Not Accepting Doctoral Students
Synthetic Organic Methods, Surface-Mediated Chemistry
Ph.D., University of Wisconsin (1962); B.S., University of Notre Dame (1957)
Traditionally, chemical reactions have been conducted principally in solution. The use of surfaces to promote chemical reactions and to control their chemo-, regio-, and stereoselectivities is a major new direction for organic chemistry. We are involved in a long-range study of the interaction of substances with surfaces, particularly those of silica gel and alumina. The knowledge gained about these interactions leads both to improved understanding of the chemical structures of the surfaces and to the development of new synthetic methods.
Our initial studies have involved the adsorption of acids to silica gel and alumina. Contrary to implications in most textbooks, addition of HCl to alkenes occurs very slowly, and alkynes undergo hydrochlorination even less readily, if at all. However, we have found that in the presence of silica gel or alumina alkenes and alkynes undergo rapid addition of HCl, HBr, and HI. Moreover, addition occurs selectively syn, and there is no competing radical addition in the case of HBr. Adsorption of acids to the surfaces involves a hydrogen bonding interaction, in which OH groups on the surface serve as hydrogen bond donors. This polarizes the H-X bond, disrupts any aggregation that the acid has in solution, and places the acid in a highly polar local environment.
Further studies have shown that adsorption of a variety of other acids, derived from nonnucleophilic bases, to silica gel affords easily prepared heterogeneous acids that are highly effective in catalyzing a number of organic reactions.
Most recently our studies have centered on the use of silica gel and alumina to mediate the oxidation of alkenes, sulfides, and sulfoxides with tert-butyl hydroperoxide. This inexpensive oxidant is much safer to handle and transport than hydrogen peroxide and peroxyacids, but requires catalysis. Silica gel and alumina are environmentally benign, recyclable replacements for the heavy metal salts that are traditionally used. Moreover, their use with tert-butyl hydroperoxide affords selectivities unattainable with traditional oxidants.