An explosive sometimes used by terrorists does not burn when it detonates. Instead, its molecules simply fall apart. The chemist who has discovered this is so concerned by its implications that he has decided to abandon this line of research.
Triacetone triperoxide (TATP) has been used by suicide bombers in Israel and was chosen as a detonator in 2001 by the thwarted "shoe bomber" Richard Reid. Now calculations by Ehud Keinan from the Technion-Israel Institute of Technology in Haifa show that most of its explosive force comes from a rapid release of gas rather than a burst of energy.
In conventional high explosives such as TNT, each molecule contains both a fuel component and an oxidising component. When the explosive detonates, the fuel part is oxidised and as this combustion reaction spreads it releases large amounts of heat almost instantaneously.
TATP molecules are made up of fragments that could react in a similar way. But Keinan says that videos showing samples of TATP being detonated show that it can do so without producing any flame.
His team's calculations indicate why. Explosions are driven by the reaction that takes the least energy to start. In this case it is not oxidation but disintegration. The TATP molecule sheds acetone units, setting free the oxygen atoms that bound them together to form the gases oxygen and ozone. It also releases just enough energy to spread the reaction to the next molecule.
One molecule of TATP produces four of gas, giving TATP its explosive power. Just a few hundred grams of the material will produce hundreds of litres of gas in a fraction of a second.
"It's different to conventional explosives," agrees Jimmie Oxley, a chemist at the University of Rhode Island in Kingston, US, who has studied TATP and worked with Keinan on other projects. But it is not unique. The decomposition of azide, for example, which produces nitrogen gas but little heat, is used to fill airbags for cars.
TATP turns out to be the most extreme example so far, and it may be possible to design molecules that behave as an even more powerful explosive. But the idea does not appeal to Keinan. "I don't want to continue this kind of research," he says. Instead, he plans to work with security agencies to develop a device that can detect TATP.
Journal reference: Journal of the American Chemical Society (DOI: 10.1021/ja0464903)