Reactivity of triarylphosphine peroxyl radical cations generated through the reaction of triarylphosphine radical cations with oxygen

One-electron oxidation of triarylphosphines (Ar3P, Ar = phenyl and substituted phenyl) in benzonitrile (PhCN) has been studied using pulse radiolysis technique. One-electron oxidation of Ar3P occurred to yield the radical cation (Ar3P center dot+) which showed an intense absorption with a peak at 360-370 nm together with a broad band at 500-600 nm. The addition of molecular oxygen (O-2) to the phosphorus atom of Ar3P center dot+ took place at the second-order rate constant of 10(7)-10(9) dm(3) mol(-1) s(-1) to yield the peroxyl triarylphosphinyl radical cation ((Ar3P+OO center dot)). It is found that the electron-releasing substituents on the para position of the phenyl ring of Ar3P influence the rate constants of the reaction of Ar3P center dot+ with O-2 and that o-methyl substituents on the phenyl ring influence the reactivity of (Ar3P+OO center dot).