Photochromic properties of ortho-methylnitrobenzothiazoles in Solution

Article abstract of DOI:10.1023/A:1013241516204

Isomeric benzothiazoles having the nitro and methyl groups ortho to each other are converted into tautomeric aci-nitro derivatives on irradiation in heptane solution; in water, the corresponding more deeply colored anions are formed. The efficiency of pho

Full text of DOI:10.1023/A:1013241516204

Russian Journal of General Chemistry, Vol. 71, No. 8, 2001, pp. 1286 1292. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 8, 2001,
pp. 1360 1367.
Original Russian Text Copyright
2001 by Matveev, Ponyaev, El’tsov.
Photochromic Properties of ortho-Methylnitrobenzothiazoles
in Solution
M. R. Matveev, A. I. Ponyaev, and A. V. El’tsov
St. Petersburg State Institute of Technology, St. Petersburg, Russia
Received May 4, 2000
Abstract Isomeric benzothiazoles having the nitro and methyl groups ortho to each other are converted
into tautomeric aci-nitro derivatives on irradiation in heptane solution; in water, the corresponding more
deeply colored anions are formed. The efficiency of photochromic transformations strongly depends on the
position of the nitro and methyl groups in the benzene ring of the benzothiazole molecule.
Hydrogen transfer from the medium to the nitro
group is a primary process occurring on photoexcita-
tion of nitro compounds. When a nitroaromatic com-
pound has a CHR1R2 substituent in the ortho position
with respect to the nitro group (structure A), this
process (as a way of dissipation of electron excitation
energy) may follow intramolecular path with forma-
tion of aci-nitro tautomer B [1]. Provided that the R1
substituent is an alkoxy, carboxy, amino, or analogous
mediate C which is capable of undergoing irreversible
ring opening to nitroso derivative D. The latter readily
decomposes (e.g., when R2 = H) to give nitroso alde-
hyde E and R3XH species. When R3 possesses labile
hydrogen atoms, the R3XH species can be protected
with the aid of an ortho-nitrobenzyl group which
can readily be removed (as nitroso derivative E) by
irradiation [2, 3]. Such photochemical processes are
used in prodrug design [4] and fine organic synthesis
[5], for generation of the active R3XH component in
photolithographic materials [6], etc.
group (R1 = XR3, where X = O or NH), tautomer B
can be stabilized in the form of 2,1-benzoxazole inter-
CR1R2
O
N
CHR1R2
CR1R2
O
H+
O
h
H+
F
S1
T1
NO2
N
OH
A
B
CR1R2
R1
O
OH
R2
OH
CR1R2
N
COR3
NO
O
1
2
R3XH
N OH
NO
E
D
C
aci-Nitro tautomers are colored species, so that the
first thermally reversible stage of hydrogen transfer
gives rise to photochromic properties of the system.
Study of this stage is of particular importance from
the viewpoint of increasing its efficiency in order to
enhance the light sensitivity of protective group and
the quantum yield for liberation of R3XH; as a result,
good photochromic materials could be created.
Published data on photolysis of aromatic compounds
having ortho-arranged CHR1R2 and NO2 groups
(A) deal mainly with the effect of the R1 and R2
Deceased.
1070-3632/01/7108-1286$25.00 2001 MAIK Nauka/Interperiodica

PHOTOCHROMIC PROPERTIES OF ortho-METHYLNITROBENZOTHIAZOLES
1287
groups, while the role of the structure of the parent
culations, only in molecule I the nitro group lies
aromatic compound remains unclear [1]. We pre- in the benzene ring plane; in molecules of the other
viously found that isomeric ortho-methylnitrobenz-
imidazoles are characterized by different parameters
of the overall phototautomerization process and
thermal conversion into the initial molecules [7]. For
example, no interaction between the methyl and nitro
groups was observed for 6-methyl-5-nitroquinoxaline
in aqueous alcohol at a flash duration of 5 10 5 s [8].
The present communication reports the results of our
study of the light-induced intramolecular hydrogen
transfer in the series of regioisomeric ortho-methyl-
nitrobenzothiazoles (there are no equivalent positions
in the benzene ring of the benzothiazole molecule).
compounds the nitro groups are turned through
an angle of 47 to 90 relative to the benzene ring
plane. All methylnitrobenzothiazoles show appreci-
able variation of the bond lengths and bond angles,
as compared to unsubstituted benzothiazole: the
C4 C5 bond length changes from 1.380 to 1.397
in the series I, III, II, V, IV, VI, VII, VIII; the
C5 C6 bond length changes from 1.406 to 1.417
in the series III, VII, II, IV, VI, I, V, VIII; and the
C6 C bond length changes from 1.394 to 1.404
in the series VII, IV, VIII, VI, III, II, V, I.
Despite the strong differences in the structure of the
ground state, solutions of all compounds in heptane
or aqueous phosphate buffer with pH 6.86 (containing
1% of EtOH) give rise to interaction between the
ortho-arranged methyl and nitro groups (Table 1)
under the action of light flash. Flash irradiation results
in coloration of solutions. The color disappears with
time; the half-conversion period ranges from 20 s to
1 2 s, depending on the medium and isomer structure.
Aqueous solutions are characterized by more intense
color as compared to heptane, and dinitro derivatives
give a more intense color than mononitro compounds
(Fig. 1), the substrate concentrations and flash
energies being equal. As shown in [10, 11], strongly
acidic aci-nitro tautomers derived from 2,4- and
2,6-dinitrotoluenes on flash photolysis in polar aceto-
nitrile and methanol undergo dissociation with forma-
tion of more deeply colored anions. Therefore, the
stronger color of aqueous solutions of compounds
I VIII can be attributed to formation of mesomeric
anions of aci-nitro tautomers [12] (structure F).
No dissociation occurs in heptane, and the detectable
products are the corresponding neutral aci-nitro forms
which absorb at shorter wavelengths.
New ortho-methylnitrobenzothiazoles II, III, and
V VIII were synthesized by nitration of the corre-
sponding methylbenzothiazoles. Compound IV was
obtained by cyclization of 2-bromo-4-methyl-5-nitro-
formanilide (XII) with Na2S, and known product I
was prepared by the procedure described in [9]. The
structure of the newly synthesized compounds was
proved by spectral data; the structure of dinitro deriva-
tives V and VIII was additionally proved by
independent synthesis from the corresponding mono-
nitro compounds: III, IV and VI, VII. The IR spectra
of all isomeric methylnitrobenzothiazoles contained
absorption bands typical of nitro groups. Compounds
1
I, III, and VII showed in the H NMR spectra AB
spin systems corresponding to protons located in the
ortho position with respect to each other.
CH3
CH3
1
S
7
O2N
O2N 6
S
5
2
N
S
N
4
3
NO2
II
I
NO2
H3C
O2N
H3C
S
The efficiency of intramolecular hydrogen transfer
in the series of compounds I VIII was estimated by
N
N
the integral optical absorption S =
D
of the
III
IV
photoinduced colored form in the visible region of
the spectrum, i.e., in the frequency range 25000
NO2
O2N
H3C
O2N
S
S
1
S
14200 cm (Fig. 1). For each isomer, the value of
S is proportinal to the oscillator strength, and the
proportionality factor is the quantum yield of forma-
tion of the corresponding aci-nitro compound.
Assuming that the oscillator strengths of aci-nitro
tautomers, as well as of the corresponding anions,
remain constant in the series I VIII and that aci-nitro
compounds in water dissociate completely, we have
H3C
N
N
N
V
VI
O2N
H3C
S
H3C
N
NO2
VIII
According to PM3 (RHF) quantum-chemical cal-
NO2
revealed parallelism in the variation of S and
for
VII
aci-nitro compounds in heptane and for their anions
in water in going from one benzothiazole derivative
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

1288
MATVEEV et al.
Table 1. Spectral parameters of the photoinduced forms of compounds I XI
Solvent Parameter
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
494
Water
max, nm 420
635
(<400)
410
495
480
490
<400
500
405
514
(<400)
0.0132
(>0.0164)
101
D
0.0256 0.011
(0.021)
86.7
0.092 0.037 0.19
0.0225 0.0055 0.035 0.0411
0.082
525
1
S, cm
130
<390
0.018
58
231
<390
167 1190
455 <435
97
453
7.6 254
400 420
93.0
Heptane
max, nm <390
D
S, cm
0.021
37
0.030 0.0167 0.125 0.012 0.0067 0.012
46 63 >264 30 9.4 18
1
to another. Here, the ratio of S for the anions and
acids changes from 2.5 to 4.5.
a much lesser extent: in going from the anion of 2-
nitrotoluene (IX) to 2,4-dinitrotoluene the anion of
increases by factors of 1.8 and 2.4, respectively [13].
This means that the thiazole ring strongly differentiates
ortho-nitromethyl fragments in photochromic proper-
ties, depending on their position in the molecule.
The integral optical absorption S of the aci-nitro
compounds under study strongly depends on the
arrangement of substituents in the benzene ring, while
the degree of coplanarity of the nitro group in the
nitro isomer is insignificant. Photoinduced coloration
of compound VII is weak, and acidifying effect of
the electron-acceptor thiazole ring in the excited state
turnes out to be negligible. In the series of mononitro-
benzothiazoles the ratio of S for the corresponding
anions changes by a factor of up to 30. 5,7-Dinitro
derivative V is characterized by the most intense color
of the anion and aci-nitro compound, despite large
deviations of the nitro group planes from the mole-
cular plane (by 60 and 90 , respectively) in the ground
state. The ratio of S for the anions of dinitro com-
pounds changes by a factor of up to 9. The ratio of the
S values for dinitro compound V, which is charac-
terized by the most efficient coloration, and mononitro
compounds VII and III showing, respectively, the
least and most efficient coloration is 160 and 5.2. On
the other hand, the oscillator strengths and hence the
intensities of photoinduced coloration for anions
(X) anion and then to 2,4,6-trinitrotoluene (XI) it
derived from aromatic aci-nitro compounds differ to
Hydrogen transfer in ortho-nitrobenzyl compounds,
as well as in nitrotoluenes, is believed to occur in the
3
*
(n ) state localized on the nitro group [3, 14]. The
results of our PM3/UHF calculations show that the
spin density in the lower triplet state of compound V
(which is the most efficient photochrome, judging by
the parameter S) is localized mainly on the 7-nitro
group (Fig. 2a). By contrast, the spin density in
compound VII which exhibits weak photochromic
properties is localized mainly on the sulfur atom of
the heteroring, while the 4-nitro group is characterized
by a negligible spin density (Fig. 2b). In the other
benzothiazole derivatives (compounds I IV, VI, and
VIII) the spin density is delocalized over the fused
ring system with more or less contribution of the nitro
groups (Fig. 2c). Therefore, the different photo-
chromic properties of compounds I VIII may be
attributed at least to differences in the fine structure
of lower triplet states whose participation in the
hydrogen transfer process may be characterized by
different quantum yields.
1
, cm
V
water
heptane
Obviously, polycyclic ortho-methylnitro derivatives
open the way to effective control of photochromic
properties and light sensitivity of ortho-nitrobenzyl
moieties.
1000
XI
VIII
III
V
IV
II
I
X
IX VI
VI
100
IV
III
EXPERIMENTAL
II
I
The elemental compositions (Table 2) were deter-
mined using a Hewlett Packard C,H,N-analyzer. The
melting points were measured with the aid of a Kofler
heating device coupled with a microscope; heating
VIII
10
VII
Fig. 1. Efficiency of photocoloration of ortho-methyl-
nitrobenzothiazoles I VIII and ortho-nitrotoluenes IX
XI in water and heptane.
1
rate 2.5 deg/min. The H NMR spectra of compounds
I VIII were recorded on a Bruker AM-500 spectrom-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

PHOTOCHROMIC PROPERTIES OF ortho-METHYLNITROBENZOTHIAZOLES
eter (500 MHz) (Table 3). The electronic absorption
1289
(a)
spectra were measured on a Specord M-40 spectro-
photometer using 1-cm quartz cells (Table 4). Sol-
vents were purified by standard procedures [15].
Photochromic properties of compounds I XI (c = 5
5
10
M, 20 1 C) in water (phosphate buffer,
pH 6.86, 1% of EtOH) and heptane were studied by
flash photolysis on a setup with a time resolution
of 2 ms [16]. Solutions were irradiated with an IFP-
5000 xenon lamp (full spectrum, 125 J) using quartz
cells (l = 20 cm). The solutions under study were not
deoxygenated. Preliminary experiments showed that
deaeration affects neither the rate of decoloration nor
the optical density of photoinduced forms. The optical
densities were averaged from the results of several
experiments (accuracy 5%). Thin-layer chromatog-
raphy was performed on Silufol UV-254 plates.
7-Methyl-6-nitrobenzothiazole (I). 6-Nitrobenzo-
thiazole, mp 175 175.5 C [17], 1.7 g, was dissolved
under argon in 40 ml of anhydrous THF, and 6.7 ml
of a 2.82 M solution of CH3MgCl in anhydrous THF
was added at 10 C. The mixture was stirred for
5 min at 10 C and for 5 min at 0 C, and a solution
of 1 g KMnO4 in 30 ml of 50% acetone was added
(dropwise) very slowly under vigorous stirring at 10
to 15 C. The mixture was kept for 0.5 h at room
temperature and filtered. The precipitate of MnO2
was extracted with hot acetone (3 10 ml), and the
extracts were combined with the filtrate. The solvent
was distilled off, and the product was extracted from
the residue into chloroform (2 10 ml); the extract
was dried over Na2SO4 and evaporated. The residue
was subjected to vacuum sublimation followed by
recrystallization from 10 ml of hexane. Yield 0.178 g
(9.7%), colorless crystals with mp 126 127 C [9].
Repeated crystallization from hexane did not increase
the melting point. Rf 0.66 (chloroform ether, 4:1).
(b)
(c)
7-Methyl-4,6-dinitrobenzothiazole (II). 7-Methyl-
6-nitrobenzothiazole, 0.038 g, was dissolved in 2 ml
of 92% H2SO4, 0.050 g of NaNO3 was added, and
the mixture was kept for 2 h at 120 C. It was then
poured onto 20 g of ice while stirring. The precip-
itate was filtered off and washed with water until
neutral washings. The yellowish crystals, 0.024 g,
were purified by vacuum sublimation. Yield 0.019 g
(41%), mp 134 135 C (subl.). Recrystallization from
hexane did not increase the melting point. Rf 0.56
(chloroform ether, 4:1).
6-Methyl-7-nitrobenzothiazole (III). 6-Methyl-
benzothiazole, mp 15 16 C [18], 0.9 g, was dissolved
in 5 ml H2SO4 (92.2%, chemically pure grade) while
stirring with no external cooling, and 3.5 ml of 93%
HNO3 was added dropwise over a period of 5 min
Fig. 2. Distribution of spin density at a distance of 1
from the molecular plane of compounds (a) V, (b) VII,
and (c) VIII in the lower triplet state.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

1290
MATVEEV et al.
Table 2. Elemental analyses of compounds I XIII
Found, %
Comp.
Calculated, %
H
Formula
no.
C
H
N
C
N
I
II
49.51
40.22
49.77
49.54
40.31
49.43
49.56
40.12
37.15
49.08
3.2
14.39
17.51
14.18
14.61
17.50
14.41
14.39
17.62
10.90
14.58
C8H6N2O2S
C8H5N3O4S
C8H6N2O2S
C8H6N2O2S
C8H5N3O4S
C8H6N2O2S
C8H6N2O2S
C8H5N3O4S
C8H7BrN2O3
C8H6N2O2S
49.48
40.17
49.48
49.48
40.17
49.48
49.48
40.17
37.07
49.48
3.09
2.09
3.09
3.09
2.09
3.09
3.09
2.09
2.70
3.09
14.43
17.57
14.43
14.43
17.57
14.43
14.43
17.57
10.81
14.43
2.10
3.08
3.30
2.07
3.11
3.19
2.05
2.81
3.31
III
IV
V
VI
VII
VIII
XII
XIII
Table 3. 1H NMR spectral parameters of compounds
I VIII in acetone-d6
and the mixture was left overnight. The large cream-
colored needles were filtered off. Yield 3.02 g (90%),
mp 172.5 173.5 C. Recrystallization from 85%
HCOOH did not increase the melting point. Rf 0.77
(2-propanol), 0.26 (ether heptane, 2:1), 0.1 (ether
heptane, 1:1).
Chemical shifts , ppm
Comp.
no.
H2
H4
H5
H7
CH13
Ia
II
9.599
9.857
9.431
9.475
9.669
9.575
9.445
9.754
8.215
8.159
8.909
7.746
2.862
3.058
2.901
2.735
2.879
2.755
2.547
2.652
6-Methyl-5-nitrobenzothiazole (IV). 2-Bromo-
4-methyl-5-nitroformanilide, 1 g, was dissolved in
33 ml of boiling ethanol, and 0.933 g of Na2S 9H2O
was added. The mixture was refluxed for 1 h and
poured into 200 ml of water, and the yellow precip-
itate of 2-bromo-4-methyl-5-nitroaniline, 0.391 g
(44.3%), was filtered off; it can be used for repeated
synthesis of 2-bromo-4-methyl-5-nitroformanilide
without additional purification. The red filtrate was
acidified with 0.1 N H2SO4 to pH 4 5, and the yellow
precipitate of crude 6-methyl-5-nitrobenzothiazole,
0.319 g (43%), was filtered off. The crude product
was dissolved in 65 ml of boiling heptane, and the hot
solution was filtered from red brown impurity and
cooled. After cooling, the precipitate was filtered off.
IIIa
IV
V
8.359
8.693
8.935
8.193
8.288
VI
VIIa
VIII
8.905
8.32
9.175
7.61b
a
The spin spin coupling constants for the ortho-arranged
protons in the aromatic ring of compounds I, III, and VII are
as follows: J
= 8.65, J
= 8.60, and J
= 8.35 Hz,
6, 7
4, 5
4, 5
b
6
respectively.
(H ).
under vigorous stirring at 20 C. The mixture was
heated for 5 min at 45 C (water bath) and was poured Yield 0.155 g (20%), mp 149 151.5 C (subl.).
(under vigorous stirring) onto 60 g of ice. The color-
less precipitate was filtered off, washed with a 5%
solution of NaOH and then with 50 ml water to pH 6,
and dried at 50 C. Yield of the crude product 0.902 g,
mp 129 130 C. It was recrystallized from 12 ml of
hot ethanol. Yield 0.749 g (64.2%), mp 131.5 C
(subl.). Recrystallization from hexane did not increase
the melting point. Rf 0.72 (toluene acetone, 1:1),
0.74 (ethyl acetate), 0.56 (chloroform ether, 4:1).
Recrystallization from hexane did not increase the
melting point. Rf 0.27 (hexane ether, 1:1), 0.64
(chloroform ether, 4:1).
5,7-Dinitro-6-methylbenzothiazole (V). a. To
2.6 g of 6-methylbenzothiazole we added while stir-
ring 11.1 ml of 92% H2SO4 without external cooling.
A colorless 6-methylbenzothiazolium sulfate dropped,
and dissolved on heating to 40 C. A 8-ml portion
of 97% HNO3 was added dropwise with stirring at
20 C, and the mixture was kept for 3 h at 120 C,
cooled to 15 C, and poured onto 100 g of ice under
vigorous stirring. The bright yellow precipitate was
filtered off and washed with water (3 7 ml), 4 ml of
2-Bromo-4-methyl-5-nitroformanilide (XII).
A solution of 3 g of 2-bromo-4-methyl-5-nitroaniline,
mp 121 C [19, 20], in 36 ml of 85% HCOOH was
refluxed for 3 h, 25 ml of HCOOH was distilled off,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

PHOTOCHROMIC PROPERTIES OF ortho-METHYLNITROBENZOTHIAZOLES
Table 4. UV and IR spectra of compounds I VIII
1291
Comp.
no.
1
max, nm (log )
215 (4.40), 286 (3.98)
Solvent
Water
IR spectrum (KBr), , cm
I
1510 s, 1350 s (NO2), 3100 m (C2H), 1600 m (C2=N)
217 (4.38), 275 (4.00), 319 sh (3.64) Heptane
207 (4.06), 276 (3.89), 318 sh (3.69) Water
II
1530 s, 1330 s (NO2), 1530 s, 1360 s (NO2), 3080 m (C2H),
1610 m (C2=N)
216 (4.30), 255 (4.20), 282 sh (4.01), Heptane
317 sh (3.66)
III
IV
V
208 (4.35), 241 (3.93), 323 (3.80)
209 (4.36), 245 (4.08), 305 (3.77)
208 (4.34), 248 (4.33), 298 (3.68)
Water
Heptane
Water
1520 s, 1320 s (NO2), 3135 w (C2H), 1615 m (C2=N)
1520 s, 1350 s (NO2), 3100 m (C2H), 1610 m (C2=N)
200 (4.38), 244 (4.42), 280 sh (3.73) Heptane
208 (4.28), 232 (4.19), 311 sh (3.74) Water
1530 s, 1330 s (NO2), 1560 s, 1360 s (NO2), 3090 m (C2H),
1610 m (C2=N)
231 (4.31), 296 sh (3.74)
217 (4.28), 287 (3.83)
222 (4.25), 278 (3.81), 320 sh (3.41) Heptane
Heptane
Water
VI
1510 s, 1320 s (NO2), 3120 m (C2H), 1620 m (C2=N)
1530 s, 1370 s (NO2), 3100 m (C2H), 1610 m (C2=N)
VII 212 (4.48), 254 (3.67), 294 (3.37)
213 (4.47), 252 (3.94), 295 (3.42)
VIII 214 (4.44), 273 (3.91)
Water
Heptane
Water
1540 s, 1360 s (NO2), 1560 s, 1370 s (NO2), 3110 m (C2H),
1620 m (C2=N)
215 (4.53), 270 sh (4.07)
Heptane
a 30% solution of Na2CO3 to pH 8, and water again
(2 10 ml) to pH 6 7. The precipitate turned beige.
Yield of the crude product 1.61 g. It was recrystallized
the mixture was stirred for 30 min at 12 C. The mix-
ture was filtered, and the filtrate was added with
stirring at the same temperature to a solution of 10.8 g
thrice from 95% ethanol (plates) and once from 80% of NaSCN, 1.16 g of Fe2(SO4)3 9H2O, and 0.273 g
ethanol (needles). Yield 0.64 g (15.3%), mp 127.5 C
(subl.). Rf 0.53 (heptane ether, 1:1), 0.71 (chloro-
form ether, 4:1).
of (NH4)2SO4 in 120 ml of water. After 14 h, the
precipitate was filtered off, washed with 350 ml of
water, a solution of 4.13 g of Na2CO3 in 40 ml of
water, and water again to pH 7, and dried at 50 C.
Yield of 3-nitro-4-thiocyanatotoluene 20 g (87%);
beige powder, mp 124.5 125 C (subl.) [22]. Rf 0.71
(2-propanol).
b. A 0.0125-g portion of 6-methyl-5-nitrobenzo-
thiazole was dissolved in 1 ml 92% H2SO4, 0.050 g
of NaNO3 was added, and the mixture was kept for
2.5 h at 120 C. The mixture was then transferred on
cooling into 4 ml of ice water, neutralized with
aqueous ammonia, and extracted with ether (3 2 ml).
The extract was dried over Na2SO4 and evaporated,
and the residue was recrystallized from a small
amount of 50% EtOH. Yield of V 0.005 g (32%).
No depression of the melting point was observed on
mixing samples obtained as described in a and b.
Their TLC and spectral parameters were also identical.
5-Methyl-4-nitrobenzothiazole
5-methyl-6-nitrobenzothiazole (VI).
(VII)
and
1.18-g
A
portion of 5-methylbenzothiazole, mp 79 C [23], was
dissolved in 8 ml of 92% H2SO4 without external
cooling. A mixture of 1 ml of 95% HNO3 and 1 ml of
92% H2SO4 was added at 20 25 C, and the resulting
mixture was kept for 15 min and slowly poured onto
50 g of ice under vigorous stirring. The crude product
separated as a light brown tarry material. The mixture
was neutralized with Na2CO3 until the tarry material
and yellow precipitate no longer separated. The brown
precipitate was filtered off, dried, and sublimed under
reduced pressure to obtain 0.738 g (48%) of light
yellow crystals. The product was recrystallized first
from 16 ml of 50% 2-propanol (yield 0.63 g) and then
from a mixture of 20 ml of hexane and 3 ml of
3-Nitro-4-thiocyanatotoluene (XIII). To a suspen-
sion of 18 g of 4-methyl-2-nitroaniline, mp 117 C
[21], in 60 ml of water we added with stirring 33 ml
92% H2SO4. The mixture strongly warmed up, and
a dark red solution was formed. It was cooled under
stirring to 10 C, a solution of 11.4 g NaNO2 in 21 ml
of water was added over a period of 20 min at such
a rate that the temperature did not exceed 15 C, and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

1292
MATVEEV et al.
chloroform. Yield of compound VII 0.42 g (27%);
colorless prisms, mp 110 111 C (subl.). Repeated
crystallization from hexane did not increase the
melting point. Rf 0.73 (chloroform ether, 4:1).
Sharma, D.K., J. Phys. Chem., 1991, vol. 95, no. 16,
pp. 6078 6081.
4. Reinhard, R. and Schmidt, B.F., J. Org. Chem.,
1998, vol. 63, no. 8, pp. 2434 2441.
5. Sternson, S.M. and Schreiber, S.L., Tetrahedron
Lett., 1998, vol. 39, no. 41, pp. 7451 7454.
The mother liquor obtained after crystallization
from 50% 2-propanol was evaporated under reduced
pressure to obtain 0.1 g of a mixture of nitration
products. It was dissolved in 1 ml of chloroform and
subjected to thin-layer chromatography on Silufol
UV-254 plates using chloroform ether (4:1) as
eluent. The upper zone, Rf 0.73, corresponded to
isomer VII, and the lower zone, Rf 0.65, was
extracted with hot chloroform (3 15 ml). Removal
of the solvent gave 0.03 g (30%) of yellowish crystals
of compound VI, mp 163 165 C (subl.). Recrystal-
lization from hexane did not increase the melting
point. Rf 0.65 (chloroform ether, 4:1).
6. Neenan, T.X., Houlihan, F.M., Reichmanis, E.,
Kometani, J.M., Bachman, B.J., and Thompson, L.F.,
Macromolecules, 1990, vol. 23, no. 1, pp. 145 150.
7. El’tsov, A.V., Dobrotina, E.D., Ponyaev, A.I., and
Shtyrkov, I.M., Zh. Obshch. Khim., 1995, vol. 65,
no. 7, pp. 1148 1160.
8. El’tsov, A.V., Selitrenikov, A.V., and Rti-
shchev, N.I., Zh. Obshch. Khim., 1997, vol. 67,
no. 2, pp. 304 313.
9. Bartoli, G., Bosco, M., and Baccolini, G., J. Org.
Chem., 1980, vol. 45, no. 3, pp. 522 524.
5-Methyl-4,6-dinitrobenzothiazole (VIII).
a. A 0.15-g portion of 5-methyl-4-nitrobenzothiazole
was dissolved in 5 ml of 92% H2SO4, 0.2 g of NaNO3
was added, and the mixture was kept for 2 h at 120 C.
It was then cooled and poured onto 30 g of ice while
stirring. The precipitate was filtered off, washed with
water until neutral washings, sublimed under reduced
pressure, and recrystallized from 2-propanol. Yield
of VIII 0.117 g (41%); colorless product, mp 147
148.5 C (subl.). Repeated crystallization from hexane
did not increase the melting point. Rf 0.71 (chloro-
form ether, 4:1).
10. McClelland, R.A. and Steenken, S., Can. J. Chem.,
1987, vol. 65, no. 2, pp. 353 356.
11. Atherton, S.J. and Craig, B.B., Chem. Phys. Lett.,
1986, vol. 127, no. 1, pp. 7 12.
12. El’tsov, A.V., Matvejev, M.R., Ponyaev, A.I., and
Styrkov, I.M., Book of Abstracts, XVIII Int. Conf. on
Photochemistry, Warsaw, 1997, 2P26.
13. Nurmukhametov, R. and Sergeev, A., Zh. Fiz. Khim.,
1990, vol. 64, no. 2, pp. 308 323.
14. Chattopadhyay, S.K. and Craig, B.B., J. Phys.
Chem., 1987, vol. 91, no. 2, pp. 323 326.
15. Gordon, A.J. and Ford, R.A., The Chemist’s Compa-
nion, New York: Wiley, 1972.
b. A 0.01-g portion of 5-methyl-6-nitrobenzothia-
zole (VI) was dissolved in 0.7 ml of 92% H2SO4,
0.03 g of NaNO3 was added, and the mixture was kept
for 2.5 h at 120 C. It was then transferred into 4 ml
of ice water (on cooling), neutralized with aqueous
ammonia, and extracted with ether (3 2 ml). The
extract was dried over Na2SO4 and evaporated, and
the residue was recrystallized from a small amount of
hexane. Yield 0.006 g (48.7%). No depression of the
melting point was observed on mixing samples ob-
tained as described in a and b. Their TLC and spectral
parameters were also identical.
16. 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.
17. Ward, E.R. and Peesche, W.H., J. Chem. Soc., 1961,
vol. 210, no. 7, pp. 2827 2831.
18. Blomquist, A.T. and Diuguid, L.I., J. Org. Chem.,
1947, vol. 12, no. 2, pp. 718 725.
19. Morgan, G.T. and Clayton, A., J. Chem. Soc., 1905,
vol. 87, pp. 944 951.
20. Claus, Ad. and Herbabny, J., Ann. Chem., 1891,
vol. 265, pp. 364 378.
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