Scavenging of acetylperoxyl radicals and quenching of triplet diacetyl by β-carotene: mechanisms and kinetics

β-Carotene scavenges triplet diacetyl generated by laser flash photolysis with a second-order rate constant of 9.1±0.9×109 M−1 s−1 in deaerated benzene at 20°C. In the presence of oxygen diacetyl dissociates to generate acetylperoxyl radicals. It is demonstrated that diacetyl does not dissociate to any appreciable extent in the absence of oxygen. The acetylperoxyl radical is scavenged by β-carotene with second-order rate constant 9.2±0.6×108 M−1 s−1 in aerated benzene at 20°C to give an adduct between the acetylperoxyl radical and β-carotene, whereas no evidence of oxidation of β-carotene by the strongly oxidizing acetylperoxyl radical to give the β-carotene radical cation is found. This adduct decays with first-order rate constant 1.35±0.16×103 s−1 to give (presumably) a β-carotene epoxide and the acetyloxyl radical.