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Issue 13, 2003
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Quantification of iodide oxidation by trichloromethyl peroxyl radicals and I + I2 ⇌ I3 equilibrium in alcohol/water mixtures

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Abstract

The molar absorption coefficient (ε) of I3 at λmax, and the equilibrium constant (Keq) for the equilibrium I2 + I ⇌ I3 were determined for various alcohol/water mixtures by using standard analytical procedures, i.e. measurement of optical densities via UV spectrophotometry. The stability of I3 is found to increase significantly with increasing amount of alcohol with Keq ranging from 7.1 × 102 dm3 mol−1 in H2O to, e.g., 2.5 × 104 dm3 mol−1 in 70% (v/v) of 2-propanol/H2O mixture. Also, by increasing the amount of alcohol, the position of λmax for I3 is shifted to longer wavelengths (from 350 to 357 nm). This red-shift is accompanied by a drop in ε from 25 400 dm3 mol−1 cm−1 in pure H2O to, e.g., 14 000 dm3 mol−1 cm−1 in a 70% (v/v) of a 2-propanol/H2O mixture. The obtained data were applied for quantitative determination of I3 by means of the time-resolved technique of pulse radiolysis, where this product was formed via oxidation of a total of three iodide ions by each CCl3OO˙. The overall process afforded formation of one equivalent each of I2 (complexed by I to I3) and I˙ (complexed to I2˙ and suffering as such disproportionation). An excellent agreement was obtained with the data from the standard analytical measurements. Furthermore, the radiation chemical yields of I3 generated in these pulse radiolysis experiments (e.g., G(I3) = 0.96 μmol J−1 in 2-propanol/H2O mixtures) are in complete correspondence with a previously suggested multi-electron oxidation mechanism. Complementary steady-state product analysis of γ-irradiated solutions confirmed the formation of I3 in high yields, with limiting values of G ≅ 0.9 μmol J−1 in 2-propanol/water mixtures over wide ranges of pH, iodide, CCl4, CH2Cl2 and 2-propanol concentrations. All the results also strongly corroborate corresponding oxidation mechanisms of organic sulfides and selenides by halogenated peroxyl radicals.

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Article information


Submitted
11 Mar 2003
Accepted
01 May 2003
First published
27 May 2003

Phys. Chem. Chem. Phys., 2003,5, 2783-2789
Article type
Paper

Quantification of iodide oxidation by trichloromethyl peroxyl radicals and I + I2 ⇌ I3 equilibrium in alcohol/water mixtures

I. Štefanić, K. Asmus and M. Bonifačić, Phys. Chem. Chem. Phys., 2003, 5, 2783
DOI: 10.1039/B302764C

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