The crystal structure and synthesis mechanism of 3,6-Bis(3,5- dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT): A key precursor of s-tetrazine

Article abstract of DOI:10.1002/jhet.1948

The single crystal structure of 1,1′-bis (3,5-dimethyl-pyrazole) methenehydrazine (BDM) was determined by X-ray single crystal diffraction for the first time. The obtained experimental results indicated that BDM was the intermediate of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT), which was the key precursor of s-tetrazine. By this evidence, the preparation mechanism of BDT was proved: At 318.15 K, triaminoguanidine and pentanedione reacted to achieve the intermediate (BDM) by molecular nucleophilic addition and intramolecular nucleophilic substitution; when heated to 363.15 K, BDT was then generated by two molecules of BDM with nucleophilic substitution reaction. Furthermore, the thermal decomposition properties and also the non-isothermal kinetic parameters have been investigated in the present work.

Full text of DOI:10.1002/jhet.1948

Month 2014
The Crystal Structure and Synthesis Mechanism of 3,6-Bis(3,5-
dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT): A Key
Precursor of S-tetrazine
Jian-Guo Zhang,* Jin-Ting Wu, Mou Sun, Jin-Ling Feng, Tong-Lai Zhang, and Zun-Ning Zhou
State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China
*
E-mail: zhangjianguobit@yahoo.com.cn
Received November 10, 2012
DOI 10.1002/jhet.1948
Published online in Wiley Online Library (wileyonlinelibrary.com).
0
The single crystal structure of 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine (BDM) was determined by
X-ray single crystal diffraction for the first time. The obtained experimental results indicated that BDM was the
intermediate of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT), which was the key
precursor of s-tetrazine. By this evidence, the preparation mechanism of BDT was proved: At 318.15K,
triaminoguanidine and pentanedione reacted to achieve the intermediate (BDM) by molecular nucleophilic
addition and intramolecular nucleophilic substitution; when heated to 363.15 K, BDT was then generated by
two molecules of BDM with nucleophilic substitution reaction. Furthermore, the thermal decomposition
properties and also the non-isothermal kinetic parameters have been investigated in the present work.
J. Heterocyclic Chem, 00, 00 (2014).
INTRODUCTION
the aromaticity and thermal stability of the whole mole-
cule; environmental harmony, just only giving out N2
High nitrogen heterocyclic compounds have developed
into a series of promising energetic materials in recent years
and attracted researchers all over the world into the five
membered (imidazole, triazole, furazan) and six membered
and CO mostly when combust completely; moreover,
2
some of these energetic materials show low sensitivity
to static electricity, friction, and impact. All of these
mentioned earlier make high nitrogen heterocyclic
compounds as promising applications in the fields of
propellants, low smoke and residues pyrotechnics, and
new insensitive explosives [2–6].
Among these high nitrogen heterocyclic compounds,
tetrazine was a typical six membered heterocyclic
compound with high nitrogen content of 68.3%, just
lower than 80.0% of the tetrazole. And tetrazine ring was
(
tetrazine, triazine) heterocyclic compounds [1]. All these
compounds have some common points: high enthalpy of for-
mation, which mainly comes from the high energy N–N
bonds, C–N bonds, and the large ring strain; relatively high
melting point, just because of the high dense molecular
structures and the large amount of hydrogen bonds in their
nitrogen and hydrogen systems; the lone pair electrons of ni-
trogen atoms participated the conjugated system, increasing
©
2014 HeteroCorporation

J.-G. Zhang, J.-T. Wu, M. Sun, J.-L. Feng, T.-L. Zhang, and Z.-N. Zhou
Vol 9999
slowly. And precipitate was collected by filtration, washed with
distilled water, and dried in explosion-proof water-bath dryer.
Elemental analysis of BDM (C11N6H16) (%): calculated: C,56.90;
N,36.21;H,6.90; found: C,56.93;N,36.22;H,6.85.
BDT: triaminoguanidine hydrochloride (9.00 g, 0.075 mol) was
dissolved into deionized water(60 mL). The resulting solution was
kept in 318.15 K, and dropwise addition was taken for Pentanedione
(15 mL, 0.15 mol), stirring for 1 h. Then increasing to 363.15 K
slowly, refluxing and stirring for an additional 1 h. Afterward, the so-
lution was cooled down to room temperature slowly, filtering and
washing with plenty distilled water. The residue was dried in explo-
sion-proof water-bath dryer. Elemental analysis of BDT
effective and outstanding in building structural unit in the
High-energy Insensitive Energetic Materials design,
especially the 1,2,4,5-tetrazine (s-tetrazine) ring [6–8].
Many researchers have done a lot of work on the
s-tetrazines all over the world not just only for their good
stability but also for the outstanding chemical properties
they have shown[2,9,10]. Hiskey [1,5,8–13] reported the
synthesis method and performances of a series of
tetrazines, and Klapötke [14–16] also have done a lot of
work on the tetrazine, both in theoretical and experimental
aspects.
(C12N8H16) (%): calculated: C,52.92;N,41.23;H,5.85; found:
3
,6-Bis (3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-
C,52.94;N,41.18;H,5.88.
tetrazine (BDT) was the most essential intermediates to
synthesize the promising high nitrogen energetic com-
pounds of s-tetrazine. At the same time, they can also
serve as ligands to prepare some significant complexes.
Therefore, in-depth analysis of their crystal structures
and synthesis mechanism are particularly important.
Although many researchers have done a lot of work on
BDT, but the preparation mechanism of BDT has not been
proven yet [13].
Data collection and structure determination.
After few
days’ growing, a yellow flaky crystal of BDM and a colorless
block single crystal for BDT were chosen for X-ray
determination. The X-ray diffraction data collection was
+
performed on a Rigaku AFC-10/Saturn 724 CCD detector
diffractometer with graphite monochromatic Mo Ka radiation
(l = 0.071073 nm). The structures were solved by direct methods
using SHELXS-97[17] and refined by full-matrix least squares
2
methods on F with SHELXL-97[18]. All non-hydrogen atoms
were obtained from the difference Fourier map and subjected to
2
anisotropic refinement by full-matrix least squares on F . Detailed
In order to take a deep study into the synthesis mechanism
of BDT, meaningful experiments have been taken. The
information concerning crystallographic data collection and
structures refinement are summarized in Table 1.
CCDC 884108 and 884109 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
0
crystal structure of 1,1 -bis (3,5-dimethyl-pyrazole) methe-
nehydrazine (BDM) as the intermediate of BDT has been
determined by X-ray diffraction for the first time; as
evidence, the synthesis mechanism of BDT has been
proven at the same time. One step further, the thermal
decomposition mechanism and non-isothermal kinetic
parameters were also studied in present work.
RESULTS AND DISCUSSION
Structure description.
The molecular structure views
EXPERIMENTAL
were shown in Figure 1, and the cell stacking views were
shown in Figure 2, the selected bond distances and angles
were listed in Table 2, 3, and the hydrogen bond lengths
and angles were listed in Table 4.
In BDM molecule, there were two pyrazole rings and a
half-tetrazine ring. These rings were non-coplanar. And
the three ring plane equations were as follows: C(6)-N
General caution. The titled compounds are energetic and
tend to kindle or even explode under certain conditions.
Appropriate safety precautions (safety glasses, face shields,
leather coat, and ear plugs) should be taken, especially when
these compounds are prepared on a large scale.
Material and physical technique.
All chemical reagents
and solvents of analytical grade were bought from the reagents
company (Sinopharm Chemical Reagent Beijing Co., Ltd.,
Beijing, China) and used as supply. Triaminoguanidine
hydrochloride was purchased commercially and recrystallized
twice with distilled water before use.
(
3)-N(4) (flat A): 0.5691x ꢀ 0.8177y + 0.0865z = ꢀ0.4524;
C(8)-C(9)-C(10)-N(6)-N(5) (flat B): 0.3220x ꢀ 0.5530y
.7684z = ꢀ15.1096; C(2)-C(3)-C(4)-N(2)-N(1) (flat C):
0
ꢀ
0.9841x + 0.1117y ꢀ 0.1381z = ꢀ0.6591. Because of the
steric effects, the two pyrazole rings have a rather big angle
Elemental analyses were performed on a Flash EA 1112 full-
automatic trace element analyzer. DSC and TG–DTG measure-
ments were carried out by using Pyris-1 differential scanning cal-
orimeter and Pyris-1 thermogravimetric analyzer (Perkin Elmer,
USA) under dry nitrogen atmosphere with a flowing rate of
ꢁ
of 74.184 , which made the whole molecule low-energy
and stable. And the angle of C(6)-N(3)-N(4) was 120.2 ,
ꢁ
similar with the interior angle of six-membered ring. These
might enlarge the substitution reaction ability of the whole
molecule. All these characteristics made BDM easy to
eliminate a pyrazole ring when the molecule was attacked
from N(4) by another one.
ꢀ
+
1
2
0 mL min . And the crystals were determined by using Rigaku
Saturn 724 CCD detector diffractometer with graphite mono-
chromatic Mo Ka radiation (l = 0.07107 nm).
Synthesis.
BDM: a solution with triaminoguanidine
hydrochloride (9.00 g, 0.075 mol) dissolved with 60 mL deionized
water was charged into three-necked flask. Then, pentanedione
There were two types of hydrogen bonds in BDM mole-
cule, intramolecular and intermolecular hydrogen bonds. Just
as shown in the cell stacking view and the table list, the
intramolecular hydrogen bonds, such as N(4)–H(4)A.. .N(5)
(15.00 mL, 0.15 mol) was slowly dropped at 318.15 K with strong
stir for 1 h. The solution was cooled down to room temperature
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
The Crystal Structure and Synthesis Mechanism of 3,6-Bis(3,5-dimethylpyrazol-1-yl)-
1,4-dihydro-1,2,4,5-tetrazine (BDT): A Key Precursor of S-tetrazine
Table 1
Crystal data and structure refinement parameters.
BDM
BDT
Empirical formula
Formula mass
Crystal system
Space group
Temperature (K)
Z
C
11
H
16
N
6
12 16 8
C H N
232.30
monoclinic
P2 /n
153(2)
4
272.33
monoclinic
P2 /c
1
1
93(2)
4
a, b, c (nm)
h, k, l
6.795(7), 6.893(7), 26.910(3)
12.776(4), 11.426(3), 9.095(3)
ꢀ8–8,ꢀ8–8,ꢀ34–34
90.860(11)
1260(2)
1.224
0.081
496
3.03–27.51
8989
ꢀ16–16,ꢀ14–10,ꢀ11–10
ꢁ
b ( )
V (Å )
90.808(4)
3
1323.1(6)
1.367
0.092
576
3.19–27.50
10618
ꢀ3
D
c
(g cm
)
ꢀ1
m (Mo K
F(0 0 0)
θ Range ( )
a
) (mm
)
ꢁ
Measured reflections
Unique data
2822 [Rint = 0.1357]
3020 [Rint = 0.0243]
R
R
1
, wR
, wR
2
[I > 2s(I)]
(all data)
R
R
1
= 0.2089, wR
= 0.2495, wR
2
= 0.4827
= 0.5037
R
R
1
= 0.0419, wR
= 0.0499, wR
2
= 0.1103
= 0.1169
1
2
1
2
1
2
Goodness of fit
dpmax, dpmin (e nm
1.001
0.904, ꢀ0.552
0.999
0.261, ꢀ0.260
ꢀ3
)
0
BDM, 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine; BDT, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine.
a
2
2
2
2
c
w = 1/[s2(F
o
) + (0.0748p) + 0.1600p], p = (F
o
+ 2F
)/3.
0
Figure 1. The molecular structures of the 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine (BDM) and 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-
tetrazine (BDT).
0
Figure 2. The views of stacking unit cell for 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine (BDM) and 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-
1,2,4,5-tetrazine (BDT).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

J.-G. Zhang, J.-T. Wu, M. Sun, J.-L. Feng, T.-L. Zhang, and Z.-N. Zhou
Vol 9999
Table 2
ꢁ
Selected bond lengths (Å) and bond angles ( ) of BDM.
Bond
Dist.
Bond
Dist.
Bond
Dist.
N(1)–C(2)
N(1)–N(2)
N(2)–C(4)
N(2)–C(6)
N(3)–C(6)
N(3)–N(4)
1.326(11)
1.392(9)
1.387(9)
1.401(11)
1.294(11)
1.345(11)
N(5)–C(8)
N(5)–N(6)
N(5)–C(6)
N(6)–C(10)
C(1)–C(2)
C(2)–C(3)
1.384(11)
1.390(9)
1.411(12)
1.365(11)
1.497(13)
1.439(13)
C(3)–C(4)
C(4)–C(5)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
1.361(13)
1.500(11)
1.516(11)
1.334(12)
1.384(13)
1.502(12)
ꢁ
ꢁ
ꢁ
Angle
( )
Angle
( )
Angle
( )
C(2)-N(1)-N(2)
C(4)-N(2)-N(1)
C(4)-N(2)-C(6)
N(1)-N(2)-C(6)
C(6)-N(3)-N(4)
C(8)-N(5)-N(6)
C(8)-N(5)-C(6)
N(6)-N(5)-C(6)
105.3(7)
111.6(7)
128.6(7)
119.3(6)
120.2(8)
110.4(7)
130.3(7)
119.2(7)
N(1)-C(2)-C(3)
N(1)-C(2)-C(1)
C(3)-C(2)-C(1)
C(4)-C(3)-C(2)
C(3)-C(4)-N(2)
C(3)-C(4)-C(5)
N(2)-C(4)-C(5)
N(3)-C(6)-N(2)
110.2(8)
121.3(9)
128.5(9)
107.1(7)
105.7(7)
131.6(8)
122.7(8)
118.6(8)
N(2)-C(6)-N(5)
C(9)-C(8)-N(5)
C(9)-C(8)-C(7)
N(5)-C(8)-C(7)
C(8)-C(9)-C(10)
N(6)-C(10)-C(9)
N(6)-C(10)-C(11)
C(9)-C(10)-C(11)
115.7(7)
106.4(8)
132.8(9)
120.6(8)
109.0(9)
109.6(8)
119.4(8)
131.0(8)
0
BDM, 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine.
Table 3
ꢁ
Selected bond lengths (Å) and bond angles ( ) of BDT.
Bond
Dist.
Bond
Dist.
Bond
Dist.
N(1)–C(3)
N(1)–N(2)
N(2)–C(1)
N(2)–C(6)
N(3)–C(6)
N(3)–N(4)
Angle
1.325(2)
1.380(1)
1.379(2)
1.398(2)
1.277(2)
1.444(1)
N(4)–C(7)
N(5)–N(6)
N(5)–C(6)
N(6)–C(7)
N(7)–N(8)
N(7)–C(8)
1.392(2)
1.433(1)
1.379(2)
1.274(2)
1.374(1)
1.379(2)
N(7)–C(7)
N(8)–C(10)
C(1)–C(2)
C(1)–C(4)
C(2)–C(3)
1.399(2)
1.414(2)
1.364(2)
1.491(2)
1.414(2)
ꢁ
ꢁ
ꢁ
( )
Angle
( )
Angle
( )
C(6)-N(3)-N(4)
C(7)-N(4)-N(3)
C(6)-N(5)-N(6)
C(7)-N(6)-N(5)
N(3)-C(6)-N(5)
N(3)-C(6)-N(2)
N(5)-C(6)-N(2)
N(6)-C(7)-N(4)
N(6)-C(7)-N(7)
110.65(10)
112.84(9)
N(8)-N(7)-C(8)
N(8)-N(7)-C(7)
C(8)-N(7)-C(7)
C(1)-N(2)-C(6)
N(1)-N(2)-C(6)
C(10)-N(8)-N(7)
C(2)-C(1)-N(2)
C(2)-C(1)-C(4)
N(2)-C(1)-C(4)
111.93(10)
117.51(10)
130.47(11)
129.92(11)
116.86(10)
105.01(10)
105.28(11)
130.12(11)
124.56(11)
N(1)-C(3)-C(2)
N(1)-C(3)-C(5)
C(2)-C(3)-C(5)
C(9)-C(8)-N(7)
C(9)-C(8)-C(11)
N(7)-C(8)-C(11)
C(8)-C(9)-C(10)
N(8)-C(10)-C(9)
N(8)-C(10)-C(12)
110.95(11)
120.02(12)
129.02(12)
105.40(11)
129.87(11)
124.73(11)
106.72(11)
110.93(11)
120.23(11)
114.34(10)
110.62(10)
123.14(11)
121.15(11)
115.68(11)
123.32(11)
120.79(11)
BDT, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine.
Table 4
Hydrogen bond lengths (Å) and bond angles ( ).
ꢁ
d(D–HꢂꢂꢂA)
d(D–H)
d(HꢂꢂꢂA)
d(DꢂꢂꢂA)
∠DHA
BDM-N(4)-H(4)A. . .N(5)
BDM-N(4)-H(4)A. . .N(6)
BDM-N(4)-H(4)B. . .N(6)#1
BDT-N(5)-H(1). . .N(1)
BDT-N(5)-H(1). . .N(3) #1
BDT-N(4)-H(4). . .N(8)
BDT-N(4)-H(4). . .N(6) #2
BDT-C(4)-H(4)B. . .N(3)
0.88
0.88
0.88
0.94
0.94
0.93
0.93
0.98
2.48
2.42
2.18
2.19
2.17
2.19
2.28
2.60
2.794
2.956
3.039
2.620
2.917
2.641
3.027
2.935
101
119
164
106
135
108
137
100
0
BDM, 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine; BDT, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine.
Symmetry transformations for BDM: #1:1/2 ꢀ x, ꢀ1/2 + y, 1/2 ꢀ z.
Symmetry transformations for BDT: #1: x, 1/2 ꢀ y, 1/2 + z; #2: x, 1/2 ꢀ y, ꢀ1/2 + z.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
The Crystal Structure and Synthesis Mechanism of 3,6-Bis(3,5-dimethylpyrazol-1-yl)-
,4-dihydro-1,2,4,5-tetrazine (BDT): A Key Precursor of S-tetrazine
1
and N(4)–H(4)A.. .N(6), linked with the neighboring bonds
to form a large amount of stable five-membered or six-
membered rings. All these rings formed a 2-D lamellar struc-
ture, and the intermolecular hydrogen bonds, just like N(4)–H
was the intramolecular hydrogen bonds between N–H of
tetrazine rings and N atoms of the homolateral pyrazole
rings, such as N(5)–H(1). . .N(1) bond with a length of
2.620 Å. These hydrogen bonds formed steady five-
membered rings with the neighboring bonds. Two was the
faintish weaker intramolecular hydrogen bonds between
the Me-H of the pyrazole rings with N atoms of tetrazine
rings on the same side, such as C(4)–H(4)B. . .N(3) hydro-
gen bond with the length of 2.935 Å. These hydrogen bonds
formed six-membered rings with the neighboring bonds.
Three was the intermolecular hydrogen bonds that connected
the molecule into a huge network in a larger scale.
Synthesis mechanism of BDT. The crystal structure of
BDM as the evidence had indicated that the synthesis of
BDT can be divided into two section: firstly, the formation
of BDM under 318.15 K; secondly, the generation of BDT
under 348.15–363.15 K and refluxing condition. Scheme 1
has shown the mechanism of BDT preparation.
(4)B. . .N(6), connected the 2-D structure into a regular 3D
network that was much more stable in a larger scale.
In BDT molecule, two hydrogen atoms were separated
on different sides of the tetrazine ring, which made the
whole molecule more balance and stable. And there were
also two flats in the BDT molecule: N(2)-N(3)-N(5)-C(6)
(
flat D): 0.6481x + 0.4849y ꢀ 0.5837z = 6.5801; N(4)-N
(6)-N(7)-C(7) (flat E): 0.2664x + 0.8761y ꢀ 0.4019z =
ꢁ
7
.9657. The two flats had an included angle of 33.55 .
The pyrazole rings in the molecule were slightly distorted,
the dihedral angles of C(3)-N(1)-N(2)-C(1) and N(2)-N(1)-
ꢁ
ꢁ
C(3)-C(2) were 0.58 and ꢀ0.20 , homogeneously, N(2)-C
(
1)-C(2)-C(3) and C(1)-C(2)-C(3)-N(1) have dihedral
ꢁ
ꢁ
angles of 0.57 and ꢀ0.24 . Meanwhile, the interior angles
ꢁ
of pyrazole rings also twisted lightly, 1.28–3.93 , compar-
At 318.15 K, intermolecular nucleophilic addition reac-
tion initiated by the aggression of the two hydrazine terminal
amino groups of triaminoguanidine to the carbonyl carbon
ing with standard planar five-membered ring. The distor-
tion of the whole molecule also had an influence upon
the bond length. The bond length of N(3)-N(4) was
atom during which eliminated two molecules of H O; then
2
1
.433 Å, that of N(5)-N(6) was 1.444 Å, and they were
the amino attacked the carbonyl carbon atom, leading to
the occurrence of intramolecular nucleophilic substitution
reaction that also eliminated two molecules of H O; in the
2
meantime, BDM was generated; when heated to 363.15 K,
the intermolecular nucleophilic substitution between two
molecules of BDM bechanced, eliminating two molecules
of pyrazole and generating one molecule of BDT. Just as
both close to the N–N bond. In the meantime, the length
of N(1)-N(2) was 1.380 Å and the length of N(7)-N(8)
was 1.374 Å, also close to the N═N bond.
Many intramolecular and intermolecular hydrogen
bonds of BDT built up a huge 3D network. All these
hydrogen bonds may divide into three categories. One
Scheme 1. The synthesis mechanism of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

J.-G. Zhang, J.-T. Wu, M. Sun, J.-L. Feng, T.-L. Zhang, and Z.-N. Zhou
Vol 9999
shown in Scheme 1, the probability of nucleophilic addition
reaction between carbonyl carbon and the two distinct amino
groups is completely different.
at 509.65–587.75 K temperature range with an exothermic
ꢀ
1
enthalpy of 681.2 J g . There was an exothermic tempera-
ture peak of 539.05K in the process. At 418.35–525.95K
temperature range, BDT performed a rapid weight loss,
maximum weight loss rate occurred at 522.35K, and the to-
tal weight loss of this process was 87.8%; between 522.25
and 773.15K, BDT showed a slow weight loss process with
the weight loss of 12.2%, no remaining residue at last.
Thermal decomposition. For the purpose of investigating
the thermal behavior of the two compounds of BDM and
BDT, the DSC and TG–DTG tests have been conducted
–
1
under the linear heating rate of 10 K min in N atmosphere
2
ꢀ
1
at the flowing rate of 20 mL min , and the curves are
shown in Figures 3 and 4, respectively.
Non-isothermal kinetics analysis.
Kissinger’s method
[
19], Ozawa’s method [20], and Starink’s method [21]
It could be seen from the curves that BDM decomposed
directly, without melting, and the exothermic decomposi-
tion process was in 373.15–399.35 K range with a peak
temperature of 384.05 K. It also could be observed from
the TG–DTG curve that the major weight loss of 92.67%
occurred at 383.55–499.45 K range, and the maximum
weight loss rate corresponded to 473.35 K, and from
were widely used to study the kinetics parameters. The
equations were just as follows:
2
p
lnb=T ¼ ln½RA=Eaꢃ ꢀ Ea=RTp
(1)
0
:4567Ea
logb þ
¼ C1
(2)
(3)
RTp
4
99.45 to 773.15 K, kept on losing weight slowly until
no remaining residue.
ln b=T p1 :8 ¼ C ꢀ 1:0037E =RT ;
2
a
p
As for BDT, the thermal decomposition included an endo-
thermic process and an exothermic process between 323.15
and 773.15 K. At 407.35–435.45K, BDT melt first with a
melting peak temperature of 422.65 K, and then decomposed
where T was the peak temperature, K; R was the gas
p
ꢀ
1
ꢀ1
constant, 8.314 J K mol ; b was the linear heating rate,
K min ; C , C were constant.
1 2
ꢀ
1
1
0
0
.0
.5
.0
0
.0
-
-
-
-
-
0.2
0.4
0.6
0.8
1.0
-
-
0.5
1.0
1
00
200
300
400
500
100
200
300
400
500
°
°
Temperature / C
Temperature / C
(b) BDT
(
a) BDM
0
ꢀ1
Figure 3. The DSC and TG–DTG curves of 1,1 -bis (3,5-dimethyl-pyrazole) methenehydrazine (BDM) under N
2
atmosphere with a heating rate of 10 K min
1
00
0.5
.0
1
00
0.5
0
8
6
4
2
0
0
0
0
0
8
6
4
0
0
0
0.0
-
-
-
-
-
0.5
1.0
1.5
2.0
2.5
-0.5
-1.0
-1.5
-2.0
20
0
-3.0
1
00
200
300
400
500
100
200
300
400
500
600
Temperature/ °C
Temperature/ °C
(a) BDM
(b) BDT
2
Figure 4. The DSC and TG–DTG curves of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (BDT) under N atmosphere with a heating
ꢀ1
rate of 10 K min
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
The Crystal Structure and Synthesis Mechanism of 3,6-Bis(3,5-dimethylpyrazol-1-yl)-
,4-dihydro-1,2,4,5-tetrazine (BDT): A Key Precursor of S-tetrazine
1
Table 5
Acknowledgments. We gratefully acknowledge the financial
support from the National Natural Science Foundation of China
and China Academy of Engineering Physics (No. 10776002),
the project of State Key Laboratory of Science and Technology
(No. ZDKT12-03, QNKT11-06), and the Program for New
Century Excellent Talents in University (No. NCET-09-0051).
The peak temperatures of the first main exothermic at different heating
rates and the chemical kinetics parameters.
ꢀ
1
2
ꢀ1
Method
E (kJ mol
)
R
Ln(A/s
)
a
Kissinger’s method
86.67
90.94
87.24
0.9987
0.9990
0.9988
4.547
Ozawa–Doyle’s method
Starink’s method
a
ꢀ1
b (K min )/T
P
(K): 5/522.56; 10/538.58; 15/549.51; 20/557.72.
REFERENCE AND NOTES
[
1] Huynh M. H. V.; Hiskey, M. A.; Chavez, D. E.; Naud, D. L.;
With the peak temperatures measured under 5, 10, 15, and
Gilardi, R. D. JACS 2005, 127, 12537.
ꢀ
1
2
0K min
heating rates, the activation energy E, pre-
[2] Saracoglu, N. Tetrahedron 2007, 63, 4199.
[
3] Coombes, D. S.; Price, S. L.; Willock, D. J.; Leslie, M. J Phys
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Propell Explos Pyrot 1999, 24, 168.
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Pyrot 2004, 29, 209.
exponential factor A, and linear correlation coefficient R were
determined by the three methods just as shown in Table 5.
Take the average of the three calculated activation
[
ꢀ
1
[
energy as the final one, 88.28 kJ mol . In this way, the
Arrhenius equations of BDT could be expressed as: ln
[6] Feng, J. L.; Zhang, J. G.; Wang, K.; Zhang, T. L. Chem J
3
k = 4.547–88.28 ꢄ 10 /(RT).
Chinese U 2011, 32, 1519.
[
7] J. C. Oxley, J. L. Smith, J. Zhang, J. Phys. Chem A, 104
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(
CONCLUSIONS
M. A. Chem Commun 2006, 38, 4007.
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Edit 2000, 39, 1791.
The single crystal structure of BDM as the intermediate
of BDT has been determined by X-ray diffraction for the
first time. And the synthesis mechanism of BDT has been
proved in this paper. At 318.15 K, triaminoguanidine
reacted with pentanedione to achieve the intermediate
[
10] Coburn M. D.; Hiskey, M. A.; Lee, K. Y.; Ott, D. G.;
Stinecipher, M. M. J Heterocyclic Chem 1993, 30, 1593.
[11] Huynh, M. H. V.; Hiskey, M. A.; Archuleta, J. G.; Roemer,
E. L.; Gilardi, R. Angew Chem Int Edit 2004, 43, 5658.
[
12] Chavez, D. E.; Hiskey, M. A. J Heterocyclic Chem 1998, 35,
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Lee, K. Y.; Ott, D. G. J Heterocyclic Chem 1991, 28, 2049.
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H.; Schwab, I.; Vogt, M. Eur J Inorg Chem 2002, 10, 2701.
16] Crawford, M. J.; Klapotke, T. M. Rev Inorg Chem 1999,
9, 1.
17] Sheldrick, S. G. M. Program for the Solution of Crystal
(
BDM) by molecular nucleophilic addition and intramolec-
1
ular nucleophilic substitution; when heated to 363.15 K,
BDT was generated by two molecules of intermediate with
nucleophilic substitution reaction.
[
[
2
For the purpose of investigating the thermal behavior of
the two compounds, the DSC and TG–DTG have been con-
ducted. BDM decomposed directly without melting; thermal
decomposition of BDT included an endothermic process
and an exothermic process. Non-isothermal kinetics analysis
of BDT has been conducted by three different methods:
Kissinger’s method, Ozawa’s method, and Starink’s method.
The results indicated that the Arrhenius Equation of BDT
[
[
1
[
Structure, University of Göttingen, Germany, 1990.
[18] Sheldrick, S. G. M. Program for Crystal Structure Refinement
from Diffraction Data, University of Göttingen, Germany, 1997.
[
[
19] Kissinger, H. E. Anal Chem 1957, 29, 1702.
20] Ozawa, T. B Chem Soc JPN 1965, 38, 1881.
[21] Starink, M. J. Thermochim Acta, 1996, 288, 97.
3
could be expressed as follows: ln k= 4.547–88.28 ꢄ 10 /(RT).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet