Thermostable Insensitive Energetic Materials Based on a Triazolopyridine Fused Framework with Alternating Nitro and Amine Groups

Abstract

In this work, we designed and synthesized a series of novel triazolopyridine fused-ring compounds with alternating nitro and amine groups. Three compounds showed remarkable thermal stability at 256, 310, and 294 °C, respectively, and a low mechanical sensitivity [impact sensitivity (IS) = 40 J, friction sensitivity (FS) = 324 N; IS = 35 J, FS = 240 N; and IS > 40 J, FS = 324 N, respectively]. Significantly, two of these compounds exhibited a better detonation performance [detonation velocity (D) = 8200 and 8335 m s^–1, Detonation pressure (P) = 25.6 and 27.2 GPa, respectively] than the widely used heat-resistant explosive hexanitrostilbene (HNS; D = 7612 m s^–1, P = 24.3 GPa). Additionally, a nitramine derivative displayed a detonation performance (D = 8569 m s^–1, P = 31.3 GPa) similar to that of the high-energy explosive RDX. The superior properties of the materials were further confirmed by X-ray diffraction analysis and by several theoretical calculations (ESP, LOL–π, Hirshfeld surfaces, RDG, and NCI analyses). These results indicated that the three compounds might be potential candidates for use as heat-resistant energetic materials.

Key words

energetic materials - explosives - triazolopyridines - thermal stability

Publication History

Received: 31 August 2023

Accepted after revision: 25 September 2023

Article published online:
27 October 2023

• References and Notes

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• 43 CAUTION! These new compounds are energetic materials with a high potential for explosion under certain conditions. It is therefore essential to take appropriate protective measures at all times when handling these materials.Amine 1 (2.53 g, 10 mmol) was dissolved in CH₂Cl₂ (100 mL) and 25% aq NH₃ (3 mL) in EtOH (30 mL) was added dropwise at 0 °C. The mixture was allowed to react for 24 h and then the solids were collected by filtration and washed with H₂O and MeOH. The crude product was crystallized from DMSO–EtOAc to give a faintly yellow solid; yield: 1.65 g (71%).IR (KBr): 3416, 3285, 3167, 1596, 1522, 1283, 1021, 969, 871, 831, 786, 629 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 8.75–8.89 (m, 4 H, NH₂). ¹³C NMR (100 MHz, DMSO-d₆): δ = 113.7, 123.0, 147.3, 147.6, 154.4. HRMS (ESI^–): m/z [M – H]⁺ calcd for C₅H₃ClN₅O₄: 231.9879; found; 231.9876.6-Hydrazino-3,5-dinitropyridine-2,4-diamine (3) A solution of N₂H₄·H₂O (0.7 mL, 15 mmol) in EtOH (10 mL) was slowly added to a mixture of 2 (1.16 g, 5 mmol) and EtOH (30 mL). The mixture was stirred for 3 h and then filtered. The resulting solid was washed sequentially with H₂O and EtOH and dried to give a yellow solid; yield: 1.02 g (95%).IR (KBr pellet): 3393, 3343, 3242, 3181, 1615, 1542, 1268, 1201, 1059, 973, 784, 697, 545 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 5.46 (s, 2 H, NH₂), 8.66 (d, J = 157.2 Hz, 2 H, NH₂), 10.47 (d, J = 72.8 Hz, 2 H, NH₂), 10.88 (s, 1 H, NH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 108.8, 109.5, 148.3, 151.7, 155.7. HRMS (ESI^–): m/z [M – H]⁺ calcd for C₅H₆N₇O₄: 228.0487; found: 228.0488.6,8-Dinitro[1,2,4]triazolo[4,3-a]pyridine-3,5,7-triamine (4) A solution of BrCN (508.8 mg, 4.8 mmol) in MeCN (14 mL) was added to a suspension of 3 (890 mg, 4 mmol) in MeOH (14 mL) and H₂O (21 mL) at r.t. The mixture was heated to 50 °C for 12 h, then cooled to r.t. The solid was collected by filtration, washed successively with H₂O and EtOH, and dried to give a yellow powder; yield: 888 mg (87%).IR (KBr ): 3370, 3322, 3213, 1673, 1628, 1597, 1525, 1474, 1397, 1270, 1215, 1172, 1081, 961, 881, 690 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 8.17 (s, 2 H, NH₂), 10.60–10.67 (m, 3 H, NH₂ and C=NH), 14.11 (s, 1 H, NH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 104.0, 110.6, 138.2, 148.7, 150.3, 151.8. HRMS (ESI^–): m/z [M – H]⁺ calcd for C₆H₅N₈O₄: 53.0439; found: 253.0449. Anal. Calcd for C₆H₆N₈O₄ (254.16): C, 28.35; H, 2.38; N, 44.09. Found: C, 28.14; H, 2.56; N, 41.15.3,7-Diamino-6,8-dinitro[1,2,4]triazolo[4,3-a]pyridin-5(1H)-one (5) A mixture of 4 (254 mg, 1 mmol) and 20% H₂SO₄ (6 mL) was treated with potassium peroxomonosulfate (Oxone) (770 mg, 2.5 mmol) at r.t. The mixture was heated to 90 °C with stirring for 12 h, then cooled to r.t. The resulting mixture was filtered, and the solids were washed successively with H₂O and EtOH, then dried to afford a yellow solid; yield: 216 mg (85%).IR (KBr pellet): 3478, 3333, 3249, 1609, 1509, 1282, 1228, 1175, 1108, 778, 693, 593 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 7.42 (s, 2 H, NH₂), 9.55 (s, 1 H, NH₂), 10.04 (s, 1 H, NH₂), 14.10 (s, 1 H, NH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 104.6, 113.7, 139.1, 150.6, 151.4, 153.0. HRMS (ESI^–): m/z [M – H]⁺ calcd for C₆H₄N₇O₅: 254.0279; found. 254.0270. Anal. Calcd for C₆H₅N₇O₅ (255.15): C, 28.24; H, 1.98; N, 38.43. Found: C, 28.98; H, 2.60; N, 35.24.6,8-Dinitro[1,2,4]triazolo[4,3-a]pyridine-3,5,7-triamine (7) A solution of N₂H₄·H₂O (0.7 mL, 15 mmol) in EtOH (10 mL) was added slowly to a mixture of amine 6 (1.09 g, 5 mmol) and EtOH (30 mL) at r.t., and the mixture was allowed to react for 3 h, The resulting solid was washed sequentially with H₂O and EtOH, then dried to give a green solid; yield: 1.0 g (94%).IR (KBr): 3408, 3371, 3338, 3286, 3251, 1610, 1550, 1495, 1381, 1268, 1205, 1120, 1067, 962, 777, 709, 653 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 5.94 (s, 2 H, NH₂), 8.94 (s, 1 H, CH), 9.71 (d, J = 15.48 Hz, 2 H, NH₂), 11.43 (s, 1 H, NH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 111.8, 121.0, 148.5, 148.8, 153.7. HRMS (ESI⁺): m/z [M + H]⁺ calcd for C₅H₇N₆O₄: 215.0523; found: 215.0526.6,8-Dinitro[1,2,4]triazolo[1,5-a]pyridine-2,7-diamine (8) A solution of BrCN (508.8 mg, 4.8 mmol) in MeCN (14 mL) was added to a suspension of 7 (856 mg, 4 mmol) in MeOH (14 mL) and H₂O (21 mL) at r.t., and the mixture was stirred at 50 °C for 12 h. The mixture was then cooled to r.t. and filtered to give a solid that was washed successively with H₂O and EtOH, then dried to give an orange powder; yield: 812.6 mg (85%).IR (KBr pellet): 3415, 3298, 3159, 3049, 1645, 1547, 1494, 1432, 1289, 1042, 900, 776, 608 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 7.03 (s, 2 H, NH₂), 9.22 (s, 2 H, NH₂), 9.68 (s, 1 H, CH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 115.0, 123.7, 134.0, 143.9, 149.7, 169.0. HRMS (ESI⁺): m/z [M + H]⁺ calcd for C₆H₆N₇O₄: 240.0476; found: 240.0477. Anal. Calcd for C₆H₅N₇O₄ (240.16): C, 30.01; H, 2.52; N, 40.83. Found: C, 30.44; H, 2.16; N, 37.77.N²,6,8-Trinitro[1,2,4]triazolo[1,5-a]pyridine-2,7-diamine (9) 8 (478 mg, 2 mmol) was added in portions to a mixture of concd H₂SO₄ (4 mL) and fuming HNO₃ (4 mL) at 0 °C. The mixture was stirred for 24 h at 0 °C, then poured onto ice. The resulting precipitate was collected by filtration, washed successively with H₂O and EtOH, and dried to give a yellow solid; yield: 528 mg (93%).IR (KBr pellet): 3429, 3312, 1674, 1625, 1537, 1445, 1291, 1252, 899, 775, 646 cm^–1. ¹H NMR (400 MHz, DMSO-d₆): δ = 9.28 (s, 2 H, NH₂), 10.19 (s, 1 H, CH). ¹³C NMR (100 MHz, DMSO-d₆): δ = 116.5, 128.4, 136.5, 144.1, 148.5, 159.7. HRMS (ESI^–): m/z [M – H]⁺ calcd for C₆H₃N₈O₆: 283.0181; found: 283.0181. Anal. Calcd for C₆H₄N₈O₆ (284.15): C, 25.36; H, 1.42; N, 39.44. Found: C, 25.39; H, 2.65; N, 35.38.