A detailed analysis has been made of the products formed when 1% of pent-1-ene and of cis-pent-2-ene are added to slowly reacting mixtures of H₂+ O₂ in aged boric-acid-coated vessels at 480°C. The primary products are formed through four different types of attack on the pentenes of almost equal importance, radical addition of H, OH and HO₂, and H atom abstraction from the pentenes by all three radicals. Penta-1,3-diene is the only C₅ diene observed, in marked contrast to an earlier study of pentene oxidation. From measurements of the initial relative yields of penta-1,3-diene and buta-1,3-diene, a value of k₂= 2.1 × 10⁶ dm³ mol^–1 s^–1 at 480°C is obtained. [graphic omitted]CH₂CH₃+ O₂→ CH₂CH—CHCHCH₃+ HO₂. This is the first value determined for a reaction of this type and is at least ten times lower than rate constants for the formation of an alkene from an alkyl radical. This decrease is consistent with the considerably lower enthalpy change in reaction (2).

Product analysis suggests that H atoms add almost equally at the two positions in pent-2-ene, and in the ratio of 0.65 ± 0.2 for non-terminal/terminal addition in pent-1-ene. In contrast to the behaviour of vibrationally-excited propyl and butyl radicals formed by H atom addition to alkenes, there is no evidence for an enhanced rate of decomposition of the pentyl radicals formed from the pentenes. Conjugate oxirans are formed mainly by HO₂ addition to the pentenes, and lower aldehydes mainly by OH addition.