Die Kinetik des thermischen Zerfalls von ClNO2 / Thermal Decomposition of ClNO2

Abstract

ClNO2 decomposes incompletely at temperatures between 353 K and 373 K in the nonpolar inert solvent C7F15Cl according to 2 ClNO2=2 NO2+Cl2. (a) Some ClNO is formed as by-product according to 2 ClNO2 = 2 ClNO+O2 . (b) The reactions were followed photometrically by the arising NO2 . The time dependence of the brutto-reaction is described on the basis of the reaction scheme ClNO2⇄NO2+Cl (1, - 1); NO3+NO2⇄NO+O2+NO2 (5, - 5); ClNO2+ClNO2⇄Cl2+2NO2 (2, - 2); NO+ClNO2⇄ClNO+NO2 (6, - 6); Cl+ClNO2⇄Cl2+NO2 (3, - 3); ClNO+ClNO2⇄NO±Cl2+NO2 (7, - 7); NO2+ClNO2⇄NO3±ClNO (4, - 4); Cl+ClNO⇄Cl2+NO (8, - 8). Arrhenius parameters for the steps (1) and (2) were obtained: A1/s-1 = 1016.47±0.78, E1/kJ mol-1 = 152.3 ± 5.4; A2/cm3 mol-1 s-1 = 1012.99±0.02 E2/kJ mol-1 = 88.7 ± 0.8. The other parameters entering the rate equations were determined at 373 K as k-1/k3 = 1.5 ± 0.3; k4/cm3 mol-1 s-1 = 0.17; k7/cm3 mol-1 s-1 = 11.2. The enthalpies and entropies of the overall reactions (a), (b) and N2O4 = 2 NO2 (c) were measured directly (c) or indirectly: (a) (b) (c) ⊿RH/kJ mol-1 46.4 83.7 65.3 ⊿RS/J K -1 mol-1 61.8 85.7 97.8 (standard state 1 mol cm-3, T = 363 K). Former investigations of the reaction in the gas phase and in solution which were interpreted exceptionally by step (1) followed by the fast step (3) are now interpreted on the basis of the new reaction scheme discussed here and are found to be consistent with it.