Bruce Foxman
Professor of Chemistry
Ph.D., Massachusetts Institute of Technology, 1968
781-736-2532
foxman1@brandeis.edu
Traditional chemistry curricula are responsible for creating the impression (in the budding inorganic or organic chemist) that "all real chemistry is done in solution." In many curricula, little more than a few lectures over four years are allocated to a discussion of the solid state. On the other hand, the "traditional" solid-state chemist has preferred to remain aloof from organic or inorganic molecular crystals, which are generally low-melting, difficult to get pure, and are soft and readily distorted so that they tend to contain many defects and imperfections. Such attitudes as the above are unfortunate, since there is a wide variety of natural processes which take place within, or on the surfaces of ordered aggregates or crystals.
Surprisingly, the broad mechanistic behavior patterns observed in solution reactions are also found in the solid state. A chemist studying solid-state reactions finds a fascination in his work similar to that of a biochemist studying reactions in a fixed environment -- the active site of an enzyme. Using a combination of spectroscopic, thermodynamic and X-ray crystallographic techniques, the chemist is able to study the kinetics and mechanism of a solid-state reaction, with one extra-special added attraction: the determination via X-ray diffraction studies of the geometrical course of the reaction, that is, the complete three-dimensional relationship between reactants and products. Further, solid-state reactions are of singular interest since many of them are highly selective, giving very pure products which may not be available from solution processes. For example, irradiation of solid sodium crotonate 1 leads to trimer 2, one of eight possible diastereomers! This reaction represents the first efficient solid state synthesis of a small molecule using ionizing radiation. The reaction is all the more remarkable since it is stereospecific, and the molecule cannot be prepared at all in solution.
A second unprecedented reaction occurs when metal pentenoates are irradiated in air. In this reaction, which is general for all metal pentenoates, the pentenoate moiety 3 undergoes a regiospecific oxidation to acetylacrylate 4. Pentenoate salts incorporating heavy metals show the greatest sensitivity to ionizing radiation, and are more readily oxidized than the analogous lighter-metal salts. The production of acetylacrylate may actually occur by a mechanism similar to that proposed for the oxidation of polymers; this possibility is under further investigation in our laboratory.