Synthesis and photochromic properties of 2-(3-nitro-2-pyridylmethyl)benzazoles

Article abstract of DOI:10.1023/A:1013237222718

2-(3-Nitro-2-pyridylmethyl)benzazoles were synthesized, and their photochromic properties were studied by flash photolysis. Introduction of a nitropyridyl instead of the nitrophenyl moiety into the 2-methyl group insignificantly increases the basicity of the methylene group. Nitropyridyl-substituted benzazoles give rise to three detectable photoinduced forms: the corresponding union at pH > 10, azamerocyanine at pH ≈ 4, and monomethinecyanine at pH ≈ 1. Irradiation of solutions of weakly basic henzoxazole and benzothiazole derivatives at pH ≈ 4 results in formation of neutral chelate structures in which the hydrogen atom is linked simultaneously to two nitrogen atoms: one in the pyridine ring, and the second, in the azole ring.

Full text of DOI:10.1023/A:1013237222718

Russian Journal of General Chemistry, Vol. 71, No. 7, 2001, pp. 1076 1087. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 7, 2001,
pp. 1142 1153.
Original Russian Text Copyright
2001 by Zakhs, Ponyaev, Subbotina, El’tsov.
Synthesis and Photochromic Properties
of 2-(3-Nitro-2-pyridylmethyl)benzazoles
E. R. Zakhs , A. I. Ponyaev, M. A. Subbotina, and A. V. El’tsov
St. Petersburg State Institute of Technology, Petersburg, Russia
Received April 26, 2000
Abstract 2-(3-Nitro-2-pyridylmethyl)benzazoles were synthesized, and their photochromic properties were
studied by flash photolysis. Introduction of a nitropyridyl instead of the nitrophenyl moiety into the 2-methyl
group insignificantly increases the basicity of the methylene group. Nitropyridyl-substituted benzazoles give
rise to three detectable photoinduced forms: the corresponding anion at pH > 10, azamerocyanine at pH 4 ,
and monomethinecyanine at pH 1. Irradiation of solutions of weakly basic benzoxazole and benzothiazole
derivatives at pH 4 results in formation of neutral chelate structures in which the hydrogen atom is linked
simultaneously to two nitrogen atoms: one in the pyridine ring, and the second, in the azole ring.
Photochromic properties of ortho-nitroalkyl-
aromatic compounds originate, depending on the
acidity of the medium, either from transfer of hydro-
gen atom from the alkyl to nitro group (as a result,
aci-nitro isomer is formed) or from ionization of the
alkyl group with formation of mesomeric anion [1, 2].
When the molecule contains a basic center, light-
induced hydrogen transfer from the alkyl group to
such center is possible. In the latter case, the corre-
sponding azamerocyanine is detected as colored
isomer. With dinitrobenzyl derivatives of benzimid-
azole and 2-(2,4-dinitrobenzyl)pyridine as examples
we previously showed [3] that these bases, their
protonated forms, photochemically generated anion,
and azamerocyanine are interrelated through a system
of acid base equilibria. The decoloration process, i.e.,
the formation of the original o-nitroalkyl derivative, is
catalyzed by acids, and its rate depends on the nature
of the substituents and heteroring [4, 5].
Photochromic compounds of this type are more
advantageous than the others due to the lack of reverse
photoreaction; theoretically, this provides the pos-
sibility for attaining 100% conversion into the colored
form and a large contrast in the absorption of the
initial and photoinduced forms ( 200 300 nm). All
compounds of this type reported up to now contain
a nitroaryl moiety as photoactive center. In the present
work we have synthesized 2-(3-nitro-2-pyridyl-
Deceased.
1070-3632/01/7107-1076$25.00 2001 MAIK Nauka/Interperiodica

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
1077
methyl)benzazoles and examined their photochromic
properties. Replacement of the 2,4-dinitrobenzyl frag-
ment by 3,5-dinitro-2-pyridylmethyl in the series of
benzimidazole derivatives gave strongly colored
compounds of the dihydrobenzimidazole series [6].
tion, which unambiguously proves its structure. Tri-
fluoroacetic acid protonates the pyridine ring: signals
from all protons shift downfield by 0.35 (singlet from
the methylene group) and 0.55 ppm (multiplet from
3-H), and the 2-H and 4-H protons give rise to one
signal at about 9.1 ppm. Our attempt to obtain ethyl
(3-nitro-2-pyridyl)acetimidate by addition of ethanol
to nitrile IX in ether in the presence of HCl was also
unsuccessful: The initial compound remained un-
changed. The same reaction in methylene chloride
gave a color- less intermediate product (compound X)
Heterocyclic fragments in the molecules of (di-
nitropyridylmethyl)benzimidazole I possess strongly
different basicities; therefore, protonation of these
compounds occurs mainly at the imidazole ring. As
follows from the electronic absorption spectra of the
model 1,3-dimethyl-2-(3,5-dinitro-2-pyridylmethyl-
ene)-2,3-dihydrobenzimidazole, compounds I exist as
isomers IB. This structure is fully consistent with the
structure of colored isomers of diquinolylmethanes II
and their analogs in which two heterocyclic systems
are linked through a methylene bridge. Enhanced
acidity of the bridging unit in II gives rise to displace-
ment of the tautomeric equilibrium from a colorless
methane isomer IIA to an intensely colored chelate
structure like IIB or a bis-cis-structure with proto-
nated heteroring [7]. In order to reduce the electron-
acceptor influence of the dinitropyridine fragment, we
made an attempt to synthesize compounds with one
nitro group in the pyridine moiety.
1
with mp 119 120 C. Its H NMR spectrum in tri-
fluoroacetic acid lacked signal from ethyl group, a
singlet from the CH2 group was located at
5 ppm,
the 3-H signal was observed at 8.3 ppm, and the
2-H and 4-H protons gave a multiplet at 9.2 ppm;
in addition, a one-proton triplet (1:1:1; J = 52 Hz)
was observed at
6.7 ppm. Presumably, the latter
belongs to the proton on the cyano nitrogen atom.
This is consistent with the absence of CN stretching
vibration band in the IR spectrum of X. Repeated
saturation with hydrogen chloride of a solution of X
and EtOH in chloroform gave (after appropriate
workup) (3-nitro-2-pyridyl)acetamide.
X
N
CH2CN
CH2
NO2
O
NO2
CN
COOEt
PCl5
COOEt
N
HetCl
POCl3
O2N
N
H
N
H
VII
III, X = NMe; IV, X = NH; V, X = O; VI, X = S.
VIII
HetCH2CONH2,
We planned to prepare 2-(3-nitro-2-pyridylmethyl)-
benzazoles III VI using the imidate technique, but
we failed to obtain required amounts of the corre-
sponding imidate. 2-Chloro-3-nitropyridine (VII) [8]
fairly readily reacted with ethyl cyanoacetate to afford
an orange ethyl (3-nitro-1,2-dihydro-2-pyridylidene)-
cyanoacetate (VIII). Katz and Voyle [9] and Willette
[10] reported on their failure to obtain (3-nitro-
2-pyridyl)acetonitrile (IX) by hydrolysis of VIII.
Therefore, Katz and Voyle [9] used tert-butyl cyano-
acetate for the synthesis of nitropyridylacetonitriles.
We succeeded in obtaining pyridylacetonitrile IX in
70% yield by heating compound VIII in boiling 1 M
hydrochloric acid. The IR spectrum of product IX
characteristically contained bands from the CN and
NO2 groups. On dissolution in 0.01 N NaOH ”®-
originally colorless compound IX gives a colored
EtOH/HCl
CH2Cl2
HCl
CH3Cl
HetCH2CN
X
IX
Het = 3-nitro-2-pyridyl.
The second version of the synthesis of compounds
III VI implied introduction of a nitropyridyl fragment
into activated methylene group of (benzazolyl)aceto-
nitriles or (benzazolyl)acetates. Preliminarily, we
tried to find conditions under which chloronitropyri-
dine VII is capable of reacting with 1,3-dimethyl-
2-(cyanomethylene)-2,3-dihydrobenzimidazole (XI).
CH3
N
CH3
N
CN
anion (
560, 590 nm), which absorbs at a longer
VII
max
XIII.
NO2
CHCN
wavelength than anions derived from the known (2,4-
dinitrophenyl)- and (2,4-dinitronaphthyl)acetonitriles
110 C
N
N
N
1
(445, 550 and 440, 580 nm, respectively). The H
CH3
CH3
NMR spectrum of IX in acetone almost coincided
with that reported in [9] for deuterochloroform solu-
XII
XI
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1078
ZAKHS et al.
advantage of using not the cyano but the more readily
D
removable ethoxycarbonyl group. By condensation of
ortho-substituted anilines with ethyl ethoxycarbonyl-
acetimidate hydrochloride [11] we obtained (2-benz-
azolyl)acetates XIV XVII. Compounds XIV and XV
were also prepared from the corresponding 2-(cyano-
methyl)benzimidazoles by the action of HCl in
alcohol. The reaction of XIV with chloronitropyridine
VII was carried out by melting in DMSO with di-
methyl sulfoxide sodium salt as base. The best
results were obtained when the reaction was per-
formed in DMF in the presence of sodium hydrides.
Unlike the reaction with 2-chloro-3,5-dinitropyridine
[6], the arylation at the nitrogen atom almost did not
occur. Ester XVIII was difficult to purify, but this
procedure was unnecessary for the subsequent hy-
drolysis. Compound XVIII was isolated as a dark
brown oil which showed in the IR spectrum absorp-
tion bands from stretching vibrations of the ester
0.15
0.10
0.05
5
4
1
3
2
500
600
700 , nm
Fig. 1. Electronic absorption spectra of photoinduced
forms of (1 4) 1-methyl-2-(3-nitro-2-pyridylmethyl)-
benzimidazole (III), c = 7.2 10 M, and (5) its anion,
c = 7.2 10 M, in water containing 1% of ethanol;
(1) pH 1.04, (2) pH 3.15, (3) pH 4.3, (4) pH 11.75, and
(5) 2.5 N KOH.
5
5
Fusion of the reactants at 110 C in 40 min afforded
dark red compound XII whose spectral parameters
and elemental composition were in agreement with
the given formula. However, our attempt to remove
the cyano group from XII by solvolysis in methanol
in the presence of hydrogen chloride resulted in
elimination of the pyridyl moiety, yielding product
XIII.
1
carbonyl and nitro groups (1750 and 1520, 1355 cm ,
respectively). The developed procedure was also
suitable for preparation of the other benzazoles. Esters
XVIII, XIX, and XXI are red or orange, while the
weakly basic benzoxazole derivative XX is colorless;
i.e., the latter has a structure of bis(heteryl)acetate.
Target compounds III VI were then synthesized from
esters XVIII XXI by hydrolysis of the ethoxycar-
bonyl group in boiling 10% hydrochloric acid:
Therefore, in further experiments we took
COOEt
X
NH*HCl
X
N
XH
NO2
VII
CH2C
CH2COOEt
COOEt
+
III VI
NaH/DMF
NH2
COOEt
N
H
N
XIV XVII
Me
N
XVIII XXI
18% HCl/EtOH
CH2CN
N
XIV, XVIII, X = NMe; XV, XIX, X = NH; XVI, XX, X = O; XVII, XXI, X = S.
1,3-Dimethyl-2-(3-nitro-2-pyridylmethyl)benzimid-
azolium perchlorate XXII was obtained by quaterniza-
tion of benzimidazole derivative III with methyl
p-toluenesulfonate, followed by treatment with sodium
perchlorate. Salt XXII was converted into deeply
colored 1,3-dimethyl-2-(3-nitro-2-pyridylmethylene)-
2,3-dihydrobenzimidazole (XXIII) by the action of
0.01 N alcoholic potassium hydroxide:
Me
Me
1) TsOMe;
2) NaClO4
N
N
NaOH
NO2
III
NO2
+
N
N
N
N
Me
Me
XXII
XXIII
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
1079
D
D
0.5
1
2
0.20
4
4
0.2
1
3
0.10
3
2
0.1
400
500
600
700 , nm
400
500
600
700 , nm
Fig. 2. Electronic absorption spectra of photoinduced
forms of (1 3) 2-(3-nitro-2-pyridylmethyl)benzoxazole
Fig. 3. Electronic absorption spectra of photoinduced
forms of (1 4) 2-(3-nitro-2-pyridylmethyl)benzothiazole
(VI), c = 1.9 10 M, in water containing 1% of ethanol;
5
(V), c = 5.85 10 M, and (4) its anion, c = 1.4
5
4
10 M, in water containing 1% of ethanol; (1) pH 1.06,
(2) pH 4.2, (3) pH 10.75, and (4) 2.5 N KOH.
(1) pH 0.75, (2) pH 4.15, (3) pH 10.7, and (4) 2.5 N KOH.
Photochromic properties of nitropyridylmethyl-
benzazole derivatives III VI were studied by flash
photolysis and were compared with those found for
mononitro- (XXIV, XXV) and dinitrobenzyl analogs
(XXVI XXIX):
Flash photoexcitation of compounds III VI in
aqueous and aqueous-ethanolic solutions gives rise to
reversible absorption in the visible region (Figs. 1 3).
As with compounds XXIV XXIX, the rate constants
of decoloration and the spectra of photoinduced forms
depend on pH.
X
R
CH2
O2N
In the case of mono- (XXIV, XXV) [12] and di-
nitrobenzylbenzazoles (XXVI XXIX) [5], two colored
photoinduced forms are observed (anion B at pH >
8.5 and azamerocyanine B at pH < 4), whereas for
compounds III VI we detected three photoinduced
forms.
N
XXIV, X = NH, R = H; XXV, X = O, R = H; XXVI, X =
NCH3, R = NO2; XXVII, X = NH, R = NO2; XXVIII, X =
S, R = NO2; XXIX, X = O, R = NO2.
X
R
CH
O2N
+
N
H
B
H+
+H+
X
X
h
R
CH
CH2
O2N
R
N
N
N
A
O
O
B
At pH 0 2 the colored forms are characterized by
absorption maxima at 408 nm for benzimidazoles
(pH 4) the long-wave absorption maxima are
600, 550, and 580 nm for compounds III, VI, andmVax,
respectively. In alkaline medium (pH > 10) we ob-
III and IV and benzoxazole V and
450 nm for
benzothiazole derivatives VI. In less acidic media
served colored forms with
540 nm for com-
max
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1080
ZAKHS et al.
pounds III and IV and 595 nm for benzoxazole and
benzothiazole derivatives V and VI. We believe that
mesomeric anions are generated from all three types
of compounds in aqueous alcoholic buffer solutions
with pH > 10, for the absorption spectra of their
photoinduced forms (the shape and position of the
absorption bands) are similar to those observed for
the corresponding anions obtained by dark ionization
in much more alkaline solutions (Fig. 1 3). The color
of the anion depends on the nature of the heteroring
which is involved in the chromophore system.
protonated salts (AH+2) can undergo photolysis simul-
taneously. Protonation of both heterocyclic fragments,
at least for benzimidazole derivatives III and IV, is
quite probable: the pKa values of 3-nitropyridine,
2-(2,4-dinitrobenzyl)benzimidazole, and benzothiazole
are 0.81 [13], 3.95 [3], and 1.2 [14], respectively.
Therefore, the detectable colored species may be
monomethinecyanine like BH+. We previously
showed [5] that the basicity of heterocycle in anion
is greater than in the original molecule, so that mono-
methinecyanine BH+ can be formed not only from
dication AH+2 but also via protonation of azamero-
cyanine B derived from monocation AH+ (Scheme 1).
In strongly acidic media (pH 0 1) both initial
neutral molecule A and its mono- (AH+) and di-
Scheme 1.
O2N
X
O2N
X
O2N
X
O2N
X
H+
H+
H+
H+
+
+
N
+
N
+
N
+
N
N
CH2
N
CH2
N
CH2
N
CH2
H
H
H
H
AH2+
AH+
A
h
h
h
h
O2N
O2N
H+
H+
O2N
X
O2N
X
H+
H+
X
X
+
+
N
+
N
+
N
+
N
N
N
CH
N
CH
N
CH
CH
B
H
H
H
H
BH+
or
B
O2N
X
X
+
N
CH
N
H
N
H
CH
NO2
N
H
According to Kiprianov [15], the color of
an unsymmetric monomethinecyanine dye is deter-
mined by addition of colors of the two symmetric
parent dyes; here, the deviation from additivity
depends on the difference in the basicity of two
heterorings involved. Unfortunately, we have found
no published data on symmetric monomethinecyanines
on the basis of benzimidazole and nitropyridine. From
the data for symmetric monomethinecyanines based
without taking into account the deviation and in-
fluence of the nitro groups (Scheme 2).
Such approximation is fairly justified, for the nitro
group in the pyridine ring could strongly affect only
the color of the anion through delocalization of the
negative charge (the anion is thus stabilized). How-
ever, it is incapable of delocalizing positive charge
and hence of stabilizing cations. These statements
on benzothiazole (benzoxazole) and pyridine we can are supported, e.g., by the similar in the absorption
estimate absorption maxima of unsymmetric dyes spectra of bis(benzothiazolyl)methane in acidic and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
1081
Scheme 2.
D
D
1.0
S
S
CH
I
0.04
+
N
N
3
1
CH3
CH3
0.5
0.02
S
max 425 nm [16]
2
CH
I
+
N
N
CH3
CH3
400
500
600
700
+
CH
I
, nm
N
N
max (calc) 450 nm
CH3
CH3
Fig. 4. Electronic absorption spectra of (1, 2) 1,3-dimethyl-
2-(3-nitro-2-pyridylmethyl)benzimidazolium perchlorate
(XXIV), c = 8.2 10 M, and (3) its anion in water
containing 1% of ethanol; (1) pH 1.07, (2) pH 4.4,
(3) 0.01 N KOH.
max 477 nm [17]
O
5
CH
I
+
N
N
O
O
CH3
C2H5
CH
I
+
N
has azamerocyanine structure B . This conclusion
was drawn on the basis of the fact that the absorption
spectrum of the colored form coincided with the
spectrum of model 2-(2-nitrobenzylidene)-2,3-di-
hydrobenzimidazole. The spectra of colored species
generated from 2-(3-nitro-2-pyridylmethyl)benzimid-
azoles III and IV at the same pH values resemble
those observed for the nitrophenyl analog; therefore,
these species can also be assigned the azamerocyanine
structure. This conclusion is proved by the results for
a model compound, 1,3-dimethyl-2-(3-nitro-2-pyridyl-
methyl)benzimidazolium perchlorate (XXII). Unlike
the carbocyclic analog, flash photoexcitation of com-
pound XXII in solutions with various acidities gives
rise to two rather than one detectable forms. At pH 1
N
max (calc) 423 nm
C2H5
C2H5
max 370 nm [17]
alkaline alcoholic solutions [18] due to the similarity
in the chromophoric systems of the cation and anion.
S
S
CH
N
S
N
S
CH
I
+
N
N
H
H
the
of the photoinduced form is 390 nm, which
max
corresponds to a monomethinecyanine structure; at
pH 4 the long-wave absorption maximum is located
at 580 nm (Fig. 4). Its shape and position resemble
Therefore, the spectra of cations containing a nitro
group and lacking it should be similar. The calculated
values of
of unsymmetric monomethinecyanines
max
Me
approach those found for the colored photoinduced
forms of nitropyridylmethyl derivatives of benzoxa-
zole (V) and especially of benzothiazole (VI) at
pH 0 1 (Figs. 1 3). This fact counts in favor of the
monomethinecyanine structure of the colored forms
of 2-nitropyridylmethylbenzazoles in strongly acidic
media. The greater difference in the calculated and
N
NO2
N
Me
N
H N+
Me
ClO4
h
NO2
H+ H+
+
N
experimental values of
for benzoxazole V, as
compared to benzothiazomleax VI, may be attributed
to the greater difference in the basicity of these
heterocycles, on the one hand, and nitropyridine, on
the other.
N
Me
Me
N
ClO4
XXII
NO2
N
In moderately acidic media (pH 4) the absorption
maximum of the colored species appreciably shifts to
the red region. We showed in [12] that at pH 4 the
photoinduced form of 2-(2-nitrobenzyl)benzimidazole
N
Me
ClO4
XXIII
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1082
ZAKHS et al.
Absorption maxima (nm) of photoinduced forms of compounds III, V, VI, XXIV, XXV, XXVI, XXVIII, and XXIX
in aqueous buffer solutions with pH 4 and of model azamerocyanines based on ethylrodanin in ethanol
X
X
X
N
R
S
CH
O2N
CH
CH CH
O
+
+
+
N
N
N
X
S
N
O2N
H
H
H
C2H5
III, V, VI
R = H
R = NO2
NCH3
O
S
610
515
520
503
535
600
380, 580 sh
396, 550 sh
511
492
526
those observed for base XXIII as a model of the aza-
merocycanine structure (it was prepared by treatment
of perchlorate XXII with alkali).
[20]). Taking into account that the basicity of the
heteroring in the anion is greater than in the original
molecule, we may presume an azamerocyanine struc-
ture of the photoinduced forms of these dyes. As was
shown in [5] for the same series of heterocycles, the
lower the basicity of the heteroring, the greater the
pKa value.
Base XXIII shows a strong positive solvato-
chromism, indicating charge delocalization over the
chromophore system and lower polarization of the
ground state of XXII, in contrast to the dinitrobenzyl
analog exhibiting a weak negative solvatochromism.
Presumably, this difference is responsible for the
deeper color of azamerocyanines derived from pyridyl-
Unlike dinitrobenzyl derivatives of benzoxazole
and benzothiazole XXIX and XXVIII, 2-nitropyridyl-
substituted compounds have two centers with similar
basicities: nitrogen atoms in the azole ring and in the
nitropyridine ring. Therefore, protonation of the azole
and pyridine nitrogen atoms is equally probable. At
pH 4 photoexcitation could give neutral chelate Ch
as colored species in which hydrogen atom is linked
simultaneously to two nitrogen atoms. The strong
short-wave absorption maximum of the photoinduced
forms of nitropyridylmethylbenzoxazole and nitro-
pyridylmethylbenzothiazole derivatives V and VI is
most likely to result from the chelate structure which
is typical of such compounds [7]. The formation of
a colored tautomeric form from nitropyridylmethyl-
benzazoles is governed not only by the acidity of the
methylene bridge but also by the ability of hetero-
cyclic nitrogen atoms to chelation. The compounds
under study are just those capable of chelating. As
we already noted, replacement of the dinitroaryl
fragment in the colorless dinitrobenzylbenzimidazole
XXVI by dinitropyridyl gives rise to appearance of
color. This may be due to stabilization of the colored
tautomeric form as chelate structure, as also follows
from the absence of NH vibration bands in the IR
spectrum. Presumably, the formation of chelate aza-
merocyanine structures from pyridylbenzoxazole and
pyridylbenzothiazole derivatives V and VI is respons-
ible for the observed specific features in their spectral
behavior, which differentiate them from the benzyl
derivatives (see table).
methyl compounds (
600 nm), as compared to
520 nm).
the dinitrobenzyl analmogaxs (
max
At pH 4 about a half of molecules III and IV are
protonated, and they exist in solution as salts. There-
fore, both neutral molecules and the corresponding
cations can absorb light. In the two cases, formation
of the same colored species is expected; their chromo-
phoric system is analogous to that in 1,3-dimethyl-2-
(3-nitro-2-pyridylmethyl)-2,3-dihydrobenzimidazole
(XXIII) having an azamerocyanine structure. The
common azamerocyanine nature of the colored species
generated from nitrobenzyl (XXIV) and nitropyridyl-
methyl derivatives (III and IV) under the given
conditions is also confirmed by similar shifts of their
absorption bands relative to the corresponding anions.
In all cases, azamerocyanines derived from dihydro-
benzimidazoles have a deeper color than their anions.
The same pattern in the variation of
in going
max
from benzimidazole to benzoxazole and benzothiazole
heteroring in the series of mono- and dinitrobenzyl
derivatives was observed for model merocyanine dyes
based on 3-ethylrodanin [19]; however, this pattern
slightly differs from that found for nitropyridylmethyl
derivatives (see table).
Protonation of benzoxazole and benzothiazole
derivatives V and VI at the azole ring at pH 4 is
hardly probable because of their low basicity (pKa of
benzothiazole is 1.2 [14], and of benzoxazole, 0.5
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
1083
Thus, introduction of a basic center into the nitro-
benzyl chromophore gives rise to an additional photo-
induced form having a chelate structure.
stand for 1 h at that temperature, cooled, and poured
onto 200 g of ice. The yellow precipitate was filtered
off to obtain 3 g (22%) of 3-nitropyridin-2-one with
mp 222 223 C, which can be used in further syn-
theses without additional purification. The product can
be recrystallized from water (1:15) or ethanol (1:20).
EXPERIMENTAL
The molecular weights were determined by reverse
ebullioscopy using a Hewlett Packard B-302 osmom-
eter. The IR spectra of samples pelleted with KBr
were obtained on a UR-20 spectrometer. The electronic
absorption spectra were measured on a Specord M-40
2-Chloro-3-nitropyridine (VII) [23]. A mixture of
4 g of 3-nitropyridin-2-one and 8 g of phosphorus
pentachloride wetted with 1.5 ml pf phosphoryl chlo-
ride was heated for 1 h on a boiling water bath. The
brown melt was poured onto 200 g of ice. The yellow
precipitate was filtered off, washed with water to
neutral reaction of the washings, and recrystallized
from 60 ml of a 1:1 benzene petroleum ether mixture.
Yield 2.8 g (62%), colorless needles, mp 100 101 C.
1
spectrophotometer. The H NMR spectra of solutions
in CCl4 were recorded on a Bruker WP-200 instru-
ment. Photochromic properties of nitropyridylmethyl-
benzazoles were studied on a modified flash photo-
lysis setup described in [21]. Solutions of the com-
pounds under study were irradiated with an IFP-5000
flash lamp (full spectrum or through a UFS-2 light
1,3-Dimethyl-2-[(3-nitro-2-pyridyl)cyanomethyl-
ene]-2,3-dihydrobenzimidazole (XII). A mixture
of 0.5 g 2-chloro-3-nitropyridine VII and 1.17 g of
1,3-dimethyl-2-cyanomethylene-2,3-dihydrobenzimid-
azole (XI) was kept for 40 min at 110 C. The mixture
first turned red and then it melted and solidifed. The
solid product was recrystallized from 80 ml of
n-butanol. Yield 0.75 g (70%), dark red needles.
filter which transmits in the
range from 270 to
380 nm). The change in the transmission, induced by
light flash, was measured using a KGM-12 halogen
lamp (100 W) whose irradiation was passed through
a 20-cm quartz cell. The outgoing beam (after
a DMR-4 monochromator) was recorded at a selected
wavelength with a FEU-84 photoelectron multiplier,
and the signal was transferred to an S8-13 recording
oscillograph or CAMAC spectral kinetic unit, where
it was processed with an FK71-2 AD converter and
was transferred through a KK-111 CAMAC crate
(manufactured at the Vilnius factory of electrical-type
instruments) to a PC. With the aid of special software
we obtained kinetic curve for the outgoing signal
from the photoelectron multiplier in the time range
from 1 ms 200 s and treated it according to first-,
second-, and mixed-order equations. The results were
output as the corresponding rate constants and devia-
tions of the experimental data from appropriate
approximation. The spectrum of the photoinduced
form (referred to any moment of time within the
kinetic curve) was derived from the set of kinetic
curves obtained at different wavelengths. The setup
operating in the mode of compensation for a steady
component and RC-shunting of noise ensured registra-
tion of as small change in the optical density as
0.0005.
1
IR spectrum, , cm : 1330 and 1530 (NO2), 2130
(CN). Found, N, %: 22.9. C16H13N5O4. Calculated N,
%: 22.8.
Solvolysis of compound XII. A suspension of
0.3 g of compound XII in 20 ml of methanol was
saturated on cooling with dry hydrogen chloride until
the precipitate dissolved completely. The yellow
solution was evaporated, and 3 ml of acetone was
added to the oily residue. The yellow precipitate
(compound X) was filtered off. Yield 0.15 g,
1
mp 230 C. IR spectrum, , cm : 1400, 1520, 1740,
3000. UV spectrum, max, nm: in 50% ethanol
(neutral solution and a solution containing 0.01 N
H2SO4): 273, 280; in 0.01 N NaOH: 270, 336. Found
N, %: 12.3.
Ethyl (3-nitro-2-pyridyl)cyanoacetate (VIII). To
a suspension of 2.42 g of powdered NaOH in 50 ml
of DMF we added 7.4 g of ethyl cyanoacetate. A solu-
tion of 5 g of 2-chloro-3-nitropyridine in 15 ml of
DMF was then added with stirring at 10 20 C over
a period of 30 min. The mixture was stirred for
30 min at 25 C and was poured into 1 l of cold water.
The orange precipitate was filtered off, washed with
water, and recrystallized from 250 ml of ethanol.
Yield 5 g (67%), bright orange plates with mp 135
3-Nitropyridin-2-one [22]. To a solution of 10 g
of 2-pyridinone in 50 g of concentrated sulfuric acid
we slowly added while stirring and cooling (with
an ice salt mixture) a mixture of 15 g of HNO3
(d = 1.5) and 5 g of H2SO4 (d = 1.84) at such a rate
that the temperature did not exceed 10 C. The mixture
was then left to stand for 30 min at room temperature.
If the mixture spontaneously warmed up to above
30 C, it should be cooled down to room temperature.
The mixture was slowly heated to 70 80 C, left to
1
136 C. IR spectrum, , cm : 1330 and 1530 (NO2),
1640 (C O), 2200 (CN). UV spectrum (ethanol;
neutral solution and a 0.01 N solution of H2SO4),
max, nm (log ): 235 (4.26), 280 (3.97), 342 (3.94),
460 (3.22). Found, %: C 51.0; H 3.8; N 17.8. M 230
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1084
ZAKHS et al.
(in toluene). C10H9N3O4. Calculated, %: C 50.9;
H 4.1; N 17.8. M 235.
amine in 30 ml of anhydrous methanol. The mixture
was kept for 30 min at 0 C and was heated for 45 min
under reflux. It was then poured into a cold solution
of 3.5 g of sodium hydrogen carbonate in 250 ml of
water. The solution turned turbid, and colorless plates
gradually separated. Yield 4.2 g (52%), mp 126
127 C.
(3-Nitro-2-pyridyl)acetonitrile (IX). A solution
of 1 g of ester VIII in 100 ml of 1 M hydrochloric
acid was refluxed for 1 h. After cooling, unreacted
ester VIII ( 0.3 g) was filtered off, and the product
was extracted from the filtrate into 120 ml of
methylene chloride. The extract was washed with
a saturated solution of sodium carbonate (2 25 ml),
b. A solution of 5 g of 2-cyanomethylbenzimid-
azole in 75 ml of 9% ethanolic HCl was refluxed for
dried over sodium sulfate, and filtered through a layer 1.5 h. The mixture was cooled, filtered from ammo-
(3 4 cm) of aluminum oxide. The solvent was dis-
tilled off, and the solid residue (0.47 g) was recrystal-
lized from 100 ml of benzene petroleum ether (1:5)
to isolate 0.39 g (80%) of compound IX as color-
less lustrous plates with mp 108 109 C. IR spectrum,
, cm : 1350 and 1540 (NO2), 2260 (CN). Found, %:
C 51.5; H 3.1; N 25.6. M 161 (in toluene). C7H5N3O2.
Calculated, %: C 51.5; H 3.1; N 25.8. M 163.
nium chloride liberated during the reaction, the
filtrate was evaporated, and 150 ml of a saturated
solution of sodium hydrogen carbonate was added to
the brown oily residue. The precipitate was filtered
off and recrystallized from benzene (1:10). Yield
2.8 g (45%), colorless lustrous plates, mp 126 127 C
(published data [24]: 128.5 129.5 C).
1
Ethyl 1-methyl-2-benzimidazolylacetate (XIV).
A solution of 5.5 g of 1-methyl-2-cyanomethylbenz-
imidazole in 110 ml of 18% HCl in ethanol was
refluxed for 2 h. The mixture was then cooled and
filtered, and the filtrate was evaporated to leave
an oily residue which was treated with a solution
of sodium hydrogen carbonate. The product was
extracted with 500 ml of chloroform. The extract
was dried with sodium sulfate, the solvent was dis-
tilled off, and the oily residue was made crystalline
by grinding. After recrystallization from petroleum
ether (1:40) we obtained 4.2 g (60%) of colorless
plates with mp 66 68 C (60 62 C [25]). Found, %:
C 66.1; H 6.5; N 13. C12H14N2O2. Calculated, %:
C 66.0; H 6.5; N 12.8.
Compound X. A solution of 0.7 g of pyridylaceto-
nitrile IX in 20 ml of methylene chloride containing
0.25 g of anhydrous ethanol was saturated at 0 2 C
with dry gaseous hydrogen chloride. After 24 h, the
colorless precipitate was filtered off and washed with
1
ether (2 3 ml). Yield 0.45 g, mp 119 120 C. H
NMR spectrum (CF3COOH), , ppm: 5.02 s (CH2),
9.3 m ( -H, -H, pyridine), 8.34 s ( -H, pyridine),
7.35 6.03 (NH, J = 52 Hz).
3-Nitro-2-pyridylacetamide. A solution of 0.3 g
of compound XIII in 20 ml of chloroform was
saturated at 0 2 C with dry gaseous HCl. After 24 h,
the solution was evaporated to isolate 0.17 g of
a colorless product with mp 190 191 C. Recrystal-
lization from 4 ml of ethanol gave 0.08 g (34.8%) of
colorless plates with mp 169 170 C. IR spectrum, ,
Ethyl 2-benzoxazolylacetate (XVI). To a solution
of 7.8 g of ethyl ethoxycarbonylacetimidate hydro-
chloride in 100 ml of anhydrous methanol at 0 C we
added a solution of 4.3 g of o-aminophenol in 50 ml
of anhydrous methanol. The mixture was kept for
30 min at 0 C and was heated for 40 min under reflux.
It was then cooled and poured into 300 ml of water.
The product was extracted with ether (5 100 ml).
The yellow extract was dried over sodium sulfate.
After removal of the solvent, the dark brown oil
was ground to obtain light yellow plates which were
recrystallized from 300 ml of petroleum ether (bp 70
100 C). Yield 5.8 g (72%), colorless lustrous plates
with mp 54 55 C [11].
1
cm : 1350 and 1530 (NO2), 1680 (C O), 3330
(NH2). 1H NMR spectrum (CF3COOH), , ppm:
4.82 s (CH2), 7.52 s (NH2), 8.1 m ( -H, J
= 1,
J
= 2.5 Hz, pyridine), 9.3 s ( -H, -H, py,ridine).
,
Found, %: C 46.2; H 3.9; N 23.3. C7H8N3O3. Cal-
culated, %: C 46.5; H 3.9; N 23.2.
Ethyl ethoxycarbonylacetimidate hydrochloride
[11]. A stream of dry gaseous hydrogen chloride was
passed over a period of 1 h through a mixture of 18 g
of ethyl cyanoacetate and 9.3 ml of anhydrous ethanol
in dry diethyl ether. The mixture was kept for 48 h
in a refrigerator, and the colorless precipitate was
filtered off and washed with dry ether. Yield 29 g
(90%), colorless plates, mp 102 103 C.
Ethyl 2-benzothiazolylacetate (XVII) was syn-
thesized from o-aminobenzenethiol [26] and ethyl
ethoxycarbonylacetimidate hydrochloride, following
the procedure described above for ethyl 2-benzoxa-
zolylacetate XVI. Removal of the solvent left a yellow
liquid which was distilled under reduced pressure,
a fraction with bp 150 C (1 mm) being collected;
Ethyl 2-benzimidazolylacetate (XV) [11]. a. To
a solution of 7.8 g of ethyl ethoxycarbonylacetimidate
hydrochloride in 100 ml of anhydrous methanol at
0 C we added a solution of 4.3 g of o-phenylenedi-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
1085
n2D0 1.5070. Yield 3.5 ml (60%). IR spectrum, , cm :
trum, , cm : 1355 and 1520 (NO2), 2920 (CH3),
1
1
1
1750 (C O), 2990 (CH3). Found, %: C 59.5; H 5.0;
N 6.5; S 14.3. C11H11NO2S. Calculated, %: C 59.7;
H 4.9; N 6.3; S 14.5.
3080 (C Harom). H NMR spectrum (CCl4), , ppm:
3.68 s (CH3), 4.65 s (CH2), 7.09 m ( -H, -H, -H,
pyridine). Found, %: C 62.9; H 4.5; N 21.0. M 273
(in chloroform). C14H12N4O2. Calculated, %: C 62.7;
H 4.5; N 20.9. M 268.
1-Methyl-2-[(3-nitro-2-pyridyl)(ethoxycarbonyl)-
methylene]-2,3-dihydrobenzimidazole (XVIII).
a. A mixture of 1 g of 2-chloro-3-nitropyridine and
2.75 g of ethyl 1-methyl-2-benzimidazolylacetate
(XV) was heated until melting (70 C), and 0.8 g of
finely powdered sodium hydroxide was added under
vigorous stirring. The mixture was stirred for 20 min
at 70 C, cooled, and dissolved in 150 ml of water.
The solution was acidified to pH 6 with concentrated
hydrochloric acid, and product XVIII was extracted
into 500 ml of chloroform. We isolated 2.5 g of a dark
brown oil containing some impurities in addition to
the main substance. The product was brought into
further synthesis to obtain target compound III.
Ethyl 2,3-dihydrobenzimidazol-2-ylidene-
(3-nitro-2-pyridyl)acetate (XIX). A flask was
charged with 5 ml of freshly distilled DMSO and
0.3 g of sodium hydride. The mixture was heated to
60 70 C and was kept at that temperature for 30 min.
It was then cooled to room temperature, and a solution
of 2.58 g of ethyl 2-benzimidazolylacetate (XV) in
8 ml of DMSO was added in small portions. The
mixture was kept for 20 min at 25 C, and a solution
of 1 g of 2-chloro-3-nitropyridine in 10 ml of DMSO
was added. The mixture was stirred for 1 h at room
temperature, poured into 100 ml of water, and
acidified to pH 4 with concentrated hydrochloric acid.
The precipitate was filtered off, washed with a small
amount of water, and recrystallized from 20 ml of
n-butanol. We obtained 0.66 g (32%) of dark cherry
b. To a suspension of 0.16 g of sodium hydride
in 2 ml of DMF at 25 30 C we added under argon
a solution of 1.38 g of ethyl 1-methyl-2-benzimid-
azolylacetate (XV) in 3 ml of DMF. The mixture was
kept for 20 min at 40 C, and a solution of 2-chloro-
3-nitropyridine in 3 ml of DMF was added. The
originally yellow reaction mixture turned violet.
It was stirred for 30 min at 50 C and for 1 h at 25 C.
The progress of the reaction was monitored by chrom-
atography on Silufol UV-254 plates using ethyl
acetate as eluent: 2-chloro-3-nitropyridine, Rf 0.8
(colorless spot in daylight), compound XVIII, Rf 0.6
(brown spot). The mixture was poured into 200 ml of
water, neutralized with hydrochloric acid to pH 7, and
extracted with ether (400 ml). The extract was dried
over sodium sulfate and evaporated to obtain 0.98 g
of a dark brown oil which was brought into further
1
crystals. IR spectrum, , cm : 1350 and 1520 (NO2),
1650 (C O), 3275 (NH). Found, %: C 58.9; H 4.4;
N 17.2. M 273 (in dioxane). C14H14N4O4. Calculated,
%: C 58.9; H 4.3; N 17.2. M 326.
2-(3-Nitro-2-pyridylmethyl)benzimidazole (IV).
A mixture of 0.15 g of compound XIX and 20 ml of
10% hydrochloric acid was heated under reflux for
40 min. The progress of the reaction was monitored
by thin-layer chromatography on Silufol UV-254
plates using ethyl acetate as eluent: XIX, Rf 0.6
(brown spot); IV, Rf 0.16. When only traces of XIX
remained in the mixture, it was diluted with 60 ml
of water and neutralized with a solution of alkali to
pH 7. The solution changed from yellow to dark red.
The product was extracted into 300 ml of chloroform.
The extract was dried over sodium sulfate, and the
solvent was distilled off. The oily residue was dis-
solved in 20 ml of benzene on heating. The benzene
solution was treated with charcoal. Colorless needles
precipitated from the solution. Yield 0.08 g (68%),
1
synthesis of target product III. IR spectrum, , cm :
1355 and 1520 (NO2), 1750 (C O).
1-Methyl-2-(3-nitro-2-pyridylmethyl)benzimid-
azole (III). To 1 g of oily compound XVIII we added
40 ml of 10% hydrochloric acid, and the mixture was
refluxed for 1 h. The progress of the reaction was
monitored by TLC (Silufol UV-254, ethyl acetate):
XVIII, Rf 0.6; III, Rf 0.4. When only traces of XVIII
remained in the mixture, it was diluted with 100 ml
of water and neutralized with a solution of sodium
carbonate to pH 6. Product III was extracted into
300 ml of ether (the extract turned violet). The extract
was dried over sodium sulfate and evaporated. The
dark grey precipitate was recrystallized from 150 ml
of benzene petroleum ether (1:10) and then from
100 ml of petroleum ether (bp 70 100 C). Yield
0.33 g (50%, calculated on the chloronitropyridine
taken), colorless needles, mp 121 122 C. IR spec-
1
mp 157 C. IR spectrum, , cm : 1350 and 1530
(NO2). 1H NMR spectrum (CF3COOH), , ppm:
5.17 s (CH2), 7.28 s (4H, benzimidazole), 7.7 s ( -H,
pyridine), 8.78 m ( -H, -H, pyridine). Found, %:
C 61.1; H 4.0; N 22.1. M 254 (in dioxane).
C13H10N4O2. Calculated, %: C 61.4; H 4.0; N 22.0.
M 253.
Ethyl 2,3-dihydrobenzothiazol-2-ylidene-
(3-nitro-2-pyridyl)acetate (XXI). A solution of 2.3 g
of ethyl 2-benzothiazolylacetate (XVII) in 10 ml
of DMF was added under argon to a suspension of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1086
ZAKHS et al.
0.25 g of sodium hydride in 2 ml of DMF. During
the addition the mixture spontaneously warmed up to
50 C. When the addition was complete, the mixture
was kept for 20 min at 30 C, and a solution of 0.82 g
of 2-chloro-3-nitropyridine in 5 ml of DMF was
added in portions at such a rate that the temperature
was within the range 35 40 C. When only traces of
2-chloro-3-nitropyridine remained in the mixture, it
was stirred for 30 min at 25 C, poured into 100 ml
of water, and acidified to pH 5 with concentrated
hydrochloric acid. A red viscous material separated
from the orange solution. It was filtered off, washed
with water, and dried. The aqueous solution was
extracted with 100 ml of chloroform to recover
a small amount of compound XIX. The extract was
dried over sodium sulfate and evaporated. The product
was recrystallized from 60 ml of ethanol to obtain
1.1 g (63%) of XXI as orange crystals with mp 156
167 C. Rf 0.7 (ethyl acetate, brown spot). IR spec-
temperature, poured into 100 ml of water, and
acidified to pH 4 with concentrated hydrochloric acid
(the mixture changed from violet to orange). The
product was extracted into 300 ml of chloroform. The
extract was dried over sodium sulfate and evaporated
to obtain a dark brown oil which was ground with
petroleum ether to give light yellow crystals. The
product was recrystallized from 50 ml of n-butanol.
Yield 1.7 g (82.5%), colorless needles, mp 107 C. IR
1
spectrum, , cm : 1350 and 1530 (NO2), 1745
(C O), 2980 (CH3). Found, %: C 58.9; H 4.1;
N 12.7. M 318 (in dioxane). C16H13N3O5. Calculated,
%: C 58.7; H 4.0; N 12.8. M 327.
2-(3-Nitro-2-pyridylmethyl)benzoxazole (V). To
a solution of 0.2 g of compound XX in 30 ml of
benzene we added 30 ml of a 2 N solution of sodium
hydroxide, and the mixture was refluxed for 2 h under
vigorous stirring. The aqueous phase gradually
changed from violet to brown. The progress of the
reaction was monitored by TLC on Silufol UV-254
plates using ethyl acetate as eluent: XX, Rf 0.6
(yellow spot); V, Rf 0.5. When initial compound XX
disappeared almost completely, the mixture was
cooled, the organic phase was separated, and the
aqueous phase was extracted with benzene (3 10 ml).
The benzene extracts were combined with the organic
phase, washed with water until neutral reaction, dried
over sodium sulfate, and evaporated. The residue was
a dark brown oil which was dissolved in 50 ml of
boiling petroleum ether (bp 70 100 C). The solution
was treated with charcoal and evaporated to 1/6 of
the initial volume. After cooling, an oily product
separated and was ground to obtain a light gray
powder. The precipitate was filtered off and recrystal-
lized from butanol (1:10). Yield 0.087 g (56%),
1
trum, , cm : 1355 and 1520 (NO2), 1660 (C O).
Found, %: C 56.1; H 3.8; N 12.4. M 340 (in dioxane).
C16H13N3O4S. Calculated, %: C 56.0; H 3.8; N 12.2.
M 343.
2-(3-Nitro-2-pyridylmethyl)benzothiazole (VI).
A mixture of 0.2 g of compound XXI and 10 ml of
18% hydrochloric acid was refluxed for 1 h. The
progress of the reaction was monitored by TLC
(Silufol UV-254 plates, ethyl acetate): XXI, Rf 0.7;
VI, Rf 0.5. When only traces of initial compound XXI
remained in the mixture, it was cooled, diluted with
equal volume of water, and neutralized with a solu-
tion of alkali. The dark brown oil was separated from
the aqueos phase and was dissolved in 50 ml of
petroleum ether (bp 70 100 C) on heating. The solu-
tion was treated with charcoal and evaporated to
1/5 of the initial volume. After cooling and grinding,
0.056 g of a yellow solid was isolated. It was dis-
solved in 3 ml of alcohol, and hot water was added to
the solution until it became turbid. After a long time,
a slightly yellowish solid precipitated. Yield 30%,
1
colorless plates, mp 70 C. IR spectrum, , cm :
1350 and 1530 (NO2). Found, %: C 61.0; H 3.6;
N 16.3. M 250 (dioxane). C13H9N3O3. Calculated, %:
C 61.2; H 3.6; N 16.5. M 255.
1,3-Dimethyl-2-(3-nitro-2-pyridylmethyl)benz-
imidazolium perchlorate (XXII). Methyl p-toluene-
sulfonate, 0.9 g, was added to 0.1 g of compound III.
At room temperature the mixture became liquid and
turned dark blue. It was kept for 40 min at 50 C.
1
mp 91 92 C. IR spectrum, , cm : 1360 and 1540
(NO2). Found, %: C 57.4; H 3.4; N 15.3. M 277
(in dioxane). C13H9N3O2. Calculated, %: C 57.6;
H 3.3; N 15.5. M 271.
Ethyl 2,3-dihydrobenzoxazol-2-ylidene(3-nitro- By the end of the reaction, the mixture solidified and
2-pyridyl)acetate (XX). To a suspension of 0.32 g
of sodium hydride in 2 ml of DMF we added in
portions at 40 C under argon 2.56 g of ethyl 2-benz-
oxazolylacetate (XVI). The dark brown mixture was
kept for 20 min at 30 C, and 1 g of 2-chloro-3-nitro-
pyridine was added in small portions. During the
addition the mixture spontaneously warmed up to
40 C and turned violet. When the addition was
complete, the mixture was stirred for 40 min at room
lost its color. It was ground with 10 ml of ether, and
the precipitate was filtered off, washed with ether
(3 5 ml) on a filter, and dissolved in 5 ml of ethanol.
The solution was poured into 10 ml of a saturated
aqueous solution of sodium perchlorate. On standing,
plates separated from the solution and were recrystal-
lized from 20 ml of 50% ethanol. Yield 0.07 g (49%),
colorless plates with mp 253 254 C. 1H NMR
spectrum (CF3COOH), , ppm: 3.73 s (CH3), 5.2 s
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

SYNTHESIS AND PHOTOCHROMIC PROPERTIES
(CH2), 7.4 s (4H, benzimidazole), 7.67 m ( -H, pyr- izdat, 1971, pp. 179 181.
1087
idine), 8.58 m ( -H, -H, pyridine). Found, %:
C 47.0; H 3.9; Cl 9.2; N 14.3. C15H15ClN4O6. Cal-
culated, %: C 47.1; H 3.9; Cl 9.3; N 14.6.
12. Subbotina, M.A., Zakhs, E.R., Ponyaev, A.I., and
El’tsov, A.V., Zh. Org. Khim., 1981, vol. 17, no. 2,
pp. 203 204.
13. Physical Methods in Heterocyclic Chemistry, Kat-
ritzky, A.R., Ed., New York: Academic, 1963.
Translated under the title Fizicheskie metody
v khimii geterotsiklicheskikh soedinenii, Moscow:
Khimiya, 1966, pp. 79, 109.
ACKNOWLEDGMENTS
This study was financially supported by the State
Budget in the framework of the Obschaya i tekhni-
cheskaya khimiya Section, Interinstitution Scientific
Technical Program Nauchnye issledovaniya vysshei
shkoly v oblasti khimii i khimicheskikh produktov of
the Ministry for Education of the Russian Federation.
14. Poesche, W.H., J. Chem. Soc. B, 1966, no. 6,
pp. 469 471.
15. Kiprianov, A.I., Tsvet i stroenie tsianinovykh krasi-
telei (Color and Structure of Cyanine Dyes), Kiev:
Naukova Dumka, 1979, pp. 248 250.
REFERENCES
16. Kiprianov, A.I. and Shaburovich, V.A., Zh. Obshch.
Khim., 1956, vol. 26, pp. 2891 2893.
1. Margerum, J.D. and Miller, L.J., Photochromism,
Brown, G.H., Ed., New York: Wiley, 1971, pp. 580
590, 628.
17. Hamer, F.M., The Cyan Dyes and Related Com-
pounds, New York: Interscience, 1964, pp. 30, 58.
2. Organic Photochromes, El’tsov, A.V., Ed., New
18. Kiprianov, A.I., Yakovleva, A.P., and Rozum, Yu.S.,
Zh. Obshch. Khim., 1952, vol. 22, no. 2, pp. 302
309.
York: Plenum, 1990, pp. 178 228.
3. El’tsov, A.V., Zakhs, E.R., Ponyaev, A.I., and
Frolova, T.I., Zh. Org. Khim., 1978, vol. 14, no. 8,
pp. 1760 1769.
19. Deichmeister, M.V., Levkoev, I.I., and Livshits, E.B.,
Zh. Obshch. Khim., 1953, vol. 23, no. 11, pp. 1529
1535.
4. El’tsov, A.V., Zakhs, E.R., and Ponyaev, A.I.,
Zh. Org. Khim., 1982, vol. 18, no. 7, pp. 1528 1533.
20. Snyder, L. and Buell, B., J. Chem. Eng. Data, 1966,
5. Zakhs, E.R., Ponyaev, A.I., Sergeev, A.M., Frolo-
va, T.I., and El’tsov, A.V., Zh. Org. Khim., 1979,
vol. 15, no. 10, pp. 2129 2136.
vol. 11, no. 4, pp. 547 552.
21. Ponyaev, A.I., Frolova, T.I., Zakhs, E.R., and
El’tsov, A.V., Zh. Org. Khim., 1977, vol. 13, no. 7,
pp. 1548 1553.
6. Zakhs, E.R., Subbotina, M.A., and El’tsov, A.V.,
Zh. Org. Khim., 1979, vol. 15, no. 1, pp. 200 206.
22. Burton, A.G., Halls, P.I., and Katritzky, A.R., Tetra-
hedron Lett., 1971, no. 24, pp. 2211 2212.
7. Scheibe, G. and Daltrozzo, E., Adv. Heterocycl.
Chem., 1966, vol. 7, pp. 153 181.
23. Berrie, A.H., Newbold, G.T., and Spring, F.S.,
8. Beilsteins Handbuch der organischen Chemie,
J. Chem. Soc., 1952, no. 20, pp. 2042 2046.
vol. 20 (EI), p. 82.
24. Barnikow, G., Kath, V., and Conrad, H., J. Prakt.
Chem., 1966, vol. 31, no. 2, pp. 262 265.
9. Katz, R.B. and Voyle, M., Synthesis, 1989, no. 4,
pp. 314 316.
25. Osegowski, W. and Krebs, D., J. Prakt. Chem.,
10. Willette, R.E., J. Chem. Soc., 1965, pp. 5874 5876.
1965, vol. 29, no. 1, pp. 18 25.
11. Gorbatov, E.I., Neft’ i gaz i ikh produkty (Oil and
26. Ushenko, I.K. and Usenko, N.M., Ukr. Khim. Zh.,
Gas and Products Therefrom), Moscow: Goskhim-
1950, vol. 16, no. 6, pp. 441 445.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001