Peroxy radical reactions in the photo-oxidation of CH3CHO

Abstract

The behaviour of reactants, products and radical intermediates during the photo-oxidation of acetaldehyde at room temperature and 700 Torr pressure has been studied using a novel apparatus. The apparatus consists of a ‘double multi-path’ spectrometer, combining both i.r. and u.v. absorption spectrometry with the additional capability of modulated photolysis for transient detection. Photo-oxidation of CH3CHO gave CO, CO2, H2O, CH2O, HCOOH, CH3OH, CH3OOH, CH3COOH and CH3COOOH as identifiable products by long-path F.t.i.r. spectrometry. The effect of variation of the O2 and CH3CHO concentration upon the different photolysis products was studied, and computer simulation of experimental data was used to test a proposed mechanism containing 50 elementary reactions. Absorption vs. time profiles at selected wavelengths in the 210–275 nm region were recorded in the modulated photolysis of CH3CHO–air mixtures. Transient absorptions were assigned to peroxy radicals, and kinetic analysis of the data assisted by computer simulation resulted in a value k10= 4.8 × 10–12 cm3 molecule–1s–1for the reaction HO2+ CH3O2→ products. This value is somewhat higher than the value k10a= 3.5 × 10–12 cm3 molecule–1s–1 for the reaction HO2+ CH3O2→ CH3OOH + O2 obtained from the computer simulations of the methyl hydroperoxide formation, indicating that an additional product channel may occur.