Explosives

Monday 1 November 2010

What might be flying with you – or even with your IB exam scripts, extended essays or IA samples for moderation as they are sent round the world as cargo courtesy of DHL? On 29 October 2010 two parcels that contained explosives were detected in cargo planes bound for the USA – one in Dubai and one in East Midlands Airport in the UK. The parcels are thought to have originated from Yemen.

The explosives (which in one of the parcels were concealed inside a printer ink cartridge) contained the explosive PETN. Explosives are not on the IB course as such although as part of the Nature of Science it is well worth mentioning the role Fritz Haber played in fixing nitrogen which very probably prolonged the First World War. Most people have heard of nitroglycerine or nitrocellulose – but what exactly is PETN?  In fact it is not new and was used as an explosive in World War I. It was first synthesised in 1891 by the German chemist Bernhard Tollens (1841 – 1918). Many will recognise the name Tollens as it is the same Tollens who introduced Tollens’ reagent, the silver mirror test for the presence of aldehydes using ammoniacal silver nitrate which also produces an explosive solid. Tollens and his co-worker Wigand nitrated pentaerythritol, C(CH2OH)4, to form pentaerythritol tetranitrate or PETN. It obviously has many similarities with nitroglycerine except of course it contains an extra nitro-group as the starting material possesses four –OH groups rather than the three in propane-1,2-3-triol (glycerol).

I wouldn’t recommend discussing the synthesis of this with your students – MI5 (or is it MI6?) are probably logging this already(!) - but since many of us and our students travel internationally it seems reasonable to have some chemical knowledge of what we might be up against. PETN has been the explosive of choice recently. On Christmas Day 2009 a Nigerian student tried to blow up a NorthWest Airlines flight as it approached Detroit – the PETN was contained in his underwear  - and a few years earlier in 2001 the ‘shoe bomber’ Richard Reid, had PETN concealed in his shoes and was prevented in his attempt to blow up an American Airlines flight en route from Paris to Miami. There are several reasons why terrorists are using PETN. Although not impossible, it is very difficult to detect and it is also considerably more stable than many other nitro- explosives such as nitroglycerine. I have seen one report that the recent bombs contained lead azide, Pb(N3)2 to initiate the reaction but it can also be detonated by an electric spark and a mobile phone was reported to be present with the bomb at East Midlands Airport. The ‘shoe bomber’ attempted to use triacetone triperoxide as his detonator. For this reason there are severe restrictions on the amount of liquids that most air travellers are allowed to take on board with them.

Like many substances, nitro- compounds can often be used for both good and bad purposes. Both nitroglycerineand PETN are used in medicine as vasodilators in heart conditions – so maybe there should be a small amount of these 'explosives' kept in the medicine cabinet on all planes!

Happy (and safe) flying!

1.There is a nice TOK point here related to language. In the same way that nuclear magnetic resonance is called magnetic resonance imaging in hospitals to avoid the use of the word nuclear, nitroglycerine is called glyceryl trinitrate to avoid the connotation with explosives. 


Tags: PETN, terrorism, Tollens, test for aldehydes, security, bombers, explosives, nitration