Arrhenius parameters for the addition of HO2radicals to (E)-but-2-ene over the range 400–520°C

Abstract

Studies have been made of the addition of HO2 radicals to (E)-but-2-ene in the temperature range 400–520°C, by use of the co-oxidation of (E)-but-2-ene and propene in the presence of tetramethylbutane as a source of HO2 radicals. From measurements of the relative yields of 2,3-dimethyloxirane and methyloxirane and the known Arrhenius parameters for reaction (6), values of A7= 108.61 ± 0.30 dm3 mol–1 s–1 and E7= 50.0 ± 4 kJ mol–1 have been obtained. HO2+ C3H6→ C3H6O + OH (6), HO2+(E)-C4H8-2 → C4H8O + OH (7)The values are compared with data for HO2 addition to other alkenes. The excellent correlation between the activation energy for addition and the ionisation energy of the alkene is used to provide a kinetic data base for HO2 addition to alkenes over the range 600–1000 K, where the reactions are of major importance.From studies of the relative yields of 2,3-dimethyloxirane and (Z)-but-2-ene from (E)-but-2-ene + H2+ O2 mixtures, further evidence is presented to show that the decomposition of hydroperoxyalkyl radicals, such as CH3CH(OOH)CHCH3, into alkene + HO2 is at most a minor process compared with formation of an oxirane + OH radical.