G Model
CCLET 4042 No. of Pages 4
2
Q. Wang et al. / Chinese Chemical Letters xxx (2017) xxx–xxx
B.01) [14]. The geometric optimization of the functional with 6-31
G** basis set, and single energy points were calculated at the MP2
full)/6-311++G** level. The calculated heats of formation of
compounds 2a, 2b and 2d–2g range from 26.0 kJ/mol to
+
(
9
49.1 kJ/mol (Table 1). Due to cyano and azido groups, triazenes
2
a and 2g exhibit high positive heats of formation (949.1 kJ/mol
and 923.2 kJ/mol, respectively). The densities of triazene com-
pounds range from 1.49 g/cm to 1.55 g/cm, except compound 2d
Scheme 1. Synthesis of triazenes 2a–2f.
(
1.32 g/cm), as measured using a gas pycnometer (Table 1).
Based on heats of formation and densities, the detonation
performance of 1,3-bis(2-alkyltetrazol-5-yl)triazenes was pre-
dicted using the EXPLO5 (5.05 version) program (Table 1). Without
surprise, long alkyl substituents have a negative effect on
detonation performance but a benefit to reducing the melting
point. The negative effect of increased molecular weight is more
than offset introduction of energetic moieties. The detonation
velocities and pressures of most 1,3-bis(2-alkyltetrazol-5-yl)
triazenes (except 2b and 2d) were predicted between 6992 m/s
and 7122 m/s, and 16.6 GPa and 18.4 GPa, respectively, which are
comparable with TNT but lower than those of 1,3-bis(2-methyl-
tetrazol-5-yl)triazene.
Scheme 2. Synthesis of 2g.
intense absorption bands at 1230 cmꢁ1 and 1460 cm are assigned
to the tetrazole ring. The single characteristic resonances at
4.19–14.61 in H NMR spectra belong to the amino groups of
ꢁ1
d
1
1
13
triazenes.
C NMR spectra of tetrazole ring show a weak
resonance, even not in 2b, ranging from 165.4 to 169.0 ppm. The
1
13
other resonances in H NMR and C NMR spectra are produced by
substitute groups of tetrazoles.
3
. Conclusion
The thermal properties of triazenes 2a, 2b and 2d–2g were
investigated using differential scanning calorimetry (DSC). Grati-
fyingly, most of triazenes display suitable melting points (from
In summary, a series of novel nitrogen-rich energetic com-
pounds based on tetrazolyl triazene were synthesized using a
straightforward method. Most of these compounds exhibit low
ꢀ
ꢀ
8
1 C to 106 C) for melt-cast explosives, except 2e (not observed)
ꢀ
ꢀ
melting points ranging from 81 C to 106 C, which are suitable for
melt-cast explosives. All compounds show moderate thermal
ꢀ
and 2f (peak, 135 C) (Fig. 1). With a long alkyl chain on tetrazole,
the tetrazolyl triazene shows a lower melting point than methyl
substituted one. In contrast, vinyl substituent cannot lower the
melting point because of the planarity caused by conjugation effect
ꢀ
stabilities with onset decomposition temperature between 158 C
ꢀ
ꢀ
and 207 C, except compound 2a (139 C). The detonation
performance of most compounds is comparable with TNT, while
these compounds are more sensitive to impact stimulation than
TNT. Among these compounds, 1,3-bis(2-azidoethyltetrazol-5-yl)
triazene (2g) displays the best performance, including a low
between C C double bond and tetrazole ring. For triazene 2f,
¼
hydroxyl groups enhance the effect of hydrogen bond, which
results in a higher melting point than other long alkyl substituted
tetrazolyl triazenes. On the other hand, substituents show
electronic effect on thermal stability of tetrazolyl triazene since
triazene compound always decomposes from the rupture of N ꢁꢁ N
single bond in the triazene moiety upon heating [13]. Thus,
ꢀ
melting point (106 C), moderate onset decomposition tempera-
ture (183 C) and good detonation performance (D: 7087 m/s; P:
ꢀ
1
7.6 GPa), apart from impact sensitivity (0.75 J).
electron-donating substituent causes higher thermal stability
4
. Experimental
ꢀ
(
such as 2d, which decomposes onset at 207 C), whereas
electron-withdrawing one gives lower thermal stability (such as
1H NMR and 13C NMR spectra were recorded on a 400 MHz
Buruker Avance 400) nuclear magnetic resonance spectrometers
ꢀ
2e, which decomposes onset at 158 C).
(
Impact sensitivities were determined by using the standard
operating at 400 and 100 MHz, respectively, by using DMSO-d as
6
BAM techniques. As shown in Table 1, due to lack of hydrogen bond,
all 1,3-bis(2-alkyltetrazol-5-yl)triazenes are very sensitive to
impact, similar with 1,3-bis(2-methyltetrazol-5-yl)triazene, espe-
cially 2g (bearing two azido groups) showing an impact sensitivity
of 0.75 J.
solvent and field locking solvent. IR spectra were recorded using
KBr pellets for solids on a Bruker Alpha FT-IR-Spektrometer. The
melting (peak) and decomposition (onset) points were obtained on
a differential scanning calorimeter (METTLER TOLEDO) at a scan
ꢀ
rate of 5 C/min. The preparation of substituted-5-aminotetrazoles
Heats of formation of 1,3-bis(2-alkyltetrazol-5-yl)triazenes
were calculated using the program package Gaussian 09 (Revision
is deposited in Supporting information.
4
.1. General procedure for synthesis of triazene 2a–2e
2
NaNO (0.690 g, 10 mmol, 0.5 equiv.) in water (40 mL) was
added dropwise to a solution of substituted-5-aminotetrazole (1a–
1
e, 20 mmol) and concentrated HCl (4 mL, 48 mmol) in water
ꢀ
(
100 mL) at 0 C. After 2 h, the reaction was stirred additional 2 h at
room temperature. The precipitate was filtered, washed with
water, and dried to provide high purity product.
1
,3-Bis(2-cyanomethyltetrazol-5-yl)triazene (2a): White solid
ꢀ
ꢀ
ꢁ1
(
2
(
(
(
2.234 g, 86%); mp 85 C, 139 C (dec.); IR (KBr, cm ): ~v 3490, 3454,
999,1603,1468,1378,1301,1229,1041, 936, 828, 776, 741; H NMR
400 MHz, DMSO-d
100 MHz, DMSO-d
6 5
C H N13, 259.19) calcd.: C 27.80, H 1.94, N 70.25; found: C 28.22, H
1
13
6
):
):
d
d
14.61 (s, 1H), 6.24 (s, 4H); C NMR
166.2, 113.4, 41.1; Elemental analysis:
6
ꢀ
Fig.1. DSC thermograms of compounds 2a, 2b and 2d–2g (heating rate of 5 C/min).
Wang, Qi
