DECOMPOSITION OF 4,4-DIMETHYLPENT-1-ENE IN THE PRESENCE OF OXYGEN BETWEEN 400-DEGREES-C AND 500-DEGREES-C - OXIDATION CHEMISTRY OF ALLYL RADICALS

The decomposition of 4,4-dimethylpent-1-ene (DMP) in the presence of O2 has been used as a source of allyl radicals over the temperature range 400-500-degrees-C. The reaction has been studied in both KCl-coated (peroxy species destroyed at the surface) and aged boric-acid-coated vessels (peroxy species preserved), and the basic mechanism shown to be: [GRAPHICS] Previous studies have shown that 99% of the t-butyl radicals undergo reaction (2), so that the system is an excellent source of allyl and HO2 radicals. A full product analysis has been carried out over a wide range of mixture composition and associated mechanistic aspects discussed. It is shown that allyl radicals are unreactive towards both DMP and O2 and that they react mainly in radical-radical processes. [GRAPHICS] Values of k8/k18 = 0.37, 0.38 and 0.42 are obtained at 400, 440 and 480-degrees-C, respectively. From a reasonably reliable estimate of [HO2] and [allyl], values of k8 = (3.3 +/- 0.9) x 10(9) and k18 = (7.4 +/- 2.4) x 10(9) dm3 mol-1 s-1 are obtained at 480-degrees-C. No previous estimates of these rate constants are available in the literature. Values of k4 have been determined and when combined with independent data at higher temperatures give log(A4/s-1) = 14.19 +/- 0.25 and E4 = 255.5 +/- 5.3 kJ mol-1 over the range 400-1025-degrees-C. [GRAPHICS] A value of k11 = (2.5 +/- 1) x 10(2) dm3 mol-1 s-1 has been obtained at 480-degrees-C and shown to be consistent with the reaction's high endothermicity. [GRAPHICS]