Naslov
Rate Constants for the Reaction of Halogenated Alkylperoxyl Radicals with Iodide: Influence of Substituents, Solvent Polarity, and Proton Concentration

Autori
Štefanić, Igor ; Asmus, Klaus-Dieter ; Bonifačić, Marija

Izvornik
Journal of physical organic chemistry (0894-3230) 18 (2005); 408-416

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
multi-electron oxidation; peroxyl radical; pH effect; pulse radiolysis; rate constants; solvent polarity effect; substituent effect

Sažetak
This pulse radiolysis study deals with the reaction of iodide ions (I ) with a series of halogenated alkylperoxyl radicals in 2-propanol/water mixtures. Under investigation were CF3OO• , CFCl2OO• , CCl3OO• , C2Cl5OO• , CHCl2OO• , and CF3CHClOO• . Each of these peroxyl radicals oxidizes a total of three I ions in a fast and practically simultaneous reaction sequence. An overall 2-electron step, involving a transient peroxyl-iodide adduct radical, results in the oxidation of two iodide ions to yield molecular I2 and the corresponding halogenated alkoxyl radical, R(Hal)O• . The latter is responsible for the oxidation of the third iodide to yield iodine atoms, I• . The overall second-order rate constants for these multi-electron oxidation processes were determined by following the formation kinetics of I3 /I2•  , the spectrophotometrically accessible forms of I2 and I• in I containing solutions. These rate constants were determined as a function of pH, polarity of solvent mixtures, and electronegativity of the substituents at the  -C atom of the peroxyl radicals. They strongly depend on all these variables, with the actual numbers covering a range from 3 × 105 to 7.0 × 108 M 1 s 1. A good linear relationship is obtained between log k and the dielectric constant of the solvent mixture. Within a particular solvent mixture the rate constants strongly depend on the substituents at the alkylperoxyl moiety and correlate with Taft's inductive substituent constants  *. The overall multi-electron oxidation mechanism of alkylperoxyl radicals is discussed in the light of the new results.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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