 (m, 1H),
7.57 (s, 1H), 7.38–7.27 (m, 2H), 3.81 (s, 3H, -NCH3), 2.79 (s, 3H), 2.42 (s,
3H). Anal. Calcd. for C14H14N4S: C, 62.20; H, 5.22; N, 20.72; S, 11.86%.

Hetarylazoindole Dyes
1249
Found: C, 62.39; H, 5.10; N, 20.61; S, 11.84%. LC-MS (m/z, 100 eV):
271.1 (100%) (M+1)+, 172.1 (83.7%), 144.1 (13.0%).
2-Phenyl-3-(5-methylthiazol-2-yldiazenyl)-1H-indole (2c)
This compound was obtained from 2-amino-5-methylthiazole and 2-
phenylindole as orange crystals. Yield: 0.41 g, 65%; m.p.: 285◦C (dec.);
FT–IR (KBr) νmax: 3448 (indole NH), 3070, 3052 (aromatic C H), 2954,
1
2903 (aliphatic C H), 1464 (C C) cm−1; H NMR (DMSO-d6/CDCl3):
δ = 12.31 (br, 1H, indole -NH), 8.42 (m, 1H), 8.08 (m, 2H), 7.53-7.42
(m, 5H), 7.28–7.17 (m, 2H), 2.48 (s, 3H). Anal. Calcd. for C18H14N4S: C,
67.90; H, 4.43; N, 17.60; S, 10.07%. Found: C, 68.04; H, 4.44; N, 17.59;
S, 10.11%. MS (m/z, 70 eV): 318 (M+).
1-Methyl-2-phenyl-3-(5-methylthiazol-2-yldiazenyl)-1H-
indole (2d)
This compound was obtained from 2-amino-5-methylthiazole and 1-
methyl-2-phenylindole as orange crystals. Yield: 0.56 g, 84%; m.p.: 222–
224◦C ), FT–IR (KBr) νmax: 3044 (aromatic C H), 2940, 2920 (aliphatic
C H), 1464 (C C) cm−1; 1H NMR (DMSO-d6/CDCl3): δ = 8.72 (m, 1H),
7.70–7.40 (m, 9H), 3.88 (s, 3H, NCH3), 2.44 (s, 3H). Anal. Calcd. for
C19H16N4S: C, 68.65; H, 4.85; N, 16.86; S, 9.65%. Found: C, 68.58; H,
4.88; N, 16.79; S, 9.66%. MS (m/z, 70 eV): 332 (M+).
2-Methyl-3-(5-nitrothiazol-2-yldiazenyl)-1H-indole (3a)
This compound was obtained from 2-amino-5-nitrothiazole and 2-
methylindole as violet purple powder. Yield: 0.45 g, 79%; m.p.: 194◦C
(dec.); FT–IR (KBr) νmax: 3409–3278 (indole NH), 3072, 3056 (aromatic
C H), 2972, 2921 (aliphatic C H), 1562 (C C) cm−1; 1H NMR (DMSO-
d6/CDCl3): δ = 12.67 (br, 1H, indole NH), 8.48 (s, 1H), 8.31 (m, 1H),
7.32 (m, 1H), 7.25 (m, 2H), 2.71 (s, 3H). Anal. Calcd. for C12H9N5O2S:
C, 50.17; H, 3.16; N, 24.38; S, 11.16%. Found: C, 50.39; H, 3.29; N, 24.46;
S, 11.25%. MS (m/z, 70 eV): 287 (M+).
1,2-Dimethyl-3-(5-nitrothiazol-2-yldiazenyl)-1H-indole (3b)
This compound was obtained from 2-amino-5-nitrothiazole and 1,2-
dimethylindole as dark red powder. Yield: 0.45 g, 77%; m.p.: 234◦C
(dec.); FT–IR (KBr) νmax: 3093 (aromatic C H), 2940, 2920 (aliphatic
1
C H), 1490 (C C) cm−1; H NMR (DMSO-d6): δ = 8.78 (s, 1H), 8.27
(m, 1H), 7.50 (m, 1H), 7.44 (m, 2H), 3.88 (s, 3H, NCH3), 2.79 (s, 3H).
Anal. Calcd. for C13H11N5O2S: C, 51.82; H, 3.68; N, 23.24; S, 10.64%.
Found: C, 51.59; H, 3.62; N, 23.11; S, 10.44%. LC-MS (m/z, 100 eV):
302.1 (100%) (M+1)+, 172.1 (76.7%), 144.2 (42.3%).

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Z. Seferoglu and N. Ertan
1250
2-Phenyl-3-(5-nitrothiazol-2-yldiazenyl)-1H-indole (3c)
This compound was obtained from 2-amino-5-nitrothiazole and 2-
phenylindole as violet purple powder. Yield: 0.46 g, 66%; m.p.: 234◦C
(dec.), FT–IR (KBr) νmax: 3442 (indole NH), 3056 (aromatic C H), 1529
(C C) cm−1; 1H NMR (DMSO-d6): δ = 13.82 (br, 1H, indole NH), 8.31
(m, 2H), 8.12 (m, 1H), 7.66–7.33 (m, 7H). Anal. Calcd. for C17H11N5O2S:
C, 58.44; H, 3.17; N, 20.05; S, 9.18%. Found: C, 58.59; H, 3.26; N, 20.19;
S, 9.25%. MS (m/z, 70 eV): 349 (M+).
1-Methyl-2-phenyl-3-(5-nitrothiazol-2-yldiazenyl)-
1H-indole (3d)
This compound was obtained from 2-amino-5-nitrothiazole and 1-
methyl-2-phenyl-indole as violet purple powder. Yield: 0.54 g, 75%;
m.p.: 236◦C (dec.); FT–IR (KBr) νmax: 3056, 3031 (aromatic C H), 2935
(aliphatic C H), 1496 (C C) cm−1
;
1H NMR (DMSO-d6/CDCl3): δ =
8.53 (s, 1H), 7.62–7.41 (m, 7H), 7.28 (m, 1H), 7.08 (m, 1H), 3.78 (s, 3H,
NCH3). Anal. Calcd. for C18H13N5O2S: C, 59.49; H, 3.61; N, 19.27; S,
8.82%. Found: C, 59.77; H, 3.66; N, 19.36; S, 8.85%. MS (m/z, 70 eV):
363 (M+).
REFERENCES
[1] A. D. Towns, Dyes and Pigments, 42, 3 (1999).
[2] G. Hallas and J. H. Choi, Dyes and Pigments, 42, 249 (1999).
[3] O. Annen, R. Egli, R. Hasler, B. Henzi, H. Jakob, and P. Matzinger, Rev. Prog. Col.,
17, 72 (1987).
[4] M. S. Yen and I. J. Wang, Dyes and Pigments, 61, 243 (2004).
[5] M. S. Yen and I. J. Wang, Dyes and Pigments, 63, 1 (2004).
[6] A. S. Amin and G. O. El-Sayed, Monatsh. Chem., 132, 587 (2001).
[7] G. Hallas and J. H. Choi, Dyes and Pigments, 42, 249 (1992).
[8] M. F. Abdel-Mgeed, M. M. Azaam, and G. A. El-Hiti, Monatsh. Chem., 138, 153
(2007).
[9] M. S. Yen and I. J. Wang, Dyes and Pigments, 62, 173 (2004).
[10] M. S. Yen and I. J. Wang, Dyes and Pigments, 67, 183 (2005).
[11] J. B. Dickey, E. B. Towne, M. S. Bloom, W. H. Moore, H. M. Hill, H. Heynemann,
D. G. Hedberg, D. C. Sievers, and M. V. Otis, J. Org. Chem., 24, 187 (1958).
[12] R. W. Sabnis and D. W. Ragnekar, Dyes and Pigments, 10, 295 (1989).
[13] G. Hallas and A. D. Towns, Dyes and Pigments, 33, 205 (1997).
[14] M. A. Weaver and L. Shuttleworth, Dyes and Pigments, 3, 81 (1982).
[15] N. Ertan and F. Eyduran, Dyes and Pigments, 27, 313 (1995).
[16] F. Karcı and N. Ertan, Color. Techn., 121, 153 (2005).
[17] N. Ertan, Dyes and Pigments, 44, 41 (2000).
[18] A. Saylam, Z. Seferog˘lu, and N. Ertan doi:10.1016/J.dyepig.2006.10.005
[19] H. A. Albar, A. S. Shawali, and M. A. Abdaliah, Can. J. Chem., 71, 2144 (1993).
[20] J. H. Binks and J. H. Ridd, J. Chem. Soc., 2398 (1957).

Hetarylazoindole Dyes
1251
[21] A. H. Jackson, N. Prasitpan, P. V. R. Shannon, A. C. Tinker, J. Chem. Soc., Perkin
Trans. I, 2543 (1987).
[22] A. H. Jackson, N. Prasitpan, P. V. R. Shannon, A. C. Tinker, J. Chem. Soc., Perkin
Trans. II., 10, 1483 (1987).
[23] R. Raue and H. L. Dorsch, U.S. Patent 4,006,127 (1977).
[24] R. Bermes and H. Keilhauer H., DE Patent 28 25 298 A1 (1979).
[25] S. Yamada and K. Tsunemitsu, JP Patent 47 045 172 B4 (1972).
[26] S. Inoue, H. Honda, Y. Magara, and K. Abe, JP Patent 50 013 682 A2 (1975) and JP
Patent 57 002 831 B4 (1982).
[27] K. Yamada and K. K. Kenkyusho, JA Patent 7 245 172–R (1972).
[28] H. L. Dorsch, K. Stammheim, and R. Raue, U.S. Patent 4 104 268 (1978).
[29] H. L. Dorsch, K. Stammheim, and R. Raue, CH Patent 568 441 B5 (1975).
[30] H. L. Dorsch, K. Stammheim, and R. Raue, CH Patent 562 853 A5 (1975).
[31] H. L. Dorsch and R. Raue, DT Patent 1 405 313 (1975).
[32] P. Rhyner and H. Illy, CH Patent 341 248 (1959).
[33] H. L. Dorsch and R. Raue, DE Patent 2 228 147 A1 (1973).
[34] K. Hohmann, R. Mohr, and M. Hahnke, U.S. Patent 4 046 752 (1977).
[35] R. Raue and H. P. Ku¨hlthau, CH Patent 626 391 A5 (1978).
[36] A. Saylam, Z. Seferog˘lu, and N. Ertan, Russ. J. Org. Chem., 2007, in press.
[37] Z. Seferog˘lu and N. Ertan, Russ. J. Org. Chem, 2007, 43, 1035 (2007).
[38] Z. Seferog˘lu and N. Ertan, Heteroatom Chem., 18, 1 (2007).
[39] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E62, 2108 (2006).
[40] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E62, o3492 (2006).
[41] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E62, o3835 (2006).
[42] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, A. Salyam, and N. Ertan, Acta Cryst., E62, o5488
(2006).
[43] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E63, o148 (2007).
[44] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E63, o351 (2007).
[45] Z. Seferog˘lu, T. Ho¨kelek, E. S¸ahin, and N. Ertan, Acta Cryst., E63, o568 (2007).
[46] T. Ho¨kelek, Z. Seferog˘lu, E. S¸ahin, and F. B. Kaynak, Acta Cryst., E63, o2837 (2007).
[47] Z. Seferog˘lu, PhD Thesis, Institue of Science and Technology, Gazi University (2006).
[48] C. J. Pouchert and J. Behmke, The Aldrich Library of 13C and 1H, FT NMR Spectra
(Aldrich Chemical Company, Milwaukee, 1993) 1st ed., 3, 121A–160A.
[49] A. Lycka, Z. Vrba and M. Vrba, Dyes and Pigments 47, 45 (2000).
[50] A. Lycka, Dyes and Pigments 43, 27 (1999).
[51] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, (New York, VCH,
1990), pp. 408–409.
[52] C. J. Yang and S. A. Jenekhe, Macromolecules, 28, 1180 (1995).