The Gas-Phase Pyrolysis of 2,2-Dinitropropane:  Shock-Tube Kinetics

The thermal decomposition of 2,2-dinitropropane (DNP) was investigated in a shock tube over the temperature range 970−1200 K, under high dilution in argon at total pressures 4.5−5.5 atm. The decay of DNP and the production of NO2 were followed spectrophotometrically at 280 and 405 nm, respectively. The derived unimolecular rate constant for dissociation is k uni = 1013.1 exp(−23 000/T) s-1. The products of pyrolysis were identified and quantitated using FTIR, GC, and GC/MS. The principal products are CO, NO, acetone, CH3C⋮H, CH2CCH2, CH3CN, CO2, CH3OH, CH4, H2O, and CH2O. The first step in the decomposition appears to be C−NO2 bond fission. However, the temporal profiles of NO2 during the decomposition are distinctively different from those recorded during the decompositions of CH3NO2 or 2-nitropropane, thus pointing to distinctive features in the mechanism. A compilation of 90 elementary steps is proposed. Numerical simulations based on this mechanism reproduce quantitatively the experimentally determined [NO2] vs time profiles for a range of conditions, as well as the distributions of major products. Sensitivity analysis of the mechanism reveals that only 57 steps are essential for describing the overall pyrolysis under the current experimental conditions. The following intermediates play critical roles in the decomposition: H, OH, NO2, HCO, and HNO.