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Evaluated Kinetics of Terminal and Non-Terminal Addition of H Atoms to 1-Alkenes: A Shock Tube Study of H + 1-Butene



Jeffrey A. Manion, Iftikhar A. Awan


Single-pulse shock tube methods have been used to thermally generate hydrogen atoms and investigate the kinetics of their addition reactions with 1-butene at temperatures of 880 K to 1120 K and pressures of 145 kPa to 245 kPa. Rate parameters for the unimolecular decomposition of 1-butene are also reported. Addition of H atoms to the pi bond of 1-butene results in displacement of either methyl or ethyl depending on whether addition occurs at the terminal or non-terminal position. Post-shock monitoring of the initial alkene products has been used to monitor the relative and absolute reaction rates. Absolute rate constants have been derived relative to the reference reaction of displacement of methyl from 1,3,5-trimethylbenzene (135TMB). With k(H + 135TMB → m-xylene + CH3) = 6.7×1013 exp(-3255/T) cm3 mol-1 s-1, we find k(H + 1-butene → propene + CH3) = k10 = 4.16×1013 exp(-1220/T) cm3 mol-1 s-1, [880-1120 K; 145- 245 kPa] k(H + 1-butene → ethene + C2H5) = k11 = 3.30×1013 exp(-1919/T) cm3 mol-1 s-1, [880-1120 K; 145- 45 kPa] k_10/k_11 =1.26 exp⁡(699⁄T);980 K to 1120 K Uncertainties (2 σ) in the absolute rate constants are about a factor of 1.5, while the relative rate constants should be accurate to within 15%. The displacement rate constants are shown to be very close to the high pressure limiting rate constants for addition of H, and the present measurements are the first direct determination of the branching ratio for 1-olefins at high temperatures. At 1000 K, addition to the terminal site is favored over the non-terminal position by a factor of 2.55 ± 0.36, where the uncertainty is 2σ and includes possible systematic errors. Combining the present results with data from the literature at temperatures of
Journal of Physical Chemistry A


shock tube, kinetics, H atoms, 1-butene, 1-butyl, 2-butyl, propene
Created December 17, 2014, Updated February 19, 2017