The Exciting Chemistry of 1,1-Diamino-2,2-dinitroethene and 1-Amino-1-hydrazino-2,2-dinitroethene

Article abstract of DOI:10.1021/acs.jpca.7b01742

1,1-Diamino-2,2-dinitroethene (FOX-7) is a relatively new highly energetic material, with good explosive performance and low sensitivity against mechanical stimuli and thermal stress. Therefore, on the one hand, FOX-7 is very stable and a starting material with fairly low reactivity. On the other hand, chlorosulfonyl isocyanate ClSO₂NCO is a very reactive reagent and represents a highly activated form of isocyanic acid HNCO. New derivatives of FOX-7 and its hydrazine analogue 1-amino-1-hydrazino-2,2-dinitroethene, as well as unusual potassium salts, are described. Besides the usual spectroscopic characterization, the structures of all compounds were investigated and discussed by single-crystal X-ray diffraction. The compounds demonstrate good thermal stabilities, very high densities, and excellent sensitivity values. The heats of formation were calculated, and together with the room-temperature densities, the energetic parameters were estimated. The compounds are potential candidates as insensitive high-energy-density materials and starting materials for further chemistry.

Full text of DOI:10.1021/acs.jpca.7b01742

Article
pubs.acs.org/JPCA
The Exciting Chemistry of 1,1-Diamino-2,2-dinitroethene and
1‑Amino-1-hydrazino-2,2-dinitroethene
Quirin J. Axthammer, Burkhard Krumm,* and Thomas M. Klapotke*
̈
Department of Chemistry, Energetic Materials Research, Ludwig-Maximilian University of Munich, Butenandtstraße 5−13 (D),
81377 Munich, Germany
S
* Supporting Information
ABSTRACT: 1,1-Diamino-2,2-dinitroethene (FOX-7) is a relatively new highly
energetic material, with good explosive performance and low sensitivity against
mechanical stimuli and thermal stress. Therefore, on the one hand, FOX-7 is very
stable and a starting material with fairly low reactivity. On the other hand,
chlorosulfonyl isocyanate ClSO2NCO is a very reactive reagent and represents a
highly activated form of isocyanic acid HNCO. New derivatives of FOX-7 and its
hydrazine analogue 1-amino-1-hydrazino-2,2-dinitroethene, as well as unusual
potassium salts, are described. Besides the usual spectroscopic characterization, the
structures of all compounds were investigated and discussed by single-crystal X-ray
diffraction. The compounds demonstrate good thermal stabilities, very high
densities, and excellent sensitivity values. The heats of formation were calculated,
and together with the room-temperature densities, the energetic parameters were
estimated. The compounds are potential candidates as insensitive high-energy-
density materials and starting materials for further chemistry.
the three types of reactions are (1) nucleophilic substitution on
the NH2 groups, (2) reaction with the double bond, and (3)
electrophilic attacks on either the amino groups or the
negatively charged carbon atom.9 In spite of that, rather a
broad range of chemical reactions are reported, including
alkylation, acylation, acetylation, coordination, halogenation,
transamination, nitration, and salt formation.10−12
In an ongoing effort to design less sensitive, powerful, green
explosives the modification of the molecular structure of FOX-7
could be a promising route, to obtain new insensitive energetic
materials. The enlargement of the planar π-system of FOX-7
with a carbamoyl group (−CONH2) should lead to a further
improvement of the structure and enhance the stability.
Additionally, the ability for the creation of hydrogen bonds is
increased, due to further additional donor and acceptor groups.
But which kind of influence does this have on the physical
properties and the explosive performance?
INTRODUCTION
■
The 1,1-diamino-1,1-dinitroethene molecule (FOX-7) was first
mentioned two decades ago in 1998 and was shown to be a
relatively new highly energetic dense molecule.1 FOX-7 has
captured an important role in the research of energetic
materials, due to its thermal stability and its insensitivity to
impact and friction, while the performance is similar to the
currently used common secondary explosives hexogen, cyclo-
trimethylene trinitramine (RDX) and pentaerythritol tetrani-
trate (PETN).2 The typical structural features of FOX-7 are
demonstrated by alternating amino and nitro groups in the
solid state.
This special arrangement and the highly associated grade of
hydrogen bonds cause an extremely insensitive energetic
material.3−5 The location of two electron-donating, NH2
groups on one carbon and two electron-withdrawing NO2
groups on the other carbon make FOX-7 a good example of a
push−pull alkene with strong polarization of the double bond.6
The molecule can be seen as a resonance hybrid between the
mesomeric structures A, A1, A2, A3, and A4 and the tautomers
B and C (Scheme 1).
The main consequences of this polarization are (1) the
carbon bearing the amino groups are relatively electron-
deficient and susceptible to attack by nucleophiles, (2) the
hydrogen atoms are more acidic than those of simple amines,
and (3) the amine nitrogen atoms are poor nucleophiles.6
All of these aspects make the chemistry of FOX-7
unpredictable.6 Furthermore, the reactivity is low, and the
three possible active sites of this quite small molecule make
chemistry with FOX-7 extremely challenging.7,8 Consequently,
EXPERIMENTAL SECTION
■
Caution! All compounds discussed here are energetic materials with
sensitivity toward heat, impact, and friction. No hazards occurred
during preparation and manipulation; additional proper protective
precautions (face shield, leather coat, grounded equipment and
shoes, Kevlar gloves, and ear plugs) should be used when
undertaking work with these materials. Special care should be
taken when working with 1-amino-1-hydrazino-2,2-dinitroethene
Received: February 22, 2017
Revised: April 3, 2017
© XXXX American Chemical Society
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Scheme 1. Resonance Hybrid Structures of FOX-7
(HFOX). It is reported that HFOX undergoes spontaneous
energetic decomposition!!!
1H NMR ([D6]DMSO): δ = 9.47 (s, 1H, CNH2), 8.52 (s,
1H, CNH2), 6.11 (s, 1H, CONH2), 5.90 (s, 1H, CONH2) ppm.
13C{1H} NMR ([D6]DMSO): δ = 167.0 (CO), 157.1 (CNH2),
133.6 (CNO2) ppm. 14N NMR ([D6]DMSO): δ = −24 (s,
NO2) ppm. IR (cm−1): ν = 3443 (w), 3276 (w), 3166 (w),
1674 (m), 1630 (w), 1595 (s), 1503 (s), 1367 (m), 1350 (m),
1302 (m), 1245 (vs), 1171 (m), 1155 (m), 1130 (vs), 1077
(m), 925 (w), 851 (w), 816 (w), 779 (w), 769 (w), 749 (w).
Raman (1064 nm, 500 mW): ν = 3280 (3), 1595 (5), 1503
(12), 1397 (32), 1352 (44), 1238 (31), 1172 (36), 1132 (39),
1123 (34), 1083 (4), 926 (10), 852 (100), 750 (9), 653 (9),
525 (12). Anal. Calcd (%): C3H4N5O5K (229.19): C 15.72, H
1.76, N 30.56; found: C 15.75, H 1.85, N 30.17. DSC (5 °C
min−1, onset): 155 °C (melt), 191 °C (dec). BAM drop-
hammer: 20 J. Friction tester: 360 N, ESD: 0.5 J (grain size
<100 μm).
1-(1-Amino-2,2-dinitrovinyl)urea (1). Dry acetonitrile
(50 mL) was placed in an ice bath, and chlorosulfonyl
isocyanate (CSI) (2.12 g, 15 mmol) was added. The FOX-7
(1.48 g, 10 mmol) was added in portions, and the mixture was
further stirred 10 min at 0 °C. The ice bath was removed, and
stirring at room temperature was continued for 1.5 h, whereby
the solution became homogeneous. The clear reaction mixture
was again cooled with an ice bath and quenched carefully with
water (20 mL). The stirring was continued at room
temperature for 0.5 h. The organic solvent was removed on
the rotary evaporator. The formed precipitate was filtered off,
washed with water, and dried under high vacuum to obtain
yellow pure 1 (72%).
1H NMR ([D6]DMSO): δ = 11.37 (s, 1H, NH), 10.71 (s,
1H, CNH2), 10.58 (s, 1H, CNH2), 7.70 (s, 1H, CONH2), 6.87
(s, 1H, CONH2) ppm. 13C{1H} NMR ([D6]DMSO): δ =
156.8 (CNH2), 155.1 (CO), 128.5 (CNO2) ppm. 15N NMR
([D6]DMSO): δ = −25.8 (s, NO2), −250.1 (d, NH, 1JNH = 90.8
2-(1-Amino-2,2-dinitrovinyl)hydrazine-1-carboxa-
mide (3). HFOX (0.82 g, 5.0 mmol) was dissolved in dry
acetonitrile (20 mL) and placed in an ice bath. CSI (0.74 g, 5.2
mmol) was added slowly at 0 °C. The ice bath was removed,
and stirring at room temperature was continued for 1 h. The
reaction mixture was again cooled in an ice bath, water (10 mL)
was added with caution, and the mixture was stirred for 10 min
at room temperature. The organic solvent was removed on the
rotary evaporator. The formed yellow precipitate was filtered
off, washed with a little cold water, and dried to obtain pure 3
(77%). The water-free product was obtained by dehydration at
70 °C for 24 h under high vacuum.
Hz), −253.0 (t, NH2, 1JNH = 91.8 Hz), −289.1 (t, NH2, 1JNH
=
90.0 Hz) ppm. IR (cm−1): ν = 3425 (m), 3321 (m), 3304 (m),
3221 (m), 3188 (m), 1716 (s), 1639 (m), 1620 (w), 1536 (m),
1503 (s), 1374 (m), 1337 (m), 1269 (m), 1195 (s), 1153 (s),
1129 (m), 1103 (m), 1062 (m), 933 (w), 869 (w), 783 (w),
751 (m), 711 (m), 682 (w). Raman (1064 nm, 500 mW): ν =
3305 (8), 1701 (9), 1629 (9), 1556 (5), 1493 (5), 1356 (29),
1334 (31), 1274 (44), 1204 (100), 1159 (27), 1131 (31), 1106
(8), 1065 (35), 941 (7), 871 (60), 788 (6), 685 (5), 602 (22).
MS (DEI+) m/e: 191.2 [M+], 148.2 [(M−HNCO)+]. Anal.
Calcd (%): C3H5N5O5 (191.10): C 18.86, H 2.64, N 36.36;
found: C 19.01, H 2.59, N 36.38. Differential scanning
calorimetry (DSC; 5 °C min−1, onset): 209 °C (dec). BAM
drophammer: 40 J. Friction tester: 360 N, ESD: 1.0 J (grain size
<100 μm).
1H NMR ([D6]DMSO): δ = 11.49 (s, 1H, CNH), 9.90 (s,
1H, CNH2), 9.70 (s, 1H, CNH2), 8.83 (s, 1H, CONH), 6.26 (s,
2H, CONH2) ppm. 13C{1H} NMR ([D6]DMSO): δ = 158.9
(CNH2), 157.6 (CO), 125.6 (CNO2) ppm. 15N NMR
1
([D6]DMSO): δ = −26.5 (s, NO2), −247.5 (d, NH, JNH
=
1
102.7 Hz), −265.9 (t, NH2, JNH = 90.5 Hz), −274.9 (d, NH,
1JNH = 95.8 Hz), −305.5 (t, NH2, JNH = 85.3 Hz) ppm. IR
1
(cm−1): ν = 3588 (w), 3473 (w), 3369 (m), 3264 (w), 3197
(w), 1689 (s), 1610 (m) 1570 (m), 1522 (s), 1500 (s), 1363
(m), 1297 (w), 1227 (m), 1187 (vs), 1140 (s), 1093 (s), 1035
(m), 871 (w), 800 (m), 780 (w), 749 (w), 715 (w), 667 (w).
Raman (1064 nm, 800 mW): ν = 3380 (5), 3290 (7), 1709 (7),
1589 (10), 1555 (25), 1535 (52), 1423 (21), 1379 (30), 1353
(76), 1300 (100), 1270 (46), 1206 (30), 1147 (27), 1103 (50),
1048 (26), 959 (7), 873 (91), 802 (9), 789 (8), 751 (13). Mass
spectometry (MS) (DEI+) m/e: 206.1 [M+]. Anal. Calcd (%):
C3H6N6O5 × 0.5H2O (206.12): C 16.75, H 3.28, N 39.07;
Potassium 2-Amino-2-(carbamoylimino)-1,1-dinitroe-
than-1-ide (2). The urea 1 (0.38 g, 2.0 mmol) was suspended
in 4 mL of water and was placed in an ice bath. To this
suspension a cooled solution of potassium hydroxide (4 mL of
water, 0.12 g, 2.1 mmol) was added dropwise, whereupon the
reaction mixture became a clear solution. The solution formed
was diluted with methanol (30 mL) and cooled in an ice bath.
The resulting orange precipitate was filtered off, washed with
methanol, and dried to obtain the potassium salt 2 (82%).
B
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found: C 16.68, H 3.29, N 39.00. DSC (5 °C min−1, onset): 97
°C (loss of water). 170 °C (dec). BAM drophammer: 6 J.
Friction tester: 360 N, ESD: 0.3 J (grain size <100 μm
dehydrated).
Potassium 2-Amino-2-(2-carbamoylhydrazono)-1,1-
dinitroethan-1-ide (4). The carboxamide 3 (0.41 g, 2.0
mmol) was suspended in 4 mL of water and was placed in an
ice bath. To this suspension a cooled solution of potassium
hydroxide (4 mL of water, 0.12 g, 2.1 mmol) was added
dropwise, whereupon the reaction mixture became a clear
solution. The solution formed was diluted with methanol (30
mL). The resulting yellow precipitate was filtered off, washed
with methanol, and dried to obtain the yellow potassium salt 4
(62%).
39.04. DSC (5 °C min−1, onset): 129 °C (dec). BAM
drophammer: 9 J. Friction tester: 360 N, ESD: 0.2 J (grain
size <100 μm).
Potassium (1-Carbamoyl-5-oxo-1,2,4-triazol-3-yl) di-
nitromethanide (6_K). 5 (0.49 g, 2.0 mmol) was stirred in
water (10 mL), and a saturated solution of potassium
bicarbonate was added to the reaction mixture until the pH
value was stable at ∼7.5. The formed lemon-yellow precipitate
was filtered off and washed with water. The product was
recrystallized from hot water to obtain pure 6_K (81%).
1H NMR ([D6]DMSO): δ = 12.15 (s, 1H, NH), 7.70 (s, 1H,
NH2), 7.67 (s, 1H, NH2) ppm. 13C{1H} NMR ([D6]DMSO): δ
= 154.0 (CO), 149.6 (CO), 140.7 (CNN), 123.9 (CNO2) ppm.
15N NMR ([D6]DMSO): δ = −22.9 (s, NO2), −115.5 (s,
CNNCONH2), −188.5 (s, CNNCONH2), −235.3 (s, NH),
1H NMR ([D6]DMSO): δ = 8.17 (s, 1H, CNNH), 5.91 (s,
2H, CNH2), 5.87 (s, 2H, CONH2) ppm. 13C{1H} NMR
([D6]DMSO): δ = 158.2 (CO), 139.6 (CNN), 132.0 (CNO2)
ppm. 14N NMR ([D6]DMSO): δ = −22 (NO2) ppm. IR
(cm−1): ν = 3595 (w), 3495 (w), 3418 (m), 3329 (w), 3227
(w), 3038 (w), 2911 (w), 1726 (m), 1652 (m), 1621 (w), 1573
(w), 1495 (m), 1470 (m), 1383 (s), 1345 (m), 1203 (s), 1133
(m), 1095 (vs), 1065 (vs), 1001 (m), 850 (w), 753 (m), 738
(w). Raman (1064 nm, 500 mW): ν = 1668 (14), 1622 (7),
1570 (4), 1510 (4), 1483 (5), 1442 (4), 1372 (29), 1347 (31),
1227 (9), 1205 (20), 1153 (14), 1105 (22), 1075 (11), 1010
(7), 853 (100), 774 (6), 762 (8). Anal. Calcd (%): C3H5N6O5K
(244.21): C 14.76, H 2.06, N 34.41; found: C 14.56, H 2.32, N
33.85. DSC (5 °C min−1, onset): 165 °C (dec.). BAM
drophammer: 20 J. Friction tester: 360 N, ESD: 0.3 J (grain size
<100 μm dehydrated).
1
−295.5 (t, NH2, JNH = 90.3 Hz) ppm. IR (cm−1): ν = 3441
(w), 3324 (m), 3285 (w), 1767 (m), 1736 (s), 1719 (m), 1583
(m), 1506 (m), 1485 (m), 1440 (w), 1386 (s), 1198 (vs), 1123
(vs), 1081 (s), 957 (s), 835 (w), 785 (w), 775 (w), 749 (s), 690
(m), 680 (m), 655 (w). Raman (1064 nm, 800 mW): ν = 3331
(5), 1733 (7), 1590 (47), 1505 (9), 1442 (5), 1442 (5), 1379
(93), 1319 (10), 1288 (18), 1215 (30), 1155 (10), 1138 (38),
1087 (21), 959 (100), 836 (63), 794 (31), 758 (6), 681 (3).
MS (FAB+) m/e: 233.3 [(M+H)+], 188.3 [(M−HNCO)+].
Anal. Calcd (%): C4H3N6O6K (270.20): C 17.78, H 1.12, N
31.10; found: C 17.75, H 1.28, N 30.81. DSC (5 °C min−1,
onset): 198 °C (dec). BAM drophammer: 20 J. Friction tester:
360 N, ESD: 0.3 J (grain size <100 μm dehydrated).
RESULTS AND DISCUSSION
■
2-(2,2-Dinitro-1-ureidoethylidene)hydrazine-1-car-
boxamide (5). HFOX (1.64 g, 10.0 mmol) was dissolved in
dry acetonitrile (20 mL) and placed in an ice bath. CSI (3.54 g,
25.0 mmol) was added slowly at 0 °C. The ice bath was
removed, and stirring at room temperature was continued for 2
h. The reaction mixture was again cooled in an ice bath, water
(15 mL) was added with caution, and the mixture was stirred
for 10 min at room temperature. The organic solvent was
removed completely on the rotary evaporator. The formed
colorless precipitate was filtered off and dried to obtain 5
(56%).
The lone-pair electrons of the two amino groups make FOX-7
act as a nucleophilic molecule to undergo nucleophilic addition
reactions. However, the nucleophilicity of FOX-7 is not very
high; therefore, it reacts only with strong electrophilic reagents.
An indication of the low reactivity of the amino nitrogen atoms
is the low conversion rate with acetyl chloride or methyl
isocyanate. Although in the presence of the catalyst hafnium
triflate, pure acetyl chloride reacts with FOX-7 only with 23%
yield to the mono-N-acetyl product.13 For the conversion or
implementation of an urea moiety to the FOX-7 unit, only
highly activated reagents should be considered. For this reason,
FOX-7 shows neither nucleophilic substitution reactions with
urea or ethyl carbamate (transamination), nor a nucleophilic
addition to isocyanic acid, HNCO, to form a corresponding
urea derivative.
1H NMR ([D6]DMSO): δ = 12.17 (s, 1H, CNH), 7.69 (s,
2H, CNH), 6.93 (s, 4H, CONH2), 13C NMR ([D6]DMSO): δ
= 154.0 (CO), 149.5 (CO), 140.5 (CNN), 123.5 (br, CNO2)
ppm. 15N NMR ([D6]DMSO): δ = −26.5 (s, NO2), −247.5 (d,
1
1
NH, JNH = 102.7 Hz), −265.9 (t, NH2, JNH = 90.5 Hz),
The formal insertion of HNCO into one NH bond was
successful with the two extremely activated isocyanates
trichloroacetyl isocyanate (TAI) and chlorosulfonyl isocyanate
(CSI). Both reagents are easy-to-handle liquids, which quickly
react with nucleophiles mostly already at low temper-
atures.14−17 Advantageous is also the formation of a
trichloroacetyl, respectively chlorosulfonyl intermediate, which
prevents multiaddition during the reaction time. The new urea
derivative 1-(1-amino-2,2-dinitrovinyl)urea (1) is released by
aqueous workup of the reaction mixture.17,18 However, the
rather expensive TAI reagent prompted the use of the more
inexpensive reagent CSI, which also is more activated, due to
the strong electron-withdrawing chlorosulfonyl group.16,17
During experiments with CSI and FOX-7, it became obvious
that the order of addition, the temperature, as well as the
dilution are very critical parameters for a successful preparation
of 1. Furthermore, slow addition of CSI to FOX-7 resulted in
the formation of different side products, via the reaction with
1
1
−274.9 (d, NH, JNH = 95.8 Hz), −305.5 (t, NH2, JNH = 85.3
Hz) ppm. H NMR (CD3CN): δ = 7.88 (s, 1H, CH), 7.68 (s,
1
1H, CNH), 6.44 (s, 1H, CNH), 3.6 (br s, 4H, CONH2) ppm.
13C NMR (CD3CN): δ = 153.4 (CO), 149.0 (CO), 135.3 (d,
2
1
CNN, JCH = 4.8 Hz), 104.8 (d, CH(NO2)2, JCH = 172.7 Hz)
ppm. 14N NMR ([CD3CN): δ = −24 (NO2) ppm. IR (cm−1):
ν = 3636 (m), 3363 (m), 3237 (w), 3005 (m), 2908 (w), 2761
(w), 2698 (w), 1760 (s), 1724 (s), 1629 (w), 1604 (s), 1584
(vs), 1498 (s), 1381 (m), 1357 (m), 1322 (s), 1299 (m), 1270
(m), 1241 (m), 1184 (m), 1150 (w), 1091 (m), 1013 (s), 936
(w), 867 (m), 826 (s), 791 (m), 759 (w), 746 (m), 715 (w),
683 (w). Raman (1064 nm, 800 mW): ν = 3125 (12), 3007
(22), 1776 (14), 1603 (31), 1577 (81), 1398 (13), 1372 (25),
1323(24), 1243 (18), 1186 (22), 1153 ((26), 1104 (28), 939
(100), 914 (32), 870 (8), 795 (8), 619 (10), 573 (9), 538 (16).
MS (DEI+) m/e: 249.2 [M+]. Anal. Calcd (%): C4H7N7O6
(249.14): C 19.28, H 2.83, N 39.35; found: C 19.48, H 2.92, N
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the second active site, the chlorosulfonyl group of CSI. This
problem was overcome by rapid addition of the CSI reagent. A
more practical solution was to adopt an inverse addition
protocol with a quite large excess of the CSI reagent. This
method reproducibly afforded clean conversion into 1 (Scheme
2). The hydrolysis of the chlorosulfonyl intermediate was
potassium 2-amino-2-(2-carbamoylhydrazono)-1,1-dinitro-
ethan-1-ide (4).
The remaining amino group of the HFOX molecule is
nucleophilic enough to attack a second CSI reagent to form
another carboxamide, which was proven to be 2-(2,2-dinitro-1-
ureidoethylidene)hydrazine-1-carboxamide (5). The structure
of 5 contains no longer a CC double bond. The
dinitromethyl moiety is now protonated, which is also visible
due to the appearance of colorless 5. During recrystallization
from water, the solution immediately turned yellow, which
most likely is from the proton transfer of the dinitromethyl unit
to the hydrazine moiety by reforming the double bond (see
Scheme 4). Such double bonds often absorb light in the visible
Scheme 2. Synthesis of 1-(1-Amino-2,2-dinitrovinyl)urea (1)
and Its Potassium Salt (2)
Scheme 4. Tautomerization of 2-(2,2-Dinitro-1-
ureidoethylidene)hydrazine-1-carboxamide (5)
performed upon addition of water to the reaction mixture.
Subsequent concentration of the organic solvents and simple
filtration allowed the isolation of pure 1 in a yield of 72%. No
reaction of both amino groups of FOX-7 under any conditions
could be observed.
The anion of 1 (Scheme 2) can be generated by treatment
with potassium hydroxide to give potassium 2-amino-2-
(carbamoylimino)-1,1-dinitroethan-1-ide (2). The experimental
procedure with cold aqueous KOH solution was one-to-one
adopted from the synthesis of the potassium salt of FOX-7.19
The hydrazine derivative of FOX-7, 1-amino-1-hydrazino-
2,2-dinitroethene (HFOX, Scheme 3), was synthesized by
blue region and thus appear as yellow material. The attempt to
obtain the isomer with a CC double bond by an induced
proton transfer with slightly basic potassium bicarbonate failed.
Instead, the formation of another anion, the (1-carbamoyl-5-
oxo-1,2,4-triazol-3-yl)dinitromethanide (6_K) as the potassium
salt, was observed and isolated. This unexpected intermolecular
cyclization reaction to the heterocycle 1,2,4-triazol-5-on 6 is
very fast with good yields. The reaction mechanism for this
cyclization was not further investigated but presumably resulted
from nucleophilic attack of the urea moiety by the neighboring
hydrazino group with elimination of ammonia. This is even
more remarkable, since the hydrazino moiety is deactivated by
the attached carbamoyl group. In the literature this type of
reaction was observed only once before by treating
alkoxycarbonylthioamides with hydrazine under elimination of
H2S.26 This condensation−cyclization reaction with intra-
molecular elimination of ammonia could be a valuable synthetic
tool for the preparation of 1,2,4-triazol-5-ones. The ammonia
salt of (1-carbamoyl-5-oxo-1,2,4-triazol-3-yl)dinitromethanide
(6_NH4) was prepared similarly by the reaction of 5 with
ammonium bicarbonate. Both these salts exhibit differing
solubility properties in water; whereas the potassium salt 6_K
is poorly soluble, the ammonium salt 6_NH4 is very soluble in
water.
Scheme 3. Synthesis Overview of Reaction of 1-Amino-1-
hydrazino-2,2-dinitroethene and Chlorosulfonyl Isocyanate
a. NMR and Vibrational Spectroscopy. All compounds
1
were thoroughly characterized by H, 13C, and 14/15N NMR
spectroscopy (Table 1). In the 1H NMR spectrum the attached
carbamoyl group appears at 7.70/6.87 (1), 6.26 (3), and 7.70/
7.67 ppm (6_K) and is often separated in two signals due to
restricted rotation about the C−NH2 bond.27 This phenom-
enon was also observed for the ethylene-bound C−NH2 group,
which appears at 10.71/10.58 (1) and 9.90/9.70 ppm (3), ∼2
ppm shifted to lower field compared to the starting materials
FOX-7 and HFOX. The C−NH groups are located at rather
low field at 11.37 (1), 11.49 (3), 12.17 (5), and 12.15 ppm
(6_K) and are the most acidic hydrogens.
reaction with hydrazine hydrate,20−22 and it is reported that
HFOX undergoes spontaneous energetic decomposition.22,23
Our intention was to use the relatively high energy of the
hydrazine group in the HFOX molecule and subsequently to
add a carbamoyl moiety to hope for a reduction of the
sensitivity and safer handling.24,25 In contrast, the reaction of
CSI and HFOX occurs more readily than with FOX-7, due to
the increased electron density of the NH2 group in the
hydrazine moiety. The formation of 2-(1-amino-2,2-
dinitrovinyl)hydrazine-1-carboxamide (3) is very fast, proceed-
ing already at low temperature and without the need of an
excess of CSI. Furthermore, again an interesting anion can be
generated upon treatment with KOH to form the salt
As already indicated, compound 5 shows a special chemical
behavior in different solvents. In the solid state as well as in
acetonitrile solution, a dinitromethyl group is formed by
migration of one former amino hydrogen with imine bond
D
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Table 1. Multinuclear NMR Data (1H, 13C, 15N) of 1, 3, 5 and 6_K in ppm (Number of Hydrogens/Multiplicity)
1
3
5
6_K
solvent
CNH2
[D6]DMSO
[D6]DMSO
[D6]DMSO
CD3CN
[D6]DMSO
1H
10.71/10.58 (2)
7.70/6.87 (2)
11.37 (1)
9.90/9.70 (2)
6.26 (2)
CONH2
NH
6.93 (4)
12.17 (1)
7.69 (2)
3.64 (4)
6.44 (1)
7.68 (1)
7.88 (1)
104.8
7.70/7.67 (2)
12.15 (1)
11.49 (1)
8.83 (1)
N(H)NHCO
CH
13C{1H}
CNO2
CNH2/CN
CO
128.5
156.8
155.1
125.6
158.9
157.6
123.5
123.9
140.7
154.0
149.6
140.5
135.3
154.0
153.4
CO
149.5
149.0
15N
CNH2
CONH2
NH
−253.0 (t)
−289.1 (t)
−250.1 (d)
−265.9 (t)
−305.5 (t)
−247.5 (d)
−274.9 (d)
not measured
−295.5 (t)
−235.3 (s)
NH
CN
NNCO
NO2
−115.5 (s)
−118.5(s)
−22.9 (s)
−25.8 (s)
−26.5 (s)
(14N − 24 (s))
formation, whereas in the slightly basic DMSO this hydrogen
remains at the hydrazine moiety (Scheme 4).
172.7 Hz. The hydrogen of the dinitromethyl group couples
also with the carbon of the CNNH group and appears as a
doublet at 135.3 ppm (C) with a smaller coupling constant of
2JCH 4.8 Hz. In contrast, in the spectrum with DMSO as solvent
no such 1H−13C coupling is visible due to the prevailing
structure of isomer 5−2. In the 13C NMR spectra the most
significant carbon resonances are of the carbonyl moieties. The
signals of the carbonyl groups of the urea moieties are located
in the narrow range from 157.6 to 154.0 ppm. After insertion of
a second urea group, the resonances are observed upfield at
149.5 (5) and 149.6 ppm (6_K). The carbon signal of the
dinitromethyl moiety is observed in the range from 128.5 to
123.5 ppm. In the case of 5−1, where the dinitromethyl group
is protonated, the resonance is shifted strong upfield to 104.8
ppm, due to the decreased electron density on the carbon atom.
The CNH2N-group resonance is located at 155.1 (1) and 158.9
ppm (3), being less intense and broadened compared to the
other carbon resonances. In the molecule 5 and in the
heterocyclic anion 6_K the resonances are shifted to 140.5
(DMSO)/135.3 (CD3CN) (5) and 140.7 ppm (6_K), due to
the double bond imine character to one of the nitrogen atoms.
In the 14N NMR spectra of all compounds as expected, only the
resonances of the nitro groups are detected in the range from
−23 to −27 ppm. Additionally, the compounds 1, 3, and 6_K
were further investigated by 15N NMR spectroscopy (Figure 2),
and the assignments were based and supported on comparison
with theoretical calculations (MPW1PW91/aug-cc-pVDZ) and
reported analoguous compounds.28,29 The carboxamide 5 could
not be investigated by 15N NMR spectroscopy, due to its
instability and slow conversion to 6. The nitrogen resonance of
the carbamoyl C(O)NH2 group is located in the high-field area
at −289.1 (1), −305.5 (3), and −295.5 ppm (6_K). The
This phenomenon is also observable in the 1H and 13C NMR
spectra with assignments based on the acquisition of different
NMR experiments in several solvents and concentrations. The
NH2 hydrogen atoms of the two chemically different
−C(O)NH2 groups are located in DMSO at 6.93 ppm and
in CD3CN at 3.64 ppm, both as slightly broadened resonances.
While in DMSO two NH resonances at 12.17 (1H) and 7.69
ppm (2H) are present, in CD3CN solution two NH resonances
at 7.68 and 6.44 ppm and one CH resonance at 7.88 ppm are
found. These tautomer structures were also confirmed by the
1H coupled 13C NMR spectra, shown in Figure 1. In acetonitrile
the dinitromethyl group according isomer 5−1 is detected as a
1
doublet at 104.8 ppm (D) with a coupling constant of JCH
1
signals are split into a triplet, due to the J coupling with the
two NH2 hydrogen atoms. The triplets of the C−NH2 moieties
are shifted to lower fields at −253.0 (1) and −265.9 ppm (3)
compared to the carbamoyl groups. The NH resonances that
are split into doublets are located at −250.1 (1) and −247.5/
274.9 ppm (3). The 1,2,4-triazol-5-on unit in compound 6_K
shows three resonances at −235.3, −188.5, and −115.5 ppm.
The imine-type nitrogen (B) is located at −115.5 ppm, and
the neighboring trivalent nitrogen (C) is at −188.5 ppm. The
resonance of the NH nitrogen is located at −235.3 ppm (D); a
Figure 1. 13C NMR spectra of 2-(2,2-dinitro-1-ureidoethylidene)-
hydrazine-1-carboxamide (5) in CD3CN (red) and [D6]DMSO
(blue).
E
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Information. In Table 2 are summarized the most important
atom distances and angles of all structures in comparison to
FOX-7 and HFOX.
The compound 1 crystallizes in the triclinic space group P1.
̅
The unit cell contains six molecules, and the density is as high
as FOX-7 with a value of 1.898 g cm−3. The asymmetric unit
consists of three nearly identical molecules; the molecular
structure of one molecule is shown in Figure 3. The C−C atom
Figure 3. X-ray molecular structure of 1-(1-amino-2,2-dinitrovinyl)-
urea (1). Selected atom distances (Å) and angles (deg): O1−N1
1.234(3), O5−C3 1.227(3), N1−C1 1.418(3), N2−C1 1.404(3),
N3−C2 1.309(3), N4−C2 1.362(3), N4−C3 1.408(3), N5−C3
1.327(3), C1−C2 1.443(3), N4−C2−N3 118.7(2), N4−C2−C1
119.9(2), N3−C2−C1 121.4(2), C2−C1−N1 122.1(2), N1−C1−
N2 116.1(2), N2−C1−C2 121.7(2), N3−C2−C1−N1−165.8(2),
N2−C1−C2−N4−169.8(2), N3−C2−N4−C3 5.5(4), N5−C3−
N4−C2 175.1(2).
Figure 2. 15N NMR spectrum of 1 (blue), 3 (orange) and 6_K
(green) in [D6]DMSO.
distance is 1.440 Å, which is very close to that of the starting
material (1.456 Å). The C2−N4 (1.361 Å) bond is longer than
the C2−N3 (1.306 Å) bond, where no carbamoyl group is
attached. The C3−O5 (1.230 Å) bond seems to be a regular
carbonyl bond. The N4−C3 (1.408 Å) is slightly and the C3−
N5 (1.327 Å) bond is significantly shorter than the atom
distances of common amides/ureas.31 These shortened bonds
indicate that the urea moiety participates in the π-system of the
FOX-7 molecule.13 Another evidence is the essential planarity
of the molecule, only the nitro groups are little out of the plane
with a twist from 3 to 14°. This behavior was also observed in
the FOX-7 structure, where the torsion angle N−C−C−N is
∼5°.5 An additional similarity is the molecular packing. In both
cases infinite two-dimensional layers are formed (Figure 4)
with extensive intra- and intermolecular hydrogen bonds within
N−H coupling is not observed, probably due to the high acidity
and therefore fast proton exchange in DMSO. The vibrational
analysis showed the characteristic asymmetric NO2 stretching
vibrations in the range from 1639 to 1604 cm−1 and the
symmetric stretching vibrations at 1386 to 1337 cm−1. The
carbonyl group of the urea moieties appear around 1715 cm−1.
The N−H stretching vibration in all compounds are quite
dominant in the infrared spectrum and are in the range from
3450 to 3100 cm−1, which indicates strong hydrogen bonds.30
b. X-ray Crystallography. Single crystals suitable for X-ray
diffraction measurements were obtained by crystallization at
room temperature, always from hot water. Full details of the
crystallographic refinement parameters, structure data, and
additional information are displayed in the Supporting
a
Table 2. Bond Lengths and Torsion Angles of FOX-7 Derivatives at 173 K
C−C
C−NH2
C−NH
C−N
C−NO2
N−N
∠, N−C−C−N
FOX-7
HFOX
1
1.456
1.476
1.440
1.322
1.293
1.306
1.413
1.373
1.412
177.8/172.9
90.6/89.4
1.297
1.361
1.404
169.5/165.9
178.2/176.8
170.7/168.0
−83.4/−81.7
175.8/173.6
175.2/172.6
81.5/83.9
2
3
1.490
1.448
1.331
1.316
1.306
1.373
1.410
1.342
1.381
1.382
4
5
1.486
1.500
1.346
1.291
1.274
1.376
1.510
1.411
1.370
102.8/−14.5
92.8/−24.6
88.9/90.5
6_K
1.461
1.448
1.375
1.378
1.295
1.313
1.380
1.391
1.394
1.393
6_NH4
170.8/167.3
a
If more than one unique molecule is in the unit cell, the average atom distance is given.
F
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bond and a shorter C2−N4 bond. Furthermore, the higher
negative charge on the nitrogen N4 leads to a poorer bonding
ability of the carbonyl group and is displayed by the
significantly longer C3−O5 (1.253 Å) bond. The anion can
be separated into two planar π-systems, the dinitromethanide
and the aminomethyl urea unit. Because of the almost
orthogonal arrangement of the two π-systems no attractive
interactions to each other are possible.
The crystal structure of HFOX was already investigated in
the literature.33 For a better comparison, the crystal structure
measurement was repeatedly measured at 173 K, whereupon it
was noticed that the literature measurement is not that good
and that the structure of the hydrazino moiety was
misinterpreted. HFOX crystallizes in the orthorhombic space
group Pnma and with a density of 1.855 g cm−3 (Figure 6). The
Figure 4. Representation of the layered structure of 1.
the layers and weaker van der Waals interactions between the
layers. The good physical-chemical properties of FOX-7, such
as the low sensitivity, are explained by the molecular packing
structure with strong hydrogen bonds.32 In compound 1 the
initial H-bond donors and acceptors are increased, due to the
added carbamoyl group, which leads to higher cross-linking and
thus a lower sensitivity. Intramolecular hydrogen bonds may
also limit the free rotation of the two different amino groups,
which in turn results in four different NH resonances in the 1H
NMR spectrum.
The potassium salt 2 crystallizes in the orthorhombic space
group P212121 with four molecules in the unit cell and one
molecule as asymmetric unit (Figure 5). The single-crystal X-
Figure 6. X-ray molecular structure of HFOX. Selected atom distances
(Å) and angles (deg): C1−C2 1.476, C1−N1 1.373, C1−N1 1.373,
C2−N2 1.294, C2−N3 1.297, N1−O1 1.245(2), N1−O2 1.252(2),
N3−N4 1.404, N1−O1 1.245(2), N3−C2−N2 122, N3−C2−C1 117,
N2−C2−C1 121, N1−C1−N1 123.7, N4−N3−C2−C1 180, N2−
C2−N3−N4 0, N3−C2−C1−N1−90.6, N2−C2−C1−N1−89.4.
molecule is divided by a mirror plane through the following
atoms C1, C2, N2, N3, N4, H1, and H2, which leads to the
asymmetric unit with just one nitro group and a disorder of H3.
HFOX can be regarded as a zwitterion or dipolar ion, where the
negative charge is located at C1 and the positive is at C2.34
Albeit in the optimized calculated gas-phase structure the
molecule is almost planar, in the solid state the dinitromethyl
unit is twisted out of the 1-amino-1-hydrazinomethyl plane by
89.4°. The reason for this behavior may be the strong
electrostatic interactions and the strong hydrogen bonds
between the amino and nitro groups.22,23 This significant
difference of the optimized gas-phase structure and the solid
structure could be a reason for the low stability and the quite
high mechanical sensitivity of HFOX.
Figure 5. X-ray molecular structure of potassium 2-amino-2-
(carbamoylimino)-1,1-dinitroethan-1-ide (2). Selected atom distances
(Å) and angles (deg): C1−C2 1.489(2), C1−N1 1.366(2), C1−N2
1.382(2), C2−N3 1.330(2), C2−N4 1.308(2), C3−N4 1.402(2), C3−
N5 1.331(2), C3−O5 1.251(2), N1−O2 1.240(2), N1−C1−N2
122.7(1), N1−C1−C2 117.3(1), N2−C1−C2 120.0(1), N3−C2−N4
127.9(2), C2−N4−C3 119.5(1), N4−C3−N5 113.1(1), N2−C1−
C2−N3 99.9(2), N1−C1−C2−N4 95.1(2), N3−C2−N4−C3 1.5(3),
C2−N4−C3−N5 177.4(2), C2−N4−C3−O5 0.8(2).
Compound 3 crystallizes in the orthorhombic space group
Pca21 with two molecules and one crystal water in the
asymmetric unit (Figure 7). The molecular structure shows
more similar features with the FOX-7 structure than with
HFOX. For instance, the HFOX part of the molecule 3 is now
planar, only the nitro groups are slightly rotated out of plane.
Furthermore, the C−C, C−NH2, and the C−NO2 atom
distances (Table 2) are in the same range as for FOX-7 and
may explain the significantly higher stability of 3 compared to
HFOX.
ray analysis confirmed the assumption that the deprotonation
takes place at the NH group with the highest acidity, which is
induced by the neighboring electron-withdrawing carbamoyl
moiety. From Table 2, it can be seen that the C−C atom
distance of 1.490 Å is elongated compared to 1 and thus closer
to a single- than a double-bond distance.
In contrast, the C−NO2 bond lengths of C1−N1 (1.366 Å)
and C1−N2 (1.382 Å) are shortened compared to FOX-7 and
1 for an enhanced delocalization and stabilization of the
negative charge on the carbon C1. The carbon atom C2 has, as
a result of the deprotonation of the neighboring nitrogen, also a
higher electron density, which is reflected by a longer C2−N3
The attached urea unit at the hydrazine group generates a
second planelike structure, which is shown by the torsion angle
of N6−C3−N5−N4−170.6(1) and is twisted to the HFOX
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The disubstituted carbamoyl compound 5 crystallizes as
colorless blocks in the triclinic space group P1 with four
̅
molecules in the unit cell and a density of 1.732 g cm−3. The
asymmetric unit contains two nearly identical molecules; one is
displayed in Figure 9. The carbon atom C1 bearing the two
Figure 7. X-ray molecular structure of 2-(1-amino-2,2-dinitrovinyl)-
hydrazine-1-carboxamide (3). Selected atom distances (Å) and angles
(deg): O5−C3 1.233(2), O2−N1 1.229(2), O1−N1 1.246(2), O4−
N2 1.238(2), O3−N2 1.236(2), N2−C1 1.412(2), N1−C1 1.409(2),
N4−N5 1.389(2), N4−C2 1.345(2), N3−C2 1.315(2), N5−C3
1.386(2), N5−H4 0.84(3), N6−C3 1.341(2), C1−C2 1.443(2), N1−
C1−N2 115.5(1), N1−C1−C2 123.1(1), N2−C1−C2 121.4(1), C1−
C2−N3 120.9(1), N3−C2−N4 118.7(1), C2−N4−N5 118.2(1), N4−
N5−C3 118.0(1), N2−C1−C2−N4 172.6(1), N1−C1−C2−N3
175.2(1), C1−C2−N4−N5−179.4(1), N6−C3−N5−N4−170.6(1),
O2−N1−C1−C2−162.0(1), C2−N4−N5−C3−99.7(1).
Figure 9. X-ray molecular structure of 2-(2,2-dinitro-1-
ureidoethylidene)hydrazine-1-carboxamide (5). Selected atom dis-
tances (Å) and angles (deg): C1−C2 1.506(3), C1−N1 1.518(2),
C1−N2 1.509(3), C1−H1 0.87(2), C2−N4 1.377(3), C2−N5
1.273(3), C3−N3 1.331(4), C3−N4 1.378(3), C3−O5 1.225(3),
C4−N6 1.369(3), C4−N7 1.323(4), C4−O6 1.243(3), N1−O1
1.209(2), N5−N6 1.373(2), N1−C1−N2 105.5(2), N1−C1−C2
111.8(2), C2−N5−N6 118.3(2), N5−N6−C4 119.3(2), C2−N4−C3
127.2(2), N1−C1−C2−N4−77.0(2), N2−C1−C2−N4 165.9(2),
N3−C3−N4−C2−179.9(2), N4−C2−N5−N6−1.2(3), C2−N5−
N6−C4 176.5(2), N7−C4−N6−N5 3.6(3), O6−C4−N6−N5−
177.7(2).
unit by ∼100° owing to the sp3 hybridized nitrogen N5. The
molecular packing with extensive hydrogen bonds leads to a
layer structure of the HFOX units with interlocking urea groups
between the layers. The potassium salt of 3, compound 4,
crystallizes in the monoclinic space group P21/n having four
molecules in each unit cell (Figure 8). The structure is more
nitro groups is rather protonated than the imine nitrogen N5.
The C1−C2 (1.506 Å) bond distance is very close to that of a
single C−C bond (1.52 Å). The C−NO2 bond distances are
significantly elongated to ∼1.51 Å compared to those structures
above, containing no hydrogen atom at the dinitromethyl
carbon. Furthermore, the bond angle of N1−C1−N2 (105.5°)
in the CH(NO2)2 group is strongly compressed. This is caused
by a N···O intramolecular attraction between the partial
positively charged nitrogen N1 and O3 of the second nitro
group and is confirmed by the very short distance of 2.575 Å. In
contrast, the chain with the two urea groups forms an almost
perfect plane, which builds up a π-type system. This in turn
leads to special interactions and a strong shortening of the
imine C−N (1.274 Å) and the N−N (1.370 Å) bonds, which
are shorter than the regular C−N double (1.30 Å) and N−N
single bonds (1.42 Å), respectively.
Figure 8. X-ray molecular structure of potassium 2-amino-2-(2-
carbamoylhydrazono)-1,1-dinitroethan-1-ide (4). Selected atom dis-
tances (Å) and angles (deg): C1−C2 1.486(3), C1−N1 1.391(2),
C2−N3 1.346(3), C2−N4 1.291(3), N1−O1 1.245(2), N4−N5
1.411(2), N2−C1−N1 122.1(2), N1−C1−C2 119.5(2), N3−C2−N4
127.8(2), C2−N4−N5 112.9(2), N4−N5−C3 119.7(2), C1−C2−N4
115.1(2), N1−C1−C2−N3−99.3(2), N2−C1−C2−N4−95.3(2),
C2−N4−N5−C3 139.6(2).
The potassium salt of the 1,2,4-triazol-5-on heterocycle 6_K
crystallizes in the orthorhombic space group Pbca containing
eight molecules in the unit cell. The smallest asymmetric unit of
the crystal structure made of one cation and one anion is
displayed in Figure 10. On the one hand, the five-membered
heterocyclic ring and the adjoining carbamoyl group are almost
in a plane with small deviation of ∼5° (N3−C3−N5−C4−
175.0 Å). On the other hand, the heterocycle and the plane of
the dinitromethyl unit are twisted by ∼90° (N1−C1−C2−
N3−86.3°, N2−C1−C2−N4−94.4°). A consequence of this
arrangement is a reduction of the C−NO2 bond distance (1.380
Å) as in the structures of HFOX, 2, and 4 with the same
orthogonal arrangement. Nevertheless the C1−C2 (1.461 Å)
bond distances are shortened and therefore in the range of
FOX-7. The heterocyclic ring and the attached carbamoyl
group form a big π-system supported by the conjugated C−N
and C−O bonds and the sp2 hybridized nitrogen N5.29,35 The
similar to the HFOX structure and shows the same trans-
formation as the potassium salt 2. Here, the structure is
subdivided into three planar units, the dinitromethylene, the 1-
amino-1-hydrazinomethyl, and the urea part, whereas the
dinitromethylene unit is ∼80° and the urea unit is ∼40° twisted
relative to the 1-amino-1-hydrazinomethyl layer.
The C1−NO2 (1.376 Å) and the C2−N4 (1.291 Å) bond
lengths are shortened compared to the neutral compound 3 for
a better stabilization of the negative partial charge on the
carbon C1 and the nitrogen N4. Further effects of the
deprotonation of the nitrogen N4 and the associated higher
negative charge are the elongated C−NH2 atom distances to
the here observed maximum of 1.381 Å, as well as the very long
N−N (1.411 Å) bond, which is, despite the attached carbamoyl
group, longer than in the starting material.
H
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Figure 12. Representation of the zigzag structure of 6_NH4, view
along the a axis.
Figure 10. X-ray molecular structure of 6_K. Selected atom distances
(Å) and angles (deg): C1−C2 1.461(2), C1−N1 1.381(2), C1−N2
1.379(2), C2−N3 1.375(2), C2−N4 1.295(2), C3−N3 1.362(2), C3−
N5 1.387(2), C3−O5 1.224(2), C4−N5 1.429(2), C4−N6 1.320(2),
C4−O6 1.219(2), N1−O1 1.252(2), N4−N5 1.394(2), N1−C1−N2
122.0(1), N3−C2−N4 112.2(1), C2−N4−N5 104.0(1), N4−N5−C3
112.0(1), N5−C3−N3 103.1(1), C3−N3−C2 108.8(1), N1−C1−
C2−N3−86.3(2), N2−C1−C2−N4−94.4(2), C1−C2−N3−C3
175.2(1), N3−C3−N5−C4−175.0(1), C3−N5−C4−N6 8.7(2),
C2−N4−N5−C4 175.3(1), O5−C3−N3−C2 179.9(1).
the FOX-7 structure. The ammonium cation here is
coordinated each time by four anion molecules, three within
the layer and one between two layers.
c. Physicochemical Properties. The investigated physical
properties of all compounds are shown in Table 3. All
compounds are stable toward moisture and air. Compound 1
shows a decomposition point of 209 °C, which is thus slightly
less thermally stable than FOX-7 (218 °C; Figure 13).
However, the corresponding derivative of HFOX, 3, shows a
great improvement of the thermal stability from 110 °C
(HFOX) to 170 °C (3). Upon addition of two carbamoyl units,
in compound 5, the decomposition point decreases to 129 °C.
The formed dinitromethyl unit with the strong acidic hydrogen
next to the two nitro groups often shows low thermal
stabilities.37−39 The potassium and ammonium salts of (1-
carbamoyl-5-oxo-1,2,4-triazol-3-yl)dinitromethanide show de-
composition points of 198 °C (6_K) and 202 °C (6_NH4),
respectively.
ring forms an irregular pentagon (108°), whereas the carbonyl
group has the most acute angle (N5−C3−N3 103.1°), and the
N3−C2−N4 angle (112.2°) shows the highest value. In the
crystal structure, each potassium is connected to eight oxygen
atoms of the carbonyl and the nitro groups and to one nitrogen
atom N4 of the imine moiety.
The ammonium salt 6_NH4 crystallizes in the same
orthorhombic space group Pbca also with eight molecules in
the unit cell as the potassium salt 6_K. The structure shows a
high density of 1.848 g cm−3, and the asymmetric unit is
illustrated in Figure 11. The atom distances and angles are
For initial safety testing the impact and friction sensitivities as
well as the electrostatic discharge sensitivity were determined
and assigned according to the UN recommendations on the
transport of dangerous goods.40 The friction sensitivity (FS) is
determined by rubbing a small amount between a pin and a
porcelain plate with different contact pressures.41 All
compounds were classified as insensitive toward friction with
the exception of HFOX, which must be classified as very
sensitive to friction (≥360 N insensitive, 360−80 N sensitive,
80−10 N very sensitive, ≤ 10 N extremely sensitive). The more
important value for energetic compounds is the sensitiveness
toward impact (IS), which is tested by the action of a dropping
weight on a sample and at which benchmark a decomposition
or explosion occurs.2 The HFOX exhibits an extraordinarily
high sensitivity of 2 J and is therefore a primary explosive,
classified in the most dangerous class (≥40 J insensitive, 40−35
J less sensitive, 35−4 J sensitive, ≤ 3 J very sensitive).2,41 In
comparison compound 3 shows only a impact sensitivity of 15 J
and can hence be handled with much lower risk. FOX-7 is
already very insensitive (20 J), but compound 3 (40 J) with the
added carbamoyl unit is not sensitive to impact any more. The
corresponding salts 2 and 4 show slightly higher impact
sensitivities compared to their neutral compounds. Compound
5 has the highest sensitivity (9 J) of all here presented
compounds, due to the unstable nature of such dinitromethyl
groups. The ammonium and potassium salts of the 1,2,4-triazol-
5-on heterocycle are both quite insensitive toward impact (20
J) and are both in the range of FOX-7.
Figure 11. X-ray molecular structure of ammonium (1-carbamoyl-5-
oxo-1,2,4-triazol-3-yl)dinitromethanide (6_NH4). Selected atom dis-
tances (Å) and angles (deg): C1−C2 1.448(2), C1−N2 1.380(2),
C1−N1 1.403(2), C2−N3 1.378(2), C2−N4 1.313(2), C3−N3
1.355(2), C3−N5 1.379(2), C3−O5 1.229(2), C4−N5 1.426(2),
C4−N6 1.317(2), C4−O6 1.221(2), N4−N5 1.393(2), N2−C1−N1
117.7(1), C2−N4−N5 104.2(1), N4−N5−C3 111.9(1), N5−C3−N3
103.5(1), C3−N3−C2 109.4(1), N3−C2−N4 111.0(1), O2B−N1−
C1−C2−164.0(2), N2−C1−C2−N4 170.8(1), N4−N5−C3−N3−
1.0(2), C2−N4−N5−C4−177.3(1), C3−N3−C2−N4−0.0(2), N4−
N5−C4−N6 178.0(1).
almost equal between these two salts (Table 2). However, the
ammonium salt has an important feature: the whole anion is in
a planar environment. Only the nitro groups are rotated slightly
out of the plane by ∼9 and 12°, due to disorder of one nitro
group (N2).36
The crystal packing consists of zigzag layers (Figure 12) with
extensive strong intra- and intermolecular hydrogen bond
forces within the layers and weak intermolecular forces between
the molecular waved sheets (Figure 12), as was also observed in
The main performance criterion of energetic materials is the
detonation velocity Vdet. The performance data were calculated
by the computer code EXPLO5 V.6.0242 and based on the
calculated energy of formation using CBS-4 M ab initio
calculation. All detonation and combustion parameters for
I
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Article
Table 3. Physical Properties of 1-5, 6_K and 6_NH4 in Comparison to FOX-7, HFOX, and AP
1
2
3
4
5
6_K
6_NH4
FOX-741
HFOX
AP
formula
C3H5N5O5 C3H4N5O5K C3H6N6O5 C3H5N6O5K C4H7N7O6 C4H3N6O6K C4H7N7O6 C2H4N4O4 C2H5N5O4 NH4ClO4
a
Tm /°C (onset)
-
155
191
-
-
-
-
198
20
-
-
218
20
-
-
b
Tdec /°C (onset)
209
40
170
15
165
10
129
9
202
20
110
2
240
c
IS /J
20
20
d
FS /N
360
1.0
360
360
0.3
360
0.3
360
0.2
360
0.5
360
0.5
360
0.5
64
360
e
ESD /J
N /% )
0.5
0.1
0.50
11.9
54.5
66.4
+34.0
+34.0
f
36.7
41.9
78.6
−4.2
30.4
34.8
65.2
−4.2
−29.3
40.8
38.8
79.6
−7.8
−31.0
34.3
32.6
66.9
−7.8
−31.0
39.4
38.5
77.9
−9.6
−35.3
31.1
35.5
66.6
0
39.4
38.5
77.9
−9.6
−35.3
37.8
43.2
81.0
0
42.9
39.2
82.1
−4.9
g
O /%
h
N + O /%
i
ΩCO /%
j
ΩCO2 /%
−29.3
−27.6
−21.6
−24.5
a
b
c
Onset melting Tm and onset decomposition point Tdec from DSC measurement carried out at a heating rate of 5 °C min−1. Impact sensitivity.
Friction sensitivity. Sensitivity toward electrostatic discharge. Nitrogen content. Oxygen content. Sum of nitrogen and oxygen content. Oxygen
balance assuming the formation of CO and the formation of the formation of CO2 at the combustion.
d
e
f
g
h
i
j
explosives like TNT (trinitrotoluene, 7241 m s−1) and PETN
(pentaerythritol tetranitrate, 8403 m s−1).
CONCLUSIONS
■
New compounds based on the FOX-7 molecule were
synthesized and thoroughly characterized. The molecular
structures are discussed on the basis of single-crystal X-ray
diffraction studies. Especially the neutral compounds 1 and 3
show good energetic properties with detonation velocities Vdet
of above 8500 m s−1 and only low or no sensitivity against
mechanical stimuli. Acidic hydrogen atoms in 1 and 3 allow
easy deprotonation to the potassium salts 2 and 4, repectively.
Whereas the FOX-7 molecule reacts only once with the very
reactive CSI, the HFOX molecule reacted twice at the −NH2
and −NHNH2 groups to form 5, which is explained by the
higher electron density of the hydrazinium moiety.
An interesting heterocycle formation was observed by
treating 5 with the weak base potassium bicarbonate with
elimination of ammonia to lead to the triazol-3-yl)-
dinitromethanide 6. The ammonium salt of 6 exhibits a high
thermal stability, with low sensitivity against impact (20 J) and
pleasing detonation properties. This new route for the
formation of the 1,2,4-triazol-5-on heterocycle may be
transferable to other starting materials, resulting in a variety
of further interesting materials.
Figure 13. Comparison of DTA measurements (5 °C min−1) of FOX-
7 (green), HFOX (blue), 1 (yellow), and 3 (red).
compounds 1, 3, 5 and 6_NH4 are summarized in Table 4. The
compounds 1 and 3 both demonstrate good detonation
velocities Vdet with values higher than 8500 m s−1 which are
only slightly lower than FOX-7 (8852 m s−1). This high
performance is even more impressive considering the low
sensitivity toward external mechanical stimuli. The ammonium
salt 6_NH4 exhibits a quite good detonation velocity Vdet of
8359 m s−1, and therefore is in the range of well-known
As indicated already in the Introduction, some more
chemistry of the FOX-7 skeleton is reported. Most of these
Table 4. Calculated Heat of Formation and Predicted Detonation Parameters (EXPLO5 V6.02) for 1, 3, 5 and 6_NH4 in
Comparison to FOX-7 and HFOX
1
3
5
6_NH4
1.82
FOX-7
1.88
HFOX
1.82
a
density RT/g cm−3
1.86
1.79
1.70
b
ΔfH° /kJ mol−1
−277
−1350
−4096
2913
768
−153
−641
−4506
3101
808
−355
−1325
−3816
2823
802
−337
−1254
−3897
2793
790
−134
−805
−4739
3218
780
+46
+373
−5535
3562
827
c
ΔfU° /kJ kg−1
d
Qv /kJ kg−1
e
Tex /K
V0 /L kg−1
f
g
PCJ /kbar
Vdet /m s−1
305
293
231
279
344
348
h
8516
8507
7805
8359
8852
9036
a
b
c
RT densities are recalculated from X-ray densities. Enthalpy of formation calculated by the CBS-4 M method using Gaussian 09. Energy of
d
e
f
formation calculated by the CBS-4 M method using Gaussian 09. Heat of explosion. Explosion temperature. Volume of gaseous products.
g
h
Detonation pressure calculated by using the EXPLO5 (Version 6.02) program package. Detonation velocity calculated by using the EXPLO5
(Version 6.02) program package.42
J
DOI: 10.1021/acs.jpca.7b01742
J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A
Article
transformations were performed to achieve higher energetic
performance and better physical properties. In this regard, these
advancements could also be applied to the here presented
compounds 1, 3, 5, and 6 (Scheme 5), probably being likely
more stable due to the higher hydrogen bond ability of the
attached carbamoyl groups.
CBS-4 starts with a HF/3-21G(d) geometry optimization,
which is the initial guess for the following self-consistent field
(SCF) calculation as a base energy and a final MP2/6-31+G
calculation with a CBS extrapolation to correct the energy in
second order. The used CBS-4 M method additionally
implements an MP4(SDQ)/6-31+(d,p) calculation to approx-
imate higher-order contributions and also includes some
additional empirical corrections.46 The enthalpies of the gas-
phase species were estimated according to the atomization
energy method.47 The liquid (solid)-state energies of formation
(ΔHf°) were estimated by subtracting the gas-phase enthalpies
with the corresponding enthalpy of vaporization (sublimation)
obtained by Trouton’s rule.48,49 All calculations affecting the
detonation parameters were performed using the program
package EXPLO5 V6.02 (EOS BKWG-S).42,50 The detonation
parameters were calculated at the Chapman−Jouguet (CJ)
point with the aid of the steady-state detonation model using a
modified Becker−Kistiakowski−Wilson equation of state for
modeling the system. The CJ point is found from the Hugoniot
curve of the system by its first derivative. The specific impulses
were also calculated with the program package EXPLO5 V6.02,
assuming an isobaric combustion of a composition of an
oxidizer, aluminum as fuel, 6% polybutadiene acrylic acid, 6%
polybutadiene acrylonitrile as binder, and 2% bisphenol A as
epoxy curing agent.42 A chamber pressure of 70.0 bar, an initial
temperature of 3300 K, and an ambient pressure of 1.0 bar with
equilibrium expansion conditions were estimated for the
calculations.
The low-temperature single-crystal X-ray diffraction measure-
ments were performed on an Oxford XCalibur3 diffractometer
equipped with a Spellman generator (voltage 50 kV, current 40
mA) and a KappaCCD detector operating with Mo Kα
radiation (λ = 0.7107 Å). Data collection was performed using
the CRYSALIS CCD software.51 The data reduction was
performed using the CRYSALIS RED software.52 The solution
of the structure was performed by direct methods (SIR97)53
and refined by full-matrix least-squares on F2 (SHELXL)54,55
implemented in the WINGX software package56 and finally
checked with the PLATON software.57 The absorptions were
corrected by a SCALE3 ABSPACK multiscan method.58 All
non-hydrogen atoms were refined anisotropically. The hydro-
gen atom positions were located in a difference Fourier map.
ORTEP plots are shown with thermal ellipsoids at the 50%
probability level. Additional crystallographic data and structure
refinement parameters are listed in the Supporting Information.
Scheme 5. Potential Chemistry of 1, 3, 5, and 6 for Further
Enhancement of Energetic Properties
METHODS
■
All chemicals were used as supplied. Raman spectra were
recorded in a glass tube with a Bruker MultiRAM FT-Raman
spectrometer with Nd:YAG laser excitation up to 1000 mW (at
1064 nm). Infrared spectra were measured with a Perkin−
Elmer Spectrum BX-FTIR spectrometer equipped with a
Smiths DuraSamplIR II ATR device. All spectra were recorded
at ambient (25 °C) temperature. NMR spectra were recorded
with a JEOL/Bruker instrument, and chemical shifts were
determined with respect to external Me4Si (1H, 399.8 MHz;
13C, 100.5 MHz) and MeNO2 (15N, 40.6 MHz; 14N, 28.9
MHz). Mass spectrometric data were obtained with a JEOL
MStation JMS 700 spectrometer (DEI+ or FAB+ modes).
Analysis of C/H/N was performed with an Elemental Vario EL
Analyzer. Melting and decomposition points were measured
with a PerkinElmer Pyris6 DSC and an OZM Research DTA
552-Ex (DTA = differential thermal analysis) with a heating
rate of 5 °C min−1 in a temperature range from 15 to 400 °C
and checked by a Buchi Melting Point B-540 apparatus (not
̈
corrected). The sensitivity data were performed using a BAM
drophammer and a BAM friction tester.40
COMPUTATIONAL DETAILS
ASSOCIATED CONTENT
■
■
All ab initio calculations were performed using the program
package Gaussian 09 (Revision A.03)43 and visualized by
GaussView 5.08.44 The initial geometries of the structures were
taken from the corresponding experimentally determined
crystal structures. Structure optimizations and frequency
analyses were performed with Becke’s B3 three-parameter
hybrid functional using the LYP correlation functional
(B3LYP). For C, H, N, and O a correlation-consistent
polarized double-ξ basis set was used (cc-pVDZ). The
structures were optimized with symmetry constraints, and the
energy is corrected with the zero-point vibrational energy.45
The enthalpies (H) and free energies (G) were calculated using
the complete basis set (CBS) method to obtain accurate values.
The CBS models use the known asymptotic convergence of
pair natural orbital expressions to extrapolate from calculations
using a finite basis set to the estimated complete basis set limit.
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.7b01742.
Further crystallographic details and X-ray crystallo-
graphic data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*Fax: (+49) 89-2180-77492. E-mail: tmk@cup.uni-muenchen.
de.
ORCID
Burkhard Krumm: 0000-0002-2100-4540
Thomas M. Klapotke: 0000-0003-3276-1157
̈
K
DOI: 10.1021/acs.jpca.7b01742
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The Journal of Physical Chemistry A
Article
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Author Contributions
The manuscript was written through with contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
́
(13) Herve, G.; Jacob, G. Novel Illustrations of the Specific Reactivity
The authors declare no competing financial interest.
CCDC 1523279 (2), CCDC 1523280 (3), CCDC 1523281
(5), CCDC 1523282 (6_NH4), CCDC 1523283 (HFOX),
CCDC 1523284 (4), CCDC 1523285 (6_K) and CCDC
1523286 (1) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
of 1,1-Diamino-2,2-dinitroethene (DADNE) Leading to New
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ACKNOWLEDGMENTS
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This paper is dedicated to Professor Wolfgang Beck on
occasion of his 85th birthday. Financial support of this work by
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2062, and the Bundeswehr-Wehrtechnische Dienststelle fur
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Waffen und Munition (WTD 91) under Grant No. E/E91S/
FC015/CF049 is gratefully acknowledged. The authors
acknowledge collaborations with Dr. M. Krupka (OZM
Research, Czech Republic) in the development of new testing
and evaluation methods for energetic materials and with Dr. M.
Suceska (Brodarski Institute, Croatia) in the development of
new computational codes to predict the detonation and
propulsion parameters of novel explosives. We are indebted
to and thank Drs. B. M. Rice, J. Sabatini, and B. Forch (ARL,
Aberdeen, Proving Ground, MD) for many inspired
discussions.
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DOI: 10.1021/acs.jpca.7b01742
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