Thermal Decomposition of Isopropyl Nitrate: Kinetics and Products

Kinetics and products of the thermal decomposition of isopropyl nitrate (IPN, C₃H₇NO₃) have been studied using a low pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of IPN decomposition was measured as a function of pressure (1-12.5 Torr of helium) and temperature in the range 473-658 K using two methods: from kinetics of nitrate loss and those of reaction product (CH₃ radical) formation. The fit of the observed falloff curves with two parameter expression [Formula: see text] provided the following low and high pressure limits for the rate constant of IPN decomposition: k₀ = 6.60 × 10^-5exp(-15190/T) cm³ molecule^-1 s^-1 and k_∞ = 1.05 × 10¹⁶ exp(-19850/T) s^-1, respectively, which allows one to determine (via the above expression) the values of k₁ (with 20% uncertainty) in the temperature and pressure range of the study. It was observed that thermal decomposition of IPN proceeds through initial breaking of the O-NO₂ bond, leading to formation of NO₂ and isopropoxy radical (CH₃)₂CHO, which rapidly decomposes forming CH₃ and acetaldehyde as final products. The yields of NO₂, CH₃, and acetaldehyde upon decomposition of isopropyl nitrate were measured to be (0.98 ± 0.15), (0.96 ± 0.14), and (0.99 ± 0.15), respectively. In addition, the kinetic data were used to determine the O-NO₂ bond dissociation energy in isopropyl nitrate, 38.2 ± 4.0 kcal mol^-1.