Nitrocarbamoyl Azide O2NN(H)C(O)N3: A Stable but Highly Energetic Member of the Carbonyl Azide Family

Article abstract of DOI:10.1021/jacs.0c12507

The diazotization of nitrosemicarbazide (1) resulted in the formation and isolation of nitrocarbamoyl azide (2), which was thoroughly characterized by spectroscopic and structural methods. This compound shows surprising stability but also high reactivity and sensitivity, with a melting point of 72 °C and a detonative decomposition point at 83 °C. In addition, five selected salts were synthesized by careful deprotonation. The decomposition mechanism of 2 in solution was investigated and could be clarified by performing experiments using methanol and hydrazine as trapping reagents. The energetic and physicochemical properties of all these compounds were investigated and classified.

Full text of DOI:10.1021/jacs.0c12507

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Nitrocarbamoyl Azide O NN(H)C(O)N : A Stable but Highly Energetic
2
3
Member of the Carbonyl Azide Family
Maximilian Benz, Thomas M. Klapotke,* Burkhard Krumm, Marcus Lommel, and Jorg Stierstorfer*
̈ ̈
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sı Supporting Information
ABSTRACT: The diazotization of nitrosemicarbazide (1) resulted in the formation and isolation of nitrocarbamoyl azide (2),
which was thoroughly characterized by spectroscopic and structural methods. This compound shows surprising stability but also
high reactivity and sensitivity, with a melting point of 72 °C and a detonative decomposition point at 83 °C. In addition, five selected
salts were synthesized by careful deprotonation. The decomposition mechanism of 2 in solution was investigated and could be
clarified by performing experiments using methanol and hydrazine as trapping reagents. The energetic and physicochemical
properties of all these compounds were investigated and classified.
lthough in most cases they are short-lived, carbonyl azides
In addition, several questions regarding the molecule arise
from an academic point of view. On one hand, the acidic
proton of the nitramine unit offers many possibilities for
functionalization of this site, but on the other hand, it is also
uncertain to what extent the decomposition mechanism is
affected. By following the Curtius rearrangement for the
decomposition of carbonyl azides, HNCA would provide a
platform for further chemistry with various nucleophiles.
Furthermore, reactions with energetic building blocks could
generate an innovative access to future energetic materials. In
this contribution, the synthesis, properties, and crystal
structures of pure nitrocarbamoyl azide and several of its
salts and decomposition products are reported.
1
,2
A
(RC(O)N ) have been known for more than a century.
3
Especially their decomposition to form isocyanates, named
after Curtius, makes them interesting and indispensable from a
3
−5
synthetic point of view.
Nevertheless, there are only a small
number of well-characterized low-molecular-weight represen-
tatives. Synthesis and proper analysis are complicated by the
6
low stability and often by the explosive nature of acyl azides.
Nevertheless, over the past few years it has been possible to
completely analyze some simple carbonyl azides such as formyl
7
−9
azide and carbonyl diazide.
Other simple carbonyl azides
such as carbamoyl azide or oxalyl diazide have been described
in the literature, but their structures and properties are not yet
10−14
fully understood (Figure 1).
HNCA (2) can be synthesized by diazotization of
16,17
nitrosemicarbazide (1)
with a slight excess of sodium
nitrite in 2 M HCl at 0 °C. Yields of up to 76% can be achieved
by rapid extraction of the reaction solution with diethyl ether
and quick removal of the solvent under a nitrogen stream.
These conditions proved to be particularly practicable and
favorable, as direct access to neutral 2 was gained. (Caution: it
is strongly recommended that full body protection be worn during
work with any compound discussed here.) HNCA crystallizes in
the form of colorless needle-shaped crystals and is stable under
ambient conditions for several weeks. Salts were obtained by
dissolving 2 in cold methanol and then adding 1 equiv of the
respective bases (Scheme 1).
In order to obtain insight into the structure and bonding of
HNCA, the molecular orbital (MO) energies were calculated
for three different potential tautomers using the G09W code
and various resonance structures using the VB2000 code
Figure 1. Smallest representatives of the carbonyl azide family.
Nitrocarbamoyl azide (HNCA, 2) is another representative
of this substance class that is interesting from many
perspectives. Above all, this compound is characterized by
the fact that with azide and nitramine functions it should have
good energetic potential. This was also recognized by Bottaro
Received: December 9, 2020
Published: January 12, 2021
−
et al., who attempted to synthesize NCA salts by nitration of
1
5
carbamoyl azides. However, the claimed ionic materials were
15
examined only by IR spectroscopy.
©
2021 The Authors. Published by
American Chemical Society
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J. Am. Chem. Soc. 2021, 143, 1323−1327
1
323

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Scheme 1. Synthetic Pathway toward HNCA (2) and Its
Salts 3−7
(
version 2.8) (further details and results are provided in the
Supporting Information). Of particular interest were the
proton location as well as whether there was some indication
supporting the presence of the closed tetrazole tautomer. The
MO energies of the three tautomers in Figure 2 were
Figure 3. (a) Molecular structure and bond lengths of 2 as
determined by low-temperature X-ray diffraction with thermal
ellipsoids drawn at the 50% probability level. (b, c) Views of the
packing of 2 (b) slightly twisted along the a axis and (c) along the c
axis. Intramolecular H···O interactions are shown as dotted lines.
Figure 2. Tautomers of HNCA (2): A, amide form; B, iminol form;
C, 1-nitrotetrazolone form. Energies relative to A are shown.
calculated at the B3LYP/cc-pVDZ level. The energies of
conformations B and C relative to the amide form A are 10.3
−
1
and 4.8 kcal mol , respectively. The equilibrium is therefore
strongly in favor of tautomer A.
Figure 4. 15N NMR spectrum of 2 in CD OD at 0 °C.
3
To confirm the theoretical findings, the focus was set on
low-temperature single-crystal X-ray diffraction measurements.
The crystal structures of compounds 1−8 were successfully
determined. All of the data and structures are shown in the
Supporting Information. Despite their high sensitivity toward
external stimuli, crystalline 2 is fine to handle, and crystals
suitable for X-ray measurements were obtained directly from
the crude product. HNCA crystallizes in the monoclinic space
−147.2, −184.6, and −262.7 ppm). The resonance of the α-
nitrogen atom (N-1) of the azido moiety is significantly shifted
to lower field compared with those of organic azides, which is
20
typical for carbonyl azides. In a similar fashion, the resonance
of the γ-nitrogen atom (N-3) is also shifted to lower field and
detected “left” of that of the β-nitrogen atom (N-2). The
assignments of N (Δν = 50 Hz) and N (Δν = 140 Hz)
group P2 /c with four molecular units per unit cell (Figure 3).
1
β
1/2
γ
1/2
Similar to other comparable carbonyl azides, the azide group
were based on the line widths of the resonances in the
1
4
is syn to the carbonyl function with respect to the C−N
corresponding N NMR spectrum. The resonances of the
nitramine moiety are found in the typical regions, with the
nitro group at −45.6 ppm and the amine resonance at −184.6
α
8
,18,19
bond.
The molecule itself is nearly planar. Although the
azide group is almost in a plane with respect to CO (N3−
N2−N1−C1, 2.1(15)°; N2−N1−C1−O1, 178.62(15)°), the
nitro group of the nitramine is twisted out of this plane (O1−
C1−N1) by about 10°. As expected, the azide functionality
shows an angle of 174.03(13)° due to negative hyper-
conjugation and long bonding effects. This is in accordance
1
9,21
ppm.
Because of the low solubility and quick decom-
1
4
position even in cold methanol, only N NMR data for the
−
NCA anion are available. With ammonium salt 5 as a
representative example, in addition to the ammonium signal
(−367 ppm, Δν
= 6 Hz), four further resonances are
detectable for the NCA anion. The signals for the azide
1
/2
−
with the angle in HC(O)N (174.49(17)°) and only slightly
3
larger than those in OC(N ) (172.1(5)°, 172.6(6)°). The
nitrogen atoms at −135 ppm (Δν = 45 Hz), −143 ppm
3
2
1/2
N1−N2 (1.2685(18) Å) and N2−N3 (1.233(5) Å) bond
(Δν = 112 Hz), and −267 ppm (Δν = 162 Hz) are similar
1
/2
1/2
lengths show no divergence toward other members of the
to those of the neutral compound. However, the signal of the
nitro group is significantly downfield-shifted to −10 ppm
(Δν = 42 Hz) upon deprotonation (the nitramide nitrogen
8
,9
carbonyl azide family (Figure 1).
The sufficient stability and solubility of the parent molecule
1
/2
1
3
14
2
(
allowed characterization not only by C NMR spectroscopy
resonance was not observed in the N NMR spectrum
because of the extremely large line width).
1
15
δ = 152.1 ppm, H resonance not observed) but also by
N
NMR spectroscopy. Since significant decomposition was
observed at room temperature, the N spectrum was recorded
As already mentioned above, 2 is bench-stable but
decomposes rapidly in solution at ambient temperature,
especially in protic solvents. The decomposition of 2 probably
does not proceed via a Curtius rearrangement to the
15
at 0 °C in methanol-d . All five resonances were observed, with
4
assignments as displayed in Figure 4 (δ = −45.6, −140.0,
1
324
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J. Am. Chem. Soc. 2021, 143, 1323−1327

Journal of the American Chemical Society
pubs.acs.org/JACS
Communication
isocyanate, as usually occurs for carbonyl azides. 2−24
However, neither isocyanatonitramine nor derivatives thereof
were observed as decomposition products. In our opinion,
2
elimination of HN to form an intermediate nitroisocyanate in
3
solution seems likely. The latter has already been reported and
2
5
analyzed. This hypothesis is supported by trapping reactions
with hydrazine hydrate and methanol as nucleophiles, yielding
compounds 1 and 8. In an attempt to form a hydrazinium salt
of 2, the precursor molecule 1 was obtained and isolated in
almost quantitative yield. Furthermore, treatment of 2 in
methanol at 60 °C furnished methyl nitrocarbamate (8)
Figure 5. Schematic initiation test setup (left), result of the initiation
test of potassium salt 4 toward PETN (center), and flame test of 5 mg
of 4 with the moment of detonation (right).
(Scheme 2).
The sensitivities cover almost the entire spectrum and range
from the insensitive guanidinium salt 6 (impact sensitivity (IS)
Scheme 2. Proposed Decomposition Mechanism of 2 and
Trapping Reactions of the Intermediate Nitroisocyanate
with Methanol and Hydrazine Hydrate As Nucleophiles
=
40 J; friction sensitivity (FS) = 324 N) to the extremely
sensitive potassium salt 4 (IS < 1 J; FS < 0.1 N). Neutral
HNCA has sensitivities of <1 J toward impact and 0.5 N
toward friction, which are in the ranges for a primary explosive.
The electrostatic discharge (ESD) sensitivities follow the
general sensitivity trend. No ESD sensitivity values are given
for 3 and 7 because those salts melted under the electrical load.
For all of the water-free compounds, the detonation
parameters were calculated using the EXPLO5 code (further
details and results are provided in the Supporting Informa-
tion). All of the metal-free compounds (2 and 5−7) show
26
positive enthalpies of formation. The calculated detonation
−
1
velocity (V ) values range from 7441 m/s for the potassium
det
salt 4 to a remarkable value of 9460 m/s for the
hydroxylammonium salt 7 (Table 1). Thus, 7 outperforms
HMX (Vdet = 9193 m/s) in terms of detonation velocity and
has a value close to that of CL-20 (Vdet = 9772 m/s). The
neutral compound 2 has Vdet = 8333 m/s and a detonation
Besides the guanidinium salt 6 (115 °C), the most
temperature-stable compound is the potassium salt, which
decomposes by detonation at 120 °C (Table 1). Therefore,
KNCA (4) was investigated in a classic initiation capability test
using pressed pentaerythritol tetranitrate (PETN) as the main
charge. Salt 4 (30 mg) was loosely filled on top of the
secondary explosive and ignited using an electrical ignitor, and
it was able to cause a positive deflagration-to-detonation
transition (DDT) toward the PETN loading (Figure 5). This
was indicated by a hole in the copper plate and fragmentation
of the shell.
pressure (P ) of 270 kbar, which are similar to those of PETN
CJ
(Vdet = 8429 m/s; PCJ = 308 kbar).
In summary, the synthesis and thorough characterization of
nitrocarbamoyl azide (HNCA, 2) and several salts are
reported. HNCA is solid at room temperature (because of
the strong hydrogen bridge with a length of d(D−H···A =
2.808(2) Å), melts at 72 °C, and decomposes at 83 °C. The
predominantly sensitive compounds show interesting results in
the calculation of the detonation parameters, especially the
hydroxylammonium salt 7 with Vdet = 9460 m/s. The
potassium salt 4 is a high-performing primary explosive that
Table 1. Energetic Properties and Detonation Parameters of 1−7
1
2
3
4
5
6
7
formula
CH N O ·H O
5
48
0.1
1.814
87.0
−11.6
156
−88.5; −0.65
CHN O
<1
0.5
n.d.
1.708
90.0
6.1
NaCN O ·H O
<1
0.4
0.065
1.891
78.4
0
KCN O3
<1
<0.1
<0.01
1.986
69.8
0
120
CH N O
6
20
0.16
1.683
89.2
−10.8
79
C H N O
40
324
0.27
1.604
84.2
−33.7
115
CH N O
4
4
4
3
2
5
3
5
3
2
5
4
6
3
2
6
8
3
4
6
a
IS [J]
FS [N]
≤3
b
≤40
n.d.
1.803
90.2
0
c
ESD [J]
ρ [g/cm]
d
e
N+O [%]
f
Ω [%]
g
Tdec [°C]
83
81
93
0
h
Δ H [kJ/mol; kJ/g]
147.5; 1.13
−350.6; −2.05
−63.4; −0.375
85.6; 0.578
63.6; 0.334
141.8; 0.864
f
EXPLO5 V6.05.02
0
i
−
Δ U [kJ/kg]
−
−
−
5066
270
8333
−
−
−
4227
223
7441
4924
293
8620
3853
222
7879
6233
367
9460
ex
j
PCJ [kbar]
Vdet [m/s]
k
a
b
c
d
e
Impact sensitivity. Friction sensitivity. Electrostatic discharge. From X-ray diffraction analysis recalculated to 298 K. Combined nitrogen and
f
g
−1
h
oxygen content. Oxygen balance with respect to CO formation. Decomposition temperature (onset values; β = 5 °C min ). Calculated
enthalpy of formation. Calculated energy of formation. Detonation pressure. Detonation velocity.
2
i
j
k
1
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J. Am. Chem. Soc. 2021, 143, 1323−1327

Journal of the American Chemical Society
pubs.acs.org/JACS
Communication
showed a positive result in an initiation test on 200 mg of
PETN. A mechanism for the decomposition of 2 was proposed
and verified by two trapping experiments. The mechanism
does not follow the Curtius rearrangement as is usual for
carbonyl azides, but instead, elimination of hydrazoic acid to
form an intermediate nitroisocyanate occurs.
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An Exploding Diversity of a Unique Class of Compounds. Angew.
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ASSOCIATED CONTENT
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c12507.
■
(7) Banert, K.; Berndt, C.; Hagedorn, M.; Liu, H.; Anacker, T.;
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Synthesis, Spectroscopic Data, and Reactions of Formyl Azide. Angew.
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AUTHOR INFORMATION
Corresponding Authors
■
(
10) Thiele, J.; Stange, O. Ueber Semicarbazid. Liebigs Ann. Chem.
1
894, 283, 1−46.
Thomas M. Klapo
̈
(11) Mohan, S.; Durairaj, K. S. P.; Jose, S. P. Vibrational Spectra and
Normal Coordinate Analysis of Carbamoylazide. Spectrochim. Acta,
Part A 2003, 59, 1697−1704.
Maximilian University of Munich, D-81377 Munich,
Germany; orcid.org/0000-0003-3276-1157;
Email: tmk@cup.uni-muenchen.de
̈
(12) Roesky, H. W.; Glemser, O. Uber die Darstellung von
Oxalsau
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COCl) with AgN : Evidence for the Formation of Oxalyl Diazide
̈
rediazid. Chem. Ber. 1964, 97, 1710−1712.
Jorg Stierstorfer − Department of Chemistry, Ludwig-
̈
Maximilian University of Munich, D-81377 Munich,
Germany; orcid.org/0000-0002-2105-1275;
Email: jstch@cup.uni-muenchen.de
(
(
2
3
O C (N ) . Bull. Chem. Soc. Jpn. 2005, 78, 1246−1250.
2
2
3 2
(14) Banert, K.; Berndt, C.; Firdous, S.; Hagedorn, M.; Joo, Y.-H.;
Authors
Ruffer, T.; Lang, H. Extremely Simple but Long Overlooked:
̈
Maximilian Benz − Department of Chemistry, Ludwig-
Maximilian University of Munich, D-81377 Munich,
Germany
Burkhard Krumm − Department of Chemistry, Ludwig-
Maximilian University of Munich, D-81377 Munich,
Germany; orcid.org/0000-0002-2100-4540
Marcus Lommel − Department of Chemistry, Ludwig-
Maximilian University of Munich, D-81377 Munich,
Germany
Generation of α-Azido Alcohols by Hydroazidation of Aldehydes.
Angew. Chem., Int. Ed. 2010, 49, 10206−10209.
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Malhotra, R. NANO/HEDM Technology: Late Stage Exploratory Effort;
Report No. A466714; DARPA/AFOSR-funded, Contract F49620-02-
C-0030; SRI International: Menlo Park, CA, 2003.
(16) Glukhacheva, V. S.; Il’yasov, S. G.; Sakovich, G. V.; Tolstikova,
T. G.; Bryzgalov, A. O.; Pleshkova, N. V. Synthesis, Properties, and
Application of 4-Nitrosemicarbazones. Russ. Chem. Bull. 2016, 65,
5
(
50−560.
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c12507
17) Il’yasov, S. G.; Lobanova, A. A.; Popov, N. I.; Sataev, R. R.
Chemistry of Urea Nitro Derivatives: III. Reactions of N,N′-
Dinitrourea with Bases. Russ. J. Org. Chem. 2002, 38, 1731−1738.
Notes
(
18) Ramos, L. A.; Zeng, X.; Ulic, S. E.; Beckers, H.; Willner, H.;
The authors declare no competing financial interest.
Della Vedova, C. O. Chlorodifluoroacetyl Azide, ClF CC(O)N :
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ACKNOWLEDGMENTS
■
(
19) Baumann, A.; Erbacher, A.; Evangelisti, C.; Klapotke, T. M.;
̈
This work is dedicated to the memory of Professor Klaus
Banert. Financial support of this work by Ludwig-Maximilian
University (LMU), the Office of Naval Research (ONR) under
Grant ONR N00014-19-1-2078, and the Strategic Environ-
mental Research and Development Program (SERDP) under
Contract W912HQ19C0033 is gratefully acknowledged. We
thank Dr. Jiabo Li for providing us with VB2000 version 2.8
and for his help with the CAS calculation. We also thank Dr.
Constantin Hoch for taking the photos of HNCA.
Krumm, B.; Rest, S. F.; Reynders, M.; Sproll, V. Multiply Nitrated
High-Energy Dense Oxidizers Derived from the Simple Amino Acid
Glycine. Chem. - Eur. J. 2013, 19, 15627−15638.
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(
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tke, T. M.; Krumm, B.; Stierstorfer, J.
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