OZONOLYSIS OF TRANS-2-BUTENES AND CIS-2-BUTENES IN LOW PARTS-PER-MILLION CONCENTRATION RANGES

Ozonolysis of 1-5 ppm concentrations of trans- and cis-2-C4H8 was carr ied out in a 580 l spherical glass reaction vessel at 730 +/- 5 torr a nd 296 +/- 2 K. The yields of CH3CHO, HCHO, CO, CO2, CH4, and CH3OH we re determined by long-path FTIR spectroscopy. About 60% of C4H8 that r eacted with O3 decomposed via the formation of the excited CH3CHO2 in termediates into the following pathways: (4a) CO2 + CH4, (4b) CO2 + H + CH3, (4c) CO + OH + CH3, and (4d) CO + CH3OH. The branching ratios f or each channel, expressed as the percent of the total pathways, were determined for trans isomer: 20, 30, 40, and 10, and for cis isomer: 2 9, 35, 24, and 12, respectively. The conversion of C4H8 relative to th e reacted O3 was about 1.6 and 1.4 for trans and cis isomers, respecti vely. These results were explained by the reactions of OH radicals for med in (4c) with C4H8, in which secondary OH radicals were generated: C4H8 + OH + O2 --> CH3-CH(OH)-CH(CH3)OO, followed by CH3-CH(OH)-CH(CH3 )OO --> 2 CH3CHO + OH. About 40% of C4H8 that reacted with O3 yielded a mixture of a carbonyl and a noncarbonyl product, assigned as hydroxy ethyl formate, CH3CH(OH)-O-CHO, and secondary butene ozonide, respecti vely. The addition of HCHO increased the formation of the former while the latter was unaffected. These results were consistent with the mec hanism proposed by Cremer et al. [Chem. Phys. Lett., 187, 491 (1991)], where the primary ozonide rearranges, before dissociation, to the car bonyl oxide-aldehyde complex (the dipole complex) which is the precurs or of the secondary ozonide. (C) 1994 John Wiley & Sons, Inc.