SAFER EXPLOSIVES STILL PACK A PUNCH ENERGETIC MATERIALS: Compounds are less sensitive, less toxic than the military explosives RDX and HMX
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HREE NEW EXPLOSIVES from three different
labs have attractive properties such as simple syntheses and relative insensitivity, making some of them possible candidates to replace current military explosive favorites, the nitramines RDX and HMX, observers say. The design of new energetic materials stems from the need to improve the safety and reduce the environmental impact of the manufacture and use of military explosives. “The greening of its ammunition is a high priority of our defense department,” notes Keith Butler, chief chemist at American Ordnance at the Milan Army Ammunition Plant in Tennessee. With these needs in mind, Thomas M. Klapötke, a chemistry professor at the University of Munich, and colleagues synthesized dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50). They say TKX-50 is not only safer to handle and more thermally stable than RDX but also has a higher explosive punch (J. Mat. Chem., DOI: 10.1039/c2jm33646d). Additionally, University of Michigan chemistry professor Adam J. Matzger and colleagues report that a crystal combination of the explosives HMX and CL-20 yields an explosive more powerful than and as safe to use as HMX alone (Cryst. Growth Des., DOI: 10.1021/ cg3010882). Finally, Jean’ne M. Shreeve, a chemistry professor at the University of Utah, and colleagues describe a new class of high-density energetic compounds based
on tris(triazolo)benzene (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201205134). RDX (cyclotrimethylenetrinitramine) has been one of the most widely used military explosives since it was synthesized more than 100 years ago. Its cousin HMX (cyclotetramethylenetetranitramine), while a superior explosive to RDX, is more friction sensitive. CL-20, or 2,4,6,8,10,12-hexanitro-2,4,6,8,10,13-hexazaisowurtzitane, is the most unstable of all—too unstable for military use. Although RDX and HMX are superior to early explosives such as trinitrotoluene (TNT), they are highly toxic and difficult and expensive to make. David E. Chavez, an explosives chemist at Los Alamos National Laboratory, says all three groups’ approaches hold promise to overcome such limitations. For example, the Klapötke group’s report, which includes preliminary toxicity studies, shows that TKX50 has “promise as a potentially environmentally friendly energetic material,” he says. The properties of the Matzger group’s HMX and CL-20 cocrystals lie somewhere between those of the two individual compounds, Chavez adds. Calculations predict that the cocrystal should be more stable than CL-20 and more powerful than HMX. “The promise these cocrystallization methods show is quite high,” Chavez says. The Shreeve group’s tris(triazolo)benzene derivatives may lead to syntheses of promising high-nitrogen-content materials, Chavez adds. The work from the three labs demonstrates “that chemistry is at the forefront of technological advances contributing to the effectiveness of our soldiers,” Butler says.—ELIZABETH WILSON
C RYST. GROWTH DES.
NEWS OF THE W EEK
A unit cell of a cocrystal of HMX (blue) and CL-20.
DRUG SAFETY China investigates use of waste cooking oil by antibiotic makers China’s State Food & Drug Administration (SFDA) is investigating claims that several drug manufacturers have used cooking oil discarded by restaurants to produce antibiotics. SFDA says it is “highly concerned” that antibiotic makers have made use of 7-aminocephalosporanic acid (7-ACA), a cephalosporin antibiotic intermediate, produced with the aid of an oily liquid waste collected from restaurant gutters instead of fresh soybean oil. SFDA calls the practice “wrong” but adds that it is as yet unsure whether the use of gutter oil affects the quality of
the resulting drugs. Soybean oil is added to antibiotic fermentation broths to increase yield of cephalosporin C, a 7-ACA precursor. The use of out-of-specification raw materials violates current Good Manufacturing Practices (cGMP), says Peter Saxon, president of Saxon International Associates, a New Jersey-based consulting firm that has advised dozens of Indian and Chinese drug companies on meeting U.S. drug manufacturing regulations. cGMP is a set of standards that all companies supplying drugs to the U.S. must meet.
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Saxon says he has encountered numerous firms in India and China that try to justify their use of substandard starting materials by saying that they do not affect the final product. China is one of the world’s largest antibiotic suppliers. Qilu Pharmaceutical and Joincare Pharmaceutical, two companies alleged to have used gutter oil, issued statements denying the practice. Joincare says it has gone back to its sourcing invoices and verified that it has consistently purchased soybean oil. Qilu says it thoroughly audits the quality of all its raw materials.—JEAN-FRANÇOIS TREMBLAY
