A Mass-spectrometric study of propionaldehyde oxidation in the negative temperature coefficient region

The oxidation of propionaldehyde has been investigated in a 1-L Pyrex reactor at total pressures of 50–120 torr and temperatures 553–713 K. Detection of reactants and products was principally by molecular beam mass spectrometry, although certain species could only be measured by gas-chromatographic analysis. At 553 K the yield of water was ～83% of the propionaldehyde consumed, leading to the conclusion that OH is the principal chain carrier near the beginning of the negative temperature coefficient region. Many oxygenated organics (CH₂O, CH₃CHO, C₂H₅OH, C₂H₅O₂H, CH₃O₂H) and C₂H₄ are formed during the oxidation process. These oxidation products are consistent with the important role of O₂ addition to C₂H₅ radicals at 553 K followed by subsequent reactions of the C₂H₅O₂ radical. As the temperature is increased, the product concentrations smoothly change to a much simpler distribution in which C₂H₄, H₂O₂, and CO are the dominant products.