Kinetics and Mechanism of the Oxidation of Bromide by Periodate in Aqueous Acidic Solution

Abstract

The periodate–bromide reaction has been studied spectrophotometrically mainly in excess of bromide ion, monitoring the formation of the total amount of bromine at 450 nm at acidic buffered conditions and at a constant ionic strength in the presence of a phosphoric acid/dihydrogen phosphate buffer. The stoichiometry of the reaction was established to be strictly IO4(–) + 2Br(–) + 2H(+) → Br2 + IO3(–) + H2O. The formal kinetic order of the reactants was found to be perfectly one and two in the cases of periodate and bromide, respectively, but that of the hydrogen ion lies between one and two. We have also provided experimental evidence that dihydrogen phosphate accelerates the formation of bromine, suggesting the appearance of strong buffer assistance. On the basis of the experiments, a simple two-step kinetic model is proposed involving BrIO3 as a key intermediate that perfectly explains all of the experimental findings. Furthermore, we have also shown that in huge excess of bromide, the apparent rate coefficient obtained from the individual curve fitting method of the absorbance–time series is necessarily independent of the initial periodate concentration that may falsely be interpreted as the rate of bromine formation is also independent of the concentration of periodate.

Bromide Ion Impurity-Induced Reaction between Selenium(IV) and Acidic Bromate: Prototype of a Cycle with Autocatalytic Behavior

“…To avoid time-consuming calculations, the number of the absorbance–time data pairs in each kinetic curves has been reduced approximately to 60 based on the principle of equivalent arc length, the method which was described in detail elsewhere. 17 The absorbance–time traces (measured at 450 nm where only Br 2 and Br 3 – absorb the light, where ε Br 2 = = 104 M –1 cm –1 18 ) obtained by this way were evaluated by the ChemMech program package developed for determination of the kinetic parameters by minimizing the average absolute deviation between the measured and calculated data-pairs of all the measurements taken into account simultaneously. 19 The criterion of the best fit was to obtain not more than 2% relative average deviation, which is the experimentally achievable and reasonable limit of error in this system.…”

Kinetics and Mechanism of Selenium(IV) Oxidation by Aqueous Bromine Solution

“…The bromine stock solution was made from dissolving elemental bromine in 0.001 M perchloric acid solution to prevent the hydrolysis of bromine. Its concentration was checked by UV–vis spectroscopy at the isosbestic point of the bromine–tribromide system at 450 nm, where ε Br 2 = ε normalB normalr 3 − = 104 M –1 s –1 . The ionic strength of all solutions was adjusted to 0.5 M by addition of the necessary amount of sodium perchlorate.…”

“…Its concentration was checked by UV–vis spectroscopy at the isosbestic point of the bromine–tribromide system at 450 nm, where = = 104 M –1 s –1 . 27 The ionic strength of all solutions was adjusted to 0.5 M by addition of the necessary amount of sodium perchlorate.…”

Electrochemical Umpolung of Bromide: Transition-Metal-Free Bromination of Indole C–H Bond

“…Halogen ions, especially bromide ions, are typical nucleophiles, which are frequently used for nucleophilic substitution and addition. In order to achieve the umpolung of bromide to bromo-based electrophiles, strong chemical oxidants are regularly required [20,21,22,23,24,25,26,27,28]. However, based on the intrinsic disadvantages of chemical oxidants, such as toxicity, environmental pollution, explosion risk, and economic costs, there is a growing need for green and sustainable approaches for the umpolung of bromides.…”