Kinetics and mechanism of oxidation of hydrazine by tri-iodide ion in aqueous acidic media
Abstract
The kinetics of oxidation of hydrazine (L) by I3– follows a pseudo-first-order rate law in aqueous acetic acid–sulphuric acid media in the range [H+] 2.0–1.58 × 10–3 mol dm–3. The pseudo-firstorder rate constants (kobs.) exhibit: (1) at [H+]= 0.9 mol dm–3 a linear dependence on [L]o at low [L]o, with a tendency to a limiting value at high relative [L]o; (2) a decreasing and complex trend in [I–] and in [H+]; (3) a decreasing trend with decreasing dielectric constant of the medium; and (4) negligible dependences on the ionic strength of the medium, on added Cu2+(aq), and on added ethylenediaminetetra-acetate. The results are interpreted in terms of a mechanism which envisages (a) negligible reactivities of I3– and of HL+ predominant in the medium, (b) an inner-complex mechanism of electron transfer (i.e. a 1 : 1 σ-charge-transfer co-ordination prior to the electron transfer) involving I2 and L, and (c) an encounter reaction between IOH and L. Mechanistic ambiguities of some earlier reports of the same reaction are explained.