Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 2827 - 2842 (1984)
Update date:2022-08-16
Topics:
Baldwin, Robert R.
Drewery, George R.
Walker, Raymond W.
The decomposition of 2,3-dimethylbutane (DMB) in the presence of O2 in KCl-coated vessels has been studied at 480, 500 and 540 deg C over a wide range of mixture composition.At low pressures of O2 the main initiation reaction is (CH3)2CHCH(CH3)2 -> 2i-C3H7 (10) but the reaction (CH3)2CHCH(CH3)2 + O2 -> HO2 + (CH3)2CHC(CH3)2 (0) becomes dominant at the higher pressures of O2 used. From measurements of the yield of propene, formed in 99percent yield from i-C3H7 radicals, accurate values of k10 are obtained after extrapolation to zero O2 and DMB pressures.Combination with Tsang's high-temperature results gives log10(A10/s-1) = 16.42(+/-)0.10 and E10 = 319.1 (+/-)1.5 kJ/mol over the temperature range 750-1200 K.These values are compared with parameters for similar systems and a simple relation has been developed to calculate the activation energy for C-C homolysis in alkanes and alkenes.By use of the published values for k-10 a value of ΔfH0298(i-propyl) = 79.6(+/-)2.0 kJ/mol is obtained, which corresponds to D2980(CH3CHCH3-H) = 401.3(+/-)2.0 kJ/mol.With these values a self-consistent set of data is available for the heats of formation of the prototypical alkyl-radicals, ethyl (117.0(+/-)4.0 kJ/mol), i-propyl and t-butyl (37.6(+/-)2.0 kJ/mol).From measurements of the yield of but-2-ene in the initial stages of reaction, values of k12 of (3.0(+/-)0.3)E-8 s-1 at 480 deg C and (1.15(+/-)0.15)E-7 s-1 at 500 deg C are obtained for the reaction (CH3)2CHCH(CH3)2 -> (CH3)2CHCHCH3 + CH3 (12). Arrhenius parameters of log10(A12/s-1) = 16.6 and E12 = 348 kJ/mol are recommended.
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