Hot Spot Kinetics of the Sonolysis of Aqueous Acetate Solutions

Summary

Water and acetate solutions were irradiated under argon by 300 kHz ultrasonic waves. Oxygen was found to be generated besides the products H₂ and H₂O₂, already known. In the presence of acetate the O₂ yield decreased rapidly while that of H₂O₂ decreased more slowly. Succinic acid was found as a product of the attack of OH radicals on acetate. Appreciable amounts of glyoxylic and glycolic acid and smaller amounts of formaldehyde and carbon dioxide were also detected. They resulted from the reaction of sonolytically generated oxygen with CH₂CO⁻₂ radicals, produced upon attack of OH on acetate. Methane was a minor product of sonolysis. At acetate concentrations above 0·4 mol dm⁻³ CO₂ and CO became the predominant products of sonolysis. This is explained by a second kind of action of ultrasound on dissolved acetate, i.e. by a thermal decomposition. This decomposition is possibly facilitated by radical attack on acetate. The results are discussed in terms of a ‘structured hot spot’ model, in which three regions for the occurrence of chemical reactions are postulated: (a) a hot gaseous nucleus, (b) an interfacial region with radial gradient in temperature and local radical density; and (c) the bulk solution at ambient temperature.

• ultra sound
• kinetics
• free radicals