Environmental Science and Technology

Texto completo: acesso restrito. p.975–983Carbonyl products have been identified and their yields measured in experiments involving the gas-phase reaction of ozone with eight simple alkenes in purified air. Sufficient cyclohexane was added to scavenge the hydroxyl radical (OH) in order to minimize the reaction of OH with the alkenes and with their carbonyl products. Formation yields of primary carbonyls (carbonyl formed/ozone reacted) were 1.060 ± 0.071 (one standard deviation) for formaldehyde from ethylene, 1.150 ± 0.104 for acetaldehyde from 2-butene (ca. 40% cis and 60% trans isomers), 1.011 ± 0.049 for propanal from trans-3-hexene, 1.006 ± 0.049 for acetone from 2,3-dimethyl-2-butene, 0.980 ± 0.036 for formaldehyde + propanal from 1-butene, 0.987 ± 0.020 for acetaldehyde + acetone for 2-methyl-2-butene, 1.300 ± 0.030 for formaldehyde + acetaldehyde from propene, and 1.290 ± 0.103 for formaldehyde + acetone from 2-methylpropene. After correction for the estimated contribution of biradical reactions to formaldehyde, primary carbonyl yields were ca. 1.22 ± 0.03 for acetaldehyde + formaldehyde from propene and 1.08 ± 0.11 for acetone + formaldehyde from 2-methylpropene. These yields are consistent with the value of 1.0 for primary carbonyl yields according to the reaction mechanism: O3 + R1R2C = CR3R4 → α(R1COR2 + R3R4COO) + (1 − α)(R3COR4 + R1R2COO) which, for symmetrical alkenes, reduces to O3 + R1R2C = CR1R2 → one primary carbonyl (R1C(O)R2) + one biradical (R1R2COO). The results suggest modest preferential formation of the more substituted biradical for 1-butene (CH3CH2CHOO vs H2COO, α = 0.643 ± 0.039), 2-methyl-2-butene [(CH3)2COO vs CH3CHOO, α = 0.694 ± 0.024], 2-methylpropene [(CH3)2COO vs H2COO, estimated α = 0.68 ± 0.12], and perhaps propene (CH3CHOO vs H2COO, estimated α = 0.57 ± 0.03). Reaction of the biradicals resulted in the formation of carbonyls and of hydroxycarbonyls and/or dicarbonyls, which together accounted for ca. 0.25, 0.31, and 0.57 of the biradical reactions for CH3CHOO, CH3CH2CHOO, and (CH3)2COO, respectively. Carbonyls and hydroxycarbonyls and/or dicarbonyls from propene, 2-methylpropene, 1-butene, and 2-methyl-2-butene were consistent in nature and yields with those that form from the symmetrical alkenes that lead to the same biradicals