A temperature-dependent relative-rate study of the OH initiated oxidation of n-butane: The kinetics of the reactions of the 1- and 2-butoxy radicals
Abstract
The kinetics of the reactions of 1-and 2-butoxy radicals have been studied using a slow-flow photochemical reactor with GC-FID detection of reactants and products. Branching ratios between decomposition, CH3CH(O˙)CH2CH3 → CH3CHO + C2H5, reaction (7), and reaction with oxygen, CH3CH(O˙)CH2CH3 + O2 → CH3C(O)C2H5 + HO2, reaction (6), for the 2-butoxy radical and between isomerization, CH3CH2CH2CH2O˙ → CH2CH2CH2CH2OH, reaction (9), and reaction with oxygen, CH3CH2CH2CH2O˙ + O2 → C3H7CHO + HO2, reaction (8), for the 1-butoxy radical were measured as a function of oxygen concentration at atmospheric pressure over the temperature range 250–318 K. Evidence for the formation of a small fraction of chemically activated alkoxy radicals generated from the photolysis of alkyl nitrite precursors and from the exothermic reaction of 2-butyl peroxy radicals with NO was observed. The temperature dependence of the rate constant ratios for a thermalized system is given by k7/k6 = 5.4 × 1026 exp[(−47.4 ± 2.8 kJ mol−1)/RT] molecule cm−3 and k9/k8 = 1.98 × 1023 exp[(−22.6 ± 3.9 kJ mol−1)/RT] molecule cm−3. The results agree well with the available experimental literature data at ambient temperature but the temperature dependence of the rate constant ratios is weaker than in current recommendations.