Selective electrofluorination of phenylacetonitrile and α-(phenylthio)acetonitrile -: the role of sulfur and other operating parameters

Cyclic voltammetric and constant current electrolysis were employed to study the electrochemical fluorination of PhCH2CN and PhSCH2CN in Et3N . 3HF/CH3CN using Pt electrodes. The presence of a sulfur atom near the methylene group in PhSCH2CN ensures the oxidative fluorination of this compound at much lower potential (around 1.75 V) when compared to PhCH2CN (2.0 V in solvent-free Et3N . 3HF). Operating parameters such as drying the solvent, pre-electrolysis, polarity reversal, temperature, current density, and concentration of HF as well as Et3N in CH3CN medium show significant influence on the overall yield of more easily oxidisable PhSCH2CN when compared to PhCH2CN. Maximum yields of 23% in the case of PhCHFCN and 61% in the case of PhSCHFCN were achieved. (C) 1998 Elsevier Science S.A. All rights reserved.