Nitrolysis

A reagent composed of tetra-n-butylammonium nitrate and TFAA in methylene chloride has been used to nitrate a series of A-alkyl and A-aryl amides (40-90 %). The formation of significant amounts of A-nitrosamides was noted. Tetra-n-butylammonium nitrate and triflic anhydride in methylene chloride has been used to successfully nitrate a variety of heterocyclic amides, imides and ureas (66).  

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 range of reagents used for nitrolysis is also vast and includes absolute nitric acid, acid anhydride-nitric acid, mixed acid, dinitrogen pentoxide-nitric acid, nitronium salts and many more. 

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Ma.nufa.cture. The two most common processes for making RDX and HMX use hexamethylenetetramine (hexamine) as starting material. The Woolwich or direct nitrolysis process used ia the United Kingdom proceeds according to ... 

J. Solomon, Pi Study of the Nitrolysis of Hexamine to Increase HMX Yields, Illinois Institute of Technology, Chicago, 1973. 

Historical. MEDINA was first isolated as a degradation prod from the nitrolysis of hexa-mine (WWI1 work done at the Univ of Bristol, cited in Ref 5). It was prepd by the hydrolysis of PCX (qv) in boiling et ale and isolated as the Ba salt (Ref 4) and by the hydrolysis of N,N -DiacetylMEDINA with aq ammonia, yield 25% (Ref 5)... 

An important preparative method for nitra-mines is nitrolysis as described by Urbahski (Ref 82, p 13) ... 

The term nitrolysis is usually applied to a nitrating mechanism in which both the rupture of the C-N bond and the formation of a nitramine occur simultaneously with the formation of an alcohol which subsequently undergoes esterification (1) ... 

Nitrolysis may also proceed without giving rise to alcohol in accordance with Eq (2), Nevertheless, a nitric ester is formed by the possible action of the N03— ion on a free alkyl cation ... 

Compound I is formed from Hexamine Dinitrate via nitrolysis... 

Further nitrolysis (with cleavage of bond A) forms a hypothetical compound (compound II) as follows ... 

Compound II now undergoes further nitrolysis (with cleavage of bond, B) to give another hypothetical material, Compound III, and a known material, Compound IV ... 

RDX. Gilpin Winkler (Ref 38b) measured a heat of nitration of — 88.0kcal/mole of hexa-mine for the reaction of hexamine with 97.5% nitric acid. They also obtained a value of — 140kcal/mole of hexamine for the formation of RDX from hexamine and Bachmann reagents (acetic anhydride, acetic acid, ammonium nitrate and nitric acid). Incidentally, Gilpin Winkler interpret their results to mean that hexamine dinitrate is an intermediate in the direct nitrolysis of hexamine to give RDX, while hexamine mononitrate is an intermediate in the Bachmann process of producing RDX... 

Tracer Studies on the Nitro lysis of Hexamine to RDX and HMX. The formation of RDX and/or HMX molecules from the nitration or nitrolysis of Hexamethylenetetramine (Hexamine) is a complex process and has been postulated to take place via two separate paths. One involves the selective cleavage of the Hexamine molecule to the appropriate cyclic nitramine (RDX, HMX or both) depending on the specific... 

Detailed reviews of the chemistry of Hexamine and its nitrolysis to RDX, HMX and other related cyclic and linear polynitramines, including discussions of various postulated reaction mechanisms, are given by Smolin and Rapoport (Ref 9) and by Wright (Ref 15), Methods for the prepn of RDX are also described in Encycl 3, C611 to C615... 

The McGill workers postulated that, in their process, methylene nitramine (CH2=N—N02) is formed as an intermediate, which then tri-merizes to RDX. However, the existence of methylene nitramine has never been proven. Werner Bachmann (Ref 2) of the University of Michigan, during WWII, conceived of a combination process in which the Hale nitrolysis of Hexamine would occur first, and the remaining methylene would be converted to RDX by the Ross-Schiessler route. Using three feed streams Ac20, Hexamine In acetic acid, and AN in nitric acid, the Bachmann process results in an 80% yield of RDX (two moles from one of Hexamine), including a small amount of HMX. 

From this process, the yield of HMX/RDX is approx 90% of theory (based on Hexamine molecule), and 85% of this mixt is HMX The tracer expts conducted to study the mechanism of nitrolysis and product formation in the above process are briefly outlined in... 

Bell and Dunstan (Ref 16) have reported that the addition of me thy lene dinit ramine to Hexamine nitrolysis mixts, aged at 0° for 5 and 120 minutes, gave RDX in yields of 120 and 106%, respectively, compared with 52 and 83% in the absence of the dinitramine. However, rather than supporting a synthesis from small molecules, the authors contend that these results substantiate the existence of a postulated bis(nitroxymethyl) aminomethyl precursor of RDX, namely ... 

Although the yield of RDX is high, the economic advantage of the Thatcher Process over Hexamine nitrolysis is yet to be demonstrated (Ref 19)... 

During the attempted nitrolysis of the triacetyl compound to the 1-acetyl-3,5-dinitro compound with 99% nitric acid in trifluoroacetic anhydride at 30°C, following a general procedure [1], a violent explosion occurred on the 1 g scale [2], This was ascribed to the formation of acetyl nitrate, expected to be formed under the reaction conditions [3,4], Caution with nitrolysis of any acetyl compound is urged [3],... 

A solution of nitric acid in acetic anhydride is a versatile reagent for nitrolysis reactions and for the A-nitration of amines (see Chapters 5 and 6). This reagent has also found considerable use for the C-nitration of aromatic substrates. ... 

Nitric acid-trifluoroacetic anhydride mixtures are used extensively for nitrolysis and N-nitration reactions (see Chapters 5 and 6). The same is not true for aromatic nitrations. This reagent contains trifluoroacetyl nitrate, which can ionize to nitronium and trifluoroacetate ions in the presence of strong acid. 

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. 

The direct A -nitration of the amino groups of the hexahydrotriazine (23) is only possible due to the inherent low basicity of the methylenediamine functionality. The methylenediamine unit is present in many cyclic and bicyclic polyamines and these are potential precursors to energetic polynitramines. Unfortunately, this route to polynitramines is rarely possible because such polyamines are usually intrinsically unstable and will readily equilibrate to a lower energy, less strained system. For the same reason, polyamines containing the methylenediamine functionality are difficult to prepare and isolate, often rapidly decomposing in both aqueous and acidic solution. A far more common route involves the preparation of iV-protected versions of the polyamine followed by nitrolysis (Section 5.6). Even so, examples of heterocyclic methylenediamine iV-nitration exist. 

Nitrolysis is a term originally used for the rupture of a N-C bond leading to the formation of the N-NO2 group. A prime example is the nitrolysis of the N-CH2 bonds of hexamine to form the important military explosives RDX and HMX. Nitrolysis is the most important route available to polynitramine energetic materials. 

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