Oxidation of allyl radicals: kinetic parameters for the reactions of allyl radicals with HO2 and O2 between 400 and 480 °C

Abstract

The decomposition of 4,4-dimethylpent-1-ene (DMP) in the presence of O₂ has been used as a source of allyl and HO₂ radicals between 400 and 480 °C. Propene was added to the mixtures of DMP and O₂ in order to monitor [HO₂] from the yields of propene oxide by use of the known value of k₁₄. HO₂+ C₃H₆→ C₃H₆O + OH (14) From measurements of the initial yields of CO, hexa-1,5-diene and propene oxide over a range of mixture composition, rate constants have been obtained for reactions (9) and (10). [graphic omitted] + HO₂→ CO + product (9), [graphic omitted] + HO₂→ C₃H₆+ HO₂(10) At 400 °C, k₉= 3.95 × 10⁹ and k₁₀= 1.42 × 10⁹ dm³ mol^–1 s^–1 and both show a slight increase (within experimental error) with temperature, 15% and 30%, respectively, at 480 °C.

Strong evidence is obtained for the formation of CO in the reaction between allyl radicals and O₂[reaction (15)] and values of A₁₅= 10^{9.4 ± 0.6} dm³ mol^–1 s^–1 and E₁₅= 79 ± 8 kJ mol^–1 are obtained. [graphic omitted] + O₂→ CO + products (15)

The mechanisms of reactions (10) and (15) are discussed. Based on current thermochemistry it is shown by calculation that reaction (10) probably occurs only to a minor extent through a direct H-atom abstraction route which is the reverse of the chain initiation reaction (16). C₃H₆+ O₂→ [graphic omitted] + HO₂(16)

The available kinetic data for the reaction between allyl radicals and O₂ are summarised.