Direct nitration reactions of photochromic spirooxazines

Article abstract of DOI:10.1080/15421400590946875

A direct nitration of photochromic spirooxazines was carried out by three different methods. The molecular structure of main products was determined by NMR ¹H and ¹³C spectra. The nitration mechanisms were proposed. It was shown that only nitration by mixture of nitric and sulfuric acids gives photochromic compounds with nitrogroup in aryloxazine ring.

Full text of DOI:10.1080/15421400590946875

This article was downloaded by: [University of Colorado at Boulder Libraries]
On: 30 December 2014, At: 03:21
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Molecular Crystals and Liquid
Crystals
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gmcl20
Direct Nitration Reactions of
Photochromic Spirooxazines
N. L. Zaichenko a , A. I. Shiyonok a , L. S. Kol'tsova a
& V. S. Marevtsev a
a Semenov Institute of Chemical Physics of Russian
Academy of Sciences , Moscow, Russia
Published online: 31 Aug 2006.
To cite this article: N. L. Zaichenko , A. I. Shiyonok , L. S. Kol'tsova & V. S. Marevtsev
(2005) Direct Nitration Reactions of Photochromic Spirooxazines, Molecular Crystals
and Liquid Crystals, 431:1, 383-389, DOI: 10.1080/15421400590946875
To link to this article: http://dx.doi.org/10.1080/15421400590946875
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.

This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Mol. Cryst. Liq. Cryst., Vol. 431, pp. 83=[383]–89=[389], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590946875
Direct Nitration Reactions of Photochromic Spirooxazines
N. L. Zaichenko
A. I. Shiyonok
L. S. Kol’tsova
V. S. Marevtsev
Semenov Institute of Chemical Physics of Russian Academy of Sciences,
Moscow, Russia
A direct nitration of photochromic spirooxazines was carried out by three different
methods. The molecular structure of main products was determined by NMR 1H
and 13C spectra. The nitration mechanisms were proposed. It was shown that only
nitration by mixture of nitric and sulfuric acids gives photochromic compounds
with nitrogroup in aryloxazine ring.
Keywords: nitration; NMR; photochromism
Photochromic spirooxazines (SO) are very promising objects from
both scientific and practical points of view. However, the fact that
well-known multiple-step synthesis of SO is rather laborious gave us
an impetus to the development of procedures for modifying SO struc-
tures by direct chemical reactions. Present work describes the results
of our study of direct nitration reactions of photochromic compounds
1–3.
All these compounds synthesized by methods [1–3] were nitrated by
mixture of nitric and sulfuric acids [2,4] yielding corresponding
photochromic mononitroderivatives 4 (8-nitro-1), 5 (8-nitro-2) and
6 (7-nitro-3). In the case of 2 dinitrosubstituted photochromic
compound 7 (70,8-dinitro-2) was isolated too.
The Russian Foundation for Basic Research (Grant 04-03-32628) and Presidium of
RAS (program ‘‘Directional synthesis of substances with given properties and creation
functional materials on their base’’) financially supported this work.
Address correspondence to V. S. Marevtsev, Semenov Institute of Chemical Physics of
Russian Academy of Sciences, 4, Kosygin St., Moscow, 119991, Russia. E-mail: marvic@
polymer.chph.ras.ru
83=[383]

84=[384]
N. L. Zaichenko et al.
Two other methods of nitration, namely by action of Cu(NO3)2 in
acetic anhydride (method 2) [5] and by means of NaNO2 in acetic acid
(method 3) [6] were additionally used for 3, but only nonphotochromic
compounds 8 and 9 were obtained under these conditions.
The structures of the resulting compounds were established using
1
1H and 13C NMR spectroscopy, Table 1 lists H NMR spectral para-
meters, Table 2 – 13C NMR spectral data for SOs studied. The complete
signal assignment in NMR spectra of the starting SO 1–3 has been
made previously [2–4].
1
Analysis of the H NMR spectrum of 4 shows that one hydrogen
atom of naphthoxazine fragment of the molecule is substituted by
NO2 group. The presence of three-proton spin system of AKX type with
3
4
spin-spin coupling constants JAK ¼ 9,2 Hz and JKX ¼ 2,4 Hz shows
that substitution takes place at position 8 or 9. It is known [7] that the
presence of NO2 group in the position 2 of naphthalene leads to the
downfield shift of the signals for H(1) and H(3) protons by 0,93 and
0,78 ppm, respectively, compared to those observed in the spectrum
of unsubstituted naphthalene. In this case the spin-spin coupling
3
constant J3,4 increases from 7,54 to 8,36 Hz. As it can be seen from
Tables 1, the position of the signals for H(9) and H(10) protons and

85=[385]

86=[386]
N. L. Zaichenko et al.
TABLE 2 13C NMR Spectra of Compounds 3, 6, 8 and 9 in CDCl3
Compound
3
6
8
9
Carbon atom
CꢁCH3
20,9; 25,5
29,6
20,7; 26,2
29,7
27,7
36,1
189,2
50,5
20,7; 25,5
29,6
NꢁCH3
20
30
99,0
51,5
99,0
50,1
99,8
51,9
30a
40
136,1
121,6
119,8
128,0
107,2
147,6
150,3
120,0
129,4
122,2
127,4
124,9
122,5
126,4
131,4
122,7
127,7
126,7
122,7
124,3
139,4
135,9
121,7
119,3
128,0
107,4
148,3
165,0
133,7
126,1
123,0
127,6
126,4
123,4
128,9
129,4
123,7
126,8
127,3
121,0
120,2
145,7
142,9
128,6
129,7
128,0
127,2
140,4
155,4
134,4
125,8
122,8
127,6
126,8
123,4
129,2
130,7
123,8
127,6
128,0
122,1
120,5
145,3
135,7
121,6
120,2
128,1
107,3
147,3
151,0
119,5
134,1
123,4
121,1
144,8
119,0
125,7
131,3
123,9
128,9
128,0
123,0
124,8
142,9
50
60
70
70a
3
4a
4b
5
6
7
8
8a
8b
9
10
11
12
12a
12b
increase of spin-spin coupling constant 3J9,10 from 8,6 Hz in 1 to 9,2 Hz
in 4 are in complete agreement with above-mentioned rule, indicating
that NO2 group is located at position 8.
1
The same situation is observed in H NMR spectrum of 5. All spec-
tral parameters of naphthoxazine fragment of this compound coincide
with those for 4.
Analysis of 1H NMR spectrum of 6 shows that NO2 group takes one
of the following positions – 6,7,10 or 11 – in the phenanthrene frag-
ment. Full analysis of 1H and 13C NMR spectra using standard hetero-
nuclear double resonance techniques evidences the NO2 group location
in position 7.
In the case of dinitrosubstituted 7, one of the NO2 groups is located
at the position 8 as in the 5, and the second one is at positions 40 or 70 of
the benzindoline fragment. Above-mentioned data on the influence of
NO2 group in naphthalene on chemical shifts and coupling constants

Direct Nitration Reactions of Photochromic Spirooxazines
87=[387]
of the neighboring protons (3J5 ,6 is equal 6,7 Hz in 2 and 7,6 Hz in 7)
indicate on the structure 7.
0
0
The structures of nonphotochromic compounds 8 and 9 were estab-
1
lished by analysis of H and 13C NMR spectra using COSY, NOESY,
HSQC and HMBE techniques.
Now let us discuss some peculiarities of mechanisms of described
nitration reactions. Nitration by mixture of nitric and sulfuric acids
is a reaction of electrophilic substitution. Since the equilibrium
between initial closed form A and opened colored form B (A $ B) for
SOs is known to exist in any solvent and nitration by method 1 is
carried out in a strongly acidic medium, where B is transformed into
the salt form BH.
It is reasonable to propose that precisely this form participates in
nitration reaction. Then the positions 5, 8, 10 for 1, 2 and positions
5, 7, 9, 11 for 3 appear to become the most reactive for electrophilic
substitution due to activating effect of the OH group. Nitration at
the positions 5 and 10 is strongly hindered and therefore nitration of
1 and 2 occurs mainly at position 8, and of 3 – at position 7.
We failed to find the dinitrosubstituted products of 1 and 3,
although the methods for their nitration were similar with that
for 2. This fact can probably be explained by deactivation of the
benzene ring in the indoline heterocycle of 1 and 3 by the positively
charged quaternary N atom. Introduction of one more benzene
ring into compound 2 decreases this effect. Since it is well known
that the a-positions in naphthalene are the most reactive, nitration
of 2 occurs at position 70 because position 40 is shielded by methyl
group.
Two other nitration methods were selected for 3 on the base of
literature data [3] and because they yield nitrosubstituted derivatives
in more soft conditions and without gumming. But contrary to the case
of spirobenzopyrans [6] these methods gave no photochromic SOs. In
both these methods the initial substance acts as a salt form BH. In
the nitration method 2 the amount of crystallohydrate water in the
salt Cu(NO3)2ꢂ6H2O is evidently sufficient for nitric acid formation
in the reaction medium leading to formation of BH.

88=[388]
N. L. Zaichenko et al.
Then an oxidizing ring-formation showed takes place with high
yields in both nitration methods. Cu2 þ ions act as an oxidant in the
second method. HNO2 and O2 are the oxidants in the third one.
ƒƒƒ!
ƒƒƒ
CuðNO Þ þ H O
CuðNO ÞðOHÞ þ HNO
3
2
3
3
2
It should be noted that analogue of 8 was earlier obtained [8] as one of
the products of SO photo destruction process.
In the method 3 formation of 8 is not the end of the reaction,
indoline cycle then opens and is nitrosated at ‘‘former indoline’’ N
atom, yielding N-nitrosocompound 9.
TABLE 3 Photochromic Properties of SO 1–7 at 295 K
Toluene
Acetone
Ethanol
Compound
kB=nm
kBꢂ102=sꢁ1
kB=nm
kBꢂ102=sꢁ1
kB=nm
kBꢂ102=sꢁ1
1
2
3
4
5
6
7
592
621
592
621
645
640
616
28,0
30,0
0,3b
7,3
1,5
14,0
2,0d
596
624
616
620
640
638
612
99,0
68,0
1,4b
2,0
0,7
7,4
0,7d
610
629a
625
618
637a
630
615
61,0
44,0a
3,3b
0,4
0,1a
4,2c
0,6d
aIn BuOH.
bAt 253 K.
cIn acetonitrile.
dAt 273 K.

Direct Nitration Reactions of Photochromic Spirooxazines
89=[389]
Compounds 4–7 have pronounced photochromic properties in solu-
tions, i.e., they undergo transition from the uncolored form A to the
colored form B under UV radiation and then thermally bleached after
irradiation cessation. The long wave bands kB in the absorption spec-
tra of 4–7 in toluene and other solvents and rate constants kB of dark
bleaching are listed in Table 3. From these data it is clear that nitro-
substituted SOs exhibit negative solvatochromism due to bipolar
structure of their form B contrary to the unsubstituted compounds,
which have quinoid structure of form B in non-polar solvents and
therefore demonstrate positive solvatochromism. Moreover, increase
in the medium polarity leads to the acceleration of the unsubstituted
SOs bleaching and hindrance of this process for nitrosubstituted
compounds due to stronger solvatation of their bipolar molecules by
polar solvents.
REFERENCES
[1] Chu, N. Y. S. (1983). Canad. J. Chem., 61, 300.
[2] Nedoshivin, V. Yu., Zaichenko, N. L., Shienok, A. I., & Marevtsev, V. S. (1995). Russ.
Chem. Bull., 44, 712.
[3] Grummt, U.-W., Reichenbacher, M., & Paetzold, R. (1981). Tetrahedron Lett., 22,
3945.
[4] Nedoshivin, V. Yu., Lyubimov, A. V., Zaichenko, N. L., & Marevtsev, V. S. (1989).
Bull. Acad. Sci. USSR, Div. Chem. Sci., 38, 2363.
[5] Polaszkowa, W. (Ed.), Preparatica Organiczna, (1954). Panst wowe Wydawnictwa.
[6] Samoylova, N. P.
(in Russian), 1065.
& Galbershtam, M. A. (1977). Chem. Heterocycle Comp.,
[7] Ionin, B. I. & Ershov, B. A. (1967). NMR Spectroscopy in Organic Chemistry,
(in Russian), Khimiya: Leningrad.
[8] Malatesta, V., Neri, C., & Wis, M. L. (1997). Mol. Cryst. Liq. Cryst., 298, 145.