You are here:
SOLVENT-FREE ALTERNATIVES TO ORGANIC SYNTHESES USING MICROWAVES
Citation:
Varma*, R S. SOLVENT-FREE ALTERNATIVES TO ORGANIC SYNTHESES USING MICROWAVES. Presented at RCRA 2002 National Meeting on "Partnerships for Cleaner Communities", Washington, DC, 1/15-18/2002.
Description:
Microwave irradiation has been used for a variety of synthetic transformations wherein chemical reactions are accelerated because of selective adsorption of microwave (MW) energy by polar molecules, non-polar molecules being inert to the MW dielectric loss. The application of microwave irradiation under solventless conditions enables expedited synthetic transformatons at ambient pressure thus providing unique processing conditions with special attributes such as ease of manipulation and higher yields. Results from our laboratory on this MW-accelerated approach will be described for the synthesis of a variety of industrially significant compounds and intermediates namely, imines, enamines, nitroalkenes, enones, oxidized sulfur compounds and ionic liquids. This solvent-free synthetic methodology involves microwave exposure of reactants in neat forms or their reaction in presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral oxides namely silica, alumina, clay, or 'doped' surfaces, such as, Fe(NO3)c-clay (clayfen), Cu(NO3)2-clay (claycop), NH2OH-clay, PhI(OAc)2-alumina, NaIO4-silica and NaBH4-clay. A variety of condensation, cyclization, oxidation and reduction reactions wll be presented including the convergent onepot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and a-tosyloxyketones. The application of this solvent-free MW approach to multi-component reactions will be highlighted which can be adapted for high-speed parallel synthesis of the library of biologically active molecules. The salient features of this strategy, that reduces or presents pollution 'at-source', will be exemplified by efficient functional group transformations. This general approach may be extended to in situ remediation or degradation of hazardous materials and pollutants.