Acceleration of reaction rates and enhancement in product yields

1 Acceleration of reaction rates and enhancement in product yields 

The sudden collapse of a cavitation bubble in an acoustic field results in an inrush of liquid to fill the partial vacuum enclosed by the bubble. The shock wave produced by this bubble collapse can disrupt the weak inter-molecular forces which contribute to the structural characteristics of solvents. The disruption can influence chemical reactivity by altering solvation of the reactive species present. An example of this is to be found in the ultrasonically assisted reaction of 2-chloro-2-methylpropane in aqueous alcoholic media (Table 10.3) where the ratio of the first-order rate constants (in the presence of ultrasound) and knon (under conventional conditions) are compared [7]  

The effect of ultrasound on this solvolysis reaction increases as the reaction temperature is lowered. Thus the sonochemical effect increases from 1.7 at 25°C to 20 at 10°C. This inverse relationship between temperature and ultrasonic effect is a common observation in sonochemistry. In simple terms the more vapour which enters the cavitation bubble the more of a cushion it will provide against violent collapse. Hence any reduction in 

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