Of nitramine

S. Bulusu, Photochemical Studies of Secondary Nitramines. 1. Absorption Spectra of Nitramines and Photolysis of DimethyInitramine in Solution , PATR 4068 (1970) 45) S. 

Before proceeding to describe the manufacture of the nitramines, RDX and Tetryl, a few general remarks about the preparation of nitramines... 

Raman spectroscopy has been utilized in the quant detn of nitramines and nitrosamines (Vol 1, A177-R Ref 61), and ultra-violet spectroscopy is employed for the quant measurement of TNT in HBX compn (Refs 39, 61 63)... 

Irradiation of the UDMH + Oq Reaction Products. One experiment was conducted in which the UDMH + O3 reaction products (with UDMH in slight excess) were irradiated by sunlight. The results are shown in Table I and Figure 1. It can be seen that rapid consumption of UDMH, the nitrosamine, and HONO occurred, with N-nitrodimethylamine (also dimethyInitramine) and additional formaldehyde being formed. The formation of nitramine upon irradiation of the nitrosamine is consistent with results of previous studies in our laboratories (9,10), and probably occurs as shown ... 

Nitramines are known to photodissociate from their jt,jt state to give aminyl and nitric oxide radicals in the presence of an acid the aminyl radicals are protonated to give aminium radicals, which can initiate addition to olefins. As a synthetic reaction, photolysis of nitramines in the presence of acids can be conveniently run under oxygen to give oxidative addition similar to those shown in equation 145 indeed TV-nitrodimethylamine is photolysed with triene 299 under such conditions to give a mixture of 301 and 302, similar to results observed in the oxidative nitrosamine photoaddition169. To simplify the isolation, the crude products are reduced with LAH to form the open-chain amino alcohol 303. Some other oxidative photoadditions of N-nitro dimethylamine to other olefins are reported. As the photoreaction has to use a Corex filter and product yields are no better than those shown by nitrosamines, further investigations were scarcely carried out. 

The important result of the studies on nitromethane at high pressure is the bimolecular character of the reaction and the relevance of intermolecular interactions. The importance of the anisotropy and strains in the sample has been stressed in recent electronic stmcture calculations in the solid [481]. The leading role of intermolecular interactions has been most clearly demonstrated in studies of the chemical transformations of nitramines [475, 482, 483]. 

Alkaline hydrolysis of nitramines also leads to the formation of nitrite ions [1, 34]. 

In the Franchimont test [42], nitramines are reduced to nitrite ions by zinc and acetic acid and then subjected to the Griess reaction. A modification of this test was used for the identification of nitramine impurities in RDX [43]. 

Melius, C. F., and Binkley, J. S., Thermochemistry of the decomposition of nitramines in the gas phase., in 21st Symposium (Inti) Combustion. The Combustion Institute, Pittsburgh, 1986, p. 1953. 

A number of nitramine-nitrate explosives have been prepared by Millar and co-workers from the action of dinitrogen pentoxide on aziridines and azetidines (Section 5.8). Millar and co-workers used their aziridine ring-opening nitration methodology (Section 5.8.1) to synthesize the high performance melt-castable nitramine-nitrate explosive known as Tris-X... 

While we believe our discussions of nitramine and nitrate ester synthesis to be comprehensive, it would be quite impossible to have a comprehensive discussion of aromatic nitration in this short chapter - published studies into aromatic nitration run into many tens of thousands. The purpose of this chapter is primarily to discuss the methods used for the synthesis of polynitroarylene explosives. Undoubtedly the most important and direct method for the synthesis of polynitroarylenes involves direct electrophilic nitration of the parent aromatic hydrocarbon. This work gives an overview of aromatic nitration but the discussion doesn t approach mechanistic studies in detail. Readers with more specialized interests in aromatic nitration are advised to consult several important works published in this area which give credit to this important reaction class.The use of polynitroarylenes as explosives and their detailed industrial synthesis has been expertly covered by Urbanski in Volumes 1 and 4 of Chemistry and Technology of Explosives ... 

The replacement of amine and amide hydrogen with a nitro group via direct nitration is an important route to A-nitro functionality. However, the cleavage of other bonds is also important. In the case of C-N bond cleavage the process is known as nitrolysis and is an invaluable route to many energetic materials (Section 5.6). The nitrolysis of hexamine and the syntheses of the important explosives HMX and RDX are discussed in Section 5.15. This area of chemistry could easily demand a separate chapter of its own and is the most complex and diverse in the field of nitramine chemistry. 

A large number of nitramine-based explosives have been synthesized via Mannich-type condensation reactions (Section 5.13.2). The amines generated from these reactions often have the powerful electron-withdrawing trinitromethyl or fluorodinitromethyl groups positioned on the carbon a to the amino group. This reduces amine basicity to an extent that A-nitration becomes facile. The energetic nitramines (17), (19) and (21) have been synthesized from the condensation of ethylenediamine with 2,2,2-trinitroethanol, 2-fluoro-2,2-dinitroethanol with ethanolamine, and 2-fluoro-2,2-dinitroethylamine with 2,2-dinitro-l,3-propanediol respectively, followed by A-nitration of the resulting amine bases (16), (18) and (20), respectively. 

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. 

Emmons and co-workers prepared a series of aliphatic secondary nitramines by treating amines with a solution of dinitrogen pentoxide in carbon tetrachloride at —30 C (Equation 5.9). The amine component needs to be in excess of two equivalents relative to the dinitrogen pentoxide if high yields of nitramine are to be attained. This is wasteful because at least half the amine remains unreacted. However, yields are high and there is no reason why the amine cannot be recovered as the nitrate salt. The method is particularly useful for the nitration of hindered secondary amines substrates such as those with branching on the a carbon. 

The scope of nitrolysis is huge, with examples of nitramine formation from the cleavage of tertiary amines, methylenediamines, carbamates, ureas, formamides, acetamides and other amides. The deflnition of nitrolysis must be extended to the nitrative cleavage of other nitrogen bonds because sulfonamides and nitrosamines are also important substrates for these reactions. The nitrative cleavage of silylamines and silylamides is also a form of nitrolysis (Section 5.7). 

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. 

Millar and Philbin have explored the nitrodesilylation of silylamines with dinitrogen pen-toxide for the synthesis of nitramines and their derivatives. These reactions, which involve nitra-tive Si-N heteroatom cleavage, are conducted in methylene chloride at subambient temperature. Trimethylsilylamines give high yields of nitramine product and reactions are clean (Table 5.8). 

Synthesis of nitramines, nitramides and nitroureas via the nitrodesilylation of A/-trimethyisilyl compounds with dinitrogen pentoxide (ref. 122)... 

In view of the highly carcinogenic nature of many nitrosamines any experiments involving their isolation must be discouraged, and for this reason, this section has only been written for completeness. This high toxicity is unfortunate because the preparation of nitrosamines from the parent amines is often facile and they provide a route to highly pure nitramines. Other equally useful methods for the synthesis of nitramines, such as the chloride-catalyzed nitration of secondary amines, also suffer from the formation of nitrosamines in appreciable amounts and must also be viewed with caution. 

The oxidation of aryl diazoates with oxidants like hypochlorite, permanganate and ferri-cyanide anion has seen some limited use for the synthesis of nitramines. This method finds use for the synthesis of arylnitramines where aromatic ring nitration is not required and so excludes the use of standard nitrating agents. 

Secondary nitramines have been prepared from the metathesis of dialkylcarbamyl chlorides with silver nitrate in acetonitrile followed by the spontaneous decomposition of the resulting dialkylcarbamyl nitrates.Yields of nitramine are low and accompanied by nitrosamine impurities. 

The products obtained from these condensations are predictable for simple mono-functional substrates primary amines usually form compounds where two equivalents of primary nitramine are incorporated into the product (Equation 5.19), whereas simple secondary amines can only combine with one equivalent of nitramine (Equation 5.20). The bis-nitramine (185) is formed from the reaction of methylamine with two mole equivalents each of methyl-nitramine and formaldehyde. 

However, the yield of DPT from such reactions is often poor (15-25 %). DPT has also been synthesized from the reaction of hexamine dinitrate with acetic anhydride or cold 90 % aqueous sulphuric acid. Both methods under optimum conditions give yields of DPT of approximately 31 The reaction of nitramine (NH2NO2) with aqueous formaldehyde, followed by neutralization of the reaction mixture with ammonia to pH 5.5-6.5, gives DPT in 73 % yield based on the nitramine starting material. This last reaction presumably involves the formation of dimethylolnitramine as an intermediate (Section 5.15.4.2). 

The nitration of nitramine (153) with nitronium tetrafluoroborate, followed by neutralization of the resulting dinitraminic acid with ammonia, also generates ammonium dinitramide (152). Neutralization of this reaction with alkylamines, instead of ammonia, yields the corresponding alkylammonium salts of dinitramide. The nitration of ammonia with dinitrogen pentoxide (15 %) or nitronium salts like the tetrafluoroborate (25 %) yield ammonium dinitramide (152) through the initial formation of nitramine. 

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