Thermally insensitive explosives

Thermally insensitive explosives from halide displacement with nitrogen nucleophiles... 

The thermally insensitive explosive (112) is synthesized by a similar route from the reaction of l,3-dichloro-2,4,6-trinitrobenzene (106) (styphnyl chloride) with two equivalents of 3-chloroaniline, followed by nitration and subsequent displacement of the chloro groups with... 

Amino derivatives of polynitrobiphenyls often exhibit high thermal stability. The thermally insensitive explosive (156) is synthesized in three synthetic steps from 3,5-dimethoxychlorobenzene (154) in a route employing nitration, Ullmann coupling and ammonolysis. 3,3 -Diamino-2,2, 4,4, 6,6 -hexanitrobiphenyl (DIPAM) (157) is synthesized from 3-chloroanisole by a similar route. DIPAM (m.p. 304 °C, d = 1.82 g/cm ) is... 

The tetraazapentalene ring system forms the core of the thermally insensitive explosive TACOT (Section 7.10) and so its fusion with the furoxan ring would be expected to enhance thermal stability and lead to energetic compounds with a high density, y-DBBD (95) is prepared from the nitration of tetraazapentalene (91), nucleophilic displacement of the o-nitro groups with azide anion, further nitration to (94), followed by furoxan formation on heating in o-dichlorobenzene at reflux. The isomeric explosive z-DBBD (96) has been prepared via a similar route. ... 

Formal sequential addition of amino groups to 2,4,6-trinitroaniline gives 1,3-diamino-2,4,6-trinitrobenzene (DATB, 56) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB, 57). TATB is more stable than expected from the additivity calculation. The ability to have hydrogen bonding with three amino groups both intra- and inter-molecularly in the crystal stabilizes the molecule. The molecule that results is thermally stable and used as an explosive in situations where a very insensitive explosive is needed. 

Interest in polynitroarylenes has resumed over the past few decades as the demand for thermally stable explosives with a low sensitivity to impact has increased. This is mainly due to advances in military weapons technology but also for thermally demanding commercial applications i.e. oil well exploration, space programmes etc. Explosives like 1,3-diamino-2,4,6-trinitrobenzene (DATB) (13), l,3,5-triamino-2,4,6-trinitrobenzene (TATB) (14), 3,3 -diamino-2,2, 4,4, 6,6 -hexanitrobiphenyl (DIPAM) (15), 2,2, 4,4, 6,6 -hexanitrostilbene(HNS, VOD 7120 m/s, = 1.70 g/cm ) (16) and A,A -bis(l,2,4-triazol-3-yl)-4,4 -diamino-2,2, 3,3, 5,5, 6,6 -octanitroazobenzene (BTDAONAB) (17) fall into this class. TATB is the benchmark for thermal and impact insensitive explosives and finds wide use for military, space and nuclear applications. 

ANTA (114) readily forms a stable anion on reaction with bases like sodium ethoxide and this anion has been used as a nucleophile for the synthesis of many ANTA derivatives. Laval and co-workers synthesizedDANTNP (116) (calculated VOD 8120 m/s, = 1.84 g/cm, m.p. > 330 °C) from the reaction of 4,6-dichloro-5-nitropyrimidine (115) with two equivalents of ANTA (114) in the presence of sodium ethoxide. Agrawal and co-workers studied the thermal and explosive properties of both ANTA and DANTNP and suggested their use for applications in propellant/explosive formulations where insensitivity coupled with thermal stability is of prime importance. The activation energies of ANTA and DANTNP indicate that DANTNP is more thermally stable than ANTA. 

The direct nitration of 2,6-diaminopyridine (168) with mixed acid yields 2,6-diamino-3,5-dinitropyridine (ANPy) (173). Oxidation of ANPy (173) with peroxyacetic acid yields ANPyO (174) (calculated VOD 7840 m/s, d = 1.88 g/crc ) C-Amination of ANPyO (174) with hydroxylamine hydrochloride in aqueous base yields the triamine (175), an impact insensitive explosive of high thermal stability. ... 

The data indicate that BTATNB is slightly more thermally stable (m.p. 320 °C as compared with 310°C for PATO) coupled with better insensitivity toward impact and friction. Similarly, 5-picrylamino-l,2,3,4-tetrazole [72] (PAT) [Structure (2.28)] and 5,5 -styphnylamino-l,2,3,4-tetrazole [73] (SAT) [Structure (2.29)] have been synthesized by condensing picryl chloride and styphnyl chloride respectively with 5-amino-l,2,3,4-tetrazole in methanol. A comparison of thermal and explosive properties of newly synthesized PAT (deflagration temperature 203 °C and calc. VOD 8126ms"1) and SAT (deflagration temperature 140 °C and calc. VOD 8602 ms"1) reveals that PAT is more thermally stable than SAT but more sensitive to impact and friction. 

A number of explosives for various applications have been synthesized, characterized for structural aspects, thermal and explosive properties by us in India and are being evaluated [193-198] for their intended end-use. The evaluation of BTATNB [Structure (2.27)] indicates that it is slightly more thermally stable than PATO [Structure (2.24)] coupled with better insensitivity toward impact and friction [71]. The data on thermal and explosive properties of some aromatic nitrate esters suggest that l,3,5-tris(2-nitroxyethyl nitramino)-2,4,6-trinitrobenzene [Structure (2.54)] is a potential substitute of PETN [193]. An explosive called 2,4,6-tris (3,5 -diamino-2, 4, 6 -trinitrophenylamino)-l,3,5-triazene [designated as PL-1 Structure (2.55)] is a new thermally stable and insensitive explosive which on comparison with TATB suggests that it is slightly inferior to TATB [Structure... 

TATB/Kel-F800 (90/10 wt.%) is best in terms of thermal stability coupled with a respectable performance [200]. Similarly, PBXs based on TATB, HMX and Kel-F800 are available, and sensitivity data on TATB/HMX-based PBXs clearly show that insensitivity rapidly decreases with increasing HMX content, even at relatively low levels of HMX. Evidently, some trade-off must be made between VOD and safety [201] (Table 2.5). Further, sensitivity and thermal test data (Table 2.6) also indicate that TATB-based formulations rank as the most insensitive explosive formulations [202]. 

High Performance, Thermally Stable and Insensitive Explosives... 

G.K. Williams, S.F. Palopoli, T.B. Brill, Thermal Decomposition of Energetic Materials 65. Conversion of Insensitive Explosives (NTO,... 

Popolato W.C. Davb, The Insensitive Explosives Nitroguanidine and Triaminotrinitrobenzene , Los Alamos Sci Lab, Los Alamos (1978) 75) J.R. Kolb H.F. Rizzo, Growth of 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) I. Anisotropic Thermal Expansion , UCRL-81189, LLL, Livermore (1978) 76) A.G. Osborn T.L. 

We have shown a relationship between impact and shock sensitivity and illustrated how a sensitivity index based on oxygen balance can be used to estimate sensitivity in closely related series of molecules. It is shown that the critical temperature of an explosive calculated by the Frank-Kamenetskii equation correlates fairly well with the shock sensitivity of the material. This supports the idea that the shock or impact initiation of an explosive is primarily a thermal event and not dominated by pressure driven chemistry. The concept of the "trigger linkage" in explosives is discussed and it is pointed out that insensitive explosives will require early chemistry that is thermochemically neutral or endothermic and leads to the build-up of later strongly exothermic chemistry. 

RDX is a white, crystalline solid with a melting temperature of 204 °C. It attained military importance during World War II since it is more chemically and thermally stable than PETN and has a lower sensitiveness. Pure RDX is very sensitive to initiation by impact and friction and is desensitized by coating the crystals with wax, oils or grease. It can also be compounded with mineral jelly and similar materials to give plastic explosives. Insensitive explosive compositions containing RDX can be achieved by embedding the RDX crystals in a polymeric matrix. This type of composition is known as a polymer bonded explosive (PBX) and is less sensitive to accidental initiation. 

The material is impact-sensitive when dry and is supplied and stored damp with ethanol. It is used as a saturated solution and it is important to prevent total evaporation, or the slow growth of large crystals which may become dried and shock-sensitive. Lead drains must not be used, to avoid formation of the detonator, lead azide. Exposure to acid conditions may generate explosive hydrazoic acid [1], It has been stated that barium azide is relatively insensitive to impact but highly sensitive to friction [2], Strontium, and particularly calcium azides show much more marked explosive properties than barium azide. The explosive properties appear to be closely associated with the method of formation of the azide [3], Factors which affect the sensitivity of the azide include surface area, solvent used and ageing. Presence of barium metal, sodium or iron ions as impurities increases the sensitivity [4], Though not an endothermic compound (AH°f —22.17 kJ/mol, 0.1 kj/g), it may thermally decompose to barium nitride, rather than to the elements, when a considerable exotherm is produced (98.74 kJ/mol, 0.45 kJ/g of azide) [5]. 

Amino-1,2,4-triazole is a useful starting material for the synthesis of many 1,2,4-triazole-based explosives. Jackson and Coburn synthesized a number of picryl- and picrylamino-substituted 1,2,4-triazoles. PATO (99) is synthesized from the reaction of 3-amino-1,2,4-triazole (98) with picryl chloride (67). ° PATO has also been synthesized from the reaction of 3-amino-l,2,4-triazole with A,2,4,6-tetranitromethylaniline (tetryl). PATO has a low sensitivity to impact and is thermally stable up to 310 °C. PATO (VOD 7469 m/s) exhibits lower performance to TATB (VOD 8000 m/s) which is the common benchmark standard for thermal stability and insensitivity in explosives. 

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