New nerve gas deactivation method offered
What to do with thousands of tons of chemical weapon stored in rusting drums on military bases in the United States? Bleach reacts indiscriminately — even explosively — with many chemicals such as propellants, and using alkaline hydrolysis has its own drawbacks; researchers develop a deactivation method based on dealkylating agents
Next time you take your family to the beach, you may want to ask yourself the following question: How did the United States, United Kingdom, and the Soviet Union dispose of chemical weapons they no longer wanted to keep? The answer: They dumped the weapons in the ocean. The British buried many tons of German gas collected after the Second World War in the Baltic Sea. The United States conducted Operation Davey Jones’ Locker from 1946-1948 in which German ships were filled with chemical munitions and scuttled in the North Sea and Skaggerak Straight between Norway and Denmark. The United States later conducted the CHASE Program (CHASE stood for “cut holes and sink ‘em”). The CHASE Program involved loading unwanted chemical and conventional munition into aging ships and scuttling them at sea. Here is a list of chemical CHASE Program disposals:
* CHASE 8 — 1967: Disposed of mustard agents and Sarin filled M55 rockets
* CHASE 11 — June 1968:- Disposed of Sarin and VX
* CHASE 12 — August 1968: Disposed of mustard agents
* CHASE 10 — August 1970: Disposed of about 3,000 tons of nerve agent rockets encased in concrete vaults
Environmental concern over the sea dumping of chemical weapons eventually led to a public law prohibiting further such missions (if you want to red more about this topic, the best book is Jonathan Tucker’s War of Nerves: Chemical Warfare from World War I to Al-Qaeda [New York: Pantheon Books, 2006]).
Thousands of tons of chemical weapons are still stocked on land, though, in rusting drums on military bases, and once or twice a year there is a big debate in professional journals about what would be more dnagerous: To keep these volatile weapons as is in their dusty tombs, or to try and deactivate them. Here, perhaps, is a solution: A new decontamination agent devised by U.S. chemists can deactivate toxic chemicals such as nerve agents and pesticides leaving only non-toxic, easily disposable by-products, according to research in the New Journal of Chemistry. The work could lead to cheaper and more effective cleanup of contaminated sites such as chemical weapons stockpiles. Existing methods for destroying nerve agents, such as treatment with bleach, are limited. Nerve agents in chemical weapons are often found as chemical mixtures, and bleach reacts indiscriminately — even explosively — with many chemicals such as propellants. It is also corrosive to other materials and surfaces. Other approaches such as alkaline hydrolysis have several drawbacks, including low solubility and slow reaction rates. Furthermore, some decontamination methods give by-products, such as thioic acids, which are themselves almost as toxic as the original nerve agent.
Now David Atwood from the University of Kentucky and Daniel Williams from Kennesaw State University and coworkers have developed a destruction method based on dealkylating agents. The result is that organophosphate-based nerve agents and pesticides can now be cleaved in a single reaction. “The resulting non-toxic byproducts would be solids that could be easily handled or disposed of,” explained Atwood. “Looking to the future, the technology could also be used to decontaminate vehicles or other objects that have been exposed to nerve agents,” he added. The dealkylating agents are based on Schiff bases containing boron or aluminium and specifically cleave the phosphate ester bond in nerve agents or pesticides, preventing unwanted side reactions and surface corrosion. “The search for a non-corrosive decontamination of sensitive material and skin after exposure by toxic chemicals, for example pesticides and nerve agents, is an important but challenging task,” said Franz Worek, an expert in organophosphate toxicology at the Bundeswehr Institute of Pharmacology and Toxicology, Munich, Germany. “This new and promising approach may ultimately lead to a new type of mild and effective decontamination,” he added.
A word about Schiff base From Chemistry 101 you should recall that a Schiff base is a functional group containing a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group — but not hydrogen. Schiff bases are of the general formula:
R1R2C=N-R3 where R3 is an aryl or alkyl group that makes the Schiff base a stable imine. A Schiff base derived from an aniline, in which R3 is a phenyl or substituted phenyl, can be called an anil.
-read more in Amitabha Mitra et al., “Group 13 Chelates in Nerve Gas Agent and Pesticide Dealkylation,” New Journal of Chemistry (5 March 2008) (DOI: 10.1039/b717041f)
