Spin Trapping of Phosphorus-Centered Radicals Produced by the Reactions of Dibenzoyl Peroxide with Organophosphorus Compounds

The reactions of dibenzoyl peroxide (BPO) with organophosphorus compounds have been studied by means of an ESR technique combined with spin trapping. The intermediate phosphorus-centered radicals were trapped by N-benzylidene-t-butylamine N-oxide (PBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The spin adducts with a characteristic hyperfine coupling constant (hfcc) due to a phosphorus atom were observed. From identification of trapped radicals, possible mechanisms of the reactions have been proposed. The hfccs due to β-hydrogen and phosphorus atoms exhibited a large temperature dependence for phosphoranyl–PBN spin adducts, while for phosphinyl–PBN spin adduct the dependence was small. Based on the P and H hfccs, the conformational positions of the adducts trapped by PBN and DMPO are discussed.