Oleum has some advantages over pure sulfur trioxide and may be successfully used for preparation of beta-sultones from hexafluoropropene, 2H-pentafluoropropene, 6H-perfluoro-1-hexene and perfluoro(propylvinyl) ether (VE). Depending on the reaction conditions, the VE-sultone and tetrafluoroethane-beta-sultone (TFE-sultone) are different from other sultones. They are not stable in the presence of oleum