Synthesis and Properties of 4,4',5,5'-Tetranitro-1H,1'H-2,2'-Biimidazole Salts: Semicarbazidium, 3-Amino-1,2,4-Triazolium, and 5-Aminotetrazolium Derivatives

Article abstract of DOI:10.1007/s10593-017-2111-z

[Figure not available: see fulltext.] Ionic derivatives of 4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole have recently been identified as interesting low-sensitivity explosive compounds that combine low vulnerability to mechanical stimuli with high performance. In this work, the synthesis of bis-semicarbazidium), bis(3-amino-1H-1,2,4-triazol-4-ium), and bis(5-amino-4H-tetrazol-1-ium) 4,4',5,5'-tetranitro-2,2'-biimidazol-1-ides is described, and some of their experimental and calculated explosive properties are presented. 4,4',5,5'-Tetranitro-1H,1'H-2,2'-biimidazole was synthesized by nitration of 2,2'-biimidazole with nitric acid in polyphosphoric acid and produced the salts in good yields and purity by reaction with semicarbazide hydrochloride in water, 3-amino-1,2,4-triazole in methanol, and 5-aminotetrazole in diethyl ether. The obtained salts were characterized by NMR and infrared spectroscopy, elemental analysis, thermal analysis, and small-scale safety testing impact and friction sensitivity). The measured densities and standard enthalpy of formation, as well as calculated performance characteristics are reported. The compounds are thermally stable up to 180–210°C and insensitive to mechanical stimuli and have slightly better performance than trinitrotoluene with regard to calculated detonation parameters.

Full text of DOI:10.1007/s10593-017-2111-z

DOI 10.1007/s10593-017-2111-z
Chemistry of Heterocyclic Compounds 2017, 53(6/7), 697–701
Synthesis and properties of 4,4',5,5'-tetranitro-
1
H,1'H-2,2'-biimidazole salts: semicarbazidium,
3
-amino-1,2,4-triazolium, and 5-aminotetrazolium derivatives
1
1
1
Rafał Lewczuk *, Mateusz Szala , Judyta Rećko ,
2
1
Thomas M. Klapötke , Stanisław Cudziło
1
Department of Explosives, Military University of Technology,
Kaliskiego, Warsaw 00-908, Poland; e-mail: rafal.lewczuk@wat.edu.pl
Department of Chemistry, Ludwig-Maximilian University of Munich,
-13 Butenandtstr., Munich 81377, Germany; e-mail: tmk@cup.uni-muenchen.de
2
2
5
Russian translation is published in Khimiya Geterotsiklicheskikh
Soedinenii, 2017, 53(6/7), 697–701
Submitted October 18, 2016
Accepted November 9, 2016
Ionic derivatives of 4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole have recently been identified as interesting low-sensitivity explosive
compounds that combine low vulnerability to mechanical stimuli with high performance. In this work, the synthesis of bis-
(
semicarbazidium), bis(3-amino-1H-1,2,4-triazol-4-ium), and bis(5-amino-4H-tetrazol-1-ium) 4,4',5,5'-tetranitro-2,2'-biimidazol-1-ides is
described, and some of their experimental and calculated explosive properties are presented. 4,4',5,5'-Tetranitro-1H,1'H-2,2'-biimidazole
was synthesized by nitration of 2,2'-biimidazole with nitric acid in polyphosphoric acid and produced the salts in good yields and purity
by reaction with semicarbazide hydrochloride in water, 3-amino-1,2,4-triazole in methanol, and 5-aminotetrazole in diethyl ether. The
obtained salts were characterized by NMR and infrared spectroscopy, elemental analysis, thermal analysis, and small-scale safety testing
(
impact and friction sensitivity). The measured densities and standard enthalpy of formation, as well as calculated performance
characteristics are reported. The compounds are thermally stable up to 180–210°C and insensitive to mechanical stimuli and have slightly
better performance than trinitrotoluene with regard to calculated detonation parameters.
Keywords: biimidazoles, 4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole, energetic salts, explosive properties, synthesis.
Many of nitro and amino-nitro derivatives of diazoles
imidazoles and pyrazoles) are known for their good
hydrogen bonding causes an increase in the lattice energy
that makes the compounds less sensitive to thermal and
mechanical stimuli.5
(
–8
thermal stability, low sensitivity, and excellent perfor-
mance.1 One of them is 4,4',5,5'-tetranitro-1H,1'H-2,2'-bi-
imidazole (TNBI) which combines relative insensitivity to
,2
Examples of such compounds include 3,6-dihydrazinyl-
1,2,4,5-tetrazinium TNBI salt. Its synthesis and properties
9
10
various stimuli (especially in the form of dihydrate,
were reported by Chavez and Oxley. Chavez described
,4
TNBI·2H
2
O) and favorable detonation parameters.3 Its
also synthesis and energetic properties of amino-substituted
guanidinium TNBI salts.1
1,12
Hydrazinium and guanyl-
synthesis can be performed at low cost from readily avai-
lable starting materials. Unfortunately, strong hygroscopic
properties, high acidity, and activity toward nucleophiles at
ureanium salts of TNBI were synthesized and characterized
by Kim and Kim.13 Hydrazinium and ammonium salts of
3
14
positions 1 and 1' prevent its practical application.
TNBI were also described by Paraskos in 2015. Most of
One approach to solve this problem is the formation of
TNBI salts with nitrogen-rich cations. High percentage of
nitrogen in these compounds enhances density, improves
oxygen balance, and produces larger amount of gaseous
products upon decomposition. Protonated amines derived
from guanidines, azoles, and azines are preferred because
the large number of N–N and C–N bonds results in a high
positive enthalpy of formation. In addition, the extensive
these compounds are not hygroscopic, have high detonation
parameters, low sensitivity, and high thermal stability. In
the present article, synthesis and explosive properties of bis-
(semicarbazidium) (1), bis(3-amino-1H-1,2,4-triazol-4-ium)
(2), and bis(5-amino-4H-tetrazol-1-ium) (3) 4,4',5,5'-tetra-
nitro-2,2'-biimidazol-1-ides are described.
The synthetic routes that were used in this work are
presented in Scheme 1. The synthesis of 2,2'-biimidazole (4)
0
009-3122/17/53(6/7)-0697©2017 Springer Science+Business Media New York
6
97

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 697–701
Scheme 1
from ammonium acetate and aqueous glyoxal was performed
thermal decomposition is fast (narrow decomposition
peaks) and proceeds in one apparent step that can be
14
according to literature method. Nitration of compound 4 with
nitric acid in a mixture of phosphoric acid and phosphorus(V)
oxide followed by recrystallization from water gave TNBI
attributed to the breaking of the C–NO bonds in TNBI
2
anions followed immediately by the degradation of the
carbon–nitrogen backbone. At lower temperatures, the
samples do not undergo any changes which are
accompanied by mass or energy exchange (no mass loss
nor phase transitions). This means that salts 1–3 are not
hygroscopic.
The onset of thermal decomposition of semicarbazidium
salt 1 takes place at ~187°C, and the decomposition peak
temperature is ~190°C. 3-Amino-1,2,4-triazolium salt 2 is
the most thermally stable as it displays the highest
decomposition temperature of 211°C. Under the same
conditions, 5-aminotetrazolium salt 3 begins to decompose
at a temperature that is lower by 30°C. Moreover the
decomposition is much faster and accompanied by a higher
gas release (mass loss of approx. 85%). A mass increase
seen in the TG curve at the beginning of decomposition of
salt 3 (Fig. 3) is caused by vigorous gasification of the
16
dihydrate (5), free of sulfate impurities, in 30% yield. Bis-
(
(
semicarbazidium) 4,4',5,5'-tetranitro-2,2'-biimidazol-1-ide
1) was synthesized by the ion-exchange reaction from
TNBI disodium salt and semicarbazide hydrochloride in
water. 3-Amino-1,2,4-triazolium salt 2 was precipitated
from methanol solution of TNBI upon addition of a
solution of 3-amino-1,2,4-triazole in methanol. 5-Amino-
tetrazolium salt 3 was formed after mixing solution of
TNBI in diethyl ether and powdered 5-aminotetrazole.
Simultaneous thermal gravimetric and differential thermal
analyses (TG/DTA) were carried out using a LabSys-TG/DTA
apparatus (Setaram). Samples of ~8 mg were heated from
2
0 to 400°C, at a rate of 5°C/min in contact with
atmosphere. TG/DTA thermograms of the TNBI salts 1–3
are presented in Figures 1–3. Under the experimental condi-
tions, all compounds start to decompose above 180°C. The
Figure 1. TG/DTA curves of bis(semicarbazidium) 4,4',5,5'-
tetranitro-2,2'-biimidazol-1-ide (1).
Figure 2. TG/DTA curves of bis(3-amino-1H-1,2,4-triazol-4-ium)
4,4',5,5'-tetranitro-2,2'-biimidazol-1-ide (2).
6
98

Chemistry of Heterocyclic Compounds 2017, 53(6/7), 697–701
Table 1. Performance and sensitivity properties of compounds 1–3
Parameter*
1
2
3
Empirical formula
M, g·mol–1
N, %
C
8
H
12
N
14
O
10
C
10
H
10
N
16
O
8
8 8 18 8
C H N O
464.27
42.24
–41.36
1.65
482.29
46.47
–56.40
1.64
484.26
52.06
–39.65
1.54
OB, %
d, g·cm–3
T
decomp, °C
190
215
184
IS, J
>20
>20
>20
FS, N
>360
9583
–13.9
>360
11353
+113.2
>360
9848
+478.1
ΔH
c
°, J·g–1
°, kJ·mol–1
ΔH
f
Cheetah values
D, m·s–1
P, GPa
Figure 3. TG/DTA curves of bis(5-amino-4H-tetrazol-1-ium)
,4',5,5'-tetranitro-2,2'-biimidazol-1-ide (3).
7345
20.23
3793
3048
7163
19.30
3798
3104
7341
19.58
4245
3626
4
U, J·g–1
sample. Sign of the violent decomposition can be seen also
in Figure 2, but it is less intense. The observed trend in the
course of thermal degradation of salts 2 and 3 is obvious
and expected as the presence of two tetrazolium cations in
salt 3 provide both more energy and a higher nitrogen
content in the molecule.
T, K
*
N – nitrogen content; OB – oxygen balance; d – density, pressed pellet;
T
decomp – temperature of decomposition (DSC onset); IS – impact
sensitivity; FS – friction sensitivity; ΔH
standard enthalpy of formation; D – velocity of detonation; P – detonation
pressure; U – total energy of detonation; T – detonation temperature.
c
° – heat of combustion; ΔH
f
° –
Friction sensitivity measurements were performed with
BAM friction tester. The impact sensitivity was determined
by the Fall Hammer method with a five kilogram drop
hammer. A water calorimeter (static jacket) equipped with
an oxygen bomb was used for the calorimetric measure-
ments. Pressed samples of about 2.0 g were loaded in open
quartz crucibles and initiated with an electrically heated
wire. The calorimeter was calibrated by combusting a benzoic
acid standard in an oxygen atmosphere at a pressure of
Only semicarbazidium salt 1 has negative standard
–1
enthalpy of formation (–413.9 kJ·mol ). The most positive
–1
enthalpy of formation (+478 kJ·mol ) characterizes 5-amino-
tetrazolium salt 3 which has the largest number of single
and double N–N bonds. Also for this reason, compound 3
–1
has the highest detonation energy (4245 J·g ) and
detonation temperature according to the calculations.
Thus, new energetic salts were easily prepared in good
yield and purity by reaction of 4,4',5,5'-tetranitro-1H,1'H-
2,2'-biimidazole with semicarbazide, 3-amino-1,2,4-
triazole, and 5-aminotetrazole. The investigated com-
pounds rank only slightly higher than trinitrotoluene with
regard to calculated detonation parameters, but owing to
their high nitrogen content, low detonation temperature,
stability, and insensitivity to mechanical stimuli they may
be used in low-vulnerability explosive compositions.
3
.0 MPa just prior to testing. The reported values are the
average of three single measurements. The enthalpy of
formation was calculated at 25°C using a Hess thermo-
chemical cycle with an assumption that the combustion
products contain solely carbon dioxide, water, and nitrogen.
1
7
The Cheetah code was used to estimate theoretically
the combustion and detonation parameters of the tested
explosive. The Becker–Kistiakowsky–Wilson equation of
state (BKW EOS) was assumed to characterize the physical
properties of the gaseous products. The BKW EOS set of
1
8
Experimental
IR spectra were recorded on a PerkinElmer Spectrum
parameters α 0.5, β 0.298, κ 10.50, and Θ 6620, as well as
the experimental densities and the values of formation
enthalpies were used in the calculations.
BX-FTIR spectrometer equipped with
a
Smiths
The physical and explosive properties of TNBI salts 1, 2
and 3 are listed in Table 1. All TNBI salts are quite
insensitive to mechanical stimuli. Even the least thermo-
dynamically stable 5-aminotetrazolium salt 3 proves to be
as insensitive to friction and impact as trinitrotoluene
DuraSamplIR II ATR device; solid powdered samples were
1 13 15
used. H, C, and N NMR spectra were recorded on a
Bruker Avance III spectrometer (500, 125, and 51 MHz,
1
13
respectively). The chemical shifts in H and C NMR
spectra were given with respect to TMS as external
1
9
15
(
(
TNT; 15.0 J, <353 N) or 3-nitro-1,2,4-triazol-5-one
standard. Chemical shifts in N NMR spectra were given
2
0
15
NTO; 22.0 J, >353 N).
Of the three compounds under study 3-amino-1,2,4-
with respect to liquid ammonia. N NMR spectra of
compounds 1 and 2 were recorded by the pulse technique
with inverse gated decoupling (IG) sequence. Measure-
ments were conducted at room temperature in standard
triazolium salt 2 has the most negative oxygen balance and,
–1
therefore, the highest heat of combustion value (11353 J·g ).
6
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Chemistry of Heterocyclic Compounds 2017, 53(6/7), 697–701
5
mm sample tube. DMSO-d
6
was used as the solvent and
Bis(5-amino-4H-tetrazol-1-ium) 4,4',5,5'-tetranitro-
internal locking agent. Elemental analyses of TNBI salts
were performed with a Vario El Cube CHNS-O-Cl analy-
zer in the CHNS mode. Melting points were determined on
a Stuart Scientific SMP3 apparatus. TG/DTA were carried
out using a Setaram LabSys-TG/DTA apparatus. Differen-
tial scanning calorimetry (DSC) measurements to deter-
mine the melt and decomposition temperatures (about 2.0 mg
of each energetic material) were performed in covered
Al-containers containing a hole (0.1 mm) in the lid for gas
release and a nitrogen flow of 20 ml per minute on a
Linseis DSC PT10 apparatus calibrated with standard pure
indium and zinc at a heating rate of 5°C/min. Ammonium
acetate (Chempur), 40% aqueous glyoxal (Carl Roth),
methanol (POCh), phosphorus(V) oxide (Carl Roth), phos-
phoric acid (Chempur), nitric acid (Merck-Millipore),
sodium hydroxide (Chempur), semicarbazide hydrochloride
2,2'-biimidazol-1-ide (3). TNBI dihydrate (5) (3.50 g,
10 mmol) was dissolved in diethyl ether (60 ml) at room
temperature. Powdered 5-aminotetrazole (1.70 g, 20 mmol)
was added to the solution in one portion with stirring. The
resulting suspension was stirred at 20°C for 24 h. The
orange solid product was separated by filtration under
reduced pressure, washed with diethyl ether (50 ml), and air-
dried for 24 h at 50°C. Yield 4.26 g (88%), yellow powder,
–1
mp 184–186°C (decomp.). IR spectrum, ν, cm : 3010,
2694, 2360, 1706, 1484, 1373, 1301, 1208, 1114, 1026,
1
857, 812, 754, 704, 678, 619. H NMR spectrum, δ, ppm:
13
8.25 (4H, br. s, H aminotetrazole). C NMR spectrum,
δ, ppm: 138.7; 139.2; 156.4. 15N NMR spectrum, δ, ppm:
44.2; 110.6; 152.1; 236.3; 359.3. Found, %: C 19.88;
H 1.70; N 51.85. C
H 1.67; N 52.06.
8
H
8
N
18
8
O . Calculated, %: C 19.84;
(
5
Sigma-Aldrich), 3-amino-1,2,4-triazole (Merck-Millipore),
-aminotetrazole (ABCR) were used as supplied.
This work was supported by the Ministry of Science and
Higher Education through the Institute of Chemistry,
Military University of Technology in Warsaw, under Grant
RMN 08-895 and 08-729/2015. Financial support of this
work by the Ludwig-Maximilian University of Munich
(LMU), the U. S. Army Research Laboratory, the Armament
Research, Development and Engineering Center of the
Office of Naval Research under grant no. ONR.N00014-12-
1-0538, and the Bundeswehr – Wehrtechnische Dienststelle
für Waffen und Munition under grant no. E/E91S/FC015/
CF049 is gratefully acknowledged.
Bis(semicarbazidium) 4,4',5,5'-tetranitro-2,2'-biimidazol-
1
-ide (1). TNBI dihydrate (5) (3.50 g, 10 mmol) was
dissolved in a solution of sodium hydroxide (0.20 g,
mmol) in distilled water (100 ml) at room temperature.
5
The obtained orange mixture was slowly heated, and next,
at a temperature of 75°C, a solution of semicarbazide
hydrochloride (2.23 g, 20 mmol) in water (25 ml) was
added dropwise within 10 min with stirring. Yellow
precipitate immediately formed with each drop. After cooling
to 5°C, the resultant yellow solid precipitate was filtered
off under reduced pressure, washed with cold water, and air-
dried at 60°C for 24 h. Yield 1.99 g (43%), yellow plates,
The authors thank Dipl.-Chem. Tomasz Witkowski,
Department of Chemistry, LMU, for his help and support.
–
1
mp 195–197°C (decomp.). IR spectrum, ν, cm : 3447,
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8
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