ABSTRACT
Scienti›c discussions and political mandates in recent decades have enforced both academic and industrial chemical societies to move toward designing and employing more environmentally friendly techniques and methodologies in order to minimize the quantities of chemical disposals and energy consumptions. In this regard, ultrasonic irradiation has emerged as one of the most successful means to signi›cantly help develop the so-called “green” chemistry by enhancing the reactivity and selectivity of the reactions and lowering the energy uses at the same time (Mason and Cintas, 2002; Mason and Lorimer, 2002; Cravotto and Cintas, 2007; Bruckmann et al., 2008). The interaction between the matter and the ultrasonic waves and the subsequent chemical changes is called sonochemistry and is attributed to cavitation, a physical process caused during ultrasonic irradiation of liquids by creation, enlargement, and collapse of bubbles (Bremner, 1990). The cavitation would result in induction of extremely high local pressure and temperature, enhancing mass transfer and mechanical effects in the reaction mixture. On many occasions, irradiation leads to more effective mixing of the reaction phases, and, therefore, increased rates and yields are observed because of better mechanical effects of the ultrasound (US) waves (Flint and Suslick, 1991; Suslick and Kemper, 1993; Brennen, 1995). In other cases, ultrasonic energy causes the formation of new reactive intermediates and species that are not usually formed in regular thermal reactions. This is called “true sonochemistry” (Cravotto and Cintas, 2006) or “sonochemical switching” (Cintas and Luche, 1999), where changes in the reaction mechanism occur and thus the distribution of the products and the reaction selectivity are altered.
