Preparation and characterization of nitrogen-rich bis-1-methylimidazole1H,1′H-5,5′-bistetrazole-1,1′-diolate energetic salt

Article abstract of DOI:10.1007/s10973-018-7481-7

A new nitrogen-rich energetic salt of bis-1-methylimidazole 1H,1′H-5,5′-bistetrazole-1,1′-diolate salt, (1-M)₂BTO, was synthesized and characterized (FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, and X-ray single-crystal diffraction). Results indicated that (1-M)₂BTO crystallizes in the triclinic space group P-1. The thermal decomposition behavior of (1-M)₂BTO was determined by differential scanning calorimetry (DSC) and thermogravimetric tandem infrared spectroscopy. The decomposition peak temperature of (1-M)₂BTO was 530 K, which suggested that the salt is strong heat resistance. The apparent activation energies were 130.56 kJ mol^?1 (Kissinger’s method) and 132.50 kJ mol^?1 (Ozawa’s method), respectively. The enthalpy of formation for the salt was calculated as 917.3 kJ mol^?1. The detonation velocity and detonation pressure of (1-M)₂BTO were 7448 m s^?1 and 20.7 GPa, respectively, using the Kamlet-Jacobs equation. Furthermore, the sensitivity test results showed that its impact sensitivity is greater than 50 J and friction sensitivity is 180 N, indicating that it has a lower sensitivity.

Full text of DOI:10.1007/s10973-018-7481-7

Journal of Thermal Analysis and Calorimetry
https://doi.org/10.1007/s10973-018-7481-7(0123456789(). -, vo Vl
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Preparation and characterization of nitrogen-rich bis-1-
methylimidazole1H,10H-5,50-bistetrazole-1,10-diolate energetic salt
Liqiong Luo1 Bo Jin1 Rufang Peng1 Yu Shang1 Lipengcheng Xiao1 Shijin Chu1
•
•
•
•
•
Received: 1 March 2018 / Accepted: 14 June 2018
´
´
Ó Akademiai Kiado, Budapest, Hungary 2018
Abstract
A new nitrogen-rich energetic salt of bis-1-methylimidazole 1H,10H-5,50-bistetrazole-1,10-diolate salt, (1-M)2BTO, was
1
synthesized and characterized (FT-IR, H NMR, 13C NMR, elemental analysis, and X-ray single-crystal diffraction).
Results indicated that (1-M)2BTO crystallizes in the triclinic space group P-1. The thermal decomposition behavior of (1-
M)2BTO was determined by differential scanning calorimetry (DSC) and thermogravimetric tandem infrared spectroscopy.
The decomposition peak temperature of (1-M)2BTO was 530 K, which suggested that the salt is strong heat resistance. The
apparent activation energies were 130.56 kJ mol-1 (Kissinger’s method) and 132.50 kJ mol-1 (Ozawa’s method),
respectively. The enthalpy of formation for the salt was calculated as 917.3 kJ mol-1. The detonation velocity and
detonation pressure of (1-M)2BTO were 7448 m s-1 and 20.7 GPa, respectively, using the Kamlet-Jacobs equation.
Furthermore, the sensitivity test results showed that its impact sensitivity is greater than 50 J and friction sensitivity is
180 N, indicating that it has a lower sensitivity.
Keywords Bis-1-methylimidazole Á 1H,10H-5,50-bistetrazole-1,10-diolate Á Energetic properties Á Crystal structure
Introduction
A very promising candidate that fulfills a variety of the
desirable properties is 1H,10H-5,50-bistetrazole-1,10-diolate
(BTO) since it was firstly reported by Tselinskii in 2001
[16]. Nitrogen content and oxygen balance of BTO are 66.7
and –28.2%, respectively, because two hydroxyl groups are
introduced in the tetrazoles. Thus, it can easily form intra-
or intermolecular hydrogen bonds. The hydroxyl hydrogen
of BTO is acidic and makes it easy to separate from the
salt. Therefore, BTO is a good candidate of energetic
anions [17, 18]. Recently, a series of energetic salts based
on BTO anion were synthesized as potential energetic
materials, such as diuronium 1H,10H-5,50-bistetrazole-1,10-
diolate [19], 1,2,4-triazolium, 3-amino-1,2,4-triazolium,
2-methylimidazolium, dicyandiamidine [20], bis(semicar-
bazide) 5,50-bistetrazole-1,10-diolate [21]. The most repre-
Energetic materials including explosives, propellants,
pyrotechnics play an important role in the materials and
technology [1, 2], whereas nitramines including RDX,
HMX, and CL-20 decompose into a significant mass of
toxic products such as nitro- and nitrosoamines after
degradation [3–5]. Therefore, exploring environment-
friendly and high-energy density materials (HEDMs)
insensitive to impact and friction is becoming an intensi-
fying endeavor worldwide [6–12]. In pursuit of HEDMs,
azole heterocycles and their derivatives circumvent the
drawbacks as well as possess high heat of formation, high
nitrogen content, high density, excellent thermal stability,
and environment friendliness [13–15].
sentative
achievement
was
the
synthesis
of
dihydroxylammonium 5,50-bistetrazole-1,10-diolate (TKX-
¨
50) by Fischer and Klapotke in 2012 [18]. The combination
& Bo Jin
jinbo0428@163.com
between nitrogen-rich cations and BTO anion are expected
to possess excellent energetic properties and perfect
sensitivities.
& Rufang Peng
rfpeng2006@163.com
1
In this study, a new nitrogen-rich energetic salt, (1-
M)2BTO, was synthesized and fully characterized. Its
State Key Laboratory of Environmental-friendly Energy
Materials, Southwest University of Science and Technology,
Mianyang 621010, Sichuan, China
123

L. Luo et al.
Scheme 1 Synthesis route of
(1-M)2BTO
O
N
OH
N OH
Cl
N3
N
OH
Cl
N
NH2OH HCl
NaOH
Cl2
NaN3
DMF
EtOH
HO
N
O
HO
HO
N
N3
CH3
N
+HN
O–
H
O
N
N
N
N
N
N
1-methylimidazole
H2O
N
N
N
6H2O
HCl(g)
Et2O
N
N
N
N
N
N
N
–O
2H2O
H
O
NH+
N
H
2BTO
CH3
(1-M)2BTO
crystal structure, thermal decomposition, and energetic
properties were investigated. The result exhibited that the
title salt is an energetic material with favorable thermal
stability properties.
Table 1 Crystal data and structure refinement parameters of (1-
M)2BTO
Compound
(1-M)2BTO
Empirical formula
Formula mass
CCDC number
Size
C10 H26 N12 O8
442.43
1825802
0.21 9 0.20 9 0.19
150(2)
Results and discussion
Temperature/K
Crystal system
Space group
Synthesis
Triclinic
P-1
As shown in scheme 1,1H,10H-5,50-bistetrazole-1,10-dio-
late dihydrate (H2BTO) can be readily obtained by a four-
step reaction from the raw material glyoxal in accordance
with a previously reported procedure [17]. The target
product (1-M)2BTO was synthesized after H2BTO reacted
with 1-methylimidazole in water with 1:2 molar quantities.
˚
a/A
4.7662(13)
8.579(2)
13.182(4)
80.609(3)
89.133(3)
86.337(3)
530.7(2)
1
˚
b/A
˚
c/A
a/°
b/°
c/°
3
˚
Crystal structure
Cell volume/A
Z
A high-quality crystal of (1-M)2BTO for X-ray single-
crystal diffraction was obtained by slowly evaporating
water at room temperature. The parameters of the structural
analysis are listed in Table 1. The molecular unit and
packing diagram of the salt are shown in Figs. 1 and 2. The
selected bond lengths and bond angles of (1-M)2BTO are
summarized in Table 2. The hydrogen bond parameters are
given in Table 3.
q
calcd/g cm-3
F(000)
Rint
1.384
234
.
0.0445
Data
1869
Restraints
0
Parameters
GOFa on F2
Rb1,[I [ 2r (I)]
xR2,[I [ 2r (I)]
R1, (all data)
xRc2, (all data)
136
1.085
0.0445
The salt crystallizes in the triclinic system space group P-1
with six H2O per molecule and exhibits a density of
1.384 g cm-3 at 150 K, which is lower than that of H2BTO
0.1062
0.0532
0.1109
P
(1.811 g cm-3
)
but superior to that of imidazole
P
aGOF goodness of fit, bR1 ¼ jjFoj À jFcjj= jFoj;
cxR2 ¼
(1.030 g cm-3). As shown in Fig. 1, the energetic salt
(1-M)2BTO can be presented as the form of (C2N8O2)2-
(C4H7N2)?2 Á6H2O, which is composed of a BTO anion, two
1-methylimidazole cations, and six H2O formed by the combi-
nation of ionic bonds and hydrogen bonds each other. The two
hydroxyl H atoms deliver from H2BTO in the reaction, forming
a negative bivalence anion. Although 1-methylimidazole is
h
.
i
1=2
À
Á
À
Á
2
2
x Fo2 À Fc2
x Fo2
weakly alkaline, its ability to attract protons for N(6) atoms is
increased, thereby causing the transfer of proton from BTO to
the N(6) position, and subsequently generating the cation.
Finally, the energetic salt (1-M)2BTO is formed by
123

Preparation and characterization of nitrogen-rich…
Fig. 1 Molecular structure of
(1-M)2BTO
Fig. 2 Ball-and-stick packing
diagram of (1-M)2BTO viewed
down the a-axis (a), b-axis (b),
and c-axis (c). Dashed lines
indicate hydrogen
1-methylimidazole cations and BTO anion through ionic bonds
and hydrogen bonds.
[22]. Additionally, the N–O bond of hydroxyl is
˚
1.321(18) A, which is found between N–O bond (1.370 A)
˚
˚
and N=O bond (1.205 A) [23]. These indicate the two
In the BTO anion (Table 2), the N–N bond lengths range
˚
˚
from 1.310(20) A for N(2)–N(3) to 1.348(19) A for N(3)–
pentagons in the BTO are coplanar in the salt. Some
multiple bonds show that the (1-M)2BTO exists as a large
p-conjugated system.
In the energetic salt, the 1-methylimidazole cations and
BTO anion are interconnected with each other via hydro-
gen bonds. And the hydrogen bond is an important factor in
N(4), which is shorter than the normal N–N bond length
˚
˚
(1.454 A) and longer than the normal N=N bond (1.245 A)
[22]. The C–C bond connecting the two tetrazole moieties
˚
are 1.445(29) A, which is located within the normal range
˚
of 1.32 A for the C=C bond and 1.53 A for the C–C bond
˚
123

L. Luo et al.
˚
85
80
Table 2 Bond lengths/A and bond angles/° for (1-M)2BTO
˚
Length/A Bond
Bond
Angle/°
O(1)–N(1)
N(1)–N(2)
N(1)–C(1)
N(2)–N(3)
N(3)–N(4)
N(4)–C(1)
N(5)–C(4)
N(5)–C(3)
N(5)–C(5)
N(6)–C(4)
N(6)–C(2)
1.321(18) H(1 WB)–O(1W)–H(1WA)
98.08
1.344(18) H(2 WB)–O(2W)–H(2WA) 102.47
1.345(20) H(3 WB)–O(3W)–H(3WA) 112.69
1.310(20) O(1)–N(1)–N(2)
1.348(19) O(1)–N(1)–C(1)
1.328(22) N(2)–N(1)–C(1)
1.316(23) N(3)–N(2)–N(1)
1.369(22) N(2)–N(3)–N(4)
1.462(22) C(1)–N(4)–N(3)
1.312(24) C(4)–N(5)–C(3)
1.357(24) C(4)–N(5)–C(5)
121.88(12)
75
70
129.85(13)
108.26(14)
106.49(12)
110.76(13)
106.01(14)
108.31(16)
126.30(16)
125.39(16)
109.28(17)
108.48(13)
127.01(19)
124.49(19)
107.05(16)
108.66(16)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/cm–1
C(1)–C(1)a 1.445(29) C(3)–N(5)–C(5)
Fig. 3 IR spectrum of (1-M)2BTO
C(2)–C(3)
1.344(28) C(4)–N(6)–C(2)
N(4)–C(1)–N(1)
N(4)–C(1)–C(1)a
N(1)–C(1)–C(1)a
C(2)–C(3)–N(5)
8
530 K
6
Exo
N(6)–C(4)–N(5)
a
4
2
Àx; Ày þ 1; Àz þ 1
Table 3 Hydrogen bonds for (1-M)2BTO
0
D–HÁÁÁA
Length Length Length Angle
(D–H) (HÁÁÁA) (DÁÁÁA) (D–
– 2
HÁÁÁA)
O(1 W)–
H(1WB)ÁÁÁO(2 W)a
O(1 W)–
0.859
0.863
0.865
0.861
1.973
1.966
1.924
1.991
2.801
2.819
2.770
2.843
161.54
– 4
412 K
350
400
450
500
550
600
650
169.94
165.37
169.89
H(1WA)ÁÁÁO(3 W)b
O(2 W)–
Temperature/K
Fig. 4 DSC curve of (1-M)2BTO at 10 K min-1
H(2WB)ÁÁÁO(1 W)c
O(2 W)–
H(2WA)ÁÁÁO(3 W)d
hydrogen bond, which connect tightly between the
1-methylimidazole cations and BTO anion.
O(3 W)–H(3 WB)ÁÁÁO(1)
O(3 W)–H(3WB)ÁÁÁN(1)
O(3W)–H(3WA)ÁÁÁO(1)e
N(6)–H(6A)ÁÁÁO(1)f
0.867
0.867
0.861
0.880
0.880
1.918
2.690
1.950
2.166
2.293
2.776
3.516
2.807
2.891
2.950
c
170.58
159.62
173.24
139.33
131.50
Characterization of (1-M)2BTO
N(6)–H(6A)ÁÁÁN(4)
The structure of (1-M)2BTO was supported further by its
1
corresponding FT-IR, H NMR, 13C NMR, and elemental
a
b
½Àx À 1; Ày; ÀzŠ,
½Àx À 1; Ày; Àz þ 1Š,
½Àx À 2; Ày; ÀzŠ,
d
e
f
analysis. FT-IR spectrum of (1-M)2BTO (Fig. 3) reveals
that the intense broad bands at 3434, 3152, and 2919 cm-1
are attributed to the N–H, =C–H, and –CH3 stretching
vibrations of (1-M)2BTO, respectively. The sharp peak at
1404 cm-1 is ascribed to the bending vibration of –CH3. In
addition, the peak at 732 cm-1 is caused by the out-of-
plane bending vibration of =C–H. Consequently, the N-
oxide of the aromatic tetrazole ring system generates
vibrations at 1384–700 cm-1 [17]. Thus, the FT-IR spec-
trum was suggested that (1-M)2BTO was successfully
prepared.
½Àx À 1; Ày þ 1; Àz þ 1Š, ½x À 1; y; zŠ, ½Àx; Ày þ 1; Àz þ 1Š
stabilizing the crystal structure. Table 3 further lists details
about the hydrogen bonds. In addition, Fig. 2 shows the
extensive hydrogen-bonding interactions between cations
and anions from a complex 3D network along the a-, b-,
and c-axes. The 1-methylimidazole cation is an H-bond
donor, and the BTO anion is a H-bond acceptor. The N(6)
atoms from 1-methylimidazole cation and O(1), N(4)
atoms from the BTO anion are involved in the N(6)–
H(6A)ÁÁÁO(1) hydrogen bond and N(6)–H(6A)ÁÁÁN(4)
123

Preparation and characterization of nitrogen-rich…
– 4
– 3
– 2
– 1
0
Thermal analysis of (1-M)2BTO
100
Thermal behavior of energetic materials is a signification
factor to evaluate their practical safety and storage.
Therefore, differential scanning calorimetry (DSC) and
thermogravimetry–derivative thermogravimetry (TG-
DTG) were used to investigate the thermal behavior of the
new energetic salt. The DSC and TG-DTG curves with a
linear heating rate of 10 K min-1 in flowing high-purity
nitrogen were obtained and were shown, respectively, in
Figs. 4 and 5. Endothermic and exothermic processes both
occur in the DSC curve (Fig. 4). The intense endothermic
peak appeared at a temperature of 412 K, indicating that
the salt began to melt. The strong exothermic decomposi-
tion stage was shown in the DSC curve, and the peak was
observed at 530 K. Thermal behavior of (1-M)2BTO was
further investigated by TG-DTG (Fig. 5), which revealed a
severe mass loss step of 80.2% in the range of 481–558 K.
Thermogravimetric analysis tandem infrared spectrum
(TGA-IR) was used to identify the constituents of the
thermal decomposition gas and understand the thermal
decomposition mechanism of (1-M)2BTO (Fig. 6). The
results showed that main decomposition products were
likely H2O (3750 cm-1), N2O (2240, 2204, 1300, and
714 cm-1), NH3 (964 and 930 cm-1), and NO
(1912 cm-1) [24]. When the temperature increased to
582.7 K, infrared signals were hardly observed, which
indicated that (1-M)2BTO is completely decomposed.
Therefore, the salt was decomposed into H2O, NH3, NOx,
and a small amount of residue. Based on the discussion
above, a possible mechanism for the thermal decomposi-
tion of (1-M)2BTO has been proposed as follows and
illustrated in Fig. 7.
535 K
80
60
80.2%
40
20
0
350
400
450
500
550
600
650
Temperature/K
Fig. 5 TG-DTG curve of (1-M)2BTO at 10 K min-1
H2O
NH3
N2O NO
H2O N2O NH3
N2O
582.7 K
562.3 K
0.12
0.08
0.04
0.00
554.4 K
547.9 K
540.0 K
528.4 K
515.5 K
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/cm–1
Fig. 6 FT-IR spectra of gas products of (1-M)2BTO during decom-
position at individual temperatures
The H NMR and 13C NMR spectra also confirmed the
1
correct structure of (1-M)2BTO. In the H NMR spectrum,
1
Thermal decomposition kinetics of (1-M)2BTO
the signal for the methyl of salt occurred as a singlet at d/
ppm = 3.76 [s, CH3]. The signals in the 13C NMR [DMSO-
d6] spectrum of salt was found at d/ppm = 34.67 [CH3],
and d/ppm = 135.55 [CN4O].
The effects of (1-M)2BTO on the thermal decomposition
kinetics were investigated by DSC at different heating rates
of 5, 10, 15, 20 K min-1 (Fig. 8). The methods of Kis-
singer’s [25] and Ozawa-Doyle’s method [26, 27] were
applied to obtain kinetic parameters, the apparent activa-
tion energy (Ea) and pre-exponential factor (A). The
CH3
N
Fig. 7 Possible mechanism for
the thermal decomposition of
(1-M)2BTO in flowing high-
purity nitrogen
(1 – M)2BTO
H2O
+HN
NH3
N2
Cations decomposition
Decomposed
residue
Anions decomposition
O–
NO
N2O
N
N
N
N
N
N
N
N
–O
Heating
123

L. Luo et al.
Table 5 Calculation of the parameters using Kamlet-Jacobs equation
20 K min–1 540.1 K
15 K min–1 533.3 K
12
8
M/g mol-1 q/g cm-3 N/mol g-1
M/g mol-1 DHfh/kJ mol-1
442.43 1.384 0.0429
17 917.3
10 K min–1 528.3 K
5 K min–1 516.5 K
4
0
The kinetic parameters of Ea and A basing on the
methods of Kissinger and Ozawa-Doyle are derived from
the slope and the intercept of the linear dependence
between Tp and b according to Eqs. (1) and (2). The results
are listed in Table 4.
– 4
– 8
The calculated results by Kissinger and Ozawa-Doyle
methods are similar, and they all fall within the normal
range of the kinetic parameters for the thermal decompo-
sition reaction of solid materials [28]. From Table 4, the
exothermic peak Tp shifts to higher temperatures as the
heating rate increasing and the linear correlation coeffi-
cients are extremely close to 1 demonstrating that the
results are credible. The Arrhenius equation can be
expressed using the obtained Ea (the average of Ek and Eo)
and ln Ak values: ln k = 29.18–131.53 9 103/RT.
350
400
450
500
550
600
650
Temperature/K
Fig. 8 DSC curves of the main exothermic decomposition of (1-
M)2BTO at different heating rates
Kissinger Eq. (1) and Ozawa-Doyle Eq. (2) are as follows,
respectively:
!
ꢀ
ꢁ
b
Tp2
AR
Ea
Ea
ln
¼ ln
À
ð1Þ
ð2Þ
RTp
Energetic properties
lg b ¼ C À 0:4567Ea=RT
Detonation parameters including detonation velocity
(D) and detonation pressure (P) are critical parameters for
energetic materials. The empirical Kamlet-Jacobs equa-
tions [29] were applied to estimate detonation velocity and
detonation pressure for (1-M)2BTO as shown in the fol-
lowing equations:
where Tp is the peak temperature (K), A is the pre-expo-
nential factor (s-1), Ea is the apparent activation energy
(kJ mol-1), R is the gas constant (8.314 J mol-1 K–1), b is
the linear heating rate (K min-1), and C is a constant.
Table 4 Peak temperatures of
b/K min-1
Tp/K min-1
Kissinger’s method
Ozawa–Doyle’s method
the exothermic stage at different
heating rates and kinetic
parameters
Ek/kJ mol-1
ln A/s-1
rk
Eo/kJ mol-1
ro
5
516.5
528.3
533.3
540.1
130.56
29.18
0.994
132.50
0.995
10
15
20
– Δ H Θf
Fig. 9 Born-Haber circle of
ionic salt
m C(s) + n H2(gas) + o N2(gas) + p O2(gas)
Cation anion solid or liquid
Δ HL
– Δ H Θf
anion
Cation (gas) + anion (gas)
– Δ H Θf
cation
123

Preparation and characterization of nitrogen-rich…
Table 6 Energetic properties of
Sample
qa/g cm-3
Tbdec/K
N ? Oc/%
DHdf /kJ mol-1
Pe/GPa
Df/m s-1
ISg/J
(1-M)2BTO compared with
TNT, RDX, TATB
(1-M)2BTO
1.384
1.648
1.806
1.930
530
568
503
597
70.14
18.50
37.84
69.74
917.3
95.3
20.7
19.5
34.9
31.1
7448
6881
8748
8114
[ 50
15
TNTh
RDXh
TATBi
83.8
7.5
50
- 139.7
aCalculated density, bdecomposition peak temperature, cnitrogen and oxygen content, dcalculated molar
e
f
g
h
formation enthalpy of the salts, detonation pressure, detonation velocity, impact sensitivity, Ref. [33].
iRef. [34]
ꢂ
ꢃ
D ¼ 1:01 NM1=2Q1=2 1=2ð1 þ 1:3qÞ
P ¼ 1:558q2NM1=2Q1=2
ð3Þ
ð4Þ
Conclusions
In summary, the energetic salt, (1-M)2BTO was synthe-
sized successfully and its structure was confirmed by sin-
gle-crystal X-ray diffraction and other spectroscopic
analysis. Furthermore, thermal stability analysis and ther-
mal decomposition kinetics suggested that (1-M)2BTO
exhibits good resistance to thermal decomposition of up to
530 K, and incurred 80.2% mass loss in the temperature
range of 481–558 K. The apparent activation energies
obtained through the methods of Kissinger and Ozawa are
130.56 and 132.50 kJ mol-1, respectively, with pre-expo-
nential factor of ln A(s-1) = 29.18. The enthalpy of for-
where D is the detonation velocity (km s-1), P is the det-
onation pressure (GPa), N is the explosive detonation that
generated gas moles per gram (mol g-1), M is the gaseous
product of the average molecular weight (g mol-1), Q is
the explosive detonation chemical energy (kJ g-1) per
gram, and q is the density (g cm-3). The value of Q should
be calculated firstly to calculate the values of D and P. The
Q is determined by heat of formation (DHfh) of the deto-
nation reactants and products.
mation for the salt was calculated as 917.3 kJ mol-1
.
Basing on Born-Haber’s [30] (m, n, o, and p stand for
the factor of C, H2, N2, O2, respectively) energy cycle
(Fig. 9), the standard heat of formation (DHfh) of a salt can
be simplified in the formula (5):
Based on the Kamlet-Jacobs equation, the detonation
velocity and detonation pressure of (1-M)2BTO are
7448 m s-1 and 20.7 GPa, respectively.
DHfhðionic salt; 298 KÞ ¼ DHfhðanion salt; 298 KÞ
þ DHfhðcation salt; 298 KÞ
Experimental
À DHL
ð5Þ
Caution!
where DHL is the lattice energy of salt and can be predicted
using the formula suggested [31]. The calculated standard
enthalpy of formation for the 1-methylimidazole and
BTO2– was 126.0 kJ mol-1 [32] and 587.7 kJ mol-1
[6, 17], respectively. Detonation parameters in the Kamlet-
Jacobs equation are shown in Table 5.
Although we experienced no difficulties in the synthesis
and characterization of the salt, small-scale syntheses are
strongly encouraged. All of compounds should be handled
extremely with care by using the best safety equipment and
the correct experimental manipulation.
The Q estimated through DHfh was 917.3 kJ g-1, and the
theoretically computed detonation velocity (D) and detona-
tion pressure (P) were determined as 7448 m s-1 and
20.7 GPa, which show superior detonation performance than
those of TNT (6881 m s-1, 19.50 GPa) and lower than those
of RDX (8478 m s-1, 34.9 GPa), respectively, (Table 6).
Sensitivity must be seriously considered in the research
because it is closely related to the safety of handling and
storage of explosives. For initial safety testing, impact and
friction sensitivities are measured using the fall hammer test
with approximately 30 mg of samples (10 kg drop hammer).
The result presents that (1-M)2BTO has low impact sensi-
tivity ([ 50 J) and low friction sensitivity (180 N), so it may
be applied as insensitive energetic materials owing to their
high nitrogen content, low mechanical sensitivity, good
stability, and environmental compatibility.
General
All chemicals and solvent were purchased commercially
from Aladdin (Shanghai China) and used as received.
Fourier-transform infrared spectroscopy (FT-IR) was
recorded with a Nicolet-5700 FT-IR spectrometer using
pressed KBr pellet in the range from 4000 to 400 cm-1. 1H
NMR and 13C NMR spectra of (1-M)2BTO were performed
on a JEOL GSX 600 MHz nuclear magnetic resonance
(NMR) spectrometer in a d6-DMSO solution by using
tetramethylsilane as an internal standard. X-ray single-
crystal diffraction analysis was collected by a Bruker Smart
APEX II CCD diffractometer. DSC was performed by a
Q200 DSC instrument (TA Instruments, USA) in flowing
123

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H2BTO was synthesized by a four-step reaction from the
raw material glyoxal in accordance with a previously
reported procedure [17]. Firstly, glyoxal was treated with
hydroxylamine to form glyoxime. Glyoxime was then
chlorinated with Cl2 gas in ethanol. And then chloro/azido
exchange occurred and yielded diazidoglyoxime. Diazi-
doglyoxime was cyclized under acidic conditions (HCl gas
in diethyl ether) to produce H2BTO.
Bis-1-methylimidazole 1H,10H-5,50-bistetrazole-
1,10-diolate salt (1-M)2BTO
H2BTO (206 mg, 1 mmol) was dissolved in 5 mL of dis-
tilled water. Then, 0.16 mL 1-methylimidazole was added
dropwise to the above solution with magnetic stirring. The
mixed solution was refluxed for 10 min. After cooling to
room temperature, (1-M)2BTO crystallized as a solid. The
samples were filtered and were dried under vacuum, yield
287 mg (0.65 mmol, 76%). 1H NMR (600 MHz, [D6-
]DMSO, 25 °C) d/ppm = 8.37, 7.41, 7.30, 3.76. 13C NMR
(150 MHz, [D6]DMSO, 25 °C) d/ppm = 137.18, 135.55,
124.06, 122.38, 34.67. IR (KBr) v cm-1: 3434, 3152, 2919,
2850, 1631, 1404, 1356, 1282, 1234, 1165, 1057, 999, 732,
626, 503. Elemental analysis (EA): Found/%: C 27.12, H
5.88, N 37.97; Calculated/%: C 27.15, H 5.92, N 37.99.
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Acknowledgements This work was supported by the financial sup-
port received from the Science Challenge Project (Project No.
TZ2018004), the National Natural Science Foundation of China
(Project No. 51372211), the China Academy of Engineering Physics
Research Institute (Project No. 18zh0079) and Open Project of State
Key Laboratory Cultivation Base for Nonmetal Composites and
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