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 x 10(26) exp[(-47.4 +/- 2.8 kJ mol(-1))/RT] molecule cm(-3) and k9/k8= 1.98 x 10(23) 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.

Gas-phase degradation of 2-butanethiol initiated by OH radicals and Cl atoms: kinetics, product yields and mechanism at 298 K and atmospheric pressure

“…Our results are in agreement with previous studies focused in the RO radicals fate [45][46][47][48] that proposed that the OH-initiated oxidation in presence of NO X occur via the formation of a chemically activated oxy radical which decomposes promptly to yield shorter carbon chain aldehydes. In contrast, the Cl-initiated oxidation does not lead to C-C bond scission, even in the presence of NO [45][46][47][48] (see Fig. S3 of ESI †).…”

The Effect of Alcohol and Carbonyl Functional Groups on the Competition between Unimolecular Decomposition and Isomerization in C4 and C5 Alkoxy Radicals

“…Figure compares intra‐H migration rates computed here with high‐level results computed by Zhang et al , Somnitz and Zellner , and Xu et al , along with available experimental values . All computed β ‐scission rates are in good agreement, within 30% at 1400 K. The β ‐scission to CH 2 O + n ‐propyl and intra‐H migration rates computed here are in fair agreement with those computed by Zhang et al (lower by 40% at 300 K, decreasing to 20% at 1500 K).…”

“…Blue: Klippenstein et al ; red: Truhlar et al ; orange: Somnitz and Zellner ; black: this work. Experimental measurements of isomerization channels: open square: Cox et al ; filled circle: Heiss and Sahetchian ; purple line: experimentally fitted data of Cassanelli et al . Blue transparent circle included to highlight variations in computed crossover temperatures.…”

Kinetics of hydrogen-transfer isomerizations of butoxyl radicals

“…7,26 For example, Heiss and Sahetchian 7 measured the ratio of isomerization rate to decomposition rate of 1-butoxyl radical and derived the isomerization rate from this ratio and the known decomposition rate. This indirect measurement can introduce large uncertainty into the derived isomerization.…”

“…Calculated rate constants of the forward reaction R1 by CVT/SCT in this work and by the RRKM/CVET/ME method (CVET denotes CVE tunneling and ME denotes master equation) by Somnitz 10 together with experimental data by Heiss and Sahetchian 7 and by Cassanelli et al26 …”