Untersuchungen zur Photolyse von Diaryliodoniumsalzen

Investigations on Photolysis of Diaryliodonium Salts The photolysis of diaryliodonium salts in solution leads to various competitive and consecutive reactions. Upon irradiation, the excited state desactivates mainly through homolytic cleavage of the CI‐bond, but to a minor extent also through heterolytic cleavage of the same bond. Thus, several photolysis products have been obtained: aromatics, new iodonium salts, iodoaromatics, substitution products of the solvent, protonic acid in aqueous solutions, iodide and iodate ions and iodine. In the case of diphenyliodonium iodide the yields of iodine are higher compared to those of other salts because of electron transfer processes. The quantum yields of the disappearance of the iodonium salt (ΦI) and of the formation of protonic acids (ΦP) are equal within the experimental error. These values do not depend on the nature of the solvent, with the exception of H‐donor solvents, on the initial salt concentration and on oxygen. But, they depend strongly on the light intensity and on the substituent at the aromatic ring. The ΦP‐data also depend on the oxidation potential of the anion used. For diphenyliodonium chloride, the quantum yield of iodobenzene formation reaches only the half of the values for ΦI and ΦP. A kinetic scheme is given for the explanation of the light intensity dependence, which is based on 1. and 2. order reactions of intermediates formed by the homolytic pathway. It is assumed, that the electron transfer reaction by iodide salts proceeds only between the iodide ion and the intermediate products.