MOLECULAR REARRANGEMENTS IN THE REACTIONS OF OXYGEN ATOMS WITH OLEFINS

Abstract

Reactions of oxygen atoms with propylene, butene-1, iso-butene, cis-butene-2, trans-butene-2, cis-pentene-2, and tetramethyl ethylene have been studied at room temperature and at pressures between 50 and 600 mm. The following generalizations can be made. The oxygen atom adds predominantly to the "less-substituted" carbon atom of the olefinic double bond to form a short-lived biradical which rapidly rearranges into isomeric epoxy and carbonyl compounds. Rearrangements involve migration of radicals (including H atoms) from the carbon atom to which oxygen is attached to the other carbon atom of the original double bond. Partly inhibited rotation around the original double bond also takes place. Migration of H atoms is exclusively internal. Migration of larger radicals, such as CH₃, is only partly internal: a large fraction of these radicals become completely detached from the rest of the molecule and the particular carbonyl compound is produced both by radical combination and by internal migration. The fragmentation resulting from the splitting off of a migrating radical is pressure independent. The final addition products formed are "hot" as a result of high heats of reaction and undergo decomposition if the excess energy is not removed by collisions. This second type of fragmentation is, therefore, pressure dependent. It is very extensive in the case of ethylene and appears to be completely suppressed in the investigated pressure range in the case of more complex olefins (possessing a greater number of degrees of freedom) such as butenes and higher homologues. Propylene exhibits an intermediate behavior. For orientation of addition of oxygen atoms a carbon atom of an olefinic double bond to which CH₃ is attached is "less substituted" than a corresponding carbon atom to which C₂H₅ is attached.