Directing effects of phenyl substitution in the reaction of OH radical with aromatics: The radiolytic hydroxylation of biphenyl

The initial yields for formation of 2-, 3- and 4- hydroxybiphenyl following the radiolytic oxidation of biphenyl in the presence of ferricyanide are, respectively, 2.19, 1.13 and 1.55 molecules/100eV. These yields reflect relative rates of 0.71:0.37:1 for [sup [sm bullet]]OH radical attack on each of the ortho, meta, and para positions of biphenyl. Comparison of the corresponding partial rate constants to that for benzene shows that phenyl substitution has a significant effect in directing [sup [sm bullet]]OH addition to the ortho and para positions of aromatic systems. Comparison with phenol shows that a phenyl substitution has only a slightly smaller effect than does OH in increasing the partial rate constant at the ortho and para positions but is substantially less effective in decreasing the rate of [sup [sm bullet]]OH reaction at the meta position. 15 refs., 9 figs.