Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg-1, the total yield [G(.OH) + 2 G(H2O2)], equals 16 x 10(-10) mol J-1. This represents the total of .OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, the lower the H2O2 production as more of the OH free radicals are scavenged, in competition with their recombination. Fricke dosimetry, in the absence and presence of Cu2+ ions, shows that the yield of H atom reaching the liquid phase is much lower, with G(H.) of the order of 3 x 10(-10) mol J-1. These sonolytic yields are smaller in solutions that are at the point of gas saturation, and increase to an optimum as the initial sonication-induced degassing and effervescence subsides. The probing of the sonic field has shown that the rate of sonolytic free-radical formation may vary across the sonicated volume depending on frequency and power input.

A highly efficient method for the synthesis of chloro‐substituted subphthalocyanines employing a 1 M boron trichloride solution in p‐xylene is described and compared to other previously described results. The substitution reaction of the axial chlorine atom by a phenoxy group has been optimized. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

In ozone reactions in aqueous solutions, • OH and O 2 •are often generated as short-lived intermediates and hydroperoxides are formed as labile or stable final products. Tertiary butanol reacts with ozone only very slowly but readily with • OH. In the presence of dioxygen, formaldehyde is a prominent final product, 30 ( 4%, whose ready determination can be used as an assay for • OH. Although dimethyl sulfoxide reacts much more readily with ozone, its fast reaction with • OH which gives rise to methanesulfinic acid can also be applied for the determination of • OH, at least in fast ozone reactions. The formation of O 2 •can be assayed with tetranitromethane (TNM), which yields nitroform anion (NF -) at close to diffusion-controlled rates. TNM is stable in neutral and acid solution but hydrolyzes in basic solution (k ) 2.7 M -1 s -1 ), giving rise to NFplus nitrate ion (62%) and CO 2 plus 4 nitrite ions (38%). TNM reacts with O 3 (k ) 10 M -1 s -1 ), yielding 4 mol of nitrate (plus CO 2 ) and 4 mol of O 3 are consumed in this reaction. NFreacts with O 3 (k ) 1.4 × 10 4 M -1 s -1 ) by O-transfer. The resulting products, (NO 2 ) 3 COand (NO 2 ) 2 CdO, rapidly hydrolyze (k > 10 s -1 ), and most of the nitrite released is further oxidized by ozone to nitrate. In the case of slow ozone reactions, these reactions have to be taken into account; i.e. the NO 3yield has to be measured as well. For the determination of hydroperoxides, Fe 2+ -based assays are fraught with considerable potential errors. Reliable data may be obtained with molybdate-activated iodide. The kinetics of this reaction can also be used for the characterization of hydroperoxides. Reactive hydroperoxides undergo rapid O-transfer to sulfides, e.g., k(HC(O)OOH + (HOCH 2 CH 2 ) 2 S] ) 220 M -1 s -1 , and the corresponding reaction with methionine may be used for their quantification (detection of methionine sulfoxide by HPLC). Distinction of organic hydroperoxides and H 2 O 2 by elimination of the latter by reaction with catalase can often be used with advantage but fails with formic peracid, which reacts quite readily with catalase (k ) 1.3 × 10 -3 dm 3 mg -1 s -1 ). Some examples of • OH and O 2 •formation in ozone reactions are given.

A product study of the sonolysis of the volatile substrate t-butanol in aqueous solution indicates that substrate decomposition is practically completely determined, even at concentrations as low as millimolar, by oxidative pyrolysis going on in the gas phase within the collapsing cavitational bubble. OH-Radical-induced reactions in solution are insignificant since the volatility of this substrate, its gas-phase concentration within the bubble enhanced by a certain degree of hydrophobicity, causes OH radicals generated thermolytically from water vapour to be intercepted before they can reach the aqueous phase. The nature of the products, as well as the t-butanolconcentration dependence of the product yields, can be qualitatively explained on the basis of the t-butanol-pyrolysis mechanism. Kinetic considerations involving the relative yields of the pyrolysis products ethane, ethylene and acetylene lead to an estimate of a value of 3600 K for the average pyrolysis temperature at a t-butanol bulk concentration of 10 Ϫ3 molar.

No abstract