Sonoelectrochemistry

The factors which make power ultrasonic irradiation such a powerful tool in promoting chemical reactivity in liquids at solid surfaces include continuous surface cleaning, degassing and improved mass transport. For many years metallurgists have harnessed these effects to improve electroplating by the use of simultaneous ultrasonic irradiation. There are, however, very few examples of purely electrosynthetic processes enhanced by ultrasound. In this paper we review the background evidence which suggests the advantages of ultrasonic irradiation in electrosynthesis and report the results obtained in our own laboratories on the Kolbe electrolysis of several carboxylic acid salts. Evidence is presented for a change in reaction pathway for cyclohexane carboxylate from a one to a two electron process induced by ultrasound; the elimination of an additive (pyridine) normally necessary to facilitate the electrolysis of phenylethanoate; and the sonolytically enhanced current efficiency which is found in all such reactions but is particularly evident in the electrolysis of the 4-chlorophenyl-ethanoate system.