Comparison of reactions of radical cations of 1-phenylalkanols produced by photoionization and by one-electron oxidation in aqueous solution

Abstract

Benzyl alcohols in aqueous solution react with photo- and radiation-chemically produced ˙OH and SO₄˙⁻ radicals with diffusion-controlled rates to yield OH-adducts and benzyl alcohol radical cations, respectively. The former can be converted to the radical cations by H⁺-induced (heterolytic) dehydroxylation, whereas the latter decay by a) electrophilic reaction with water (= reverse of the dehydroxylation reaction) giving rise to C_nucleus–OH-adducts and by b) side chain C–H deprotonation yielding α-hydroxybenzyl-type radicals. If, however, the radical cation is produced by biphotonic ionization of the benzyl alcohol, the pattern of C_nucleus–OH bond formation and side chain C–H bond breakage is different from that in the reaction with SO₄˙⁻. It is concluded that, at least in this reaction, it is not the free, solvated radical cation that reacts with water but the ion pair [radical cation–SO₄²⁻].