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 Ton 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 k(1) = k(0)k(infinity)[M]/k(0)[M] + k(infinity) x 0.6((1+(log(k0[M]/k infinity))2)-1) provided the following low and high pressure limits for the rate constant of IPN, decomposition: k(0) = 6.60 X 10(-5) exp(-15190/T) cm(3) molecule(-1) s(-1) and k(infinity) = 1.05 x 10(16) exp(-19850/T) s(-1), respectively, which allows one to determine (via the above expression) the values of k(1) (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)(2)CHO, 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).