Carbenium and carbonium ions in liquid- and solid-superacid-catalyzed
activation of small alkanes*
J. Sommer** and R. Jost
Laboratoire de Physico-Chimie des Hydrocarbures, UMR
7513 CNRS Faculté de Chimie, Université Louis Pasteur,
Strasbourg, France
Abstract: Acid-catalyzed hydrocarbon reactions involve by far
the largest amount of catalyst and the largest volume of transformation
in oil refinery and chemical industry. However, despite the general
agreement on the carbocationic nature 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 physical 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 vary 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 intermediates,
as well as the reaction mechanism in which carbenium and carbonium ions
intervene.
*Plenary lecture presented at the 15th
International Conference on Physical Organic Chemistry (ICPOC 15), Göteborg,
Sweden, 8 –13 July 2000. Other presentations are published in this
issue, pp. 2219 –2358.
**Corresponding author
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