Kinetic studies on the reaction of decafluorobiphenyl and di- and tetra(phenylthio)-substituted perfluorobiphenyl with thiophenol in the presence of triethylamine were performed by in situ 19F NMR spectroscopy to determine rate constants. In well-defined consecutive reactions, the even-numbered phenylthio derivatives are main products whereas the odd-numbered derivatives are much more reactive and were observed only in low concentrations. Very pronounced differences in rate constants and reactivity were obtained.