Side-Chain Nitration of Styrene and Para-Substituted Derivatives with a Combination of Nitrogen Dioxide and Ozone

Article abstract of DOI:10.1021/jo9705024

The side-chain nitration of styrene and four para-substituted derivatives 1 with a combination of nitrogen dioxide and ozone has been investigated as part of our continued effort to define the scope of applicability of this new nitration methodology (kyodai nitration). Styrene and derivatives underwent a smooth addition reaction across the olefinic bond in dichloromethane at -20°C, affording the corresponding isomeric nitro-nitrato adducts 2 and 3 in excellent combined yield. ¹H-NMR data were collected for all possible nitro-nitrato adducts of styrene and derivatives. The mechanism of the formation of these addition products is discussed in terms of the reversible addition of nitrogen dioxide to form unstable nitroso-nitrates 9 and 10 followed by rapid oxidation of these to the corresponding nitro-nitrates 2 and 3.

Full text of DOI:10.1021/jo9705024

6498
J . Org. Chem. 1997, 62, 6498-6502
Sid e-Ch a in Nitr a tion of Styr en e a n d P a r a -Su bstitu ted Der iva tives
w ith a Com bin a tion of Nitr ogen Dioxid e a n d Ozon e
Hitomi Suzuki* and Tadashi Mori
Department of Chemistry, Graduate School of Science, Kyoto University,
Kitashirakawa, Sakyo-ku, Kyoto 606-01, J apan
Received March 18, 1997X
The side-chain nitration of styrene and four para-substituted derivatives 1 with a combination of
nitrogen dioxide and ozone has been investigated as part of our continued effort to define the scope
of applicability of this new nitration methodology (kyodai nitration). Styrene and derivatives
underwent a smooth addition reaction across the olefinic bond in dichloromethane at -20 °C,
affording the corresponding isomeric nitro-nitrato adducts 2 and 3 in excellent combined yield.
1H-NMR data were collected for all possible nitro-nitrato adducts of styrene and derivatives. The
mechanism of the formation of these addition products is discussed in terms of the reversible addition
of nitrogen dioxide to form unstable nitroso-nitrates 9 and 10 followed by rapid oxidation of these
to the corresponding nitro-nitrates 2 and 3.
In tr od u ction
across the olefinic bond,4,7 while sonic treatment of
styrenes in the presence of NaNO2-Ce(NH4)2(NO3)6-
AcOH in a sealed tube gives a high yield of â-nitrosty-
renes.8 Other reagents used for the conversion of sty-
renes to the â-nitro derivatives include AgNO2-PhSeBr-
HgCl29 and AgNO2-I2-ethylene glycol.10 A recent report
of interest describes the action of nitrogen monoxide on
styrenes in 1,2-dichloroethane followed by treatment with
activated acidic alumina. The reaction is clean and
smooth, but it consumes 4 equiv of nitrogen monoxide
per one nitro group to be introduced.11 In order to explore
further the possibility of obtaining â-nitrostyrenes di-
rectly from styrenes, we have investigated the reaction
of styrene and derivatives 1 with nitrogen dioxide in the
presence of ozone. The combination of nitrogen dioxide
and ozone has recently been shown to be highly efficient
as a nitrating agent for a wide variety of arenes (kyodai
nitration).12
â-Nitrostyrenes and derivatives are useful as interme-
diates for the synthesis of aryl-substituted nitroalkanes,
hydroxylamines, aldoximes, ketoximes, amines, and ke-
tones.1 However, it is quite difficult to achieve direct
transformation of styrenes to â-nitrostyrenes due to the
highly sensitive nature of the vinylic hydrocarbons
concerned; the action of nitration agents commonly used
for aromatic nitration results in the formation of an
intractable mixture of products. Thus, the literature to
date contains only a few scattered reports, which include
the treatment of styrene with sodium or potassium
nitrate in polyphosphoric acid,2 nitration of a deactivated
styrene with 98% HNO3 in concentrated H2SO4,3 nitro-
halogenation with nitryl halide (NO2X) followed by de-
hydrohalogenation with triethylamine,4 and reaction with
tetranitromethane (TNM) in the presence of pyridine.5
The photochemical charge transfer activation of the
electron donor-acceptor (EDA) complex derived from
TNM and styrenes in acetonitrile has been reported to
give different products depending on the structures of
styrenes:isoxazolidines from styrene and p-methylsty-
rene, a â-nitrostyrene from p-methoxystyrene, and an
R-nitroacetophenone from p-chlorostyrene.6 The action
of HgCl2-NaNO2 on styrene results in a varying degree
of ring nitration in parallel with the expected addition
Resu lts
In the present work, the reaction of styrenes with
nitrogen dioxide and ozone has been investigated using
mainly p-chlorostyrene as the substrate in dichlo-
romethane at -20 to 0 °C owing to the ease of product
analysis and stability of the substrate as well as clean-
ness of the reaction. Under these conditions, p-chlorosty-
rene gave the best combined yield of nitro-nitrates 2 and
3. Above this temperature range, the concurrent ring
nitration began to be detectable, although its extent was
not so significant even at 0 °C, while the reaction carried
out below -40 °C began to afford the dinitro adduct 6 at
* Corresponding author. Tel: +81-75-753-4041. Fax: +81-75-751-
2085. E-mail: suzuki@kuchem.kyoto-u.ac.jp.
X Abstract published in Advance ACS Abstracts, September 1, 1997.
(1) (a) Perekalin, V. V.; Lipina, E. S.; Berestovitskaya, V. M.;
Efremov, D. A. Nitroalkenes, Conjugated Nitro Compounds; J ohn Wiley
& Sons, Ltd.: Chichester, 1994; Chapter 2, pp 53-168. (b) Ono, N. In
Organic Nitro Chemistry Series, Nitro Compounds, Recent Advances
in Synthesis and Chemistry; Feuer, H., Nielsen, A. T., Eds.; VCH
Publishers, Inc.: New York, 1990; Chapter 1 (pp 1-135. (c) Barrett,
A. G. M.; Graboski, G. G. Chem. Rev. 1986, 86, 751. (d) Kabalka, G.
W.; Guindi, L. H. M.; Varma, R. S. Tetrahedron 1990, 46, 7443. (e)
Kabalka, G. W.; Varma, R. S. Org. Prep. Proc. Int. 1987, 19, 283.
(2) Grebenyuk, A. D.; Ismailova, R. A.; Tokbolatov, R. B.; Ovodova,
T. Zh. Org. Khim. 1990, 26, 680.
(7) Corey, E. J .; Estreicher, H. J . Am. Chem. Soc. 1978, 100, 6294.
(8) (a) Hwu, J . R.; Chen, K.-L.; Ananthan, S.; Patel, H. V. Organo-
metallics 1996, 15, 499. (b) Hwu, J . R.; Chen, K.-L.; Ananthan, S. J .
Chem. Soc., Chem. Commun. 1994, 1425.
(9) Hayama, T.; Tomoda, S.; Takeuchi, Y.; Nomura, Y. Tetrahedron
Lett. 1982, 23, 4733.
(10) J ew, S.-S.; Kim, H.-D.; Cho, Y.-S.; Cook, C.-H. Chem. Lett. 1986,
1747.
(11) (a) Hata, E.; Yamada, T.; Mukaiyama, T. Bull. Chem. Soc. J pn.
1995, 68, 3629. (b) Mukaiyama, T.; Hata, E.; Yamada, T. Chem. Lett.
1995, 505.
(12) For aromatic nitration using nitrogen dioxide and ozone, see:
(a) Mori, T.; Suzuki, H. Synlett 1995, 383. (b) Mori, T. Ph.D. Thesis,
Kyoto University, 1997; electronic version of this thesis is available
via World Wide Web: URL, http://kuchem.kyoto-u.ac.jp/www/yugo/
user/tmori/th/cont.html. (c) Also, see: Suzuki, H.; Nonoyama, N. J .
Chem. Soc., Chem. Commun. 1996, 1783.
(3) Tinsley, S. W. J . Org. Chem. 1961, 26, 4723.
(4) Sy, W.-W.; By, A. W. Tetrahedron Lett. 1985, 26, 1193.
(5) (a) Masnovi, J . M.; Kochi, J . K. Recl. Trav. Chim. Pays-Bas 1986,
105, 286. (b) Penczek, S.; J agur-Grodzinski, J .; Szwarc, M. J . Am.
Chem. Soc. 1968, 90, 2174. (c) Schmidt, E.; Fischer, H. Chem. Ber.
1920, 53, 1529.
(6) Mathew, L.; Varghese, B.; Sankararaman, S. J . Chem. Soc.,
Perkin Trans. 2 1993, 2399.
S0022-3263(97)00502-1 CCC: $14.00 © 1997 American Chemical Society

Side-Chain Nitration of Styrene
J . Org. Chem., Vol. 62, No. 19, 1997 6499
Ta ble 1. Rea ction of P a r a -Su bstitu ted Styr en es 1 w ith
Nitr ogen Dioxid e a n d Ozon e in Dich lor om eth a n e u n d er
Va r iou s Con d ition sa
Ta ble 3. Rea ction of p-Ch lor ostyr en e 1 (R ) Cl) w ith
Nitr ogen Dioxid e in th e P r esen ce of Ozon e in Va r iou s
Solven tsa
temp yield of nitro-nitrates
yield of â-nitroolefin
4 (%)
yields (%)
R
(°C)
2 and 3 (%)
2:3
solvent
2
3
6
material balance (%)
b
NO2
CF3
Cl
-20
-20
0
95
99
96
54:46
52:48
51:49
47:53
41:59
62:38
57:43
54:46
37:63
49
50
CH2Cl2
Cl(CH2)2Cl
CHCl3
CCl4
n-C6H14
MeCN
47
52
50
37
11
36
21
52
45
45
43
47
40
37
0
0
0
99
97
b
95
-20
-20
-20
-20
-20
-40
-78
-20
-20
99
51
0
80b
91b
88
98c
33
12
36
100d
89e
MeNO2
94
97f
62 (29g)
0 (46h)
94
a
All reactions were carried out in a given solvent (0.4 M, 25
b
mL) at -20 °C as shown in footnote a in Table 1. Unidentified
products were also detected by 1H-NMR.
H
40:60
53:47
58
43
Me
MeO -20
94
0 (21i)
are also included in Table 1. These â-nitrostyrenes 4
were no doubt derived from â-nitro-R-nitrato compounds
3, whereas the counterpart adducts, R-nitro-â-nitrato
compounds 2, were retained on the column (probably as
R-nitro alcohol and/or its descendants) and could not be
eluted under the conditions employed. The transforma-
tion of adducts 3 into â-nitrostyrenes 4 was also feasible
by treating the crude product mixture with a weak base
such as aqueous sodium hydrogen carbonate followed by
chromatographic separation on a silica gel column. Us-
ing the latter method, the R-nitro-â-nitrato adducts 2
were also obtained in acceptable isolated yields (∼40%).
The reaction of p-chlorostyrene with nitrogen dioxide
and ozone was also examined in several different solvent
systems (Table 3). In chlorinated hydrocarbons such as
dichloromethane, chloroform, and 1,2-dichloroethane, the
reaction was very clean and the addition of NO2 and
ONO2 moieties across the olefinic bond was the only
reaction that took place. The reaction in carbon tetra-
chloride was somewhat sluggish, and the expected ad-
dition products were accompanied by small amounts of
unidentified products. As expected, the reaction in
n-hexane led to the dinitro adduct 6 in 33% yield in
addition to the â-nitro-R-nitrato compound 3 (47%).
Interestingly, the reaction in polar solvents such as
nitromethane and acetonitrile also produced an ap-
preciable amount of dinitro compound 6 (12-36%) in
addition to nitro-nitrates 2 and 3 (21-36% and 37-40%,
respectively). A possible explanation for the unexpected
results may be that N2O4 might have added partly in the
form of nitronium nitrite (NO2+NO2-) to the olefinic bond,
leading to the adducts 6 and 7 in these polar solvents.
This aspect of the kyodai nitration of styrenes remains
to be clarified.
a
Unless otherwise indicated, all reactions were carried out as
follows: A dichloromethane solution of substrate (0.4 M, 25 mL)
was mixed with nitrogen dioxide (1.0 mL) and kept for 1 h at an
indicated temperature; then ozone was introduced at a rate of 10
b
mmol/h for 1 h. Scale was reduced to one-half (substrate, 0.2 M,
c
25 mL; nitrogen dioxide, 0.5 mL; reaction time, 0.5 + 0.5 h).
Nitrogen dioxide in dichloromethane (10 mL) was slowly added
to a solution of substrate (15 mL) over 2 h followed by introduction
d
of ozone. The reaction was carried out with nitrogen dioxide (0.1
mL) in dichloromethane (0.04 M, 25 mL) for 6 min. e A dichlo-
romethane solution (10 mL) of methanesulfonic acid (10 mol %)
and nitrogen dioxide (1.0 mL) was added dropwise to a solution
of substrate (15 mL) over 1 h. f Lithium nitrate (5 equiv) was
g
h
added. Yield of 1,2-dinitro-1-(4-chlorophenyl)ethane. Yield of
p-chlorobenzaldehyde. Polymeric by-products were also formed.i
Yield of p-anisaldehyde. Small amounts of unidentified products
were also detected by 1H-NMR.
Ta ble 2. 1H-NMR Ch em ica l Sh ifts of Alip h a tic P r oton s
of Nitr o-n itr a tes 2 a n d 3 Der ived fr om P a r a -Su bstitu ted
Styr en es 1
R
product chemical shift (δ, ppm)a coupling constant (J , Hz)
NO2
2
3
2
3
2
3
2
3
2
3
6.77, 4.88, 4.69
6.35, 5.62, 4.82
6.63, 4.86, 4.65
6.28, 5.60, 4.78
6.54, 4.83, 4.61
6.17, 5.55, 4.74
6.56, 4.83, 4.62
6.19, 5.55, 4.73
6.54, 4.84, 4.59 (2.38b)
6.14, 5.57, 4.70 (2.38b)
9.5, 4.0, 15
10.3, 3.3, 16
9.8, 3.7, 14
10.6, 3.1, 16
9.8, 3.7, 14
10.6, 3.1, 16
10.0, 3.6, 15
10.7, 2.8, 16
10.0, 3.7, 14
10.7, 3.0, 16
CF3
Cl
H
Me
a
b
All but methyl protons appear in a double doublet form.
Methyl protons.
the expense of nitro-nitrates 2 and 3. At -78 °C,
p-chlorobenzaldehyde (46%) was the major product ob-
tained along with some polymeric byproducts, and no
further nitro-nitrates could be obtained. A control ex-
periment carried out in the absence of nitrogen dioxide
under similar conditions gave the same aldehyde in 41%
yield, when no reductive treatment was undertaken.
Other styrenes, excepting the p-methoxy compound,
reacted with nitrogen dioxide with similar ease and
cleanness at -20 °C, giving the corresponding addition
products 2 and 3 in nearly quantitative combined yield
(Table 1). For the convenience of interested researchers,
1H-NMR chemical shifts and coupling constants of ali-
phatic protons of all nitro-nitrato adducts obtained are
collected in Table 2, thus providing a useful means for
identification of these types of compounds.
Discu ssion
The reaction of alkenes with nitrogen dioxide has not
so often been used for the synthesis of nitroalkenes,
probably because of the complicated nature of the reac-
tion product arising from competing addition, substitu-
tion, oxidation, and C-C bond cleavage. Accordingly, the
reported results are often confusing in the literature.13
The reaction usually affords a complex mixture of dinitro,
nitro-nitrito, and nitro-nitrato compounds, often ac-
companied by further degradation products of these.
(13) (a) Shechter, H. Rec. Chem. Prog. 1964, 25, 55. (b) Brand, J . C.
D.; Stevens, I. D. R. J . Chem. Soc. 1958, 629. (c) Baldock, H.; Levy,
N.; Scaife, C. W. J . Chem. Soc. 1949, 2627. (d) Levy, N.; Scaife, C. W.;
Smith, A. E. W. J . Chem. Soc. 1948, 52. (e) J . Chem. Soc. 1946, 1096.
(f) Levy, N.; Scaife, C. W. J . Chem. Soc. 1946, 1093. (g) Seifert, W. K.
J . Org. Chem. 1963, 28, 125.
Treatment of the crude product mixture over a short
alumina column using a mixture of n-hexane and ethyl
acetate (5-20:1) as the eluent provided a simple way to
obtain (E)-â-nitrostyrenes 4, the isolated yields of which

6500 J . Org. Chem., Vol. 62, No. 19, 1997
Suzuki and Mori
Sch em e 1
Sch em e 2
15N nuclear polarization has revealed that the addition
of two molecules of nitrogen dioxide to alkene in n-hexane
occurs stepwise and gives rise to both dinitro and nitro-
nitrito compounds (Scheme 2, path a).20 However, dif-
ferent modes of addition may also be operative under
certain conditions, since the kinetic order of the reaction
becomes higher in [NO2]. Thus, at high nitrogen dioxide
concentration, the initial attack by dimeric molecule N2O4
may partly contribute to the addition (path c),18 while
the reaction between an intermediate carbon radical and
N2O4 may also be competitive (path b).19 In chloroform
solution, however, the reaction of alkenes with nitrogen
dioxide has been reported to give only the corresponding
nitroso-nitrates.21 A recent paper22 reported the quan-
titative formation of â-nitro-R-nitrato adducts from the
nitration of p-nitro- and p-(trifluoromethyl)styrenes with
dinitrogen pentoxide at low temperatures in dichlo-
romethane.23 However, for more activated substrates
such as the parent styrene as well as the 4-chloro and
4-methyl derivatives, the reaction proceeded quickly and
gave a complex mixture of products composed of nitro-
nitrates, dinitrates, dinitro compounds, and ring nitration
products, among which the nitro-nitrato adducts were
prominent.24-26
Addition products 2 and 3 are known to release the
elements of nitrous or nitric acid by the action of a base
to give nitroalkenes. However, the product yields are low
to modest at best.
As for the styrenes, the yields of nitroolefins are quite
poor, and the nitro alcohols (ArCH(OH)CH2NO2) obtained
are usually accompanied by a complex mixture of prod-
ucts arising from addition, substitution, and oxidative
degradation.14 In the presence of ozone, however, the
initially formed unstable nitroso-nitrates 9 and 10 are
rapidly converted to nitro-nitrates 2 and 3, which are
stable enough to show little tendency to revert to the
original olefin 1 (Scheme 1). This would probably be the
reason why the nitro-nitrates 2 and 3 were obtained in
good combined yield in the kyodai nitration of styrenes
and derivatives. The aliphatic nitroso compounds are
known to form oximes, which may undergo either hy-
drolysis to carbonyl compounds, cyclization with a neigh-
boring nitro group to form furoxans, or oxidation to
reactive gem-nitro-nitroso compounds. The nitroso com-
pounds may also be transformed to diazonium compounds
in the presence of excess nitrogen oxides and go into
further complicated modes of degradation.15 Ozone can
convert the unstable nitroso-nitrates 9 and 10 rapidly
to the stable nitro-nitrates 2 and 3, thus removing all
complexities arising otherwise from the reactions.
Recently, the reaction of nitrogen dioxide with various
hexenes has been intensively investigated in n-hexane
and several other solvent systems, and the major prod-
Based on our experimental results, a tentative path-
way from styrene 1 to the side-chain nitration products
2 and 3 in the kyodai nitration is depicted in Scheme 3.
In dichloromethane, 1,2-dichloroethane, and chloroform,
the addition of nitrogen dioxide to the olefinic double
bond may occur via a heterolytic mode, where the NO+
and ONO2- moieties add successively to yield the corre-
sponding nitroso-nitrato adducts 9 and 10. This addition
process is considered to be reversible, since the initially
formed nitroso-nitrato adducts were found to be gradually
transformed into the dinitro products 6 when the reaction
mixture stood in the absence of ozone. As far as can be
ucts were fully identified.16 The heterolytic reaction of
- 17
nitrogen dioxide via nitrosonium nitrate (NO+NO3
)
1
judged from the H-NMR spectra, the major compounds
was effectively depressed by using n-hexane as the
solvent, where the dinitro adducts resulted as the major
products.16 The reversible nature of this addition reac-
present in the reaction mixture were the addition prod-
ucts, especially so at higher temperatures. In order to
estimate the relative stability of these two unstable
nitroso-nitrato adducts 9 and 10, PM3 calculations were
carried out to obtain the heats of formation of the
relevant adducts. The results disclosed that the dinitro
1
tion has been confirmed by H-NMR monitoring using
2,3-dimethyl-2-butene as a substrate and benzene, ether,
or n-hexane as the solvent.16 The mechanism of the
addition of nitrogen dioxide to alkenes has been studied
extensively by kinetic18,19 and spectroscopic means.20 The
(21) (a) Duynstee, E. F. J .; Housmans, J . G. H. M.; Voskuil, W.;
Berix, J . W. M. Recl. Trav. Chim. Pays-Bas 1973, 92, 698. (b) Michael,
A.; Carlson, G. H. J . Org. Chem. 1940, 5, 14. (c) Schoenbrunn, E. F.;
Gardner, J . H. J . Am. Chem. Soc. 1960, 82, 4905.
(22) Lewis, R. J .; Moodie, R. B. J . Chem. Soc., Perkin Trans. 2 1996,
1315.
(23) Addition of N2O5 to the olefinic bond is known to occur in a
cis-mode at low concentration.24 Thus, the electrogenerated N2O5 has
been reported to add to trans-stilbene to yield a threo product,25 and
the nitration of styrene with acetyl nitrate has been reported to give
the â-nitroacetate via cis-addition.26
(14) Bryant, D. K.; Challis, B. C.; Iley, J . J . Chem. Soc., Chem.
Commun. 1989, 1027.
(15) Metzger, H.; Meier, H. In Methoden der Organischen Chemie,
Band X/ 1; Stroh, H., Ed.; Georg Thieme Verlag: Stuttgart, 1971, p
891.
(16) Golding, P.; Powell, J . L.; Ridd, J . H. J . Chem. Soc., Perkin
Trans. 2 1996, 813.
(17) (a) Bosch, E.; Kochi, J . K. J . Am. Chem. Soc. 1996, 118, 1319.
(b) Res. Chem. Intermed. 1996, 22, 209. (c) Hubig, S. M.; Bockman, T.
M.; Kochi, J . K. J . Am. Chem. Soc. 1996, 118, 3842.
(18) Giamalva, D. H.; Kenion, G. B.; Church, D. F.; Pryor, W. A. J .
Am. Chem. Soc. 1987, 109, 7059.
(24) (a) Stevens, T. E.; Emmons, W. D. J . Am. Chem. Soc. 1957, 79,
6008. (b) Stevens, T. E. J . Org. Chem. 1959, 24, 1136.
(25) Bloom, A. J .; Fleischmann, M.; Mellor, J . M. Electrochim. Acta
1987, 32, 785.
(19) Chatterjee, J .; Coombes, R. G.; Barnes, J . R.; Fildes, M. J . J .
Chem. Soc., Perkin Trans. 2 1995, 1031.
(20) (a) Powell, J . L.; Ridd, J . H.; Sandall, J . P. B. J . Chem. Soc.,
Chem. Commun. 1990, 402. (b) Appl. Magn. Reson. 1993, 5, 151.
(26) Bordwell, F. G.; Garbisch, E. W., J r. J . Org. Chem. 1962, 27,
2322.

Side-Chain Nitration of Styrene
J . Org. Chem., Vol. 62, No. 19, 1997 6501
Sch em e 3
which subsequently couples with either the nitrate anion
or nitrogen monoxide, eventually leading to the isomeric
nitro-nitrates 2 and 3 via intermediates like 9/10. PM3
calculation of the frontier electron densities for the
styrene radical reaction (fd-R, fR)27,28 showed that the
initial addition of nitrogen dioxide occurs at the terminal
â-carbon (see Table 5 in Supporting Information). The
calculated LUMO densities or frontier densities (fd-R)
of the relevant radical cations also showed higher values
at the â-carbon than at the R-carbon, indicating that the
coupling of the nitrate anion or nitrogen monoxide with
the styrene radical cation in an intermediate pair (8)
occurs preferentially at the â-carbon in accord with the
prediction of the Pross-Shaik CM model.29 Thus, the
present reaction of styrenes with nitrogen dioxide and
ozone may well be characterized such that the initial
addition of N2O4 to the olefinic bond occurs reversibly via
the electron transfer mechanism to form the nitroso-
nitrates 9 and 10, which undergo rapid oxidation of the
nitroso group to the nitro group in the presence of ozone
to yield the nitro-nitrates 2 and 3 as the final products.
Su m m a r y
Ta ble 4. P M3-Ca lcu la ted Hea ts of F or m a tion of
Nitr oso-n itr a tes 9 a n d 10 a n d Din itr o Com p ou n d s 6 a n d
Ion iza tion P oten tia l of P a r a -Su bstitu ted Styr en es 1
Successive treatment of styrene and derivatives 1 with
nitrogen dioxide and ozone in dichloromethane at 0 to
-20 °C afforded the corresponding isomeric nitro-nitrato
adducts 2 and 3 in excellent combined yield. The â-nitro-
R-nitrato adducts 3 easily released the elements of nitric
acid by the action of a weak base such as sodium
hydrogen carbonate or alumina, giving the corresponding
â-nitrostyrenes 4 in good yield. The reaction most likely
starts with a reversible addition of N2O4 ()NO+NO3-) to
form the labile nitroso-nitrato adducts 9 and 10 followed
by rapid oxidation of these nitroso-nitrates to the nitro-
nitrates 2 and 3 in the presence of ozone. Semiempirical
PM3 calculations carried out on styrenes 1 and their
radical cations also support the initial electron transfer
between the styrene donor and nitrosonium nitrate,
although more detailed studies are needed to reach a
conclusion.
Hf (kJ /mol)
R
IP (eV)
9
10
6
∆Hf (kJ /mol)a
NO2
CF3
Cl
10.00
9.72
9.01
8.94
9.13
8.73
26.99
27.70
11.95
15.4
13.2
22.0
22.0
22.7
23.2
-600.50 -599.74 -613.27
30.81
57.65
17.90
31.42
55.28
15.44
9.16
34.51
-6.01
H
Me
MeO
-102.26 -105.02 -126.79
a
∆Hf values are obtained as the difference of a heat of formation
of dinitro compound and a mean heat of formation of two isomeric
nitroso-nitrates.
compounds 6 are generally preferred in energetic terms
by 13-23 kJ /mol as compared to the mean values of the
isomeric nitroso-nitrates 9 and 10, in accordance with
the above observation (Table 4). Thus, this would prob-
ably be the major reason why the relative contribution
of nitrosonium nitrate (NO+NO3-) is lowered and the
radical addition of nitrogen dioxide becomes preferred in
nonpolar solvents. In n-hexane as the solvent, the ratio
of â-nitro-R-nitrato versus R-nitro-â-nitrato adducts was
quite large, and the initial addition of nitrogen dioxide
to the â-carbon was apparently favored. Although the
GLC and 1H-NMR monitorings of the reaction process
confirmed the complete disappearance of styrenes 1 about
1 h after the addition of nitrogen dioxide, the reaction
profiles obtained at -78 °C were found to be almost
identical with those of simple ozonolysis of styrenes
examined under similar conditions, clearly showing the
reversible nature of the addition of nitrosonium nitrate
to the olefinic bond even at such a low temperature.
The reversible addition of nitrosonium nitrate to the
styrenes may be initiated via the electron transfer
between the olefin donor 1 and nitrosonium ion. Al-
though the calculated ionization potentials of the styrene
derivatives vary considerably (Table 4), the charge
Exp er im en ta l Section
Nitr a tion of Styr en e a n d Der iva tives w ith a Com bin a -
tion of Nitr ogen Dioxid e a n d Ozon e. Typ ica l P r oced u r e.
To a solution of styrene in freshly distilled CH2Cl2 (10 mmol,
0.4 M, 25 mL) was added nitrogen dioxide (1 mL) in one portion
with a glass syringe in the dark at a given temperature
externally controlled by a cooling bath. After 1 h, ozonized
oxygen was bubbled in continuously from the glass inlet tube
for 1 h (10 mmol of ozone in a flow of 10 L of oxygen). The
reaction was quenched with ice-cooled water, and the organic
phase was separated, extracted, washed with brine and water,
dried with anhydrous sodium sulfate, and evaporated, leaving
a mixture of two isomeric nitro-nitrates as an oily residue. The
progress of the reaction was monitored by GLC at a low
(27) For calculation methods, see: (a) Stewart, J . J . J . omput. Chem.
1989, 10, 209. (b) 1989, 10, 221. (c) Dewar, M. J . S.; Zoebish, E. G.;
Healy, E. F.; Stewart, J . J . P. J . Am. Chem. Soc. 1985, 107, 3902.
(28) For frontier electron densities in radical reactions, see: (a)
Fukui, K.; Yonezawa, T.; Nagata, V.; Shingu, H. J . Chem. Phys. 1954,
22, 1433. (b) Fukui, K.; Yonezawa, T.; Shingu, H. J . Chem. Phys. 1952,
20, 722.
transfer bands of the EDA complexes of [olefin, NO+]NO3
-
have been observed and the olefinic radical cations have
also been spectrally identified as the first observable
intermediate upon irradiation.17 In our case, therefore,
the first intermediate would be a styrene radical cation,
(29) (a) Shaik, S. S.; Pross, A. J . Am. Chem. Soc. 1989, 111, 4306.
(b) Shaik, S. S.; Canadell, E. J . J . Am. Chem. Soc. 1990, 112, 1452. (c)
Shaik, S. S. J . Org. Chem. 1990, 55, 3434. (d) Pross, A. J . Am. Chem.
Soc. 1986, 108, 3537.(e) Pross, A.; Shaik, S. S. Acc. Chem. Res. 1983,
16, 363.

6502 J . Org. Chem., Vol. 62, No. 19, 1997
Suzuki and Mori
injection-port temperature (typically 100 °C), and the final
product composition was determined by H-NMR analysis.
Su p p or tin g In for m a tion Ava ila ble: Results of semiem-
pirical calculations and one 1H-NMR chart of a typical product
mixture (2 and 3 for R ) Cl) (2 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
1
Ack n ow led gm en t. Financial support of this work
from a Grant-in-Aid for Specially Promoted Scientific
Research of the Ministry of Education, Science, Sports
and Culture of J apan (No. 08101003) is gratefully
acknowledged. T.M. thanks the J apan Society for the
Promotion of Science for a fellowship (No. 5026).
J O9705024