Browsing by Author "Dixon, David J."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Low Temperature Gas-phase Oxidation of Aldehydes: Part 1.—The Reaction Below 120°C
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Dixon, David J.; Skirrow, Geoffrey; Tipper, Charles F. H.
    The gas-phase oxidation of acetaldehyde, propionaldehyde and the butyraldehydes, in an unpacked and a packed vessel between 45 and 120°C, has been studied using a static system with a very small dead volume. Contrary to earlier reports, below 70–80°C with very high aldehyde/oxygen ratios the final pressure decreases were not greater than, but agreed very closely with, the overall stoichiometry RCHO + O2→RCO3H. The variation of pressure with time agreed with that deduced from the usual autocatalytic chain mechanism 2 and confirmed, in particular, that the initiation process is first order with respect to both aldehyde and oxygen, that the addition of oxygen to CH3CO radicals is second order and that the branching process is first order with respect to both peracid and aldehyde. The variation of the second order rate coefficients with temperature and surface/volume ratio indicated that both initiation and branching are heterogeneous. However, the addition process is homogeneous, the rate coefficient being about 1.2 × 107 dm3 mol–1 s–1 between 62.5 and 83.5°C. Analyses of the minor products (CO, CO2, H2O, CH4, C2H6, CH2O, CH3OH, CH3COCH3, CH3COCOCH3) of the acetaldehyde oxidation and of the peracetic acid/acetaldehyde interaction after the oxygen was used up has given information on the chemical nature of the elementary steps occurring in initiation and branching.
  • No Thumbnail Available
    Item
    Low Temperature Gas-phase Oxidation of Aldehydes: Part 2.—Retardation by Formaldehyde above 120°C
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Dixon, David J.; Skirrow, Geoffrey; Tipper, Charles F. H.
    The effect of added formaldehyde on the oxidation of acetaldehyde and propionaldehyde between 119 and 188°C has been studied using a static system. Formaldehyde retards the oxidation, and at 188°C the rate after 25 % consumption of CH3CHO(ρ0.25) is linearly related to the reciprocal of the initial concentration of CH2O(Fi). However, at 119°C ρ0.25 decreases to a minimum and then increases as Fi is increased. The change in formaldehyde concentration during retarded oxidations showed that CH3CHO and CH2O are both removed mainly by reaction with peracetyl radicals, CH3CO3+ CH3CHO→CH3CO3H + CH3CO (3), CH3CO3+ HCHO→CH3CO3H + HCO (7)k7/k3 being about 2.4 at 119 and 188°C. Only about one in seven of the formyl radicals give carbon monoxide at 119°C. The kinetic and analytical data are explained on the basis of the mechanism given in Part 1 with the addition of reaction (7). It is suggested that some performic acid is formed at 119°C and causes extra branching by reaction with acetaldehyde.