Arrhenius parameters for the addition of HO2 radicals 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= 10^{8.61 ± 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.