Activation, isomerization and H/D exchange of small alkanes in triflic acid

Abstract

In contrast with the HF/SbF₅ superacid system and despite its strong acidity (H₀= -14.1), CF₃SO₃H is not able to protonate reversibly small alkanes. At room temperature propane and n-butane do not exchange their hydrons for deuteriums with deuterated triflic acid. The H/D exchange occurring between isobutane and the CF₃SO₃D acid is regiospecific as observed in weaker acids such as D₂SO₄ or solid acids such as sulfated zirconia or zeolites. In the same way, the formation of C₅ alkanes during C₄ isomerization is indicative of a classical bimolecular process. In the presence of carbon monoxide, isomerization as well as H/D exchange are suppressed due to chemical trapping of the carbenium intermediates.