Hydrogen Isotope Effects and Mechanism of Aqueous Ozone and Peroxone Decompositions
Abstract
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.
Additional Information
© 2004 American Chemical Society. Received October 6, 2003.Attached Files
Supplemental Material - ja038907vsi20040120_083246.pdf
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Additional details
- Eprint ID
- 58477
- DOI
- 10.1021/ja038907v
- Resolver ID
- CaltechAUTHORS:20150623-154756056
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2015-07-28Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field