THE ELECTROPHILIC ACTIVATION PATHWAYS FOR N-BUTANE IN HF-SBF5 THAT COMPETE WITH FAST REVERSIBLE PROTONATION

The relative importance of competitive activation pathways For n-butan e in HF-SbF5 superacid has been studied in a flow reactor over the -15 degrees C to +15 degrees C temperature range. In order to inhibit the reversible protide transfer between the hydrocarbon and the carbenium ions generated in the superacid solution, all experiments were run in the presence of carbon monoxide, thereby converting the reactive ions into stable oxocarbenium ions. Analysis of the product distribution b etween gras and acid phases identifies the main activation step as bei ng protolytic cleavage of the central C-C bond, forming ethane and the ethyl cation. The secondary butyl cation is formed via hydride abstra ction from n-butane by the primary ions formed in the first step. No i somerization of n-butane was noticed under these conditions. Fast reve rsible protonation of the sigma-bonds of n-butane is evidenced by obse rvation of significant protium-deuterium exchange in the ''recovered'' alkane when DF-SbF5 was used as superacid.