A new nitrite ionic liquid (IL-ONO) as a nitrosonium source for the efficient diazotization of aniline derivatives and in-situ synthesis of azo dyes

Article abstract of DOI:10.1016/j.dyepig.2010.11.010

A new task-specific nitrite containing ionic liquid derived from the O-nitrosation of N-methyl-N-hydroxybutylimidazolinium chloride was synthesized and used as a source of nitrosonium ion to affect the efficient diazotization of arylamines. The diazonium salts thus obtained were coupled, using standard experimental procedures, to a range of tertiary anilines, phenols and naphthols to afford the requisite azo dyes in good yield. The diazotization and subsequent azo-coupling generated the related azo dyes at 0-5 °C in short reaction times with a simple experimental procedure.

Full text of DOI:10.1016/j.dyepig.2010.11.010

Dyes and Pigments 92 (2012) 1138e1143
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Dyes and Pigments
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A new nitrite ionic liquid (IL-ONO) as a nitrosonium source for the efficient
diazotization of aniline derivatives and in-situ synthesis of azo dyes
*
Hassan Valizadeh , Ashkan Shomali
Department of Chemistry, Faculty of Sciences, Azarbaijan University of Tarbiat Moallem, Tabriz, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A
new task-specific nitrite containing ionic liquid derived from the O-nitrosation of N-methyl-
Received 30 July 2010
Received in revised form
18 November 2010
Accepted 19 November 2010
Available online 27 November 2010
N-hydroxybutylimidazolinium chloride was synthesized and used as a source of nitrosonium ion to affect
the efficient diazotization of arylamines. The diazonium salts thus obtained were coupled, using standard
experimental procedures, to a range of tertiary anilines, phenols and naphthols to afford the requisite
azo dyes in good yield. The diazotization and subsequent azo-coupling generated the related azo dyes
at 0e5 ꢀC in short reaction times with a simple experimental procedure.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Azo-coupling
Azo dyes
Diazotization
Nitrite ionic liquid
Task-specific ionic liquid
Nitrosonium ion
1. Introduction
Sodium or potassium nitrites are used as nitrous acid sources
because of the instability of free nitrous acid. Organic nitrite esters,
Ionic liquids are an important class of solvents which have
attracted growing interest over the past few years due to their
unique physical and chemical properties [1]. They usually consist of
poorly coordinating ion pairs, and a classical example is the readily
accessible 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]
BF4, which is a colourless mobile but non-volatile liquid [2]. Recent
advances in ionic liquid research provided another route for
achieving task-specific ionic liquids (TSILs) in which a functional
group is covalently tethered to the cation or anion of the ionic
liquid, especially to the two N atoms of the imidazole ring. TSILs
have been increasingly used as solvents and reagents or catalysts
due to their specific properties [3e7].
In recent decades, Organic colour chemistry is undergoing very
exciting developments as a result of the opportunities presented by
dye applications in high technology fields e.g., electronic devices,
linear and non linear optics, reprography, sensors and biomedical
uses [8]. Azo dyes are very important synthetic dyes which are used
extensively in industry [9]. Aromatic diazonium salts are important
building blocks in the preparation of azo dyes which were
synthesized via the diazotization of aryl amines using nitrous acid.
such as t-butyl nitrite and ethyl nitrite have been used as alterna-
tive sources of nitrous acid in organic solvents [10]. Many studies
have reported the diazotization of aniline derivatives [11e15].
ꢀ
Lycka and co-workers reported the synthesis of some phenyl-
azonaphthols in 1-butyl-3-methylimidazolium tetrafluoroborate
using
a coupling reaction of (4-X-benzene)diazonium tetra-
fluoroborates (X ¼ H and NO2) with 1- and 2-naphthols and their
sodium salts [16]. Noroozi et al. synthesized azo dyes via diazoti-
zation of aniline derivatives and subsequent azo-couplings in the
presence of p-toluenesulfonic acid by grinding [17]. In continuation
of our work on the using of task-specific phosphinite ionic liquid as
solvent and catalyst/reagent for the synthesis of some heterocyclic
compounds and nitrones [18e21], we now introduce a new nitrite
ionic liquid (IL-ONO) that can act as nitrosonium source for the
efficient conversion of aryl amines to their corresponding diazo-
nium salts. In situ azo-coupling of these diazonium salts afforded
the related azo dyes in good yields.
2. Experimental
2.1. Materials and instrumentation
All reagents were purchased from Merck Company and used
without further purification. Infrared spectra were recorded in KBr
* Corresponding author. Tel.: þ98 411 3856447; fax: þ98 412 4327541.
E-mail address: h-valizadeh@azaruniv.edu (H. Valizadeh).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.11.010

H. Valizadeh, A. Shomali / Dyes and Pigments 92 (2012) 1138e1143
1139
Me
Me
Me
Cl-
N
N
Neat, 80°C
4h, 92%
OH
N
N
+
N
+
Cl
N
OH
O
1
Me
Cl-
Cl-
+
+
NaNO2, HCl
0oC , 45 min
N
N
OH
NO
2 = IL-ONO
Scheme 1. Preparation of nitrite ionic liquid (IL-ONO).
and were determined on a Perkin Elmer FT-IR spectrometer. 1H
NMR spectra were recorded on a Bruker Avance AC- 400 MHz using
DMSO-d6 or CDCl3 as the deuterated solvents and TMS as internal
standard. All melting points measured in open glass-capillaries
using a Stuart melting point apparatus.
nitrite (15 mL, 7.59 g, 0.11 mol). While stirring of the mixture, 37%
HCl (11 mL) was added slowly at 0 ꢀC. While cold, the mixture was
washed with cold water (20 mL) and dried under vacuum at room
temperature for 4 h. Isolated yield was 87%. FT-IR (KBr, cmꢂ1): 1651,
1625, 1605. 1H NMR (400 MHz, DMSO-d6)
d 1.27 (2H, m, CH2); 1.43
(2H, m, CH2); 2.89 (3H, s, NeCH3); 3.78 (2H, t, NeCH2); 4.23 (2H, t,
CH2eONO); 7.75, 7.76 (2H, two singlets, C(4,5)eH); 9.15 (1H, s,
C(2)eH). 13C NMR (100 MHz, DMSO-d6); 19.15 (eCH2); 25.96
(eCH2); 37.13 (NeCH3); 51.50 (NeCH2); 67.78 (CH2(ONO)); 124.06
(C(4 or 5)); 124.42 (C(4 or 5)); 136.70 (C(2)). Anal. Calcd (%) for
C8H14ClN3O2: C, 43.74; H, 6.42; N,19.13. Found (%): C, 43.90; H, 6.46;
N, 19.10.
2.2. Synthesis of 1-(4-hydroxybutyl)-3-methylimidazolium chloride
1-Methylimidazole (20 mL, 0.25 mol) and 4-chloro-1-butanol
(27 mL, 0.27 mol) was stirred at 80 ꢀC for 4 h in the absence of any
catalyst and solvent. The unreacted materials were washed by
diethyl ether (3 ꢁ 8 mL). The diethyl ether was removed under
reduced pressure at room temperature, followed by heating under
high vacuum, to yield a colourless liquid that became more viscous
upon extensive drying, but did not solidify. Isolated yield was 92%.
FT-IR (KBr, cmꢂ1): 3510 (bs), 1656, 1612. 1H NMR (400 MHz, CDCl3)
2.4. Diazotization and subsequent azo-coupling with phenolic
compounds using IL-ONO, general procedure
d
1.31 (2H, m, CH2); 1.41 (2H, m, CH2); 2.92 (3H, s, NeCH3); 3.84 (2H,
The aniline derivative (20 mmol) was dissolved in 37% HCl
(10 mL). The mixture was stirred at 0e5 ꢀC for 5 min. While stirring
of the mixture, IL-ONO (30 mmol) was added over 2 min. The
diazonium salt product was assayed by well-known azo-coupling
reaction with phenol or aniline derivatives. For the coupling reac-
tion with phenolic compounds, the reaction mixture was continu-
ously added to the solution of phenolic compound (20 mmol) and
NaOH (1 g) in water (10 mL). The participated dyes were filtered
and washed three times with cold water to afford the crude
azo dyes. The crude dyes were purified by recrystallization on
EtOH/water. For azo-coupling with aniline derivatives, the reaction
mixture containing diazonium salts was continuously added to the
t, NeCH2); 4.15 (2H, dt, CH2eOH); 5.56 (1H, t, OH); 7.76, 7.78 (2H,
two singlets, C(4,5)eH); 9.09 (1H, s, C(2)eH). 13C NMR (100 MHz,
CDCl3) 21.75 (eCH2); 26.31 (eCH2); 35.83 (NeCH3); 39.54 (NeCH2);
64.88 (CH2(OH)); 123.16 (C(4 or 5)); 124.09 C(4 or 5)); (137.00
(C(2)). Anal. Calcd (%) for C8H15ClN2O: C, 50.39; H, 7.93; N, 14.69.
Found (%): C, 51.02; H, 7.95; N, 14.66.
2.3. Synthesis of Il-ONO
Freshly prepared 1-(4-hydroxybutyl)-3-methylimidazolium
chloride (22 g, 0.1 mol) was added to an aqueous solution of sodium
R1
N
+
+
NH3 Cl-
N
N2
O
H
6a
2-naphtol
IL-ONO
0-5 oC , 25 min
+
0 0C , 30 min
R1
R1
3
4
O
H
N
N
R1
5a
Scheme 2. Diazotization of anilines using IL-ONO and diazo-coupling with 2-naphtole.

1140
H. Valizadeh, A. Shomali / Dyes and Pigments 92 (2012) 1138e1143
Table 1
Diazotization of anilines using IL-ONO and synthesis of azo dyes.
Entry
Coupling reagent (AreH)
Amine
Amine number
Product
Structure number
OH
O2N
NH2
N
N
NO2
1
3a
5a
OH
OH
NH2
N
N
2
3b
5b
OH
OH
HO
NH2
N
N
OH
3
3c
5c
OH
CHO
CHO
OH
O2N
NH2
O2N
N
N
OH
4
5
6
3d
3e
3f
5d
5e
5f
CHO
Cl
CHO
OH
O2N
N
N
OH
NH2
O2N
Cl
OH
OH
OH
O2N
NH2
O2N
N
N
OH
OH
HO
O2N
NH2
O2N
N
N
OH
7
3g
5g
OH
O2N
N
N
NH2
NH2
O2N
NH2
8
3h
3i
5h
5i
N
N
NMe2
NMe2
NMe2
NH2
9
O2N
N
N
NMe2
O2N
NH2
10
3j
5j

H. Valizadeh, A. Shomali / Dyes and Pigments 92 (2012) 1138e1143
1141
Table 1 (continued )
Entry
Coupling reagent (AreH)
Amine
Amine number
Product
Structure number
O2N
N
N
NEt2
NEt2
OH
O2N
O2N
NH2
NH2
11
3k
5k
5l
O2N
N
N
OH
12
3l
solution of aniline derivative (20 mmol) in water (10 mL) at 0e5 ꢀC.
The pH of mixture was adjusted to 6e7 by addition of NaOH
solution (1 M). The participated dyes were isolated and purified as
described above.
7.28 Hz); 7.49 (1H, dd, J ¼ 7.21 and 2.10 Hz); 7.40 (1H, dt, J ¼ 7.25
and 1.98 Hz); 7.43 (1H, dt, J ¼ 7.29 and 2.09 Hz); 7.32 (2H, d, J ¼
7.51); 7.15 (2H, d, J ¼ 7.51); 6.62 (1H, d, J ¼ 7.28 Hz); 13C NMR (100
MHz, CDCl3)
d (ppm): 159.51, 138.90, 135.54, 129.23, 128.51, 127.11,
123.63, 122.29, 122.20, 121.56, 120.32, 116.87, 115.89, 111.23.
Compound 5d (azo): C13H9N3O4: FT-IR (KBr, cmꢂ1): 3413, 3104,
1658, 1606, 1524, 1478, 1342, 1284. 1H NMR (400 MHz, CDCl3)
2.5. Selected spectroscopic data
d
(ppm): 11.43 (1H, s); 10.05 (1H, s); 8.39 (2H, d, J ¼ 7.26 Hz); 8.27
Compound 5a (azo): C16H11N3O3: FT-IR (KBr, cmꢂ1): 3409 (bs),
(1H, d, J ¼ 2.21 Hz); 8.22 (1H, dd, J ¼ 7.21, 2.21 Hz); 8.01 (2H, d, 7.26
1665, 1621. 1H NMR (400 MHz, CDCl3)
d (ppm): 12.02 (H, broad,
Hz); 7.14 (1H, d, J ¼ 7.21 Hz). 13C NMR (100 MHz, CDCl3)
d (ppm):
OH); 8.42 (1H, dd, J ¼ 8.11 and 2.03 Hz); 7.82 (2H, d, J ¼ 7.98 Hz);
7.56 (2H, d, J ¼ 7.98); 7.53 (1H, d, J ¼ 7.25 Hz); 7.45 (1H, d, J ¼ 7.25
Hz); 7.43 (1H, dd, J ¼ 7.96 and 2.02 Hz); 7.41 (1H, dt, J ¼ 7.65 and
1.98 Hz); 7.39 (1H, dt, J ¼ 7.75 and 1.96 Hz); 13C NMR (100 MHz,
160.09, 135.87, 134.14, 130.25, 129.36, 128.63, 121.54, 117.68, 112.17,
110.95.
Compound 5g (azo): C12H9N3O4: FT-IR (KBr, cmꢂ1): 3460 (bs),
3380, 1628, 1611. 1H NMR (400 MHz, CDCl3)
d (ppm): 12.01 (s, OH);
CDCl3) d (ppm): 142.58, 137.45, 134.04, 130.21, 128.57, 127.18, 124.87,
8.98 (s, OH); 7.81 (d, 2H, J ¼ 8.20 Hz); 7.79 (d, 2H, J ¼ 8.20 Hz); 7.75
121.86, 120.25, 119.50, 119.12, 117.07, 115.65, 112.32.
(d, 1H, J ¼ 8.15 Hz); 6.64 (dd, 1H, J ¼ 8.15 and 2.41 Hz); 6.33 (d, 1H,
Compound 6a (hydrazone): C16H11N3O3: FT-IR (KBr, cmꢂ1): 3395,
J ¼ 2.41 Hz). 13C NMR (100 MHz, CDCl3)
d (ppm): 156.25, 149.79,
1684, 1668, 1610. 1H NMR (400 MHz, CDCl3)
d (ppm): 14.16 (NH);
148.12, 146.06, 130.98, 128.36, 127.36, 120.98, 110.74, 105.98.
Compound 6g (azo): C12H9N3O4: FT-IR (KBr, cmꢂ1): 3421 (bs),
8.47 (1H, dd, J ¼ 7.35 and 2.09 Hz); 7.49 (1H, d, J ¼ 7.81 Hz); 6.59
(1H, d, J ¼ 7.81 Hz); 7.48 (1H, dd, J ¼ 7.54 and 2.13 Hz); 7.65 (2H, d,
J ¼ 7.65); 7.51 (1H, dt, J ¼ 7.41 and 2.11 Hz); 7.41 (1H, dt, J ¼ 7.48 and
3341, 1688, 1668. 1H NMR (400 MHz, CDCl3)
d (ppm): 14.21 (s, NH);
7.72 (d, 2H, J ¼ 7.95 Hz); 7.63 (d, 2H, J ¼ 7.95 Hz); 6.31 (d, 1H, J ¼ 8.12
2.54 Hz); 7.15 (2H, d, J ¼ 7.65); 13C NMR (100 MHz, CDCl3)
d (ppm):
Hz); 6.22 (d, 1H, J ¼ 8.12 Hz); 6.05 (s, 2H); 13C NMR (100 MHz,
158.49, 138.78, 136.54, 129.65, 128.12, 126.17, 123.68, 122.54, 122.68,
121.05, 120.97, 118.37, 116.76, 108.72.
CDCl3) d (ppm): 160.15,159.52,142.16,140.12,129.63,128.06,111.00,
105.41, 103.32, 78.27.
Compound 5b (azo): C16H12N2O: FT-IR (KBr, cmꢂ1): 3420 (bs),
Compound 5j (azo): C14H14N4O2: FT-IR (KBr, cmꢂ1): 1611, 1519,
1660, 1605. 1H NMR (400 MHz, CDCl3)
d (ppm): 12.13 (OH); 8.02
1475, 1531, 1345. 1H NMR (400 MHz, CDCl3)
d
(ppm): 7.78 (d, 2H, J ¼
(1H, dd, J ¼ 7.38 and 2.14 Hz); 7.65 (2H, m); 7.49 (1H, d, J ¼ 7.82 Hz);
7.45 (1H, dd, J ¼ 7.21 and 2.10 Hz); 7.43 (1H, dt, J ¼ 7.73 and 2.03
Hz); 7.39 (1H, d, J ¼ 7.82 Hz); 7.36 (1H, dt, J ¼ 7.55 and 1.89 Hz); 7.15
8.02 Hz); 7.75 (d, 2H, J ¼ 8.0 2); 7.70 (d, 2H, J ¼ 7.95 Hz); 6.69 (d, 2H,
J ¼ 7.95 Hz); 3.65 (s, 6H, eNMe2); 13C NMR (100 MHz, CDCl3)
d
(ppm): 135.54, 128.89, 126.63, 125.54, 123.35, 120.19, 117.85,
(3H, m); 13C NMR (100 MHz, CDCl3)
d (ppm): 140.01, 138.20, 135.35,
115.12, 35.12.
128.96, 128.31, 127.54, 124.52, 121.31, 120.28, 120.06, 119.12, 117.17,
116.29, 110.28.
Compound 6b (hydrazone): C16H12N2O: FT-IR (KBr, cmꢂ1): 3391,
3. Results and discussions
1685, 1667, 1612. 1H NMR (400 MHz, CDCl3)
d (ppm): 14.26 (NH);
8.42 (1H, dd, J ¼ 7.78 and 2.35 Hz); 7.62 (1H, d, J ¼ 7.74 Hz); 7.44
(1H, dd, J ¼ 7.61 and 2.13 Hz); 7.41 (1H, dt, J ¼ 7.81 and 2.42 Hz);
7.39 (1H, dt, J ¼ 7.60 and 2.05 Hz); 7.58 (2H, m); 7.35 (3H, m); 6.70
The IL-OH, 1-(4-hydroxybutyl)-3-methylimidazolium chloride 1
was prepared by the efficient alkylation of the 3-methylimidazole
with 4-chlorobutanole at 80 ꢀC in 92% yield. The resulting ionic
liquid when left in contact with 3 M NaNO2 and HCl (1:1) solution
at 0 ꢀC was transformed into the ester-ionic liquid 2 in 87% yield
(Scheme 1). Synthesis of nitrite ionic liquid 2 was confirmed by its
FT-IR spectrum. The broad band at 3510 cmꢂ1 arising from OeH
stretching vibration in compound 1 was disappeared and a new
band emerged around 1605 cmꢂ1 can be ascribed to the asym-
metrical stretching of the nitrite ester group, which is characteristic
for nitrite esters group [22].
The new nitrite ionic liquid was used for the diazotization of
aniline derivatives at 0e5 ꢀC in the presence of HCl. In a pilot
experiment, the mixture of freshly prepared nitrite ionic liquid and
4-nitroaniline 3a was stirred with 37% HCl for 25 min to obtain the
4-nitrodiazonium intermediate 4a (R1 ¼ 4-NO2). The 4-nitro-
diazonium intermediate was not isolated. The mixture of reaction
(1H, d, J ¼ 7.74 Hz); 13C NMR (100 MHz, CDCl3)
d (ppm): 159.69,
139.45, 137.8 4, 130.13, 129.19, 126.23, 124.51, 122.12, 122.00, 121.56,
120.02, 117.12, 113.80, 109.28.
Compound 5c (azo): C16H12N2O2: FT-IR (KBr, cmꢂ1): 3415, 3395,
1668, 1610. 1H NMR (400 MHz, CDCl3)
d (ppm): 12.12 (2H, OH); 7.65
(1H, d, J ¼ 7.58 Hz); 7.59 (1H, d, J ¼ 7.58 Hz); 7.51 (1H, dd, J ¼ 7.45
and 2.13 Hz); 7.45 (1H, dt, J ¼ 7.61 and 2.08 Hz); 7.49 (1H, dt, J ¼ 7.59
and 2.14 Hz); 8.32 (1H, dd, J ¼ 7.54 and 2.20 Hz); 7.65 (2H, d, J ¼
7.51); 7.57 (2H, d, J ¼ 7.51); 13C NMR (100 MHz, CDCl3)
d
(ppm):
159.51, 138.90, 135.54, 129.23, 128.51, 127.11, 123.63, 122.29, 122.20,
121.56, 120.32, 116.87, 115.89, 111.23.
Compound 6c (hydrazone): C16H12N2O2: FT-IR (KBr, cmꢂ1): 3415,
3395, 1672, 1658, 1610. 1H NMR (400 MHz, CDCl3)
d
(ppm): 15.1 6
(NH); 12.12 (OH); 8.42 (1H, dd, J ¼ 7.23 and 2.23 Hz); 7.51 (1H, d, J ¼

1142
H. Valizadeh, A. Shomali / Dyes and Pigments 92 (2012) 1138e1143
Table 2
Comparison of the reaction times and yields with the reported values.
Entry
Structure
number
Reaction time (min)
M.P (ꢀC)
Found
Yield (%)
Found
Found
Reported [Ref.]
Reported [Ref.]
Reported [Ref.]
1
2
3
4
5
6
7
8
5a
5b
5c
5d
5e
5f
5g
5h
5i
22
25
20
24
22
20
25
25
25
20
25
22
30 [23]
e
250e252
131e132
196e199
185e186
126e128
187e190
196e198
199e202
108e112
218e222
145e146
203e204
248e252 [24]
131e132 [25]
192e193 [26]
184e186 [27]
127e128 [28]
188e190 [29]
185 [29]
89
87
85
84
90
88
89
90
84
83
85
86
83 [23]
e
e
e
e
93.7 [26]
e
e
e
e
e
80 [14]
e
e
200 [29]
111 [29]
9
20 [23]
30 [23]
e
81 [23]
85 [23]
e
10
11
12
5j
5k
5l
225e228 [30]
a
30 [23]
207 [30]
86 [23]
a
The melting point of this product was not found in the literature.
[2] Suarez PAZ, Dullius JEL, Einloft S, De Souza R, Dupont J. The use of new ionic
liquids in two-phase catalytic hydrogenation reaction by rhodium complexes.
Polyhedron 1996;15:1217e9.
[3] Gong K, Fang D, Wang H-L, Zhou X-L, Liu Z-L. The one-pot synthesis of
14-alkyl- or aryl-14 H-dibenzo[a, j]xanthenes catalyzed by task-specific ionic
liquid. Dyes Pigments 2009;80:30e3.
[4] Wang L, Li H, Li P. Task-specific ionic liquid as base, ligand and reaction
medium for the palladium-catalyzed Heck reaction. Tetrahedron 2009;65:
364e8.
[5] Yue C, Mao A, Wei Y, Lü M. Knoevenagel condensation reaction catalyzed by
task-specific ionic liquid under solvent-free conditions. Catal Commun
2008;9:1571e4.
[6] Dhar L, Yadav S, Patel R, Rai V, Vishnu K, Srivastava P. An efficient conjugate
hydrothiocyanation of chalcones with a task-specific ionic liquid. Tetrahedron
Lett 2007;48:7793e5.
[7] Siyutkin DE, Kucherenko AS, Struchkova MI, Zlotin SG. A novel (S)-proline
modified task-specific chiral ionic liquiddan amphiphilic recoverable catalys
for direct asymmetric aldol reactions in water. Tetrahedron Lett 2008;49:
1212e6.
was added to the solution of b-naphthol sodium salt to obtain the
azo dye 5a via the well-known azo-coupling reaction with diazo-
nium intermediate (Scheme 2). The structure of azo dye 5a was
characterized by comparing its (1H, 13C NMR and IR) spectroscopic
data and melting point with literature values.
Optimization of the reaction conditions was studied with
different molar ratios of the aniline, ionic liquid and b-naphthol.
The best ratio was found to be 1:1.5:1. Increasing the amount of
ionic liquid led to the mixture of products and low yield of azo dye
was obtained. In this method the IL-ONO acts as a nitrosonium
source reagent. This ionic liquid was then used for diazotization of
aniline derivatives and subsequent transformation to azo dyes via
the reaction with a variety of phenolic compounds and aniline
derivatives (Table 1). The in-situ azo-coupling reaction product of
p-nitrobenzodiazonium chloride, benzenediazonium chloride and
[8] Noroozi PN, Khalafy J, Malekpoor Z. Prog Color Colorants Coat 2009;2:
61e70.
p-hydroxybenzodiazonium chloride with
b-naphthol existed as
[9] Zollinger H. Color chemistry-syntheses, properties and applications of organic
dyes and pigments. New York: VCH Publishers; 1987. pp. 92e102.
[10] Okuzumi T, Nakanishi E, Tsuji T, Makino S. Efficient solid-phase synthesis of
diverse 1,2,3-benzotriazin-4-ones using tert-butyl nitrite. Tetrahedron Lett
2003;44:5539e42.
[11] Dabbagh HA, Teimouri A, Chermahini AN. Green and efficient diazotiza-
tion and diazo coupling reactions on clays. Dyes Pigments 2007;73:
239e44.
[12] Li F, Chen W, Dong P, Zhang S. A simple strategy of probe DNA immobilization
by diazotization-coupling on self-assembled 4-aminothiophenol for DNA
electrochemical biosensor. Biosens Bioelectron 2009;24:2160e4.
[13] Gorlushko DA, Filimonov VD, Krasnokutskaya EA, Semenischeva NI, Go BS,
Hwang HY, Cha EH, Chi K-W. Iodination of aryl amines in a water-paste form
via stable aryl diazonium tosylates. Tetrahedron Lett 2008;49:1080e2.
[14] Faustino H, El-Shishtawy RM, Reis LV, Santos PF, Almeida P. 2-Nitro-
sobenzothiazoles: useful synthons for new azobenzothiazole dyes. Tetrahe-
dron Lett 2008;49:6907e9.
a mixture of (5a and 6a in molar ratio 1.2:0.1), (5b and 6b in molar
ratio 1:0.1) and (5c and 6c in molar ratio 1.2:0.1) respectively. The
molar ratios of the isomers were determined by 1H NMR spec-
troscopy by comparison of the relative integrals of the OH/NH
signals of the respective isomers. As can be seen from Table 1,
electron withdrawing or releasing groups on both reactants have
no significant effect on the reaction times and yields of products in
this procedure. All of the products were characterized by
comparing their (1H, 13C NMR and IR) spectroscopic data and
melting points with literature values.
We also compared the results (reaction times and yields of
products) of the preparation of selected products via present
method with those reported in the literature. As shown in Table 2,
azo dyes were prepared in yields comparable with those obtained
by traditional routes reported in the literature.
[15] Ramachary DB, Narayana VV, Ramakumar K. Direct ionic liquid promoted
organocatalyzed diazo-transfer reactions: diversity-oriented synthesis of
diazo-compounds. Tetrahedron Lett 2008;49:2704e9.
In conclusion, using newand easily prepared nitrite ionic liquid as
a nitrosonium source provides an attractive and practical method for
the clean diazotization and subsequent azo-coupling for the prepa-
ration of azo dyes. To our knowledge, this is the first report con-
cerning the diazotization of anilines in TSILs under mild conditions.
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[16] Lycka A, Kolonicnỳ A, Simunek P, Machacek V. Synthesis of some phenyl-
azonaphthols in an ionic liquid. Dyes Pigments 2007;72:208e11.
[17] Noroozi NP, Khalafy J, Malekpoor Z. Can be azo dyes obtained by grinding
under solvent-free conditions? J Chin Chem Soci 2009;56:1018e27.
[18] Valizadeh H. Efficient combination of task-specific ionic liquid and microwave
dielectric heating applied to synthesis of a large variety of nitrones. Hetero-
atom Chem 2010;21:78e83.
[19] Valizadeh H, Shockravi A. Task-specific ionic liquid as reagent and reaction
medium for the one-pot HornereWadswortheEmmonseType reaction under
microwave irradiation. Synth Commun 2009;39:4341e9.
Acknowledgments
[20] Valizadeh H, Golipour H. Imidazolium-based phosphinite ionic liquid (IL-
OPPh2) as reusable catalyst and solvent for the Knoevenagel condensation
reaction. Synth Commun 2010;40:1477e85.
[21] Valizadeh H, Shockravi A. Imidazolium-based phosphinite ionic liquid as
reusable catalyst and solvent for one-pot synthesis of 3,4-dihydropyrimidin-
2(1 H)-(thio)ones. Heteroatom Chem 2010;20:284e8.
The partial financial assistance from the Research Vice Chan-
cellor of Azarbaijan University of Tarbiat Moallem is gratefully
acknowledged.
References
[22] Bicak N, Bulbul H. Polymer supported nitrite esters as diazotising reagent.
Polym Bull 2001;46:139e45.
[1] Welton T. Room-temperature ionic liquids. Solvents for synthesis and catal-
[23] Williamson KL. Macroscale and microscale organic experiments. 2nd ed.
Boston: Houghton Mifflin; 1994.
ysis. Chem Rev 1999;99:2071e83. and references cited therein.

H. Valizadeh, A. Shomali / Dyes and Pigments 92 (2012) 1138e1143
1143
[24] Long MJD, Prochaska HJ, Talalay P. Med Sci 1986;83:787e91.
(b) Hewitt JT, Mitchell HV. Colour and constitution of azo-compounds Part I.
J Chem Soc 1907;91:1262.
[28] Hartmann H, Zug I. J Chem Soc Perkin Trans 1 2000;1:4316e20.
[29] Lutfor MR, Tschierske C, Yusoff M, Silong S. Tetrahedron Lett 2005;46:2303e6.
[30] Zarei A, Hajipour Abdol R, Khazdooz L, Mirjalili BF, Najafi AC. Dyes Pigments
2009;81:240e4.
[25] Khanmohammadi H, Darvishpour M. Dyes Pigments 2009;81:167e73.
_
[26] Dinçalp H, Toker F, Durucasu I, Avcıbas¸ ı N, Icli S. Dyes Pigments 2007;75:
11e24.
[27] (a) Kobayashi H, Sonoda A, Sonoda T. Syntheses of some arylazospiropyrans.
Rep Inst Adv Mat Study 1992;6:87e92;