Nitrolysis hexamine

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)... 

The importance of cyclic nitramines as military explosives has meant that an enormous amount of research has been conducted in this area. Only some of the rich array of products and by-products obtainable from hexamine nitrolysis are discussed in this section. For mechanistic smdies and detailed analysis of these reactions the primary research papers should be consulted. " ... 

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 acetolysis of hexamine closely resembles that of hexamine nitrolysis. Accordingly, acidity is of key importance, with high concentrations of acetic acid favouring the formation of the 6-membered 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT) and weakly acidic conditions favouring the 8-membered l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (TAT). ... 

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. 

Dimethylolnitramine (252) is inevitably present as its dinitrate ester (256) under the conditions of hexamine nitrolysis. This compound is extremely sensitive to hydrolysis but can be... 

In method 5, as in method 1, nitrolysis of hexamethylenetetramine occurs, the alcohol groups so produced being esterified with acetic anhydride and not with nitric anhydride as in method 1. The most important by-product formed to the extent of nearly 10% by method 5 is octogen (XI). It is produced as outlined above, as a result of hexamine nitrolysis (p. 90). 

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. 

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

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... 

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. 

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. 

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 most important nitrolysis reaction to date is the formation of RDX (3) and HMX (4) from the caged methylenediamine known as hexamine (104). These important military explosives were first mass manufactured by this route towards the end of the Second World War and they are still prepared by this route today. The process uses a mixture of acetic anhydride, ammonium nitrate and nitric acid. The nitrolysis of hexamine is one of the most widely studied reactions in the history of explosives. Many other cyclic and linear polynitramines have been isolated from these reactions and this rich chemistry is discussed in more detail in Section 5.15. 

Chapman studied the nitrolysis of symmetrical methylenediamines. The nitrolysis of N, N, N, M-tetramethylmethylenediamine with nitric acid-acetic anhydride-ammonium nitrate mixtures gives both dimethylnitramine and RDX the latter probably arises from the nitroT ysis of hexamine formed from the reaction of ammonium nitrate and formaldehyde released from the hydrolysis of the methylenediamine. The same reaction with some morpholine-based methylenediamines (105) allows the synthesis of l,3,5-trinitro-l,3,5-triazacycloalkanes (106). 

In this method, first established by Herz and later studied by Hale, hexamine is introduced into fuming nitric acid which has been freed from nitrous acid. The reaction is conducted at 20-30 °C and on completion the reaction mixture is drowned in cold water and the RDX precipitates. The process is, however, very inefficient with some of the methylene and nitrogen groups of the hexamine not used in the formation of RDX. The process of nitrolysis is complex with formaldehyde and some other fragments formed during the reaction undergoing oxidation in the presence of nitric acid. These side-reactions mean that up to eight times the theoretical amount of nitric acid is needed for optimum yields to be attained. 

The stoichiometry of the Hale nitrolysis reaction is very dependent on reaction conditions. Even so, this reaction has been postulated to conform to the stoichiometry in Equation (5.21) °° and Equation (5.22). ° Based on the assumption that one mole of hexamine produces one mole of RDX the Hale nitrolysis reaction commonly yields 75-80 % of RDX. 

Nitrolysis of hexamine dinitrate with nitric acid - ammonium nitrate - acetic anhydride... 

An unusual feature of the KA-process is that the reaction is conducted at 60-80 °C. Solutions of nitric acid in acetic anhydride are known to be prone to dangerous fume off at temperatures above ambient. However, a saturated solution of ammonium nitrate in fuming nitric acid can be added to warmed acetic anhydride without such danger. In fact, these reactions are commonly conducted at 60-80 °C as a matter of safety by preventing a build-up of unreacted starting material. The hexamine used in these reactions is in the form of the dinitrate salt, which is formed as a crystalline salt on addition of a saturated aqueous solution of hexamine to concentrated nitric acid below 15 °C. The use of hexamine dinitrate in this process reduces the amount of nitric acid needed for the nitrolysis. 

Nitrolysis of hexamine with ammonium nitrate - nitric acid... 

This method is known as the K-process after its discoverer Koffier. Like method 5.15.1.2 it uses ammonium nitrate to compensate for the nitrogen deficiency in hexamine and works to Equation (5.24) where two moles of RDX are produced per mole of hexamine. As observed with method 5.15.1.2, the addition of ammonium nitrate to nitric acid appears to prevent dangerous oxidation reactions from occurring. In fact, this nitrolysis reaction only occurs at elevated temperature and so a constant temperature of 80 °C is usually maintained throughout the reaction. Yields of approximately 90 % are attainable based on one mole of hexamine producing two moles of RDX. 

The nitrolysis of hexamine with 40 equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid in carbon tetrachloride at —20 °C is reported to give a 57 % yield of RDX. The product is free from HMX as determined by NMR (>95 % pure)." ... 

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