Mechanism of the reaction of OH radicals with acetone and acetaldehyde at 251 and 296 K

Photoreactors combined with FTIR analysis techniques were used to investigate the formation of acids in the reactions of OH radicals with acetone and acetaldehyde in one atmosphere of air at 296 K and 251 K. In contrast to two recent reports, we find no evidence for direct formation of either formic acid or acetic acid (<10% yield of acids in both reactions). We conclude that under atmospheric conditions the reaction of OH radicals with acetone and acetaldehyde proceeds predominantly (>90%), if not exclusively, via H-atom abstraction. In atmospheric chemistry models we recommend use of OH + CH₃C(O)CH₃ → CH₃C(O)CH₂ + H₂O and OH + CH₃CHO → CH₃C(O) + H₂O to describe the mechanism of the title reactions. Curvature in the Arrhenius plots for these reactions is most likely due to formation of a pre-reaction complex rather than a change in mechanism from carbonyl addition to abstraction.