SONOCHEMISTRY - THEORY AND APPLICATIONS

Ultrasound can be used in chemistry to increase both reaction rates an d yields of products. Most effects of ultrasound on chemical reactions are due to cavitation: the formation and collapse of small bubbles in the solvent. In this review, we first outline the physical background of cavitation, and discuss its dependence on factors such as sound in tensity and frequency, solvent and temperature. The impact of ultrasou nd on chemical reactions is considered for homogeneous reactions and f or heterogeneous liquid-solid systems. The first area is mainly illust rated by a discussion of the effect of ultrasound on polymerization an d depolymerization reactions, the second by selected examples in organ ic synthesis. The tendency of ultrasound to change reaction mechanisms in favour of homolytic (instead of heterolytic) pathways, is also bri efly discussed. The specific preference for a particular pathway under sonochemical conditions, different from that under mechanical stirrin g has been termed ''sonochemical switching''. Ultrasonic equipment for lab-scale experiments are compared, and some practical ''tricks and t raps'' are given.