Photochemistry of Diaryliodonium Salts

Abstract

The photochemistry of diphenyl- and bis(4-methylphenyl)iodonium salts was investigated by product analysis, measurement of acid, and determination of the consumption of the iodonium salts. The primary products formed upon direct and triplet-sensitized irradiation of diphenyliodonium salts are iodobenzene, 2-, 3-, and 4-iodobiphenyl, acetanilide, benzene, and acid. Similarly, iodotoluene, iodobitolyls, 4-methylacetanilide, toluene, and acid are formed from photolysis of bis(4-methylphenyl)iodonium salts. The photolysis products are formed by heterolysis of the diaryliodonium salt to phenyl cation and iodobenzene and also by homolysis to phenyl radical and iodobenzene radical cation. Direct photolysis favors product formation by the heterolytic cleavage pathway, whereas triplet sensitization gives more products from homolytic cleavage. Interconversion between phenyl cation pair and the phenyl radical pair can occur by an electron transfer. Sensitized photodecomposition of the iodonium salt by anthracene gives iodoarene and arylated anthracenes by an electron-transfer mechanism. Electron-transfer quenching and triplet quenching by the iodonium salt are competitive reactions for some sensitizers. The similarities and differences between diaryliodonium and triarylsulfonium photochemistry will be described. © 1990, American Chemical Society. All rights reserved.