The synthesis of HMX

HMX can be synthesized from hexamine by any of the routes discussed below. Both methods 

1 and 5.15.2.2 have been used for the industrial synthesis of HMX. However, the recent commercial availability of dinitrogen pentoxide means that method 5.15.2.3 is achieving industrial importance. 

Variations in the conditions used for the nitrolysis of hexamine have a profound effect on the nature and distribution of isolated products, including the ratio of RDX to HMX. It has been shown that lower reaction acidity and a reduction in the amount of ammonium nitrate used in the Bachmann process increases the amount of HMX formed at the expense of Bachmann and co-workers ° were able to tailor the conditions of hexamine nitrolysis to obtain an 82 % yield of a mixture containing 73 % HMX and 23 % RDX. Continued efforts to provide a method for the industrial synthesis of HMX led Castorina and co-workers to describe a procedure which produces a 90 % yield of a product containing 85 % HMX and 15 % RDX. This procedure conducts nitrolysis at a constant reaction temperature of 44 °C and treats hexamine, in the presence of a trace amount of paraformaldehyde, with a mixture of acetic acid, acetic anhydride, ammonium nitrate and nitric acid. Bratia and co-workers ° used a three stage aging process and a boron trifluoride catalyst to obtain a similar result. A procedure reported by Picard uses formaldehyde as a catalyst and produces a 95 % yield of a product containing 90 % HMX and 10 % RDX. 

The different solubilities of HMX and RDX in organic solvents means that pure HMX is easily isolated from RDX-HMX mixtures the higher solubility of RDX in acetone means that recrystallization of such mixtures from hot acetone yields pure HMX.  

HMX (3) can be synthesized from the nitrolysis of l,5-dinitroendomethylene-l,3,5,7-tetraazacyclooctane (DPT) (239). Wright and co-workers reported that the reaction of 

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Solomon, of the Illinois Institute of Technology Research Institute (IITR1), has reported the synthesis of HMX from the condensation of straight chained nitramines, bis(hydroxy methyl) methylene dinitramine and methylene dinitramine. However, details of this work were not available as of this writing... 

In conclusion, there appears to be some supporting evidence, other than these tracer studies, that the synthesis of HMX and RDX molecules can be accomplished thru a build-up from single methylene-containing spedes or other small molecules, and that this route can also take place via a total degradation and resynthesis from molecules such as Hexamine. However, die development of an economical process for the large scale production of these expl nitramines, in particular HMX, via a method precluding the use of Hexamine, is vet to be accomplished... 

The synthesis of HMX from the nitrolysis of hexamine with conventional reagents is far more problematic. However, HMX (25) is synthesized in high yield from the nitrolysis of l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (TAT) (23) and l,5-diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooctane (DADN) (24) with dinitrogen pentoxide in nitric acid. DADN (24) is readily synthesized from the acetolysis of hexamine followed by mild nitration with mixed acid. The synthesis of HMX (25) via the nitrolysis of DADN (24) is now a pilot plant... 

Marsuguma et al, "Behavior of Nitramide and Linear Polynitramines as Intermediates in the Synthesis of HMX" PATR 2442 (July 1957) (Conf, not used as a source of info)... 

In addition to the Ross-Schiessler process, utilising p-CH20 and AN, the synthesis of RDX/ HMX mixts has also been reported starting with other smail molecules (Ref 7), namely, methyl-amine nitrate methylene diamine dinitrate and nitramine (NH2N02) in combination with CH20. In these reactions, the intermediate formation of Hexamine or a cyclic analog, is not necessarily established... 

The nitrolysis of A,A-disubstituted amides is one of the key tools for the synthesis of nitramine containing energetic materials. The present synthesis of the high performance explosive HMX is via the nitrolysis of hexamine (Section 5.15). This is an inefficient reaction requiring large amounts of expensive acetic anhydride. An alternative route to HMX (4) is via the nitrolysis of either l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (79) (79%) or 1,5-dinitro-3,7-diacetyl-l,3,5,7-tetraazacyclooctane (80) (98 %) with dinitrogen pentoxide in absolute nitric acid. These reactions are discussed in more detail in Section 5.15. 

The above observations allow the selective formation of RDX, HMX or the two linear nitramines (247) and (248) by choosing the right reaction conditions. For the synthesis of the linear nitramine (247), with its three amino nitrogens, we would need high reaction acidity, but in the absence of ammonium nitrate. These conditions are achieved by adding a solution of hexamine in acetic acid to a solution of nitric acid in acetic anhydride and this leads to the isolation of (247) in 51 % yield. Bachmann and co-workers also noted that (247) was formed if the hexamine nitrolysis reaction was conducted at 0 °C even in the presence of ammonium nitrate. This result is because ammonium nitrate is essentially insoluble in the nitrolysis mixture at this temperature and, hence, the reaction is essentially between the hexamine and nitric acid-acetic anhydride. If we desire to form linear nitramine (248) the absence of ammonium nitrate should be coupled with low acidity. These conditions are satisfied by the simultaneous addition of a solution of hexamine in acetic acid and a solution of nitric acid in acetic anhydride, into a reactor vessel containing acetic acid. 

The chemistry of l,5-dinitroendomethylene-l,3,5,7-tetraazacyclooctane (239) (DPT) is interesting in the context of the nitramine products which can be obtained from its nitrolysis under different reaction conditions. The nitrolysis of DPT (239) with acetic anhydride-nitric acid mixtures in the presence of ammonium nitrate is an important route to HMX (4) and this has been discussed in Section 5.15.2. The nitrolysis of DPT (239) in the absence of ammonium nitrate leads to the formation of l,9-diacetoxy-2,4,6,8-tetranitro-2,4,6,8-tetraazanonane (248) the latter has found use in the synthesis of energetic polymers. 

Picric acid and tetryl, both yellow powders, are no longer used by the military, though do-it-yourself books outline the synthesis of picric acid for the would-be criminal/terrorist and tetryl is still found in old munitions. Most of the military explosives are white-colored powders (TNT is cream colored). Since all, but TNT, decompose upon or instead of melting, they require some sort of compounding in order to be shapeable. They can be blended into TNT in a variety of ratios to make the formulations listed in Table 2.3. They can also be formulated in wax or plasticizer. The use of plasticizer is preferred because less dilution of the explosive occurs. (In the world of performance, TNT, with detonation velocity of 6900 m/s is considered a dilutant of HMX, detonation velocity of 9100 m/s.)... 

Bachmann s products were known as Type B RDX and contained a constant impurity level of 8-12%. The explosive properties of this impurity were later utilized and the explosive HMX, also known as Octogen, was developed. The Bachmann process was adopted in Canada during World War II, and later in the USA by the Tennes-see-Eastman Company. This manufacturing process was more economical and also led to the discovery of several new explosives. A manufacturing route for the synthesis of pure RDX (no impurities) was developed by Brockman, and this became known as Type A RDX. 

In general, compounds containing N-N02 have more positive heats of formation than those containing C-N02, and multi-cyclic compounds achieve higher density than mono-cyclic. For these reasons, the synthesis of caged nitramines is pursued, and in 1987 Nielsen patented the synthesis of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW or Cl-20) [64,65]. Like HMX, CL-20 exists in several solid polymorphs, four of which can be isolated at ambient conditions [66, 67]. CL-20 can be... 

The only known adamantane containing more than three endocyclic ring nitrogens is hexamethylenetetramine (hexamine, 1,3,5,7-tetraaza-adamantane, 4). It is readily prepared by reaction of formaldehyde and ammonia and was first described by Butlerov in 1859 (Ref. 82). Its preparation and properties have been reviewed (Ref. 83). The mechanism of formation from formaldehyde and ammonia has been studied (Refs. 84,85). Hexamine is employed as a reactant in the synthesis of RDX (3) and HMX (1). 

G. A. Olah in Chapter 7 reviews some of the most useful methods in preparing nitro compounds (i.e., electrophilic nitrations with superacid systems, nitronium salts, and related Friedel-Crafts type complexes). Polynitro compounds were traditionally and still are the most widely used explosives [e.g., nitroglycerol, trinitrotoluene (TNT), and Af-nitramines (RDX and HMX)]. Methods of preparing nitro compounds thus remain a key part of the synthesis of energetic materials. 

A lot of work has been done for the synthesis of azido nitroamino compounds, their properties and applications [32]. Reed and Dolah first started the study of this kind of compounds. Rosher, Morton, and Eimslic synthesized series of azido nitroamino compounds, and applied them as the composition of propellants. They notably rise the combustion/buming rate and specific impulse without influencing the pressure index. Their energy approximately equals that of HMX. Their detonation sensitivity is relatively low. They are widely applied in smoke-free propellants with low sensitivity to replace HMX. 

Its calculated energy content is 85% that of HMX and 15% more than that of TATB. It is thermally stable, insensitive to shock, spark and friction and has impact insensitivity level approaching that of TATB. These combined properties make it a realistic high performance IHE material attractive for applications that require moderate performance and insensitivity. The synthesis of LLM-105 through the oxidation of 2,6-diamino-3,5-dinitropyrazine with trifluoroaceticperacid at room temperature was first reported in 1995 at the Lawrence Livermore Laboratories. Some of its properties are presented in Table 2.26. 

Thyagarajan and Majumdar (Ref 18) have studied the condensations of urethanes with formaldehyde under various exptl conditions and accomplished the selective synthesis of either six-membered 1,3,5-triazines or eight-membered 1,3,5,7-tetrazocines. These are nonnitrated analogs of RDX and HMX respectively. Their results are summarized in Fig 4... 

Gilbert and co-workers showed that the nitrolysis of 1,3,5-triacyl-1,3,5-triazacyclohexanes offered little benefit over the conventional synthesis of RDX via the nitrolysis of hexamine. This is not the case for HMX where its synthesis via the Bachmann process is far from perfect. This process and its modifications are expensive, requiring large amounts of acetic anhydride. The rate of production is slow and the maximum attainable yield is 75 %. In fact, HMX is five times as expensive as RDX to produce by this process and this prevents the widespread use of this high performance explosive. Many efforts have focused on finding more economical routes to HMX. 

Heat of formation and density calculations correlate so well with performance parameter like detonation velocity that chemists have a good idea of the performance of an energetic material before its synthesis and testing. The pyrazolo[4,3-c]pyrazoles DNPP (9) and LLM-119 (10) were predicted to exhibit performances equal to 85 % and 104 % relative to that of HMX. 

The dithioformates of Os(II) and Ru(II) MX(LXCO)(PPh3)2 (X = Cl, Br, L = S2 CH) have been reported. Their synthesis is accomplished by the CS2 insertion reaction into the Os-H or Ru-H bond of the HMX(CO)(PPh3)3 complexes. Both the cis and trans isomers of these complexes were obtained (556). 

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