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US researchers have used NMR to study the products of research into a new high explosive material that can nevertheless be melt cast into a charge with any shape. One might think that the last thing the world needs right now is another high explosive material. However, there are countless applications for civilian explosives in demolition, mining, and engineering, so researchers are always on the look out for compounds with a lot of pent up energy that can be put to good use. Now, David Chavez of the of High Explosives Science and Technology group at Los Alamos National Laboratory, New Mexico, USA, and colleagues Michael Hiskey and Darren Naud, in collaboration with Damon Parrish of the Naval Research Laboratory, in Washington, DC, have produced a melt-castable nitrate ester that is a highly explosive solid at room temperature. Ever since the discovery of nitroglycerine (1,2,3-trinitroxypropane) in 1846 by Ascanio Sobrero working at the University of Turin, the nitrate ester group of compounds have become well-known for their explosive properties. There is whole series of nitrate esters available as explosives and fuels, including ethylene glycol dinitrate and propylene glycol dinitrate. However, they are organic compounds that exist as liquids at room temperature making it very difficult to handle them safely. Famously, Alfred Nobel mixed them with various other components to form a solid composite, dynamite, that is distinctly safer and easier to handle than liquid nitroglycerine-based explosives. The only solid nitrate ester commonly used until now was nitropenta (pentaerythritol tetranitrate, PETN), but its relatively high melting point of about 140 Celsius means it has to be pressed into the desired form for detonator applications, rather than being cast. "A more practical material would be a melt-castable explosive, which would allow the simplification of manufacturing processes," explain Chavez and colleagues, who have now added just such a material to the list of solid, but castable, explosive nitrate esters. The team has now used the Kaplan-Shechter reaction to construct the necessary novel energetic nitrogen-ring groups to synthesise their new energetic nitrate ester. The new compound contains four nitrate ester groups (?ONO2) and two nitrate groups (-NO2) bound to a total of six carbon atoms. The novel material is solid at ambient temperature but melts at just 85-86 Celsius and has the highest density of any known nitrate ester composed of only carbon, hydrogen, nitrogen, and oxygen atoms. Because its melting point is well below its decomposition point (141 Celsius), it can be melted and poured into moulds, a much easier process for the production of explosive components. Computer calculations predict that the new tetranitrate ester should have an explosive power as high as that of octogen (HMX) - currently one of the highest-performance explosives. The sensitivity of the new compound toward shocks, friction, and sparks is equivalent to that of nitropenta. "Because of its amazing properties, the new nitrate ester opens up a unique opportunity to produce castable explosive components," explains Chavez, "In addition, it could also be used as a highly energetic softener for other explosives, and as an oxidizer component." The researchers also plan to use their new synthetic route for the development of other explosive materials. As is standard in such research, the team cautions others that although they experienced no problems during the synthesis and handling of the new compound, it is an explosive and laboratories and personnel should be properly grounded and should use safety equipment such as Kevlar gloves, blast shields, and ear plugs when working on large-scale reactions of this substance. Intriguingly, nitrate esters are also now well known as having medicinal properties as vasodilators in humans. They have been used to treat heart problems such as angina. It is their ability to release nitric oxide, which endows them with this physiological property and the same mode of action is familiar to those studying sildenafil citrate (Viagra) and drugs of abuse, including so-called "poppers", nitrite compounds, including amyl nitrite, butyl nitrite, and isobutyl nitrite. Reference:
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 Chavez, explosive synthesis
 Explosive, yet castable nitrate
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