A kinetic study of the oxidation of hydrazine by tris(1,10-phenanthroline)iron(III) in acidic medium

The oxidation of hydrazine by tris(1,10-phenanthroline)iron(III) in acidic medium shows first order kinetics in the oxidant, FeIII(phen)33+. With respect to N2H4 saturation kinetics, consistent with reactant association (small k-values) prior to the redox step, has been observed. Irreversible decomposition of FeII(phen)32+ and FeIII(phen)33+ cause unwanted interference in the latter stages of the reaction. An increase of [H+] has a decreasing effect on the rate of the N2H4 oxidation by FeIII(phen)33+ and a value of Ka1 = 0.42 ± 0.05 M (pKa1 = 0.38) at μ = 1.0 M with N2H5+ the more reactive species has been obtained. Activation parameters, applicable to the specific experimental conditions, for the oxidation of hydrazine by FeIII(phen)33+ have been determined as ΔH‡ΔH‡ = 69 ± 6 kJ mol−1 and ΔS‡ΔS‡ = −53 ± 20 J K−1 mol−1. A study of the decomposition of FeII(phen)32+ and FeIII(phen)33+ have also been performed to quantify the effect of these decomposition reactions on the oxidation rate of the hydrazine. The rate of decomposition of the FeII(phen)32+ and FeIII(phen)33+ are ca 50 and 75 fold slower than the N2H4 induced reduction of the tris(1,10-phenanthroline)iron(III).

The kinetics of the oxidation of hydrazine by FeIII(phen)33+ was studied as a function of [H+], ionic strength and temperature under pseudo first order conditions, while allowing for the decomposition of Fen(phen)3n+ (n = 2 or 3).Figure optionsDownload as PowerPoint slide