Synthetic Methods -- Stereoselective Synthesis
Surface Chemistry
Reaction Mechanisms -- Supercritical Fluids

Surface Effects on Reactivity

There are numerous reports in the literature in which it was observed, often inadvertently, that the presence of silica gel or alumina mediates chemical reactivity. Since, however, this was usually not the major thrust of the research, the observations are reported in a short note or letter with little or no useful insight into the origin of the remarkable changes in reactivity. Hence we are involved in long–term, systematic studies of the adsorption of organic and inorganic substrates to the surfaces of silica gel and alumina and the resulting enhancement or change in their chemical reactivity.

Goals

• develop new reactions or new methods of conducting known reactions

• discern what is happening mechanistically

• gain insights into the structures of the surfaces and how various types of substrates interact with them

Benign—by Design

Since silica gel and alumina are readily recycled and are environmentally benign, their use as a reagent or catalyst represents environmentally sound, green chemistry.

Additions to Alkenes and Alkynes

Contrary to the conventional wisdom found in most organic chemistry textbooks, HCl adds only very slowly, if at all, to most alkenes and alkynes. However, our studies have shown that in the presence of silica gel or alumina addition is rapid and synthetically viable.

HBr adds more readily but affords predominantly the radical addition product unless numerous special precautions are taken. However, we have found that in the presence of silica gel or alumina only the ionic addition product is formed.

Acid-Catalyzed Rearrangements and Cyclizations

Our studies have further shown that adsorption of acids to the surface of silica gel affords easily prepared, heterogeneous acid catalysts that are highly effective in promoting a wide variety of rearrangements and cyclizations.

Oxidations

Inexpensive, easily handled, and readily available, (CH₃)₃COOH and KOSO₂OOH would be oxidizing agents of choice were it not for their low reactivities. However, we have learned that on adsorption to silica gel or alumina they become powerful, yet highly selective, oxidants.

Publications

Recent Kropp Group Alumni

Contact Dr. Paul J. Kropp

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This page was created by James M. Pearson, Jr.