Kinetics and mechanism of the oxidation of hydrazine with iron(III) in acidic perchlorate media

Abstract

The title reaction was investigated by determining iron(III) with thiosulphate under the condition [N₂H₅⁺]/[Fe^III] > 1 and the stoicheiometry is 1 : 1. Reproducible results were obtained from the same stock solution of iron(III) perchlorate. The mechanism proposed for the reaction is shown in equations (i)–(iii), and the corresponding rate law is as in equation (iv); K₁ and K₂/K₃ were found to be Fe³⁺+ H₂O [graphic omitted] [Fe(OH)]²⁺+ H⁺(i), [Fe(OH)]²⁺+ N₂H₅⁺ [graphic omitted] Fe²⁺+ N₂H₄⁺+ H₂O (ii), N₂H₄⁺+ N₂H₅⁺ [graphic omitted] products (iii), –d[Fe^III]//_dt=K_Hk₁k₃[Fe^III][N₂H₅⁺]²//_{[H⁺](k2[Fe^II]+k3[N2H5⁺])}(iv), 2.0 ± 0.2 s ¹ and 0.66 ± 0.03 at 55 °C. The rate law has been verified under all conditions except that where [Fe^II][N₂H₅⁺] since Fe^II retards the rate and the lower limit of concentration of N₂H₅⁺ is governed by [Fe^III]. The rate of reaction decreases in the presence of sulphate ions showing that sulphate complexes of iron(III) are not reactive.