Main reaction of peroxy radicals in the gas-phase oxidation of ethylene

Addition of Peroxyl Radicals to Alkenes and the Reaction of Oxygen with Alkyl Radicals

“…15 kJ mol -1 , all their other evaluations would also need to be reduced, thus maintaining the excellent correlation between activation energy and alkene ionization energy that they observed. The ∆H r (298 K) energies quoted in Figure 9 are sourced from: C 2 H 4 + HO 2 , 40 T 1 , 69 T 3 , 70,71 C 2 H 4 O 2 H, 64 and T 2 from evaluations of a 1,4p hydrogen transfer reaction 31 and excited states. 46 If it were accepted that E -6 ≈ 60 kJ mol -1 , and E 4 ≈ 5 kJ mol -1 and that there was an unavoided crossing of the 2 A′′ and 2 A′ states of the system in the vicinity of the transition state for the addition of the peroxyl radical to the alkene, then the benefits for the understanding of hydrocarbon oxidation are considerable, as it could be contended that the two well-developed mecha-nisms describing O 2 + alkyl f alkene + HO 2 and HO 2 (or RO 2 ) + alkene f epoxide + OH (or RO) are able to coexist without contradiction.…”

“…There has however been one reported epoxidation rate constant obtained by more “direct” methods. Arsentiev et al , monitored the total peroxyl radical concentration in the gas phase by ESR during the autoxidation of ethene. The rate of production of the ethene oxide was found to correlate well with the product of the peroxyl radical and alkene concentrations and was used to derive (effectively, species averaged) rate constants for the epoxidation of the ethene by the peroxyl radicals present.…”

“…The rate of production of the ethene oxide was found to correlate well with the product of the peroxyl radical and alkene concentrations and was used to derive (effectively, species averaged) rate constants for the epoxidation of the ethene by the peroxyl radicals present. For ethene autoxidation at the temperatures used (637−688 K), the dominant peroxyl radical present is very likely to be the hydroperoxyl radical, so the rate constant of Arsentiev et al , can be used to give a barrier height for the addition of HO 2 to ethene of E - 6 = 56.6 ± 3.4 kJ mol -1 . This value is consistent with that derived from Kaiser's work of 60.7 ± 4.6 kJ mol -1 .…”

Variety of Kinetic Manifestations of Branched Chain Reactions

“…The study of the oxidation of ethylene, an olefinic hydrocarbon at the radical level, showed [15][16][17] that the process in this case proceeds with the participation of the same peroxide radicals as the oxidation of ethane [18], a paraffinic hydrocarbon. It should also be noted that the stable intermediate products during the oxidation of these hydrocarbons are practically the same.…”

“…Thus, the primary alkylperoxide RO 2 radicals forming in degenerately branched chain reactions of hydrocarbon oxidation transform into the more active alkoxy RO radicals, which in subsequent elementary acts provide for the further development of chains and the formation of basic stable intermediate products [17]. Summarizing the results of studies on the mechanism of hydrocarbon oxidation based on the direct data on free radicals, the basic mechanism can be summarized as follows:…”