Effect of fluorination on thiol reactivities. Reaction of 2,2,2-trifluoroethanethiol on Mo(110)

Article abstract of DOI:10.1021/j100021a047

The reactions of 2,2,2-trifluoroethanethiol on Mo(110) were studied using temperature-programmed reaction, Auger electron, and infrared spectroscopies. Most significant is the evolution at 265 K of tritluoroethyl radical from a saturation coverage of CF₃CH₂S-. The strong coverage dependence for trifluoroethyl radical evolution and models depicting trifluoroethyl thiolate orientation at saturation coverage strongly suggest that surface crowding plays a significant role in radical formation. The stability of the radical and the steric inhibition to finding an adsorption site explain the evolution of the radical into the gas phase. C-S bond hydrogenolysis, yielding trifluoroethane, and defluorination, yielding difluoroethylene, are of nearly equal importance in the reaction of trifluoroethyl thiolate, whereas C-S bond hydrogenolysis of ethyl thiolate to form ethane predominates. The C-S bond hydrogenolysis pathway is similar for the two thiols, occurring at approximately 300 K in both cases. Dehydrogenation and alkene elimination from CH₃CH₂S- occur at approximately 340 K, as the supply of surface hydrogen is depleted through hydrogen recombination. In contrast, defluorination and fluoroalkene elimination from CF₃CH₂S- occur over a wide temperature range, 200-520 K. The formation of difluoroethylene on Mo(110) is nearly thermoneutral, due to the comparable strengths of the C-F and Mo-F bonds and the stability of difluoroethylene.