Abstract
Ultrasound generates cavitation, which is "the formation, growth, and implosive collapse of bubbles in a liquid. Cavitation collapse produces intense local heating (similar to 5000 K), high pressures (similar to 1000 atm), and enormous heating and cooling rates (> 109 K/sec)" and liquid jet streams (similar to 400 km/h), which can be used as a source of energy for a wide range of chemical processes. This review will concentrate on theory, reactions and synthetic applications of ultrasound in both homogeneous liquids and in liquid-solid systems. Some recent applications of ultrasound in organic synthesis, such as, Suzuki reaction, Sonogashira reaction, Biginelli reaction, Ullmann coupling reaction, Knoevenagel condensation, Claisen-Schmidt condensation, Reformatsky reaction, Bouveault reaction, Baylis-Hillman reaction, Michael addition, Curtius rearrangement, Diels-Alder reaction, Friedal-Craft acylation, Heck reaction, Mannich type reaction, Pechmann condensation and effect of ultrasound on phase transfer catalysis, oxidation-reduction reactions, ionic liquids and photochemistry are reviewed. Ultrasound found to provide an alternative to traditional techniques by means of enhancing the rate, yield and selectivity to the reactions.