Electrochemical radiofluorination. Part 2. Anodic monofluorination of substituted benzenes using [18F]fluoride

Electrochemical fluorination of various monosubstituted aromatic compounds was performed with [18F]fluoride using potentiostatic anodic oxidation on platinum electrodes in an undivided cell in acetonitrile with a mixture of Et3N·3HF/Et3N·HCl as electrolyte. Maximum radiochemical yields were obtained after a charge of 50 C passed the solution. The results showed a clear dependence of the radiochemical yields on the oxidation potentials E1/2 of the substrates as a consequence of different substituents namely CH3CO-, F-, Cl-, Br- and tert.-Butyl. With increasing E1/2, the fluorination yields decreased from 7.9% (tert.-butylbenzene) to 1.5% (acetophenone). The ratio between F-for-X substitution and F-for-H substitution correlated with the bond energies of the C–X bond. With higher bond energies, less X-substitution was observed.