EPR STUDY OF FREE-RADICALS INDUCED BY ULTRASOUND IN ORGANIC LIQUIDS .2. PROBING THE TEMPERATURES OF CAVITATION REGIONS

The spin trap nitrosodurene was used for the detection of radical inte rmediates formed by 50 kHz ultrasound in argon-saturated n-alcohols, n -alkanes, cyclic ethers, toluene, N,N-dimethylformamide (DMF) and dime thylacetamide (DMA). Radicals, produced by pyrolysis in collapsing cav itation bubbles, such as 'CH(2)R in n-alkanes, 'CH(2)R and 'CH2OH in n -alcohols, 'CH2-phenyl in toluene, 'CH(2)OR and 'CH(2)R in cyclic ethe rs and 'CH3 and 'N(CH3)R in DMF and DMA were spin trapped. Secondary r adicals formed by hydrogen abstraction from organic liquids (such as ' CHRR' radicals in n-alcohols and n-alkanes and 'CH2N-type radicals in DMF and DMA) by the primary pyrolysis radicals were also spin trapped. For a series of n-alcohols, the logarithm of the rate of radical form ation decreases linearly with the vapour pressures of the n-alcohols. The kinetic isotope effect, k(H)/k(D) for the ultrasound-induced produ ction of 'CHRR' and 'CDRR' radicals in mixtures of n-dodecane and n-do decane-d(26) was found to be 2.6. For the 'CH2-phenyl and 'CD2-phenyl- d(5) radicals from toluene-toluene-d(8), the ratio k(H)/k(D) = 1.09 wa s obtained. From the temperature dependence of the kinetic isotope eff ect, the temperature region of hydrogen abstraction radical formation ('CHRR') in n-dodecane was estimated to be 750 +/- 150 K; the effectiv e temperature of the region where benzyl radicals are formed from tolu ene by sonochemical pyrolysis was estimated to be about 6000 K. This m ethod appears to be a promising tool for probing the temperatures of d ifferent sonochemical regions.