Kinetics and mechanism of the hydrolytic disproportionation of iodine

Abstract

Kinetics of the hydrolytic disproportionation of I 2 3I 2 + 3H 2 O ⇔ IO+ was studied by UV-VIS spectrophotometry at 298 K and at the ionic strength 0.2 M (NaClO 4 ) in buffered solutions in the pH range 8.91-10.50 at different initial iodide concentrations. The characterization of this reaction is fundamental for modeling oscillatory and front reactions in the presence of iodine as reactant or intermediate as well as for drinking water treatment. A matrix rank analysis confirmed three absorbing species in the beginning of the reaction, whereas later assumption of two species is enough to describe the experimental data in the visible part of the spectrum. A reaction mechanism was proposed for disproportionation by using fitting/simulation with a multipurpose program package ZiTa, by simultaneous evaluation of 17,906 points in 79 experimental curves. A parameter set was suggested, which was obtained by absolute, relative, and orthogonal fittings of the experimental data. C 2004 Wiley Periodicals, Inc. Int J Chem

Kinetics of Oxidation of Iodide (I–) and Hypoiodous Acid (HOI) by Peroxymonosulfate (PMS) and Formation of Iodinated Products in the PMS/I–/NOM System

“…Interestingly, the presence of I – and IO 3 – was also observed in the case of NH 2 Cl, which was somewhat unexpected according to the kinetic rate constants of I – and HOI with NH 2 Cl (Figures b and b). This finding was explained by the contributions of side reactions, including (i) the disproportionation of HOI, − (ii) the reduction of HOI back to I – by NOM (i.e., oxidation pathway for the reaction of HOI with NOM other than a substitution pathway), , and (iii) further oxidation of HOI by HOCl in situ formed from the slow hydrolysis of NH 2 Cl. − …”

Modification of Ozone Deposition and I2 Emissions at the Air–Aqueous Interface by Dissolved Organic Carbon of Marine Origin

“…23 HOI formation: (5) ⇌ HOI(aq) HOI(g) (6) Note that the disproportionation reaction 4 is a complex reaction of several steps. 24 As well as providing a viable route for I 2 (g) and HOI(g) production, the reaction of O 3 (g) with I − in the SML contributes a significant fraction of the chemical loss of O 3 (g) to the ocean surface and thus to dry deposition. 25 The total annual global sink of O 3 (g) through dry deposition to land and sea surfaces is estimated to be comparable to the tropospheric source of ozone from stratospheric-tropospheric exchange (600−1000 Tg yr −1 ).…”

“…HOI/I 2 equilibra: HOI ( aq ) + normalI − + normalH + ⇌ normalI 2 ( aq ) + normalH 2 normalO normalI 2 ( aq ) ⇌ normalI 2 ( g ) HOI ( aq ) ⇌ HOI ( g ) Note that the disproportionation reaction is a complex reaction of several steps …”

Mechanism of N2 Reduction to NH3 by Aqueous Solvated Electrons

“…The observed yields of NH 3 , H 2 , and I 2 are presented in Table for several pH values ranging from 2 to 8. Throughout this manuscript, we refer to the product “yield” as the absolute amount produced under the experimental conditions and reaction times reported in the Methods section, consistent with the prior work of Zhu et al Higher pH conditions were not considered due to the dominance of the disproportionation reaction of I 2 with OH – under basic conditions . The majority of the reduced product is H 2 , accounting for most of the electrons lost by the oxidized I – .…”