Synthesis of Novel and Thermally Stable Water Insoluble Coumarin-based Azo Dyes via a Mild and Green Procedure

Article abstract of DOI:10.1002/jccs.201500135

A series of novel azo coumarin dyes were synthesized by the diazotization of 7-amino coumarins in the presence of catalytic amounts of tungstate sulfuric acid (TSA) followed by coupling with phenol derivatives. Tungstate sulfuric acid catalyzes this reaction at room temperature and short reaction time with high yields. A series of novel azo coumarin dyes were synthesized by the diazotization of 7-amino coumarins in the presence of catalytic amounts of tungstate sulfuric acid (TSA) followed by coupling with phenol derivatives. Tungstate sulfuric acid catalyzes this reaction at room temperature and short reaction time with high yields.

Full text of DOI:10.1002/jccs.201500135

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Communication
Synthesis of Novel and Thermally Stable Water Insoluble Coumarin-based Azo Dyes
via a Mild and Green Procedure
Mahtab Kiani and Bahador Karami*
Department of Chemistry, Yasouj University, Yasouj 75918-74831, Iran
(Received: Apr. 4, 2015; Accepted: Aug. 11, 2015; Published Online: Sept. 7, 2015; DOI: 10.1002/jccs.201500135)
Aseries of novel azo coumarin dyes were synthesized by the diazotization of 7-amino coumarins in the pres-
ence of catalytic amounts of tungstate sulfuric acid (TSA) followed by coupling with phenol derivatives.
Tungstate sulfuric acid catalyzes this reaction at room temperature and short reaction time with high yields.
Keywords: Azo coumarin dyes; Diazotization; 7-Amino coumarins; Tungstate sulfuric acid.
INTRODUCTION
Diazoniums are an important group of organic salts
opment of the heterocyclic synthetic methodologies,21-24
herein, we wish to report a simple and benign procedure for
the synthesis of novel coumarin-based azo dyes through
the diazotization of coumarins followed by coupling with
phenols in the presence of tungstate sulfuric acid (TSA) as
a heterogeneous and efficient catalyst.
which have interesting applications in synthetic organic
chemistry.1,2 These compounds can be reduced into radi-
cals and used for the covalent surface modification of car-
bon, metal, and semiconductors.3,4 Diazoniums also have
been used for the preparation of the important synthetic azo
dyes via famous azo-coupling reaction.5-7 Nitrous acid is
well-known reagent for the diazotization of aniline deriva-
tives under acidic conditions. The main limitation of such
synthetic processes is their environmental incompatibility.
The acidic and basic effluents from the laboratory and in-
dustry cause permanent damage to the environment and
disturb the ecological balance.8,9 Many methods have been
reported for the diazotization and subsequent azo-coupling
reaction.10-15 However, some of these mentioned reports
suffer from drawbacks, such as long reaction times, low
product yields, harsh reaction conditions, and the use of ex-
cessive amounts of catalyst.
Firstly, 7-amino coumarin 3 was synthesized via the
ZrOCl2×8H2O/SiO2-catalyzed Pechmann condensation of
3-amino phenol (1) with b-ketoesters 2 under solvent-free
conditions (Scheme 1).22
Catalyzed synthesis of 7-amino coumarins
Scheme 1
Tungstate sulfuric acid (TSA) is an alternative to sul-
furic acid that was synthesized by reaction of anhydrous
sodium tungstate with chlorosulfonic acid.16 This inor-
ganic solid acid has been applied as an efficient catalyst in a
variety of organic transformations.17-20
In this work, a new methodology to obtain novel azo
coumarin dyes using tungstate sulfuric acid (TSA) as efficient
catalyst is reported. In addition, a new application of tungstate
sulfuric acid as a safe and recyclable catalyst for the synthesis
of novel azo coumarin dyes derivatives is introduced.
Subsequently, the novel azocoumarin dyes 6 were
prepared by the diazotization of 7-amino coumarins 3 in the
presence of tungstate sulfuric acid (TSA) as catalyst fol-
lowed by coupling with phenol derivatives 5. (Scheme 2,
Table 1).
This reaction was performed according to conven-
tional methods (The diazotization and diazo coupling reac-
tions are usually carried out with protonation of nitrous
RESULTS AND DISCUSSION
In continuation of our programmatic interest in devel-
* Corresponding author. Email: karami@yu.ac.ir
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201500135
756
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J. Chin. Chem. Soc. 2015, 62, 756-760

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Synthesis of Novel Coumarin-based Azo Dyes
step, nucleophilic addition of amino group of 3 was done
by nitrous acid to produce intermediate 7. Elimination of
water from 7 produces diazonium salt 8. Finally, the
nucleophilic attack of phenol derivatives 5 to 8 forms azo
dye 6 (Scheme 3).
Synthesis of azocoumarin dyes
Scheme 2
The main disadvantage of many reported methods for
these reactions is that the catalysts are destroyed in the
work-up procedure and cannot be recovered or reused. In
these processes, as outlined in Fig. 1, the TSA showed
recyclability up to four cycles, during which there are a lit-
tle losses in the catalytic activity.
EXPERIMENTAL
Materials and instrumentation: Solvents were purified
and dried by standard procedures and distilled prior to use. Com-
mercially available reagents were purchased from Merck Chemi-
cal Co. TSA was prepared according to previous method.16 Melt-
ing points were measured on an electrothermal KSBIN apparatus.
IR spectra were recorded in the matrix of KBr with JASCO
FT-IR-680 plus spectrometer. 1HNMR and 13CNMR spectra were
recorded on a FT-NMR Bruker Avance Ultra Shield Spectrometer
at 400 MHz in DMSO-d6 as solvent. TLC was performed on
TLC-Grade silica gel-G/UV 254 nm plates. Chemicals were pur-
chased from Merck and Fluka chemical companies and were used
without further purification. The varioEl CHNS Isfahan Indus-
trial University was used for elemental analysis. Mass spectra
were obtained by the Fisons Trio 1000 (70 ev).
acid under strongly acidic conditions in aqueous media)
and the results showed several byproducts. When this reac-
tion was carried out with TSAas a new heterogeneous cata-
lyst, the formation of these byproducts was prevented and
the recrystallization was also much easier. A literature sur-
vey shows a few reports on the use of solid acids as catalyst
and there is no method about employing TSA.25,26
General procedure for the synthesis of 7-amino-4-sub-
stituted coumarins 3: b-ketoester 2 (1 mmol) was added to a
mixture of 3-amino phenol (1) (1 mmol) and ZrOCl2×8H2O/SiO2
(0.27 g, 10 mol %) in a screw-cap vial. The mixture was stirred in
a preheated oil bath (90 °C). After completion of the reaction, the
resulting solid product was suspended in H2O (20 ml), filtered and
recrystallized from hot EtOH to give the pure product 3.
General procedure for the synthesis of azo coumarin
dyes 1a-8a: To a mixture of (1 mmol) of 7-amino coumarins 3 in
ethanol (3 ml) was added tungstate sulfuric acid (10 mol %). After
stirring for 30 minutes, 0.14 g NaNO2 (2 mmol) in 1 mL water was
added dropwise for a period of 30 min. Then, (1 mmol) phenol de-
rivatives 5 was added to the diazonium- tungstate complex and
slowly brought to room temperature with constant stirring and
kipping at room temperature for 2 h. The resulting precipitate was
isolated by filtration and washed with water and cold ethanol (1:1,
3 ´ 10 ml). The crude dye was purified using recrystallization
from EtOH.
The 1H NMR spectrum of 6a exhibited a sharp singlet
identified as methyl (d = 2.41 ppm), an olefinic C–H of the
coumarin ring (d = 6.40 ppm), a singlet corresponded to the
OH group (d = 15.70 ppm). The peaks appearing in the
6.7-8.5 ppm are attributed to aromatic rings protons. The
proton decoupled 13C NMR spectrum of 6a showed 20 dis-
tinct resonances in agreement with the proposed structure.
The infrared spectra (IR) of these dyes show intense
carbonyl bands appearing at 1700-1750 cm-1. The broad
bands in region of 3000-3450 cm-1 are attributed to n (O-H)
vibrations. The peaks appearing at 1000-1350 cm-1 are at-
tributed to n (C-N) and n (C-O) stretching vibration. The
spectra also show the existence of (–N=N–) group at
1450-1500 cm-1.
The proposed mechanism for acid-catalyzed diazo
coupling reaction of diazonium salt of 7-amino coumarin 3
with phenol derivatives 5 in the presence of NaNO2 was de-
picted in Scheme 3. Initially, TSA was converted to sodium
salt and nitrous acid in the presence of NaNO2. In the next
Spectral data of some compounds: 7-((2-hydroxynaph-
thalen-1-yl)diazenyl)-4-methyl-2H-chromen-2-one (6a): IR
J. Chin. Chem. Soc. 2015, 62, 756-760
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Communication
Kiani and Karami
Table 1. Synthesis of azo coumarin dyes 1a-8a by the coupling of 7-amino coumarins and
phenol derivatives
Entry
6a
Coupling reactant
R1, R2
Product
Yield (%)a Mp (°C)
CH3
O
OH
N
O
Me, H
87
211-212
N
OH
CH3
O
OH
OH
6b
6c
Me, H
Me, H
74
58
253-255
138-140
O
N
N
CH3
O
OH
OH
N
N
O
OH
HO
CH3
O
OH
N
O
N
6d
Me, H
66
118-120
OH
OH
N
O
O
6e
6f
-(CH2)4-
79
60
216-218
176-178
N
OH
OH
OH
-(CH2)4-
N
O
O
N
OH
N
O
O
N
6g
-(CH2)4-
62
233-235
OH
OH
OH
OH
N
O
O
N
6h
-(CH2)4-
77
198-200
OH
a Isolated yield.
(KBr) (nmax, cm–1): 3432, 1731, 1614, 1498, 1384, 1246, 1127,
1
1064, 835, 750. HNMR (400 MHZ, DMSO): dH 15.7 (b, 1H,
6.75 (d, 1H, aromatic CH), 6.35 (s, 1H, CH), 2.45 (s, 3H, CH3).
13CNMR (100 MHZ, DMSO): dC 160.67, 154.95, 152.01, 146.29,
142.60, 133.21, 133.62, 131.28, 129.62, 128.99, 128.40, 127.02,
OH), 8.50 (b, 1H, aromatic CH), 7.4-8.00 (m, 7H, aromatic CH),
758
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Synthesis of Novel Coumarin-based Azo Dyes
Proposed mechanism for the formation of
119.91, 116.26, 111.27, 109.97, 104.59, 24.83. Anal. Calcd. for
C16H12N2O4: C, 64.86; H, 4.05; N, 9.46. Found: C, 64.63; H, 4.13;
N, 9.33. 7-((4-hydroxybiphenyl-3-yl)diazenyl)-4-methyl-2H-
chromen-2-one (6d): IR (KBr) (nmax, cm–1): 3446, 1743, 1621,
Scheme 3
compounds 6.
1
1480, 1425, 1383, 1255, 1193, 1148, 885, 756. HNMR (400
MHZ, DMSO): dH 10.99 (s, 1H, OH), 8.00 (m, 4H, aromatic CH),
7.81 (dd, J = 2.4 Hz, J = 7.81 Hz, 1H, aromatic CH), 7.68 (d, J =
7.6 Hz, 2H, aromatic CH), 7.48 (t, J = 7.6 Hz, 2H, aromatic CH),
7.38 (m, 1H, aromatic CH), 7.2 (d, J = 8.4 Hz, 1H, aromatic CH),
6.49 (s, 1H, CH), 2.48 (s, 3H, CH3). 13CNMR (400 MHZ, DMSO):
dC 160.17, 155.90, 154.09, 153.20, 139.48, 139.20, 133.36,
132.35, 129.46, 129.26, 128.20, 127.66, 126.89, 126.82, 126.71,
126.42, 122.05, 120.21, 119.61, 109.84, 18.65. Anal. Calcd. for
C22H16N2O3: C, 74.15; H, 4.49; N, 7.86. Found: C, 74.02; H, 4.53;
N, 7.69. 3-((2-hydroxynaphthalen-1-yl)diazenyl)-7,8,9,10-tetra-
hydrobenzo[c]chromen-6-one (6e): IR (KBr) (nmax, cm–1): 3374,
1706, 1612, 1566, 1509, 1446, 1393, 1255, 1098, 1031, 837, 753.
1HNMR (400 MHZ, DMSO): dH 11.58 (s, 1H, OH), 8.57 (d, J = 8
Hz, 1H, aromatic CH), 8.09 (s, 1H, aromatic CH), 7.7 (m, 3H, aro-
matic CH), 7.4 (m, 2H, aromatic CH), 7.1 (d, J = 8 Hz, 1H, aro-
matic CH), 6.82 (d, J = 9.6 Hz, 1H, aromatic CH), 2.68 (t, J = 8
Hz, 2H, CH2), 2.3 (t, J = 8 Hz, 2H, CH2), 1.7 (m, 4H, 2CH2). Anal.
Calcd. for C23H18N2O3: C, 74.59; H, 4.86; N, 7.56. Found: C,
74.47; H, 4.79; N, 7.32.
CONCLUSIONS
In summary, a new class of coumarin-based azo dyes
6 was obtained by coupling of the 7-amino coumarins and
phenol derivatives. The use of coumarin as a diazotized
aromatic amine is new. By this study, the scope of he-
terocyclic compounds has been also developed. Short reac-
tion times, high yields, a clean process, simple method-
ology, easy work-up and green conditions are the advan-
tages of this method.
Fig. 1. Recyclability of TSA for synthesis of 1a. Reac-
tion time: 60 min.
ACKNOWLEDGEMENTS
125.90, 122.26, 117.85, 117.59, 113.98, 113.87, 104.57, 18.71.
MS (m/z): 330 [C20H14N2O3]+, 171 [C10H7N2O]+, 159 [C10H7O2]+,
143 [C10H7O]+, 115 [C9H7]+, 103, 89, 77, 51. Anal. Calcd. for
C20H14N2O3: C, 72.72; H, 4.24; N, 8.48. Found: C, 72.45; H, 4.33;
N, 8.22. 7-((2,4-dihydroxyphenyl)diazenyl)-4-methyl-2H-chro-
men-2-one (6c): IR (KBr) (nmax, cm–1): 3433, 1718, 1611, 1498,
1387, 1243, 1127, 1064, 668, 450. 1HNMR (400 MHZ, DMSO):
dH 11.94 (b, 1H, OH), 10.75 (b, 1H, OH), 7.86 (d, 3H, aromatic
CH), 7.68 (d, 2H, aromatic CH), 6.48 (m, 2H, aromatic CH), 1.29
(s, 3H, CH3). 13CNMR (100 MHZ, DMSO): dC 161.31, 159.29,
154.28, 134.36, 133.14, 130.24, 130.03, 127.84, 126.49, 121.98,
Financial support for this work by the research af-
fairs, Yasouj University (Iran), is gratefully acknowledged.
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