Disubstituted azidotetrazoles as energetic compounds

Article abstract of DOI:10.1002/chem.200900034

Disubstituted azidotetrazoles are synthesized by the base-catalyzed activation of the C - F bond in the tri-fluoromethylazo-substituted cyclic and acyclic alkanes. From the reaction of trans-l,4-bis(trifluoromethylazo)cyclo- hexane with four equivalents o

Full text of DOI:10.1002/chem.200900034

DOI: 10.1002/chem.200900034
Disubstituted Azidotetrazoles as Energetic Compounds
Takashi Abe, Young-Hyuk Joo, Guo-Hong Tao, Brendan Twamley, and
Jean’ne M. Shreeve*[a]
Abstract: Disubstituted azidotetrazoles
are synthesized by the base-catalyzed
ylimino)cyclohexenyl]amine
was
substituted acyclic alkanes, correspond-
ing alkyl-bridged N,N’-bis(5-azido-1H-
tetrazol-1-yl)diiminoalkanes were ob-
tained. For example, from 1,2-bis(tri-
formed as the principal product. The
structure of these new disubstituted
azidotetrazoles was determined by
crystal structure analysis as well as
NMR and IR spectroscopy. In a similar
fashion, from three trifluoromethylazo-
ꢀ
activation of the C F bond in the tri-
fluoromethylazo-substituted cyclic and
acyclic alkanes. From the reaction of
trans-1,4-bis(trifluoromethylazo)cyclo-
hexane with four equivalents of NaN3,
N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,4-
diiminocyclohexane was formed in
good yield. While, from the similar re-
action using cis/trans-1,2-bis(trifluoro-
methylazo)cyclohexane, (5-azido-1H-
tetrazol-1-yl)-[6-(5-azido-1H-tetrazol-1-
fluoromethylazo)ethane,
N,N’-bis(5-
azido-1H-tetrazol-1-yl)-1,2-diimino-
ethane was obtained in 75% yield.
Heats of formation, detonation pres-
sures, detonation velocities, and impact
sensitivities are reported for these new
disubstituted azidotetrazoles.
Keywords: azidotetrazoles
·
C–F
activation · energetic materials ·
heterocycles · high-nitrogen com-
pounds
Introduction
with the preparation of azidotetrazoles,[3] for example,
nearly 70 years ago, 5-azidotetrazole and sodium 5-azidote-
trazolate were prepared by the reaction of cyanogen halide
(ClCN or BrCN) with sodium or barium azide and acid.[4]
More recently detailed investigations on the synthesis and
characterization of 5-azidotetrazoles have been reported.[5]
The blue gas, trifluoronitrosomethane, reacts with various
primary amines to give corresponding trifluoromethylazo
compounds in good yields.[6] Several reactions of polyfluor-
oazaalkanes have been reported also.[7] Recently, we have
The synthesis of energetic heterocyclic compounds has at-
tracted considerable interest in recent years, especially with
regard to the syntheses and applications of new members of
heterocyclic-based energetic materials.[1] High-nitrogen com-
pounds constitute a unique class of energetic materials. The
energy is derived from their high heats of formation rather
than from the total heat of combustion. The high heats of
formation are directly related to the large number of ener-
[2]
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
getic N N, N C, and N O bonds. Therefore, new method-
ology for the ready introduction of high-nitrogen groups
into the molecule is important for the development of high-
energetic compounds. Azidotetrazole is a ligand that has a
reduced carbon content relative to nitrogen content. The
creation of more high-energy materials can be expected by
shown that the trifluoromethylazo group (CF3 N=N ) was
transformed into the (5-azido-1H-tetrazol-1-yl)imino group
in reaction with sodium azide by taking advantage of the ac-
[8]
ꢀ
tivation of the C F bond (Scheme 1). Based on this new
method, high-nitrogen compounds consisting of two or more
(5-azido-1H-tetrazol-1-yl)imino groups were prepared from
ꢀ
ꢀ
ꢀ
integrating the N N bond in the molecule based on the in-
herent lability of the azidotetrazole. Many papers have dealt
compounds that contained one or more CF3 N=N
group(s).
[a] Dr. T. Abe, Dr. Y.-H. Joo, Dr. G.-H. Tao, Dr. B. Twamley,
Prof. Dr. J. M. Shreeve
Department of Chemistry, University of Idaho
Moscow, ID 83844-2343 (USA)
Fax : (+1)208-885-9146
E-mail: jshreeve@uidaho.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900034.
Scheme 1. Transformation of the trifluoromethylazo group into the (5-
azido-1H-tetrazol-1-yl)imino group
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FULL PAPER
To explore the scope of this reaction, we have extended
the study of the synthesis of high-nitrogen compounds
hydrazono compound 4 from isopropyl(trifluoromethyl)di-
AHCTUNGTREGaNNUN zene (3), which results from a base-catalyzed [1,3]-proton
ꢀ
ꢀ
beyond those having disubstituted CF3 N=N groups, which
may provide new high-energetic compounds. The prepara-
tion of compounds having disubstituted azidotetrazoles is
known, for example, 1,4-bis(5-azido-1H-tetrazol-1-yl)ben-
zene was obtained by the reaction of 1,4-(dichloromethyl-
eneamino)benzene with sodium azide where the azidotetra-
zoles are bonded at the 1,4-positions of the benzene ring.[9]
However, by using our new reaction scheme, N,N’-bis(5-
azido-1H-tetrazol-1-yl)-1,4-iminocyclohexane is formed
from the reaction of trans-1,4-bis(trifluoromethylazo)cyclo-
hexane with sodium azide. This is the first report of com-
pounds that contain disubstituted azidotetrazoles linked to
the parent cyclic and/or acyclic alkyl through the imino
group. In our current work, we report the preparation of
new disubstituted azidotetrazoles, which are more energetic
than those of monosubstituted azidotetrazoles.
shift from the carbon of the isopropyl group to the nitrogen
of the CF3N< group, is the impetus for the reaction of 3
with sodium azide (Scheme 3).[12] Intermediate 4 transforms
Scheme 3. Synthesis of 5-azido-N-(propan-2-ylidene)-1H-tetrazole (6).
into a reactive difluorocarboimino compound, 5, followed
by reaction with sodium azide to give the azidotetrazole 6.[8]
Similarly, when trans-2a reacts with sodium azide, the corre-
sponding hydrazono compounds 7 and 8 are considered to
be the primary reaction intermediates. This is based on the
formation of 1-(trifluoromethylazo)-4-(N-trifluoromethyla-
mino)iminocyclohexane (7) and 1,4-bis(trifluoromethylhy-
drazono)-cyclohexane (8), which were identified by examin-
ing the products obtained from trans-2a in acetonitrile that
contained a catalytic amount of potassium fluoride or by
monitoring the behavior of trans-2a in [D6]DMSO by 1H
and 19F NMR spectroscopy (see the Supporting Information)
(Scheme 4).
Results and Discussion
Precursors (2a–e) having two trifluoromethylazo groups
were prepared by the reaction of diamines (1a–e) with tri-
fluoronitrosomethane (Scheme 2). With the exception of
Scheme 2. Preparation of bis(trifluoromethylazo)alkanes.
1,2-bis(trifluoromethylazo)ethane (2c),[10] all starting materi-
als 2a, 2b, 2d, and 2e are new compounds. trans-1,4-Bis(tri-
fluoromethylazo)cyclohexane (2a) is a light brown solid,
whereas 2b–e are green-yellow oily liquids. When compared
with bis(trifluoromethylazo)cyclohexanes (2a, 2b) and al-
kyl(trifluoromethyl)diazenes (alkyl=n-C3H7, iso-C3H7, iso-
C4H9, cyclo-C5H11, cyclo-C6H13, n-C8H17),[8] the shelf life of
the bis(trifluoromethylazo)alkanes (2c–e) is rather low due
to the presence of adventitious traces of water. For example,
the trifluoromethylazo group of 1,2-bis(trifluoromethylazo)-
ethane (2c) gradually degrades into the trifluoromethylhy-
Scheme 4. Isomerization of trans-1,4-bis(trifluoromethylazo)cyclohexane
(2a) into hydrazono compounds 7 and 8.
ꢀ
drazono group (CF3NH N<) even when stored at ꢀ408C.
When retained at room temperature, decomposition occurs
rapidly leading finally to an orange solid. Therefore, these
linear bis(trifluoromethylazo)alkanes (2c–e) were prepared
in methanol solution and reacted with sodium azide without
isolation.
Although no apparent change was observed when trans-
2a was held for a week in acetonitrile without base, addition
of small quantities of potassium fluoride to the solution
caused
a
change both in 1H and 19F NMR spectra
The reaction of trans-1,4-bis(trifluoromethylazo)cyclohex-
(Scheme 4). For example, trans-2a was isomerized into a
mixture of mono- and dihydrazono compounds 7 and 8 after
being heated at 608C for 10 h. In [D6]DMSO, which is more
coordinating (larger donor number DN) than CD3CN, trans-
2a was isomerized completely into 1,4-bis(trifluoromethyl-
ꢀ
ane (2a) with NaN3: The C F bond of CF3 group only
rarely succumbs to nucleophilic substitution.[11] However, ac-
ꢀ
ꢀ
ꢀ
tivation of C F bonds is required for reaction of CF3 N=N
alkyl to occur. We have found that the initial formation of
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4103

J. M. Shreeve et al.
hydrazono)cyclohexane (8) after three days at room temper-
ature.
The reaction of trans-2a with four equivalents of sodium
azide in the presence of a base (NaHCO3) at room tempera-
ture proceeded smoothly to give a turbid light brown solu-
tion (Scheme 5). Workup of this solution gave a white
Supporting Information). Subsequent reaction of 9 with an
additional two equivalents of sodium azide gave N,N’-bis(5-
azido-1H-tetrazol-1-yl)-1,4-diiminocyclohexane (10) in 53%
yield. Access to 10 from trans-2a was also possible by utiliz-
ing trimethylsilylazide, although rather harsh reaction condi-
tions (708C, three days) were required vis-ꢁ-vis the reaction
with sodium azide. However, the yield of 10 is considerably
higher (78%).
The reaction of cis/trans-1,2-bis(trifluoromethylazo)cyclo-
hexane (2b) with NaN3: When cis/trans-2b was allowed to
react with two equivalents of sodium azide in the presence
of a base (NaHCO3) at room temperature, the formation of
the expected monosubstituted azidotetrazole, (5-azido-1H-
tetrazol-l-yl)-[2-(trifluoromethylhydrazono)cyclohexylidene]-
amine did not occur. However, the reaction of cis/trans-2b
with four equivalents of sodium azide under the same reac-
tion conditions gave a light brown solid, (5-azido-1H-tetra-
zole-1-yl)-[6-(5-azido-1H-tetrazole-1-yl-imino)cyclohexenyl]-
amine (13) (Scheme 6). Recrystallization of the product
Scheme 5. Synthesis of (5-azido-1H-tetrazol-l-yl)-[4-trifluoromethylhydra-
zonocyclohexylidene]amine (9) and N,N’-bis(5-azido-1H-tetrazol-1-yl)-
1,4-diiminocyclohexane (10).
powder, which was identified as N,N’-bis(5-azido-1H-tetra-
zol-1-yl)-1,4-diiminocyclohexane (10) in 85% yield. The
structure was determined by single-crystal X-ray crystallog-
raphy; a thermal ellipsoid plot is given in Figure 1.[13a] The
infrared spectrum of 10 shows two characteristic strong
bands at 1542 and 2171 cmꢀ1 (asymmetric N=C< and N3
stretching bands, respectively), which are normally observed
ꢀ
ꢀ
ꢀ
for azidotetrazoles bonded through the imino group ( N=
Scheme 6. Synthesis of (5-azido-1H-tetrazol-1-yl)-[6-(5-azido-1H-imino)-
cyclohexenyl]amine (13).
C<).[8]
Different products were obtained from the reaction of
trans-2a with sodium azide depending on the molar ratio
(trans-2a/NaN3) used. This suggests a stepwise reaction
from chloroform gave a straw-colored crystalline solid,
whose structure was determined by X-ray crystallography; a
thermal ellipsoid plot of 13 is given in Figure 2.[13] Due to
the inequivalence of the two azidotetrazole groups at the
1,2-positions of the cyclohexane ring of 13, the asymmetrical
ꢀ
ꢀ
mode for the two CF3 N=N groups of trans-2a with
sodium azide. When trans-2a was allowed to react with two
equivalents of sodium azide (one half of the stoichiometric
ꢀ
ꢀ
amount required), only one of the two CF3 N=N groups
reacted to give (5-azido-1H-tetrazol-1-yl)-[4-(trifluorome-
thylhydrazono)cyclohexylidene]amine (9) selectively, which
was isolated and characterized. The 1H and 19F NMR spectra
of 9 are rather complex due to the presence of two different
imino groups bonded at the 1- and 4-positions of cyclohex-
stretching bands of the azide groups are found as two strong
ꢀ1
~
bands at n=2151 and 2166 cm in the infrared spectrum.
When this reaction was conducted in the absence of a base,
the yield of 13 was low (44%) even though the reaction
time was four days. It is likely that 13 was derived from an
intermediate in which a [1,3]-proton shift from the 3-posi-
tion of the cyclohexane ring to the imino nitrogen at the 1-
position occurred before or concomitantly with the introduc-
tion of another azidotetrazole from the monosubstituted azi-
dotetrazole intermediates 11 and 12 to give 13 (Scheme 6).
The reaction of bis(trifluoromethylazo)alkanes 2c–2e
with NaN3: The reaction of 2c with four equivalents of
sodium azide at room temperature under similar conditions
proceeded smoothly to give a turbid brown solution from
ꢀ
ane. However, the presence of the CF3(NH) group in 9
1
was confidently confirmed on this basis. The H NMR spec-
tra displayed three quartets centered at d=6.02 [3J
ACHTUNGTRENNUNG
6.2 Hz], 6.12 [3J
N
ACHTUNGTRENNUNG
ꢀ
ACHTUNGTRENNUNG
ꢀ
AHCTUNGTRENNUNG
[3J
G
ꢀ63.16
ACHTUNGTRENNUNG
ꢀ63.07 ppm [3J
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Disubstituted Azidotetrazoles as Energetic Compounds
FULL PAPER
Table 1. Crystallographic data and structure refinement parameters.
which a new disubstituted azidotetrazole, N,N’-bis(5-azido-
1H-tetrazol-1-yl)-1,2-diimino-ethane (14) was isolated as a
light brown solid. Following several attempts to optimize
this reaction, it was found that lowering the temperature to
08C without base (NaHCO3) gave a clean reaction and im-
proved the yield to produce a white powder suspended in
solution. This reaction differs from that of trans-2a in that
the behavior of the two trifluoromethylazo groups is identi-
cal irrespective of the molar ratio (2c/NaN3). When 2c was
allowed to react with two equivalents of sodium azide under
analogous conditions, only 14 was formed in low yield
(13%). Utilizing the same reaction conditions as for 2c,
10
13
formula
formula wt
space group
exposure [s]
a [ꢂ]
C8H8N16
328.30
P21/a
C8H8N16
328.30
P21/n
10
20
7.7095(9)
8.5955(9)
9.9351(11)
93.924(2)
656.83(13)
4
8.7779(11)
17.984(2)
9.7162(13)
113.755(2)
1403.9(3)
4
b [ꢂ]
c [ꢂ]
b [8]
V [ꢂ3]
Z
T [K]
90(2)
90(2)
l[ꢂ]
0.71073
1.660
0.125
0.71073
1.553
0.117
N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,4-diiminobutane
(15)
1calcd [Mgmꢀ3
]
(mmꢀ1
)
and N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,5-diiminopentane
(16) were obtained as white or a light brown powders in
moderate to good yield, respectively, from the reaction of
2d and 2e with sodium azide (Scheme 7). Isolation of single
crystals of 14, 15, and 16 was not successful.
GF
1.085
0.0382
0.0913
1.067
0.0389
0.0919
R1 [I>2s(I)][a]
wR2 [I>2s(I)][b]
2
2
[a] R1 =SjjFo jꢀjFc jj/SjFo j. [b] wR2 ={S[w
G
(Fo )2]}1/2
ACHTUNGTERNNUNG .
ꢀ
C15 N16=1.408(2) ꢂ. The ring now has an endocyclic
ꢀ
double bond C14 C15=1.345(3) ꢂ. The hydrogen atoms as-
sociated with the imine and endocyclic bond positions were
located and refined. Although the azido groups are both co-
facial, the dihedral angle of each azidotetrazole plane to the
Scheme 7. Synthesis of alkyl-bridged bis(5-azido-1H-tetrazol-1-yl)-1,2-di-
ACHTUNGTRENNUNGimine 14, 15, and 16.
Structures: Compounds 10 and 13 were characterized by
crystal structure analysis (Table 1). Both structures were
solved by using a Bruker SMART APEX diffractometer
equipped with a Cryocool Never-Ice low temperature device
using MoKa radiation. The data for compound 10 were rota-
tionally twinned and were successfully deconvoluted byusing
CELL_NOW,[24] and refined in the non-standard space
group P21/a. Calculated densities are 1.660 and
1.553 mgmꢀ3 for compound 10 and 13, respectively. The
strucutre of compound 10 is shown in Figure 1a with the
para-oriented azidotetrazole linked to the central alicyclic
ring via an imine that is exocyclic to the ring system with
ꢀ
N9 C10=1.285(2) ꢂ. Each azidotetrazole is twisted back
towards the ring and forms a dihedral angle of about 628 to
the mean plane of the ring and exocyclic imine nitrogen
atoms. The extended structure (Figure 1b) shows that the
alicyclic rings stack in the ab plane and the azidotetrazole
groups point towards each other and are stacked in a step-
ped fashion. There are no significant intermolecular interac-
tions between the azidotetrazole moieties.
Compound 13 also crystallizes in the monoclinic system,
in this case the space group is P21/n. The data is not twin-
ned and the structure is shown in Figure 2a. In this case, the
substitution is ortho, but the molecule is no longer symmet-
Figure 1. a) Molecular structure of 10 (thermal displacement at 30%
probability). Hydrogen atoms are unlabelled for clarity. b) Packing dia-
gram of 10 with hydrogen atoms omitted for clarity.
ꢀ
ric with one of the imines protonated, N9 C10=1.307(2) ꢂ,
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J. M. Shreeve et al.
Figure 3. The 15N NMR spectrum of disubstituted 15N-labeled azidotetra-
zole 16.
of the chemical shifts of substituted azidotetrazoles on com-
parison with the literature.[8]
Properties: Being different from energetic compounds
having an azidotetrazole which tended to form super-cooled
liquids,[8] these disubstituted azidotetrazoles are solids and
exhibit poor solubility in common solvents. They do not
melt but decompose violently at 162–1858C. Impact sensitiv-
ity tests were carried out using
a BAM Fallhammer
method.[14] The disubstituted azidotetrazoles blowup on
impact at 1 J for 10 and 13 and 0.5 J for 14–16, respectively,
and thus they are very sensitive energetic materials which
may have some promise as primaries. To avoid the hazard
due to high shock sensitivity, densities were not measured
for 14–16 by using a pycnometer. Their densities were calcu-
lated by using an empirical method.[15]
Theoretical study: Computations were performed by
using the Gaussian 03 (Revision D.01) suite of programs.[16]
The geometric optimization and the frequency analyses are
carried out at the level of Becke three Lee–Yan–Parr
Figure 2. a) Molecular structure of 13 (thermal displacement at 30%
probability). Hydrogen atoms are unlabeled for clarity. b) Packing dia-
gram of 13 with hydrogen atoms omitted for clarity. Dashed lines indicate
hydrogen bonding. Chains are perpendicular to plane of page.
(B3LYP) parameters up to 6-31+GACHTUNGTRNEUNG
(d,p) basis sets.[17] All of
the optimized structures were characterized to be true local
energy minima on the potential energy surface without
imaginary frequencies. The enthalpy of reaction (DHro298) is
obtained by combining the MP2/6-311++G**[18] energy dif-
ference for the reaction, the scaled zero-point energies, and
other thermal factors. The heats of formation of the prod-
ucts were determined by using the method of isodesmic re-
actions (Scheme 8).[19] The heats of formation for com-
pounds 10, 13, 14, 15, and 16 were calculated and are sum-
marized in Table 2. All disubstituted azidotetrazoles exhibit
high positive heats of formation per mole with 13 having the
highest value (1683.1 kJmolꢀ1). Their heats of formation per
unit mass are higher than the corresponding structurally
similar monosubstituted azidotetrazoles.[8] Due to its lower
molecular weight, 14 has the highest heat of formation per
unit mass (6.13 kJgꢀ1).
central ring are slightly different: ring to imine azidotetra-
zole is about 778 and ring to protonated aminotetrazole is
about 708. The amino group forms an intermolecular inter-
ꢀ
action, N16 H16···N20i=2.937(2) ꢂ, (i=symmetry transfor-
mation to generate symmetry generated atoms: x+1/2,
ꢀy+1/2, z+1/2) tying the extended structure into a double
chain as seen in Figure 2b.
Isotopically labeled bis(5-azidotetrazole) 15N-16 was ob-
tained from Na15N3 and 2e in acetonitrile. The six 15N NMR
signals of 15N-16, which are found at d=ꢀ297.1, ꢀ143.8,
ꢀ139.2, ꢀ72.6, ꢀ26.3, and 4.8 ppm, are observed in the 15N
NMR spectrum. (Figure 3) The Na signal from the azide ap-
pears at highest field. The labeled nitrogen Nb was coupled
with Na and Ng as a doublet of doublets, respectively. The
15N4, 15N2, and 15N3 signals for tetrazole were observed at
lowest field. The assignments are given based on the values
The detonation pressures (P) and velocities (D) of the
disubstituted azidotetrazoles were calculated based on tradi-
tional Chapman–Jouget thermodynamic detonation theory
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Disubstituted Azidotetrazoles as Energetic Compounds
FULL PAPER
from cyclic and/or acyclic alkyl-
bridged bis(trifluoromethylazo)
groups has been established.
The ability of the trifluorome-
thylazo group to undergo reac-
ꢀ
tion by activating the C F
bond, when an H atom exists at
the carbon of the alkyl group,
contributes greatly to its syn-
thetic value. The new type of
high-energetic compounds were
fully characterized and shown
to be highly energetic.
Experimental Section
Caution: For handling these energetic
materials, small scale and best safety
practices (leather gloves, face shield)
are strongly encouraged in undertak-
ing preparation of compounds 10, 13,
14, 15, and 16. Compound 14 is ex-
tremely shock sensitive (IS <0.5).
These compounds should not be con-
tacted with metal.
General methods: 1H, 19F, and
13C NMR spectra were recorded on a
300 MHz Bruker Avance nuclear mag-
netic resonance spectrometer operat-
ing at 300.1, 282.4, and 75.5 MHz, re-
Scheme 8. Isodesmic reactions used for calculation of disubstituted azidotetrazoles.
spectively, using CDCl3, CD3CN, and
[D6]DMSO as solvent. The 15N NMR
spectra were recorded on a 500 MHz
Bruker Avance nuclear magnetic reso-
nance spectrometer operating at 50.7 MHz. Chemical shifts: 1H and 13C
are reported relative to Me4Si; 19F relative to CFCl3; 15N relative to exter-
nal CH3NO2. The melting and decomposition points were obtained on a
differential scanning calorimeter at a scan rate of 108C minꢀ1. Densities
of solids were obtained at room temperature by employing a Micromerit-
ics Accupyc1330 gas pycnometer. Electrospray MS was obtained by pro-
tonating the product using formic acid. Elemental analyses were deter-
mined by using an Exeter CE-440 elemental analyzer.
Table 2. Decomposition points (Td), density, heats of formation (DfH8),
and detonation pressure (P) and detonation velocity (D) of the energetic
materials.
[a]
Compd Td
Density DfH8[d]
P[e]
[GPa]
D[e]
[msꢀ1
IS[f] [J]
[oC]
A
)
[kJmolꢀ1, kJgꢀ1
]
G
N
]
10
13
14
15
16
185
154
185
168
162
1.63[b]
1586.7, 4.83
1683.1, 5.13
1679.8, 6.13
1625.2, 5.38
1602.9, 5.07
21.9
23.2
27.9
23.5
22.5
7793
7980
8614
7950
7750
<1.0
<1.0
<0.5
<0.5
<0.5
1.65[b]
(1.70)[c]
ACHTUNGTRENNUNG
X-ray crystallography: Crystals of 10 and 13 were removed from the
flask and covered with a layer of hydrocarbon oil. A suitable crystal was
selected, attached to a glass fiber, and placed in the low-temperature ni-
ACHTUNGTRENNUNG
[a] DSC under nitrogen gas, 108C minꢀ1. [b] Gas pycnometer (258C).
[c] Calculated. Ref. [16]. [d] Calculated in Gaussian 03. [e] Calculated by
Cheetah 5.0. [f] Impact sensitivity (BAM Fallhammer).
trogen stream.[22] Data were collected at low temperatures using
a
Bruker/Siemens SMART APEX instrument (MoKa radiation, l=
0.71073 ꢂ) equipped with a Cryocool NeverIce low temperature device.
Data were measured by using omega scans of 0.38 per frame for various
exposures, and a full sphere of data was collected in each case. A total of
2400 frames was collected with final resolutions of 0.83 ꢂ. Cell parame-
ters were retrieved by using SMART[23] software and refined by using
SAINTPlus[24] on all observed reflections. The data were rotationally
twinned for 10 and were deconvoluted by using CELL_NOW[25] giving a
two-component twin relationship: 1808 rotation about the reciprocal axis
0.499, ꢀ0.001, 1.000. The matrix used to relate the second orientation to
the first domain is:
using Cheetah 5.0.[20] The heats of formation in the con-
densed phase are calculated by using 83.68 kJmolꢀ1 as the
enthalpy of sublimation for each compound.[21] These new
azidotetrazoles exhibit higher detonation values than TNT
(P=20 GPa, D=6900 msꢀ1).
Each cell component was refined by using SAINTPlus[24] on all observed
reflections. Absorption corrections were applied by using TWINABS for
10 and SADABS for 13.[26] Data reduction and correction for Lp and
decay were performed by using the SAINTPlus software. Structures were
solved by direct methods and refined by least squares method on F2
using the SHELXTL program package.[27] Each structure was solved by
analysis of systematic absences. All non-hydrogen atoms were refined
Conclusions
A straightforward synthetic procedure for new high-nitrogen
compounds containing disubstituted azidotetrazoles starting
Chem. Eur. J. 2009, 15, 4102 – 4110
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4107

J. M. Shreeve et al.
(CDCl3): d=2.96–3.27 ppm (m, 8H; CH2); 13C NMR (CD3CN): d=179.6,
150.4, 31.6, 29.4 ppm; IR (KBr): n˜ =1094, 1236, 1294, 1536, 1542 (s; asACHTUNGTRENNUNG(C=
N)), 2172 (s; as(N3)), 1636 cmꢀ1; elemental analysis calcd (%) for C8H8N16
(328.3): C 29.27; H 2.46; N 68.27; found: C 30.66, H 2.69, N 61.11 (ex-
ploded during analysis).
ii) With two equivalents of NaN3 to give 9: Into a 50 mL flask was placed
2a (0.115 g, 0.42 mmol) in acetonitrile (3 mL), and NaN3 (0.055 g,
0.85 mmol). The solution was stirred at room temperature overnight.
After the reaction, the solvent was removed to give a light brown solid.
The solid mixture was dissolved in dry acetone (3 mL) and filtered. Evap-
oration of the solvent left a light brown solid, which was washed with
water (3ꢃ1 mL) to give (5-azido-1H-tetrazol-1-yl)-[4-trifluoromethylhy-
drazono)cyclohexylidene]amine (9). This compound is a mixture of three
isomers in a ratio of 0.2:0.5:1. Light brown solid; Yield: 0.132 g, 98%: Td
anisotropically. No decomposition was observed during data collection.
Details of the data collection and refinement are given in Table 1.
Preparation of trans-1,4-bis(trifluoromethylazo)cyclohexane (2a):
CF3NO (3 mmol) was condensed by PVT techniques at ꢀ1968C into a
50 mL Schlenk tube with a Teflon stopcock that contained trans-1,4-dia-
minocyclohexane (1a; 0.16 g, 1.4 mmol) in methanol (1.0 mL). The reac-
tion mixture was allowed to warm from ꢀ788C to room temperature
overnight while stirring. After the reaction, the solid material was dis-
solved in CH3CN, and the solvent (CH3OH, CH3CN) was removed by
rotary evaporator to give 2a as a light brown solid. Yield: 0.29 g, 77%;
1
3
3
1168C; H NMR (CDCl3): d=6.27 (q, J
(H,F)=5.8 Hz, NH), 6.02 (q, 3J
(H,F)=6.1 Hz, NH), 2.43–3.30 ppm (m,
(H,F)=6.2 Hz; CF3),
(H,F)=6.2 Hz, CF3),
ACHTUNGTNER(NUNG H,F)=6.0 Hz, NH), 6.12 (q, J-
A
ACHTUNGTRENNUNG
8H; CH2); 19F NMR (CDCl3): d=- 63.07 (d, 3J
ACHTUNGTRENNUNG
ꢀ63.16 (d, 3J
A
ACHTUNGTRENNUNG
ꢀ74.19 ppm; IR (liq. film): n˜ =906, 1113, 1198, 1267, 1317, 1485, 1537 (s;
asACHTUTGNRENNUNG
(C=N)), 2158 (s; as(N3)), 2921, 2971 cmꢀ1; elemental analysis calcd (%)
for C8H9N10F3 (302.2): C 31.79, H 3.00, N 46.35; found: C 31.52, H 3.17,
N 33.40 (exploded during analysis).
1
m.p. 878C; H NMR (CDCl3): d=3.97 (br. s, 2H; CH), 2.12–2.21 (m, 4H;
CH2), 1.91–2.01 ppm (m, 4H; CH2); 19F NMR (CDCl3): d=ꢀ74.9 ppm (s,
CF3); 13C NMR (CDCl3):
d =119.8 (q, JACHTUNTGERNUNG(C,F)=275 Hz, CF3), 75.2,
iii) With four equivalents of (CH3)3SiN3 to give 10: Analogously, into a
50 mL flask was placed 2a (0.124 g, 0.45 mmol) in acetonitrile (5 mL),
and TMSN3. (0.239 g, 2.1 mmol). The reaction mixture was stirred at
room temperature for 24 h, and then at 67–708C for three days. The reac-
tion was monitored by 1H and 19F NMR spectroscopy. After completion,
the solvent was removed to give a brown powder (0.113 g), which was
identified as 10 by spectroscopic analysis (IR and 1H NMR). Yield 78%.
27.5 ppm; elemental analysis calcd (%) for C8H10N4F6 (276.2): C 34.78, H
3.65, N 20.29; found: C 34.56, H 3.57, N 20.01.
Preparation of cis/trans-1,2-bis(trifluoromethylazo)cyclohexane (2b):
The reaction mixture of cis/trans-1,2-diaminocyclohexane (1b; 0.16 g,
1.4 mmol) and CF3NO (3 mmol) in methanol (1.0 mL) was allowed to
warm from ꢀ788C to room temperature overnight while stirring. After
the reaction, brine (2 mL) and concentrated HCl (one drop) were added.
The lower layer was separated to give 2b as a yellow-green oil. Yield:
0.268 g, 69% (cis/trans mixture); 1H NMR (CDCl3): d=4.46–4.56 (m,
2H), 4.36–4.38 (m, 2H), 1.54–2.29 ppm (m, 16H). 19F NMR (CDCl3): d=
ꢀ74.29 (s, CF3), ꢀ74.16 ppm (s, CF3); MS (EI): m/z (%): 180 (13)
[C7H11F3N2+], 179 (100) [M+ ꢀCF3N=N], 151 (27) [C5H6F3N2+], 94 (15)
[C6H8N+], 82 (12) [C6H10+], 81 (68) [C6H9+], 69 (100) [CF3+], 67 (42)
[C5H7+]; MS (Cl): m/z (%): calcd for C8H11N4F6 (pseudo molecular ion
[M+ + H]), 277.0888; found; 277.0866.
Preparation of 1,2-bis(trifluoromethylazo)ethane (2c):[10] The reaction
mixture of 1,2-diaminoethane (1c; 0.066 g, 1.1 mmol) and CF3NO
(2.5 mmol) in methanol (0.75 mL) was allowed to warm from ꢀ196 to
ꢀ788C, and then held at 08C for 2 h. After recovering unreacted CF3NO
in vacuo while immersing the reactor in a cold bath (ꢀ988C), the reac-
tion mixture was used for the further reaction immediately. All of 1c was
consumed and the formation of 2c was confirmed by 1H and 19F NMR
spectroscopy. 1H NMR (CDCl3) (in methanol solution): d=4.78 ppm (s,
CH2); 19F NMR (CDCl3) (in methanol solution): d=ꢀ74.26 ppm (s, CF3).
Reaction of (5-azido-1H-tetrazol-1-yl)-[4-trifluoromethylhydrazono)cy-
clohexylidene]amine (9) with two equivalents of NaN3: Into a 50 mL
flask was placed 9 (0.115 g, 0.38 mmol) in acetonitrile (3 mL), and NaN3
(0.067 g, 1.00 mmol). The solution was stirred at room temperature over-
night and was removed to give a brown solid. The solid was washed with
water (3ꢃ1 mL) to give a light brown powder (0.066 g) which was found
1
to be 10 by spectroscopic analysis (IR and H NMR). Yield 53%.
Reaction of cis/trans-1,2-bis(trifluoromethylazo)cyclohexane (2b) with
four equivalents of NaN3: Into a 50 mL flask was placed 2b (0.270 g,
0.98 mmol) in acetonitrile (8 mL), NaHCO3 (0.164 g), and NaN3 (0.270 g,
4.16 mmol). After stirring the reaction mixture for 9 h at room tempera-
ture, a turbid red wine solution was obtained. The solution was filtered,
the residue washed with water (3ꢃ1 mL), and dried to give a light pink
solid (0.114 g) (Product A). Evaporation of the filtrate left a red wine
colored solid (0.163 g), which was washed with acetonitrile (3ꢃ1 mL), to
leave a light brown solid (0.123 g) (Product B). The compound which
could be dissolved in acetonitrile easily was investigated by MS (FAB;
thioglycerol). The main component has a moleculr weight of 219 which
corresponded to C7H9N9 {[3-(5-azido-1H-tetrazol-1-yl)imino]-2-aminocy-
clohexene-1}. Products A and B were found to be identical based on IR
spectroscopy. The structure was determined to be (5-azido-1H-tetrazole-
Preparation of 1,4-bis(trifluoromethylazo)butane (2d): Prepared as for
2c and obtained from 1,4-diaminobutane (1d; 0.052 g, 0.59 mmol) in
methanol (0.75 mL). 1H NMR (CDCl3) (in methanol solution): d=4.17
(m, 4H; CH2), 2.02 ppm (m, 4H; CH2); 19F NMR (CDCl3) (in methanol
solution): d=ꢀ74.19 ppm (s, CF3).
1-yl)-[6-(5-azido-1H-tetrazole-1-yl-imino)cyclohexenyl]amine (13) by
X
ray crystallography using crystals obtained by recrystallization from
chloroform. Light brown solid: yield; 0.237 g, 75%: Td 1618C; 1H NMR
(CDCl3): d=7.92 (s, NH), 5.66 (t, 3J=4.9 Hz, 1H), 2.91 (t, 3J=6.2 Hz),
2.34 (td, 1J=6.0 Hz, 2J=4.9 Hz), 1.84 ppm (quin, J=6.2 Hz); 13C NMR
(CD3CN): d=168.2, 152.1, 149.0, 135.6, 123.6, 27.7, 23.2, 21.0 ppm; IR
Preparation of 1,5- bis(trifluoromethylazo)pentane (2e): Prepared as for
2c and obtained from 1,5-diaminopentane (1e; 0.047 g, 0.46 mmol) in
methanol (0.75 mL). 1H NMR (CDCl3) (in methanol solution): d=4.13
3
5
3
(tq, JACHTUNGTRENNUNG(H,H)=7.0 Hz, JACHTUNGTRENNUNG(H,F)=1.6 Hz, 4H; CH2), 1.97 (m, JACHTNUGRTEN(NUGN H,H)=7.0–
~
(KBr): n=2166, 2151 (s; as(N3)), 1643, 1564, 1533 (s;
asACHTUNGTRENUN(NG C=N)), 1310,
7.9 Hz, 4H; CH2), 1.49 ppm (m, 2H; CH2); 19F NMR (CDCl3) (in metha-
1290, 1236, 1094 cmꢀ1; elemental analysis calcd (%) for C8H8N16 (328.3):
C 29.27, H 2.46, N 68.27; found: C 30.98, H 2.51, N 65.10 (exploded
during analysis).
nol solution): d=ꢀ74.19 ppm (s, CF3).
Reaction of trans-1,4-bis(trifluoromethylazo)cyclohexane (2a): i) With
four equivalents of NaN3 to give 10: Into a 50 mL flask were placed
trans-2a (0.127 g, 0.46 mmol) in acetonitrile (5 mL), NaHCO3 (0.08 g),
and NaN3 (0.139 g, 2.14 mmol). After stirring the reaction mixture at
room temperature for 18 h, a turbid light brown liquid was obtained. The
solution was filtered, washed with water (3ꢃ1 mL), and dried to give
N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,4-iminocyclohexane (10). Suitable
crystals for single-crystal X-ray structure determination were obtained
Reaction of 1,2-bis(trifluoromethylazo)ethane (2c) with NaN3: i) With
four equivalents to give 14: Into a 50 mL flask was placed a solution of
2c in MeOH (0.75 mL), which was prepared from the reaction of 1c
(0.070 g, 1.18 mmol) with CF3NO, acetonitrile (3 mL), and NaN3 (0.330 g,
5.08 mmol). The solution was stirred at 08C for 24 h. After the reaction,
the mixture was filtered. The solid was washed with water (3ꢃ1 mL), and
dried to give N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,2-diiminoethane (14) as
a white powder. Yield: 0.245 g, 75%; 1H NMR (CDCl3,): d=8.99 ppm (s,
1
from chloroform. White powder; yield: 0.129 g, 85%; Td 1858C; H NMR
4108
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4102 – 4110

Disubstituted Azidotetrazoles as Energetic Compounds
FULL PAPER
>CH ); 13C NMR (CD3CN): d=153.8, 152.1 ppm; MS (electrospray):
[6] a) S. P. Makarov, A. Y. Yakubovich, V. A. Ginsburg, A. S. Filatov,
M. A. Englin, N. F. Privezentseva, T. Y. Nikiforova, Dokl. Akad.
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A. Y. Yakubovich, Zh. Obshch. Khim. 1967, 37, 158–163; d) A. S.
Filatov, S. P. Makarov, A. Y. Yakubovich, Zh. Obshch. Khim. 1967,
37, 837–841; e) S. P. Makarov, A. Y. Yakubovich, A. S. Filatov,
M. A. E’nglin, T. Y. Nikiforova, Zh. Obshch. Khim. 1968, 38, 709–
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[7] a) V. A. Ginsburg, A. Y. Yakubovich, A. S. Filatov, V. A. Shpanskii,
E. S. Vlasova, G. E. Zelenin, L. F. Sergienko, L. L. Martynova, S. P.
Makarov, Dokl. Akad. Nauk SSSR 1962, 142, 88–91; b) V. A. Gins-
burg, A. Y. Yakubovich, A. S. Filatov, G. E. Zelenin, S. P. Makarov,
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va, Dokl. Akad. Nauk SSSR 1962, 142, 354–357; c) A. S. Filatov,
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35; d) A. S. Filatov, S. P. Makarov, A. Y. Yakubovich, Zh. Obshch.
Khim. 1968, 38, 35–38; e) A. S. Filatov, S. P. Makarov, A. Y. Yaku-
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47, 7087–7090.
ꢀ
C4H2N16, 274.7 [M+]; IR (KBr): n˜ =962, 1082, 1165, 1325, 1427, 1442,
1540 (s; asACHTUNGTRENNUNG
(C=N)), 2174 cmꢀ1 (s; as(N3)). ii) With two equivalents of NaN3
to give 14: Similarly, into a 50 mL flask was placed a solution of 2c in
MeOH (0.75 mL), which was prepared by the reaction of 1c (0.069 g,
1.14 mmol) with CF3NO, acetonitrile (3 mL), and NaN3 (0.147 g,
2.28 mmol). The solution was stirred at 08C for 24 h to give a turbid
yellow solution. After the reaction, the mixture was filtered, washed with
water (3ꢃ1 mL) and dried to give 14 (0.042 g, 0.15 mmol) as a white
powder. Yield 13%.
Reaction of 1,4-bis(trifluoromethylazo)butane (2d) with four equivalents
of NaN3: N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,4-diiminobutane (15):
White powder; Yield: 0.118 g, 66%; 1H NMR (CDCl3): d=8.74 (m, 1H;
CH), 2.97 ppm (m, 2H; CH2); 13C NMR (CDCl3): d=164.2, 149.9,
28.7 ppm; MS (electrospray): C6H6N16, 302.9 [M+]; IR (KBr): n˜ =2176 (s;
as(N3)), 1543 (s; asACHTUNGTRENNUNG .
(C=N)), 1450, 1359, 1242, 1176 cmꢀ1
Reaction of 1,5-bis(trifluoromethylazo)pentane (2e) with four equiva-
lents of NaN3:N,N’-bis(5-azido-1H-tetrazol-1-yl)-1,5-diiminopentane (16):
White powder; Yield: 0.126 g, 87%; 1H NMR (CDCl3): d=8.68 (t, 3J=
5.0 Hz, 2H; CH), 2.69 (td, 3J=5.3 Hz, 3J=5.0 Hz, 4H; CH2), 2.06 ppm
(quin, 3J=7.3 Hz, 2H; CH2); 13C NMR (CDCl3): d=151.2, 149.8, 165.6,
118.1, 32.6, 21.3 ppm; IR (KBr): n˜ =1171, 1243, 1359, 1451, 1559 (s;
asACHTUNGRTEN(NUNG C=
N), 2163 (s; as(N3)), 2180 cmꢀ1
.
Reaction of 1,5-bis(trifluoromethylazo)pentane (2e) with four equiva-
lents of Na15N3: Into a 50 mL flask was placed a solution of 2e in MeOH
(0.5 mL), which was prepared by the reaction of 1e (0.019 g, 0.18 mmol),
acetonitrile (2.5 mL), and Na15N3 (45.5 mg, 0.67 mmol). The solution was
stirred at 08C for 12 h, and then at room temperature for two days. After
the reaction, the solution was filtered to give a 15N-labeled azidotetrazole
15N-16: White solid; yield: 0.045 g (0.14 mmol). Yield 77%.
[9] This compound has been reported to be extremely shock sensitive
and explodes on rubbing with spatula. See ref. [3a].
[10] It is reported that 2c was successfully isolated and distilled (b. p.
998C). See ref. [6d].
[11] B. J. Liddle, J. R. Gardinier, J. Org. Chem. 2007, 72, 9794–9797, and
references therein.
[12] It is reported that some aliphatic trifluoromethylazocarboxylic acids
rearrange to trifluoromethylhydrazonocarboxylic acid by a proton
shift during distillation. See ref. [6f].
[13] CCDC-710866 (10) and CCDC-710867 (13) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data center
via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
The authors gratefully acknowledge the support of AGFOSR (F49620–
03–1–0209), NSF (CHE0315275), and ONR (N00014–02–1–0600). The
Bruker (Siemens)SMART APEX diffraction facility was established at
the University of Idaho with the assistance of the NSF-EPSCoR program
and the M. J. Murdock Charitable Trust, Vancouver, WA.
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Published online: February 26, 2009
4110
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Chem. Eur. J. 2009, 15, 4102 – 4110