Relative rate study of the addition of HO2 radicals to ethylene and to tetramethylethylene
Studies of the competitive oxidation of ethylene and tetramethylethylene in the presence and absence of tetramethylbutane as a source of HO2 radicals have been carried out between 400 and 500 °C over a range of mixture composition and total pressure using aged boric-acid-coated Pyrex vessels. From measurements of the initial relative yields of oxirane and tetramethyloxirane, values of log10(A7/A5)=–0.77±0.09 and E5–E7= 36.5±0.9 kJ mol–1 have been obtained: HO2+ C2H4→ C2H4O + OH (5) [graphic omitted] Use of the published values of the Arrhenius parameters for reaction (5) gives log10(A7/dm3 mol–1 s–1)= 9.24±0.29 and E7= 40.0±4.5 kJ mol–1. No other values are available in the literature, but the present results are consistent with the very limited data available for the addition of HO2 radicals to ethylene, propene and i-butene. Trends in the variation of the values of the rate constant and of the activation energy for HO2 addition with structure of the alkene are very similar to those observed for the addition of CH3O2 and i-C3H7O2 radicals. The relative rate of addition of i-C3H7O2, CH3O2 and HO2 radicals to any alkene at 130 °C is ca. 1:4:30.