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.

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The ozone decomposition quantum yield (phi) in millimolar and higher-concentration aqueous tertiary butanol solution is 0.64 +/- 0.05 (observed over a wavelength range from 250 to 280 nm) and rises toward lower tertiary butanol concentrations (phi approximately 1.5 at 10(-5) M at pH 2) on account of the onset of the well-known *OH-radical-induced chain reaction. The destruction of the organic is initiated by hydrogen-atom abstraction through OH radicals which are produced via the reaction of the photolytically generated O(1D) with the solvent water at a quantum yield of phi(*OH) of about 0.1. There is no decomposition of ozone in the dark on the time scale of the photolysis experiment. The efficiency of tertiary butanol destruction with respect to ozone consumption ([O3]0 = 3 x 10(-4) M), defined by the ratio delta[t-BuOH]/delta[O3], termed eta(t-BuOH), is 0.26 at millimolar tertiary butanol concentrations, determined at the stage of essentially complete ozone consumption. It diminishes toward lower tertiary butanol concentrations (delta[t-BuOH]/delta[O3] approximately 0.17 at [t-BuOH]0 = 1 x 10(-4) M). Part of the effect of the ozone, apart from being a source of *OH radicals, rests on the intervention of HO2*/O2*- which is produced in the course of the peroxyl-radical chemistry of the tertiary butanol in this dioxygen-saturated environment and converted into further *OH radical by reaction with ozone. Moreover in this system, organic free radicals and peroxyl radicals react with the ozone. On the basis of the experimental and mechanistic-simulation data, the quantum yield of direct (by hv) ozone cleavage in aqueous solution is estimated at about 0.5.

Kinetics and transformation products for the reactions of ozone with pyrrole, imidazole, and pyrazole were determined. For the imidazole–ozone reaction, all possible transformation products were identified, completing the mass balance.