Synthesis of funetionalized tetrazenes as energetic compounds

Article abstract of DOI:10.1021/jo802738c

1,4-Bis[1-(2-hydroxyethyl)-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12a), 1,4-bis[1-isopropoxycarbonylmethyl1H-tetrazol-5-yl]-1,4-dimethyl-2- tetrazene (12b), and 1,4-bis[1-carboxymethyl-1H-tetrazol-5yl]-1,4-dimethyl-2- tetrazene (13) have been synthes

Full text of DOI:10.1021/jo802738c

Synthesis of Functionalized Tetrazenes as Energetic Compounds
Johannes Heppekausen, Thomas M. Klapo¨tke,* and Stefan M. Sproll
Department of Chemistry and Biochemistry, UniVersity of Munich (LMU),
Butenandtstr. 5-13, D-81377, Germany
tmk@cup.uni-muenchen.de
ReceiVed December 16, 2008
1,4-Bis[1-(2-hydroxyethyl)-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12a), 1,4-bis[1-isopropoxycarbo-
nylmethyl-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12b), and 1,4-bis[1-carboxymethyl-1H-tetrazol-5-
yl]-1,4-dimethyl-2-tetrazene (13) have been synthesized as new nitrogen-rich compounds. The tetrazenes
were obtained by oxidation of the corresponding tetrazolylhydrazines using bromine. Moreover, a new
method to prepare tetrazolylhydrazines in high yield using 5-bromotetrazoles has been developed. 12a,
12b, and 13 were characterized using vibrational spectroscopy (IR, Raman), mass spectrometry, and
multinuclear NMR spectroscopy. The crystal structures of 12a, 12b, and 13 were determined using single
crystal X-ray diffraction. Furthermore, the energetic properties of 12a, 12b, and 13 have been investigated
using DSC and bomb calorimetric measurements. The sensitivity data toward impact and friction has
been determined using BAM methods.
Introduction
energetic materials based on nitrogen-rich compounds like
tetrazoles can be used as gas generating agents for civil
applications.6 To obtain even higher contents of nitrogen,
tetrazoles were used as anions to form salts with nitrogen-
containing cations of guanidine, aminoguanidine, diaminoguani-
dine, or triaminoguanidine.7
Tetrazoles are nitrogen-rich compounds, covering a wide
range of applications. They are used as pharmaceuticals,1 for
biomedical applications,2 as membranes,3 as antifoggants in
photographic materials,4 or as energetic materials.5 The advan-
tages of tetrazoles include their high nitrogen content along with
a sufficiently high thermal stability,3 rendering them as unique
nitrogen building blocks. Beside the usage for military devices,
Another method to build nitrogen-rich tetrazole-containing
molecules is the usage of moieties like tetrazine,8 nitramine,9
or azide.10 The disadvantages of these compounds lie in their
low physical and thermal stability and high explosion temper-
ature. In particular, with regard for possible application as air
bags in vehicles, a low heat of explosion is desired to protect
the person from burns. Moreover, a reduced heat of explosion
lessens the erosion of guns. Therefore, the investigation and
(1) (a) Makino, E.; Iwasaki, N.; Yagi, N.; Kato, H.; Ito, Y.; Azuma, H. Chem.
Pharm. Bull. 1990, 38, 201. (b) Reddy, R. P.; Ravindrath, A.; Ramaiah, T. S.;
Rao, M. V. Ind. J. Chem. Sci. 1987, 1, 45. (c) Alabaster, C. T.; Bell, A. S.;
Campbell, S. F.; Ellis, P.; Henderson, C. G.; Morris, D. S.; Roberts, D. A.;
Ruddock, K. S.; Samuels, G. M. R.; Stefaniak, M. H. J. Med. Chem. 1989, 32,
575. (d) Uchida, M.; Komatsu, M.; Morita, S.; Kanbe, T.; Nagakawa, K. Chem.
Parm. Bull. 1989, 37, 322.
(2) (a) Matyjaszewski, K.; Sumerlin, B. S.; Tsarevsky, N.; Spanswick, J.
Int. Patent 2005087818, 2005. (b) Mwale, F.; Girard-Lauriault, P.-L.; Wang,
H. T.; Lerouge, S.; Antoniou, J.; Wertheimer, M. R. Tissue Eng. 2006, 12, 2639.
(c) Truica-Marasescu, F.; Wertheimer, M. R. Plasma Process. Polym. 2008, 5,
44.
(3) Gaponik, P. N.; Ivashkevich, O. A.; Karavai, V. P.; Lesnikovich, A.;
Chernavina, N.; Sukhanov, G. T.; Gareev, G. A. Angew. Makromol. Chem. 1994,
219, 77.
(4) Tuites, R. C.; Whiteley, T. E.; Minsk, L. M. U.S. Patent 1,245,614, 1971.
(5) (a) Singh, R. P.; Verma, R. D.; Meshri, D. T.; Shreeve, J. M. Angew.
Chem., Int. Ed. 2006, 45 (22), 3584. (b) Klapo¨tke, T. M. Structure and Bonding:
High Energy Density Compounds; Springer: Berlin/Heidelberg, 2007; Vol. 125.
(6) (a) Ganta, S. R.; Williams, G. K.; Miller, C. G. Int. Patent
WO2008054531, 2008. (b) Khandhadia, P. S.; Mizuno, H. U.S. Patent
US2008078486, 2008.
(7) (a) Takacs, E. A. U.S. Patent US3354172, 1967; (b) Klapoetke, T. M.;
Stierstorfer, J.; Wallek, A. Chem. Mater. 2008, 20, 4519.
(8) (a) Butler, R. N.; Ni Bhradaigh, E. P.; McArdle, P.; Cunningham, D.
J. Chem. Res 1995, 6, 224. (b) Sauer, J.; Pabst, G.; Holland, U.; Kim, H.-S.;
Loebbecke, S. Eur. J. Org. Chem. 2001, 4, 697.
(9) (a) Herbst, R. M.; Garrison, J. A. J. Org. Chem. 1953, 18, 941. (b) Gao,
A.; Rheingold, A. L.; Brill, T. B. Propellants, Explos., Pyrotech. 1991, 16, 97.
(10) Marsh, F.; Thatcher, D. N. U.S. Patent US3374188, 1968.
2460 J. Org. Chem. 2009, 74, 2460–2466
10.1021/jo802738c CCC: $40.75 2009 American Chemical Society
Published on Web 02/17/2009

Synthesis of Functionalized Tetrazenes
SCHEME 1. Synthesis of Tetrazolylhydrazines from Thiosemicarbazides
SCHEME 2. Synthesis of 5-Bromotetrazoles
development of new nitrogen-rich compounds with a low heat
of explosion is of great interest.
A suitable class of nitrogen-rich compounds are 1,4-bistet-
razolyltetrazenes. 1,4-Bis[1-methyltetrazol-5-yl]-1,4-dimethyl-
2-tetrazene was first prepared in 2004 by nitrosylation of N,1-
dimethyl-1H-tetrazol-5-amine and reduction to the corresponding
1-methyl-1-(1-methyl-1H-tetrazol-5-yl)hydrazine. The tetra-
zolylhydrazine was then oxidized to form the 1,4-bis[1-
methyltetrazol-5-yl]-1,4-dimethyl-2-tetrazene using bromine.11
In this work, we present a general route for the preparation of
tetrazenes in high yields. The synthesis of bromotetrazoles12
was generalized and used to establish a new route to form the
corresponding methyltetrazolylhydrazines in high yields.
SCHEME 3. Synthesis of the Tetrazolylhydrazines
Results and Discussion
Tetrazenes can be prepared by oxidation of hydrazines.13 As
a consequence, the tetrazolyltetrazenes presented in this work
have been obtained via the corresponding tetrazolylhydrazines.
Therefore, efficient routes for the synthesis of tetrazolylhydra-
zines were necessary. A possible pathway reported in literature
starts from thiosemicarbazides, which are converted to the
corresponding S-methylthiosemicarbazides. The methylated
sulfur atom is subsequently substituted by sodium azide,
followed by an electrocyclic ring closure yielding the tetra-
zolylhydrazine14 (Scheme 1).
isopropyl ester proved to be a stable protecting group against
an intramolecular attack of the monomethylhydrazine moiety
later inserted, in contrast to the ethyl or methyl ester. To form
the tetrazoles, the amine group was converted into the 5H-
tetrazole using standard reactions of triethyl orthoformate and
sodium azide in acetic acid.17 In the following step, the
5-position of the tetrazole was brominated using elemental
bromine (Scheme 2).
In the case of 8a, the resulting 5-bromotetrazole was
deprotected by hydrochloric acid. A purification by column
chromatography was not possible because of decomposition
during the process. Crude 8a and 8b were converted into the
corresponding tetrazolylhydrazines by substitution of the bro-
mine atom by monomethylhydrazine. The experiments showed
that isopropanol was a suitable solvent, whereas the yields
dropped using alcohols, acetonitrile, or other organic solvents.
When the reaction was carried out, neither the 2-methyl isomer
nor side products arising from a hydrolysis of the bromotetrazole
were observed (Scheme 3). The tetrazolylhydrazines were
obtained as slightly impure oil. The crude products were used
for further reactions.
Taking into account that a purification of tetrazole 5 by
column chromatography is necessary, the reaction proves not
to be efficient for upscaling.
To improve the synthesis, a new route using 5-bromotetra-
zoles as intermediates has been developed. Despite being useful
starting materials for 5-substituted tetrazoles, only a small
number of 5-bromotetrazoles have been reported in the litera-
ture.15 The synthesis of 2-(5-bromo-tetrazol-1-yl)-ethanol (8a)
reported as a patent by Bayes16 was generalized and used to
prepare the (5-bromo-tetrazol-1-yl)-acetic acid isopropyl ester
(8b), with 2-aminoethyl acetate and isopropyl 2-aminoacetate
as suitable starting materials. The experiments showed that in
case of the aminoacetate derivative (to form 8b) only the
A deprotection of 9b using potassium hydroxide in water
yielded the bicycle 11 as crystalline solid along with several
other compounds, which were not identified. The formed carbon
acid undergoes immediately an intra- or intermolecular con-
densation with the hydrazine moiety, even in alkaline medium,
yielding either 11 or polymeric side products (Scheme 4).
(11) Klapoetke, T. M.; Mayer, P.; Schulz, A.; Weigand, J. J. Propellants,
Explos., Pyrotech. 2004, 29, 325.
(12) (a) Lim, G. M. F.; Endo, M. U.S. Patent US4374994, 1983. (b) Bayes,
D. E. European Patent EP0117368A1, 1982.
(13) (a) Back, T. G. J. Chem. Soc., Chem. Commun. 1981, 11, 530. (b) Bae,
D. H.; Shine, H. J. J. Org. Chem. 1981, 46, 4700. (c) Klapo¨tke, T. M.; Mayer,
P.; Schulz, A.; Weigand, J. J. Propellants, Explos., Pyrotech. 2004, 29, 325.
(14) (a) Atherton, R. A.; Lambert, R. W. Tetrahedron 1983, 39, 2599. (b)
Weigand, J. J. Dissertation, University of Munich (LMU), 2005. (c) Banert, K.;
Klapo¨tke, T. M.; Sproll, S. M. Eur. J. Org. Chem. 2009, 2, 275.
(15) (a) Collibee, W. L.; Nakajima, M.; Anselme, J.-P. J. Org. Chem. 1995,
60, 468. (b) Bayes, D. E. European Patent EP0117368A1, 1982. (c) Bruns, R.;
Uhr, H.; Vogl, E. International Patent WO2006161228, 2006.
(17) (a) Justiz, O. H.; Fernandez-Lafuente, R.; Guisan, J. M.; Negri, P.;
Pregnolato, M.; Terreni, M. J. Org. Chem. 1997, 62, 9099. (b) van Konings-
bruggen, J. P.; Garcia, Y.; Bravic, G.; Chasseau, D.; Kahn, O. Inorg. Chim.
Acta 2001, 326, 101. (c) Potewar, T. M.; Shafi, A.; Lahoti, R. J.; Srinivasan,
K. V. Tetrahedron Lett. 2007, 48, 1721.
(16) Bayes, D. E. European Patent EP0117368A1, 1982.
J. Org. Chem. Vol. 74, No. 6, 2009 2461

Heppekausen et al.
SCHEME 4. Formation of 11
SCHEME 5. Synthesis of the Tetrazolyltetrazenes
Bicycle 11 crystallizes in the orthorhombic space group Pcnn
with eight molecular formulas per unit cell. Two hydrogen bonds
are present in the crystal structure. The donor atom N6 forms
one intermolecular hydrogen bond to O1, leading to dimers.
The tetrazolylhydrazines 9a and 9b were converted into the
corresponding tetrazenes using saturated bromine water at 0 °C.
The product precipitates from the clear reaction mixture and
was filtered off. The yields varied between 50% and 60%
(Scheme 5).
Compound 12b was deprotected using boiling concentrated
sodium hydroxide solution. The corresponding carbon acid 13
was recovered by neutralizing the alkaline solution using
hydrochloric acid.
FIGURE 1. Molecular structure and intermolecular hydrogen bonds
of 13. Thermal ellipsoids are drawn at the 50% probability level.
TABLE 1. Hydrogen Bonds of 12a and 13
donor
atom
acceptor
atom
D-H
[pm]
H· · ·A
[pm]
D· · ·A
[pm]
(D-H· · ·A)
Compound 12a crystallizes in the orthorhombic space group
Pbca with four molecular formulas per unit cell. The bond
distances and angles of the tetrazole moiety and the alkyl
substituent are in accordance with values reported in the
literature.18 The bond distance between N6 and N7 (125.5 pm)
equates to common values of double bonds (125 pm).19 The
bond distance of N5-N6 (136.6 pm) lies between a N-N single
bond (146 pm) and a double bond (125 pm). Furthermore the
C1-N5 bond (136.6 pm) is shortened by 12.6 pm, compared
to C-N single bonds (147 pm) commonly observed. The crystal
structure is stabilized by an intermolecular hydrogen bond
between the donor atom O1 and the acceptor atom N4. Thereby,
the tetrazole moieties are connected by two hydrogen bonds
between each other. As a result, three molecules are connected
by four hydrogen bonds.
Compound 12b crystallizes in the triclinic space group P-1
with one molecular formula per unit cell. The bond distances
and angles are in correspondence with 12a. As a result of the
protected carbon acid no inter- or intramolecular interactions
are observed.
Compound 13 crystallizes in the monoclinic spacegroup P21/c
with four molecular formulas per unit cell (Figure 1). The bond
distances and angles are in accordance with those of compounds
12a
13
O1
O2
O4
N4
N4
N12
88.8
94.1
93.9
201.0
181.0
179.1
289.5
273.7
271.4
173.8
167.8
166.8
12a and 12b. The crystal structure is stabilized by four
intermolecular hydrogen bonds, one between the donor atom
O2 and the acceptor atom N4 and the other between the donor
atom O4 and the acceptor atom N12. In contrast to the structure
of 12a, five molecules are connected to each other by the four
hydrogen bonds.
A comparison between the hydrogen bonds of 12a and 13 is
given in Table 1.
Compounds 12a, 12b, and 13 were identified using vibrational
IR spectroscopy. Selected values are given in Table 2. The
calculated values given in Table 2 were used to assign the
frequencies.
A comparison between the 15N spectra of 13 and 12a is given
in Figure 2. The assignment of the nitrogen atoms was carried
out in analogy to values reported in literature.20 In the case of
12a, N2 shows a clear triplet, resulting of a J-coupling (3J )
3
2
2.0 Hz) with the CH2 group. N1 forms a muliplet by the J-
3
and J-coupling with the hydroxyethyl group. In contrast, 13
only shows the triplet of N2 (3J ) 1.7 Hz). N1 forms a broad
2
signal without showing any clear J-coupling with the CH2-
(18) (a) Lyakhov, A. S.; Voitekhovich, S. V.; Gaponik, P. N.; Ivashkevich,
L. S. Acta Crystallogr. 2004, C60, o293. (b) Klapoetke, T. M.; Kuffer, C.; Mayer,
P.; Polborn, K.; Schulz, A.; Weigand, J. J. Inorg. Chem. 2005, 44, 5949.
(19) Holleman, A. F.; Wiberg, E.; Wiberg, N. Lehrbuch der Anorganischen
Chemie, 101 Auflage; Walter de Gruyter Verlag: Berlin, New York, 1995; p
1842.
group. An explanation for the missing 2J-coupling could be the
much lower concentration, due to the low solubility of 13 in
(20) Klapo¨tke, T. M.; Minar, N.; Stierstorfer, J. Polyhedron 2009, 28, 13.
2462 J. Org. Chem. Vol. 74, No. 6, 2009

Synthesis of Functionalized Tetrazenes
TABLE 2. Comparison between Selected Vibrations of 12a, 12b,
and 13 with the Calculated Values of 13 using DFT BLYP/6-31G*
12a 12b 13 theory ×
exptl exptl exptl 0.9940 theory
vibration
3347
3436
3502
3036
3007
2977
1778
1777
1527
1479
1436
1421
1417
1416
1397
1360
1312
1282
1250
1190
1100
3524 νs/νas(OH)
3055 νas(CH3)
3026 νs(CH2)
2972 2999 3012
2944 2984 2972
2885 2944 2945
1754 1747
2995 νs(CH3)
1789 νas(COOH)
1788 νas(COOH)
1537 νas(tetrazol)
1488 δs(CH3)
1445 νs(tetrazene)/δs(CH3)
1430 δs(CH3)/δs(CH2)
1426 νs(tetrazene)/δs(CH3)
1425 δs(CH3)/δs(CH2)
1406 νs(tetrazole)/δs(CH3)/δs(CH2)
1369 νs(CH2COOH)
1320 νs(tetrazene)/δas(CH2)
1290 νs(CH2COOH)
1258 νs(tetrazol)
1198 νs(tetrazole)/δas(tetrazole)/δas(CH2)
1107 νas(COOH)/νas(tetrazole)/
νas(tetrazene)/νs(N-CH3)
1738
1572 1569 1565
1470 1470 1478
1444 1450 1447
1417
1433
1423
1414 1413
1394 1400
1360 1348 1351
1337 1332
1295 1278 1295
1261 1262
1224 1218 1207
1106 1106 1100
1098 1083 1075
1015 1007 1020
1060
1023
1067 νas(tetrazole)/δas(tetrazole)/νas(tetrazene)
1030 νas(CH2COOH)/νas(tetrazole)/
νas(tetrazene)/δs(N-CH3)
986 νs(tetrazole)/δs(N-CH3)/νas(tetrazene)
978 νas(tetrazole)/δs(N-CH3)/νas(tetrazene)/
γ(COCH2)
FIGURE 2. 15N-spectra of 13 and 12a in d6-DMSO.
978
993
980
972
959 965
857 848 854
798
866
778
872 νas(tetrazole)/γ(COCH2)
783 νs(CH2COOH)/νas(tetrazole)/
νas(tetrazene)/δs(N-CH3)
658 656
654
658 γs(COOH)
FIGURE 3. Combustion reactions of 12a, 12b, and 13.
2
3
DMSO. In both cases neither the J- nor the J-coupling with
the methyl moiety was obvious.
The isopropyl ester should lead to a reduction of the electron-
withdrawing effect of the carbon acid. Electron-rich tetrazole
moieties are known to be much more stable than tetrazoles
bearing electron-withdrawing groups.23 As a result, compound
12b should be more stable than 13. Since the experimental
data proves 13 as being more stable than 12b, this effect
can be ascribed to the crystal structure and not to electronic
effects of the substituents.
To analyze the energetic properties of the compounds, the
energies of combustion (∆Uc) were measured using bomb
calorimetry. Using these values, the enthalpy of formation was
calculated by applying the Hess thermochemical cycle, as
reported in the literature.24 The heats of formation of H2O (l)
and CO2 (g), -286 and -394 kJ mol-1, were obtained from
the literature,25 and the combustion reactions of 12a, 12b, and
13 are given in Figure 3.
Since 12a, 12b, and 13 are energetic materials, determination
of the energetic properties was or interest of us. Therefore, the
thermal behavior was investigated by DSC measurements, the
heats of combustion by bomb calorimetric measurements, and
the sensitivity toward impact and friction by BAM methods.21,22
The tetrazenes show no melting points but sharp decom-
position points. Comparing the DSC data of the tetrazenes,
compound 12a and 12b possess similar points of decomposi-
tion of 167 and 160 °C. In contrast, the point of decomposi-
tion of 13 (207 °C) is about 40 °C higher than those of 12a
and 12b. This effect can be rationalized by strong intermo-
lecular interactions of the molecules in the crystal structure,
as already shown in Figure 1, resulting in a stabilization of
the molecule. Taking the crystallographic data of 12a, 12b,
and 13 into account, the points of decomposition can be
correlated with the amount of intermolecular interactions.
Compound 12b shows no intermolecular interactions at all
and possesses a decomposition point of 160 °C. Compound
12b forms four hydrogen bonds between a hydroxyl group
and the tetrazole moiety connecting three molecules (de-
composition point 167 °C). The structure of 13 stabilized
most by four hydrogen bonds between the carboxylic acid
and the tetrazole moiety shows the highest decomposition
point (207 °C). Electronic effects of the different moieties
of the tetrazoles 12b and 13 can be neglected. The difference
between 12b and 13 is the esterfication of the carbon acid.
The energetic values of the energy of explosion, the explosion
temperature, the detonation pressure, the detonation velocity,
and the gas volume have been calculated using the enthalpies
of formation and the EXPLO5 programm26 (Table 3).
(23) Gao, A.; Rheingold, A. L.; Brill, T. B. Propellants, Explos., Pyrotech.
1991, 16, 97.
(24) Klapo¨tke, T. M.; Stein, M.; Stierstorfer, J. Z. Anorg. Allg. Chem. 2008,
634, 1711.
(25) (a) Holleman, A. F.; Wiberg, E.; Wiberg, N. Lehrbuch der Anorganis-
chen Chemie/Holleman-Wiberg, 101st ed.; de Gruyter: Berlin, 1995, p 141. (b)
Holleman, A. F.; Wiberg, E.; Wiberg, N. Lehrbuch der Anorganischen Chemie/
Holleman-Wiberg, 101st ed.; de Gruyter: Berlin, 1995; pp 250, 859, 1176. (c)
http://webbook.nist.gov/chemistry/.
(21) (a) Suceska, M. Test Methods for ExplosiVes; Springer: New York, 1995;
pp 21 (impact); 27 (friction). (b) http://www.bam.de/.
(22) Impact: insensitive > 40 J, less sensitive > 35 J, sensitive > 4 J, very
sensitive < 4 J. Friction: insensitive > 360 N, less sensitive ) 360 N, 80 N <
sensitive <360 N, very sensitive < 80 N, extreme sensitive <1 0 N. According
to the UN Recommendations on the Transport of Dangerous Goods (+) indicates
not safe for transport.
(26) (a) Suceska, M. Proceedings of the 30th International Annual Conference
of ICT, Karlsruhe, Germany; Fraunhofer-Institut fu¨r chemische Technologie,
DWS Werbeagentur und Verlag GmbH: Karlsruhe, 1999; p 50/1. (b) EXPLO5.V2,
Computer program for calculation of detonation parameters, P. Suceska, M.
Proceedings of the 32th International Annual Conference of ICT, Karlsruhe,
Germany; Fraunhofer-Institut fu¨r chemische Technologie, DWS Werbeagentur
und Verlag GmbH: Karlsruhe, 2001; p 110/1.
J. Org. Chem. Vol. 74, No. 6, 2009 2463

Heppekausen et al.
nitrocellulosek
TABLE 3. Energetic Properties of 12a, 12b, and 13
12a
12b
13
TNTk
RDXk
formula
C8H16N12O2
312.33
1.539
4528
473
435
C14H24N12O4
424.45
1.401
4976
-101
-151
C8H12N12O4
340.26
1.614
3528
153
119
C3H6N6O6
227.1
1.65
C3H6N6O6
222.1
1.82
C6H7.26N2.74O10.48
285
1.3-1.7 (1.5 for calculation)
molecular mass
a
density (g cm-1
)
b
-∆Ucomb (cal g-1
)
c
-∆Hcomb (kJ mol-1
)
d
∆fHm (kJ mol-1
)
Values Calculated by EXPLO5 V5.02
e
-∆EUm° (kJ kg-1
TE (K)f
)
3586
2441
197
7662
773
2560
1914
121
6355
730
3363
2588
179
7073
721
5099
3737
205
7176
620
6052
4358
356
9055
793
4479
3736
167
6673
711
pC-J (kbar)g
h
D (m s-1
)
i
gas vol (L kg-1
)
Is (s)l
160
238
163
240
200
240
252
232
227
230
Is (s)m (70% AND)
216
a Estimated from a structure determination. b Experimental (constant volume) combustion energy. c Experimental molar enthalpy of combustion.
d Molar enthalpy of formation. e Energy of explosion. f Explosion temperature. g Detonation pressure. h Detonation velocity. i Assuming only gaseous
products. k Obtained from the database of EXPLO5 V5.02. l Specific impulse (isobaric combustion, chamber pressure 60 bar, frozen expansion).
m Specific impulse of a mixture containing 70% ammonium dinitramide as oxidizer.
Isopropyl-2-aminoacetate hydrochloride was synthesized accord-
ing to the literature,27 2-(5-bromo-1H-tetrazol-1-yl)ethanol (8a)
according to Bayes,16 and isopropyl 2-(1H-tetrazol-1-yl)acetate (7b)
according to the literature.28
Compared to RDX (a common high explosive) and nitrocel-
lulose (a common propellant), the values of 12a and 13 lie
between those of RDX and nitrocellulose. The temperature of
explosion is about 1300 K (nitrocellulose) and 2000 K (RDX)
lower. Compared to nitrocellulose, a common propellant, the
detonation pressure is comparable, whereas the temperature of
explosion is significantly lower.
Synthesis of (5-Bromo-1H-tetrazol-1-yl)-Acetic Acid Isopro-
pyl Ester (8b). Crude 1H-tetrazol-1-yl-acetic acid isopropyl ester
(7b) (33.4 g, 214 mmol) and bromine (81.1 g, 508 mmol) were
dissolved in a mixture of 350 mL of chloroform and 175 mL of
acetic acid. The solution was stirred at 80 °C under reflux for
48 h. Afterward the bromine and the acetic acid were removed
under reduced pressure. The residue was neutralized with
saturated sodium carbonate solution, extracted with ethyl acetate,
and washed with 2 M HCl and saturated sodium carbonate
solution. The organic phase was dried over MgSO4, and solvent
was removed under reduced pressure. The product was obtained
as slightly impure orange oil (26.3 g, 106 mmol, yield 50%).
IR (KBr) (cm-1): ν˜ 3390 (w), 3141 (w), 2986 (m), 2941 (w),
2881 (w), 2160 (w), 1749 (vs),1630 (w), 1542 (w), 1455 (m),
1419 (m), 1377 (s), 1344 (w), 1300 (w), 1272 (m), 1233
(vs),1184 (m), 1147 (w), 1058 (w), 1021 (w), 978 (w), 957 (w),
The sensitivity toward impact and friction was determined
according to BAM standard. The sensitivity toward friction of
12a and 13 is lower than 240 N, and the sensitivity toward
impact is lower than 5 J. In the case of 12b, the sensitivity
toward friction is lower than 160 N, and the sensitivity toward
impact lower than 7 J. The lower sensitivity toward friction of
12b compared to 12a and 13 can be rationalized by the lack of
intermolecular interactions and the resulting lower stabilization
in the crystal structure.
1
901 (w), 843 (w), 776 (w), 702(w), 584 (w). H NMR (CDCl3,
Conclusions
3
400 MHz, 25 °C): δ 1.20 (d, 6H, J ) 6.3 Hz, CH3), 5.03 (sept,
3
1H, J ) 6.2 Hz, CH), 5.08 (s, 2H, CH2). 13C NMR (CDCl3,
1,4-Bis[1-(2-hydroxyethyl)-1H-tetrazol-5-yl]-1,4-dimethyl-
2-tetrazene (12a), 1,4-bis[1-isopropoxycarbonylmethyl-1H-
tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12b), and 1,4-bis[1-
carboxymethyl-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene
(13) were prepared as nitrogen-rich compounds. The evalu-
ation of the energetic properties points out that these com-
pounds are suitable as propellants or gas-generating agents.
The advantage lies in the high thermal stability and the low
temperature of explosion, along with average detonation
velocities and pressures. Moreover, a new synthesis of
tetrazolylhydrazines via bromotetrazoles has been developed
that results in high yields.
100 MHz, 25 °C): δ 14.0 (CH3), 21.3 (CH3), 48.9 (CH), 70.3
(CH2),135.6 (Cq), 165.0 (CO). m/z (DEI+): 249.0 [M + H] (8),
248.0 [M] (2), 235.0 (11), 233.0 (9), 191.0 (42), 189.0 (43),
164.0 (45), 163.0 (8), 162.0 (43), 134.9 (42), 132.9 (43), 107.9
(22), 105.9 (22), 92.9 (10), 90.9 (10), 55.0 (47), 54.0 (20), 53.0
(23), 43.0 (100), 42.0 (11), 41.0 (31). C6H9BrN4O2 (247.9909
found M 247.9890).
Synthesis of N-[5-(N-Methyl-hydrazino)-1H-tetrazol-1-yl]-
acetic Acid Isopropyl Ester (9b). Crude (5-bromo-1H-tetrazol-
1-yl)-acetic acid isopropyl ester (8b) (6.50 g, 26.1 mmol) and
monomethylhydrazine (2.40 g, 52.0 mmol) were dissolved in
50 mL of propan-2-ol and heated under reflux for 6 h. Afterward
the solution was evaporated to dryness, and 50 mL of dichlo-
romethane was added. The precipitate was filtered off, and the
filtrate was concentrated under reduced pressure. The product
was obtained as slightly impure orange oil (5.30 g, 24.7 mmol,
yield 95%). IR (KBr, cm-1): ν˜ 3337 (m), 3202 (w), 2982 (m),
2938 (m), 2879 (w), 1747 (vs), 1661 (s), 1574 (s), 1450 (m),
1412 (m), 1379 (m), 1281 (m), 1223 (vs), 1147 (m), 1103 (s),
Experimental Section
CAUTION! Tetrazoles and tetrazolyltetrazenes are energetic
compounds with sensitivity toward heat and impact. Although
we had no problems in synthesis, proper protective measures
(safety glasses, face shield, leather coat, grounded equipment
and shoes, Kevlar gloves, and ear plugs) should be used when
undertaking work involving tetrazoles or tetrazenes on larger
scales.
(27) Casas, J.; Grigg, R.; Najera, C.; Sansano, J. M. Eur. J. Org. Chem.
2001, 10, 1971.
(28) Konstantinov, M.; Nikolov, A.; Tsoneva, N.; Petcov, N. Appl. Biochem.
Biotechnol. 1992, 33, 177–182.
2464 J. Org. Chem. Vol. 74, No. 6, 2009

Synthesis of Functionalized Tetrazenes
1047 (m), 958 (m), 915 (m), 903 (m), 845 (w), 779 (w), 737
(9b) (6.30 g, 29.4 mmol) in a mixture of 20 mL of water and 5
mL of acetic acid was added dropwise 400 mL of a saturated
solution of bromine in water at 0 °C. The precipitate was filtered
off and evaporated to dryness. The product was obtained as
colorless solid (5.65 g, 13.3 mmol, yield 60%). IR (KBr) (cm-1):
ν˜ 3487 (w), 3395 (w), 2999 (m), 2984 (m), 2965 (w), 2944 (w),
2884 (w), 1754 (s), 1627 (w), 1569 (vs), 1470 (m), 1450 (m),
1414 (m), 1383 (m), 1348 (w), 1329 (w), 1278 (w), 1218 (s),
1181 (w), 1144 (m), 1106 (s), 1083 (m), 1007 (m), 959 (m),
944 (w), 903 (w), 848 (m), 732 (w), 711 (w), 658 (m), 586 (w),
476 (w), 458 (w). Raman (200 mW, 25 °C, cm-1): ν˜ 2999 (26),
2963 (32), 2945 (24), 1753 (11), 1601 (44), 1500 (100), 1471
(24), 1445 (24), 1408 (34), 1351 (17), 1328 (11), 1226 (23),
1188 (10), 1149 (8), 1104 (23), 1010 (6), 971 (6), 904 (9), 866
(20), 835 (10), 770 (7), 723 (9), 683 (7), 593 (5), 537 (7), 417
1
(w), 627 (vw), 589 (vw). H NMR (d6-DMSO, 400 MHz, 25
°C): δ 1.13 (d, 6H, 3J ) 6.3 Hz, CH3), 3.09 (s, 3H, NCH3), 4.90
3
(sept, 1H, J ) 6.2 Hz, CH), 4.73 (s, 2H, NH2), 5.18 (s, 2H,
CH2). 13C NMR (d6-DMSO, 100 MHz, 25 °C): δ 21.4 (CH3),
29.5 (CH3), 43.1 (NCH3), 49.8 (CH2), 68.8 (CH), 158.3 (Cq),
166.9 (CO). 15N NMR (d6-DMSO) δ: 1.6 (N3), -18.0 (N2),
-91.3 (N4), -180.9 (N1), -300.4 (N6), -309.7 (N5). m/z
(DEI+): 214.1 (5) [M], 172.1 (7), 156.1 (10), 155.1 (16), 141.1
(10), 127.1 (5), 101.0 (32), 85.1 (6), 73.1 (26), 56.0 (12), 55.0
(48), 46.0 (6), 45.0 (29), 44.0 (11), 43.0 (100), 42.0 (8), 41.0
(20). C7H14N6O2 (214.1178 found M 214.1166).
Synthesis of N-[1-(2-Hydroxyethyl)-1H-tetrazol-5-yl]-N-me-
thylhydrazine (9a). 2-(5,2-(5-Bromo-tetrazol-1-yl)-ethanol (8a)
(4.70 g, 20.0 mmol) and monomethylhydrazine (1.90 g, 41.2
mmol) were dissolved in 50 mL of propan-2-ol and heated under
reflux for 6 h. Afterward the solution was evaporated to dryness,
and 50 mL of DCM was added. The precipitate was filtered off,
and the filtrate was concentrated under reduced pressure. The
product was obtained as colorless solid (5.30 g, 24.7 mmol, yield
95%). Mp 111.0-117.8 °C. IR (KBr, cm-1): ν˜ 3350 (s), 3266
(s), 2967 (w), 2926 (w), 2878 (w), 1656 (vs), 1563 (vs), 1455
(m), 1415 (m), 1373 (m), 1340 (w), 1325 (w), 1282 (m), 1233
(m), 1122 (m), 1104 (m), 1069 (vs), 1039 (m), 983 (m), 948
(w), 903 (m), 864 (m), 745 (m), 707 (m), 684 (m), 493 (m).
Raman (200 mW, 25 °C, cm-1): ν˜ 3351 (40), 3232 (38), 3193
(34), 3028 (32), 2976 (100), 2928 (37), 2882 (38), 2809 (24),
1654 (41), 1566 (35), 1466 (56), 1418 (47), 1378 (32), 1352
(34), 1284 (66), 1268 (59), 1231 (30), 1105 (55), 1071 (29),
987 (19), 950 (23), 864 (52), 692 (91), 633 (54), 523 (28), 498
1
(13), 381 (19), 290 (19), 227 (13). H NMR (d6-DMSO, 400
3
MHz, 25 °C): δ 1.13 (d, 6H, J ) 6.32 Hz, CCH3), 3.58 (s, 3H,
3
NCH3), 4.91 (sept, 1H, J ) 6.32 Hz, CH), 5.53 (s, 2H, CH2).
13C NMR (d6-DMSO, 100 Hz, 5 °C): δ 21.9 (CCH3), 35.3
(NCH3), 50.4 (CH), 70.5 (CH2), 154.6 (Cq), 166.9 (CO). m/z
(DEI+): 424.3 [M] (89.1), 410.3 (6.6), 337.3 (8.7), 282.3 (1.9),
226.3 (42.0), 199.3 (47.8), 156.3 (26.3), 127.2 (25.7), 113.2
(15.9), 101.2 (6.7), 84.2 (8.4), 73.2 (13.5), 55.2 (20.1), 43.2
(17.8). Impact sensitivity: 7 J. Friction sensitivity: 160 N.
Synthesis of 1,4-Bis[1-carboxymethyl-1H-tetrazol-5-yl]-1,4-
dimethyl-2-tetrazene (13). A suspension of bis(1,1′-methyl-1,1′-
(iso-propyl-2-(1H-tetrazolyl) acetate))tetrazene (0.10 g, 0.24
mmol) in a 10 M solution of NaOH in water was heated until
the solid was dissolved. Afterward concentrated hydrochloric
acid was added to the cooled solution, and the precipitate was
filtered off. The product was obtained as colorless solid (0.07
g, 0.19 mmol, yield 78%). IR (KBr) (cm-1): ν˜ 3436 (m),
3012(m), 2972 (m), 2945 (w), 2718 (w), 2592 (w), 2515 (w),
1786 (w), 1747 (s), 1738 (s), 1607 (m), 1565 (vs), 1478 (m),
1433 (w), 1423 (w), 1413 (w), 1400 (m), 1351 (vw), 1332 (vw),
1262 (vw), 1207 (s), 1140 (m), 1100 (m), 1075 (m), 1020 (w),
1009 (m), 993 (m), 965 (vw), 942 (vw), 893 (vw), 854 (vw),
818 (m), 798 (m), 733 (vw), 728 (vw), 693 (w), 689 (w), 565
(m), 648 (m), 463 (w). Raman (200 mW, 25 °C, cm-1): ν˜ 3044
(7), 3014 (19), 2973 (37), 2947 (16), 1739 (15), 1603 (94), 1492
(92), 1467 (100), 1446 (41), 1404 (61), 1354 (35), 1330 (18),
1312 (16), 1271 (11), 1235 (27), 1185 (16), 1117 (19), 1103
(27), 964 (9), 943 (8), 898 (14), 855 (24), 795 (12), 733 (13),
694 (9), 651 (9), 583 (13), 528 (9), 428 (26), 380 (15), 327
(20), 291 (20), 249 (15). 1H NMR (d6-DMSO, 400 MHz, 25
°C): δ 3.62 (s, 6H, CH3), 5.46 (s, 2H, CH2), 13.68 (br.s, 1H,
COOH). 13C NMR (d6-DMSO, 100 MHz, 25 °C): δ 35.3 (CH3),
50.8 (CH2), 154.7 (Cq), 169.0 (CO). 15N NMR (d6-DMSO) δ:
3.1 (N6), -3.6 (N3), -12.7 (N2), -84.3 (N4), -175.6 (N1),
-243.7 (N5). m/z (DEI+): 340.4 [M] (6), 322.2 (16), 256.3 (13),
212.2 (14), 211.2 (13), 191.1 (10), 189.1 (9), 177.3 (11), 167.2
(9), 164.1 (13), 162.2 (10), 161.2 (9), 152.2 (9), 149.2 (32), 137.3
(8), 135.2 (37), 133.1 (10), 129.2 (12), 127.2 (21), 125.3 (10),
121.2 (8), 113.2 (9), 112.2 (14), 111.2 (23), 109.2 (10), 105.2
(11), 99.2 (9), 98.2 (13), 97.2 (36), 96.2 (9), 95.2 (16), 91.2
(10), 85.2 (19), 84.2 (18), 83.2 (42), 82.1 (27), 81.2 (29), 80.0
(11), 79.1 (8), 77.1 (10), 71.2 (31), 70.2 (21), 69.2 (58), 68.2
(11), 67.2 (12), 60.1 (9), 57.1 (52), 56.1 (19), 55.1 (53), 54.1
(11), 45.1 (9), 44.1 (43), 43.1 (100), 41.1 (34); C8H12N12O4
(340.3 found M 340.4). C8H12N12O4 calcd: C, 28.24; H, 3.55;
N, 49.40. Found: C, 28.25; H, 3.95; N, 49.09. Impact sensitivity:
5 J. Friction sensitivity: 240 N.
1
(27). H NMR (d6-DMSO) δ: 3.09 (s, 3H, NCH3), 3.72 (t, 2H,
OCH2), 4.49 (t, 2H, NCH2), 4.82 (s, 2H, NH2), 4.96 (br. t, 1H,
OH). 13C NMR (d6-DMSO) δ: 44.4 (CH3), 50.8 (OCH2), 59.5
(NCH2), 159.2 (Cq). 15N NMR (d6-DMSO) δ: -11.0 (N3), -21.9
(N2), -100.1 (N4), -174.5 (N1), -301.6 (N6), 313.3 (N5). m/z
(DEI+): 158.1 [M], 143.1, 127.1, 113.1, 87.1, 69.1, 55.1, 43.1,
31.1, 28.1. C4H10N6O (158.1 found M 158.1). C4H10N6O calcd:
C 30.77, H 5.16, N 53.82. Found: C 30.63, H 5.13, N 53.29.
Synthesis of 1,4-Bis[1-(2-hydroxyethyl)-1H-tetrazol-5-yl]-1,4-
dimethyl-2-tetrazene (12a). To a solution of N-[1-(2-hydroxy-
ethyl)-1H-tetrazol-5-yl]-N-methylhydrazine (9a) (0.25 g, 1.70
mmol) in a mixture of 2 mL of water and 0.5 mL of acetic acid
was added dropwise 25 mL of a saturated solution of bromine
in water at 0 °C. The precipitate was filtered off and evaporated
to dryness. The product was obtained as a colorless solid (0.13
g, 0.45 mmol, yield 53%). IR (KBr) (cm-1): ν˜ 3347 (m), 2972
(w), 2944 (w), 2885 (w), 1717 (w), 1636 (w), 1572 (vs), 1470
(m), 1444 (m), 1417 (m), 1381 (w), 1360 (w), 1337 (w), 1295
(w), 1274 (w), 1261 (w), 1224 (m), 1149 (m), 1106 (m), 1098
(m), 1059 (m), 1036 (w), 1015 (m), 978 (w), 945 (w), 857 (w),
802 (w), 728 (m), 696 (m), 668 (m), 639 (w), 551 (w); 497 (w),
459 (w). Raman (200 mW, 25 °C, cm-1): ν˜ 3022 (3), 2973 (5),
2944 (5), 1611 (23), 1502 (100), 1463 (21), 1447 (18), 1410
(32), 1382 (9), 1360 (7), 1308 (4), 1278 (4), 1240 (15), 1125
(5), 1105 (10), 1057 (3), 973 (3), 856 (6), 672 (9), 537 (4), 362
1
(5), 331 (7), 257 (3). H NMR (d6-DMSO, 400 MHz, 25 °C): δ
3
3.61 (s, 3H, CH3), 3.76 (t, 2H, J ) 5.82 Hz, OCH2), 4.58 (t,
2H, 3J ) 5.82 Hz, CH2), 5.14 (broad s, 1H, OH). 13C NMR
(d6-DMSO, 100 MHz, 25 °C): δ 35.5 (NCH3), 51.3 (OCH2),
59.1 (NCH2), 154.2 (Cq). 15N NMR (d6-DMSO) δ: 2.0 (N6), -2.4
(N3), -13.2 (N2), -83.5 (N4), -169.5 (N1), -245.4 (N5). m/z
(DEI+): 312.3 [M] (7.6), 284.3 (8.5), 225.3 (1.7), 198.3 (3.8),
172.3 (16.9), 142.3 (75.1), 113.2 (90.7), 100.2 (61.6), 45.2 (100),
28.2 (59.4). C8H16N12O2 calcd: C, 30.77; H, 5.16; N, 53.58.
Found: C, 30.59; H, 5.40; N, 53.67. Impact sensitivity: 5 J.
Friction sensitivity: 240 N.
Acknowledgment. Financial support of this work by the
Ludwig-Maximilian University of Munich (LMU), the Fonds
der Chemischen Industrie (FCI), the European Research
Office (ERO) of the U.S. Army Research Laboratory (ARL),
and ARDEC (Armament Research, Development and Engi-
neering Center) under contract nos. N 62558-05-C-0027,
Synthesis of 1,4-Bis[1-isopropoxycarbonylmethyl-1H-tetrazol-
5-yl]-1,4-dimethyl-2-tetrazene (12b). To a solution N-[5-(N-
methyl-hydrazino)-1H-tetrazol-1-yl]-acetic acid isopropyl ester
J. Org. Chem. Vol. 74, No. 6, 2009 2465

Heppekausen et al.
R&D 1284-CH-01, R&D 1285-CH-01, 9939-AN-01 &
W911NF-07-1-0569 and the Bundeswehr Research Institute
for Materials, Explosives, Fuels and Lubricants (WIWEB)
under contract nos. E/E210/4D004/X5143 & E/E210/7D002/
4F088 is gratefully acknowledged. The authors acknowledge
collaborations Dr. M. Krupka (OZM Research, Czech
Republic) in the development of new testing and evaluation
methods for energetic materials and with Dr. M. Sucesca
(Brodarski Institute, Croatia) in the development of new
computational codes to predict the detonation parameters of
high-nitrogen explosives. We are indebted to and thank Dr.
Betsy M. Rice (ARL, Aberdeen, Proving Ground) for many
helpful and inspired discussions and support of our work.
Supporting Information Available: General experimental
1
methods; H and 13C NMR spectra for 12a, 12b, and 13; and
X-ray crystallographic data (CIF files) for 11, 12a, 12b, and
13. This material is available free of charge via the Internet at
http://pubs.acs.org.
JO802738C
2466 J. Org. Chem. Vol. 74, No. 6, 2009