Paraffin disproportionation catalyzed by aluminum chloride/sulfonic acid resin

Abstract

The disproportionation of n-butane and of n-pentane was investigated as reactant vapors flowed over beads of a solid superacid catalyst (an aluminum chloride/sulfonic acid resin) at 1 atm and 70–143 °C. n-Butane reacted in the presence of HCl to give equimolar ratios of propane and pentanes; the butane isomerization reaction took place simultaneously, occurring at an order-of-magnitudehigher rate than the disproportionation. The observed i- to n-pentane ratios were less than the equilibrium ratios predicted from literature data. The conversion of n-pentane under similar conditions yielded products ranging from methane to hexanes. The main products were propane and isobutane, which indicates that extensive β-scission occurred. The results are broadly consistent with classical carbenium-ion mechanisms involving hydride and methyl shifts and CC bond-forming and -breaking steps, although some details of the mechanism of the n-butane disproportionation remain unexplained.