Electron-transfer oxidation of organic compounds with hexachloroantimonate [SbCl6]– ion

Abstract

Hexachloroantimonate [SbCl₆]^– salts of stable organic cations are shown to be active oxidising agents for aromatic amines, ferrocene, phenoxide ions, and iodide ion. Tetra-alkylammonium hexachloroantimonates oxidise Leuco Crystal Violet to Crystal Violet by apparent hydride-abstraction. Kinetic studies show that the reactions have very low activation-energies and an approximate value for the primary kinetic isotope effect k_CH/k_CD∼ 2·5. It is possible therefore that [SbCl₆]^– functions primarily as a one-electron oxidant. Complex chlorides of Sb^III are produced in the oxidations and new crystalline salts of [SbCl₄]^–, [Sb₂Cl₉]^3–, and the very unstable [SbCl₆]^3– have been characterised. Photolysis of [Me₂Ph(PhCH₂)N]⁺[SbCl₆]^– in tetrahydrofuran gives an apparent chain-reaction in which hydrogen chloride and [Me₂Ph(PhCH₂)N]⁺₃[Sb₂Cl₉]^3– are formed in very high yield.