Salts of Nitramines

In this chapter, we have decided to summarize substances that are not very well described in open literature. There are three groups of substances that we craisider interesting enough to mention here—salts of nitramines, organophosphates, and hydrazine nitrates. 

Primary nitramines are substances with acidic hydrogen and which therefore easily form salts. Since many nitramines are high explosives it is logical that their salts, especially those of heavy metals, were those investigated. Only a small number of such substances, however, fall into a group of primary explosives. 

The heavy metal salts of methylnitramine (MNA) have been reported by Davis [1] as primary explosives which had not been extensively investigated. Searching more recent literature revealed that there has not been much work published since the time of World War II. 

Silver and lead salts of methylenedinitramine (MEDINA) have, according to Urbahski, sufficient initiating properties to be used practically. The sensitivity to impact and the ignition temperatures of both salts are summarized in Table 13.1 [2]. 

Ethylenedinitramine (EDNA) is a powerful secondary explosive patented by Hale [3]. The two acidic hydrogens of the nitramino group can be relatively easily replaced with metal ions. Every once in a while speculation arises regarding the applicability of EDNA salts for use as primary explosives. The sensitivity of the metallic salts is, however, relatively low. The cupric salt of ethylenedinitramine is less sensitive than both LA and LS. It follows from Table 13.2 that it is comparable to secondary explosives. Ignition of CuEDNA occurs at 196 °C, DSC onset is at 162 °C (10 °C min ) [4]. Cupric, ferrous, lead, and potassium salts of EDNA are more sensitive then RDX but not sensitive enough to qualify for use as primary explosives. Impact sensitivities obtained by Blatt [5] and summarized in Fedoroff, Shefield, and Kaye s [6] are listed in Table 13.3. 

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Alkaline salts of nitramines arc oxidized by nitryl chloride to products possessing nitrogen in the highest oxidation state, i.e. the nitrate group.255 The free nitramines afford the nitrates in very low yields. 

Acylation of primary nit famine occurs with great difficulty. Acetyl chloride can acetylate potassium or silver salts of primary nitramines with a yield according to While and Baumgarten [31). It is rationalized that the difficulty of acetyl-ating metal salts of primary nitramines comes probably from the assumption that the metal salts of nitramines are chelate compounds and not true salts. 

Salts of nitramine can react with fluorine to yield fluoronitiamine, for example, C4H9 N F [32]. 

Methyidichloroarsine Methylene glycol dinitrate Methyl ethyl ketone peroxide, >50% alpha-Methylglucoside tetranitrate alpha-Methylglycerol trinitrate Methyl nitramine (dry) metal salts of Methyl nitrate Methyl nitrite... 

The Na salt of MEDINA was fluorinated in w, the sain extd with methylene chloride, and the solv evapd to give a yellow oil whose IR spectrum showed absence of NH and the presence of NF absorption, and analysis indicated was a mixt (Ref 22). Nitramines in the presence of sulfuric acid are capable of nitrating reactive aromatic compds, but when acetanilide was treated with MEDINA in the presence of this acid, no nitroacetanilide was isolated. Instead compds indicating that the MEDINA had been fragmented and the fragments reacted with the acetanilide were isolated (Ref 12)... 

Scholl et al (Refs 3 4) prepared the same compds by treating ketoximes (such as pina-colone) with nitrogen tetroxide, but he assigned them the structure R2C=N-N02 and called them nitrimines. One of the compds described by him in Ref 4, p 27 is a weak expl. It is the Ag salt of pinacolone-nitraminic acid which puffs off on rapid heating (this compd described below under List of Nitrimines ). Further work on... 

Eremenko and co-workers used nitryl fluoride for the deamination of amines at subambient temperatures in acetonitrile. The same reaction occurs with primary nitramines and their alkali metal salts bis-nitramines react to give the corresponding bis-nitrate esters. 

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. 

Wright illustrated the effectiveness of chloride-catalyzed nitration for a number of amines of different basicity. Wright showed that weakly basic amines like iminodiacetonitrile and its dimethyl and tetramethyl derivatives are all nitrated in high yield with nitric acid-acetic anhydride mixtures in the absence of chloride ion. In contrast, the slightly more basic 3,3 -iminodipropionitrile is not appreciably nitrated with acetic anhydride-nitric acid, but the inclusion of a catalytic amount of the hydrochloride salt of the amine base generates the corresponding nitramine in 71 % yield. ... 

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. 

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 dehydration of the nitrate salts of some primary and secondary amines can yield the corresponding nitramine. Dimethylnitramine has been prepared in 65 % yield from the dehydration of dimethylamine nitrate in acetic anhydride to which 4 mole % of anhydrous zinc chloride has been added." The same reaction in the absence of chloride ion only generates a 5 % yield of dimethylnitramine." Some arylnitramines derived from weakly basic amines have been prepared via the addition of the amine nitrate salts to acetic anhydride. " ... 

Metathesis reactions between iV-chloramines and silver nitrite in alkaline solution are reported to give the silver salt of the corresponding primary nitramine. The method is of little synthetic value. ... 

Tetryl has been synthesized by treating picryl chloride with the potassium salt of methyl-nitramine but the reaction is of theoretical interest only. ... 

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. 

Alkyl lV,lV-dinitramines (154) have been prepared from the reaction of the tetraalkylam-monium salts (155) of primary nitramines with nitryl fluoride in acetonitrile at subambient temperature. The same reaction with the primary nitramine or its alkali metal salts yields the corresponding nitrate ester. Treatment of the ammonium, potassium, or lithium salts of primary nitramines (156) with a solution of nitronium tetrafluoroborate in acetonitrile at subambient temperature yield alkyl iV,iV-dinitramines. ° The same reactions in ether or ester solvents enables the free nitramine to be used. The nitrolysis of A-alkylnitramides (157) and N,N-diacylamines with nitronium tetrafluoroborate in acetonitrile, and the nitration of aliphatic isocyanates with nitronium tetrafluoroborate and nitric acid in acetonitrile, also yield alkyl A,A-dinitramines (154). 

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). 

Very frequently the transition through urethanes is employed by treating the primary amine with chloroformate. The N-substituted urethane so obtained is nitrated by substituting the free N-hydrogen and then subjecting the product to alkaline hydrolysis which results in the formation of the salt of a primary nitramine and a base. The free nitramine is obtained by acidification. 

This scheme, however, has the disadvantage of ignoring the influence of the nitronium ion (NO ) on the reaction, whereas, as expounded in the chapter on nitration theories (Vol. I), the nitronium ion is of enormous importance for such a reaction. In this connection Lamberton [43] suggests alternative schemes which appear more probable. Scheme (8) leads to the formation of a nitramine and scheme (9) to a salt of nitric acid ... 

This substance was isolated in the form of its barium salt by Hirst et al. [12] when investigating the nitration of hexamethylenetetramine to cyclonite. They found that hexamethylenetetramine, when dissolved in nitric acid at 40°C, yields the product (II) which is hydrolysed by barium hydroxide to form the barium salt of methylene-dinitramine. From this the free nitramine may be obtained ... 

Nitroguanidine has weakly basic properties and this accounts for its ability to form salts with concentrated acids, e.g. it forms a sulphate with concentrated sulphuric acid. Nitroguanidine is hydrolysed on heating with concentrated sulphuric acid evolving nitrous oxide and carbon dioxide, the former probably derived from hydrolysis of nitramine and the latter from hydrolysis of cyanamide. The latter also yields ammonia on decomposition. 

A white crystalline precipitate of the ammonium salt of methyl-nitramine is deposited. This is dissolved in alcohol, and the solution is boiled—whereby ammonia is driven off—and concentrated to a small volume. The product is procured by completing the evaporation in a vacuum desiccator over sulfuric acid. 

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