Nitramine properties

Politzer, P., Sukumar, N. Jayasuriya, K. Ranganathan, S. (1988) Computational Evaluation and Comparison of Some Nitramine Properties Journal of the American Chemical Society 110, 3425-3430. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

N-Methyl-N-f2-Nitroxy propyl) Nitramine. (Me2NENA N-(2-NitroxypropyI) methyl nitramine. (02N)N(CH3).(CH2CH(0N02).CH3, mw 179.16, N 23.46%, OB to C02 -66.80%, pale yellow oil, mp 22—23°, d 1.320g/cc at 25/4°, RI 1.478 at 25°. Prepn from 2-hydroxy-propylamine after nitration with 98% nitric acid at 10° by reaction of the amine-nitric acid mixt with acetic anhydride acetyl chloride at 35°. Reaction mixt poured on ice. Yield is 74%. No expl properties listed Reft 1) Beil - not found 2) Blomquist, OSRD 4134, 45 119 (1944)... 

Agrawal and co-workers prepared some energetic explosives containing nitrate ester, nitramine and aromatic C-nitro functionality within the same molecule and studied their thermal and explosive properties l-(2-nitroxyethylnitramino)-2,4,6-trinitrobenzene... 

The chemical properties of primary and secondary nitramines are important in relation to their use as explosives. Primary nitramines contain acidic hydrogen in the form of —N//NO2 and, consequently, in the presence of moisture, primary nitramines corrode metals and form metal salts, some of which are primary explosives. This is one reason why powerful explosives like methyinitramine (1) have not found practical use. Ethylenedinitramine (EDNA) (2) suffers from similar problems but its high brisance (VOD 8240 m/s, d = 1.66 g/cm ) and low sensitivity to impact have seen it used for some applications. 

The synthesis and properties of nitramines derived from strained and bicyclic amines are discussed in more detail in Chapter 6. Such compounds often exhibit high performance resulting from high crystal densities and/or high heats of formation due to internal strain. 

Adolph and Cichra synthesized a number of polynitroperhydro-1,5-diazocines and compared their properties with the powerful military explosive HMX. A type of Mannich condensation was used to form the 1,5-diazocine rings the condensation of ammonia and methylamine with formaldehyde and bis(2,2-dinitroethyl)nitramine (46) forming diazocines (47) and (48) respectively. 1,3,3,7,7-Pentanitrooctahydro-1,5-diazocine (47) is A-nitrated to 1,3,3,5,7,7-hexanitrooctahydro-l,5-diazocine (52) in near quantitative yield using mixed acid. 

The Mannich reaction has been used to synthesize numerous heterocyclic nitramine explosives. Adolph and Cichra prepared a number of A-heterocycles containing ferf-butyl A-blocking groups. The nitrolysis of these f-butyl groups provides the corresponding A-nitro derivatives in excellent yields (Section 5.6.2.2). Some of the nitramine products from these reactions are powerful, energetic explosives with attractive properties. 

Y. Du, M. Jiang, Q. Sun and X. Fu, Detonation Properties and Thermal Stabilities of Furazano-Fused Cyclic Nitramines , in Proc. International Symposium on Pyrotechnics and Explosives, China Academic Publishers, Beijing, China, 412 (1987). 

In order to avoid the use of lead compounds on environmental grounds, lithium fluoride (liF) has been chosen to obtain super-rate burning of nitramine composite propellants.P7281 Typical chemical compositions of HMX composite propellants-with and without liF are shown in Table 7.4. The non-catalyzed HMX propellant is used as a reference pyrolant to evaluate the effect of super-rate burning. The HMX particles are of finely divided, crystalline (3-HMX with a bimodal size distribution. Hydroxy-terminated polyether (HTPE) is used as a binder, the OH groups of which are cured with isophorone diisocyanate. The chemical properties of the HTPE binder are summarized in Table 7.5. 

Similar to nitramine composite propellants and TAGN composite propellants, AN composite propellants produce halogen-free combustion products and thus represent smokeless propellants. However, their ballistic properties are inferior to those of other composite propellants the burning rate is too low and the pressure exponent is too high to permit fabrication of rocket propellant grains. In addition, the mechanical properties of AN composite propellants vary with temperature due to the phase transitions of AN particles. 

PBXs also include some pressed compositions where the level of nitramine is in excess of 94% (by weight). The explosives are only encapsulated by a minimum amount of binder such as Viton or Estane. The physical properties and safety characteristics of these formulations are not as good as those of castable PBXs but the performance is increased. 

A study was conducted to find out the effect of addition of these nitroplasticizers on ballistic properties of AP and RDX/HMX filled CMDB propellants. The data generated clearly indicated that the incorporation of nitroplasticizer, that is, 1 1 mixture of BDNPF and BDNPA in place of diethyl phthalate (DEP) for AP and nitramine based CMDB propellants improved the burn rates as well as /sp and thermal decomposition behavior of these propellant formulations [193]. 

This structure was deduced from their mode of preparation nitrosohydroxyl-amines are obtainable by nitrosation, nitramines by nitration. The physical properties of primary nitramines are entirely different from those of nitrosohydroxyl-amines, so that phenylnitramine C6H5NHN02, for example, differs radically from phenylnitrosohydroxylamine... 

These inferences concerning the structure of nitramines, based on their chemical properties, are confirmed by the data obtained by X-ray analysis of the simple nitramines dimethylnitramine and ethylenedinitramine. In particular, Costain and Cox [1], and Llewellyn and Whitmore [2], established that the grouping... 

Nitramines show no basic properties whatever — indeed, primary nitramines have distinct acidic properties and can form salts with alkalis. Conversely, nitr-amides may be more strongly acidic than carboxylic acids, as, for example, nitro-urethane, which is a stronger acid than formic acid. 

The concentration of alkali required depends on the properties of the radicals R and R1. The more electrophilic the radicals and the more dcidic the nitramine, the easier the course of reaction. Secondary nitramines are decomposed by an aqueous solution of sodium hydroxide. The reaction conditions, including the concentrations of NaOH solutions differ according to the substance. Van Erp and Franchimont [21] found that the reaction proceeded by the following mechanism ... 

Where there are strong bases which are nitrated with difficulty, reaction (9) predominates over reaction (8). At the same time Lambeiton called attention to the reversibility of reaction (9). Indeed, it is known that nitramines such as nitroguani-dine or nitrourethanes exhibit nitrating properties in the presence of sulphuric acid, thus behaving as if they can split off the nitronium ion or the nitric acid molecule. 

As regards explosive strength, nitramines occupy a position midway between nitro compounds and nitric esters. They also hold a central position regarding other properties, such as chemical stability and sensitiveness to impact and friction. 

Nitramine has explosive properties but it is not of any practical value for many reasons, primarily because of its high reactivity which impairs its chemical stability. It decomposes at a temperature as low as its melting point. At room temperature it decomposes slowly, to form nitrous oxide and water. On heating to 60-65°C decomposition occurs in an aqueous solution. It decomposes explosively on contact with concentrated sulphuric acid. ... 

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