Chemistry of alkoxy radicals from oxygenated solvents

Oxygenated organic compounds (ethers, esters, and ketones) are increasingly being used as replacements for hydrocarbons as solvents and fuel additives. The reaction pathways of alkoxy radical intermediates in the degradation of organic compounds may have a substantial effect on the extent of formation of ozone in polluted air, so alkoxy radicals constitute a critical branching point in VOC degradation. The fate of alkoxy radicals created in the degradation of oxygenated organic compounds was studied using computational chemistry. Three pairs of primary alkoxy radicals were considered, one pair derived from each of butanone, methyl ethyl ether, and methyl acetate. The results for these reactions were compared to the results for the decomposition and isomerization of 1-butoxy. Of all the oxygenated alkoxy radicals studied, only for CH₃OCH₂CH₂O• does isomerization out-compete O₂ reaction; however, decomposition might not be negligible. The only species for which decomposition was predicted to dominate was CH₃CH₂C(=O)CH₂O•. The computed activation barrier implied a rate constant of 10¹⁰/sec, which was five orders of magnitude faster than the expected rate of the O₂ reaction. None of the other alkoxy radicals studied had a barrier to decomposition sufficiently low to make decomposition faster than O₂ reaction. Isomerization might be non-negligible for CH₃CH₂C(=O)CH₂O•. This is an abstract of a paper originally presented at the 225th ACS National Meeting (New Orleans, LA 3/23-27/2003).