Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed activation of small alkanes

Acid-catalyzed hydrocarbon reactions involve by far the largest amount of c atalyst and the largest volume of transformation ill oil refinery and chemi cal industry. However, despite the general agreement on the carbocationic n ature of the reaction intermediates, the initial steps and the true nature of the cations on the surface are still open to debate. On these points our basic knowledge has gained enormously from landmark experiments in physica l organic chemistry with spectroscopic observations using liquid superacids as solvents. As the range of superacidity covers over 11 logarithmic units of the Hammett acidity scale, the mechanistic behavior of small alkanes va ry accordingly. This allows for comparison with strong solid acids such as zeolite or others used in industry. Isotopic labeling of the alkane and the acids is a powerful tool used to understand the nature of the intermediate s, as well as the reaction mechanism in which carbenium and carbonium ions intervene.