CARBONYL PRODUCTS OF THE GAS-PHASE REACTION OF OZONE WITH SIMPLE ALKENES

Carbonyl products have been identified and their yields measured in ex periments involving the gasphase reaction of ozone with eight simple a lkenes in purified air. Sufficient cyclohexane was added to scavenge t he hydroxyl radical (OH) in order to minimize the reaction of OH with the alkenes and with their carbonyl products. Formation yields of prim ary carbonyls (carbonyl formed/ozone reacted) were 1.060 +/- 0.071 (on e 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 ac etone from 2,3-dimethyl-2-butene, 0.980 +/- 0.036 for formaldehyde + p ropanal from 1-butene, 0.987 +/- 0.020 for acetaldehyde + acetone for 2-methyl-2-butene, 1.300 +/- 0.030 for formaldehyde + acetaldehyde fro m propene, and 1.290 +/- 0.103 for formaldehyde + acetone from 2-methy lpropene. 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 fo r acetone + formaldehyde from 2-methylpropene. These yields are consis tent with the value of 1.0 for primary carbonyl yields according to th e reaction mechanism: O-3 + R(1)R(2)C = CR(3)R(4) --> alpha(R(1)-COR(2 ) + R(3)R(4)COO) + (1 - alpha)(R(3)COR(4) + R(1)R(2)COO) which, for sy mmetrical alkenes, reduces to O-3 + R(1)R(2)C = CR(1)R(2) --> one prim ary carbonyl (R(1)C(O)R(2)) + one biradical(R(1)R(2)COO). The results suggest modest preferential formation of the more substituted biradica l far 1-butene (CH3CH2CHOO vs H2COO, alpha = 0.643 +/- 0.039), 2-methy l-2-butene [(CH3)(2)COO vs CH3CHOO, alpha = 0.694 +/- 0.024], 2-methyl propene [(CH3)(2)COO vs H-2-COO, estimated alpha = 0.68 +/- 0.12], and perhaps propene (CH3CHOO vs H2COO, estimated alpha = 0.57 +/- 0.03). Reaction of the biradicals resulted in the formation of carbonyls and of hydroxycarbonyls and/or dicarbonyls, which together accounted for c a. 0.25, 0.31, and 0.57 of the biradical reactions for CH3CHOO, CH3CH2 -CHOO, and (CH3)(2)COO, respectively. Carbonyls and hydroxycarbonyls a nd/or dicarbonyls from propene, 2-methylpropene, 1-butene, and 2-methy l-2-butene were consistent in nature and yields with those that form f rom the symmetrical alkenes that lead to the same biradicals.