Ionic liquid 1-(3-trimethoxysilylpropyl)-3-methylimidazolium nitrite as a new reagent for the efficient diazotization of aniline derivatives and in situ synthesis of azo dyes

Article abstract of DOI:10.1007/BF03249083

A new ionic liquid 1-(3-trimethoxysilylpropyl)-3-methylimidazolium nitrite was synthesized. This ionic liquid was used as a convenient nitrosonium source in diazotization of arylamines into their corresponding diazonium salts which were converted into their related azo dyes via the in situ azo-coupling with aniline derivatives or phenolic compounds. The diazotization of anilines in this ionic liquid and subsequent azo-coupling generated the related azo dyes in good to excellent yields at 0-5 °C in short reaction times via a simple experimental procedure.

Full text of DOI:10.1007/BF03249083

J. Iran. Chem. Soc., Vol. 8, No. 2, June 2011, pp. 495-501.
JOURNAL OF THE
Iranian
Chemical Society
Ionic Liquid 1-(3-Trimethoxysilylpropyl)-3-methylimidazolium Nitrite as a New
Reagent for the Efficient Diazotization of Aniline Derivatives and In Situ Synthesis of
Azo Dyes
H. Valizadeh*, M. Amiri, A. Shomali and F. Hosseinzadeh
Department of Chemistry, Faculty of Sciences, Azarbaijan University of Tarbiat Moallem, Tabriz, Iran
(
Received 10 July 2010, Accepted 4 October 2010)
A new ionic liquid 1-(3-trimethoxysilylpropyl)-3-methylimidazolium nitrite was synthesized. This ionic liquid was used as a
convenient nitrosonium source in diazotization of arylamines into their corresponding diazonium salts which were converted into
their related azo dyes via the in situ azo-coupling with aniline derivatives or phenolic compounds. The diazotization of anilines in
this ionic liquid and subsequent azo-coupling generated the related azo dyes in good to excellent yields at 0-5 °C in short reaction
times via a simple experimental procedure.
Keywords: Diazotization, Ionic liquid, Azo dyes, Azo-coupling, Diazonium salt
INTRODUCTION
catalyzed Knoevenagel condensation reaction [6]. Tajik and
co-workers reported the nitration of phenols using acidic ionic
liquid under mild conditions [7]. Pawar et al. synthesized the
The importance of green reactions in organic synthesis has
encouraged scientists to explore the use of room-temperature
ionic liquids (RTILs) as a powerful alternative to the
conventional molecular organic solvents or catalysts, due to
their particular properties, such as undetectable vapor
pressure, wide liquid range, as well as the ease of recovery and
reuse [1-5]. Most recently, special attention has been focused
on the synthesis of functionalized ionic liquids (FILs), through
the incorporation of additional functional groups as a part of
the cation and/or anion, so-called task-specific ionic liquids
flavones in [bmim]BF , ionic liquid [8]. Hajipour and co-
4
workers reported a convenient method for the preparation of
aldoximes in the presence of in situ prepared ionic liquids [9].
Very recently we used the TSIL-OPPh as a weak Lewis base
2
catalyst and reaction medium for the Biginelli and
Knoevenagel reactions and also in the synthesis of nitrones
[10-12]. We also used task-specific phosphinite ionic liquid as
a reagent and reaction medium for the one-pot Horner-
Wadsworth-Emmons-type
irradiation [13].
reaction
under
microwave
(
TSILs), and their applications in chemical research. They
have shown great promise not only as alternative green
solvents, but also as reagents or catalysts in organic
transformations. Wang and Li used TSIL as Lewis base,
ligand and reaction medium for the palladium catalyzed Heck
reaction [4]. Paun and Barkile reported the basic ionic liquid-
In recent decades, in the field of organic colour chemistry
very exciting developments have taken place as a result of the
opportunities opened up by dye applications in high
technology fields: electronic devices, linear and non-linear
optics, reprography, sensors and biomedical uses [14-15]. Azo
dyes are very important synthetic dyes which are used
extensively in industry [15]. Aromatic diazonium salts are
*Corresponding author. E-mail: h-valizadeh@azaruniv.edu

Valizadeh et al.
important building blocks in the preparation of azo dyes which
Bruker Avance AC-400 MHz using CDCl or DMSO-d as the
3 6
are synthesized via the diazotization of aryl amines using
nitrous acid. Sodium or potassium nitrites are used as nitrous
acid sources because of the instability of free nitrous acid.
Organic nitrite esters, such as t-butyl nitrite and ethyl nitrite
have been used as nitrous acid source in organic solvents [16].
Many research studies have been reported on the diazotization
of aniline derivatives [17-21]. Lyčka and co-workers reported
the synthesis of some phenylazonaphthols in 1-butyl-3-
methylimidazolium tetrafluoroborate using a coupling reaction
of (4-X-benzene)diazonium tetrafluoroborates (X = H and
deuterated solvents and TMS as the internal standard. All
melting points were measured in open glass-capillaries using
Stuart melting point apparatus.
Synthesis of 1-(3-Trimethoxysilylpropyl)-3-methyl-
imidazolium Chloride
A mixture of N-methylimidazole (20 ml, 25 mmol) and (3-
chloropropyl) trimethoxysilane (6 g, 25 mmol) was stirred at
80 °C for 48 h. The unreacted materials were washed by
diethyl ether (8 ml×3). The diethyl ether was removed under
reduced pressure at room temperature, followed by heating
under high vacuum, to yield a colorless liquid that became
more viscous upon extensive drying, but did not solidify.
Isolated yield was 96%. IR (KBr): 1637, 1572, 1190, 1078
NO ) with 1- and 2-naphthols and their sodium salts [22].
2
Noroozi et al. synthesized the azo dyes via diazotization of
aniline derivatives and the subsequent azo-couplings in the
presence of p-toluenesulfonic acid by grinding [23]. We now
introduce a new nitrite ionic liquid that can act as a
nitrosonium source for the efficient conversion of aryl amines
to their corresponding diazonium salts. In situ azo-coupling of
these diazonium salts afforded the related azo dyes in good
yields (Scheme 1).
-1
1
cm ; H NMR (400 MHz, CDCl ) δ 0.15 (2H, t, -CH -Si),
3
2
1.81 (2H, m, CH ), 3.35 (9H, s, 3(-OCH )), 3.84 (3H, s, N-
2
3
CH ), 3.95 (2H, t, -N-CH ), 7.25 (1H, d, pyr-H), 7.45 (1H, d,
3
2
1
3
pyr-H), 10.12 (1H, broad, pyr-H). C NMR (100 MHz,
CDCl ) 11.7, 18.3, 35.6, 36.4, 65.8, 125.3, 127.4, 139.3.
3
EXPERIMENTAL
Synthesis of 1-(3-Trimethoxysilylpropyl)-3-methyl-
imidazolium Nitrite
General
Freshly prepared 1-(3-trimethoxysilylpropyl)-3-methyl-
All reagents were purchased from Merck Company and
used without further purification. Infrared spectra were
recorded in KBr and were determined on a Perkin Elmer FT-
imidazolium chloride (20 mmol) and NaNO (20 mmol) were
2
added into deionized water (25 ml) and the mixture was stirred
for 24 h at room temperature. The solvent was removed under
reduced pressure at 50 °C, to obtain the crude product
1
13
IR spectrometer. H and C NMR spectra were recorded on a
_
NO2
N
+
N
Ionic Liquid =
Si(OMe)
3
1
+
+
-
NH Cl
N
2
3
Ar-H
Ionic Liquid
Coupling reagent =Ar-H
N
N
Ar
o
0
0
-5 C , 35 min
0 C , 30 min
R1
R1
R1
4a-l
2a-l
3
Scheme 1. Diazotization of anilines using nitrite ionic liquid and synthesis of azo-dyes
4
96

Ionic Liquid 1-(3-Trimethoxysilylpropyl)-3-methylimidazolium Nitrite
1
containing nitrite ionic liquid and NaCl, which was washed
with acetonitrile (3×10 ml). The remaining acetonitrile was
removed under high vacuum to yield yellow transparent liquid
that became more viscous upon extensive drying. Isolated
yield was 91%. IR (KBr): 1630, 1575, 1459, 1349, 1184, 1085
2912, 1591, 1503, 1397, 1365, 1142, 816, 743. H NMR
(DMSO-d ): δ: 8.22-8.01 (4H, m), 7.79-7.01 (3H, m), 6.91
(2H, d, J = 8.87 Hz), 3.11 (6H, s). Anal. Calcd. for C14
6
H
15
3
N :
C, 74.66; H, 6.22; N, 18.66%. Found: C, 75.99; H, 6.39; N,
18.51%.
-1
1
'
cm ; H NMR (400 MHz, DMSO-d ) δ 0.14 (2H, t, -CH -Si),
4-Dimethylamino-4 -nitroazobenzene (4j). IR (KBr)
6
2
-1
1
1
.79 (2H, m, CH ), 3.32 (9H, s, 3(-OCH )), 3.79 (3H, s, N-
cm : 3101, 2918, 1609, 1541, 1347, 1229, 1050. H NMR
2
3
CH ), 3.89 (2H, t, -N-CH ), 7.23 (1H, d, pyr-H), 7.43 (1H, d,
pyr-H), 10.02 (1H, broad, pyr-H). C NMR (100 MHz,
(DMSO-d ): δ: 8.12 (2H, d, J = 8.09 Hz), 7.98 (2H, d, J = 8.09
Hz), 7.90 (2H, d, J = 8.94 Hz), 7.01 (2H, d, J = 8.94 Hz), 3.18
3
2
6
1
3
DMSO-d ) 10.11, 19.85, 34.08, 35.05, 63.41, 127.30, 128.78,
(6H, s). Anal. Calcd. for C H N O : C, 62.22; H, 5.18; N,
6
14 14
4
2
+
+
1
37.39. MS: (EI ) m/z 291 [IL-NO
2
] .
20.74%. Found: C, 62.36; H, 5.32; N, 19.96%.
'
-
4
-Diethylamino-4 -nitroazobenzene (4k). IR (KBr) cm
1
1
General Procedure for Diazotization Using New
Nitrite Ionic Liquid
: 3041, 2931, 1622, 1510, 1600, 1554, 1379, 1218, 842. H
NMR (DMSO-d ): δ: 8.21 (2H, d, J = 7.91 Hz), 7.98 (2H, d,
6
Aniline derivative (20 mmol) was dissolved in 10 ml of
J = 7.91 Hz), 7.88 (2H, d, J = 8.45 Hz), 7.10 (2H, d, J = 8.45
Hz), 3.40 (4H, q, J = 7.31 Hz), 1.18 (6H, t, J = 7.31 Hz). Anal.
Calcd. for C H N O : C, 64.41; H, 6.08; N, 18.78%. Found:
3
7% HCl. The mixture was stirred at 0-5 °C for 35 min. Nitrite
ionic liquid (25 mmol) was added to the aniline solution.
Diazonium salt product was assayed by the well-known azo-
coupling reaction of phenol or aniline derivatives. For the
coupling reaction with phenolic compounds, the reaction
mixture was continuously added to the solution of phenolic
compound (20 mmol) and NaOH (1 g) in 10 ml water. After
1
6
18
4
2
C, 66.09; H, 5.81; N, 18.32%.
4-Hydroxy-4 -nitroazobenzene (4l). IR (KBr) cm :
3487 (bs), 1624, 1610, 1530, 1348, 1170, 710. H NMR
'
-1
1
(DMSO-d ): δ: 12.31 (1H, bs), 8.18 (2H, d, J = 8.11 Hz), 7.78
6
(2H, d, J = 8.11 Hz), 7.62 (2H, d, J = 8.35 Hz), 7.02 (2H, d,
J = 8.35 Hz). Anal. Calcd. for C H N O : C, 59.26; H, 3.73;
1
5-25 min, the precipitated dyes were filtered off and washed
1
2
9
3
3
three times with cold water to afford the crude azo dyes. The
crude dyes were purified by recrystallization on ethanol/water.
For azo-coupling with aniline derivatives, the reaction mixture
containing diazonium salts was continuously added to the
solution of aniline derivative (20 mmol) in 10 ml water at 0-5
N, 17.28%. Found: C, 61.52; H, 3.80; N, 17.95%.
RESULTS AND DISCUSSIONS
The ionic liquid, 1-(3-trimethoxysilylpropyl)-3-methyl-
imidazolium chloride, was prepared by the efficient reaction
of the N-methylimidazole with (3-chloropropyl) trimethoxy-
silane at 80 °C in 96% yield. While the resulting ionic liquid
°C. The pH of the mixture was adjusted to 6-7 by the addition
of NaOH solution (1 M) during stirring for 20 min. The
precipitated dyes were isolated and purified as described
above.
was left in contact with an equimolar amount of NaNO in
2
deionized water, nitrite ionic liquid 1 was prepared in 91%
yield (Scheme 1). This ionic liquid was air and water stable.
The new nitrite ionic liquid was used for the diazotization
of aniline derivatives at 0-5 °C in the presence of HCl. In a
pilot experiment, the mixture of freshly prepared nitrite ionic
liquid and 4-nitroaniline 2a was let to come into contact with
SELECTED SPECTROSCOPIC DATA
4
-[(2-Hydroxynaphthalen-1-yl)diazenyl]nitrobenzene
-1
(
4a). IR (KBr) cm : 3480, 1620, 1532, 1351, 1210, 1120, 831.
1
H NMR (DMSO-d ): δ: 14.81 (1H, bs), 8.61 (1H, d, J = 8.12
6
Hz), 7.78 (1H, d, J = 8.61 Hz), 7.70-7.80 (4H, m), 7.65 (2H, d,
J = 7.73 Hz), 7.01 (2H, d, J = 7.73 Hz). Anal. Calcd. for
C H N O : C, 65.53; H, 3.78; N, 14.33%. Found: C, 65.64;
37% HCl and was stirred for 25 min to obtain the 4-
1
nitrodiazonium intermediate 3a (R = 4-NO
2
). The 4-
nitrodiazonium intermediate was not isolated. The mixture of
the reaction was added to the solution of ß-naphthol sodium
salt to obtain the azo dye 4a via the well known azo-coupling
1
6
11
3
3
H, 3.90; N, 15.02%.
-Dimethylaminoazobenzene (4i). IR (KBr) cm : 3029,
-1
4
4
97

Valizadeh et al.
_
Cl
o
N
8
0 C , 48h
N
(CH2)3
N
N
+ Cl
+
Si(OMe)3
Si(OMe)3
Deionized water
NaNO2
_
2
4 h, rt
NO2
N
N
+
Si(OMe)3
1
Scheme 1. Preparation of nitrite ionic liquid
reaction with diazonium intermediate (Scheme 2). The
the amount of the ionic liquid led to the mixing of the products
and low yield of azo dye was obtained. In this method, the IL-
ONO acted 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). As shown in Table 1, some desirable results were obtained
structure of azo dye 6a was characterized by comparing its
1
13
(
H, C NMR and IR) spectroscopic data and melting point
with literature values.
Optimization of the reaction conditions was studied using
different molar ratios of the aniline, ionic liquid and ß-
naphthol. The best ratio was found to be 1:1.25:1. Increasing
Table 1. Diazotization of Anilines Using 1-(3-Trimethoxysilylpropyl)-3-methylimidazolium Nitrite as a New Reagent and
Subsequent Synthesis of Azo-Dyes
Entry Coupling reagent (Ar-H)
Amine
Product
Structure number
OH
1
4a
O
2
N
NH
2
N
N
NO
2
OH
OH
2
4b
4c
NH2
N
N
OH
OH
3
HO
NH2
N
N
OH
OH
4
98

Ionic Liquid 1-(3-Trimethoxysilylpropyl)-3-methylimidazolium Nitrite
Table 1. Continued
CHO
CHO
CHO
4
4d
O N
NH2
2
O
2
N
N
N
N
N
OH
OH
OH
CHO
Cl
4
e
5
O N
NH2
2
O N
2
OH
Cl
OH
4f
OH
O N
NH2
6
7
2
O
2
N
N
N
N
OH
OH
OH
HO
4
g
O
N
NH
2
2
O
2
N
N
N
OH
OH
NH2
4
h
8
9
O N
2
NH2
O N
2
N
NH2
4
i
NMe2
NH2
N
N
NMe
2
4
j
O N
NH2
1
0
NMe
2
2
O
2
N
N
N
NMe
2
4
k
O
2
N
N
N
NEt
2
1
1
1
2
NEt
2
O
O
2
N
N
NH
2
2
OH
4
l
NH
O
2
N
N
N
OH
2
aIsolated yield.
in the diazotization of a variety of aniline derivatives. Electron
withdrawing or releasing groups on both reactants had no
significant effect on the reaction times and the yields of
products in this procedure. Compared with the traditional
methods, the quantitative conversion without any by-products
and the stability of nitrite ionic liquid in comparison with
spectroscopic data and melting points with the literature
values.
We also compared the results (reaction times and yields of
products) of the preparation of the selected products via the
present method with those reported in the literature. As shown
in Table 2, azo dyes were prepared in satisfied yields in
comparison with the reported methods.
HNO is an attractive property of the new nitrite ionic liquid as
3
a nitrosonium source. All the well-known products were
characterized by comparing their ( H, C NMR and IR)
In conclusion, we have introduced a method for an easy
preparation of nitrite ionic liquid as a nitrosonium source
1
13
4
99

Valizadeh et al.
Table 2. Comparison of the Reaction Times and Yields with the Reported Values
Entry Structure
number
Time (min)
Reported [Ref.]
M.P (°C)
Yield (%)
Reported [Ref.]
Found
Found
Reported [Ref.]
Found
1
2
3
4
5
6
7
8
9
1
1
1
4a
4b
4c
4d
4e
4f
22
25
20
24
22
20
25
25
25
20
25
22
30 [24]
250-252
131-132
196-199
185-186
126-128
187-190
196-198
199-202
108-112
218-222
145-146
203-204
248-252 [25]
131-132 [26]
192-193 [27]
184-186 [28]
127-128 [29]
188-190 [30]
185 [30]
89
87
85
84
90
88
89
90
84
83
85
86
83 [24]
-
-
-
-
93.7 [27]
85 [28]
-
-
-
-
4g
4h
4i
-
80 [14]
-
-
200 [30]
20 [24]
30 [24]
-
111 [30]
81 [24]
85 [24]
-
0
1
2
4j
225-228 [31]
145-146 [32]
207 [33]
4k
4l
30 [24]
86 [24]
which affords an attractive, practical and clean diazotization of
aniline derivatives. Subsequent in situ azo-coupling of
diazonium salts afforded azo dyes in good yields. To the best
of our knowledge, this should be the first report concerning
the diazotization of anilines in nitrite ionic liquid under mild
conditions.
Forsyth, M. Forsyth, Chem. Commun. (2006) 1905.
C. Paun, J. Barklie, P. Goodrich, H.Q.N. Gunaratne, A.
McKeown, V.I. Pârvulescu, C. Hardacre, J. Mol. Catal.
A: Chem. 269 (2007) 64.
H. Tajik, K. Niknam F. Parsa, J. Iran. Chem. Soc. 6
(2009) 159.
[6]
[7]
[
8]
R.S. Bhosale, S.R. Sarda, R.P. Giram, D.S. Raut, S.P.
Parwe, S.S. Ardhapure, R.P. Pawar, J. Iran. Chem. Soc.
ACKNOWLEDGMENTS
6
(2009) 519.
The partial financial assistance received from the Vice
Chancellor for Research of Azarbaijan University of Tarbiat
Moallem is gratefully acknowledged.
[9]
A.R. Hajipour, F. Rafiee, A.E. Ruoho, J. Iran. Chem.
Soc. 7 (2010) 114.
[10] H. Valizadeh, A. Shockravi, Heteroatom Chem. 20
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[11] H. Valizadeh, H. Gholipour, Synth. Commun. 40
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(
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