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(F_i). However, at 119°C _ρ0.25 decreases to a minimum and then increases as F_i 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.