An Attempted Rational View on Sonochemical Reactions

Since sonication induces a specific chemical reactivity, it should follow laws, established empirically by a classification of the published material. The first rule, the only one to be considered in this chapter, states that homogeneous reactions activated by sonication are those proceeding via radical or radical ion intermediates, and ionic reactions remain mostly imaffected. This systematization, for which some limits will be delineated in the following, also leads to a schematic view on reactivity, presented in Fig. 2. 

4 Luche, J.L. Einhom, C. Einhom, J. Sinisterra-Gago, J.V. Tetrahedron Lett. 1990,31, 4125-4129. 

Recent research in organic reactivity provides an increasing number of cases where electron transfer (ET) mechanisms, e.g., in substitutions, alkylations, additions etc., are plausible even if not always imambiguously determined. It is therefore not unreasonable to envisage the existence of competitive, simultaneous polar and ET processes. 

If the polar and ET mechanisms converge to yield the same product(s), only an overall rate increase can result from sonication. If the two mechanisms are divergent and yield different products, the enhancement of the radical component leads to switching, and sonication has a true chemical role. 

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