Browsing by Author "Evans, Geoffrey A."

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    Decomposition of 2,2,3,3-Tetramethylbutane in the Presence of Oxygen
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Atri, Gulshan M.; Baldwin, Roy R.; Evans, Geoffrey A.; Walker, Raymond W.
    The oxidation of 2,2,3,3-tetramethylbutane in KCl-coated vessels has been studied between 440 and 54O°C, and over the pressure range 60-500 Torr. The results are consistent with a simple mechanism comprising reactions (l)-(3) (CH3)3C— C(CH3)3 -> 2t-C4H9 t-C4H9 + O2 —> i-C4H8 + HO2 surface HO2-> tH2O+iO2. (1) (2) (3) After allowance for a small (<20 %) contribution from a chain process, accurate Arrhenius parameters Ai = 6.0x 1016 s-1, Ei = 290.4 kJ mol-1 have been obtained by combination with Tsang’s results. From the thermochemistry of reaction (1) and literature values for k-i, values of AfJ7298 (t-Bu) = 44.0 + 4.0 kJ mob* and 5298(t-Bu) = 304.2±4.0 J K-1 mol-1 are recommended. Analysis of the products shows that ~1 % of the t-butyl radicals give isobutene oxide and over the temperature range 470-542°C, Az/Au = 13.8 and £13 — E2 = 13.0 kJ mol-1 where reaction (13) is the overall process, t-C4H9 + O2 — C4H8O+OH. (13) Reaction (13) is discussed in terms of the peroxy radical isomerisation and decomposition theory and Arrhenius parameters are suggested for the (1, 4/>) H atom transfer reaction (17) in t-butylperoxy radicals (CH3)3CO2 -> (CH3)2C(OOH)CH2. (17)
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    Molecular Decomposition of 2,2,3,3-Tetramethylbutane
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Baldwin, Roy R.; Evans, Geoffrey A.; Walker, Raymond W.
    In the presence of O2, the decomposition of 2,2,3,3-tetramethylbutane (TMB) gives 98 % of isobutene in the temperature range 420–540°C through reactions (4) and (5). (CH3)3 CC(CH3)3= 2(CH3)3C (4). (CH3)3C + O2=(CH3)2C[double bond, length as m-dash]CH2+ HO2(5). Approximately 1 % of isobutane is also obtained, and the rate of isobutane formation at a given temperature is directly proportional to [TMB], and is independent of [O2], N2 addition, and vessel diameter. It is shown that these results require the molecular reaction (3). (CH3)3 CC(CH3)3=(CH3)3 CH +(CH3)2 C[double bond, length as m-dash]CH2(3). Studies over the range 420–540°C give log10(A3/s– 1)= 13.89 ± 0.10, E3= 275 ± 1.4 kJ mol– 1. The A factor is consistent with a four-centre transition state.