Reactions of stabilized Criegee intermediates from the gas-phase reactions of O3 with selected alkenes

The gas-phase reactions of O3 with 1-octene, trans-7-tetradecene, 1,2-dimethyl-1-cyclohexene, and α-pinene have been studied in the presence of an OH radical scavenger, primarily using in situ atmospheric pressure ionization tandem mass spectrometry (API-MS), to investigate the products formed from the reactions of the thermalized Criegee intermediates in the presence of water vapor and 2-butanol (1-octene and trans-7-tetradecene forming the same Criegee intermediate). With H3O+(H2O)n as the reagent ions, ion peaks at 149 u ([M + H]+) were observed in the API-MS analyses of the 1-octene and trans-7-tetradecene reactions, which show a neutral loss of 34 u (H2O2) and are attributed to the α-hydroxyhydroperoxide CH3(CH2)5CH(OH)OOH, which must therefore have a lifetime with respect to decomposition of tens of minutes or more. No evidence for the presence of α-hydroxyhydroperoxides was obtained in the 1,2-dimethyl-1-cyclohexene or α-pinene reactions, although the smaller yields of thermalized Criegee intermediates in these reactions makes observation of α-hydroxyhydroperoxides from these reactions less likely than from the 1-octene and trans-7-tetradecene reactions. Quantifications of 2,7-octanedione from the 1,2-dimethyl-1-cyclohexene reactions and of pinonaldehyde from the α-pinene reactions were made by gas chromatographic analyses during reactions with cyclohexane and with 2-butanol as the OH radical scavenger. The measured yields of 2,7-octanedione from 1,2-dimethyl-1-cyclohexene and of pinonaldehyde from α-pinene were 0.110 ± 0.020 and 0.164 ± 0.029, respectively, and were independent of the OH radical scavenger used. Reaction mechanisms are presented and discussed. © 2001 Wiley Periodicals, Inc. Int J Chem Kinet 34: 73–85, 2002