Determination of the singlet oxygen (even singlet delta oxygen) yields from self-reaction of alkylperoxyl radicals

Yields of singlet molecular oxygen ({dollar}rm sp1Deltasb gOsb2{dollar}) from self-reaction of alkylperoxyl radicals (Eq. A) were determined by the characteristic IR emission of {dollar}sp1{dollar}O{dollar}sb2{dollar} at 1270 nm and calibration system based on the {dollar}sp1{dollar}O{dollar}sb2{dollar} yield of 1,4-dimethylnaphthalene-1,4-endoperoxide thermodissociation. The peroxyl radicals were generated continuously from different oxygen-saturated solvents by free radical initiation with di-tert-butyl hyponitrite or directly from the hydroperoxides and initiator.{dollar}{dollar}rm 2Rsb1Rsb2CHOOspcdotto Rsb1Rsb2CO + Rsb1Rsb2CHOH + Osb2 (sp1Deltasb{lcub}g{rcub}, sp3Sigmasb g)eqno{lcub}rm(A){rcub}{dollar}{dollar}; Under the conditions studied, singlet oxygen constituted a minor product, being only 3.4 to 14.0% of the amount predicted by reaction A. The structural effects on the yields of singlet oxygen suggest that alkylperoxyl radical terminations follow the original Russell scheme and give largely {dollar}sp1Sigmasb{lcub}rm g{rcub}{dollar} state of molecular oxygen which partitions between {dollar}sp1{dollar}O{dollar}sb2(sp1Deltasb{lcub}rm g{rcub}{dollar}) and {dollar}sp3{dollar}O{dollar}sb2{dollar}.; Ceric ion oxidation of hydroperoxides at {dollar}-{dollar}78{dollar}spcirc{dollar}C gave immediate IR emission of {dollar}sp1{dollar}O{dollar}sb2{dollar}, thus ruling out a mechanism involving singlet oxygen formation from an intermediate ROOOH which is stable at that temperature. The IR emission from {dollar}sp1{dollar}O{dollar}sb2(sp1Deltasb{lcub}rm g{rcub}{dollar}) may offer an advantage over visible chemiluminescence as an attractive analytical tool for studying autoxidation reactions. However, the low yields of singlet oxygen from reaction A will limit the general use of this method for oxygenation purposes.