Organothallium Compounds. XV. Thallation of Polyfluoroaromatic Compounds

Abstract

Thallic trifluoromethanesulfonate has been prepared by reaction of trifluoromethanesulfonic acid with either thallic oxide or solutions of thallic trifluoroacetate in trifluoroacetic acid, and has been isolated as the trihydrate on crystallization fromnitromethane. The polyfluoroarenes,p-CH₃OC₆F₄H, p-CH₃C₆F₄H, m-H₂C₆F₄, o-H₂C₆F₄, p-H₂C₆F₄, C₆F₅H, 1,3,5-F₃C₆H₃ or 1,2,4-F₃C₆H₃, have been thallated by thallic trifluoromethanesulfonate in trifluoroacetic acid, giving the corresponding poly- fluorophenylthallium(III) bis(trifluoromethanesulfonates), which have been characterized spectroscopically and by conversion into the corresponding (polyfluoro)iodobenzenes on treatment with sodium iodide. Only slight thallation of m-BrC₆F₄H and m-O₂NC₆F₄H was observed. By contrast with thallic trifluoromethanesulfonate, thallic trifluoroacetate in trifluoroacetic acid induced little thallation of the most reactive polyfluorobenzene, p-CH₃OC₆F₄H. Thallic trifluoromethanesulfonate also thallated p-CH₃OC₆F₄H in nitromethane, sulfolane, and with the substrate as solvent, but p-CH₃C₆F₄H failed to react. Treatment of the polyfluorophenylthallium(III) bis(trifluoromethane- sulfonates) with boiling aqueous sodium acetate caused symmetrization into the corresponding acetatobis(polyfluorophenyl)thallium(III) compounds. A similar reaction between 2,4,6-trifluoro- phenylthallium(III) bis(trifluoromethanesulfonate) and sodium acetate at room temperature yielded 2,4,6-trifluorophenylthallium(III) diacetate. 2,3,4,6-Tetrafluorophenylthallium(III) bis(trifluor0- methanesulfonate) was converted by boiling water into bis(2,3,4,6-tetrafluorophenyl)thallium(III) trifluoromethanesulfonate.