Molecules 2018, 23, 2
10 of 13
◦
eventually became dark brown. The mixture was subsequently heated to 60 C and stirred at
this temperature for 2 h, then cooled to room temperature and stirred vigorously to remove any
residual N O . The solvent was evaporated under vacuum and the residue was purified by column
2
4
chromatography, using a Biotage Isolera One apparatus (Uppsala, Sweden) with a Flash Silica-CS
column (25 g), eluting with n-hexane and dichloromethane. Both and were isolated with satisfactory
purity as a white solid (536 mg, 35.5%) and an orange solid (148 mg, 14.6%), respectively.
2
3
◦
◦
1
Compound 2: R = 0.5 (silica gel, 33% EtOAc/hexanes); m.p. 96–98 C; T = 101 C; H-NMR (CDCl ):
f
d
3
δ
8.43 (s, 1H); 13C-NMR(CDCl3):
δ
142.78 (s), 140.78 (s), 129.55 (s); IR (KBr): 3095, 2922, 2853, 1622, 1589,
450, 1349, 1291, 1170, 1078, 999, 856, 804, 785 cm ; MS (ESI) m/z: 376 [M-1] , 331 [M-46] ; Elemental
−
1
−
−
1
analysis for C H N O : calculated C 22.29, H 0.80, N 26.00%; measured C 22.21, H 1.01, N 25.68%.
7
3
7
12
◦
◦
1
Compound 3: R = 0.4 (silica gel, 33% EtOAc/hexanes); m.p. 68–72 C; T = 106 C; H-NMR (CDCl ):
8.25 (m, 2H), 8.06 (dd, J = 6.3, 2.4 Hz, 1H); C-NMR (CDCl3): δ 144.13 (s), 139.89 (s), 134.43 (s),
f
d
3
13
δ
1
9
32.26 (s), 128.42 (s), 115.12 (s); IR (KBr): 3086, 2921, 1630, 1594, 1447, 1347, 1293, 1208, 1169, 1097, 1042,
−
1
−
−
46] ; Elemental analysis for C H N O :
7 3 5 6
93, 798, 735 cm ; MS (ESI) m/z: 252 [M
−
1] , 207 [M
−
calculated C 33.21, H 1.19, N 27.67%; measured C 33.09, H 1.26, N 27.48%.
Hydrazinium 2-dinitromethylpyridine ( ): An 80% solution of hydrazine hydrate (3 mmol) was added
slowly to a solution of (1 mmol) in methanol (5 mL). The resulting mixture was stirred at room
4
1
temperature for 4 h, during which time a light-yellow precipitate was formed. The precipitate was
filtered off, washed with cold ethanol, and recrystallized from methanol:water = 1:1 (v/v) to give the
target product. (173 mg, 80.5%).
◦
1
R = 0.7 (silica gel, 80% EtOAc/MeOH); T = 181 C (decomposition without melting); H-NMR
f
d
(
DMSO-d ):
δ
8.51 (d, J = 4.4 Hz, 1H), 7.77 (dd, J = 10.9, 4.4 Hz, 1H), 7.50 (d, J = 7.9 Hz, 1H), 7.18 (m,
6
13
1
H); C-NMR (DMSO-d6):
333, 3125, 1587, 1489, 1462, 1376, 1329, 1303, 1243, 1128, 1091, 1054, 951, 797, 748, 696 cm ; Elemental
analysis for C H N O : calculated C 33.49, H 4.22, N 32.55%; measured C 33.32, H 4.31, N 32.62%.
δ 151.70 (s), 148.54 (s), 136.39 (s), 134.20 (s), 125.26 (s), 121.62 (s); IR (KBr):
−
1
3
6
9
5
4
Dihydrazinium 2,6-bis(dinitromethyl)pyridine (
5): An 80% hydrazine hydrate solution (6 mmol) was
added slowly to a solution of (1 mmol) in methanol (5 mL). The resulting mixture was stirred at room
2
temperature for 4 h, during which time a yellow precipitate was formed. The precipitate was filtered
off, washed with cold ethanol, and recrystallized from methanol:water = 1:1(v/v) to give the target
product. (267 mg, 76.1%).
◦
1
R = 0.3 (silica gel, 33% EtOAc/MeOH); T = 125 C (decomposition without melting); H-NMR
(
f
d
13
DMSO-d6): δ 7.71 (t, J = 7.5 Hz, 1H), 7.31 (d, J = 7.7 Hz, 2H); C-NMR (DMSO-d6): δ 151.30 (s), 136.43
(
1
s), 134.60 (s), 123.32 (s); IR (KBr): 3362, 3113, 1586, 1491, 1447, 1415, 1335, 1278, 1224, 1171, 1128, 1096,
−
1
070, 927, 815, 752, 720 cm ; Elemental analysis for C H N O : calculated C 23.94, H 3.73, N 35.89%;
7
13
9
8
measured C 23.85, H 3.59, N 36.02%.
4
. Conclusions
The mono and bis(trinitromethyl)-substituted pyridines
1
and 2 were synthesized in moderate
to excellent yields via the reaction of the corresponding pyridinecarboxaldoximes with N O .
2
4
The by-product
3 was also separated and identified. Compounds 1 and 2 reacted with aqueous
hydrazine to give dinitromethyl hydrazinium salts. All the compounds were fully characterized and
their energetic properties were both measured and calculated. Due to the successful introduction of
two trinitromethyl groups onto the pyridine ring,
2
possesses the best oxygen balance (
−
14.85%) and
−
superior detonation properties (D = 8700 m s
1
·
, P = 33.2 GPa) compared to other energetic pyridine
derivatives, in conjunction with moderate sensitivity values (IS = 9 J, FS = 192 N) comparable to those
of RDX, but its thermal stability is too low for practical applications making it inferior to RDX. The
formation of salt
5 significantly improves the thermal stability of 2 while maintaining much of the
detonation performance.
Supplementary Materials: Supplementary materials can be accessed online.