SONOCHEMISTRY OF ACETONE AND ACETONITRILE IN AQUEOUS-SOLUTIONS - A SPIN-TRAPPING STUDY

The 50 kHz sonolysis of argon-saturated water-acetone and water-aceton itrile mixtures was studied by EPR and spin trapping with 3,5-dibromo- 4-nitrosobenzenesulfonate over a wide range of solvent composition. Fo r both systems a single maximum was observed for the spin adduct yield of methyl radicals and of the radicals formed by H-abstraction from a cetone and acetonitrile. These results combined with previous studies of water-methanol and water-ethanol mixtures indicate that the greater the vapor pressure of the volatile organic component, the lower the c oncentration of organic solute at which the maximum radical yield occu rs. Methyl radicals from acetone are formed by C-C bond scission in th e collapsing argon bubbles. For acetonitrile, C-H bond scission at hig h temperature is followed by H-addition to the triple bond and the dec omposition of this intermediate radical to form methyl radicals. Since Anbar has shown (Science 161, 1343, 1961) that sonoluminescence and a coustic cavitation occur during the impact of liquid water on water wi th linear velocities similar to those of collapsing ocean waves, the s onochemistry of nitriles is of interest to chemical evolution studies.