Enhancement of Chemical Reactions by Microwave Irradiation

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Abstract
Microwaves are low electromagnetic energy which induce molecular perturbation by stimulation of ionic diffusion and by enhancement of dipole rotation without causing rearrangement of molecular structures. Microwave energy irradiated on the samples in various liquid media is lost or absorbed to the samples by the following two mechanisms: ionic conduction and dipole rotation. These two effects take place simultaneously to account for the phenomenon of rapid heating associated with many practical applications of microwave irradiation. In contrast to conventional heating, the salient feat ure of “dipole rotation” constitutes one efficient form of “molecular agitation” or “molecular stirring” which can be explored for many aspects in chemical reactions. We will discuss some of the useful application of “molecular agitation” by means of microwave irradiation such as: 1. rapid hydrolysis of proteins and peptides, 2. selective hydrolysis of aspartyl peptide bond, 3. the racemization of amino acids, 4. rapid hydrolysis of sugars, 5. continuous‐flow process of microwave reactions, and 6. the enhancement of coupling reactions in peptide synthesis.