Ultrasound assisted electrochemical oxidation of substituted toluenes

Investigations on ultrasound assisted electrochemical syntheses demonstrate the positive influence of ultrasound on the achievable current density, selectivity and yield, but there is still a lack of investigations concerning the ultrasound influence on electroorganic syntheses. Especially the determining parameters like operation conditions and reactor geometry are not well defined for an industrial application. Therefore, the electrooxidation of substituted toluenes to their corresponding benzaldehydes via electrochemical conversion to the dialkylacetals, which is a reaction of great interest in industrial production, is studied with and without sonification of the working electrode. Experiments in a test-cell are done to evaluate the fundamental characteristics of the combined use of ultrasound and electrooxidation. A strong dependency of the current densities on the applied ultrasound power and a shift of oxidation potentials to lower values are achieved. Work is extended by theoretical investigations concerning the ultrasound field.For technical interesting syntheses a high electrode area-reactor volume ratio is demanded. This is achieved by an experimental sono-electrochemical gap cell with an electrode distance of only a few millimetres and a sound source "face on" the working electrode. Synthesis experiments done with this experimental set-up show an increase in chemical yield.