The combined use of microwaves and ultrasound: improved tools in process chemistry and organic synthesis.

Microwave heating and ultrasonic waves are among the most simple, inexpensive, and valuable tools in applied chemistry. Besides saving energy, these green techniques promote faster and more selective transformations. Could they be combined to enhance their effects still further? As they are of a basically different nature (quantum and non-quantum fields), each must be fine-tuned by its specific parameters; a combined device will often be subject to additional hazard limitations. However, recent developments evidence that such a combination is certainly possible and safe, ranging from simple modifications to flow systems that are well suited for automation and scaling-up. By using selected examples, this concept article gives an overview of apparatus currently available for simultaneous or tandem irradiation and explains how it can be utilized in organic synthesis and analysis.