Addition of 2,2,3-trimethylbutane to slowly reacting mixtures of hydrogen and oxygen at 480 °C
The oxidation of 2,2,3-trimethylbutane (TRIMB) has been studied by adding traces of the alkane to slowly reacting mixtures of H2+ O2 in aged boric-acid-coated vessels at 480 °C. Rate constants for H and OH attack on TRIMB have been obtained and, by use of an additivity principle, Arrhenius parameters of log10(A/dm3 mol–1 s–1)= 9.32 ± 0.13 and E= 460 ± 950 J mol–1 are suggested for OH attack at a tertiary C—H bond in alkanes from a combination of the present results with studies at lower temperatures.
Propene, isobutene, and 2,2,3-trimethylbut-1-ene (TRIMB-1) are the major initial products, the yield of the latter increasing markedly at high O2 pressures. The proportions of the three species of trimethylbutyl radicals formed in each mixture have been estimated. Two of the species of trimethylbutyl radicals react almost completely by homolysis of the strained central C—C bond to give propene and isobutene as products. The third radical (CH3)3CC(CH3)2 is removed by either reaction (1 C) or (2 C), and it is suggested that (1 C) occurs by a concerted mechanism: (CH3)3CC(CH3)2→ i-C4H8+ i-C3H7(1 C)(CH3)3CC(CH3)2+ O2→(CH3)3CC(CH3)= CH2+ HO2. (2 C)
Rate constants have been obtained for a number of the homolysis reactions of the trimethylbutyl radicals, for which there is a good correlation between log k and ΔU, the internal energy change.