Thermally stable energetic salts based on 3-nitramino-4-tetrazolefurazan

Abstract

In order to develop new energetic materials with high energy and low sensitivity, a series of nitrogen-rich energetic salts based on 3-nitramino-4-tetrazolefurazan were conveniently synthesized through nitration, neutralization and metathesis reaction. All energetic salts were fully characterized by NMR (¹H, ¹³C), IR and elemental analysis. Furthermore, ammonium salt (2) was confirmed by ¹⁵N NMR and hydroxylammonium salt (5) was confirmed by single-crystal X-ray diffraction. Salt 5 crystallized in triclinic space group P1̄ with four hydroxylammonium cations and two NATF anions per unit cell at a density of 1.815 g cm⁻³. The densities of the salts are in the range of 1.621 (6) to 1.815 g cm⁻³ (5). Due to the two nitrogen-rich cations in the salts, they show high positive enthalpies of formation falling between 299.2 kJ mol⁻¹ (2) and 1040.6 kJ mol⁻¹ (9). All the salts show good thermal stabilities with the decomposition temperatures ranging from 203 °C (4) to 284 °C (6). The impact sensitivities of the energetic salts lie between 5 J (2 and 5) and >40 J (6, 7, 8) and their friction sensitivities range from 108 N (4) to >360 N (6). Their detonation performances were calculated according to Kamlet–Jacobs equations. The detonation pressures of the synthesized energetic salts were found to be in the range of 21.1 GPa (6) to 34.7 GPa (5) and their detonation velocities are between 7117 m s⁻¹ (6) and 8826 m s⁻¹ (5).

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Introduction

Demand for energetic materials with high detonation performance and low sensitivity has increased in recent years¹ because high sensitivity of the energetic materials tends to enhance the danger related to the transportation, handling and processing from production to end-use.² However, detonation performance and sensitivity are often contradictory to each other in the field of energetic materials.³ Use of energetic salts, especially nitrogen-rich ones, have been found to be a good way to overcome this problem and a large amount of energetic salts with high detonation performance and low sensitivity has been developed.⁴

Furazan and tetrazole ring are two kinds of nitrogen-rich heterocyclic rings widely used in the design and synthesis of new energetic materials.⁵ Both of them possess high positive enthalpy of formation and good thermal stability. Nitrogen-rich energetic salts based on 3-amino-4-tetrazolefurazan (ATF) have been reported,⁶ which are insensitive to impact and are thermally stable, but they show relatively poor general detonation performances due to their low density and low oxygen balance. It is well known that the introduction of nitramino groups is an efficient strategy to improve the density and oxygen balance, which has been applied in developing new energetic salts.⁷ The energetic salts based on 3,4-dinitraminofurazan (DNAF) reported by Shreeve⁹ and by our group⁸ are examples of such nitramino-containing salts (Fig. 1) and show good detonation performances due to the high oxygen balance of the DNAF anion. Unfortunately, however, some of them are quite sensitive to mechanical stimuli.

Fig. 1 Different anions based on furazan.

Aiming at developing energetic salts with better comprehensive properties, we designed new energetic salts by the combination of nitramino and tetrazole with the furazan ring. The nitramino group will improve the oxygen balance of the anion (compared with ATF anion) while the tetrazole ring is hoped to lead to lower sensitivity of the resulting salts (compared with DNAF salts). With this in mind, energetic salts based on 3-nitramino-4-tetrazolefurazan (NATF) were prepared and fully characterized by NMR, IR, elemental analysis and single-crystal X-ray diffraction. Their thermal stabilities and densities were measured and their enthalpies of formation and detonation performances were also calculated.

Results and discussion

Synthesis

The ammonium (2) and barium salt (3) of 3-nitramino-4-tetrazolefurazan were obtained by the nitration of 3-amino-4-tetrazolefurazan with mixed fuming nitric acid and concentrated sulfuric acid followed by neutralization with gaseous ammonia or aqueous Ba(OH)₂ solution, in the same yield of 81% after recrystallization (Scheme 1). The thermal gravimetric analysis–differential scanning calorimetry (TG–DSC) curve of salt 3 showed an endothermic peak at a temperature of 151 °C on the DSC curve and the corresponding weight loss on the TG curve was 14.6%, which is consistent with the loss of three molecules of water. The elemental analysis result of salt 3 also confirmed that it contains three molecules of co-crystallized water. Salts 4–9 were easily synthesized by the metathesis reaction of barium salt (3) with equal molar ratios of sulfate salts in water to give the target compounds in yields of 67–84% (Scheme 1). For salts 4 and 6–9 the sulfate salts were prepared in situ by the reaction of the chloride salt and Ag₂SO₄. The chloride salts are hydrazinium chloride, guanidinium chloride, aminoguanidinium chloride, diaminoguanidinium chloride and triaminoguanidinium chloride. For salt 5, dihydroxyammonium sulfate was used as purchased. All the salts were fully characterized by NMR, IR and elemental analysis and salt 5 was further confirmed by single-crystal X-ray diffraction.

Scheme 1 Synthesis of NATF-based energetic salts.

Spectroscopy

There is no proton in the NATF anion, so all the signals in the ¹H NMR are assigned to the cations and they are consistent with the literature data.¹⁰ The signals of the ¹³C NMR of salt 2 (δ = 156.9, 150.2, 144.8 ppm) are downshifted compared to that of ammonium 4-amino-3-(5-tetrazolate)furazan (ATF) (δ = 155.9, 151.1, 140.4 ppm) because of the electron-withdrawing property of the nitro group.⁹ The ¹⁵N NMR spectrum of salt 2 obtained in [D₆]DMSO solvent is shown in Fig. 2 in which the chemical shifts are given with respect to CH₃NO₂ as external standard. The signal assigned to the ammonium cation (N1) appears at −356.92 ppm. The signals corresponding to the nitrogen atoms on the NATF anion can be assigned based on the chemical shifts in the literature.^7c,11 The signals for N2–N7 in the NATF anion are observed at −13.28, −150.15, 4.99, 23.38, −61.65 and 10.13 ppm, respectively.

Fig. 2 ¹⁵N NMR spectrum of salt 2.

X-Ray crystallography

Crystals of salt 5 suitable for single-crystal X-ray diffraction analysis were obtained by slow evaporation of its aqueous solution at room temperature. The structure (Fig. 3) crystallized in triclinic space group P1̄ with four hydroxyammonium cations and two NATF anions per unit cell at a density of 1.815 g cm⁻³. The NATF anion is almost planar with the torsion angles of N4–C2–C3–N5, N3–C1–N2–N1 and C1–N2–N1–O3 being 2.19, −1.73 and −0.01°, respectively. The bonds on the furazan ring near the nitro group (C1–N3 1.311 Å; N3–O1 1.390 Å) are slightly longer than corresponding bonds nearer to the tetrazole ring (C2–N4 1.296 Å; N4–O1 1.368 Å), which is probably caused by the strong electron-withdrawing property of the nitro group. Comparing N–O bond lengths of the furazan ring in dihydroxyammonium DNTF (1.398 and 1.386 Å) and salt 5 (1.390 and 1.368 Å) further confirmed our deduction.

Fig. 3 (a) Displacement ellipsoid plot (30%) of salt 5. (b) Ball-and-stick packing diagram of salt 5 viewed down the a-axis. The dashed lines indicate hydrogen bonding.

Densities

According to Kamlet–Jacobs equations,¹² the detonation velocity of an energetic material is proportional to its density and its detonation pressure is proportional to the square of its density. Hence, density is one of the most important properties determining the detonation performances of an energetic material. The densities of salts 2, 4 and 6–9 were measured by using a gas pycnometer, while the density of salt 5 was obtained from its single-crystal X-ray diffraction structure. As shown in Table 1, the densities of the prepared energetic salts are in the range of 1.621 (6) to 1.815 g cm⁻³ (5), which are much higher than that of 2,4,6-trinitrotolune (TNT), and the density of salt 5 is even higher than that of RDX. Furthermore, their densities are also higher than that of the corresponding ATF-based energetic salts.

Table 1 Physical properties and thermochemical values of NATF-based energetic salts

Compd	Tm^a	Td^b	d^c	ΔfHsal^d	P^e	vD^f	IS^g	FSi^h	N^i (%)	OB^j
a Melting point (peak) [°C].b Decomposition temperature (peak) [°C].c Density measured by gas pycnometer at 25 °C; for salt 5, the density is obtained from the single-crystal X-ray diffraction structure [g cm^−3].d Calculated molar enthalpy of formation of salt [kJ mol^−1].e Detonation pressure [GPa].f Detonation velocity [m s^−1].g Impact sensitivity [J].h Friction sensitivity [N].i Nitrogen content [%].j Oxygen balance (OB) is an index of the deficiency or excess of oxygen in a compound required to convert all C into CO2 and all H into H2O, for a compound with the molecular formula of CaHbNcOd (without crystal water), OB(%) = 1600[(d − 2a − b/2)/Mw] [%].
2	—	232	1.667	299.2	25.4	7752	5	240	60.3	−48.24
4	—	203	1.753	613.8	31.8	8535	6	108	64.1	−48.82
5	198	233	1.815	425.6	34.7	8826	5	112	53.0	−30.28
6	—	284	1.621	326.7	21.1	7117	>40	>360	62.0	−65.77
7	208	238	1.708	538.3	25.4	7686	>40	288	64.2	−64.69
8	167	233	1.662	807.3	26.2	7868	>40	240	67.0	−63.78
9	189	230	1.686	1040.6	28.5	8174	29	160	68.9	−63.00
TNT	81	295	1.65	55.7	23.5	7459	15	353	18.5	−74.0

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Thermal behavior

The thermal behavior, including the melting point and decomposition temperature of the synthesized salts were measured by TG–DSC with a heating rate of 5 K min⁻¹, and the corresponding DSC curves are listed in Fig. 4. As can be seen, four of the salts melted before decomposition with the melting points being between 167 and 208 °C (5: 198 °C; 7: 208 °C; 8: 167 °C; 9: 189 °C), while salts 2, 4 and 5 decomposed directly without melting. The results show that these salts are thermally stable with decomposition temperatures ranging from 203 °C (4) to 284 °C (6). The hydrazinium (4, T_d = 203 °C), guanidinium (6, T_d = 284 °C) and triaminoguanidinium (9, T_d = 230 °C) salts based on the NATF anion exhibit even higher decomposition temperatures than the corresponding ATF based salts (hydrazinium salt: T_d = 197 °C; guanidinium salt: T_d = 257 °C; triaminoguanidinium salt: T_d = 216 °C).⁶ Additionally, all the NATF salts are more thermally stable than the corresponding DNTF salts.⁸ Except for salt 4, all the prepared salts possess better thermal stability than 1,3,5-trinitro-1,3,5-triazinane (RDX, T_d = 230 °C).

Fig. 4 The DSC curves of salts 2 and 4–9 with heating rate of 5 K min⁻¹.

Enthalpies of formation

The enthalpies of formation (HOF) of energetic materials are essential data for calculating their detonation performances. The HOF of the NATF anion was calculated to be 472.1 kJ mol⁻¹ based on the isodesmic reaction and protonation reaction shown in Schemes 2 and 3. All the geometry optimizations were performed by using B3LYP functional analyses with the 6-31+G** basis set on the Gaussian 09 (Revision A.01) suite of programs and single energy points were calculated at the MP₂/6-311++G** level. The HOFs of the cations were obtained from the literature.^13,14 Then the HOFs of the NATF-based energetic salts were calculated to be in the range of 299.2 kJ mol⁻¹ (2) to 1040.6 kJ mol⁻¹ (9) according to Born–Haber energy cycles (see ESI for details†).

Scheme 2 Isodesmic reaction for the calculation of enthalpy of formation.

Scheme 3 Protonation reaction for the calculation of enthalpy of formation.

Sensitivities

Impact sensitivities (IS) and friction sensitivities (FS) of the energetic salts were measured by using BAM drop hammer (BFH-10) and BAM friction tester (FSKM-10) according to BAM methods. As shown in Table 1, the impact sensitivities of the energetic salts lie between 5 J (2 and 5) and >40 J (6, 7, 8) and their friction sensitivities range from 108 N (4) to >360 N (6). The salts (6–9) based on guanidinium species are much less insensitive to impact and friction compared with the ammonium (2, IS = 5 J; FS = 240 N), hydrazinium (4, IS = 6 J; FS = 108 N) and hydroxylammonium salts (5, IS = 5 J; FS = 112 N). All the NATF salts show slightly lower sensitivities than the corresponding DNAF-based salts,⁸ which indicates that the substitution of the nitramino group with tetrazole will desensitize the energetic materials. According to UN recommendations on the transport of dangerous goods,¹⁵ salts 6–8 are insensitive to impact and salt 6 is also insensitive to friction.

Detonation performances

With the measured densities and calculated enthalpies of formation in hand, the detonation pressures (P) and detonation velocities (v_D) of the synthesized energetic salts were calculated according to Kamlet–Jacobs equations (see ESI for details†)¹² and the results are summarized in Table 1. The detonation pressures of the synthesized energetic salts were found to be in the range of 21.1 GPa (6) to 34.7 GPa (5) and their detonation velocities are between 7117 m s⁻¹ (6) and 8826 m s⁻¹ (5). Their detonation performances are in the following order: hydroxylammonium salt (5) > hydrazinium salt (4) > triaminoguanidinium salt (9) > diaminoguanidnium salt (8) > ammonium salt (2) > aminoguanidinium salt (7) > guanidinium salt (6). The highest detonation performances of the hydroxyammonium salt (5) should be due to its best oxygen balance and highest density while the relatively high detonation performances of the triaminoguanidinium salt (9) may be the result of its highest enthalpy of formation. The detonation performances are lower than that of the corresponding ATF and DNTF-based energetic salts.^6,8 Compared with the ATF salts, one more cation was introduced into the resulting NATF salts, while only one more nitro group was introduced onto the NATF anion. Finally, the NATF salts possess poorer oxygen balance than the corresponding ATF salts, which may be the reason for the lower detonation performances of NATF-based energetic salts compared with the ATF salts. In view of the detonation velocity, density and thermal stability, salt 5 (P = 8826 m s⁻¹; d = 1.815 g cm⁻³; T_d = 233 °C) is a promising replacement for RDX (P = 8983 m s⁻¹; d = 1.82 g cm⁻³; T_d = 230 °C).

Conclusions

A family of nitrogen-rich energetic salts based on 3-nitramino-4-tetrazolefurazan were conveniently synthesized and fully characterized by NMR (¹H, ¹³C), IR and elemental analysis. Additionally, ammonium salt (2) was confirmed by ¹⁵N NMR and hydroxyammonium salt (5) was confirmed by single-crystal X-ray diffraction. These energetic salts show good thermal stability [203 °C (4) to 284 °C (6)] and high positive enthalpy of formation [299.2 kJ mol⁻¹ (2) to 1040.6 kJ mol⁻¹ (9)]. Their impact sensitivities lie between 5 J (2 and 5) and >40 J (6, 7, 8) and their friction sensitivities range from 108 N (4) to >360 N (6). Unexpectedly, they showed slightly lower sensitivities compared with the corresponding DNTF salts. The detonation pressures of the synthesized energetic salts were calculated to be in the range of 21.1 GPa (6) to 34.7 GPa (5) and their detonation velocities were between 7117 m s⁻¹ (6) and 8826 m s⁻¹ (5). In view of the detonation velocity, density and thermal stability, salt 5 is a promising replacement for RDX.

Experimental section

General methods

¹H spectra were recorded on a 300 MHz nuclear magnetic resonance spectrometer operating at 300 MHz. Chemical shifts are reported relative to tetramethylsilane. ¹³C NMR spectra were recorded on a 400 MHz nuclear magnetic resonance spectrometer operating at 100 MHz. The solvent was [D₆]dimethyl sulfoxide ([D₆]DMSO) unless otherwise specified. ¹⁵N NMR spectra was recorded on a 400 MHz nuclear magnetic resonance spectrometer operating at 40.5 MHz. The melting and decomposition points were recorded on a NETZSCH STA 449F3 equipment at a scan rate of 5 °C min⁻¹, respectively. Infrared spectra were recorded by using KBr pellets. Densities were measured at room temperature using a MicromeriticsAccupyc II 1340 gas pycnometer. Elemental analyses were obtained on an ElementarVario MICRO CUBE (Germany) elemental analyzer.

3-Amino-4-tetrazole-furazan was synthesized according to ref. 16.

X-Ray crystallography

Crystals of salt 5 were removed from the flask and covered with a layer of hydrocarbon oil. A suitable crystal was then selected, attached to a glass fiber, and placed in the low-temperature nitrogen stream. The single-crystal X-ray diffraction data were collected at 293 K using graphite-monochromated MoKα radiation (λ = 0.71073 Å) using omega scans from a Bruker CCD area detector diffractometer. Data collection and reduction were performed and the unit cell was initially refined using Bruker SMART software. The reflection data were also corrected for Lp factors. The structure was solved by direct methods and refined by a least-squares method on F² using the Bruker SHELXTL program. The structure was solved in the space group P1̄ by analysis of systematic absences. In this all-light-atom structure the value of the Flack parameter did not allow the direction of polar axis to be determined and Friedel reflections were then merged for the final refinement. Details of the data collection and refinement are given in Table S1.†

CCDC-1476973 (5) contains the supplementary crystallographic data for this paper.†

Diammonium NATF (2)

4-Amino-3-(5-tetrazole)furazan (4.4 g, 28.7 mmol) was added in small portions into a mixture of 98% H₂SO₄ (25 mL) and fuming nitric acid (95%, 25 mL) cooled with an ice-water bath at <5 °C. The reaction mixture was allowed to warm to room temperature and stirred for 30 min followed by pouring into 500 mL ice-water. The resulting solution was extracted with ethyl acetate, and the combined organic phase was washed with brine to remove remaining acids. The organic phase was dried with MgSO₄ for 30 min followed by filtration. Ammonia gas was bubbled slowly into the filtrate to give a yellow precipitate. After filtration and washing with water and ethanol, yellow crystals were obtained (5.4 g) in 81% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 7.43 (s, 8H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 144.8, 150.2, 156.9 ppm. IR (KBr): 3185, 2812, 1697, 1592, 1513, 1437, 1371, 1292, 1155, 1045, 1012, 991, 914, 873, 824, 772, 742, 727, 585, 540, 488, 457 cm⁻¹. Elemental analysis for C₃H₈N₁₀O₃ (232.16): calculated: C: 15.52 H: 3.47 N: 60.33; found: C: 15.69 H: 3.63 N: 60.25%.

Barium NATF·3H₂O (3)

4-Amino-3-(5-tetrazole)furazan (3.6 g, 28.7 mmol) was added in small portions into a mixture of 98% H₂SO₄ (25 mL) and fuming nitric acid (95%, 25 mL) cooled with an ice-water bath at <5 °C. The reaction mixture was allowed to warm to room temperature and stirred for 30 min followed by pouring into 400 mL ice-water. The resulting solution was extracted with ethyl acetate, and the combined organic phase was washed with brine to remove remaining acids. The organic phase was dried with MgSO₄ for 30 min followed by filtration. An aqueous solution of Ba(OH)₂·8H₂O (7.4 g, 23.5 mmol) was added into the filtrate and the reaction mixture was stirred at room temperature for 30 min. A yellow solid precipitate was separated by filtration and recrystallized from water to give light yellow solid (6.1 g) in 81% yield. IR (KBr): 3562, 3412, 3269, 2960, 1682, 1611, 1523, 1443, 1420, 1382, 1356, 1293, 1169, 1149, 1085, 1070, 1036, 1019, 998, 924, 877, 847, 778, 736, 707, 545, 455 cm⁻¹. Elemental analysis for BaC₃H₆N₈O₆ (387.46): calculated: C: 9.30 H: 1.56 N: 28.92; found: C: 8.82 H: 1.58 N: 29.38%.

General procedures for the preparation of salts 4–9

Barium NATF (775 mg, 2 mmol) was added to an aqueous solution of a sulfate salt (2 mmol) and the resulting solution was stirred at room temperature for 4 h. For salts 4 and 6–9 the sulfate salts were prepared by the reaction of the chloride salt (4 mmol) and Ag₂SO₄ in 15 mL water at room temperature for 2 h. The chloride salts are hydrazinium chloride, guanidinium chloride, aminoguanidinium chloride, diaminoguanidinium chloride and triaminoguanidinium chloride. For salt 5, dihydroxyammonium sulfate was used as purchased.

Dihydrazinium NATF (4)

Recrystallization from a mixture of water and ethanol gave 400 mg of white crystals in 76% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 7.31 (s, 10H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 144.5, 150.1, 156.9 ppm. IR (KBr): 3341, 3012, 1611, 1511, 1438, 1375, 1320, 1157, 1097, 1011, 991, 970, 913, 869, 827, 771, 737, 581, 542, 453 cm⁻¹. Elemental analysis for C₃H₁₀N₁₂O₃ (262.19): calculated: C: 13.74 H: 3.84 N: 64.11; found: C: 13.99 H: 3.94 N: 63.66%.

Dihydroxyammonium NATF (5)

Recrystallization from a mixture of water and ethanol gave 355 mg of white crystals in 67% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 10.44 (s, 8H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 143.7, 149.6, 156.3 ppm. IR (KBr): 3121, 2702, 1618, 1584, 1519, 1441, 1394, 1350, 1221, 1185, 1164, 1143, 1097, 1001, 934, 881, 837, 748, 735, 720, 594, 551, 453, 405 cm⁻¹. Elemental analysis for C₃H₈N₁₀O₅ (264.16): calculated: C: 13.64 H: 3.05 N: 53.02; found: C: 13.40 H: 3.30 N: 52.28%.

Bis(guanidinium) NATF (6)

Recrystallization from a mixture of water and ethanol gave 460 mg of white crystals in 73% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 7.16 (s, 12H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 145.0, 150.3, 157.3, 158.0 ppm. IR (KBr): 3361, 3183, 1655, 1506, 1427, 1393, 1369, 1337, 1300, 1160, 1013, 993, 927, 875, 826, 771, 739, 590, 540 cm⁻¹. Elemental analysis for C₅H₁₂N₁₄O₃ (316.24): calculated: C: 18.99 H: 3.82 N: 62.01; found: C: 18.76 H: 3.97 N: 61.97%.

Bis(aminoguanidinium) NATF (7)

Recrystallization from a mixture of water and ethanol gave 520 mg of white crystals in 75% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 4.76 (s, 4H) 7.04 (s, 4H), 7.39 (s, 4H), 8.94 (s, 2H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 145.0, 150.3, 157.4, 158.8 ppm. IR (KBr): 3463, 3158, 1678, 1648, 1624, 1587, 1509, 1463, 1433, 1390, 1366, 1322, 1200, 1162, 1140, 1097, 1043, 1009, 995, 923, 875, 826, 770, 734, 692, 616, 543, 507, 453 cm⁻¹. Elemental analysis for C₅H₁₄N₁₆O₃ (346.27): calculated: C: 17.34 H: 4.08 N: 64.72; found: C: 16.82 H: 3.76 N: 64.63%.

Bis(diaminoguanidinium) NATF (8)

Recrystallization from a mixture of water and ethanol gave 620 mg of a white solid in 82% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 4.65 (s, 8H), 7.27 (s, 4H), 8.80 (s, 4H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 145.1, 150.3, 157.5, 159.8 ppm. IR (KBr): 3407, 3367, 3281, 3201, 2978, 2875, 1679, 1615, 1502, 1432, 1407, 1386, 1311, 1182, 1157, 1136, 1052, 994, 932, 875, 827, 773, 740, 656, 544, 514, 427 cm⁻¹. Elemental analysis for C₅H₁₆N₁₈O₃ (376.30): calculated: C: 15.96 H: 4.29 N: 67.00; found: C: 15.69 H: 4.32 N: 66.17%.

Bis(triaminoguanidinium) NATF (9)

Recrystallization from a mixture of water and ethanol gave 685 mg of a white solid in 84% yield. ¹H NMR (d₆-DMSO, 300 MHz): δ 4.51 (s, 12H), 8.62 (s, 6H) ppm; ¹³C NMR (d₆-DMSO, 100 MHz): δ 146.3, 150.4, 158.0, 159.1 ppm. IR (KBr): 3317, 3210, 1691, 1598, 1498, 1427, 1392, 1373, 1309, 1203, 1133, 1033, 986, 910, 864, 820, 773, 748, 725, 639, 581, 538, 459 cm⁻¹. Elemental analysis for C₅H₁₈N₂₀O₃ (406.33): calculated: C: 14.78 H: 4.47 N: 68.94; found: C: 14.34 H: 4.56 N: 68.63%.

Acknowledgements

This work was financially supported by Natural Science Foundation of Shanghai, China (Grant No. 16ZR1443600). We thank Prof. Guangyu Li for ¹⁵N NMR measurement.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Crystallographic data and refinement parameters, ab initio computational data and method for calculating detonation performances. CCDC 1476973. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra12109h

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