CHAPTER 18: Microwave Irradiation

Microwaves (MWs) represent a convenient and rapid source of heating, affecting high temperature reactions by shortening the reaction times, while significantly affecting the quality and quantity of the desired products. Depending on the organic transformation, MWs might have a specific effect in enhancing the reaction rates compared to conventional heating processes. Here, we report a brief story of MW-assisted organic synthesis (MAOS) and describe several methodologies that can be coupled with MW irradiation for designing green and sustainable synthesis. The major contribution to sustainability of MWs is not a more efficient use of the energy, as there is not significant saving in energy using MW heating compared to conventional heating working on a small scale, while a minor improvement occurs shifting to large scales. MW dielectric heating allows, however, an easier use of green solvents, heterogeneous catalysis, and continuous flow methodologies, contributing to improving the “greenness” of an organic transformation. We also describe herein a general flow diagram for the setup of a “green” MW-assisted experiment and the application of the environmental factor (E-factor) to some transformations to unravel the positive effect of MAOS both on laboratory and industrial scales.