Hexachlororhodate(III) and the photocatalytic decomposition of chloroform

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Broadband (λ > 320 nm) irradiation of solutions of (Bu4N)3RhCl6 in CHCl3 exposed to air causes chloroform decomposition, with the production of HCl and substances, including phosgene and peroxides, capable of oxidizing iodide ion, and lesser amounts of CCl4 and C2Cl6. There is a short induction period as RhCl63− is replaced by an unknown rhodium species, the spectrum of which is stable after 15 or 20 min. The rate of photodecomposition is reduced by the addition of chloride ion, and it ceases nearly completely in deoxygenated solutions or in CDCl3. Mechanistic possibilities in keeping with these observations include hydrogen atom transfer from chloroform during the primary photochemical step and a prior equilibrium involving chloride ion dissociation. A rhodium hydroperoxide offers one possible explanation for the required participation of O2.