Understanding the initial decomposition pathways of the n-alkane/nitroalkane binary mixture

Addition of nitroalkanes into n-alkanes can lower the activation barriers of free-radical production and accelerate the decomposition of n-alkanes at relatively low temperatures. Four initial decomposition mechanisms of the n-butane/nitroethane binary mixture were proposed for the promoting effect and considered theoretically at the B3LYP, BB1K, BMK, MPW1K, and M06-2X levels with MG3S basis set. Energetics above was compared to high-level CBS-QB3 and G4 calculations. Calculated results confirm the feasibility of the four initial decomposition pathways: (I) the C-NO₂ bond rupture of nitroethane to produce ethyl and ·NO₂, (II) HONO elimination from nitroethane followed by decomposition to ·OH and ·NO, (III) rearrangement of nitroethane to ethyl nitrite which further dissociates into CH ₃CH₂O· and ·NO, and (IV) direct hydrogen-abstraction of nitroethane with n-butane. The mechanism of initial decomposition step of the n-alkane/nitroalkane binary mixture was investigated using quantum chemical calculations. We reveal four initial decomposition pathways and provide insight into the energetic feasibility of all the proposed initial steps.