Sunday, 5 October 2014

An explosive Molecule of the Month: Dynamite the source of Alfred Nobel's wealth

The coming week is one of the most eagerly anticipated weeks in Science. It is the week in which the Nobel Prizes are announced and last year, we had an impromptu celebration during the week, by showing the live stream of announcements from Stockholm, where the prizes are announced . It made me think about the molecule to choose for October and I immediately thought of the organic molecule that formed the basis of Alfred Nobel's lucrative and famous invention: dynamite. The molecular structure shows that nitroglycerin (or Trinitroglycerin, NG for short)  is a rather simple compound which can be made by adding concentrated nitric acid to glycerol (see the wiki page for more information). Its formal name is 1,2,3 trinitroxypropane (A level chemists, make sure you can work this out!). Without Alfred Nobel's wealth, largely resulting from his invention of dynamite, used in construction work as well as for military purposes, there would be no Nobel Prize ceremony.

I wont spend a great deal of time on the background to the Prizes (you can read about them at the web site of the Nobel Foundation), but the prizes that are of interest to us this week are:

Monday:The Physiology or Medicine Prize
Tuesday: The Physics Prize
Wednesday: The Chemistry Prize

The countdown page can be found at this link and we will log in on Monday morning in the Innovation labs. The fuse is already burning slowly! 

Returning to the molecule, the original formulation of dynamite comprised NG, sodium carbonate and a "filler" called diatomaceous earth (a clay formed from silicates derived from fossilised diatoms). But why is NG so unstable? Why does it release so much energy when it is activated by physical shock or disruption, typically delivered via a fuse and termed detonation (from the French for "of thunder")? The release of energy in this highly exothermic process is a result of the favourable formation of gas molecules (N2/CO2/O2 and water vapour as the compound is detonated): compared with the instability of the weak bonds in NG, the hydrocarbon core is also a fuel. Looking at the charged nitrates makes me think of the three phosphates in ATP (the body's natural fuel) and the thermodynamic gain from hydrolysis of three charged moieties in a confined molecular volume. On a final note, NG is also used to treat heart conditions such as angina, the molecule releases nitric oxide following a reaction catalysed by aldehyde dehydrogenase. This duality of nitroglycerin's place in Science, was reinforced when Alfred Nobel, the inventor was prescribed NG for heart disease close to his death!

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