Ultrasonic Acceleration of Redox Reactions

Abstract

The well-documented effects of ultrasound on heterogeneous systems have been exploited to produce beneficial increases in the rates of a number of reactions that would more commonly be executed under homogeneous conditions. For instance, the reduction of aryl halides with lithium aluminium hydride occurs extremely slowly in THF solution. However, Han and Boud- jouk have reported that the reaction can be carried out in a fraction of the time if the reaction mixture is sonicated in dimethoxyethane (DME) solution [6].’ Sonolysis of the heterogeneous reaction mixture gives high yields (70–99%) of the reduced product. The effect was particularly marked in the case of deactivated aryl halides; for example, /?-bromotoluene gave a 97% yield of toluene in 5 h. In contrast, the yield of the stirred reaction was a modest 21% after 24 h at room temperature in THF (Scheme 112).