Hydroxyl Radical Formation during Peroxynitrous Acid Decomposition

• Published in: Journal of the American Chemical Society Vol. 121; no. 11; pp. 2438 - 2443
• Main Authors: Coddington, John W, Hurst, James K, Lymar, Sergei V
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.03.1999
• Subjects: 40 CHEMISTRY; DECOMPOSITION; HYDROXYL RADICALS; NITROUS ACID; OXIDIZERS; PEROXY RADICALS; SYNTHESIS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja982887t

Yields of O2 formed during decomposition of peroxynitrous acid (ONOOH) under widely varying medium conditions are compared to predictions based upon the assumption that the reaction involves formation of discrete •OH and •NO2 radicals as oxidizing intermediates. The kinetic model used includes all reactions of •OH, •O2 -, and reactive nitrogen species known to be important under the prevailing conditions; because the rate constants for all of these reactions have been independently measured, the calculations contain no adjustable fitting parameters. The model quantitatively accounts for (1) the complex pH dependence of the O2 yields and (2) the unusual effects of NO2 -, which inhibits O2 formation in neutral, but not alkaline, solutions and also reverses inhibition by organic •OH scavengers in alkaline media. Other observations, including quenching of O2 yields by ferrocyanide and bicarbonate, the pressure dependence of the decomposition rate, and the reported dynamic behavior for O2 generation in the presence of H2O2, also appear to be in accord with the suggested mechanism. Overall, the close correspondence between observed and calculated O2 yields provides strong support for decomposition via homolysis of the ONOOH peroxo bond.