Addition of cyclopentane to slowly reacting mixtures of H2+ O2 between 673 and 783 K: reactions of H and OH with cyclopentane and of cyclopentyl radicals

Abstract

A number of elementary reactions involved in the oxidation of cyclopentane (CP) have been studied by adding CP to H₂–O₂ mixtures over the temperature range 673–783 K. Kinetic studies of the relative rates of consumption of CP and H₂ have given values of k₂₁=(1.11 ± 0.25)× 10¹⁰ and k₂₂=(1.84 ± 0.32)× 10⁹ dm³ mol^–1 s^–1 at 753 K. Combination with independent data and critical analysis gives k₂₁= 3.65 × 10²T^2.5 exp(519/T) dm³ mol^–1 s^–1, which is recommended between 250 and 1500 K, with error limits of < 20%. Similarly, k₂₂= 2.4 × 10⁶T^1.5 exp(– 2440/T) dm³ mol^–1 s^–1 is recommended between 300 and 1250 K. OH + c-C₅H₁₀→ c-C₅H₉+ H₂O (21), H + c-C₅H₁₀→ c-C₅H₉+ H₂(22), Analytical studies over a range of mixture compositions have shown that the major initial products are c-pentane, 1,2-epoxycyclopentane, acrolein and, at low [O₂], C₂H₄. The mechanism of oxidation is essentially similar to that of linear alkanes and of cyclohexane, although the different stereochemistry of the two rings has a significant influence on parts of the mechanism. In particular, in the range 673–783 K and at [O₂] > 50 Torr, very little ring rupture has been observed in the initial products. The formation of C₂H₄ has been discussed in detail, and a value of k₃₂= 10^{13.14 ± 0.55} exp(– 17260/T) s^–1 has been obtained over the temperature range 580–783 K. c-C₅H₉→ CH₂= CHCH₂CH₂CH₂(32) The cyclisation of C₃, C₄, C₅ and C₆ alken-1-yl radicals has been discussed and it has been concluded that the predominant reaction of hex-5-en-1-yl radicals between 600 and 1300 K and at 1 atm O₂ pressure is cyclisation giving c-hexyl radicals. As the latter rapidly undergo successive oxidation to cyclohexene, cyclohexadiene and then benzene, it has been further concluded that such C₆ cyclisations could be major sources of benzene and substituted benzenes in the oxidation of conventional fuels.