Effect of static pressure on the ultrasonic activation of chemical reactions. Selective oxidation at benzylic carbon in the liquid phase

Abstract

The effects of sonoactivation on kinetic rates and chemical yields of a model reaction, selective oxidation at the benzylic site of indane, was studied at subatmospheric static pressures ranging from 200 to 760 Torr. The reaction occurs at a rate up to five times higher when a suitable ultrasonic field activates the reagents in solution. By varying the pressure applied to the system, the total sonochemical yields were found to follow a non-monotonic trend, with a peak value related to the frequency of ultrasounds irradiated. According to the general theory of acoustic cavitation, the results obtained are accounted for in terms of distribution and dynamics of the cavitating bubbles, whose average radius of equilibrium reaches its resonant value when tuned to a definite value of pressure, so allowing the best coupling with the ultrasonic field; under these conditions, the sonocatalytic effects on reaction parameters are maximized.