Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle-Insights to Reactivity and Sensitivity of Energetic Materials

Abstract

The chemistry of energetic materials can be described applying acid-base reaction formalism. Addressing the HSAB concept, the number of electrons transferred, ΔN, in an acid-base reaction, allows for description and prediction of properties of composite and homogeneous materials. At first ΔN helps in estimating the rate of reaction of binary systems with either given fuel or oxidizer. Nevertheless ΔN is only a relative number thus the range of comparability remains narrow. At second ΔN can be used as a measure for the sensitivity of homogeneous explosives. The increased reactivity of hypothetical fragments to recombine in a reaction such as R3C.+.NO2=R3C−NO2 given by ΔN correlates very well with experimentally determined reduced impact sensitivity of 1,3,5-trinitrobenzene compounds. On the contrary the rising impact sensitivity of metal azides correlates with rising values of ΔN of Mn+/N3− reaction because increased reactivity, that is increased electron transfer from the azide anion to the metal cation triggers formation of the azide radical (.N3). The latter then decomposes rapidly to give dinitrogen. This increased reactivity/sensitivity of metral azides coincides with covalent bonding whereas ionic azides are relatively insensitive.