Outer-sphere and inner-sphere processes in organic chemistry. Reaction of trifluoromethyl bromide with electrochemically generated aromatic anion radicals and sulfur dioxide anion radicals

Article abstract of DOI:10.1021/ja00158a044

The reduction of CF₃Br by electrochemically generated aromatic anion radicals gives rise to purely catalytic currents. An activation-driving force relationship characterizing outer-sphere electron donors can thus be established. Electrochemically generated sulfur dioxide anion radicals do not give rise to catalytic currents upon reaction with CF₃Br but rather produce trifluoromethyl sulfinate according to an overall two electron per molecule stoichiometry. The rate constant of the rate-determining step of the reaction is at least 4 orders of magnitude larger than that of an aromatic anion radical of the same standard potential, unambiguously showing that SO₂(·-) does not react as an outer-sphere electron donor. Among the various possible inner-sphere processes, bromine atom abstraction appears as the most likely.