The [CO2] [CO] ratios in the oxidation of propionaldehyde in aged boric-acid-coated vessels have been measured at 440°C as a function of reactant consumption and mixture composition. The results indicate that reaction (15) is not the sole source of CO2, and that surface formation makes a major contribution, particularly at low values of [O2] [M]. This is confirmed by variation of the surface volume ratio. The surface reaction appears to be approximately first-order in propionaldehyde, and half-order in O2, with a rate constant of 6.3 × 10-3 (litre mole-1) 1 2 sec-1. From the [CO2] [CO] ratios and [CO], time profile, values of k1 = 0.081 ± 0.015 litre mole-1 sec-1, ( k4 k5 1 2) = 34 ± 3 (litre mole-1 sec-1) 1 2 and ( k15 k2) = 0.112 ± 0.010 (M = N2) are obtained. With k5 = 2 × 109 litre mole-1 sec-1, k4 = 1.52 × 106 litre mole-1 sec-1. (1)C2H5CHO + O2 = C2H5CO + HO2(2)C2H5CO + M = C2H5 + CO + M(4)HO2 + C2H5CHO = C2H5CO + H2O2(5)HO2 + HO2 = H2O2 + O2(15)C2H5CO + O2 = C2H4 + CO2 + OH. © 1979.
