Microwave organic synthesis

Article By:

Varma, Rajender Singh Sustainable Division, U.S. Environmental Protection Agency, Cincinnati, Ohio.

Last reviewed:2002

DOI:https://doi.org/10.1036/1097-8542.YB020570

In the electromagnetic spectrum, microwaves (0.3–300 GHz) lie between the radiowave frequency (RF) and infrared (IR) frequency and have relatively large wavelengths. Microwave radiation is non-ionizing and, therefore, incapable of breaking bonds. Microwaves (a form of energy and not heat) are manifested as heat through their interaction with a medium or material. They can be reflected (by metals), transmitted (by good insulators, which will not heat), or absorbed (decreasing the available microwave energy and rapidly heating the sample). Microwave energy transfer occurs by ionic conduction, either to ions in solution or to compounds with a dipole, such as water molecules, trying to align with the electric field. The amount of energy transferred is a function of both the dipole moment and dielectric constant. Even though Percy Spencer invented the underlying principles of the microwave (MW) oven about a half century ago, until recently, the application of microwave heating has been limited in the chemical industry.

The content above is only an excerpt.