Abstract
In the presence of low concentrations of tris(3,4,7,8-tetramethyl-l,10-phenanthroline)iron(II) (FenTMP), nitrous acid decomposes to yield nitric oxide and nitrate. The kinetics of this two-stage reaction have been studied by using rapid-mixing techniques. During the first rapid phase, FenTMP is oxidized by HN02 and by N02~ to FelnTMP. The initial ferrous complex is then regenerated in a slower second phase dominated by the reaction of FelnTMP with N02. Rate constants for the reactions of FelnTMP with nitrous acid and with nitrite were found to be (7.26 ± 0.07) X 102 M'1 s~' and (2.57 ± 0.03) X 104 M"1 s_1, respectively, at 25 °C and ionic strength 0.5 M. Computer simulations have been carried out by using a mechanism developed for the hexaaquoiron(II)-nitric acid system, with appropriate modification for the different kinetic properties of the iron species. Quantitative agreement between calculation and experiment is obtained for the first phase, and the model qualitatively predicts the observed regeneration of FeTMP(II) in the second phase.