Nitramine-nitrates, synthesis

The use of oxetanes for the synthesis of polynitrate esters is generally of less value than the use of epoxides, which are readily available from the epoxidation of alkenes. The analogous reaction of azetidines with dinitrogen pentoxide is a route to 1,3-nitramine-nitrates and these reactions are discussed in Section 5.8.2. ... 

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... 

This synthesis of N-nitromorpholine is representative of a rather general reaction for the preparation of both primary and secondary nitramines.3 It represents the simplest process for obtaining both types of compounds. The reaction is unique in that a nitration is carried out under neutral or alkaline conditions. Acetone cyanohydrin nitrate may also be used for the nitration of many active methylene compounds.8... 

Mannich bases derived from polynitroalkanes are usually unstable because of the facile reverse reaction leading to stabilized nitronate anions. The nitration of Mannich bases to nitramines enhances their stability by reducing the electron density on the amine nitrogen through delocalization with the nitro group. The nitration of Mannich bases has been exploited for the synthesis of numerous explosives, some containing both C-NO2 and N-NO2 functionality. Three such compounds, (163), (164) and (165), are illustrated below and others are discussed in Section 6.10. 

Research efforts are ongoing into the use of dinitrogen pentoxide for the industrial synthesis of nitrated hydroxy-terminated polybutadiene (NHTPB) from epoxidated HTPB (Section 3.10). The reaction of aziridines with dinitrogen pentoxide is an important route to 1,2-nitramine-niU ates and these reactions are discussed in Section 5.8.1. ... 

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 ... 

Nitrations of aromatic amines often involve the intermediate formation of N-nitramines, although these are rarely seen under the strongly acidic conditions of mixed acid nitration (Section 4.5). N,2,4,6-Tetranitro-N-methylaniline (tetryl) is an important secondary high explosive usually synthesized from the nitration of N,N-dimethylaniline or 2,4-dinitro-N-methylaniline. ° The synthesis of tetryl is discussed in Section 5.14. 

Chemists at the Naval Air Warfare Center (NAWC), Weapons Division, China Lake, have reported many examples of polynitroarylamine synthesis via Bamberger rearrangements of arylnitramines. " " The nitration of 4-amino-2,5-dinitrotoluene (36) with a mixture of nitric acid and acetic anhydride in glacial acetic acid at room temperature yields the nitramine (37) which on treatment with neat sulfuric acid, provides 4-amino-2,3,5-trinitrotoluene (38) as the sole product. " Nitration of 3,4-dinitroaniline (39) with a solution of nitric acid in acetic anhydride yields A,3,4-trinitroaniline (40) acid-catalyzed rearrangement of the latter in neat sulfuric acid furnishes a 74 % yield of isomeric 2,3,4- (41) and 2,4,5- (42) trinitroanilines in a 4 6 ratio.Accordingly, a mixture of products can be expected when an unsymmetrical arylnitramine has two unsubstituted ortho positions available. 

If nitration under acidic conditions could only be used for the nitration of the weakest of amine bases its use for the synthesis of secondary nitramines would be severely limited. An important discovery by Wright and co-workers " found that the nitrations of the more basic amines are strongly catalyzed by chloride ion. This is explained by the fact that chloride ion, in the form of anhydrous zinc chloride, the hydrochloride salt of the amine, or dissolved gaseous hydrogen chloride, is a source of electropositive chlorine under the oxidizing conditions of nitration and this can react with the free amine to form an intermediate chloramine. The corresponding chloramines are readily nitrated with the loss of electropositive chlorine and the formation of the secondary nitramine in a catalytic cycle (Equations 5.2, 5.3 and 5.4). The mechanism of this reaction is proposed to involve chlorine acetate as the source of electropositive chlorine but other species may play a role. The success of the reaction appears to be due to the chloramines being weaker bases than the parent amines. 

More recently, Polish chemists have reported a synthesis of both aryl and aliphatic secondary nitramines by treating amine substrates with ethyl magnesium bromide followed by reaction with n-butyl nitrate (Equation 5.8). This method, which uses nonpolar solvents like hexane or benzene, has been used to synthesize aliphatic secondary nitramines, and At-nitro-A-methylanilines which otherwise undergo facile Bamberger rearrangement in the presence of acid. The direct nitration of At-unsubstituted arylamines usually requires the presence of an electron-withdrawing group. Reactions are retarded and yields are low for sterically hindered amines. 

Despite the moderate to good yields obtained for a range of primary and secondary nitramines, the above methods have not found wide use. Their use in organic synthesis is severely limited by the incompatibility of many functional groups in the presence of strong bases. This is particularly relevant to the synthesis of explosive materials, where nitrate ester and C-nitro functionality are incompatible with strong bases. 

The reaction of dinitrogen pentoxide with primary aliphatic nitramines and amines leads to deamination and the formation of a nitrate ester as the major product. Consequently, dinitrogen pentoxide cannot be used for the synthesis of primary nitramines. In contrast, both primary and secondary arylamines undergo efficient A-nitration with dinitrogen pentoxide in chlorinated solvents. ... 

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. 

A particularly useful synthesis of primary nitramines involves the nitration of the appropriate carbamate ester followed by ammonolysis with gaseous ammonia in diethyl ether. The ammonium salt of the nitramine precipitates in pure form and is carefully acidified to give the free nitramine. The corresponding carbamate esters are readily synthesized from the action of chlorocarboxylic acid esters on alkylamines in the presence of alkali hydroxides. 

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. 

The nitrolysis of hexamine at low temperature has led to the synthesis of a number of cyclic nitramines. The reaction of hexamine dinitrate (241) with 88 % nitric acid at -40 °C, followed by quenching the reaction mixture onto crushed ice, leads to the precipitation of 3,5-dinitro-3,5-diazapiperidinium nitrate (242) (PCX) in good yield PCX is an explosive equal in power to RDX but is slightly more sensitive to impact. The reaction of PCX (242) with sodium acetate in acetic anhydride yields l-acetyl-3,5-dinitro-l,3,5-triazacyclohexane (82) (TAX), which on further treatment with dilute alkali in ethanol yields the bicycle (243). ... 

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. 

Moore and Willer reported the synthesis of some nitramine explosives containing a furazan ring fused to a piperazine ring. The tetranitramine (46) is synthesized from the condensation of 3,4-diaminofurazan (DAF) (24) with glyoxal under acidic conditions followed by A-nitration of the resulting heterocycle (45). The calculated performance for the tetranitramine (46) is very high but the compound proves to be unstable at room temperature. Instability is a common feature of heterocyclic nitramines derived from the nitration of aminal nitrogens. 

Tselinskii and co-workers reported the synthesis of the bis(furazano)piperazine (52) and its nitration to the energetic bis-nitramine (53) (calculated VOD 9700 m/s) with nitrogen... 

Coburn " synthesized 2,4,6-tris(picrylamino)-l,3,5-triazine (TPM) (190) from the reaction of aniline with cyanuric chloride followed by nitration of the product with mixed acid. Treatment of TPM (190) with acetic anhydride-nitric acid leads to Al-nitration and the isolation of the corresponding tris-nitramine. The high thermal stability of TPM (m.p. 316 °C) coupled with its facile synthesis and low sensitivity to impact has led to its large scale manufacture in the US by Hercules Inc. China has reported a low-cost synthetic route to TPM but this has a limited production capacity. 

Displacements with azido anion are tolerant of many pre-existing explosophoric groups but the nitrate ester group readily undergoes displacement as seen for the synthesis of bis(2-azidoethyl)nitramine (13) from Ai-nitrodiethanolamine dinitrate (12) (DINA). " ... 

Nitro derivatives of several halogenated pyridazin-3(2//)-ones have been prepared by treating the pyridazinones with a mixture of a nitrate salt and acetic anhydride or trifluoroacetic anhydride <2003JOC9113>. These compounds have been used for the synthesis of nitramines (see Section 8.01.8.3). 

On synthesis of cyclonite from paraformaldehyde, ammonium nitrate and acetic acid (method 4), products with cyclic structure, chiefly cyclonite and octogen, may arise due to the polymerization of the transiently-formed, hypothetical methylene-nitramine (XXVIII) [67] ... 

Ohio State University, Columbus, Ohio (Historical and prepn props of numerous nitramides and nitramines) 2)R. Adams C.S. Marvel, OSRD Rept 86(1941) (Historical survey of nitramides, synthesis of intermediates and their nitration to the final products. Only few of the prepd nitramides were of interest as expls or as components of expl comp ns) 3)Series of papers by A.H.Lamberton, C. 

---