Synthesis of Energetic Materials

Lobbecke, S., Antes, )., Turcke, T., Marioth, E., Schmid, K., Krause, H., The potential of microreactors for the synthesis of energetic materials, in Proceedings of the 31st Int. Annu. 

A comprehensive discussion of the synthetic methods used to introduce the nitro group into aliphatic compounds, and its diverse chemistry, would require more space than available in this book. While every effort has been made to achieve this, some of these methods are given only brief discussion because they have not as yet found use for the synthesis of energetic materials, or their use is limited in this respect. The nature of energetic materials means that methods used to introduce polynitro functionality are of prime importance and so these are discussed in detail. Therefore, this work complements the last major review on this subject. ... 

Polynitroaliphatic alcohols are invaluable intermediates for the synthesis of energetic materials (see Section 1.11). The most important route to /i-nitroalcohols is via the Henry reaction where a mixture of the aldehyde and nitroalkane is treated with a catalytic amount of base, or the nitronate salt of the nitroalkane is used directly, in which case, on reaction completion, the reaction mixture is acidified with a weak acid. Reactions are reversible and in the presence of base the salt of the nitroalkane and the free aldehyde are reformed. This reverse reaction is known as demethylolation if formaldehyde is formed. 

Despite the amount of research focused on the iV-nitration of amines with nonacidic reagents, the use of conventional acidic reagents based on nitric acid and acid anhydrides has been far more extensive for the synthesis of energetic materials. 

The high nitrogen content and the endothermic nature of the tetrazole ring lends itself to the synthesis of energetic materials. Compounds such as -H tetrazole and 5-aminotetrazole can be used as nucleophiles to incorporate the tetrazole ring into other molecules. 5-Aminotetrazole is synthesized from the reaction of dicyandiamide with sodium azide in hydrochloric acid. 

Some of the major advances in the synthesis of energetic materials have arisen from the use of dinitrogen pentoxide-nitric acid solutions for nitrolysis reactions. These reactions are important routes to alicyclic, cyclic and caged energetic polynitramines. 

Millar and Philbin ° reported using dinitrogen pentoxide in methylene chloride at subambient temperatures for the nitrodesily lation of silylamines (33) and silylamides. The methodology, which results in nitramines (34), nitramides and nitroureas in excellent yields, is well suited for the synthesis of energetic materials and we believe it will find wide use in the future. 

The success of these selective nitrations relies on the application on recent nitration technology - the use of flow reactors. The following is a discussion of some important work conducted at DERA and illustrates the research and development transition from laboratory to pilot plant scale synthesis of energetic materials. ... 

Chauhan, N., Colclough, M.E., Hamid,). (1999) Synthesis of energetic materials in liquid and supercritical carbon dioxide. Proc. 6th Inti. Symp. on Applications of Supercritical Fluids, Nottingham, UK, 1999. 

Tetrazole compounds are also good starting materials for the synthesis of energetic materials with substituted side-chains attached to the tetrazole skeleton. For... 

Enzymatic reactions have been tested in SCFs on a pilot plant scale, and a detailed analysis of potential technical solutions and costs is given in Chapter 4.9. Finally, the synthesis of energetic materials has been suggested to be performed in liquid or supercritical CO2. The Indian Head Division of the US Naval Surface Warfare Center is now constructing a pilot plant with a 100 L vessel for the synthesis of such energetics as MTV (magnesium/Teflon/ Viton) and poly-3-nitratoraethy 1-3-methyl oxetane [190,191]. 

There have been a number of investigations involving the study of nitroolefins as useful intermediates in the synthesis of energetic materials. A characteristic of many of them is a large twist about the double bond. Interest in the structural characteristics that accompany the rotation motivates a discussion of details. As would be expected, the rotation out of the normal planar conformation is associated with spatial crowding. Rgure 14 illustrates some of the largest out-of-plane rotations that have been measured and, in one case, calculated for crowded ethylenes [25j. 

G. A. Olah in Chapter 7 reviews some of the most useful methods in preparing nitro compounds (i.e., electrophilic nitrations with superacid systems, nitronium salts, and related Friedel-Crafts type complexes). Polynitro compounds were traditionally and still are the most widely used explosives [e.g., nitroglycerol, trinitrotoluene (TNT), and Af-nitramines (RDX and HMX)]. Methods of preparing nitro compounds thus remain a key part of the synthesis of energetic materials. 

Tetrazole compounds are also good starting materials for the synthesis of energetic materials with substituted side-chains attached to the tetrazole skeleton. For example, tetrazole can be alkylated by reaction with l-chloro-2-nitro-2-azapropane and converted into various energetic compounds (Figs. 9.12 and 9.13). 

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