Halogen cations such as I⁺ and Br⁺ are highly unstable species, although some of them are identified in the gas phase. The electrochemical oxidation provides a powerful method for generating and accumulating highly reactive cationic species in the solution, whereas the chemical methods are not effective because of reversibility of cation generation. We have already reported that some carbocations and onium ions can be generated and accumulated as cation pools at low temperatures (the “cation pool” method). However, halogen cations are very difficult to accumulate in the solution as “cation pools” because they are too unstable.

We envisioned that the use of a stabilizing agent that coordinates the cation being generated would solve the problem. Coordination of a neutral molecule gives a positively charged species and coordination of an anionic species gives a neutral species, although the halogen is the +1 oxidation state in both cases. Some stabilizing agents have already been reported. For example, Miller and co-workers reported the generation and accumulation of “I⁺” cation in acetonitrile (CH₃CN), and later we reported the detection of CH₃CN−I⁺ and (CH₃CN)₂I⁺ by cold-spray-ionization mass spectroscopy. Shono and co-workers reported that “I⁺” could be accumulated in trimethyl orthoformate (TMOF).

In this paper we report that dimethyl sulfoxide (DMSO) serves as a neutral stabilizing agent and that TfO⁻ anion serves as a negatively charged stabilizing agent in the electrochemical generation and accumulation of halogen cations such as I⁺ and Br⁺.  We also report their reactions with organic molecules to give the corresponding halogen-containing products, which serve as useful transformations in organic synthesis.