Sonolysis, rate enhancements

In halocarbon solution, dinuclear complexes of manganese and rhenium are transformed to mixed halogenated complexes (Fig. 24). With respect to silent conditions, the rate enhancement is estimated at 10 . The vapor pressure of the starting material is very low as compared to that of the solvent, and its concentration in the bubble should be low. According to the authors, the metal-metal bond cleavage is unlikely despite its weakness, and the first reaction step is probably the solvent sonolysis. 

The same energy input dispersed over a broader area results in significant enhancement of reaction rates and energy utilization efficiency. The low energy utilization efficiency may limit the use of direct probe sonolysis to special applications such as groundwater remediation or for low-flow pretreatment of hazardous industrial wastes. However, sonolysis does not require the addition of chemical additives to achieve a viable degradation rate. 

The fact that US influences the mechanism of chemical reactions via the action of highly reactive radicals such as OH- and H- formed during solvent sonolysis is well known (see Chapter 7). Solvents sensitive to thermolysis or sonolysis (e.g. dimethylformamide [158], dimethylsulphoxide [159]) decompose slowly in the presence of intense US. Thus, radical species formed by cavitation are highly reactive and may participate as activators or enhancers in the electrode process [160]. In fast, qt/asr-reversible or irreversible systems, however, the only effect of US is to enhance mass transport without any direct effect on the rate of simple electron transfer processes. 

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