ATMOSPHERIC CHEMISTRY OF OLEFINS - A PRODUCT STUDY OF THE OZONE ALKENE REACTION WITH CYCLOHEXANE ADDED TO SCAVENGE OH

Carbonyl and carboxylic acid products of the ozone-olefin reaction, in which the hydroxyl radical is produced, have been identified and measured for eight alkenes in the presence of excess cyclohexane, i.e., under conditions that minimize subsequent reactions of OH with the alkenes and with their carbonyl products. The carbonyls expected to form directly, i.e., alkene + ozone --> 1,2,3-trioxolane adduct --> two carbonyls + two Criegee biradicals, were observed as major products (e.g., formaldehyde and 2-butanone from 2-methyl-1-butene). Their yields ranged from 9 +/- 2% for 1,3-butadiene to 88 +/- 4% for 2,3-dimethyl-2-butene. For alkenes that lead to two Criegee biradicals, carbonyl yields were consistent with preferential formation of the more substituted biradical. Criegee biradical decomposition to hydroxycarbonyl and/or dicarbonyl products (yields 20-52%) was observed in all cases. Unimolecular decomposition of Criegee biradicals was also observed, yielding formaldehyde (5-12%) from methyl-substituted biradicals and acetaldehyde (15-39%) from ethyl-substituted biradicals. Carboxylic acid yields were 8-10% for acetic acid (from trans-2-butene and 2-methyl-2-butene) and 13-17% for formic acid (from isobutene, 1-butene, 2-methyl-1-butene, and 1,3-butadiene).