Synthesis and Properties of 4,6-Dinitrobenzotriazol-3-dinitromethyl-1-oxide

HUO Huan, LIAN Peng, ZHAI Lian-jie, LI Ya-nan, WANG Bo-zhou,2, BI Fu-qiang,2

(1. Xi′an Modern Chemistry Research Institute, Xi′an 710065, China; 2. State Key Laboratory of Fluorine & Nitrogen Chemicals, Xi′an 710065, China)

1 Introduction

N-oxides have been extensively studied in the field of energetic materials[1-2]. Recently, the benzotriazol-3-ium-1-oxide compounds have attracted more attentions owing to their low sensitivities towards shock, friction, heat and electrostatic discharge[3]. For example, 4,6-dinitrobenzotriazol-3-ium-oxide(DNBTO) was identified as a kind of potential explosive with the high-performance and insensitivity. It has some desirable traits, including a low impact sensitivity(20 J), and a low friction sensitivity (>360 N)[4]. In order to search for the novel energetic derivatives with higher energy than DNBTO, a novel compound, 4,6-dinitrobenzotriazol-3-dinitromethyl-1-oxide(TNBTO) was designed and synthesized from DNBTO. Comparing with DNBTO, TNBTO exhibits higher density and detonation velocity because of the introduce of a dinitromethyl group[5-9]. In view of the above observations, the detailed studies of the synthesis and characterization of TNBTO were carried out in this work. In addition, the detonation parameters and stability were investigated.

2 Experimental

2.1 Materials and Instruments

4,6-Dinitrobenzotriazol-3-ium-1-oxide(DNBTO) was prepared and purified according to the reference[10], and other reagents were purchased from the commercial sources.1H NMR and13C NMR were obtained in DMSO-d6on a Bruker AV500 NMR spectrometer. Infrared spectra were obtained from KBr pellets on a Nicolet NEXUS870 Infrared spectrometer in the range of 4000-400 cm-1. Elemental analyses (C, H and N) were performed on a VARI-El-3 elemental analyzer.

2.2 Synthesis and Characterization

Using 4,6-dinitrobenzotriazol-3-ium-1-oxide(DNBTO) as starting materials, the title compound TNBTO was firstly synthesized via the reactions of metathesis, substitution and nitration-hydrolysis(Scheme 1).

2.2.1 Potassium 4,6-Dinitrobenzotriazol-3-ium-1-Oxide

DNBTO(1.0 g, 4.44 mmol) was dissolved in 80 mL ethanol, and then potassium hydroxide (0.25 g, 4.46 mmol) dissolved in a minimal amount of water was added dropwise at 40 ℃. The solution was stirred at 40 ℃ for other 2 h. After evaporation of the solvent, the residue was washed with diethyl ether, and dried to give 1.0 g purple solid with a yield of 85.5%. IR(KBr,ν/cm-1):3106, 2398, 1765, 1643, 1559, 1508, 1438, 1384, 1341, 1189, 1157, 1055, 983, 933, 885, 826, 806.1H NMR (DMSO-d6, 500 MHz),δ: 9.096(1H, CH), 8.880(1H, CH);13C NMR(DMSO-d6, 125 MHz),δ: 144.830, 137.430, 136.783, 130.260, 117.535, 115.295; Anal.Calcd. for C6H2N5O5K(%): C 27.38, H 0.77, N 26.61; Found: C 27.41, H 0.83, N 26.32.

2.2.2 4,6-Dinitrobenzotriazol-3-Acetone-1-Oxide

Potassium bromide (0.5 g, 4.2 mmol) and potassium 4,6-dinitrobenzotriazol-3-ium-1-oxide(0.95 g, 3.6 mmol) were dissolved in 80 mL acetone at ambient temperature. To the reaction mixture, chloroacetone(0.38 g, 4 mmol) was added dropwise. The solution was stirred for 8 h at 58 ℃. After evaporation of the solvent, the residue was washed with water and diethyl ether, and dried to give 0.41 g orange solid with a yield of 40.5% and a purity of 99.2%(HPLC). IR(KBr,ν/cm-1): 3444, 3097, 2986, 2938, 2869, 1745, 1632, 1601, 4534, 1488, 1401, 1371, 1344, 1281, 1234, 1184, 1169, 1101, 1067, 1020, 998, 935, 911, 805;1H NMR(DMSO-d6, 500 MHz),δ: 9.370(1H, CH), 8.938(1H, CH), 5.603(2H, CH2), 2.147(3H, CH3);13C NMR (DMSO-d6, 125 MHz),δ: 202.223, 146.033, 137.988, 137.217, 117.602, 115.371, 84.192, 26.524; Anal.Calcd. for C9H7N5O6(%): C 38.44, H 2.51, N 24.91; Found: C 38.40, H 2.75, N 24.82.

Scheme 1

2.2.3 4,6-Dinitrobenzotriazol-3-Dinitromethyl-1-Oxide(TNBTO)

4,6-Dinitrobenzotriazol-3-acetone-1-oxide was dissolved in 5 mL 98% sulfuric acid. To the reaction mixture, 65% nitric acid(3.9 mL, 54 mmol) was added dropwise at -5 ℃. The solution was stirred for 6 h at 40 ℃. Then the reaction mixture was poured into ice water. The yellow precipitate was filtered to obtain 1.0 g solid with a yield of 52.6%. IR(KBr,ν/cm-1): 3422, 3105, 2289, 1603, 1543, 1489, 1346, 1296, 1233, 1174, 1121, 1065, 1000, 934, 910, 847, 804, 776;1H NMR(DMSO-d6, 500 MHz),δ: 9.52-9.52 (1H, CH), 9.02-9.343(1H, CH), 7.23-7.03(H, (NO2)2);13C NMR (DMSO-d6, 125 MHz),δ: 146.61, 143.53, 133.31, 130.31, 123.16, 118.80, 76.95; Anal.Calcd. for C7H3N7O9(%): C 25.54, H 0.92, N 29.79; Found: C 25.50, H 1.04, N 29.33.

3 Physicochemical and Energetic Properties

All the quantum computations were performed using the Gaussian 09 (Revision A. 02) suite of programs[11]. The optimized structures were characterized to be true local energy minima on the potential-energy surface without imaginary frequencies. The densities of DNBTO and TNBTO were computed based on Monte-Caolo method using the optimized structure at the B3LYP/6-311+G(d, p) level of theory[12-13]. The gas phase heats of formation were calculated by the atomization method using the Gaussian 09 program package at the CBS-4M level of theory[14]. Gas phase heat of formation was transformed to solid phase heat of formation by Trouton′s rule[15]. Based on the calculated density and heat of formation, the detonation velocity and detonation pressure for DNBTO and TNBTO were calculated by Kamlet-Jacobs equations[16]. The stability was analyzed by TLC. The properties of TNBTO were obtained by calculation or test as follows: density is 1.81 g·cm-3, detonation velocity is 8161.2 m·s-1, heat of formation is 143.7 kJ·kg-1. Due to the introduce of R—C(NO2)2group, TNBTO exhibits a higher density and detonation velocity compared with DNBTO．However,the heat of formation of TNBTO was lower than that of DNBTO, and TNBTO showed a relatively poor stability because it easily decomposes at room temperature. The physicochemical and detonation properties of DNBTO and TNBTO were listed in Table 1.

Table 1 The performances of DNBTO and TNBTO

propertiesDNBTOTNBTOconditionformulaC6H3N5O5C7H3N7O9molarmass225321calculatednitrogencontent/%31．129．8calculatedoxygenbalance/%-60．4-31．6calculatedappearanceorangesolidyellowsolidEyeballing(tested)decompositiontemperature/℃201．3(DSC)roomtemperatureTLCanalysis(tested)density/g·cm-31．731．81Gaussian09program(calculated)detonationvelocity/m·s-17371．18162．2K⁃Jformula(calculated)detonationpressure/GPa24．030．2K⁃Jformula(calculated)heatofformation/kJ·mol-11232．1143．7Gaussian09program(calculated)

4 Conclusions

(1) TNBTO was firstly synthesized using 4,6-dinitrobenzotriazol-3-ium-1-oxide(DNBTO) as raw material via the reactions of metathesis, substitution and nitration-hydrolysis. Its structure was characterized by IR, NMR and element analysis.

(2) The main performance of TNBTO were obtained by theoretical calculation as follows: density is 1.81 g·cm-3, detonation velocity is 8161.2 m·s-1, heat of formation is 143.7 kJ·kg-1.

(3) TNBTO was easily decomposed at room temperature, and showed a relatively poor thermal stability.

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