Derivatives of sym-triazine. 3*. Synthesis and some conversions of monoazides of the triazine series

Article abstract of DOI:10.1023/B:COHC.0000048289.56361.4b

A convenient preparative route has been developed for the synthesis of 2-azido-4-R-6-R'-sym-triazines, which are promising synthons in organic synthesis. A series of 2-(1-triazolyl)-sym-triazine derivatives has been synthesized for the first time from the

Full text of DOI:10.1023/B:COHC.0000048289.56361.4b

Chemistry of Heterocyclic Compounds, Vol. 40, No. 9, 2004
DERIVATIVES OF sym-TRIAZINE.
3*. SYNTHESIS AND SOME CONVERSIONS
OF MONOAZIDES OF THE TRIAZINE SERIES
1
1
2
2
1
S. N. Mikhailychenko , A. A. Chesniuk , L. D. Koniushkin , S. I. Firgang , and V. N. Zaplishny
A convenient preparative route has been developed for the synthesis of 2-azido-4-R-6-R'-sym-triazines,
which are promising synthons in organic synthesis. A series of 2-(1-triazolyl)-sym-triazine derivatives
has been synthesized for the first time from the obtained azides and acetylacetone or acetoacetic ester.
Keywords: 2-azido-4-R-6-R'-sym-triazines, substituted 2-(1-triazolyl)-sym-triazines, (4-R-6-R'-sym-2-
triazinyl)trimethylammonium chlorides.
Organic azides are extremely reactive and convenient synthons for the synthesis of many heterocyclic
compounds promising for practical use [2]. However, azides of the sym-triazine series have not been described
up to the present time. The problem of the present work consists of the development of a synthetic route and the
study of certain properties of such compounds.
Our numerous attempts at the synthesis of 4,6-disubstituted 2-azido-sym-triazines by the traditional
method, the nucleophilic substitution of the chlorine atom in disubstituted monochloro-sym-triazines with the aid
of sodium and potassium azides by the known procedure [3], were not crowned with success, in spite of a
comprehensive variation of the conditions of carrying out the reaction. This is probably linked with the
extremely weak lability of the chlorine atom in the indicated compounds and the complexity of obtaining
diazonium salts from them.
Previously [1,4] we synthesized and reported the relatively stable and simultaneously highly reactive
(
4-R-6-R'-sym-2-triazinyl)trimethylammonium chlorides of the type of 1. We have discovered that salts 1a-k
react readily with sodium azide in aqueous solution even at room temperature. The desired previously
unavailable monoazides of the sym-triazine series 2a-k were formed smoothly in good yield (65-94%)
(
Scheme 1).
The synthesized azides 2a-k are extremely stable on extended storage, and are explosion-proof finely
crystalline white powders, readily soluble in aromatic hydrocarbons and the usual polar organic solvents, poorly
soluble in aliphatic hydrocarbons in the cold, and insoluble in water. Their homogeneity was verified by TLC
and their composition and structures were confirmed by results of elemental analysis, and by data of IR,
1
H NMR, and mass spectra (Tables 1, 2).
_
*
_
______
For Part 2 see [1].
_________________________________________________________________________________________
1
Kuban State Agricultural University, Krasnodar 350044, Russia; e-mail: vlad_zpl@mail.ru.
2
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1343-1350, September, 2004. Original article
submitted December 17, 2001; revision submitted July 10, 2002.
1
162
0009-3122/04/4009-1162©2004 Springer Science+Business Media, Inc.

Scheme 1
+
_
NMe Cl
N3
3
N
N
N
N
+
NMe3
+
NaCl
+
NaN3
R
N
R1
R
N
_
R1
_
1
a k
2a k
1
1
1
, 2 a–d, k R = I, e–g R = II, h R = OMe, i, j R = III, a R = I, b, g, h R = OMe,
1
1
1
1
1
c, e R = OEt, d, f R = II, i R = OMe, j R = III, k R = NPh
2
I
N
O
,
II
N
,
III
N
Me
Intense absorption bands were present in the IR spectra of azides 2 characteristic of the stretching
vibrations of the azide group at 2100-2110, and of the conjugated C=N bond of the triazine ring at
-
1
1
1
505-1620 cm . In the H NMR spectra (Table 2) the resonance signals for the protons of all the substituents of
+
the heterocycle were also sharply differentiated, however the singlet signal for the protons of the N Me group,
3
characteristic of the initial salts 1, was absent [4].
TABLE 1. Characteristics of Compounds 2-4
Found, %
Calculated, %
H
Mol.
ion,
m/z*
Com-
pound
Empirical
formula
——————
Yield,
%
mp, °С
C
3
N
5
1
2
4
6
7
8
1
85-185.5
2
2
а
C
11
H
16
N
8
O
2
45.49
5.68
5.52
4.83
4.67
5.38
5.21
6.39
6.25
6.23
6.07
7.22
6.99
5.68
5.57
3.45
3.32
5.87
5.69
7.80
7.65
4.98
4.84
6.15
5.92
5.49
5.44
5.83
5.74
6.67
6.50
6.51
6.38
38.48
38.39
41.43
41.33
39.12
39.03
38.67
38.59
39.40
39.34
38.96
38.88
41.78
41.68
46.28
46.14
37.10
36.96
35.58
35.42
30.06
29.93
29.32
29.23
30.83
30.83
29.55
29.42
30.21
30.09
29.68
29.59
292
237
251
290
249
288
235
182
265
316
374
374
319
333
372
331
370
68
94
84
72
90
65
91
69
75
75
80
79
85
76
86
85
75
4
5.20
b
C
C
C
C
8
9
H
11
N
7
7
O
2
40.77
0.50
116-17
4
2
c
H
13
N
O
2
43.19
3.02
104-105
113-114
74-75
4
2
d
12
10
H
18
15
N
8
7
O
O
49.83
9.63
4
2
e
H
N
48.29
8.18
4
2
f
C
13
H
20
N
8
54.33
4.14
96-97
5
2
2
g
C
C
9
H
13
N
7
O
46.23
5.95
85-86
4
h
5
H
6
N
6
O
2
33.20
2.97
82-83
3
2
2
i
C
10
H
15
N
7
O
2
45.42
5.27
92-93
4
j
C
15
H
24
N
8
57.09
6.94
61.13
0.95
116-117
161-162
203-204
198-199
192-193
178-179
140-141
184-185
5
2k
3а
3b
C
19
H
18
N
8
O
6
C
C
C
C
C
16
H
22
H
17
H
19
H
24
H
21
N
8
N
7
N
7
N
8
N
7
O
3
O
3
O
3
O
2
O
2
51.49
1.32
5
13
14
17
15
49.04
8.89
4
3
c
50.58
0.44
54.99
4.82
5
3
d
5
3
e
50.48
0.36
5
3
f
C
18
H
26
N
8
O
58.46
8.35
7.16
7.07
30.35
30.25
5
1
163

TABLE 1 (continued)
1
2
3
4
5
6
7
8
3
g
C
C
C
C
C
C
C
C
C
C
C
C
14
10
15
17
14
15
18
16
19
15
11
25
H
19
H
12
H
21
H
24
H
19
H
21
H
26
H
23
H
28
H
21
H
14
H
26
N
7
N
6
N
7
N
8
N
7
N
7
N
8
N
7
N
8
N
7
N
6
N
8
O
2
O
3
O
2
O
4
O
4
O
4
O
3
O
3
O
2
O
3
O
4
O
3
53.16
6.20
6.17
4.71
4.58
6.49
6.38
6.13
5.98
5.63
5.48
5.99
5.83
6.67
6.51
6.29
6.41
6.91
7.05
6.25
6.09
4.87
4.79
5.27
5.39
31.02
31.03
31.95
31.81
29.74
29.59
27.85
27.71
28.16
28.07
27.08
26.98
27.95
27.85
27.20
27.13
28.07
27.98
28.32
28.23
28.64
28.56
23.14
23.03
133-134
175-176
132-133
188-189
155-156
110-111
198-199
119-120
168-169
114-115
147-148
212-213
317
264
331
404
349
363
402
361
400
347
294
486
91
89
87
70
85
81
83
85
71
82
87
73
5
2.98
3
h
45.57
5.45
4
3
i
54.47
4.36
5
4
a
b
50.59
0.48
5
4
48.29
8.13
4
4
c
49.76
9.58
4
4
d
53.81
3.71
5
4
e
53.01
2.17
5
4
f
56.81
6.98
5
4
4
g
51.98
1.86
5
h
44.98
4.89
4
4
i
61.58
1.71
6
_
*
______
Mass spectral data may be obtained from the authors.
It is known that azidoazolopyridazines [5] and monoazidofurazans [6] form biheterocyclic systems with
,3-dicarbonyl compounds. Since substances including similar systems display high biological activity [6], it
1
seemed of interest to clarify the possibility of obtaining still unreported compounds with a single bond linking
the sym-triazine and triazole rings.
For this purpose we have studied the interaction of the synthesized azides 2a-k with such widely
available dicarbonyl compounds as acetylacetone and acetoacetic ester. As a result, the corresponding products
3
a-i and 4a-i were obtained in high yield (71-91%) (Scheme 2).
Scheme 2
Me
EtO
O
O
N
N
O
O
O
O
N
N
Me
Me
N
N
N
Me
Me; NEt3
Me
OEt; NEt3
2
a–k
N
N
N
N
R
R1
R
N
R1
4
a–i
3a–i
1
1
3
a–d, 4a–d, i R = I, 3e–g, 4e–g R = II, 3i R = OMe; 3,4 a R = I, b R = OMe,
1
1
1
c,e R = OEt, d,f R = II, 3i R = III
I
N
O
,
II
N
,
III
N
Me
1
164

TABLE 2. Spectral Characteristics of Compounds 2-4
-
1
IR spectrum, ν, cm
Com-
pound
1
N
С=О
3
or
N=N–, С=N–
and С=С-conj.
Н NMR spectrum, δ, ppm (SSCC, J, Hz)
1
2
3
4
2
2
2
a
b
c
2110
2105
2100
1570, 1550
1565, 1505
1560, 1505
3.55-3.75 (16H, m, 4NCH
3.60-3.80 (8H, m, 2NCH , 2OCH
1.30 (3H, t, J = 7.85, СН in OEt); 3.60-3.80 (8H, m,
NCH , 2OCH ); 4.35 (2H, q, J = 7.85, СН in OEt)
1.47-1.70 (6H, m, 3CH ); 3.55-3.75 (12H, m, 4NCH
1.33 (3H, t, J = 7.4, CH in OEt); 1.50-1.73 (6H, m, 3CH
.70-3.80 (4H, m, 2NCH ); 4.34 (2H, q, J = 7.4, СН in OEt)
1.40-1.62 (12H, m, 6CH ); 3.55-3.70 (8H, m, 4NCH
2
, 4OCH
2
)
2
2
); 3.85 (3H, s, OCH
3
)
3
2
2
2
2
2
2
d
e
2110
2105
1550, 1530
1500, 1580
2
2
, 2OCH
);
2
)
3
2
3
2
2
2
2
f
2100
2110
1620, 1550,
2
2
)
1
505
g
1510, 1570
1.53-1.70 (6H, m, 3CH
.86 (3H, s, OCH
3.85 (6H, s, 2OCH
1.19 (3H, d, J = 7.4, CHCH
2 2
); 3.70-3.80 (4H, m, 2NCH );
3
3
)
2
2
h
i
2100
2100
1580, 1540
1560, 1500
3
)
3
); 1.32-1.80 (6H, m, 3CH
.92-3.03 (1H, m, NCH); 3.87 (3H, s, OCH );
.44-4.99 (2H, m, NCH
2
);
2
4
3
2
)
2
j
2110
1575, 1530
1.19 (6H, d, J = 7.35, 2CHCH
.97-3.04 (2H, m, 2NCH); 4.48-4.98 (4H, m, 2NCH
3.25-3.75 (8H, m, 2OCH , 2NCH ); 7.20-7.40 (10H, m, 2C
); 2.62 (3H, s, COCH
.60-3.85 (16Н, m, 4ОСН , 4NCH
.63 (3H, s, COCH ); 2.85 (3H, s, 5'-CH
.65-3.90 (8H, m, 2OCH -, 2NCH
3 2
); 1.32-1.80 (12H, m, 6CH );
2
2
)
2
3
k
a
2100
1680
1550, 1520
1530, 1560
2
2
6
H )
5
2
3
2
3
.80 (3H, s, 5'-CH
3
3
3
);
);
2
2
)
3
3
b
c
1685
1705
1540, 1565,
3
1
595
1590, 1550,
505
2
2
-); 4.00 (3Н, s, ОСН
3
)
1.36 (3H, t, J = 7.0, CH
3
in OEt); 2.63 (3H, s, COCH
); 3.65-3.85 (8H, m, 2OCH , 2NCH
.43 (2H, q, J = 7.0, CH in OEt)
1.55-1.72 (6H, m, 3CH ), 2.65 (3H, s, COCH
3
);
2
);
1
2.82 (3H, s, 5'-CH
3
2
4
2
3
3
d
e
1670
1665
1590, 1535,
510
1590, 1550,
530
2
3
),
1
2.80 (3H, s, 5′-CH ), 3.63-3.84 (12H, m, 4NCH , 2OCH )
3
2
2
1.39 (3H, t, J = 7.0, CH
3
in OEt); 1.57-1.75 (6H, m, 3CH
);
); 4.44 (2H, q, J = 7.0, CH
); 2.63 (3H, s, COCH );
); 3.70-3.82 (8H, m, 4NCH
1.62-1.80 (6H, m, 3CH ); 2.65 (3H, s, COCH );
2.87 (3H, s, 5'-CH ); 3.85-3.95 (4H, m, 2NCH );
.03 (3Н, s, ОСН
2.65 (3H, s, COCH
1.28 (3H, d, J = 7.3, CHCH
1.62-1.83 (6H, m, 3CH ); 2.65 (3H, s, COCH
); 3.87 (3Н, s, ОСН );
2
);
1
2.64 (3H, s, COCH
.80-3.88 (4H, m, 2NCH
1.45-1.70 (12H, m, 6CH
2.80 (3H, s, 5'-CH
3 3
); 2.85 (3H, s, 5'-CH
3
2
2
in OEt)
3
3
f
1680
1685
1620, 1590,
535
1590, 1560,
535
2
3
1
3
2
)
g
2
3
1
3
2
4
3
)
3
3
h
i
1690
1680
1580, 1550
1595, 1550,
3
); 2.70 (3H, s, 5'-CH
); 1.37-1.48 (1H, m, NCH);
);
3 3
); 4.08 (6H, s, 2ОСН )
3
1
535
2
3
2
4
.85 (3H, s, 5'-CH
.55-5.11 (2H, m, NCH
3
3
2
)
4
4
4
4
a
b
c
1710
1715
1705
1710
1550, 1510
1600, 1560,
1.36 (3H, t, J = 6.6, CH
3
in СООEt), 2.81 (3Н, s, 5′-CH
3
);
3
4
.61-3.86 (16H, m, 4OCH
.39 (2H, q, J = 6.6, CH
2
, 4NCH );
2
2
in COOEt)
1.34 (3H, t, J = 7.4, CH
3.65-3.87 (8H, m, 2OCH
.37 (2Н, q, J = 7.4, ОСН
1.30-1.40 (6H, m, CH in OЕt and COOEt); 2.85 (3H, s, 5'-CH
3.65-3.83 (8H, m, 2OCH , 2NCH ); 4.35 (2H, q, J = 7.5,
CH in COOEt); 4.45 (2H, q, J = 7.35, CH in OЕt)
1.36 (3H, t, J = 7.4, CH in COOЕt); 1.53-1.73 (6H, m, 3CH
); 3.65-3.85 (12H, m, 2OCH , 4NCH );
.36 (2H, q, J = 7.4, CH in COOЕt)
3
in COOEt); 2.85 (3Н, s, 5'-CH
3
);
1
505
2
2 3
, 2NCH ); 3.97 (3Н, s, ОСН
);
4
2
in COOEt)
1590, 1550,
505
3
3
);
1
2
2
2
2
d
1600, 1550
3
2
);
2
4
.83 (3H, s, 5'-CH
3
2
2
2
1
165

TABLE 2 (continued)
1
2
3
4
4
4
4
e
1700
1600, 1575,
1.37 (6H, m, CH
2.85 (3H, s, 5'-CH
J = 7.0, CH in COOEt); 4.45 (2H, q, J = 7.0, CH
1.34 (3H, t, J = 7.35, CH in COOЕt); 1.50-1.70 (12H, m, 6CH
); 3.70-3.85 (8H, m, 4NCH );
.35 (2H, q, J = 7.35, CH in COOЕt)
in COOЕt); 1.57-1.75 (6H, m, 3CH
); 3.80-3.90 (4H, m, 2NCH );
); 4.36 (2H, q, J = 7.4, CH in COOЕt)
1.39 (3H, t, J = 7.4, CH in COOЕt); 2.56 (3H, s, 5'-CH );
.07 (6H, s, 2OСН ); 4.37 (2H, q, J = 7.4, CH in COOEt)
1.32 (3H, t, J = 7.35, CH in COOЕt); 2.42 (3H, s, 5'-CH );
3.55-3.82 (8H, m, 2OCH , 2NCH ); 4.32 (2H, q, J = 7.3,
CH in COOЕt); 7.25-7.45 (10H, m, 2C
3
in OЕt and COOEt); 1.57-1.75 (6H, m, 3CH
); 3.80-3.88 (4H, m, 2NCH ); 4.38 (2H, q,
in OЕt)
2
);
1
505
3
2
2
2
f
1705
1708
1600, 1545
3
2
);
2
4
.80 (3H, s, 5'-CH
3
2
2
g
1605, 1580,
1.37 (3H, t, J = 7.4, CH
2.85 (3H, s, 5'-CH
.98 (3Н, s, ОСН
3
2
);
1
510
3
2
3
3
2
4
4
h
i
1715
1720
1595, 1535
1580, 1540,
3
3
4
3
2
3
3
1
510
2
2
2
6 5
H )
It turned out that the reaction rate depended significantly on the type of dicarbonyl compound used. On
interacting monoazides 2 with the more reactive acetylacetone the time for the synthesis at room temperature
varied from 0.5-14 h. To obtain the same desired products 4a-i in the reaction with acetoacetic ester required far
more time (in some cases up to 72 h) at 30-40°C.
As was to be expected the structure of the initial azide influences the reaction rate. The most reactive
turned out to be azide 2h, containing the small volume OMe substituent in positions 4 and 6 of the triazine ring.
The least reactive were azides 2j,k having residues of the sterically hindering diphenylamine and
2
-methylpiperidine at the indicated positions.
The synthesized triazolyltriazines 3a-i, 4a-i were white, finely crystalline powders, readily soluble in
polar organic solvents and aromatic hydrocarbons, poorly soluble in petroleum ether in the cold, and insoluble in
water. Their melting points always somewhat exceeded those of the corresponding initial azides 2. The
homogeneity of the obtained compounds was confirmed by TLC, and their composition and structure by the
1
results of elemental analysis, and data of IR, H NMR, and mass spectra.
The absorption band for the stretching vibrations of the azide group at 2100-2110 was absent from the
IR spectra of triazolyltriazines 3a-i, 4a-i, but there were intense absorption bands characteristic of the C=O
-
1
group at 1665-1720, and also for conjugated C=C and C=N bonds at 1505-1630 cm (Table 2).
1
In all the H NMR spectra of compounds 3a-i, 4a-i (Table 2) signals were present for the protons of the
substituents in positions 4 and 6 of the triazine ring, a singlet for the protons of the 5'-Me group of the triazole
ring at 2.70-2.87 for compounds 4a-g, and at 2.42-2.56 ppm for compounds 4h,i (the displacement of the signal
towards high field is probably linked with the effect of the substituents in positions 4 and 6 of the triazine ring).
The singlet signal for the protons of the 4'-COMe group of the triazole ring of compounds 3a-i was observed at
2
.62-2.65 ppm. There were characteristic signals in the spectra of compounds 4a-i for the 4'-COOEt group, a
triplet at 1.30-1.42 (CH ) and a quartet at 4.28-4.48 ppm (CH ). The structures of the synthesized products 2-4
3
2
were also confirmed by data of mass spectroscopy.
A simple and reliable procedure is proposed for the synthesis of the difficultly available monoazides of
sym-triazines. An addition-cyclization reaction of these azides with dicarbonyl compounds has been studied and
the dependence of reaction time on reactant structure has been shown. A series of substituted
2
-(1-triazolyl)triazines has been obtained for the first time. These are promising as biologically active
compounds.
1
166

EXPERIMENTAL
The IR spectra were recorded for suspensions of samples in nujol with a Specord IR-75 spectrometer.
1
The H NMR spectra were taken for solutions of samples in DMSO-d on a Bruker WM-500 (500 MHz)
6
radiospectrometer. The mass spectra were recorded on a Finnigan MAT INCOS 50 instrument (energy of
ionizing electrons was 70 eV). Elemental analysis of the synthesized compounds was carried out with a Carlo-
Erba model 1106 analyzer. A check on the progress of reactions and the purity of the compounds obtained was
effected by TLC on Silufol UV-254 plates in acetone–hexane, 1:1.
The initial 2-chloro-sym-triazines and salts 1a-k were obtained by the known procedures of [4, 8].
Triethylamine was dried over KOH directly before use, then subjected to fractional distillation. The main
fraction was distilled once more over metallic sodium. DMF was purified and dried by the known procedure of
[9].
2
-Azido-4,6-dimorpholino-sym-triazine (2a). A solution of sodium azide (30 mmol) in water (10 ml)
was slowly added dropwise with stirring at 5-10°C to a solution of compound 1a (15 mmol) in water (20 ml) .
The reaction mixture was then stirred at room temperature for 3 h. The precipitated solid was filtered off, washed
with water until chloride ion was absent from the washings, and dried to constant weight. Azide 2a was obtained
having category A purity (content of main substance >99%), and did not require further purification.
Monoazides 2b-k were obtained analogously.
6
-(4-Acetyl-5-methyl-1,2,3-triazol-1-yl)-2,4-dimorpholino-sym-triazine (3a).
A
mixture of
acetylacetone (68 mmol) and triethylamine (68 mmol) was added dropwise with stirring at room temperature to a
solution of azide 2a (34 mmol) in dry DMF (10 ml). The reaction mixture was stirred at the same temperature for
0
.5 h and then poured into cold water (100 ml) as a fine stream with continuous stirring. The precipitated solid of
the desired product was filtered off, washed repeatedly with water, and dried. Triazolyltriazine 3a was obtained
with category A degree of purity.
Compounds 3b-i were obtained analogously.
6
-(4-Ethoxycarbonyl-5-methyl-1,2,3-triazol-1-yl)-2,4-dimorpholino-sym-triazine (4a). A mixture of
acetoacetic ester (68 mmol) and triethylamine (68 mmol) was added dropwise with stirring at room temperature
to a solution of azide 2a (34 mmol) in dry DMF (10 ml). The reaction mixture was stirred at 30-40°C for 48 h
and after treatment as described above for compound 3a triazolyltriazine 4a was obtained with category A
degree of purity.
Compounds 4b-i were obtained analogously.
REFERENCES
1
2
3
4
5
6
.
.
.
.
.
.
S. N. Mikhailychenko, A. A. Chesniuk, V. E. Zavodnik, S. I. Firgang, L. D. Koniushkin, and
V. N. Zaplishny, Khim. Geterotsikl. Soedin., 326 (2002).
D. H. R. Barton and W. D. Ollis (editors), Comprehensive Organic Chemistry, Vol. 3, Pergamon,
Oxford (1979).
Weygand-Hilgetag, Experimental Methods in Organic Chemistry [Russian translation], Khimiya,
Moscow (1962).
A. A. Chesniuk, S. N. Mikhailychenko, V. S. Zavodnov, and V. N. Zaplishny, Khim. Geterotsikl.
Soedin., 197 (2002).
A. Gorup, M. Kvacic, B. Kranjc-Skraba, B. Mihelcic, S. Simonic, B. Stanovnic, and M. Tisler,
Tetrahedron, 30, 2251 (1974).
L. V. Batog, V. Yu. Rozhkov, Yu. V. Khronov, N. V. Pyatakova, O. G. Busygina, I. S. Severina, and
N. N. Makhova, Russian Patent 2158265; Byull. Izobret., No. 30, 187 (2000).
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7
8
9
.
.
.
E. B. Nikolaenkova, V. P. Krivopalov, and O. P. Shkurko, in: Nitrogen Heterocycles and Alkaloids
in Russian], Vol. 2, Iridium Press, Moscow (2001), p. 300.
G. M. Pogosyan, V. A. Pankratov, V. N. Zaplishny, and S. G. Matsoyan, in: Polytriazines [in Russian],
Izd. Akad. Nauk ArmSSR, Erevan (1987), p. 615.
A. J. Gordon and R. A. Ford, Chemist’s Companion, Handbook of Practical Data, Techniques and
References, Wiley-Interscience, New York (1972), 560 pp.
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