Photoreduction of Triplet Thioxanthone by Amines: Charge Transfer Generates Radicals That Initiate Polymerization of Olefins

Article abstract of DOI:10.1021/jo00192a019

Thioxanthone triplet is photoreduced by amines via a charge-transfer or exciplex intermediate to thioxanthyl ketyl radical.This ion pair can be observed by nanosecond laser spectroscopy in polar solvents with easily oxidized dimethylaniline as reductant.The intermediacy of this species in benzene was indicated by the correlation of triplet quenching rates with amine ionization potential and by the absence of a significant isotope effect in triplet quenching by tert-butylamine-d2.In contrast, tri-n-butylstannane reacts more rapidly than its ionization potential would dictate and exhibits a larger isotope effect.Addition of methyl methacrylate does not significantly alter the rates of decay for the ion pair of ketyl radikal.Product studies show that the aminomethyl radical PhN(CH3)CH2* is the principal initiator of olefin polymerization.