Chemistry

Explosive Entropy

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Science  21 Jan 2005:
Vol. 307, Issue 5708, pp. 321
DOI: 10.1126/science.307.5708.321a

Explosive compounds, such as nitro- glycerin or trinitrotoluene (TNT), tend to decompose via highly exothermic pathways. The explosion is sustained by the enthalpy released as strong bonds (in the products) form. In contrast, Dubnikova et al. suggest that triacetone triperoxide (TATP), which explodes with power comparable to that of TNT, undergoes a nearly thermoneutral decomposition and derives explosive force entirely from the increase in entropy. As its name suggests, this compound incorporates three acetone equivalents: It is a nine-membered ring with three O atom pairs separated by isopropylidene (>C(CH3)2) groups. The authors used density functional theory to calculate decomposition rates along several pathways, beginning with the structure determined by x-ray diffraction. Comparison with experimental data suggests that exothermic oxidation of the hydrocarbon groups does not play a significant role. Instead, they conclude that the explosion is initiated by cleavage of an O-O bond and is driven by the liberation of four gaseous molecules (one ozone and three acetones) from the harmless-looking solid TATP. — JSY

J. Am. Chem. Soc. 10.1021/ja0464903 (2004).

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