Browsing by Author "Walsh, Robin"

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    Gas Phase Addition of HI to Ketene and the Kinetics of Decomposition of the Acetyl Radical
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Szirovicza, Lajos; Walsh, Robin
    The addition of HI to ketene results in the rapid formation of acetyl iodide at temperatures 498–525 K. The subsequent slower reaction between HI and acetyl iodide, which produces methane and acetaldehyde has been investigated at low conversions (<10 %), at various initial pressures at 507 K. Most experiments were done in the presence of the inert additives N2 or cyclo-C4F8. The results are shown to be consistent with the mechanism (M)+ CH3CO→CH3+ CO +(M)(5), CH3CO + HI→CH3CHO + I (3), CH3+ HI→CH4+ I. (6) The data at 507 K yield k∞5/k3=(2.4 ± 0.3)× 10–5 mol dm–3 and I/S= 65 ± 8 dm3 mol–1, where I and S refer to the intercept and slope of a Lindemann plot for the unimolecular step (5). An independent estimate of k3 is used in conjunction with theoretical calculations on the acetyl decomposition reaction to show that, log(k∞5/s–1)=(13.3 ± 0.5)–(91.2 ± 7.5 kJ mol–1)/2.303 RT. The limits cover all reasonable uncertainties, both experimental and theoretical. This result disposes of previous reports of a “low”A factor for this reaction.
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    Gas phase pyrolysis of cyclopropene. Part 1.—Kinetics and mechanism
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Bailey, Ivy M.; Walsh, Robin
    The vapour phase kinetics of pyrolysis of cyclopropene have been studied both by product formation and reactant loss relative to an internal standard in the temperature range 466–516 K. The major product is methylacetylene while the minor one is allene; there is evidence for some material loss under the conditions of these experiments (partial pressures of cyclopropene, ⩽ 2 Torr ‡ highly diluted in N2 or SF6). Under conditions of minimal material loss methylacetylene is formed by a homogeneous unimolecular reaction whose rate constant is dependent on total pressure. At (70 ± 2) Torr of SF6, which is close to the high pressure limit, the following Arrhenius equation is found log k/S–1=(13.09 ± 0.04)–(156.1 ± 0.4 kJ mol–1)/RTln 10. Allene appears to be formed by two pathways, one molecular the other radical in nature. A rate constant for the former has been measured. A unimolecular “fall-off” curve for methylacetylene formation has also been obtained which spans nearly five orders of magnitude in pressure and approaches closely both high and low pressure limiting behaviour (at 495 K). The significance of these results for the direct allene to methylacetylene isomerisation is discussed; for this purpose a table of thermodynamic properties of cyclopropene is also included.