On the energy efficiency of microwave-assisted organic reactions

The energy consumed for four different organic transformations carried out under microwave and conventional heating under otherwise identical reaction conditions was measured with the aid of a Wattmeter. In the case of open-vessel reflux processing, microwave dielectric heating required significantly more energy than conventional techniques using oil baths or heating mantles. This is a consequence of the comparably low energy efficiency of the magnetron in converting electrical to microwave energy. Significant savings in energy were experienced by taking advantage of sealed-vessel microwave processing at high temperatures. When comparing a conventionally heated reflux experiment with a microwave-heated experiment using a superheated solvent in a sealed vessel, reaction times were reduced significantly from hours to minutes. The energy savings in these instances are, however, largely connected to the reduced reaction time and are not an inherent feature of microwave heating.