Hydroxyacetone Production From C<sub>3</sub> Criegee Intermediates

Hydroxyacetone (CH<sub>3</sub>C­(O)­CH<sub>2</sub>OH) is observed as a stable end product from reactions of the (CH<sub>3</sub>)<sub>2</sub>COO Criegee intermediate, acetone oxide, in a flow tube coupled with multiplexed photoionization mass spectrometer detection. In the experiment, the isomers at <i>m</i>/<i>z</i> = 74 are distinguished by their different photoionization spectra and reaction times. Hydroxyacetone is observed as a persistent signal at longer reaction times at a higher photoionization threshold of ca. 9.7 eV than Criegee intermediate and definitively identified by comparison with the known photoionization spectrum. Complementary electronic structure calculations reveal multiple possible reaction pathways for hydroxyacetone formation, including unimolecular isomerization via hydrogen atom transfer and −OH group migration as well as self-reaction of Criegee intermediates. Varying the concentration of Criegee intermediates suggests contributions from both unimolecular and self-reaction pathways to hydroxyacetone. The hydroxyacetone end product can provide an effective, stable marker for the production of transient Criegee intermediates in future studies of alkene ozonolysis.