Fluoride elimination upon reaction of pentafluoroaniline with e_aq¯,H, and OH radicals in aqueous solution

Abstract

Reduction of pentafluoroaniline (PFA) leads to rapid fluoride elimination to form the aminotetrafluorophenyl radical. This radical undergoes rapid intramolecular electron transfer from the amino group to the phenyl radical site and protonates at the latter site to form the tetrafluoroaniline radical cation or its deprotonated form (pK_a = 2.3). Oxidizing radicals such as SO₄^•-, N₃^•-, and Cl₂^•- oxidize PFA to the pentafluoroaniline radical cation. The pK_a = 1.9 of the pentafluoroaniline radical cation is 3.6 units lower than that expected from the substituent effects of fluorine atoms. Addition of OH to PFA is followed by rapid HF elimination to yield the aminotetrafluorophenoxyl radical. In acidic solution, however, the reaction of OH leads to formation of the pentafluoroaniline radical cation. Fluoride elimination upon reduction and upon OH addition to PFA was confirmed by determination of fluoride ion yield.