Pentafluorosulfanylbenzene, or phenylsulfur pentafluoride, is an organosulfur compound with the formula C<sub>6</sub>H<sub>5</sub>SF<sub>5</sub>. It is colorless liquid with high chemical stability.
Pentafluorosulfanylbenzene possesses high chemical stability under a wide range of conditions including oxidizing, reducing, strongly acidic and strongly basic environments. For example, it does not react with a refluxing solution of sodium hydroxide in aqueous ethanol, but it can react with concentrated sulfuric acid at elevated temperatures. The pentafluorosulfanyl group is a strong electron withdrawing group, and leads to electrophilic aromatic substitution reactions at the meta position.
Pentafluorosulfanylbenzene was originally synthesized by fluorination of diphenyl disulfide by AgF<sub>2</sub>. Even with xenon difluoride, the method suffers from low yield. Contrariwise, using dichlorine as oxidant and a fluoride salt as fluorine source generally gives excellent yields.
Better techniques add the pentafluorosulfur moiety, then aromatize the ring. The simplest case dehydrogenates the corresponding dihydrobenzene from a Diels-Alder cycloaddition: <chem display=block>H2C=CH-CH=CH2 + F5SC#CH -> F5SC6H7</chem><chem display=block>F5SC6H7 ->[\ce{Pt},\Delta] F5SC6H5 + H2</chem> A more modern technique instead adds SF<sub>5</sub>Cl radically to a dichlorocyclohexene, then dehydrohalogenates.