Browsing by Author "Walker, Raymond W."

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Addition of i-Butane to Slowly Reacting Mixtures of Hydrogen and Oxygen at 480°C
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Baker, Richard R.; Baldwin, Roy R.; Walker, Raymond W.
Analysis has been made of the products formed when small amounts of i-C4H10 and i-C4H8 are added to slowly reacting mixtures of H2+ O2 at 480°C. The variation of [C3H6]/[C4H8] with [O2], with i-C4H10 as additive, gives the rate constant ratio k25i/k27i, from which k25i= 6.8 × 107 dm3 mol–1 s–1 with a possible error of 50 % due to uncertainty in the value of k27i. Combination with a low temperature measurement gives A25i= 6.9 × 109 dm3 mol–1 s–1 and E25i= 29.1 kJ mol–1. i-C4H9+ O2= i-C4H8+ HO2(25i), i-C4H9= C3H6+ CH3(27i), The rate constant for the 1, 4t and 1, 5p H atom transfers involved in reactions (34t) and (34p) have been obtained and compared with values estimated previously for similar isomerisations. CH3CH(CH3)CH2O2= CH3C(CH3)(CH2OOH)(34t), CH3CH(CH3)CH2O2= CH3CH(CH2OOH)CH2(34p), The rate constant ratio k34t/k34p= 4.1 at 480°C is accurate to ± 10 %, but the absolute values of k34t and k34p are dependent on thermochemical data and on the rather uncertain value of k27i. Further evidence is obtained for the importance of the reaction of alkylhydroperoxide radicals (QOOH) with O2, and rate constants for a number of elementary reactions involving QOOH radicals are given. The rate constant for the addition of OH radicals to i-C4H8 has been estimated as 2.9 × 1010 dm3 mol–1 s–1.
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)
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.
Oxidation of Formaldehyde in KCl-coated Vessels
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (07), 1974) Baldwin, Roy R.; Fuller, Alan R.; Longthorn, David; Walker, Raymond W.
In the temperature range 440-540’C, the oxidation of HCHO in KCl-coated vessels is reproducible and of short chain length for HCHO concentrations in the range 0.05-4 Torr. Interpretation of the [CO] against time profile permits evaluation of the unknown parameters A'i, k7jk^ and ka. HCHO + O2->HO2 + HCO HO2 + HO2->H2O2 + O2 surface HO2---->4H2O + JO2 surface H2o2—>H2O + 4O2. (1) (4) (7) (8) Comparison of the experimental values for k7/kf and ka with those calculated from diffusion theory indicates that the destruction of HO2 at the surface is fully diffusion controlled, whereas the destruc tion of H2O2, though moderately efficient, is not fully diffusion controlled. From measurements at HCHO concentrations below 0.5 Torr, where the chain length is close to unity, effectively direct measurements of ki have been obtained, the values being 7.65 x 10~’, 2.08 x 10-1, 8.50 x IO-2 and 2.20x 1CF2 dm3 moF* s_1 at 542.5, 500, 471 and 440.5°C, respectively. These values give the Arrhenius parameters At = 2.04x 1010 dm3 moF1 s~l, £\ = 38.9 ± 1.5 kcal moF1. The absence of any diameter effect on the value of k, confirms that the parameters refer to the homogeneous pro cess.
Reaction of n-propyl radicals with oxygen, hydrogen and deuterium
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (4), 1973) Baldwin, Roy R.; Walker, Raymond W.; Yorke, David A.
n-C3H7 radicals have been produced by the oxidation of n-C3H7CHO at 450°C. By measuring the relative yield of C3H6 and C3H8, a value for the ratio k4/k1= 0.040 ± 0.005 has been obtained. A value of k4 can be obtained, based on the value of 2.9 × 1010 l. mol–1 s–1 assumed for the combination of two C3H7 radicals, which gives k1= 3.1 × 107 at 450°C. By measuring the increased yield of C3H8(or C3H7D) in the presence of H2(or D2), the ratios k1/k2= 347 ± 10, k2/k3= 2.3 ± 0.2 at 450°C are obtained. n-C3H7+ O2→ C3H6+ HO2(1), n-C3H7+ H2→ C3H8+ H (2), n-C3H7+ D2→ C3H7D + D (3), n-C3H7+ C3H7CHO → C3H8+ C3H7CO. (4) The value for k2/k3 suggests that E3–E2= 0.7 kcal mol–1 which indicates a lowering of the zero-point energy in the transition state by about 1.1 kcal mol–1 when H2 is replaced by D2. Using entropy data, and the Arrhenius parameters for reaction (– 2), A2= 2.6 × 109 and E2= 14.8 kcal mol–1.