Addition of i-butane to slowly reacting mixtures of hydrogen and oxygen at 480°C

Abstract

Analysis has been made of the products formed when small amounts of i-C₄H₁₀ and i-C₄H₈ are added to slowly reacting mixtures of H₂+ O₂ at 480°C. The variation of [C₃H₆]/[C₄H₈] with [O₂], with i-C₄H₁₀ as additive, gives the rate constant ratio k_25i/k_27i, from which k_25i= 6.8 × 10⁷ dm³ mol^–1 s^–1 with a possible error of 50 % due to uncertainty in the value of k_27i. Combination with a low temperature measurement gives A_25i= 6.9 × 10⁹ dm³ mol^–1 s^–1 and E_25i= 29.1 kJ mol^–1. i-C₄H₉+ O₂= i-C₄H₈+ HO₂(25i), i-C₄H₉= C₃H₆+ CH₃(27i), The rate constant for the 1, 4t and 1, 5p H atom transfers involved in reactions (34t) and (34p) have been obtained and compared with values estimated previously for similar isomerisations. CH₃CH(CH₃)CH₂O₂= CH₃C(CH₃)(CH₂OOH)(34t), CH₃CH(CH₃)CH₂O₂= CH₃CH(CH₂OOH)CH₂(34p), The rate constant ratio k_34t/k_34p= 4.1 at 480°C is accurate to ± 10 %, but the absolute values of k_34t and k_34p are dependent on thermochemical data and on the rather uncertain value of k_27i. Further evidence is obtained for the importance of the reaction of alkylhydroperoxide radicals (QOOH) with O₂, and rate constants for a number of elementary reactions involving QOOH radicals are given. The rate constant for the addition of OH radicals to i-C₄H₈ has been estimated as 2.9 × 10¹⁰ dm³ mol^–1 s^–1.