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Hydrogen Isotope Effects and Mechanism of Aqueous Ozone and Peroxone Decompositions

Lesko, Timothy M. and Colussi, A. J. and Hoffmann, Michael R. (2004) Hydrogen Isotope Effects and Mechanism of Aqueous Ozone and Peroxone Decompositions. Journal of the American Chemical Society, 126 (13). pp. 4432-4436. ISSN 0002-7863. doi:10.1021/ja038907v.

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Hydrogen peroxide exalts the reactivity of aqueous ozone by reasons that remain obscure. Should H_2O_2 enhance free radical production, as it is generally believed, a chain mechanism propagated by (·OH/·O_2^-) species would account for O_3 decomposition rates in neat H_2O, ^HR_(-O_3), and in peroxone (O_3 + H_2O_2) solutions, ^(HP)R_(-O_3). We found, however, that:  (1) the radical mechanism correctly predicts H^R_(-O_3) but vastly overestimates ^(HP)R_(-O_3), (2) solvent deuteration experiments preclude radical products from the (O_3 + HO_2^-) reaction. The modest kinetic isotope effect (KIE) we measure in H_2O/D_2O:  ^HR_(-O_3)/^DR_(-O_3) = 1.5 ± 0.3, is compatible with a chain process driven by electron- and/or O-atom transfer processes. But the large KIE found in peroxone:  ^(HP)R_(-O_3)/^(DP)R_(-O_3) = 19.6 ± 4.0, is due to an elementary (O_3 + HO_2^-) reaction involving H−O_2^- bond cleavage. Since the KIE for the hypothetical H-atom transfer:  O_3 + HO_2^- →(2ℏ) HO^3· + ·O_2^-, would emerge as a KIE^(1/2) factor in the rates of the ensuing radical chain, the magnitude of the observed KIE must be associated with the hydride transfer reaction that yields a diamagnetic species:  O_3 + HO_2^- HO_3^- + O_2. HO_3^-/H_2O_3 may be the bactericidal trioxide recently identified in the antibody-catalyzed addition of O_2(^1Δ_g) to H_2O.

Item Type:Article
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URLURL TypeDescription Information
Colussi, A. J.0000-0002-3400-4101
Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 2004 American Chemical Society. Received October 6, 2003.
Issue or Number:13
Record Number:CaltechAUTHORS:20150623-154756056
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Official Citation:Hydrogen Isotope Effects and Mechanism of Aqueous Ozone and Peroxone Decompositions Timothy M. Lesko, A. J. Colussi, and Michael R. Hoffmann Journal of the American Chemical Society 2004 126 (13), 4432-4436 DOI: 10.1021/ja038907v
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58477
Deposited By: George Porter
Deposited On:28 Jul 2015 21:02
Last Modified:10 Nov 2021 22:05

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