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 k25i/k27i, from which k25i= 6.8 × 107 dm3 mol–1 s–1 with a possible error of 50 % due to uncertainty in the value of k27i. Combination with a low temperature measurement gives A25i= 6.9 × 109 dm3 mol–1 s–1 and E25i= 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 k34t/k34p= 4.1 at 480°C is accurate to ± 10 %, but the absolute values of k34t and k34p are dependent on thermochemical data and on the rather uncertain value of k27i. 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.