Peroxy radicals chemical conversion

Results of a chemical activation induced by ultrasound have been reported by Nakamura et al. in the initiation of radical chain reactions with tin radicals [59]. When an aerated solution of R3SnH and an olefin is sonicated at low temperatures (0 to 10 °C), hydroxystannation of the double bond occurs and not the conventional hydrostannation achieved under silent conditions (Scheme 3.10). This point evidences the differences between radical sonochemistry and the classical free radical chemistry. The result was interpreted on the basis of the generation of tin and peroxy radicals in the region of hot cavities, which then undergo synthetic reactions in the bulk liquid phase. These findings also enable the sonochemical synthesis of alkyl hydroperoxides by aerobic reductive oxygenation of alkyl halides [60], and the aerobic catalytic conversion of alkyl halides into alcohols by trialkyltin halides [61]. 

For example, Cantrell and co-workers (1993) estimate the efficiency of conversion of simple alkyl peroxy radicals to vary from 0.93 for CH3CH202 to 0.47 for (CH3)2C02, and it may be even less for larger alkyl peroxy radicals. This may be the reason that in some intercomparison studies, the matrix isolation-ESR technique (vide infra), which measures the sum of ROz, gives some higher concentrations for some individual measurements than the chemical amplifier method (e.g., Zenker et al., 1998). 

Reiner, T., M. Hanke, and F. Arnold, Atmospheric Peroxy Radical Measurements by Ion Molecule Reaction-Mass Spectrometry A Novel Analytical Method Using Amplifying Chemical Conversion to Sulfuric Acid, J. Geophys. Res., 102, 1311-1326 (1997). 

The discussion that follows is divided into two sections. The Spectroscopic Methods section includes those measurement techniques that involve the interaction of a photon with a peroxy radical. The Chemical Conversion Methods section describes the measurement of another molecule or radical to which a peroxy radical has been converted. 

Chemical Amplification. The measurement of a small electrical signal is often accomplished by amplification to a larger, more easily measured one. This technique of amplification can also be applied to chemical systems. For peroxy radicals, Cantrell and Stedman (117) proposed, as a possible technique, the chemical conversion of peroxy radicals to N02 with amplification (i.e., more than one N02 per peroxy radical). This method has also been used for laboratory studies of H02 reactions on aqueous aerosols (21). The following chemical scheme was proposed as the basis of the instrument ... 

Ketones, as well as hydrocarbons, are oxidized by a chain mechanism with the participation of peroxy radicals as chain carriers. The weakest bond is the a-C—H bond (due to the carbonyl group). Therefore, oxidation proceeds chiefly at the a-C atoms. The oxidation of a ketone produces a-keto hydroperoxy as the primary intermediate product, with its subsequent conversion to different oxygen-containing products. The composition of the oxidation products depends on the chemical structure of the ketone and the experimental conditions. 

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