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Organic Synthesis Using Microwaves and Supported Reagents
Citation:
VARMA, R. S. AND N. R. Baig. Organic Synthesis Using Microwaves and Supported Reagents. Chapter 10, A. de la Hoz and A. Loupy (ed.), Microwaves in Organic Synthesis, Volume 1, Third Edition, ISBN: 9783527331161 . Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, , pp. 427-486, (2012).
Impact/Purpose:
To inform the public
Description:
In the electromagnetic radiation region, microwaves (0.3GHz-300GHz) lie between radiowave (Rf) and infrared (IR) frequencies with relatively large wavelengths (1 mm-1 m). Microwaves, non-ionizing radiation incapable of breaking bonds, are a form of energy that manifest as heat through their interaction with the medium or materials wherein they can be reflected (metals), transmitted (good insulators that will not heat) or absorbed (decreasing the available microwave energy and rapidly heating the sample). This unconventional microwave (MW) energy source has been used for heating food materials for almost 50 years [1] and is now being utilized for a variety of chemical applications including organic synthesis [2-11] wherein chemical reactions are accelerated because of selective absorption of MW radiation by polar molecules, non-polar molecules being inert to the MW dielectric loss [12]. The initial experiments with microwave heating exploited the use of high dielectric solvents such as dimethylsulfoxide (DMSO) and dimethylformamide (DMF) in a household kitchen MW oven. The rate enhancements in such reactions are believed to be due to rapid superheating of the polar solvents and pressure effects [11]. However, in these solution-phase reactions, the development of high pressures, and the use of specialized sealed vessels are some of the limitations, although they have been circumvented by the introduction of commercial MW instruments with appropriate temperature and pressure controls.
