Triazidotrinitro Benzene: 1,3,5-(N3)3-2,4,6-(NO2)3C6

David Adam, Konstantin Karaghiosoff, and Thomas M. Klapˆtke*

Department of Chemistry, Ludwig-Maximilians University of Munich, D-81377 Munich (Germany)

Gerhard Holl and Manfred Kaiser

Bundeswehr Research Institute for Materials, Fuels and Lubricants, Swisttal-Heimertsheim, D-53913 Swisttal (Germany)

Summary

Triazidotrinitro benzene, 1,3,5-(N3)3-2,4,6-(NO2)3C6 (1) wassynthesized by nitration of triazidodinitro benzene, 1,3,5-(N3)3-2,4-(NO2)2C6H with either a mixture of fuming nitric andconcentrated sulfuric acid (HNO3/H2SO4) or with N2O5. Crystalswere obtained by the slow evaporation of an acetone/acetic acidmixture at room temperature over a period of 2 weeks andcharacterized by single crystal X-ray diffraction: monoclinic, P 21/c (no. 14), a� 0.54256(4), b� 1.8552(1), c� 1.2129(1) nm, ��94.91(1)�, V� 1.2163(2) nm3, Z� 4, �� 1.836 g ¥ cm�3, Rall�0.069.Triazidotrinitro benzene has a remarkably high density (1.84 g ¥cm�3). The standard heat of formation of compound 1 wascomputed at B3LYP/6-31G(d, p) level of theory to be �H�f�765.8 kJ ¥mol�1 which translates to 2278.0 kJ ¥ kg�1. The expecteddetonation properties of compound 1 were calculated using thesemi-empirical equations suggested by Kamlet and Jacobs:detonation pressure, P� 18.4 GPa and detonation velocity, D�8100 m ¥ s�1.

1. Introduction

During the last 10 years, significant advances have beenmade in the area of covalently bound azides, as indicated bythe number of recent reviews covering various aspects of thesubject(1±3). Recently, we and others also reported on theconvenient preparation of N2O5 and other nitrating agentsas well as the nitration of covalent non-metal com-pounds(4±7).Since toxic lead azide is still widely used as the initiator in

ammunition(8), there is a great demand to find suitable non-toxic, heavy metal free substitutes which can be used asprimary detonators(9). Equally important, most solid-rocketfuels are still based on mixtures of ammonium perchlorate,aluminum and epoxy resins and therefore generate exhaustplumes which contain large amounts of HCl and aluminumoxides(8). The presence of these compounds is both environ-mentally not desirable and, equally important, the trace ofsuch rockets can easily be detected by radar(9).The goal of ourwork is to find new,metal and halogen free

high energy density materials which can be used either asinitiators or solid rocket propellants. In the search for suchnew compoundswe started a few years ago to combine azide

and nitro groups in covalent molecules in order to provideboth a fuel and oxidizer in one compound (10). Thesecompounds are metal free and combust ideally to give onlygaseous products (i. e. CO, CO2 and N2).

2. Synthesis

Caution! Compound 1 is sensitive to electrostatic dis-charge and very friction and impact sensitive. Rapid heatingabove 168 �C causes explosion. Appropriate safety precau-tions should be taken at all times.1,3,5-Triazido-2,4-dinitrobenzene(10) (8 g, 27.5 mmol) was

slowly dissolved in fuming nitric acid (40 ml, Fluka). To thissolution 8 ml of concentrated sulfuric acid (Merck) wereadded dropwise. The reaction mixture was allowed to standat r. t. for 4 h (after 2 h pale yellow plates started toprecipitate) and was then cooled to 0 �C for another 12 h.The precipitated solid was filtered off and washed withwater (fraction 1). The filtrate was diluted with an equalvolume of water and the impurematerial that separatedwasrecrystallized from acetic acid (fraction 2). The combinedfractions were again recrystallized from acetic acid to yieldbright yellow plates. Additional recrystallization from an1 :1 acetone/acetic acid mixture by slow evaporation of themore volatile acetone yielded single crystals suitable for X-ray diffraction.

Yield: 8.42 g (91%).

C6N12O6 (336.1): found C 21.3, N 49.3%; calcd C 21.4, N50.0%.

Mp 128 ± 130 �C (decomposition).

13C NMR (� in ppm, CDCl3): 140.9 (C-NO2), 102.0 (C-N3).

14N NMR (� in ppm, CDCl3): �27.6 (�NO2),�144.4 (N�, �N3), �153.0 (N�, �N3), �290 br (N�, �N3).

IR (KBr, � in cm�1): 2232 vw, 2121 s (�as-N3), 1599 m,1542 s (�as-NO2), 1370 m (�s-NO2), 1343 s (�s-N3), 893 w,603 m (�-N3), 579 w (�-NO2), 520 w.

¹ WILEY-VCH Verlag GmbH, 69469 Weinheim, Germany, 2002 0721-3113/02/2701/0007 $ 17.50+.50/0

* Corresponding author; e-mail: tmk@cup.uni-muenchen.de

7Propellants, Explosives, Pyrotechnics 27, 7 ± 11 (2002)

Raman (1064 nm, 200 mW, � in cm�1): 2146 (2) (�as-N3),1568 (9), 1541 (2) (�as-NO2), 1340 (10) (�s-N3), 1144 (1),819 (4), 499 (3).

3. Explosive Properties

Compound 1 is generally sensitive towards impact,friction, heat and electrostatic discharge.The temperature at which 1,3,5-triazido-2,4,6-trinitro-

benzene explodeswas determined by putting 10 mg samplesof the compound in small glass sample vials and placingthese vials into a sand bath at a pre-determined temperatureand monitoring if an explosion occurred. 1,3,5-triazido-2,4,6-trinitrobenzene exploded immediately at all temper-atures above 168 �C. Therefore, the explosion temperaturefor 1,3,5-triazido-2,4,6-trinitrobenzene can be given as168 �C. However, if a sample was placed in a sand bath atroom temperature and the bath was gradually warmed up to250 �C no explosion was observed. The stability towardsslow heating was monitored using variable temperatureRaman spectroscopy. Compound 1was found to decomposeat its melting point of 128 ± 130 �C.In the drophammer test compound 1 exploded using both

the 250 g and the 5 kg weight dropped from a height of60 cm(11).Crystals of compound 1 exploded when subjected to an

electrical discharge of 20 kV. The friction sensitivity ofcompound 1 was established in a standard friction appara-tus.

4. X-Ray Structure Determination

Single crystals suitable for X-ray diffraction of 1 wereobtained by recrystallization from an acetone/acetic acidmixture. A crystal was mounted on a glass fibre with smallamounts of perfluoroether oil.Crystal Data. 1,3,5-Triazido-2,4,6-trinitrobenzene (1),

C6N12O6, M� 336.18, monoclinic, a� 0.54256(4), b�1.8552(1), c� 1.2129(1) nm, �� 94.91(1)�; V� 1.2163(2)nm3, space group P 21/c (no. 14), Z� 4, �� 1.836 g ¥ cm�3.Crystal dimensions 0.1�0.1�0.2 mm3, yellow. �(Mo-K�)�0.164 mm�1, � 0.071073 nm, F(000)� 672.Data Collection and Processing. STOE IPDS diffractom-

eter, 200 K, 2max.� 51.8�, graphite monochromatedMo-K�

radiation ((Mo-K�)� 0.071073 nm). 7852 total measuredreflections, 2320 independent measured reflections, 1531reflections with F0� 2� (I).Structure Analysis and Refinement. The structure was

solved by direct methods (SHELXS-97) and refined bymeans of full-matrix least square procedures usingSHELXL-97(12,13). 217 parameters, R(all reflections)�0.069, R(F0� 2� F0)� 0.042, wR� 0.10, wR(F0� 2� F0)�0.09; GoF� 0.90. Further information on the crystal-struc-ture determinations has been deposited with theCambridgeCrystallographicData Centre as supplementary publicationno. CCDC 171054.

5. Results and Discussion

1,3,5-Triazido-2,4,6-trinitrobenzene (1) could be pre-pared in high purity and high yield as yellow crystallinematerial (Fig. 1) according to Eq. (1).

1,3,5-(N3)3-2,4-(NO2)2C6H�NO2�HSO4

�

� 1� 3� 5-�N3�3-2� 4� 6-�NO2�3C6 � H2SO4

�1�(1)

The 13C NMR spectrum shows two resonances at 140.9and 102.0 ppm for the NO2- and N3-bonded carbon atoms,respectively. The 14NNMRspectrum shows four resonances,one for the NO2 group (���27.6 ppm) and three for theazide groups: N� (���290 ppm),N� (���144.4 ppm) andN� (���153.0 ppm). The 14N NMR spectrum of 1,3,5-triazido-2,4,6-trinitrobenzene is shown in Figure 2.The molecular structure of compound 1 in the crystalline

state could be elucidated by a single crystalX-ray diffractionanalysis. TheC6 ring adopts a planar structure with alternate�N3 and �NO2 substitution. As expected, both the azideand nitro groups are rotated out of the C6 plane in order toreduce steric repulsion (Fig. 3). All three covalently boundazide groups are bentwithNNNangles of 169 ± 170�. Table 1summarized some of the most important bond lengths andangles of compound 1.

6. Computational Aspects

All calculations were carried out using the programpackage Gaussian 98(14).The structure of 1,3,5-triazido-2,4,6-trinitrobenzene was

fully optimized and the vibrational frequencies and zeropoint energy computed using a hybrid-DFT calculationcarried out at the B3LYP level of theory (15±18) using a6 ± 31G(d) basis set (Table 2)(19,20). The fully optimizedstructure of 1,3,5-triazido-2,4,6-trinitrobenzene is shown inthe Fig. 4 and agrees well with the experimentally deter-mined structure in the solid state.

Figure 1. 1,3,5-Triazido-2,4,6-trinitrobenzene (1) after recrystal-lization from acetic acid.

8 Adam, Karaghiosoff, Klapˆtke, Holl, Kaiser Propellants, Explosives, Pyrotechnics 27, 7 ± 11 (2002)

Theheat of detonation according toEq. (2)was calculatedusing the DFTenergies from Table 2 (�E(2)��1479.6 kJ ¥mol�1), which after zero point energy correction (�zpeB3LYP

(2)��148.6 kJ ¥mol�1, see Table 2) and corrections for thetranslational (�Utr(2)� 33/2 ¥ R ¥ T) and rotational term(�Urot(2)� 21/2 ¥R ¥ T) and for the work term (p�V� 11 ¥R ¥ T), was converted into the reaction enthalpy (�H�(2)) at298 K(21,22):

�H�(2)��1534.0 kJ ¥mol�1.1,3,5-(N3)3-2,4,6-(NO2)3C6 (g)� 6 CO � 6 N2 (2)

(1)

Figure 2. 14N NMR (CDCl3) spectrum of 1,3,5-triazido-2,4,6-trinitrobenzene (ppm).

Figure 3. ORTEP presentation (50% probability) of the mo-lecular structure of triazidotrinitro benzene as determined by X-ray diffraction.

Table 1. Bond lengths and angles for compound 1 as determinedby X-ray diffraction.

d / nm � / �

O21-N2 0.1212(3) O21-N2-O22 124.5(2)O22-N2 0.1216(5) O21-N2-C2 119.0(2)O41-N4 0.1214(4) O22-N2-C2 116.6(2)O42-N4 0.1219(4) O41-N4-O42 126.0(2)O61-N6 0.1205(5) O41-N4-C4 117.5(2)O62-N6 0.1208(4) O42-N4-C4 116.5(2)N2-C2 0.1463(6) O61-N6-O62 123.9(2)N4-C4 0.1471(3) O61-N6-C6 117.6(2)N6-C6 0.1472(6) O62-N6-C6 118.6(2)N11-N12 0.1236(4) N12-N11-C1 118.2(2)N11-C1 0.1424(3) N13-N12-N11 169.5(3)N12-N13 0.1129(4) N32-N31-C3 119.6(2)N31-N32 0.1245(3) N33-N32-N31 169.4(2)N31-C3 0.1402(6) N52-N51-C5 119.6(2)N32-N33 0.1120(3) N53-N52-N51 169.1(2)N51-N52 0.1252(3) C6-C1-C2 116.8(2)N51-C5 0.1398(6) C6-C1-N11 115.9(2)N52-N53 0.1115(3) C1-C2-N11 127.3(2)C1-C6 0.1382(6) C1-C2-C3 122.5(2)C1-C2 0.1390(6) C1-C2-N2 120.2(2)C2-C3 0.1400(3) C3-C2-N2 117.3(2)C3-C4 0.1396(6) C4-C3-C2 117.4(2)C4-C5 0.1394(6) C4-C3-N31 128.2(2)C5-C6 0.1387(3) C2-C3-N31 114.4(2)

C5-C4-C3 122.1(2)C5-C4-N4 119.4(2)C3-C4-N4 118.5(2)C6-C5-C4 117.0(2)C6-C5-N51 114.4(2)C4-C5-N51 128.6(2)C1-C6-C5 123.8(2)C1-C6-N6 118.1(2)C5-C6-N6 118.1(2)

Triazidotrinitro Benzene: 1,3,5-(N3)3-2,4,6-(NO2)3C6 9Propellants, Explosives, Pyrotechnics 27, 7 ± 11 (2002)

With an approximated heat of sublimation of �Hsub (1)�104.7 kJ ¥mol�1 (this value was taken to be equal to the heatof sublimation of TNT (23)) the heat of detonation accordingto Eq. (3) of compound 1 can be given as:

�Hdetonation(3)��1429.4 kJ ¥mol�1.

1,3,5-(N3)3-2,4,6-(NO2)3C6 (s)� 6 CO� 6 N2 (3)(1)

Using the reaction enthalpy (�H� (Eq. 2)) at 298 K andthe standard heats of formation of CO(g) and N2(g) [�H�f(CO)��110.5 kcal ¥mol�1; �H�f(N2)�0.0 kJ ¥mol�1 (24)] thestandardheat of formationof compound 1 canbe calculated:

�H�f(1(g)) �� 870.4 kJ ¥mol�1

�H�f(1(s)) �� 765.8 kJ ¥mol�1��2278.0 kJ ¥ kg�1.

Compound 1 has a significantly higher (more positive)heat of formation compared with TNTandHMX (octogen):�H�f(1(s) ��2278.0 kJ ¥kg�1; �H�f(TNT(s)) ��295.6 kJ ¥kg�1;�H�f(HMX �� 253.7 kJ ¥mol�1) with 1 being stronglyendothermic,HMXbeing also endothermic whereas TNTismildly exothermic(25).We also experimentally determined the heat of combus-

tion of compound 1 according to Eq. (4) using an oxygencalorimeter (Parr 1356 Bomb Calorimeter, type 207A-183-C20).

1,3,5-(N3)3-2,4,6-(NO2)3C6 (g)� 3 O2� 6 CO2� 6 N2 (4)

The experimental value of �Hcombexptl.(4) �� 3232�

126 kJ ¥mol�1 is in good accord with the calculated valueof �Hcomb

calcd.(4) �� 3140 kJ ¥mol�1 (cf. Table 2, the heat ofsublimation of 1was again taken to be equal to that of TNT,105 kJ ¥mol�1 (23)).

The measured density of 1 is with 1.84 g ¥ cm�3 somewhatlower than the reported density of �-HMX which is 1.96 g ¥mol�1 but still remarkably higher than that of solid TNT(1.64 g ¥ cm�3)(25).In order to assess more quantitatively the expected

detonation properties of compound 1 we calculated theexpected detonation pressure (P) and detonation velocity(D) using the semi-empirical equations suggested byKamlet and Jacobs (Eqs. 5 and 6) (26±30).

P [kbar]� K ¥ �2 ¥� (5)with: K� 15.58; � density in g ¥ cm�3

�N ¥M0.5 ¥ Q0.5

with: N �moles of gas per g of explosive;M� g of gas per mole of gas;Q � estimated or guessed heat of detona-

tion (cf. Eq. 3) in cal g�1

D [mm ¥ �s�1]�A ¥� ¥ (1�B) (6)with: A� 1.01; B� 1.30

For compound 1 we calculated a detonation pressure ofP� 18.4 GPa and a detonation velocity of 8.10 mm ¥ �s�1

(8100 m ¥ s�1) which is slightly below RDX (8750 m ¥ s�1, ��1.82 g ¥cm�3) and �-HMX (9100 m ¥s�1, ��1.89 g ¥cm�3) attheir highest densities but is significantly higher than that ofTNT (6900 m ¥ s�1, �� 1.60 g ¥ cm�3).In order to enhance the practical handling we are

currently evaluating the possibilities of desensitization ofcompound 1.

7. Conclusions

Aneasy and straightforwardpreparationof 1,3,5-triazido-2,4,6-trinitrobenzene (1) has been described and the resultsof a single crystal X-ray structure determination have beenpresented. The standard heat of formation of compound 1was computed at B3LYP/6-31G(d, p) level of theory to be�H�f(1(s)) �� 765.8 kJ ¥mol�1 which translates to2278.0 kJ ¥ kg�1. The expected detonation properties ofcompound 1 were calculated using the semi-empiricalequations suggested by Kamlet and Jacobs: detonationpressure, P� 18.4 GPa and detonation velocity, D�8100 m ¥ s�1.

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Paul. A. J. Sanderson, and M. J. Stewart, Phil. Trans. R. Soc.Lond. A, 339, 305 (1992).

Figure 4. Molecular structure of 1,3,5-triazido-2,4,6-trinitroben-zene fully optimized at B3LYP/6-31G(d) level of theory.

Table 2. Computational results (B3LYP/6-31G(d, p)).

Compound �E / a.u. zpe / kJ ¥mol�1

1 1336.437943 316.9CO 113.309454 13.4N2 109.524129 14.7CO2 188.580940 30.6H2O 76.419736 56.1O2 150.320042 10.0

10 Adam, Karaghiosoff, Klapˆtke, Holl, Kaiser Propellants, Explosives, Pyrotechnics 27, 7 ± 11 (2002)

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Acknowledgements

Financial support of this work by the University of Munich(LMU), the Fonds der Chemischen Industrie and the GermanFederal Office of Defense Technology and Procurement (BWB) isgratefully acknowledged. We are indebted to and thank Dr.Burkhard Krumm for recording the 14N NMR spectrum and Ms.Annette Burdzy for the preparation of the starting material(triazidodinitro benzene, 1,3,5-(N3)3-2,4-(NO2)2C6H). We alsothankMr. Gunnar Spie˚ for the heat of combustionmeasurements,Dr.Holger Piotrowski for his experimental helpwith theX-ray datacollection and Dr. Margaret-Jane Crawford for providing thephotographs and improving this manuscript.

(Received August 27, 2001; Ms 2001/053)

Triazidotrinitro Benzene: 1,3,5-(N3)3-2,4,6-(NO2)3C6 11Propellants, Explosives, Pyrotechnics 27, 7 ± 11 (2002)