Mechanism of the oxidation of iron(II) by the azide radical

Abstract

The azide radical reacts with Fe²⁺_aq at pH 5.6 to produce a coloured species which is identical to that obtained by adding ferric iron to sodium azide solution at the same pH. The rate of formation of the coloured species is independent of [Fe²⁺_aq] and proportional to [N^–₃], and indicates that oxidation of Fe²⁺_aq by N₃ proceeds by rapid outer-sphere electron transfer [k(N₃+ Fe²⁺_aq) > 1.7 × 10⁹ dm³ mol^–1 s^–1] followed by a rate controlling reaction between N^–₃ and the product Fe^III[k(N^–₃+ Fe^III)= 8.4 × 10⁵ dm³ mol^–1 s^–1].