Identifying the Molecular Properties that Drive Explosive Sensitivity in a Series of Nitrate Esters

Abstract

Energetic materials undergo hundreds of chemical reactions during exothermic runaway, generally beginning with the breaking of the weakest chemical bond, the "trigger linkage." Herein we report the syntheses of a series of pentaerythritol tetranitrate (PETN) derivatives in which the energetic nitrate ester groups are systematically substituted by hydroxyl groups. Because all the PETN derivatives have the same nitrate ester-based trigger linkages, quantum molecular dynamics (QMD) simulations show very similar Arrhenius kinetics for the first reactions. However, handling sensitivity testing conducted using drop weight impact indicates that sensitivity decreases precipitously as nitrate esters are replaced by hydroxyl groups. These experimental results are supported by QMD simulations that show systematic decreases in the final temperatures of the products and the energy release as the nitrate ester functional groups are removed. To better interpret these results, we derive a simple model based only on the specific enthalpy of explosion and the kinetics of trigger linkage rupture that accounts qualitatively for the decrease in sensitivity as nitrate ester groups are removed.

Halogenated PETN derivatives: interplay between physical and chemical factors in explosive sensitivity

“…We and others have observed that impact sensitivity correlates well with the nature and number of energetic functional groups and their weakest bonds, or trigger linkages, along with the heat of explosion, Q. 21,22 An earlier systematic study of the rates of trigger linkage rupture in a set of 24 explosives, including nitrate esters, nitramines, nitro aromatic compounds, azoxyfuraxans, azides, and nitramines, suggested that impact sensitivity is (i) inversely proportional to the rate of trigger linkage rupture and (ii) that the heat of a Calculated at the B3LYP/6-31+G(d,p) level and iodine atoms are calculated at the def2svp level. 68,69 explosion tends to reduce the effective activation barrier, E a , consistent with the Bell-Evans-Polanyi principle,…”

“…We and others have observed that impact sensitivity correlates well with the nature and number of energetic functional groups and their weakest bonds, or trigger linkages, along with the heat of explosion, Q . 21,22 An earlier systematic study of the rates of trigger linkage rupture in a set of 24 explosives, including nitrate esters, nitramines, nitro aromatic compounds, azoxyfuraxans, azides, and nitramines, suggested that impact sensitivity is (i) inversely proportional to the rate of trigger linkage rupture and (ii) that the heat of explosion tends to reduce the effective activation barrier, E a , consistent with the Bell–Evans–Polanyi principle, H 50 ∝ 1/( A exp(−( E a − αQ )/ k B T ))where α is an adjustable parameter. 21 From this result, it was shown that across a set of derivatives with different numbers of energetic groups, N x , but the same trigger linkages the variation in H 50 should approximately followwhere γ is an adjustable constant and the superscript 0 denotes a reference molecule in the series of derivatives.…”

“…Overall, we have demonstrated that the number of energetic functional groups and heat of explosion account for the explosive sensitivity of a material, consistent with recent previous work by our group and others. 21,22…”

“…15,16 Other studies have identied the importance of oxygen balance, 17,18 bond dissociation energies, 19 reaction rates 20,21 and the heat of explosion. 22,23 Most sensitivity tests convolute those intrinsic properties of energetic molecules and materials that control their sensitivity, such as their functional groups, stoichiometry and oxygen balance, and decomposition kinetics with meso-and macroscopic properties including the phase, impurities, and particle shape and size, such that it is oen difficult to understand which properties of a new material are responsible for a particular result. To simplify these analyses, we have explored the use of a core chemical scaffold to which systematic modications can be made to better assess how these specic functional changes inuence explosive sensitivity.…”

“…15,16 Other studies have identified the importance of oxygen balance, 17,18 bond dissociation energies, 19 reaction rates 20,21 and the heat of explosion. 22,23…”