Synthesis of triazenes by using aryl diazonium silica sulfates under mild conditions

Article abstract of DOI:10.1016/j.dyepig.2013.10.022

An efficient, fast and straightforward procedure for the synthesis of aryltriazenes is described in the present paper by using aryl diazonium silica sulfates and secondary amines. Using the present method, different kinds of aryl diazonium silica sulfates

Full text of DOI:10.1016/j.dyepig.2013.10.022

Dyes and Pigments 101 (2014) 295e302
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Dyes and Pigments
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Synthesis of triazenes by using aryl diazonium silica sulfates under
mild conditions
,
b
,
c
,
d
e
Amin Zarei a
, Leila Khazdooz , Hamidreza Aghaei , Ghobad Azizi ,
**
*
Alireza Najafi Chermahini e, Abdol R. Hajipour e
,
f
a Department of Science, Fasa Branch, Islamic Azad University, Post Box No 364, Fasa 7461789818, Fars, Iran
b Department of Science, Fasa University, Fasa 7461781189, Fars, Iran
c Department of Science, Khorasgan Branch, Islamic Azad University, Isfahan 81595-158, Iran
d Department of Chemistry, Shahreza Branch, Islamic Azad University, Shahreza 311-86145, Isfahan, Iran
e Pharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
f Department of Pharmacology, University of Wisconsin, Medical School, 1300 University Avenue, Madison, 53706 1532 WI, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient, fast and straightforward procedure for the synthesis of aryltriazenes is described in the
present paper by using aryl diazonium silica sulfates and secondary amines. Using the present method,
different kinds of aryl diazonium silica sulfates, containing electron withdrawing groups as well as
electron donating groups, were rapidly converted to the corresponding of aryltriazenes in good yield and
short reaction time. These reactions were carried out in water at room temperature under mild and
heterogeneous conditions. Moreover, temperature dependent NMR spectra were studied for 1-(2-
nitrophenyl)-3,3-diethyltriazene to determine the rotational barrier energy around N(2)eN(3) bond of
this molecule. Simple and clean work-up, short reaction times and good yields were the advantages of
this method.
Received 2 August 2013
Received in revised form
11 October 2013
Accepted 14 October 2013
Available online 22 October 2013
Keywords:
Aryl diazonium silica sulfates
Secondary amines
Aryltriazenes
Ó 2013 Elsevier Ltd. All rights reserved.
Mild conditions
Dynamic NMR
Rotational barrier energy
1. Introduction
semiconductors and nanoelectronics [25]. Two most widely useful
methods for the synthesis of triazenes are the coupling of aryl
Triazenes are a unique class of polyazo compounds with a long
history in both biological and chemical sciences. These compounds
are used for many purposes such as anticancer agents [1], against
brain tumors [2] and malignant melanoma [3] with minimal side
effects, as protecting groups in natural product synthesis [4e6], as
useful linkers in solid-phase organic synthesis [7e12], as dyes and
photoactive substrates [13e16] and in the formation of novel het-
erocycles [17e20]. Moreover, they are known as important in-
termediates for the modern organic synthesis [21e24]. Recently,
triazenes have been used as precursors to facilitate coupling of
functionalized arenes on the silicon surfaces for the applications in
diazonium salts to primary or secondary amines [26e28] and the
addition of organometallic reagents (RMgX, RLi, etc.) to alkyl azides
[29,30]. However, some of these reagents are very reactive,
commonly flammable, which it is necessary to use special equip-
ment for safety. Therefore, these restrictions necessitate the
development of new methods for the preparation of these signifi-
cant compounds. In continuation of our studies on the stabilization
of diazonium salts on silica sulfuric acid and their application in
organic synthesis [31e40], we report herein an efficient, conve-
nient and environmentally friendly method for the synthesis of
aryltriazenes by employing aryldiazonium silica sulfates with sec-
ondary amines (Scheme 1). These reactions were carried out in
water at room temperature under mild and heterogeneous condi-
tions. Silica sulfate as a bulky counterion with high surface not only
increases the stability of the present salts but also increases the
reaction rate so that these salts can be used under solvent-free
conditions at room temperature [31,32,34,35].
* Corresponding author. Tel.: þ98 9171302525; fax: þ98 3112289113.
** Corresponding author. Department of Science, Fasa Branch, Islamic Azad Uni-
versity, Post Box No 364, Fasa 7461789818, Fars, Iran.
E-mail addresses: aj_zarei@yahoo.com (A. Zarei), Leila_khazdooz@yahoo.com,
lkhazdooz@yahoo.com (L. Khazdooz).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.10.022

296
A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
Et
Et
N
Et
H2O, 10-15 min
ArN2+ -OSO3-SiO2
HN
+
N
N
r.t.
Et
Ar
X
N
X
H2O, 10-15 min
r.t.
ArN2+ -OSO3-SiO2
X = CH2, O
+
N
N
HN
Ar
Scheme 1. An efficient, convenient and environmentally friendly method for the synthesis of aryltriazenes by employing aryldiazonium silica sulfates with secondary amines.
2. Experimental
Calcd for C11H14ClN3: C, 59.06; H, 6.31; N, 18.78. Found: C, 58.92; H,
6.45; N, 18.69.
2.1. General
2.3.3. (Table 1, entry 11) Yellow solid
All reagents were purchased from Merck and Aldrich and used
without further purification. Aryl diazonium silica sulfates were
synthesized according to the previous work [31]. All yields refer to
the isolated products after purification. The products were char-
acterized by comparison with authentic samples and by spectro-
scopic data (IR, 1H NMR, 13C NMR spectra and melting point). All
melting points were taken on a Gallenkamp melting apparatus and
were uncorrected. UV spectra were recorded on a JASCO V-570 UV/
vis/NIR spectrophotometer. IR spectra were recorded on a JASCO
FT/IR-680 PLUS spectrometer. 1H NMR spectra were recorded on
Bruker 400 and 500 MHz.
UV (lmax in CH2Cl2): 346 nm. Mp 74e75 ꢂC; FTIR (KBr) cmꢁ1
:
3034, 2945, 2858, 1639, 1594, 1457, 1394, 1355, 1300, 1273, 1188,
1142, 1105, 1019, 992, 918, 864, 794, 746, 701. 1H NMR (500 MHz,
CDCl3)
d
¼ 7.82 (2 H, d, J ¼ 8.2 Hz), 7.78 (2 H, d, J ¼ 7.4 Hz), 7.56 (1 H,
t, J ¼ 7.3 Hz), 7.51e7.45 (4 H, m), 3.85 (4 H, brs), 1.72 (6 H, brs). 13
C
NMR (125 MHz, CDCl3)
131.91, 130.28, 128.60, 120.56, 43.24, 24.50. Anal. Calcd for
18H19N3O: C, 73.69; H, 6.53; N, 14.32. Found: C, 73.58; H, 6.46; N,
d
¼ 196.53, 154.79, 138.75, 134.49, 132.37,
C
14.24.
2.3.4. (Table 1, entry 14) Yellow oil
UV (lmax in CH2Cl2): 301 nm. FTIR (KBr) cmꢁ1: 3073, 2941, 2858,
1600, 1576, 1525, 1462, 1420, 1355, 1295, 1266, 1188, 1110, 1084,
2.2. General procedure for the synthesis of triazenes
1015, 856, 775, 749, 684. 1H NMR (500 MHz, CDCl3)
d
¼ 7.65 (1 H, d,
J ¼ 8.1 Hz), 7.53, (1 H, d, J ¼ 8.2 Hz), 7.44 (1 H, t, J ¼ 8.3 Hz), 7.17 (1 H,
To a solution of a secondary amine (2 mmol) in water (10 mL),
freshly diazonium silica sulfate (1 mmol) was added and the re-
action mixture was stirred at room temperature for the time
specified in Table 1. The reaction progress was monitored by TLC
(hexane/EtOAc, 75:25). After completion of the reaction (absence of
azo coupling with 2-naphthol), the mixture was diluted with EtOAc
(15 mL) and filtered after vigorous stirring. The residue was
extracted with EtOAc (2 ꢀ 10 mL) and the combined organic layer
was washed with H2O (2 ꢀ 15 mL) and dried over anhydrous
Na2SO4. The solvent was evaporated under reduced pressure to
afford the corresponding product and if necessary, the crude
product was purified by flash column chromatography.
t, J ¼ 8.1 Hz), 3.83 (4 H, brs), 1.71 (6 H, brs). 13C NMR (125 MHz,
CDCl3)
d
¼ 145.62, 144.32, 132.63, 125.22, 124.14, 119.92, 42.41,
24.60. Anal. Calcd for C11H14N4O2: C, 56.40; H, 6.02; N, 23.92.
Found: C, 56.32; H, 6.11; N, 24.01.
2.3.5. (Table 1, entry 20) Pale yellow oil
UV (lmax in CH2Cl2): 292 nm. FTIR (KBr) cmꢁ1: 3065, 2975, 2935,
2873, 1585, 1571, 1467, 1406, 1341, 1265, 1249, 1201, 1106, 1053,
1033, 998, 939, 753, 722, 698, 632. 1H NMR (500 MHz, CDCl3)
d
¼ 7.42e7.38 (2 H, m), 7.19 (1 H, t, J ¼ 7.3 Hz), 7.04 (1 H, t, J ¼ 7.3 Hz),
3.80 (4 H, q, J ¼ 7.1 Hz), 1.31 (6 H, brs). 13C NMR (125 MHz, CDCl3)
d
¼ 148.05, 130.37, 129.70, 127.46, 126.04, 119.00, 42.63, 11.85. Anal.
Calcd for C10H14ClN3: C, 56.74; H, 6.67; N, 19.85. Found: C, 56.67; H,
6.78; N, 19.80.
2.3. The spectral data of new compounds
2.3.1. (Table 1, entry 3) Pale yellow oil
2.3.6. (Table 1, entry 23) Yellow oil
UV (lmax in CH2Cl2): 293 nm. FTIR (KBr) cmꢁ1: 3019, 2938, 2855,
1597, 1483, 1434, 1356, 1292, 1258, 1197, 1175, 1096, 1000, 853, 757,
UV (lmax in CH2Cl2): 298 nm. FTIR (KBr) cmꢁ1: 3073, 2977, 2937,
2875, 1600, 1576, 1525, 1468, 1402, 1352, 1269, 1237, 1201, 1114,
1080, 997, 949, 854, 767, 748, 680. 1H NMR (400 MHz, CDCl3)
718. 1H NMR (500 MHz, CDCl3)
d
¼ 7.34 (1 H, d, J ¼ 7.8 Hz), 7.18 (1 H,
d, J ¼ 7.5 Hz), 7.14 (1 H, d, J ¼ 7.6 Hz), 7.07 (1 H, t, J ¼ 7.3 Hz), 3.77
d
¼ 7.65 (1 H, dd, J1 ¼ 8.0 Hz, J2 ¼ 1.6 Hz), 7.53 (1 H, dd, J1 ¼ 8.0 Hz,
(4 H, brs), 2.42 (3 H, s), 1.71 (6 H, brs). 13C NMR (125 MHz, CDCl3)
J2 ¼ 1.2 Hz), 7.44 (1 H, td, J1 ¼ 8.4 Hz, J2 ¼ 1.6 Hz), 7.15 (1 H, td,
J1 ¼ 8.0 Hz, J2 ¼ 1.2 Hz), 3.80 (2 H, q, J ¼ 7.2 Hz), 3.73 (2 H, q,
J ¼ 7.2 Hz), 1.34 (3 H, J ¼ 7.2 Hz), 1.19 (3 H, J ¼ 7.2 Hz). 13C NMR
d
¼ 149.16, 133.16, 130.96, 126.69, 125.98, 116.96, 48.22, 25.62,
24.94, 18.02. Anal. Calcd for C12H17N3: C, 70.90; H, 8.43; N, 20.67.
Found: C, 70.78; H, 8.56; N, 20.75.
(100 MHz, CDCl3)
d
¼ 145.42, 144.60, 132.55, 124.83, 124.06, 119.99,
49.91, 42.53, 14.81, 11.65. Anal. Calcd for C10H14N4O2: C, 54.04; H,
6.35; N, 25.21. Found: C, 54.11; H, 6.47; N, 25.15.
2.3.2. (Table 1, entry 8) Pale yellow oil
UV (lmax in CH2Cl2): 293 nm. FTIR (KBr) cmꢁ1: 3064, 2939, 2856,
1584, 1468, 1420, 1355, 1296, 1255, 1221, 1186, 1106, 1053, 1001, 852,
753, 701, 644. 1H NMR (500 MHz, CDCl3)
d
¼ 7.46 (1 H, d, J ¼ 8.0 Hz),
3. Results and discussion
7.39 (1 H, d, J ¼ 7.9 Hz), 7.20 (1 H, t, J ¼ 7.5 Hz), 7.07 (1 H, t,
J ¼ 7.6 Hz), 3.85 (4 H, brs), 1.71 (6 H, brs). 13C NMR (125 MHz, CDCl3)
Aryldiazonium salts (ArNþ2 Xꢁ) have been prepared and studied
as useful intermediates in classical and modern organic synthesis
d
¼ 147.68, 130.45, 129.82, 127.53, 126.51, 118.97, 44.79, 24.77. Anal.

A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
297
Table 1
Preparation of (E)-aryltriazenes using aryl diazonium silica sulfates with secondary amines in water at room temperature.a
Entry
Amine
Diazonium salt
Product
Time (min)
10
Yield (%)
C6H5Nþ2 -OSO3eSiO2
86
83
N
N N
1
Piperidine
N
N N
2
3
4
5
6
4-MeC6H4Nþ2 -OSO3eSiO2
2-MeC6H4Nþ2 -eOSO3eSiO2
4-MeOC6H4Nþ2 -OSO3eSiO2
4-BrC6H4Nþ2 -OSO3eSiO2
4-ClC6H4Nþ2 -OSO3eSiO2
10
15
15
10
10
Me
N
N
N
N
80
79
82
82
Me
N
N
MeO
Br
N
N N
N
N
N
N
N
N
Cl
Cl
7
8
3-ClC6H4Nþ2 -OSO3eSiO2
2-ClC6H4Nþ2 -OSO3eSiO2
10
15
84
81
N
N N
Cl
N
N N
9
4-NCC6H4Nþ2 -OSO3eSiO2
10
15
84
83
NC
Me
N
N
N
N
10
4-MeCOC6H4Nþ2 -OSO3eSiO2
O
N
N
11
4-PhCOC6H4Nþ2 -OSO3eSiO2
15
80
Ph
O
N
N N
12
13
4-NO2C6H4Nþ2 -OSO3eSiO2
3-NO2C6H4Nþ2 -OSO3eSiO2
10
10
85
87
O2N
O2N
N
N N
(continued on next page)

298
A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
Table 1 (continued )
Entry
Amine
Diazonium salt
Product
Time (min)
15
Yield (%)
82
N
N N
14
2-NO2C6H4Nþ2 -OSO3eSiO2
NO2
Et
Et
15
16
17
Diethylamine
C6H5Nþ2 -OSO3eSiO2
10
10
15
83
80
76
N
N
N
N
Et
Et
4-MeC6H4Nþ2 -OSO3eSiO2
2-MeC6H4Nþ2 -OSO3eSiO2
Me
N
N
N
Et
Et
N
N
Me
Et
18
19
20
4-BrC6H4Nþ2 -OSO3eSiO2
4-ClC6H4Nþ2 -OSO3eSiO2
2-ClC6H4Nþ2 -OSO3eSiO2
10
10
15
81
79
78
Br
Cl
N
N
N
N
N
Et
Et
N
Et
Et
Et
N
N
N
Cl
Et
N
N N
Et
21
4-MeCOC6H4Nþ2 -OSO3eSiO2
10
81
Me
O
O2N
Et
Et
22
23
3-NO2C6H4Nþ2 -OSO3eSiO2
2-NO2C6H4Nþ2 -OSO3eSiO2
10
15
85
81
N
N
N N
Et
N
N
Et
NO2
Et
Et
24
25
4-CNC6H4Nþ2 -OSO3eSiO2
4-MeC6H4Nþ2 -OSO3eSiO2
10
10
82
80
NC
Me
N
N
N
O
N
N N
Morpholine
O
N
N N
26
4-ClC6H4Nþ2 -OSO3eSiO2
10
10
83
82
Cl
O
27
3-NO2C6H4Nþ2 eOSO3eSiO2
O2N
N N N
a
The yields refer to isolated pure products which were characterized from their spectral data by comparison with those reported in the literature [47e56].
due to their ready availability and high reactivity. These salts have
been prepared by a wide variety of methods. One of the oldest and
commonly used methods involves the diazotation of aromatic
amines with sodium nitrite in the presence of an aqueous Brønsted
acid [26,41]. The counterion (Xꢁ), determined by the choice of the
acid, has an important role for both stability and reactivity of the
diazonium salt [41]. For example, aryl diazonium chlorides are
usually highly unstable above 0 ꢂC and even explosive. Moreover,
because of this instability, subsequent reactions with diazonium
salts must be carried out under the same conditions that these salts

A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
299
density. As shown in Scheme 2, an obvious effect of this resonance
is an increase in rotation barrier around the N(2)eN(3) bond
determined by dynamic NMR spectroscopy [57].
In the present work, by studying the NMR spectral data of the
triazene derivatives, it was found that only 1-(2-nitrophenyl)-3,3-
diethyltriazene (Table 1, entry 23) showed a restriction in rotation
around the N(2)eN(3) bond at room temperature. This phenome-
non led to formation of two diastereotopic ethyl groups. Therefore,
the methylene and methyl groups gave different respective signals
in 13C NMR and 1H NMR spectroscopy (Figs. 1 and 2). At room
temperature and in CDCl3, the methylene carbons appear at 49.91
and 42.53 ppm and the methyl carbons resonate at 14.81 and
11.65 ppm (Fig. 1). Moreover, at ambient temperature, the 1H NMR
spectrum of this compound in CDCl3 indicates that the diaster-
eotopic methylene protons appear as two broad quartet peaks be-
tween 3.82 and 3.71 ppm and the diastereotopic methyl protons
resonate as two equally intense triplets at 1.34 and 1.22 ppm (Fig. 2).
By studying the temperature of the 1H NMR (400 MHz) of this
molecule in CDCl3 (Fig. 3), it is found that the methylene and methyl
peaks broaden and coalesce when the temperature is raised. The
chemical shift for all protons were unaffected by increase of the
temperature. Moreover, to increase the clearness of the spectra, we
moved each spectrum as much as 0.1 ppm to right in comparison
with the former spectrum (Fig. 3). As shown in Figs. 2 and 3, the
appearance of the 1H NMR spectra for the diastereotopic methyl
groups is clearer than that of the corresponding methylene ones.
Therefore, the thermodynamic parameters of the present com-
pound were calculated for the methyl groups. These parameters are
the coalescence temperature (Tc), the rate constant of the exchange
at the coalescence temperature (kc) and the free energy of activation
Scheme 2. Obvious effect of the resonance in rotation barrier around the N(2)eN(3)
bond.
are formed. Thus, aryldiazonium salts with higher stability and
versatility that can be easily made and stored under solid state
conditions with explosion-proof properties are desired and
necessary. Later developments showed that the stability of diazo-
nium salts can be modulated by change of the counterion. In this
area of research, tetrafluoroborates [42,43] became the most used
salts. Moreover, disulfonimides [44], carboxylates [45] and tosy-
lates [46] have also been described for their good stability. Diazo-
tization reactions of these anhydrous aryl diazonium salts are
carried out in an appropriate organic solvent and to precipitate the
corresponding aryl diazonium salt, it is necessary to add Et2O into
the reaction mixture. Moreover, in some of these procedures, it is
required to control the reaction temperature. Recently, we have
reported a new method for the preparation of anhydrous aryldia-
zonium salts on the surface of silica sulfuric acid named aryldia-
zonium silica sulfates (ArN2þ-eOSO3eSiO2) [31e40]. Diazotization
reactions of these aryl diazonium salts are easily carried out in a
few minutes under solvent-free conditions at room temperature. In
the present work, the reaction of aryldiazonium silica sulfates with
a number of secondary amines was studied. As shown in Table 1, all
reactions were carried out in water at room temperature under
mild and heterogeneous conditions. The corresponding (E)-aryl-
triazenes were obtained in good to high yields. The yields refer to
isolated pure products which were characterized from their spec-
tral data by comparison with those reported in the literature [47e
56]. Aryldiazonium silica sulfates with electron-withdrawing
groups or electron-donating groups also reacted effectively. The
steric effects of ortho substituents had relatively little influence on
the yields and reaction times. The corresponding phenol de-
rivatives were formed in trace amounts as by-products. Another
advantage of this method was the easy work-up since the crude
products were extracted with ethyl acetate and, if necessary, were
purified by flash column chromatography. Finally, after completion
of the reaction and isolation of the product, the solid support could
be recycled according to the previous work [32].
(D
Gzc) for the exchange. As shown in Fig. 3, the coalescence tem-
perature was 326 K and the rate constant was calculated to be
117 sꢁ1 for the exchange of the methyl groups at the coalescence
temperature by using the GutowskyeHolm equation (kc ¼ (
p/O2)
(
Dy2 þ 6J2)1/2) [57]. In the present equation, Dy is the difference in
chemical shift of the two sites and J is the coupling constant. So, for
this molecule the difference in chemical shift of the two methyl
groups was calculated 50 Hz and the coupling constant between the
methyl and methylene protons was obtained 6.8 Hz (Fig. 3). More-
over, the free energy of activation was obtained 16.07 kcal molꢁ1 for
the exchange of the methyl groups by following the Eyring equation
(
D
Gzc ¼ 4.57Tc [9.97 þ log (Tc/Dy)]) [57]. It is clear that the Gutow-
skyeHolm equation and the Eyring equation are strictly valid where
the populations of two sites are equal [57e59].
Wealsosynthesized[(2-nitrophenyl)diazenyl]-1-azacyclohexane
using piperidine instead of diethylamine under the same conditions
It is known that aryldialkyltriazenes with an extended
jugated system exhibit considerable delocalization of charge
p-con-
Fig. 1. 13C NMR spectrum (100 MHz) of 1-(2-nitrophenyl)-3,3-diethyltriazene in CDCl3 at room temperature.

300
A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
Fig. 2. 1H NMR spectrum (400 MHz) of 1-(2-nitrophenyl)-3,3-diethyltriazene in CDCl3 at room temperature.
(Table 1, entry 14) and studied its NMR spectral data. In contrast to 1-
(2-nitrophenyl)-3,3-diethyltriazene, it was not observed the rotation
restriction around the N(2)eN(3) bond at room temperature. It may
be due to the inversion of the piperidyl ring that decreases the
coplanarityof thelone-pairelectronson the piperidine nitrogenwith
Table 2, the rotational barrier energy of the aryltriazenes is more than
that of the aliphatic ones. It may be due to decrease of -conjugated
p
system in the structure of the aliphatic triazenes. Moreover, the
substituted functionalgroupson thearomaticringof thearyltriazenes
affect the rotational barrier. In comparison with electron donating
groups, electron withdrawing groups on the aromatic triazenes in-
N]N bond[57,60]. Thisreason decreases p-conjugated systemof the
present triazene which leads to lower rotational barrier energy
around N(2)eN(3) bond. Therefore, the rotation around the present
bond is almost unhindered at room temperature and consequently it
was not observed diastereotopic methylene in this molecule.
crease the D p-conjugated system.
Gzc values owing to extension of
Furthermore, thestericeffectofthealiphaticgroupsonN(3)hasalittle
influence on rotational barrier energy when the size of R increases
from methyl to ethyl and isopropyl (Table 2, entries 3, 7,10). Also 1-(2-
Finally, we compared
D
Gzc of 1-(2-nitrophenyl)-3,3-diethyltriazene
nitrophenyl)-3,3-diethyltriazene has the highest
these aryltriazene derivatives (Table 2, entry 9). It may be due to
D
Gzc value among
with a number of triazenes reported in the literature. As shown in
Fig. 3. Temperature-dependent 1H NMR spectra (400 MHz) of 1-(2-nitrophenyl)-3,3-diethyltriazene in CDCl3.

A. Zarei et al. / Dyes and Pigments 101 (2014) 295e302
301
Table 2
reactions proceed in water at room temperature under mild and
heterogeneous conditions in good to high yields. Furthermore,
temperature dependent NMR spectra were studied for 1-(2-
nitrophenyl)-3,3-diethyltriazene to determine the rotational bar-
rier energy around N(2)eN(3) bond of this molecule. Among the
notable advantages of this method, we can mention the following:
operational simplicity, generality, availability of reactants, short
reaction times, and easy work-up.
Rotational barrier energy of some triazenes in different solvents.
Entry Triazene
Solvent D
Gzc (kcal molꢁ1) Ref.
Me
N
N
1
CDCl3 12.7
[59]
Me
N
OMe
Me
Me
N
N
N
N
N
2
3
4
CDCl3 13
[59]
[60]
[59]
Acknowledgment
N
Me
We gratefully acknowledge the funding support received for this
project from the Islamic Azad University, Fasa Branch.
Me
Me
CDCl3 13.8
CDCl3 13.9
N
References
Me
Me
N
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