Pentane transformations over sulfated alumina catalyst

The transformation of n-pentane at 295 K in the presence of catalysts of defined acid strength from −9.6 to −15 HO units were studied. The results were compared with those for $${{\text {Al}}_2}{{\text O}_{3}-}{\text{SO}}_{4}^{2 - }$$ (8 %) of acid strength equal to −11.5 < HO ≤ −10.8. It was found that: (a) for superacids of acid strength HO < −13, the reaction begins with the protonation of the C–H σ bond of a pentane and proceeds according to the bimolecular mechanism; (b) for less acidic catalysts such as sulfated alumina, pentane is oxidized to pentene, which is converted to the pentyl cation after protonation. The latter reacts in the presence of catalysts of acid strength of at least HO equal to −9.6 according to two pathways: (a) unimolecular at an excess of H− (in the presence of additional hydride donor pentane co-substrate) with selective formation of 2-methylbutane; (b) bimolecular in the absence of H− (pentane alone is the substrate). In the latter case, the transformation proceeds through the formation of a ten-carbon dimer cation state, which upon decomposition leads to 2-methylpropane, 2-methylbutane and unsaturated coke precursors.