One-electron reduction reactions of some inorganic nitrogen radicals in water

Abstract

The technique of pulse radiolysis and kinetic absorption spectrophotometry has been used to generate various inorganic nitrogen radicals and follow their one-electron reduction reactions. The method used is based on following the one-electron reduction of these free radicals (R)by various electron donor compounds (DH) present in solution: the R^&middot;+ DH &rarr; R^- (or RH) + D^&middot; + H⁺<em>. </em>The efficiency of this reaction is usually monitored by observing the formation of the D^&middot;radicals at the wavelength of their absorption The efficiency of reduction of R^&middot; radicals is found to depend upon the known redox potentials <em>(E&nbsp;</em>at pH 7.0, 25&deg;C) of the donor compounds. Typical titration curves are obtained and from the midpoint (50% electron transfer) the "kinetic potentials" <em>E</em>of the R^&middot;radicals can be derived. The <em>E</em>&nbsp;values for the one-electron reduction of the following inorganic nitrogen radicals have been determined: ^&middot;N₃(&ge;+0.41 V), ^&middot;NH₃⁺(+O.55V), ^&middot;NH₂(+0.20V), CH₃^&middot;NH₂⁺ (+0.06V), CH₃^&middot;NH (-0.05V), ^&middot;N₂H₄ (+O.034V), ^&middot;N₂H₃(+0.20V), ^&middot;NHOH (-0.40V), and ^&middot;NHOCH₃ (-0.45V). These values are based on the two-electron redox potentials of the donor compounds. The electron transfer kinetics leading to the formation of DOradicals' are determined and rate constants <em>(S;6.0 </em>x 10⁹ <em>M^-1 </em>sec^-1 ) have been obtained. The implications of the results with regard to the reaction mechanism and kinetics of these inorganic nitrogen free radicals are discussed.