New Synthesis Routes for Energetic Materials Using Dinitrogen Pentoxide [and Discussion]

The harsh and unselective nature of conventional nitrating agents, based on nitricsulphuric acid mixtures or pure nitric acid, has led to the development of new nitration methodologies based on dinitrogen pentoxide (N 2 O 5 ) that overcome many of the draw backs of conventional media, especially when dealing with sensitive substrates. Two principal nitration system s have been developed : (i) N 2 O 5 in pure nitric acid, and (ii) N 2 O 5 in organic solvents, mainly chlorinated hydrocarbons. The former system possesses strength similar to mixed acid (HNO 3 - H 2 SO 4 ) system s and is therefore potent, but displays advantages such as ease of generation of the nitration reagent by electrolysis and com patibility with nitram ine products, facilitating the synthesis of nitram ine explosives as well as certain aromatic nitro compounds. The second system (N 2 O 5 /organic solvent) encompasses a much wider range of nitrations, and with suitable choice of substrate permits the generation of polynitrated species directly without the formation of acidic by-products, an important environmental consideration. These conditions are also compatible with sensitive substrates, particularly those possessing strained-ring heterocyclic skeletons; thus the nitration of such compounds with N2O5 perm its precursors for energetic polymers (e.g. polyNIMMO) to be prepared by selective nitration. Likewise, nitrated derivatives of suitably functionalized elastomeric pre-polymers (e.g. NHTPB ) can also be manufactured; both of the latter category of compound find important application as energetic binders for novel explosive and propellant compositions, notably low-vulnerability (LOVA) propellant charges.