Ozonolysis of trans‐ and cis‐2‐butenes in low parts‐per‐million concentration ranges

Ozonolysis of 1–5 ppm concentrations of trans ‐ and cis ‐2‐C 4 H 8 was carried out in a 580 l spherical glass reaction vessel at 730 ± 5 torr and 296 ± 2 K. The yields of CH 3 CHO, HCHO, CO, CO 2 , CH 4 , and CH 3 OH were determined by long‐path FTIR spectroscopy. About 60% of C 4 H 8 that reacted with O 3 decomposed via the formation of the excited CH 3 CHO 2 * intermediates into the following pathways: (4a) CO 2 + CH 4 , (4b) CO 2 + H + CH 3 , (4c) CO + OH + CH 3 , and (4d) CO + CH 3 OH. The branching ratios for each channel, expressed as the percent of the total pathways, were determined for trans isomer: 20, 30, 40, and 10, and for cis isomer: 29, 35, 24, and 12, respectively. The conversion of C 4 H 8 relative to the reacted O 3 was about 1.6 and 1.4 for trans and cis isomers, respectively. These results were explained by the reactions of OH radicals formed in (4c) with C 4 H 8 , in which secondary OH radicals were generated: C 4 H 8 + OH + O 2 → CH 3 CH(OH)CH(CH 3 )OO, followed by CH 3 ‐CH(OH)‐CH(CH 3 )OO → 2 CH 3 CHO + OH. About 40% of C 4 H 8 that reacted with O 3 yielded a mixture of a carbonyl and a noncarbonyl product, assigned as hydroxyethyl formate, CH 3 CH(OH)OCHO, and secondary butene ozonide, respectively. The addition of HCHO increased the formation of the former while the latter was unaffected. These results were consistent with the mechanism proposed by Cremer et al. [ Chem. Phys. Lett. , 187, 491 (1991)], where the primary ozonide rearranges, before dissociation, to the carbonyl oxide‐aldehyde complex (the dipole complex) which is the precursor of the secondary ozonide.