Abnormal solvent effects on hydrogen atom abstractions.: 1.: The reactions of phenols with 2,2-diphenyl-1-picrylhydrazyl (dpph•) in alcohols

Rate constants, k(ArOH/dpph.)(s), for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the dipheny picrylhydrazyl radical, dpph., have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents: Abnormally enhanced values of k(ArOH/dpph.)(s) have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph.. The popular assessment of the antioxidant activities of phenols with dpph. in alcohol solvents will generally lead to an overestimation of their activities.