A rational method of synthesis and chemical properties of 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole

Article abstract of DOI:10.1007/s10593-017-2121-x

[Figure not available: see fulltext.] A practical and scalable scheme for the synthesis of 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole was developed, starting from 4-aminofurazan-3-carboxylic acid amidoxime. New methods were proposed for the synthesis of 1

Full text of DOI:10.1007/s10593-017-2121-x

DOI 10.1007/s10593-017-2121-x
Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
A rational method of synthesis and chemical properties
of 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole
Andrei I. Stepanov1*, Vladimir S. Sannikov1, Dmitry V. Dashko1,
Alexey G. Roslyakov1, Alexander A. Astrat'ev1, Elena V. Stepanova2
1 Special Engineering and Design Bureau "Technolog", 33-A Sovetsky Ave., Saint Petersburg 192076, Russia;
е-mail: stepanoffai@yandex.ru
2 Russian State Hydrometeorological University,
98 Malookhtinsky Ave., Saint Petersburg 195196, Russia;
е-mail: stepanoffev@yandex.ru
Translated from Khimiya Geterotsiklicheskikh Soedinenii,
2017, 53(6/7), 746–759
Submitted December 30, 2016
Accepted after revision March 16, 2017
N3
N3
NH2
NH2
NH2
NO2
N OH
NH2
N N
N
N
N
N
N
N
N
N
N
N N
N
N
N
N
N
N
N
N
N
N
N
N
N
O N
O N
O N
O N
O N
O N
OMe
OMe
OH
OH
OMe
A practical and scalable scheme for the synthesis of 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole was developed, starting from
4-aminofurazan-3-carboxylic acid amidoxime. New methods were proposed for the synthesis of 1-hydroxy-5-(4-nitrofurazan-3-yl)-
tetrazole and 5-(4-azidofurazan-3-yl)-1-hydroxytetrazole.
Keywords: aminofurazan, azidofurazan, 1-hydroxytetrazole, nitrofurazan, 1,2,5-oxadiazole.
The chemistry of energetic compounds has shown a
trend toward the inclusion of heteroaromatic polynitrogen
motifs in their structures.1 Heterocyclic systems of this type
are characterized by positive enthalpies of formation;
during their explosive decomposition energy is liberated
not only through oxidation of carbon atoms, but also by
energetically favorable rearrangement of chemically
bonded nitrogen atoms of heterocycle into highly stable
nitrogen molecules.2–9 Another feature of nitrogen
heterocycles is the possibility of improving the oxygen
balance of energetic compound derived from them by
forming N-oxides.10 The introduction of an N-oxide group
usually increases the density of energetic compounds, as
well as in many cases helps to improve their stability.11
The values given in Figure 1 for enthalpies of formation
(in gas phase) of some azoles12 illustrate the benefits from
introduction of tetrazole and furazan (1,2,5-oxadiazole) rings
in the structures of energetic compounds. These types of
applications have substantially contributed to the progress
in the chemistry of both tetrazoles13–16 and furazans.17,18
The concept of combining furazan and hydroxytetrazole
rings in the structures of energetic compounds12,19–23 has
been used for the synthesis of compounds with structures
shown in Figure 2. For practical purposes, the preferred
compounds were salts of compounds 1–5 with nitrogen-
containing bases (ammonia, hydroxylamine, hydrazine,
guanidine, and others). Some of the obtained salts were
characterized by high thermal stability, decreased sensiti-
vity to mechanical stimuli, and calculated detonation
velocity similar to RDX.
During the current study, we developed a rational
method for the synthesis and studied the reactivity of
5-(4-aminofurazan-3-yl)-1-hydroxytetrazole (1).
It should be noted that prior to the publications on
energetic properties of dihydroxylammonium 5,5'-bistetra-
zole-1,1'-diolate (TKX-50, Fig. 3)24–26 the derivatives of
1-hydroxytetrazole were not thoroughly investigated.27–29
For example, in the series of oxadiazole derivatives,
besides compound 1 studied in this work,30,31 also the
syntheses of compounds combining the structural features
of 1-hydroxytetrazole heterocyclic system with 1,2,4-
oxadiazole,32 1,3,4-oxadiazole,33 as well as furazan and
furoxan rings were considered.21,22
Figure 1. The enthalpies of formation for azoles in gas phase.
0009-3122/17/53(6/7)-0746©2017 Springer Science+Business Media New York
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Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
Scheme 1
Scheme 2
Figure 2. The currently known energetic derivatives of 1-hydroxy-
5-(4-R-furazan-3-yl)tetrazole.
Figure 3. Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate
(TKX-50).
The general method for the synthesis of 5-R-substituted
1-hydroxytetrazole derivatives is based on intramolecular
cyclization of carboxazidoximes 7.30,34,35 The required
azidoximes 7 were obtained by nucleophilic substitution of
halide in the appropriate halooximes 6 with an azide group
via reaction with sodium azide.30,31 Anhydrous hydrogen
chloride solution in diethyl ether was used to induce the
isomerization of the stable (Z)-form of oxime 7 to the labile
(Е)-form 8, which underwent a spontaneous intramolecular
cyclization reaction of azide and oxime groups that
produced a 1-hydroxytetrazole ring (Scheme 1).
hydrochloric acid.40 Our experiments with hundreds of
grams of compound 9 showed that performing the reaction
in concentrated hydrochloric acid allowed to reduce the
solvent ratio to 3. In this case, the yield of crude chlor-
oxime 6а was 65–70% (mp 195–198°С, Scheme 2). The
crude product after filtration and washing with water
contained 20–25% of moisture and could be used in the
next step of synthesis without drying. The moisture content
in the product was determined as loss of mass upon drying
in thermostat at 90–100°С.
The step yielding tetrazole 1 involves the use of a
compound that is potentially unsafe in anhydrous state –
azidoxime 7а, which was obtained in 76% yield by a
reaction of chloroxime 6а with sodium azide in a mixture
of ethanol and water. The obtained azidoxime 7а contained
24% of moisture and was used without additional drying.
The cyclization of compound 7a was performed
The synthesis of hydroxytetrazole
1
was first
accomplished by Andrianov and coworkers in 1992.31 In
subsequent studies, compound 1 was obtained according to
an analogous procedure (for example, in reports20,34). The
synthesis was laborious, unsafe, and thus unsuitable for
further scale-up. For this reason, we started our study from
improving the known scheme for the synthesis of
compound 1, including the preparation of chloroxime 6а,
reaction with sodium azide (Scheme 2), and isomerization
of azidoxime 7а.
The preparation of chloroxime 6а was based on the
diazotation of amidoxime 9 in dilute hydrochloric acid with
NaNO2 solution at 0–5°С temperature.36–38 The yield of
compound 6а was 53–59%, the solvent ratio (mass ratio of
solvents used in the reaction and the starting material) was
in the range from 17 to 24. It has been reported39 that the
solvent ratio can be decreased to 10.8, while the yield of
crude product (mp 192–194°С) reached 76%. The
possibility of increasing the yield of chloroxime 6а to 80%
has also been described, by further minimizing the use of
according to
a previously published procedure by
saturating its suspension in diethyl ether with anhydrous
hydrogen chloride.31,40
We have shown that the cyclization of azidoxime 7а can
be successfully achieved in a 1:1 (v/v) mixture of acetic
acid and concentrated hydrochloric acid at 90–100°С over
5–8 h. The yield of tetrazole 1 after recrystallization from
water reached approximately 60%. The treatment of filtrates
and mother liquors with aqueous 25% solution of ammonia
to рН 8–9 allowed to improve the total yield of tetrazole 1
to 82–85% by precipitating its residual amount as ammonium
salt 1а that was sparingly soluble in water (Scheme 3).
The total yield of hydroxytetrazole 1 reached 40–45%,
as calculated from the amidoxime 9, and was in line with
747

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
the previously reported values.20,31,34 The proposed scheme
Scheme 4
for the synthesis of hydroxytetrazole 1 substantially
improved its synthetic availability for extended exploration
of its reactivity.
Scheme 3
HCl
NH2
NH2
N N
N N
AcOH
NH4OH
N
N
7a
N
N
N
N
90–100°C
5–8 h
H2O
60–70°C
then rt
O N
O N
+
OH
O– NH4
1
1a
60%
Compound 1 had two reactive sites – the hydroxy group
of tetrazole ring (А) and the amino group at the furazan
ring (В) (Fig. 4). We examined some reactions of
hydroxytetrazole 1 that involved these reactive sites.
The reactions of compound 1 and methoxy derivative
10 involving the amino group. N-Acylation and
N-nitration, as well as the oxidation to nitro or azo groups
represent typical reactions for an amino group linked to a
furazan ring.17,18,43
It has been reported earlier30 that acylation of compound 1
with acetic anhydride without the addition of a catalyst
occurs at the hydroxy group of tetrazole ring, leading to the
formation of compound 11. We have found that the
acylation of tetrazole 1, as well as its О-methyl derivative
10 with acetic anhydride in the presence of catalytic
amounts of sulfuric acid or sodium acetate led to the
N-acylation products 12 and 13 in 95% yields (Scheme 5).
Figure 4. Two reactive sites in the molecule of 5-(4-aminofurazan-
3-yl)-1-hydroxytetrazole (1).
Reactions of compound 1 involving the hydroxy
group. According to the results of potentiometric titration,
compound 1 exhibited the properties of a strong ОН acid
(рKа 2.45) and produced stable salts, the properties of
which have been reported previously.19,20 The ammonium
salt 1а is poorly soluble in water, which can be used for the
isolation and purification of tetrazole 1.
Scheme 5
1
(From )
Ac2O
H2SO4
NHAc
NH2
N N
N N
Ac2O
N
1, 10
N
N
N
O N
N
N
20°C
40–50°C
1–2 min
95%
O N
OR
OAc
11
12
(R = H)
13 (R = Me)
The study of alkylation reactions involving tetrazole 1
showed that the preparation of 1-alkoxy derivatives is only
possible by using such potent alkylating agent as dimethyl
sulfate in DMF–K2CO3 system (Scheme 4). Performing the
reaction with less active alkylating agents (ClCH2CONH2,
MeI, CH2I2, PhCH2Cl) in DMF–K2CO3 or MeONa–MeOH
systems did not produce any alkylation products. It should
be noted that the ambident character of 1-hydroxytetrazole
anion41 provides possibilities for alkylation reaction
occurring either at the oxygen atom of hydroxy group or
the nitrogen atoms of tetrazole ring. According to an earlier
work,42 it is important to take into account that alkylation
of amino group at the furazan ring is also possible under
the conditions of phase-transfer catalysis. NMR spectra of
the product obtained by alkylation of compound 1 with
dimethyl sulfate in DMF–K2CO3 system unequivocally
pointed to the exclusive formation of О-alkylation product
10 in 85% yield.
The nitration of tetrazole 1 with 100% HNO3 was used
for the preparation of nitramine 212 (stable only in the form
of a solution), isolated as salts 2а with cations of silver,
ammonium, hydroxylammonium, hydrazonium, and
guanidinium derivatives (Scheme 6).
Scheme 6
The investigation of chemical properties of compound
10 showed low stability of the methoxy group toward
hydrolysis, as it could be cleaved both in acidic and basic
media. Thus, refluxing a solution of compound 10 in acetic
acid in the presence of hydrochloric acid was accompanied
by the regeneration of a hydroxy group. The reaction of
compound 10 with aqueous alkali and hydrazine proceeded
analogously (Scheme 4).
For the nitration of compound 10 we used a system of
HNO3–Ac2O. Nitramine 14 precipitated when the nitration
mixture was poured onto ice, but decomposed during an
attempted recrystallization from organic solvents and was
isolated as ammonium salt 14а (Scheme 7).
748

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
Scheme 7
We also noted differences in the chemical properties of
compounds 3 and 17 when attempting to obtain their salts.
Thus, the treatment of compound 3 in diethyl ether solution
with hydrazine or hydroxylamine was accompanied by
vigorous evolution of gas and destruction of the starting
compound molecule, while acetonitrile solution of
dimethoxy derivative 17 reacted with hydrazine differently,
resulting in the reduction of azo group and formation of the
symmetrical 1,2-di(furazanyl)hydrazine 18 in 71% yield
(Scheme 10).
According to literature data, the oxidation of amino-
furazans to nitrofurazans can be performed with two-
electron oxidants based on peroxide oxygen.44 The oxidation
of compounds 1 and 10 to the respective nitro derivatives was
successfully performed by us in a 30% H2O2 – 96% H2SO4
system under the conditions that were previously used for
the synthesis of 4-(5-methyl-1,2,4-oxadiazol-3-yl)-3-
nitrofurazan45 (Scheme 8). The isolation of 1-hydroxy-5-
(4-nitrofurazan-3-yl)tetrazole (15) from the reaction
mixture was quite difficult due to its high solubility in the
oxidizing mixture and water, as well as its low affinity for
organic solvents. The procedure for isolation of compound
15 included a partial neutralization of the reaction medium
with crystalline sodium orthophosphate, followed by
multiple extractions of the obtained solution with ethyl
acetate. On the other hand, the procedure for the isolation
of 1-methoxy-5-(4-nitrofurazan-3-yl)tetrazole (16) from the
reaction mixture was simple and effective. Product 16
precipitated as a heavy oil upon diluting the reaction
mixture with water, and could be separated from the
aqueous phase by extraction with dichloromethane. The
yield of compound 16 reached 90%.
Scheme 10
O
N
N
N
N
N
N
N
N2H4·H2O
MeO
17
N
HN NH
N
MeCN
OMe
N
20–25°C, 30 min
N
N
O
71%
18
The availability of nitro derivative 16 enabled us to use
it as a precursor for the synthesis of a series of 1-hydroxy-
5-(4-R-furazan-3-yl)tetrazole derivatives. For example, the
nitro group of compound 16 underwent substitution
reactions with N- and O-nucleophiles, analogously to other
nitrofurazans49,50 (Scheme 11).
Scheme 11
OH
OMe
N N
N N
N
N
N
O N
N
O N
N
N
OMe
OMe
19
20
Scheme 8
1. KOH, MeOH 2. H2O, HCl
MeOH
NaHCO3
20–25°C, 5 h
20–25°C, 5 h
71%
82%
16
MeCN
N2H4·H2O
MeCN
NaN3
N3
15–20°C, 1 h
40–45°C, 5 h
The oxidation of aminofurazans 1 and 10 with
potassium permanganate in acidic medium was
accompanied by oxidative dimerization of amino groups to
an azo group (Scheme 9), which is characteristic for
furazans.43,46–48 The synthesis of 3,3'-bis(1-hydroxytetrazol-
5-yl)-4,4'-azofurazan (3) has been described before.12
Compound 3 is stable only as a solution in diethyl ether
and was isolated as diammonium salt. On the other hand,
performing an analogous oxidation reaction with
methoxytetrazole 10 showed that the obtained oxidation
product – 3,3'-bis(1-methoxytetrazol-5-yl)-4,4'-azofura-
zan (17) – can be isolated in crystalline form.
76%
75%
MeCN
RR1NH 30°C
1 h
H2N
N
NH
N
N
N N
N
N
N
O N
N
N
NRR1
N N
O N
O– N2H5
+
OMe
23
21
N
N
N
O N
OMe
22a–d
22 a R = H, R1 = Me (67%); b R = R1 = Me (52%)
c R = H, R1 = t-Bu (60%); d R+R1 = C2H4OC2H4 (71%)
Scheme 9
Thus, the substitution of a nitro group with methoxy
group was achieved under mild conditions (NaHCO3,
MeOH, 20–25°С) (Scheme 11, compound 19). The use of
stronger alkaline reagents (K2CO3 or KOH in MeOH)
resulted in the formation of hydroxyfurazan 20. The
reaction of compound 16 with NaN3 in MeCN at 40–45°С
led to the formation of azidofurazan 21. A smooth
substitution of nitro group was achieved in reaction with
749

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
strongly basic amines, leading to the formation of
can be removed by refluxing solutions of methoxy-
tetrazoles 16, 19, 21, 22d for 2–5 h in a 1:1 (v/v) mixture
of AcOH and concd HCl.
aminofurazans 22a–d. Compound 16 in acetonitrile
solution reacted with hydrazine hydrate not only at the
nitro group of furazan ring, but also underwent the
hydrolysis of methoxy group and formed the respective
hydrazinium salt of hydrazinofurazan 23. Salt 23 was
weakly soluble in acetonitrile and precipitated from the
reaction mixture. The high aqueous solubility and low
affinity for organic solvents did not allow us to isolate free
5-(4-hydrazinofurazan-3-yl)-1-hydroxytetrazole from salt
23. The presence of a primary hydrazino group in
compound 23 was confirmed by condensation reactions
with carbonyl and β-dicarbonyl compounds (formation of
the respective hydrazones 24, 25 and pyrazoles 26, 27,
Scheme 12). Since compound 23 is a hydrazinium salt, the
side reactions of carbonyl compounds with hydrazinium
cation also produced the respective N-unsubstituted
hydrazones and pyrazole derivatives. These impurities
could be separated by exploiting their better solubility in
organic solvents during the recrystallization of the obtained
products. Pyrazoles 26 and 27 were isolated as ammonium
salts.
Scheme 14
The oily nitrofurazan 15 obtained from hydrolysis of the
methoxy derivative 16 contained 15–20% of impurities
according to HPLC analysis and NMR spectral data. The
crystalline ammonium salt of this compound was obtained
in 65% yield by exchange reaction with ammonium acetate
in acetic acid. The treatment of nitrofurazan 15 with
aqueous ammonia or ammonium bicarbonate was
accompanied by substitution of nitro group with amino
group and was not applicable for the preparation of its
ammonium salt. The azido derivative 31 was a strong ОН
acid (рKа 2.07) and could be isolated in pure form or
converted into the stable ammonium salt 31а.
Scheme 12
The structures of the synthesized compounds were
proved by the methods of IR and 1Н, 13С NMR
spectroscopy, data of elemental analysis, and high-
resolution mass spectrometry. The assignment of carbon
atom signals in the furazan ring was performed while
taking into account the literature data.51 Azido derivative 31
was also characterized by 15N NMR spectrum (Fig. 5). The
assignment of 15N NMR signals was based on comparison
with the data12,20,52 for analogous structures: 422.0 (N-5);
388.1 (N-3); 365.5 (N-6); 360.0 (N-2); 331.0 (N-4); 269.7
(N-1); 238.3 (N-8); 235.2 (N-9); 80.0 (N-7) (atom
numbering according to Fig. 6).
The nitration of pyrazoles 26 and 27 in a system of concd
HNO3 (d 1.5) – concd H2SO4 (d 1.84) at 5–10°С proceeded
quite unusually. The nitration of pyrazole ring under these
conditions was accompanied by the destruction of
1-hydroxytetrazole ring, leading to the formation of a
nitrile group (Scheme 13).
Several of the obtained compounds could not be
characterized by mass spectrometric methods of analysis
due to their decomposition during the introduction into the
mass spectrometer input device.
Nitro and azido derivatives 15a, 16, 21, 31, which are of
interest as potential high-energy compounds, were
characterized by methods of thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC).
According to TGA and DSC data, the ammonium salt of
5-(4-nitrofurazan-3-yl)-1-hydroxytetrazole (15а) started
losing mass at 160°С, while the maximum of decom-
position exotherm was at 175°С. 1-Methoxy-5-(4-nitro-
furazan-3-yl)tetrazole (16) existed in liquid form and
noticeably evaporated already at 120–130°С, while the
evaporation of sample was complete at 175°С without
decomposition. 5-(4-Azidofurazan-3-yl)-1-methoxytetra-
zole (21) melted at 84°С, the evaporation process was
observed above 100°С, with two exotherms of
decomposition at 183 and 197°С. 5-(4-Azidofurazan-3-yl)-
Scheme 13
R
NC
O2N
R
HNO3, H2SO4
N
O
26, 27
N
5–10°C
then rt, 5 h
N
N
28 R = H (65%)
29 R = Me (68%)
The aforementioned hydrolytic susceptibility of
methoxy group in the tetrazole ring allowed us to consider
it as a protecting group during the synthesis of the
respective hydroxytetrazoles. The potential of this
approach is illustrated in Scheme 14. The methoxy group
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Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
Figure 5. 15N NMR spectrum of compound 31 (DMSO-d6, the chemical shift values of nitrogen atoms
are reported relative to NH3).
Table 1. Physicochemical properties of compounds 31 and 31а
1-hydroxytetrazole monohydrate (31) showed loss of mass
above 55°С (loss of solvate water), with the exotherm of
decomposition observed at 187–188°С. The ammonium salt
of 5-(4-azidofurazan-3-yl)-1-hydroxytetrazole (31а) under-
went vigorous sublimation at 163°С and decomposed
explosively at 179°С. The impact sensitivity of compounds
31 and 31а was at the level of pentaerythritol tetranitrate
(PETN), while the friction sensitivity was considerably
lower (Table 1).
The crystal structures of 5-(4-azidofurazan-3-yl)-1-hydr-
oxytetrazole (31) and its ammonium salt 31а were
unequivocally confirmed by X-ray structural analysis.
Suitable monocrystals were grown by slow evaporation of
solvent from aqueous solutions of the respective
compounds. The molecular structures of compounds 31
and 31а are shown in Figures 6 and 7.
Beginning
Sensitivity
Com- of vigorous Oxygen balance,
to impact*
%
to friction**
pound decomposi-
%
kg·cm–2
tion, °С
187–188
–36.9
–45.3
–10.1
20
20
4
4
3600 200
2200 200
1500
31
31a
179
PETN
140–145
20–36
* Drop hammer apparatus K-44-II (apparatus No. 1, weight of 2 kg at
25 cm height), frequency of exposions.53
** Drop hammer apparatus K-44-III (lower limit).54
Both molecules are practically planar: the torsion angles
N(1)–C(1)–C(2)–N(5) are equal to –3.25° (compound 31)
and –0.75° (compound 31a). The bond lengths and valence
angles in the furazan ring with localized C=N double bonds
are in a good agreement with the data obtained for
azidofurazan derivatives55–58 and have values typical for the
respective atoms.59 Compound 31 contains a solvated water
molecule, which forms a crystal lattice with the main
molecule via hydrogen bonding, forming a packed structure
in the (1 0 0) plane. The calculated monocrystal density for
compound 31 is equal to 1.760 g·cm–3 (100 K). The calcu-
lated monocrystal density of compound 31а is 1.757 g·cm–3
(100 K).
Figure 6. The molecular structure of compound 31 with atoms
represented by thermal vibration ellipsoids of 50% probability.
Thus, we have developed a safe method for the
preparation of 5-(4-aminofurazan-3-yl)-1-hydroxytetrazole on
the scale of several hundreds of grams. Based on the
reactivity study of 5-(4-aminofurazan-3-yl)-1-hydroxy-
tetrazole and its 1-О-methyl derivative, new routes have
been proposed for expanding the library of energetic
furazanоtetrazole derivatives. The synthesis of a series of
previously unknown 5-furazanyl-substituted 1-hydroxy-
tetrazole derivatives has been accomplished. The proposed
schemes for the synthesis of 1-hydroxy-5-(4-nitrofurazan-
3-yl)tetrazole and 5-(4-azidofurazan-3-yl)-1-hydroxy-
tetrazole allow us to consider the obtained compounds not
only from the theoretical point of view, but also as physical
samples for further practical investigation of their energetic
properties.
Figure 7. The molecular structure of compound 31а with atoms
represented by thermal vibration ellipsoids of 50% probability.
751

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
Experimental
the total amount of 80 g, 1.23 mol). After the end of
exothermic effect, the mixture was stirred for 5 h at 30°С
and diluted with water (1 l). The precipitate was filtered
off, washed with water, and pressed on filter. Azide 7а was
obtained in 159 g (76%) yield with 24% of moisture and
was used without additional drying in the synthesis of
compound 1. An analytically pure sample of compound 7а
was obtained by recrystallization of wet product from 1:2
mixture of AcOH–H2O, mp 176–177°С (mp 170–171°С30,
mp 177–178°С31). IR spectrum, ν, cm–1: 3451, 3339, 2155,
2096, 1630, 1593, 1538, 1419, 1356, 1252, 1029, 959, 910,
858, 692, 561, 439. (IR spectrum (thin film), ν, cm–1: 3461
and 3322 (NH2), 3248 (OH), 2169 (N3), 986 (furazan).31)
1H NMR spectrum, δ, ppm: 12.57 (1H, s, OH); 6.24 (2H, s,
NH2). (1H NMR spectrum (acetone-d6), δ, ppm: 11.30 (1H,
s, OH); 5.75 (2H, s, NH2).30) 13C NMR spectrum, δ, ppm:
154.9; 140.1; 135.7. Found, m/z: 192.0247 [M+Na]+.
С3H3N7NaO2. Calculated, m/z: 192.0240.
IR spectra were recorded on an FSM-1201 FT-IR
spectrometer in KBr pellets. 1Н, 13С, and 15N NMR spectra
were acquired on a Bruker DRX-400 spectrometer (400,
100, and 40 MHz, respectively) in DMSO-d6. The chemical
shifts of Н and 13С nuclei were determined relative to the
1
solvent signal (2.51 and 40.0 ppm, respectively), the
chemical shifts of 15N nuclei were determined relative to
liquid NH3. Mass spectra were recorded on a Finnigan
MAT Incos 50 instrument (EI ionization, 70 eV). High-
resolution mass spectra were recorded on a Bruker
micrOTOF II instrument using electrospray ionization.
Elemental analysis was performed on a PerkinElmer 2400
elemental analyzer. Calorimetric analyses were performed
in aluminum crucibles on a Netzsch TG 209 F1 instrument
under argon flow (100 ml/min) at the heating rate of 5 K/min.
Melting points were determined in a capillary. The
dissociation constants for compounds 1 and 31 were
determined in aqueous solutions by potentiometric titration
method with 0.1 N NaOH solution. The reaction progress
and purity of the obtained compounds were controlled by
HPLC method on a Shimadzu 20 chromatograph with a
diode matrix detector. The analytical conditions:
Phenomenex Luna 5 µm С18(2) 250 × 4.6 mm column,
MeOH–H2O–CF3COOH (74.95:24.95:0.10) mobile phase,
thermostat and detector temperature set at 40°С. The UV
wavelengths of 209, 230, and 254 nm were used for detection.
The synthesis of compound 9 was performed according
to a published procedure.60
5-(4-Aminofurazan-3-yl)-1-hydroxytetrazole (1) and
its ammonium salt 1а. Wet azidoxime 7a (150 g, 0.71 mol,
20% water content) and concd HCl (200 ml) were added to
stirred AcOH (200 ml). The mixture was heated to 90–100°С.
The reaction mixture was stirred at this temperature for 5–
8 h until complete dissolution of the starting material. The
obtained solution was cooled to room temperature, the
precipitated product was filtered off, the filtrate was
evaporated at reduced pressure to one half of the initial
volume. The precipitate that formed was filtered off,
combined with the first precipitate, and recrystallized from
water. Yield 72 g (60%), agglomerates of fine, irregularly
shaped crystals, mp 182–183°С (mp 182–183°C31).
IR spectrum, ν, cm–1: 3459, 3340, 2548, 1642, 1612, 1538,
1471, 1434, 1393, 1262, 1107, 1049, 989, 907, 860, 714,
448. (IR spectrum (thin film), ν, cm–1: 3463, 3325 (NH2),
3250 (NH), 1670 (C=N), 999 (furazan).31) 1H NMR
spectrum, δ, ppm: 6.94 (3H, br. s, OH, NH2). (1H NMR
spectrum (DMSO-d6), δ, ppm: 7.36 (2H, s, NH2); 7.06 (1H,
s, OH).20 1H NMR spectrum (acetone-d6), δ, ppm: 6.58
(2H, s, NH2); 11.20 (1H, s, OH).30) 13C NMR spectrum,
δ, ppm: 156.0 (C-4'); 138.0 (C-3'); 134.6 (C-5).* (13C NMR
spectrum (DMSO-d6), δ, ppm: 156.1; 138.0; 134.7.20) Mass
spectrum, m/z (Irel, %): 169 [M]+ (1), 111 [M–N2–NO]+
(44), 53 [HNCCN]+ (40), 42 [CNO]+ (15), 30 [NO]+ (100).
An additional amount of tetrazole 1 was isolated as
ammonium salt 1а that was sparingly soluble in water by
combining the filtrates, evaporating to dryness at reduced
pressure, dissolving the residue in hot water (100 ml, 60–
70°C), and adjusting to рН 8 by adding aqueous 25%
ammonia solution. The mixture was cooled to room
temperature, the precipitate that formed was filtered off and
recrystallized from water. The ammonium salt 1а was
obtained as white, fibrous solid (30–35 g, 16–19% yield,
mp 266–267°С (decomp.) (mp 257°C (decomp., DSC)20).
IR spectrum, ν, cm–1: 3455, 3339, 3157, 3058, 2994, 2920,
1861, 1634, 1603, 1478, 1461, 1430, 1397, 1302, 1239,
4-Amino-N-hydroxyfurazan-3-carboximidoyl chloride
(6а). Amidoxime 9 (350 g, 2.45 mol) was added with
vigorous stirring to 38% HCl (1 l, 452 g of HCl,
12.40 mol), while maintaining the temperature of mixture
at or below 20°С by external cooling with water bath. The
reaction mixture was then cooled to 5–10°С and treated at
this temperature by dropwise addition of saturated aqueous
NaNO2 solution (169 g, 2.45 mol) over 8 h. After
completing the addition of NaNO2, the reaction mixture
was maintained at 15–20°С for 2 h, the precipitate that
formed was filtered off and washed on filter with cold
water (250–300 ml). The yield of crude compound 6a with
20–25% moisture was 259–279 g (65–70% yield calculated
for dry product), mp 195–198°С. This product was used
without additional purification for the preparation of azide
7а. Analytically pure sample of compound 6а was obtained
by recrystallization from 1:1 mixture of AcOH–H2O, mp 204–
205°С (decomp.) (mp 203–206°C (decomp., Et2O –
petroleum ether),30 mp 197–212°C (decomp., DSC)61).
IR spectrum, ν, cm–1: 3460; 3338; 3250; 1640; 1628 1532;
1435; 1332; 1301; 1040; 1010; 945; 915; 868; 739; 718;
438. 13C NMR spectrum, δ, ppm: 154.0; 141.9; 126.5.
4-Amino-N-hydroxyfurazan-3-carboximidoylazide
(7а). Compound 6a from the previous step (crude mass
195 g including 20% moisture content, dry mass 162.5 g,
1 mol of anhydrous product) was added to EtOH (300 ml)
with vigorous stirring, followed by the addition of H2O
(100 ml). The obtained suspenion was maintained at 20–
30°С by external cooling with water bath and treated by
adding 10–20-g portions of sodium azide over 30 min (for
1
1148, 1059, 984, 896, 867, 769, 584, 568, 446. H NMR
* The furazan ring carbon atoms in 13С NMR spectra are denoted as C-3'
and C-4', the tetrazole ring carbon atom – as С-5.
752

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
spectrum, δ, ppm: 7.21 (4H, br. s, NH4+); 7.08 (2H, s, NH2).
addition of hydrazine hydrate (0.30 g, 6.0 mmol), stirred at
room temperature for 10 min, the solvent was evaporated at
reduced pressure. The residue was recrystallized from
МеОН, giving fine, colorless needle-shaped crystals,
mp 213–214°С. Yield 1.05 g (89%).
(1H NMR spectrum (DMSO-d6), δ, ppm: 7.10 (6H, s, NH2,
+
NH4 ).20) 13C NMR spectrum, δ, ppm: 156.2 (C-4'); 137.7
(C-3'); 135.0 (C-5). (13C NMR spectrum (DMSO-d6),
δ, ppm: 156.3; 137.9; 135.0.20).
5-(4-Aminofurazan-3-yl)-1-methoxytetrazole
(10).
5-[4-(N-Acetylamino)furazan-3-yl]-1-hydroxytetrazole
(12). Tetrazole 1 (1.00 g, 5.9 mmol) was added at room
temperature to stirred Ac2O (5 ml), then the reaction
mixture was treated with concd H2SO4 (0.01 g). After the
exothermic reaction was complete (1–2 min), the reaction
mixture was cooled to room temperature, the precipitate
that formed was filtered off, washed with water, and
recrystallized from МеОН. Yield 1.18 g (95%), white
irregular plates, mp 99–100°С. IR spectrum, ν, cm–1: 3486,
3324, 3287, 1847, 1729, 1690, 1558, 1535, 1359, 1275,
1262, 1239, 1121, 1106, 996, 908, 804, 754, 596, 583.
1H NMR spectrum, δ, ppm: 11.65 (1H, s, NH); 4.53 (1H,
Tetrazole 1 (169 g, 1.0 mol) and anhydrous K2CO3 (207 g,
1.5 mol) were added with vigorous stirring to DMF (300 ml).
The reaction mixture was stirred at room temperature until
the evolution of СО2 ceased (approximately 30 min),
cooled to 10°С, and treated at this temperature by dropwise
addition of Me2SO4 (176 g, 1.4 mol). After the addition of
Me2SO4 was complete, the stirring at room temperature was
continued for 8 h. The mixture was then diluted with ice water
(1 l), the precipitate that formed was filtered off, washed with
cold water (2×500 ml) and recrystallized from МеОН. Yield
155 g (85%), white plates, mp 140–141°С. IR spectrum,
ν, cm–1: 3453, 3340, 2956, 2920, 2853, 1642, 1615, 1468,
1451, 1427, 1269, 1094, 1034, 987, 951, 867, 559, 480, 419.
1H NMR spectrum, δ, ppm: 6.65 (2H, s, NH2); 4.40 (3H, s,
OCH3). 13C NMR spectrum, δ, ppm: 156.1 (C-4'); 138.9
(C-3'); 134.2 (C-5); 69.8 (OCH3). Mass spectrum, m/z
(Irel, %): 184 [M+1]+ (2), 183 [M]+ (22), 153 [M–NO]+ (18),
126 [M–NHCNO]+ (99), 53 [HNCCN]+ (24), 43 [HN3]+
(100), 30 [NO]+ (64), 15 [CH3]+ (21). Found, m/z: 184.0578
[M+H]+, 206.0401 [M+Na]+. С4H6N7O2, С4H5N7NaO2.
Calculated, m/z: 184.0578, 206.0397.
13
br. s, OH); 2.09 (3H, s, CH3). C NMR spectrum, δ, ppm:
169.4 (C=O); 150.5 (C-4'); 138.4 (C-3'); 138.0 (C-5); 23.2
(CH3). Found, m/z: 212.0531 [M+H]+, 234.0348 [M+Na]+.
С5H6N7O3, С5H5N7NaO3. Calculated, m/z: 212.0527,
234.0346.
5-[4-(N-Acetylamino)furazan-3-yl]-1-methoxytetrazole
(13). Methoxytetrazole 10 (1.80 g, 0.01 mol) was added at
room temperature to stirred Ac2O (5 ml), then the reaction
mixture was treated with concd H2SO4 (0.01 g). After the
exothermic reaction was complete (1–2 min), the reaction
mixture was cooled to room temperature and the precipitate
that formed was filtered off, washed with water, and
recrystallized from МеОН. Yield 2.10 g (95%), colorless
rhombic crystals, mp 109–110°С. IR spectrum, ν, cm–1:
3450, 3327, 3249, 3025, 2955, 1733, 1561, 1531, 1445,
1354, 1259, 1223, 1113, 1056, 994, 939, 909, 721, 678, 650,
594, 585, 548, 408, 401. 1H NMR spectrum, δ, ppm: 11.50 (1H,
s, NH); 4.37 (3H, s, OCH3); 2.11 (3H, s, COCH3). 13C NMR
spectrum, δ, ppm: 169.9 (C=O); 150.6 (C-4'); 138.8 (C-3');
137.7 (C-5); 70.2 (OCH3); 23.1 (CH3). Found, m/z: 248.0494
[M+Na]+. С6H7N7NaO3. Calculated, m/z: 248.0502.
Hydrolysis of 5-(4-aminofurazan-3-yl)-1-methoxy-
tetrazole (10). Method I (hydrolysis in acidic medium).
Compound 10 (2.00 g, 11 mmol) was dissolved in AcOH
(5 ml), concd HCl (5 ml) was added and the mixture was
refluxed for 3 h, cooled to room temperature, the solvents
were evaporated at reduced pressure. The residue was
recrystallized from water. Yield of compound 1 1.50 g (81%).
Method II (hydrolysis in alkaline medium). Compound
10 (2.00 g, 11 mmol) was added to a solution of NaOH
(0.50 g, 12.5 mmol) in a mixture of Н2О (2 ml) and MeOH
(2 ml). The obtained solution was refluxed for 15 min,
cooled to room temperature, and acidified with concd HCl
to рН 1. The precipitate that formed was filtered off. Yield
of compound 1 1.65 g (89%).
1-Methoxy-5-[4-(N-nitramino)furazan-3-yl]tetrazole
(14) and its ammonium salt (14а). A nitrating mixture
was prepared by slow addition of Ас2О (5 ml) to 95%
HNO3 (5 ml) while cooling to 0–10°С. The nitrating
mixture was vigorously stirred and externally cooled with
dry ice/acetone bath. Methoxytetrazole 10 (1.0 g,
5.9 mmol) was slowly added, while maintaining the
temperature of reaction mixture in the range of 0–8°С.
After the addition of the starting material was complete, the
mixture was stirred at the same temperature for 30 min and
poured into 25 ml of ice water. The precipitate that formed
was immediately filtered off, washed with water (2×10 ml),
and dried at room temperature. Yield of the crude product
1.1 g (87%), white, amorphous powder, mp 90–97°С
Hydrazinium salt of 5-(4-aminofurazan-3-yl)-1-hydr-
oxytetrazole (1b). Method I. Tetrazole 10 (5.00 g, 27 mmol)
was dissolved in 2-PrOH (50 ml) and hydrazine hydrate
(2.00 g, 40 mmol) was added. The reaction mixture was
refluxed for 3 h; then approximately 20–25 ml of solvent
was removed. The residue was cooled to room temperature,
the precipitate that formed was filtered off and
recrystallized from МеОН. Yield 4.10 g (76%), fine,
colorless needle-shaped crystals, mp 213–214°С.
IR spectrum, ν, cm–1: 3718, 3697, 3401, 3348, 3166, 2617,
1639, 1625, 1604, 1589, 1566, 1458, 1399, 1303, 1236,
1145, 1092, 980, 932, 888, 862, 771, 681, 590, 572, 495,
1
(decomp.). According to Н NMR and HPLC data, the
1
454. H NMR spectrum, δ, ppm: 7.07 (7H, br. s, NH2,
nitration product contained up to 20% of impurities.
IR spectrum, ν, cm–1: 3352, 2957, 2919, 2850, 1641, 1509,
1441, 1425, 1295, 1100, 998, 947, 781, 704, 614, 575, 559.
1H NMR spectrum, δ, ppm: 6.80–6.40 (1Н, br. s, NH); 4.40
(3H, s, OCH3). 13C NMR spectrum, δ, ppm: 153.5 (C-4');
139.4 (C-3'); 137.8 (C-5); 70.6 (OCH3).
+
N2H5 ). 13C NMR spectrum, δ, ppm: 156.2 (C-4'); 137.7
(C-3'); 135.1 (C-5). Found, %: C 17.71; H 3.68; N 62.31.
C3H7N9O2. Calculated, %: C 17.91; H 3.51; N 62.67.
Method II. Tetrazole 1 (1.00 g, 5.9 mmol) was added to
2-PrOH (10 ml). The mixture was neutralized to pH 7 by the
753

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
For the purpose of preparing the ammonium salt 14а,
dissolved in refluxing 2-PrOH. The precipitate that formed
upon cooling was filtered off, washed with Et2O (10 ml),
and recrystallized from 2-PrOH. Yield 1.4 g (65%),
amorphous light-yellow powder, mp 189–191°С (decomp.).
IR spectrum, ν, cm–1: 3238, 3052, 2911, 1822, 1607, 1575,
1518, 1478, 1438, 1409, 1341, 1242, 1225, 1119, 1057,
992, 886, 823, 761, 611, 527, 463, 406. 1H NMR spectrum,
the precipitate of nitramine 14 after filtration and washing
with water was transferred into 2-PrOH (10 ml), the
obtained suspension was adjusted to pH 8 by adding
aqueous 25% ammonia solution, the precipitate that formed
was filtered off and recrystallized from 95% EtOH. Yield
0.63 g (46%), light-yellow fine crystalline powder, mp 175–
176°С (decomp.). IR spectrum, ν, cm–1: 3175, 1616, 1525,
1385, 1365, 1277, 1116, 996, 930, 878, 824, 773, 597, 500,
430. 1H NMR spectrum, δ, ppm: 7.16 (4H, br. s, NH4+); 4.35
(3H, s, OCH3). 13C NMR spectrum, δ, ppm: 159.2 (C-4');
139.7 (C-3'); 138.8 (C-5); 70.1 (OCH3). Found, %:
C 19.38; H 3.06; N 51.87. C4H7N9O4. Calculated, %:
C 19.60; H 2.88; N 51.42.
+
δ, ppm: 7.18 (1H, br. s, NH4 ). 13C NMR spectrum, δ, ppm:
156.2 (C-4'); 139.7 (C-3'); 130.7 (C-5). Found, %: C 16.51;
H 1.94; N 52.09. C3H4N8O4. Calculated, %: C 16.67;
H 1.87; N 51.85.
1-Methoxy-5-(4-nitrofurazan-3-yl)tetrazole
(16).
Aqueous 30% solution of H2O2 (32.6 ml, 36.3 g, 0.32 mol)
was vigorously stirred and treated by dropwise addition of
96% H2SO4 (d 1.84 g/ml, 40.0 ml, 73.6 g, 0.72 mol), while
keeping the temperature in the solution at or below 50–55°С
by external cooling. Methoxytetrazole 10 (14.6 g, 0.08 mol)
was then added in 2–3-g portions, while maintaining the
temperature of reaction mixture in the range of 50–55°С.
After finishing the addition of compound 10, the mixture
was stirred for another 1 h at 50–55°С, cooled to room
temperature and poured into a mixture of ice and water
(50 ml). The reaction product was extracted with CH2Cl2
(4×30 ml). The combined organic extracts were washed
with water (2×10 ml), dried over anhydrous MgSO4, and
the solvent was evaporated at reduced pressure. Yield
15.3 g (90%), light-yellow, low viscosity liquid, insoluble
1-Hydroxy-5-(4-nitrofurazan-3-yl)tetrazole
(15).
Method I. Oxidation of 5-(4-aminofurazan-3-yl)-1-hydroxy-
tetrazole (1). Oxidizing mixture was prepared from
aqueous 30% H2O2 solution (32.6 ml, 36.3 g, 0.32 mol) and
96% H2SO4 (d 1.84 g/ml, 40.0 ml, 73.6 g, 0.72 mol). Tetrazole
1 (13.5 g, 0.08 mol) was added in 2–3-g portions to the
oxidizing mixture, while the temperature of the reaction
mixture was maintained in the range of 50–55°С. After the
addition of compound 1 was complete, the mixture was
further stirred at 50–55°С for additional 1 h, then cooled to
room temperature and poured into a mixture of ice and
water (200 ml). The obtained solution was partially
neutralized by adding crystalline Na3PO4·12H2O (300.0 g,
0.80 mol) and extracted with EtOAc (5×25 ml). The
combined organic extracts were washed with saturated
aqueous NaCl solution (2×25 ml) and dried over anhydrous
Na2SO4. The solution was passed through a layer of
alumina (column length 3 cm, diameter 1 cm), the solvent
was removed at reduced pressure. The product was dried to
constant mass (for approximately 48 h) at room
temperature in a vacuum desiccator over P2O5. Yield 3.8 g
(24%), light-yellow, viscous hygroscopic liquid, soluble in
25
in water, soluble in polar organic solvents, nD 1.512.
IR spectrum, ν, cm–1: 3450, 3327, 3249, 3025, 2955, 1733,
1561, 1531, 1445, 1354, 1259, 1223, 1113, 1056, 994, 939,
1
909, 721, 678, 650, 594, 585, 548, 408, 401. H NMR
spectrum, δ, ppm: 4.46 (3H, s, OCH3). 13C NMR spectrum,
δ, ppm: 160.1 (br., C-4'); 137.8 (C-3'); 136.3 (C-5);
70.6 (OCH3).
Diammonium salt of 3,3'-bis(1-hydroxytetrazol-5-yl)-
4,4'-azofurazan (3). Tetrazole 1 (1.69 g, 0.01 mol) was
dissolved in AcOH (10 ml), then concd HCl (10 ml) was
added. The obtained solution was vigorously stirred at 20–30°С
temperature and treated by the addition of KMnO4 (1.58 g,
0.01 mol) in 100–200-mg portions. The reaction mixture
was heated to 50°С and stirred at this temperature for 30 min.
The excess of KMnO4 was destroyed by adding several
drops of aqueous 30% Н2О2 solution. The mixture was
diluted with Н2О (50 ml), cooled to room temperature and
extracted with EtOAc (3×15 ml). The combined organic
extracts were washed with a saturated aqueous NaCl solution
(3×10 ml). The organic phase was carefully adjusted to
pH 8 by dropwise addition of aqueous 25% ammonia
solution. The precipitate that formed was filtered off and
recrystallized from 10:1 mixture of 2-PrOH–H2O. Yield
1.25 g (68%), fine orange crystals, mp 252–253°С (decomp.)
(mp 266°C (decomp., DSC)12). IR spectrum, ν, cm–1: 3182,
3045, 2831, 1597, 1498, 1434, 1414, 1377, 1280, 1224,
1127, 1071, 1015, 993, 910, 855, 772, 697, 624, 524, 404.
(IR spectrum (KBr), ν, cm–1: 3188, 3145, 1686, 1597,
1498, 1435, 1405, 1276, 1224, 1124, 989, 854, 769).12
25
water, CHCl3, EtOH, nD 1.511. IR spectrum, ν, cm–1:
2982, 2934, 1574, 1412, 1390, 1339, 1245, 1109, 1005,
926, 904, 825, 806, 534, 502, 466, 455, 439, 420, 401.
13
1H NMR spectrum, δ, ppm: 9.60 (1H, br. s, OH). C NMR
spectrum, δ, ppm: 159.6 (br., C-4'); 138.2 (C-3'); 134.6
(C-5). Found, %: C 14.96; H 2.37; N 41.23. C3HN7O4·2H2O.
Calculated, %: C 15.33; H 2.14; N 41.70.
Method II. Demethylation of 1-methoxy-5-(4-nitro-
furazan-3-yl)tetrazole (16). Compound 16 (2.13 g, 0.01 mol)
was dissolved in AcOH (5 ml), then concd HCl (5 ml) was
added and the mixture was heated at reflux for 2 h in a
flask with reflux condenser. The mixture was cooled to
room temperature, the solvents were evaporated at reduced
pressure. Yield 1.60 g (81%), light-yellow, viscous liquid,
nD25 1.513.
Ammonium salt of 1-hydroxy-5-(4-nitrofurazan-3-yl)-
tetrazole (15а). Tetrazole 15 (2.0 g, 10 mmol) was
dissolved in AcOH (5 ml) and NH4OAc (1.0 g, 13 mmol)
was added. The obtained solution was evaporated at reduced
pressure on a rotary evaporator (bath temperature 90–95°С),
the residue was dissolved in Н2О (5 ml) and again
evaporated at reduced pressure. The addition of water
followed by evaporation was repeated twice, the residue was
+
1H NMR spectrum, δ, ppm: 7.12 (8H, br. s, 2NH4 ).
(1H NMR spectrum (DMSO-d6), δ, ppm: 7.10.12) 13C NMR
spectrum, δ, ppm: 162.3 (C-4'); 138.2 (C-3'); 131.9 (C-5).
754

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
(13C NMR spectrum (DMSO-d6), δ, ppm: 162.1; 138.1;
131.8.12)
3,3'-Bis(1-methoxytetrazol-5-yl)-4,4'-azofurazan (17).
was stirred for 5 h at 20–25°С, then diluted with Н2О
(20 ml), acidified with concd HCl to рН 1 and evaporated
at reduced pressure. The residue was extracted with
refluxing 2-PrOH (2×10 ml), the inorganic solids were
removed by filtration, the hot filtrate was treated by
dropwise addition of water until the crystallization started,
then the mixture was cooled to 10°С. The precipitate that
formed was filtered off and recrystallized from aqueous
MeOH. Yield 1.30 g (71%), agglomerates of fine,
irregularly shaped crystals, mp 161–162°С (МeOH–H2O,
1:1). IR spectrum, ν, cm–1: 3557, 3473, 2958, 1638, 1439,
1352, 1304, 1221, 1106, 985, 948, 763, 738, 700, 630, 581,
441, 413. 1H NMR spectrum, δ, ppm: 7.11 (1H, br. s, OH);
4.38 (3H, s, OCH3). 13C NMR spectrum, δ, ppm: 164.8 (C-4');
138.5 (C-3'); 135.9 (C-5); 70.0 (OCH3). Calculated, %:
C 26.09; H 2.19; N 45.65. C4H4N6O3. Found, %: C 25.93;
H 2.28; N 45.38. The potassium salt of compound 20 was
obtained by mixing a solution of compound 20 (1.00 g,
5.4 mmol) in 2-PrOH (10 ml) with a solution of KOH
(0.34 g, 6.0 mmol) in MeOH (2 ml). The precipitate that
formed was filtered off, washed with acetone (10 ml), and
air-dried. Yield 1.05 g (88%), white fine crystalline
powder, mp 271–272°С (with explosion).
Tetrazole 10 (1.83 g, 0.01 mol) was dissolved in AcOH
(10 ml), then concd HCl (10 ml) was added. The obtained
solution was vigorously stirred at 20–30°С and KMnO4
(1.60 g, 0.01 mol) was added. The reaction mixture was
heated to 50°С and stirred for 30 min at this temperature.
The excess of KMnO4 was decomposed by adding several
drops of aqueous 30% Н2О2 solution. The mixture was
diluted with Н2О (50 ml), cooled to room temperature, the
precipitate that formed was filtered off and recrystallized
from МеОН. Yield 1.55 g (85%), red needle-shaped
crystals, mp 127–128°С. IR spectrum, ν, cm–1: 3437, 3027,
2958, 2920, 1618, 1452, 1439, 1422, 1382, 1254, 1112,
1046, 1003, 944, 905, 870, 611. 1H NMR spectrum,
δ, ppm: 4.40 (6H, s, 2OCH3). 13C NMR spectrum, δ, ppm:
162.2 (C-4'); 138.2 (C-3'); 137.4 (C-5); 70.3 (OCH3).
Found, m/z: 385.0590 [M+Na]+. С8H6N14NaO4. Calculated,
m/z: 385.0589.
N,N'-Bis[4-(1-methoxytetrazol-5-yl)furazan-3-yl]-
hydrazine (18). Azotetrazole 17 (1.0 g, 2.76 mmol) was
dissolved in MeCN (5 ml) and hydrazine hydrate (0.4 g,
8.00 mmol) was added at 20–25°С. The color of solution
faded after 1–2 min and white precipitate appeared. The
mixture was stirred at 20–25°С for 30 min, diluted with
H2O (10 ml), the precipitate was filtered off and recrystal-
lized from МеОН. Yield 0.71 g (71%), white powder,
mp 238–240°С (decomp.). IR spectrum, ν, cm–1: 3342,
1636, 1600, 1489, 1462, 1266, 1112, 996, 947, 803, 579.
1H NMR spectrum, δ, ppm: 9.38 (2H, s, 2NH); 4.44 (6H, s,
2OCH3). 13C NMR spectrum, δ, ppm: 157.0 (C-4'); 138.2
(C-3'); 133.3 (C-5); 70.0 (OCH3). Mass spectrum, m/z
(Irel, %): 364 [M]+ (25), 263 (13), 232 (55), 168 [M/2–CH2]+
(14), 164 (14), 141 (30), 139 (22), 137 (45), 126 (28), 122
(100), 110 (20), 99 (22), 98 (32), 96 (20), 95 (31), 83 (16),
53 [HNCCN]+ (18), 30 [NO]+ (37). Found, m/z: 365.0931
[M+H]+, 387.0744 [M+Na]+. С8H9N14O4, С8H8N14NaO4.
Calculated, m/z: 365.0926, 387.0745.
1-Methoxy-5-(4-methoxyfurazan-3-yl)tetrazole (19).
Tetrazole 16 (2.13 g, 10 mmol) was dissolved in MeOH
(20 ml) and NaHCO3 (1.50 g, 18 mmol) was added. The
reaction mixture was stirred for 5 h at 20–25°С, then
diluted with Н2О (50 ml) and cooled to 10°С. The
precipitate that formed was filtered off and recrystallized
from aqueous МеОН. Yield 1.60 g (82%), fine white
plates, mp 116–117°С (МeOH–H2O, 1:1). IR spectrum,
ν, cm–1: 3437, 2920, 2853, 1622, 1577, 1472, 1454, 1414,
1261, 1194, 1154, 1106, 1044, 996, 977, 938, 916, 873, 590,
572, 462, 418. 1H NMR spectrum, δ, ppm: 4.40 (3H, s, OCH3
(tetrazole)); 4.23 (3H, s, OCH3 (furazan)). 13C NMR
spectrum, δ, ppm: 164.6 (C-4'); 137.8 (C-3'); 134.7 (C-5);
70.0 (OCH3 (tetrazole)); 60.8 (OCH3 (furazan)). Found, m/z:
199.0576 [M+H]+, 221.0392 [M+Na]+. С5H7N6O3,
С5H6N6NaO3. Calculated, m/z: 199.0574, 221.0393.
5-(4-Azidofurazan-3-yl)-1-methoxytetrazole
(21).
Tetrazole 16 (2.13 g, 10 mmol) was dissolved in MeCN
(20 ml) and NaN3 (1.00 g, 15 mmol) was added. The
reaction mixture was stirred for 5 h at 40–45°С, then
diluted with Н2О (50 ml) and cooled to 10°С. The
precipitate that formed was filtered off and recrystallized
from aqueous MeOH. Yield 1.60 g (76%), agglomerates of
fine crystals, mp 84–85°С (МeOH–H2O, 1:1). IR spectrum,
ν, cm–1: 3023, 2957, 2922, 2148, 1546, 1454, 1432, 1383,
1291, 1183, 1097, 1034, 997, 941, 903, 878, 771, 589.
1H NMR spectrum, δ, ppm: 4.43 (3H, s, OCH3). 13C NMR
spectrum, δ, ppm: 153.6 (C-4'); 137.7 (C-3'); 137.2 (C-5); 70.2
(OCH3). Found, m/z: 210.0485 [M+H]+, 232.0296 [M+Na]+.
С4H4N9O2, С4H3N9NaO2. Calculated, m/z: 210.0482, 232.0302.
Preparation of compounds 22а–d by reaction of
1-methoxy-5-(4-nitrofurazan-3-yl)tetrazole (16) with
amines. The appropriate amine (22 mmol, amines that are
gaseous at room temperature were used as aqueous
solutions) was added dropwise to a stirred solution of
tetrazole 16 (2.13 g, 10 mmol) in MeCN (15 ml), while
cooling the reaction mixture in order to maintain the
temperature in the range of 25–30°С. The reaction mixture
was stirred for 1 h at 30°С and poured into Н2О (50 ml).
The precipitated product was filtered off and recrystallized
from aqueous MeOH.
5-[4-(N-Methylamino)furazan-3-yl]-1-methoxytetrazole
(22а) was obtained by treatment of tetrazole 16 with aqueous
34% MeNH2 solution. Yield 1.30 g (67%), agglomerates of
fine, white irregularly shaped crystals, mp 133–134°C.
IR spectrum, ν, cm–1: 3401, 3362, 2964, 2921, 1629, 1604,
1510, 1458, 1441, 1417, 1263, 1159, 1112, 1021, 998, 942,
1
862, 589, 576. H NMR spectrum, δ, ppm (J, Hz): 6.61
5-(4-Hydroxyfurazan-3-yl)-1-methoxytetrazole (20).
A solution of tetrazole 16 (2.13 g, 10 mmol) in MeOH
(20 ml) was treated by dropwise addition of KOH (1.40 g,
25 mmol) solution in MeOH (10 ml). The reaction mixture
(1H, q, J = 4.9, NH); 4.40 (3H, s, OCH3); 2.95 (3H, d,
J = 4.9, NHCH3). 13C NMR spectrum, δ, ppm: 157.0 (C-4');
136.8 (C-3'); 133.6 (C-5); 69.8 (OCH3); 31.3 (NHCH3).
Mass spectrum, m/z (Irel, %): 197 [M]+ (5), 166 [M–NO–H]+
755

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
(4), 98 [C2N2ONHCH3]+ (12), 72 [HN2CNOH]+ (15), 68
AcOH (0.2 ml). The reaction mixture was refluxed for 1 h,
then the solvent was evaporated at reduced pressure, the
residue was washed with water and recrystallized from
aqueous MeOH. Yield 0.65 g (55%), white amorphous
powder, mp 161–162°С (МeOH–H2O, 1:1). IR spectrum,
ν, cm–1: 3276, 3181, 3076, 3004, 2755, 2645, 1694, 1607,
1582, 1532, 1456, 1443, 1417, 1338, 1291, 1260, 1232,
1125, 989, 970, 930, 869, 793, 751, 678, 571, 447.
1H NMR spectrum, δ, ppm: 7.05 (2H, br. s, NH, OH); 4.17
(6H, s, 2CH3). 13C NMR spectrum, δ, ppm: 168.8 (C-4'); 157.4
(C-3'); 136.2 (N=C(CH3)2); 134.6 (C-5); 20.8 (2CH3). Found,
%: C 32.35; H 3.71; N 49.67. C6H8N8O2. Calculated, %:
C 32.15; H 3.60; N 49.98.
5-{4-[2-(1-Benzylidene)hydrazino]furazan-3-yl}-1-hydr-
oxytetrazole (25). Salt 23 (1.00 g, 4.6 mmol) was added to
MeOH (10 ml), followed by the addition of benzaldehyde
(1.00 g, 9.4 mmol) and AcOH (0.2 ml). The reaction mixture
was refluxed for 1 h, then diluted with Н2О (50 ml), the oil
that separated was decanted and crystallized from aqueous
MeOH. Yield 0.94 g (75%), fine gray plates, mp 223–225°С
(decomp.) (МeOH–H2O, 1:1). IR spectrum, ν, cm–1: 3437,
3289, 3026, 2960, 2917, 2851, 2594, 1615, 1450, 1385,
1113, 1090, 1070, 1059, 999, 990, 952, 872, 762, 696.
1H NMR spectrum, δ, ppm: 11.54 (1H, s, NH); 8.15 (1H, s,
N=CH); 7.54–7.45 (5H, m, H Ph); 4.71 (1H, br. s, OH).
13C NMR spectrum, δ, ppm: 155.4 (C-4'); 145.6 (N=CH);
137.8 (C-3'); 134.6 (C-1 Ph); 134.4 (C-5); 130.1 (C-4 Ph);
129.2 (C-3,5 Ph); 127.0 (C-2,6 Ph). Found, %: C 43.95;
H 3.13; N 41.31. C10H8N8O2. Calculated, %: C 44.12;
H 2.96; N 41.16.
[C2N2O]+ (17), 53 [HNCCN]+ (31), 42 [CNO]+ (36), 30
[NO]+ (100); 15 [CH3]+ (23). Found, m/z: 198.0738 [M+H]+.
С5H8N7O2. Calculated, m/z: 198.0733.
5-[4-(N,N-Dimethylamino)furazan-3-yl]-1-methoxy-
tetrazole (22b) was obtained by treating tetrazole 16 with
aqueous 33% solution of Me2NH. Yield 1.10 g (52%), fine
colorless needle-shaped crystals, mp 63–64°C. IR spectrum,
ν, cm–1: 3430, 3037, 3010, 2970, 2959, 2932, 2828, 1603,
1579, 1463, 1440, 1429, 1269, 1100, 997, 950, 570.
1H NMR spectrum, δ, ppm: 4.42 (3H, s, OCH3); 2.97 (6H,
s, N(CH3)2). 13C NMR spectrum, δ, ppm: 159.5 (C-4');
138.8 (C-3'); 134.1 (C-5); 70.2 (OCH3); 41.2 (N(CH3)2).
Found, m/z: 234.0715 [M+Na]+. С6H9N7NaO2. Calculated,
m/z: 234.0710.
5-[4-(N-tert-Butylamino)furazan-3-yl]-1-methoxytetr-
azole (22с) was obtained by treatment of tetrazole 16 with
tert-butylamine. Yield 1.40 g (60%), white, fine irregularly
shaped plates, mp 62–63°C. IR spectrum, ν, cm–1: 3380,
2976, 1633, 1580, 1527, 1464, 1455, 1435, 1408, 1371,
1364, 1297, 1266, 1230, 1113, 995, 956, 918, 575.
1H NMR spectrum, δ, ppm: 6.07 (1H, s, NH); 4.40 (3H, s,
OCH3); 1.43 (9H, s, C(CH3)3). 13C NMR spectrum, δ, ppm:
153.8 (C-4'); 138.8 (C-3'); 134.2 (C-5); 69.7 (OCH3); 52.4
(C(CH3)3); 28.1 (C(CH3)3). Found, m/z: 262.0999 [M+Na]+.
С8H13N7NaO2. Calculated, m/z: 262.1023.
1-Methoxy-5-[4-(morpholin-4-yl)furazan-3-yl]tetrazole
(22d) was obtained by treatment of tetrazole 16 with
morpholine. Yield 1.80 g (71%), coarse, irregularly shaped
colorless plates, mp 95–96°C. IR spectrum, ν, cm–1: 3436,
3018, 2973, 2915, 2866, 1596, 1547, 1447, 1437, 1269,
Ammonium salt of 1-hydroxy-5-[4-(pyrazol-1-yl)-
furazan-3-yl]tetrazole (26). Salt 23 (1.00 g, 4.6 mmol)
was added to MeOH (10 ml), followed by 1,1,3,3-
tetramethoxypropane (3.28 g, 20.0 mmol). The reaction
mixture was heated to 40°С, acidified with concd HCl to
рН 1 and refluxed for 1 h. The mixture was then
evaporated to dryness at reduced pressure, the residue was
extracted with aqueous 10% ammonia solution (10 ml).
The insoluble impurities were removed by filtration and the
filtrate was washed with CH2Cl2 (2×5 ml). The aqueous
layer was separated, evaporated to dryness at reduced
pressure, and the dry residue was recrystallized from
МеОН. Yield 0.77 g (71%), fine white needles, mp 194–
195°С. IR spectrum, ν, cm–1: 3436, 3201, 3122, 3045,
2940, 2848, 2818, 2773, 1607, 1576, 1506, 1455, 1417,
1406, 1391, 1379, 1230, 1211, 1171, 1120, 1053, 1021,
1001, 929, 883, 785, 756, 642, 606, 516, 450, 422.
1H NMR spectrum, δ, ppm (J, Hz): 8.48 (1H, d, J = 2.5,
1
1114, 1070, 1028, 996, 952, 913, 583. H NMR spectrum,
δ, ppm: 4.42 (3H, s, OCH3); 3.77–3.73 (4H, m, CH2OСН2);
3.38–3.34 (4H, m, CH2NСН2). 13C NMR spectrum, δ, ppm:
159.3 (C-4'); 138.8 (C-3'); 135.5 (C-5); 70.1 (OCH3); 65.7
(CH2OCH2); 49.4 (CH2NCH2). Found, m/z: 276.0817
[M+Na]+. С8H11N7NaO3. Calculated, m/z: 276.0815.
Hydrazinium salt of 5-(4-hydrazinofurazan-3-yl)-
1-hydroxytetrazole (23). Tetrazole 16 (2.13 g, 10 mmol)
was dissolved in MeCN (20 ml), then hydrazine hydrate
(1.50 g, 30 mmol) was added dropwise at 15–20°С. The
reaction mixture was stirred at this temperature for 1 h. The
precipitate that formed was filtered off and recrystallized
from МеОН. Yield 1.60 g (75%), light-gray agglomerates
of fine irregularly shaped crystals, mp 224–225°С. IR
spectrum, ν, cm–1: 3437, 3321, 3303, 3242, 3205, 3017,
2961, 2916, 2676, 1663, 1640, 1585, 1552, 1509, 1456,
1400, 1364, 1281, 1233, 1192, 1141, 1113, 1008, 989, 976,
1
+
860, 781, 421. H NMR spectrum, δ, ppm: 9.05 (1H, s,
H-5'); 7.88 (1H, d, J = 1.8, H-3'); 7.33 (4H, br. s, NH4 );
+
NH); 7.10 (5H, br. s, N2H5 ); 4.58 (2H, br. s, NH2).
6.65 (1H, dd, J = 2.5; J = 1.7, H-4'). 13C NMR spectrum,
δ, ppm: 152.5 (C-4'); 144.4 (С-3 (pyrazole)); 139.9 (C-3');
132.7 (C-5 (pyrazole)); 132.0 (C-5); 109.8 (C-4
(pyrazole)). Found, m/z: 221.0524 [M+H]+. С6H5N8O2.
Calculated, m/z: 221.0529.
13C NMR spectrum, δ, ppm: 160.2 (C-4'); 136.2 (C-3');
134.8 (C-5). Mass spectrum, m/z (Irel, %): 184 [M]+ (2), 69
(11), 68 (10), 53 [HNCCN]+ (33), 43 [HN3]+ (22), 31
[N2H3]+ (63), 30 [NO]+ (100), 29 (31). Found, m/z:
229.0170 [M–H+2Na]+. С3H3N8Na2O2. Calculated, m/z:
229.0169.
Ammonium salt of 1-hydroxy-5-[4-(3,5-dimethyl-
pyrazol-1-yl)furazan-3-yl]tetrazole (27). Salt 23 (1.00 g,
4.6 mmol) was added to AcOH (10 ml), followed by the
addition of acetylacetone (2.00 g, 20.0 mmol). The reaction
mixture was refluxed for 1 h, then worked up as described
1-Hydroxy-5-{4-[2-(1-isopropylidene)hydrazino]fura-
zan-3-yl}tetrazole (24). Salt 23 (1.00 g, 4.6 mmol) was
added to acetone (10 ml), followed by the addition of
756

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
above for the preparation of pyrazole 26. Yield 0.89 g
(3H, s, CH3). 13C NMR spectrum, δ, ppm: 164.8 (C-4');
137.0 (C-3'); 132.1 (C-5); 60.1 (OCH3). In order to isolate
the free tetrazole 30, a part of the obtained ammonium salt
(1.00 g, 4.65 mmol) was dissolved in 2-PrOH (2 ml),
acidified with concd HCl to рН 1, and evaporated to
dryness. The residue was extracted with Et2O (2×5 ml),
filtered, the filtrate was diluted with СCl4 (5 ml) and
allowed to slowly evaporate at room temperature. The
precipitate that formed was filtered off and washed with
hexane (5 ml). Yield 0.57 g (62%), colorless fine crystals,
mp 83–84°С. IR spectrum, ν, cm–1: 3385, 3012, 2952,
1797, 1616, 1575, 1457, 1415, 1392, 1263, 1198, 1169,
1138, 1069, 998, 975, 867, 586, 533, 481, 436, 407.
1H NMR spectrum, δ, ppm: 6.65 (1H, br. s, ОН); 4.12 (3H, s,
OCH3). 13C NMR spectrum, δ, ppm: 164.7 (C-4'); 136.6 (C-3');
134.9 (C-5); 60.7 (OCH3). Found, %: C 25.87; H 2.36;
N 45.21. C4H4N6O3. Calculated, %: C 26.09; H 2.19; N 45.65.
5-(4-Azidofurazan-3-yl)-1-hydroxytetrazole (31). The
azido derivative 21 (2.09 g, 10.0 mmol) was dissolved in
AcOH (5 ml) and treated with concd HCl (5 ml). The
mixture was refluxed for 3 h, cooled to room temperature,
the solvents were evaporated at reduced pressure. The
residue was dissolved in 2-PrOH (15 ml), adjusted to pH 8
with aqueous 15 N ammonia solution, diluted with PhMe
(20 ml), heated to reflux and slowly evaporated until the
start of crystallization. The mixture was cooled to room
temperature, the precipitate of ammonium salt 31а was
filtered off, washed on filter with CH2Cl2 (5 ml), and dried.
Yield 2.01 g (95%), white needles, mp 178–179°С
(decomp.). IR spectrum, ν, cm–1: 3171, 3057, 2837, 2149,
1607, 1546, 1467, 1444, 1416, 1386, 1229, 1181, 988, 876,
(73%), fine white irregularly shaped crystals, mp 221–222°С.
IR spectrum, ν, cm–1: 3195, 3121, 2984, 2854, 1601, 1572,
1474, 1454, 1437, 1424, 1410, 1373, 1342, 1293, 1223,
1
1033, 1016, 1007, 984, 864, 809, 781, 749, 454. H NMR
+
spectrum, δ, ppm: 7.24 (4H, br. s, NH4 ); 6.19 (1H, s, H-4');
2.30 (3H, s, CH3); 2.07 (3H, s, CH3). 13C NMR spectrum,
δ, ppm: 152.1 (C-4'); 151.8 (С-3 (pyrazole)); 144.7 (C-3');
143.0 (C-5 (pyrazole)); 132.2 (C-5); 109.2 (C-4
(pyrazole)); 13.7 (CH3); 11.8 (CH3). Found, m/z: 249.0838
[M+H]+, 271.0659 [M+Na]+. С8H9N8O2, С8H8N8NaO2.
Calculated, m/z: 249.0843, 271.0662.
Preparation of nitriles 28, 29. The appropriate tetrazole
26 or 27 (10 mmol) was added in small portions to stirred
HNO3 (d = 1.5 g/cm3) (20 ml), while maintaining the
temperature in the range of 5–10°С. Then at the same
temperature concd H2SO4 (20 ml) was added dropwise,
resulting in vigorous evolution of gas. The mixture was
maintained for 5 h at room temperature and poured onto
crushed ice (50 g). The precipitated product was filtered
off, washed with water, dried at room temperature, and
recrystallized from 1:1 mixture of PhH–hexane.
4-(4-Nitro-1H-pyrazol-1-yl)furazan-3-carbonitrile
(28). Yield 1.34 g (65%), agglomerates of fine, needle-shaped
crystals, mp 93–94°С. IR spectrum, ν, cm–1: 3136, 3122,
3105, 3087, 2719, 1593, 1531, 1522, 1439, 1418, 1402,
1336, 1300, 1198, 1059, 999, 933, 886, 816, 752, 580.
1H NMR spectrum, δ, ppm: 9.97 (1H, s, H-5'); 8.92 (1H, s,
H-3'). 13C NMR spectrum, δ, ppm: 152.9 (C-4); 140.0 (С-3
(pyrazole)); 139.9 (С-5 (pyrazole)); 131.8 (C-4 (pyrazole));
129.3 (C-3); 107.6 (CN). Mass spectrum, m/z (Irel, %): 206
[M]+ (100), 121 (70), 38 [NCN]+ (10), 30 [NO]+ (45).
Found, %: C 35.14; H 1.13, N 40.98. C6H2N6O3.
Calculated, %: C 34.96; H 0.98; N 40.77.
1
779, 530, 440. H NMR spectrum, δ, ppm: 7.36–7.11 (4H,
m, NH4+). 13C NMR spectrum, δ, ppm: 153.1 (C-4'); 139.3
(C-3'); 132.2 (C-5). Found, %: C 16.51; H 2.02; N 66.14.
C3H4N10O2. Calculated, %: C 16.99; H 1.90; N 66.03. In
order to isolate free tetrazole 31, the ammonium salt 31а
(1.00 g, 4.7 mmol) was dissolved in ice water (3 ml) and
acidified with concd HCl to рН 1. The mixture was stirred
and cooled to 0°С, the precipitate that formed was filtered
off, recrystallized from water, and dried in vacuum at 70°С.
Yield 0.84 g (92%), fine white plates, mp 185–187°С.
IR spectrum, ν, cm–1: 3549, 3326, 3319, 2152, 1582, 1539,
1478, 1445, 1434, 1418, 1387, 1297, 1267, 1196, 1061,
1045, 996, 887, 865, 858, 782, 530, 441. 1H NMR
spectrum, δ, ppm: 6.65 (1H, br. s, ОН). (1H NMR spectrum
(acetone-d6), δ, ppm: 8.45.30) 13C NMR spectrum, δ, ppm:
153.5 (C-4'); 137.3 (C-3'); 136.4 (C-5). Found, %: C 18.27;
H 0.94; N 64.82. C3HN9O2. Calculated, %: C 18.47;
H 0.52; N 64.61.
4-(3,5-Dimethyl-4-nitro-1H-pyrazol-1-yl)furazan-3-carbo-
nitrile (29). Yield 1.59 g (68%), long needles, mp 59–60°С.
IR spectrum, ν, cm–1: 3008, 2936, 2853, 2262, 1595, 1527,
1506, 1483, 1410, 1401, 1378, 1361, 1346, 1260, 1156,
1
1143, 1053, 1018, 883, 843, 787, 767, 599. H NMR
spectrum, δ, ppm: 2.90 (3H, s, CH3); 2.57 (3H, s, CH3).
13C NMR spectrum, δ, ppm: 152.7 (C-4); 149.4 (С-3
(pyrazole)); 145.2 (C-5 (pyrazole)); 134.2 (C-4 (pyrazole));
130.4 (C-3); 107.8 (CN); 14.2 (CH3); 13.0 (CH3). Found,
%: C 40.85; H 2.72; N 36.03. C8H6N6O3. Calculated, %:
C 41.03; H 2.58; N 35.89.
1-Hydroxy-5-(4-methoxyfurazan-3-yl)tetrazole (30).
The dimethoxy derivative 19 (1.98 g, 10.00 mmol) was
dissolved in AcOH (5 ml) and concd HCl (5 ml) was added.
The mixture was refluxed for 5 h, cooled to room
temperature. The solvents were evaporated at reduced
pressure. The residue was treated with aqueous 15 N
ammonia solution (3 ml), filtered, and the filtrate was
evaporated at reduced pressure. The solid residue of
ammonium salt 30a was recrystallized from 1:5 mixture of
2-PrOH–PhMe. The yield of salt 30a was 1.53 g (71%),
elongated irregularly shaped plates, mp 214–215°С.
IR spectrum, ν, cm–1: 3183, 3058, 2852, 1646, 1613, 1585,
1458, 1444, 1406, 1227, 1132, 1067, 991, 760, 580, 501.
1-Hydroxy-5-[4-(morpholin-4-yl)furazan-3-yl]tetra-
zole (32). Compound 22d (1.26 g, 5 mmol) was dissolved in
AcOH (5 ml), and then concd HCl (5 ml) was added. The
mixture was refluxed for 3 h, cooled to room temperature,
and poured into Н2О (25 ml). The precipitate that formed
was filtered off and recrystallized from МеОН. Yield 1.10 g
(92%), white needles, mp 235–236°С. IR spectrum, ν, cm–1:
2993, 2976, 2932, 2878, 2855, 2696, 1557, 1447, 1379,
1302, 1266, 1169, 1118, 1111, 1066, 1034, 1019, 998, 910,
1
+
1H NMR spectrum, δ, ppm: 6.90 (4H, br. s, NH4 ); 4.12
881, 845, 755, 566, 436. H NMR spectrum, δ, ppm: 8.14
757

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 746–759
(1H, br. s, OH); 3.73–3.68 (4H, m, CH2OCH2); 3.26–3.22 (4H,
15. Peng, L.; Li, Y.; Yang, Y.; Liu, W.; Zhang, X.; Pang, S. Chin.
m, CH2NCH2). 13C NMR spectrum, δ, ppm: 159.2 (C-4');
137.8 (C-3'); 135.4 (C-5); 65.7 (CH2OCH2); 48.9
(CH2NCH2). Found, m/z: 240.0833 [M+H]+, 262.0658
[M+Na]+. С7H10N7O3, С7H9N7NaO3. Calculated, m/z:
240.0839, 262.0659.
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X-ray structural studies of compounds 31 and 31а
were performed by using an Oxford Diffraction Xcalibur
monocrystal diffractometer with an Eos two-dimensional
CCD detector and MoKα radiation (0.71073
Å
wavelength). The crystal was thermostated with an Oxford
Cryosystems Cryostream cooler at 100 K. Monocrystals
suitable for analysis were obtained by slow evaporation of
solvent from aqueous solutions of the respective compounds
under isothermal conditions (20°C). Primary processing of
experimental data was performed with the Agilent
Technologies CrysAlisPro software suite.62 The structures
were solved and refined by using the Olex2 program from
the SHELX software suite.63 The colorless, well-faceted
crystals of compound 31 belong to monoclinic syngony.
The main crystallographic data: space group Р21/n;
a 10.0019(14), b 6.2195(7), c 13.5749(18) Å; β 107.701°;
V 804.48(19) Å3; Z 4; d 1.760 g/cm3; μ 0.154 mm–1. The
colorless, well-faceted crystals of compound 31а belong to
rhombic syngony. The main crystallographic data: space
group Р21/21/21; a 4.7397(3), b 12.0960(6), c 13.9889(6) Å;
β 90°; V 802.01(7) Å3; Z 4; d 1.757 g/cm3; μ 0.149 mm–1.
The complete crystallographic datasets for compounds 31
and 31a were deposited at the Cambridge Crystallographic
Data Center (deposits CCDC 1523288 and CCDC
1533574, respectively).
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