Inorganic reactions of iodine(+1) in acidic solutions

Abstract

We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H 2 OI + HOI + H + appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO 3 . Our new value, K(H 2 OI + HOI + H + ) ∼ 2 M at 25 • C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI → IO 3 − + 2I − + 3H + in perchloric acid solutions from 5 × 10 −2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M −1 s −1 at 25 • C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI I 2 O·H

Inorganic reactions of iodine(III) in acidic solutions and free energy of iodous acid formation

“…Thus, under conditions such that the rate law of reaction (+B) is (1), the rate law of reaction (−B) must be (2), with k +B / k −B = K B . The rate law (3) is also well established 37. Then, the rate law of reaction (C) in the forward direction must be (4) with k +C / k −C = K C .…”

“… A mechanism of reaction (C) is also proposed in the appendix. The product* K ° B K ° C , equal to k ° +B k ° +C / k ° −B k ° −C , is obtained from the accurately known thermodynamic equilibrium constants of reactions (A) and (D): K ° A = (9.8 ± 0.2) × 10 46 39,40 and 1/ K ° D = (5.3 ± 0.1) × 10 −13 at 25°C 37. At 25°C and 0.2 M ionic strength, k +B = 1250 M −3 s −1 36.…”

“…Reaction (A) is the combination of three reactions, (B) + (C) + 3 × (D), but they are themselves complicated. We have discussed the kinetics and mechanism of reactions (−C) and (D) in a former work 37 and discuss here reactions (B) and (+C).…”

Iodine oxidation by hydrogen peroxide and Bray–Liebhafsky oscillating reaction: effect of the temperature

“…The mechanism of reaction (R4) has been discussed before. 11 In acidic solutions, its complicated rate law can be reduced to the form given in Table 2. The rate r À4 of the reverse reaction decreases when [H + ] increases and we have shown 7 that it can control the rate of reaction (O) at high acidities.…”

Modelling iodide – iodate speciation in atmospheric aerosol: Contributions of inorganic and organic iodine chemistry

“…For example, the order of the Dushman reaction depends on the I − concentration (Schmitz, 2000): For I − concentrations below about 5×10 −7 M, the reaction rate depends linearly on [I − ], for I − concentrations above about 10 −3 M the dependence is quadratic. Reactions (I19−) and (I20−) ( The mechanism and rate laws of reaction I1 at different acidities are discussed in details in Schmitz (2004). In acidic or slightly acidic solutions, the rate law can be written:…”