Reactions of Isobutane and the tert-Butyl Radical with Atomic and Molecular Oxygen

Article abstract of DOI:10.1021/j100448a004

The reaction of oxigen atoms with isobutane in fast-flow system has been followed with a photoionization mass spectrometer.The rate constant for the initial attack of O(³P) on isobutane is (1.0+/-0.2)*1E-13 cm³ molecule^-1 s^-1, in agreement with the prediction of Herron and Huie.Direct observation of the tert-butyl radicals formed from O+(CH3)3CD demostrates that most of the initial hydrogen abstraction occurs from the tertiary carbon.The subsequent reaction of the tert-butyl radicals with atomic oxygen forms mostly isobutene (*0percent) with acetone (20percent) as an alternate channel.Competition experiments show that the tert-butyl radicals react (2.68+/-0.36)*1E-2 times more slowly with O2 than with O(³P).In the presence of an excess of O2 the same two products are observed but in a different prportion - isobutene (27percent) and acetone (73percent).This is interpreted to result from the initial formation of the tert-butyl peroxy radical, which then reacts with O(³P) to form acetone+(CH3+O2) and isobutene+(OH+O2).The behavior of the CH3 signal supports this interpretation.When a previously determined absolute rate constant is used together with the results of competition experiments, the rate constant for the reaction O(³P)+(CH3)3C -> products is calculated to be (8.7+/-1.9)*1E-10 cm³ molecule^-1 s^-1.