Low Temperature Gas-phase Oxidation of Aldehydes: Part 2.—Retardation by Formaldehyde above 120°C

Abstract

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.