Synthesis and Tautomerization of 2-Nitro-1-nitrosoethylbenzene in Acetone

Article abstract of DOI:10.1039/a801282b

2-Nitro-1-nitrosoethylbenzene has been synthesized in fairly high yield and its tautomerization studied by ¹H NMR spectroscopy.

Full text of DOI:10.1039/a801282b

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572 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 572±573$
Synthesis and Tautomerization of 2-Nitro-1-
nitrosoethylbenzene in Acetone$
Ahmad Shaabani,* Majid Ameri and Hamid Reza Bijanzadeh
Chemistry Department, Shahid Beheshti University, P.O. Box 19395-4716, Tehran, Iran
2-Nitro-1-nitrosoethylbenzene has been synthesized in fairly high yield and its tautomerization studied by 1H NMR
spectroscopy.
The reaction of dinitrogen trioxide with ole®ns a€ords 1-
nitro-2-nitroso derivatives, commonly referred to as pseudo-
nitrosites 1.1 These adducts can be converted into the more
soluble isomers, the corresponding 1,2-nitroximes 2.1,2
Reaction of styrene with arsenic3 and concentrated nitric
acid or dinitrogen trioxide1b produces 2-nitro-1-nitrosoethyl-
benzene 3. Compound 3 is transformed easily into the more
stable isomer 2-isonitroso-1-nitro-2-phenylethane 4 by boil-
ing in ethanol.4 The structure of compounds 3 and 4 were
earlier deduced only from their elemental analyses and for
1
compound 4 H NMR data were also reported.5
Fig. 1
2-Nitro-1-nitrosoethylbenzene 3 and 2-isonitroso-1-nitro-
phenylethane 4 are frequently used as useful products6 and
as versatile intermediates in organic synthesis.7 In addition 4
is used in analytical chemistry for indirect determination of
styrene.8 Various approaches can lead to these compounds.
However, much demand still exists for their preparation in
high yields and free of compound 4 under mild and safe
conditions.
Table 1. A plot of ln[4]t versus time should yield a straight
line if the reaction is ®rst order [see Fig. 2(a)]. The slope of
this line is equal to k. The rate constants were obtained at
several temperatures (298, 303 and 313 K) [Fig. 2(a)±2(d),
Table 2].
9
By taking the natural logarithm of the Arrhenius
equation, the activation energy, Ea=65.63 kJ mol 1, was
obtained from a plot ln k versus 1/T. Activation parameters,
1
We now report a new method for the preparation of
compound 3 in high yields under easy and safe conditions
and deduce the essential structure of compounds 3 and 4
DH%=57.85 kJ mol and DS%= 89.58 J K 1 mol 1, were
also determined from a plot of ln(k/T) versus 1/T. The
relatively low enthalpy of activation for this tautomerization
suggests a mechanism which is compatible with a cyclic
activated complex, in which bond making accompanies
bond breaking. In addition, a negative entropy of activation,
due to the loss of rotational degrees of freedom associated
with the highly ordered transition state, supports this
complex formation.
1
from their IR, H, 13C NMR and mass spectra. In addition,
the tautomerization of 3 to 4 was studied by using 1H
NMR spectroscopy in acetone at 25±40 8C.
For the tautomerization study
a fresh sample of
compound 3 was dissolved in (CD3)2CO [0.01 g in 0.4 ml
(CD3)2CO in a 5 mm NMR tube] and equilibrated at the
required temperature. The progress of the tautomerization
was monitored by recording the appearance and disappear-
ance of the methylene signals of
3 and 4 (Fig. 1).
Integration of the area under the methylene signal of 4
with respect to that of the methylene signals of 3 gave
the concentration of the species present. The rate of the
reaction is given by rate ˆ k[3]x or k[4]y, where x or y is
the reaction order. The integrated rate equation for a ®rst
order reaction is ln[4]t= kt ‡ ln[3]0.
The concentration of compound 4 at time t was found by
setting the peak area for 3 equal to one and measuring the
peak area of 4 relative to it. Typical data are presented in
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Fig. 2

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J. CHEM. RESEARCH (S), 1998 573
Table 1 Integrated area of compound 4 with
respect to that of 3 at different temperatures
Table 2 Temperature dependence of
rate constants for the tautomerization
of 3 4 4 in acetone
T/8C
t/min
Integrated area (At)
ln At
1
T/K
102k/min
ln(k/T)
25
0
15
34
45
60
94
0
17
30
46
59
0
14
29
46
0
10
21
31
45
2.2
3.0
4.0
5.0
6.0
9.0
2.0
3.0
4.0
6.0
8.0
2.7
5.0
9.0
13.5
2.0
4.0
7.4
12.2
20.1
0.8
1.1
1.4
1.6
1.8
2.2
0.7
1.1
1.4
1.8
2.1
1.0
1.6
2.2
2.6
0.7
1.4
2.0
2.5
3.0
298
303
308
313
1.485
2.381
3.509
5.097
9.907
9.451
9.100
8.800
30
1
‡
130.0, 130.9, 135.7 (C6H5); ꢁ~max/cm 2925, 1559, 1373; M at m/z
180, C8H8N2O3 requires 180 (Found: C, 53.6; H, 4.5; N, 15.3.
C8H8N2O3 requires C, 53.3; H, 4.4; N, 15.5%).
Preparation of 2-Isonitroso-1-nitro-2-phenylethane 4.ÐCompound
3 was completely transformed into 4 in acetone at room tempera-
ture after about 24 h. Mp 95±96 8C; ꢀH (CDCl3) 5.6 (2 H, s, CH2)
7.5 (5 H, m, C6H5), 9.3 (1 H, s, NOH exchange with D2O); ꢀC
(CDCl3) 69.9 (CNO2), 128.0, 130.6, 131.6, 135.7 (C6H5), 149.3
35
40
1
(C1NOH); ꢁ~max/cm 3279, 1559, 1373.
We gratefully acknowledge ®nancial support from the
research of Shahid Beheshti University.
Experimental
Received, 13th February 1998; Accepted, 28th May 1998
Paper E/8/01282B
NMR spectra were recorded on JEOL EX 90-MHz spectrometer
using tetramethylsilane as the internal standard. Temperature was
calibrated by the shift di€erence in methanol. The temperature
range was 25 to 40 8C. Infrared spectra were taken on a Shimadzu
IR-470 spectrophotometer, mass spectra on a Finnigan-Matt 8430
mass spectrometer. Elemental analyses were performed with a CHN
Heracus-O-Rapid analyzer.
Preparation of 2-Nitro-1-nitroseothylbenzene 3.ÐSodium nitrite
(34.5 g, 0.5 mol) and styrene (20.8 g, 0.2 mol) were added to chloro-
form (150 ml) in
equipped with condenser and dropping funnel. To this stirred mix-
ture was added phosphoric acid (57.6 g, 85 wt.% solution in water;
0.5 mol) from a dropping funnel over a period of 20 min. After
complete addition of phosphoric acid, the mixture was stirred for
4 h at 50 8C, then neutralized with saturated sodium bicarbonate
solution. The precipitate was ®ltered o€ and washed with water
(100 ml) and then n-hexane (40 ml). Compound 3 was obtained as a
white solid (25.2 g, yield 70%), mp 129 8C; ꢀH [90 MHz, (CD3)2CO]
7.60 (5 H, m, aromatic), 6.90 (1 H, dd, 3J 9.5, 3J 2.9, CH), 5.41
(1 H, dd, 2J 14.0, 3J 9.5, CH2), 4.97 (1 H, dd, 2J 14.0, 3J 2.9 Hz,
CH2); ꢀC [22.5 MHz, (CD3)2CO], 69.2 (CNO2), 74.7 (CNO), 127.4,
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