ABSTRACT
The interaction of sound waves with matter is far from being trivial, though a rather reductionist approach points to effects related to both piezo-and thermochemistries (vide infra). Sonochemistry is a branch of science that deals with the chemical and mechanical effects of ultrasound. This irradiation appears to be more general than other activation techniques as the system requires essentially an ultrasound source and a liquid (either aqueous or organic), which contrasts with speci›c requirements in electrochemistry (conducting media), microwaves (polar media or species/ions), photochemistry (presence of chromophores), or supercritical conditions (elevated pressure or temperature in closed systems). Ultrasound-assisted chemistry is generally associated with a series of key characteristics such as safety, energy savings, the use of ambient conditions, waste prevention, and improved mass transfer, among others. The greenness of sonochemistry, like other activation techniques, should however be assessed with care and from a critical point of view. If one uses either microwaves or ultrasound with toxic reagents and the subsequent separation and puri›cation steps require the extensive use of volatile organic solvents, the whole protocol is not green at all. Clearly, the bene›ts associated with a safer technique disappear. This book concentrates on the wide range of ultrasonic applications with a focus on sustainable processes. This introductory chapter intends to highlight the historical basis and fundamentals of power ultrasound, the unique phenomenon of cavitation, and the different factors in¢uencing the fate of a sonochemical reaction. This contribution
Introduction ......................................................................................................................................23 Origin of Acoustics: The Sound Spectrum ......................................................................................24 Bubble Formation in Liquids: Cavitation ........................................................................................26 Chemistry in High-Energy Cavities .................................................................................................27
