Original URL: http://www.theregister.co.uk/2009/06/26/white_phosphorus_caged/

Boffins 'cage the demon' of white phosphorus

Moleculo-prison could neutralise hellfire weapon

By Lewis Page

Posted in Science, 26th June 2009 10:48 GMT

Cambridge boffins have discovered a crafty molecular "cage" which can be used to imprison the "demon" chemical, white phosphorus, famous for burning inextinguishably and for its sometimes questionable military uses. Cleanup and transport of white phosphorus should now become much simpler and safer.

Phosphorus, as the Cambridge scientists note, has been known for centuries for its tendency to burst into flame on exposure to air. Even submerging burning phosphorus in water doesn't put it out properly - it merely slows combustion down, depending on the amount of oxygen in the water. Once the chemical is removed - perhaps just partially removed - from the water it's liable to start blazing again unpredictably as it dries out.

But phosphorus is useful stuff, handy for making weedkillers, insecticides and fertilisers. It's also popular for military use: phosphorus creates battlefield smokescreens much faster and better than any other filler, and at sea its ability to keep burning vigorously even semi-immersed makes it popular for flares and markers.

As a result, most armed forces have an array of white-phos munitions in their armouries - ranging from grenades up to heavy artillery shells. Though WP isn't designed or intended as an anti-personnel weapon - you would normally be able to inflict more casualties using the same weight of regular blast/frag rounds - it has shocking and nasty effects if purposely or accidentally used as such. Blazing particles of phosphorus can burn their way into a victim's body, where they keep on flaming and inflict excruciating pain.

Clearing up partially-burned or unexploded phosphorus rounds is particularly troublesome and hazardous owing to the tendency of the stuff to reignite when moved or disturbed. As a rule of thumb one in ten of any kind of munition doesn't function as designed, so there's always cleanup to do - and with phosphorus weapons, even a munition which works to spec will normally leave unburned particles of the chemical lying around afterwards.

An instance of this is the procedure followed by Royal Navy disposal teams dealing with the large partially-functioned phos markers which commonly wash up on UK beaches*. The responding divers generally prefer to wrap the entire munition in explosives on the spot and detonate them, so completely incinerating any remaining filler. (This follows incidents where markers being moved by hand or vehicle for disposal elsewhere burst into flame inconveniently.)

But now, Cambridge stinks brainboxes Prasenjit Mal, Boris Breiner and Jonathan Nitschke - collaborating with Finnish fellow-boffin Kari Rissanen - have invented a cunning new method for dealing with phosphorus. It seems that one can combine formyl-pyridine and diaminobiphenyl disulfonate with iron to form a molecular tetrahedron with a central void space in its middle. This four-sided "cage" can be made to form around molecules of phosphorus, locking them up so that they can't combine with oxygen.

Bigger "cages" might lock up chemical-warfare agents too

As the boffins put it on their webpage:

Within the cage, ordinarily pyrophoric P4 molecules become air-stable! ... The cage does not stabilize its guest through hermetic exclusion of oxygen, but rather through a constrictive mechanism. The reaction of O2 with P4 would proceed through a transition state too large for the cage's cavity.

"It is foreseeable that our technique might be used to clean up a white phosphorous spill, either as part of an industrial accident or in a war zone," says Dr Nitschke. "In addition to its ability to inflict grievous harm while burning, white phosphorous is very toxic and poses a major environmental hazard."

The chemicals required to make the cage are apparently "inexpensive". The trick might also be used as a means of handling and transporting phosphorus in industry, as well as cleaning up spills. According to the chemists one can easily release the demon from its cage as desired, by adding benzene.

Apart from phosphorus, the Cambridge boffins are now working on new cube and dodecahedron cages which could hold bigger molecules. They think these could be used to deliver chemical "payloads" such as drugs or fragrances, which would be released from the cages by a suitable signal compound. Dr Nitschke also believes that the new, larger cages could be used to clean up or transport other harmful molecules such as chemical weapons.

Full-on boffinry detail is published in Science magazine (subscription required) today. ®


*The Royal Navy has responsibility for all explosive ordnance disposal (EOD) tasks below the high-water mark around the UK's coasts. Teams of mine-clearance divers based at Plymouth, Portsmouth and Faslane deal with these jobs among other things. Your correspondent commanded the Plymouth team from 2001 to 2004.

Munitions found above the high-water mark are usually (but not exclusively) an Army responsibility. It is rumoured that teams from both services, faced with a tiresome or inconveniently-timed task, have been known to move a piece of ordnance up or down the beach to the other side of the high-tide line in order to hand the problem off to someone else.