Kinetic salt effects in the bromide oxidation by bromate

Burgos, Francisco Sánchez; Graciani, Marı́a del Mar; Múñoz, Ernestina; Moyá, Marı́a Luisa; Capitán, M. J.; Galán, Miguel Á.; Hubbard, Colin D.

doi:10.1007/bf00645976

Cited by 14 publications

(8 citation statements)

References 12 publications

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“…As can be seen in Table 4, our values for the fourthorder rate constant are in good agreement with the values obtained by most other authors, especially those of Domínguez and Iglesias 8 . At high I values our results show an increase in the rate constant with the increase of the ionic strength as has been observed by many authors, but not the very strong increase observed by Burgos et al 10 . We are not able to explain the reason for this disagreement.…”

Section: Resultssupporting

confidence: 84%

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Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Côrtes

Faria

2001

J. Braz. Chem. Soc.

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A reação bromato-brometo, em meio de ácido perclórico, foi observada numa faixa de acidez até então não estudada. A reação foi acompanhada através da medida da absorvância no ponto isosbéstico para as espécies Br 2 e Br 3 -(λ = 446 nm). Observou-se um comportamento de primeira ordem para o bromato e para o brometo e um comportamento de segunda ordem para o H + , levando à lei de velocidade ν = k[BrO 3 -][Br -][H + ] 2 . Esta lei de velocidade sugere um mecanismo envolvendo duas protonações sucessivas do íon bromato, formando o H 2 BrO 3 + , que então reage com o íon brometo.Estes resultados discordam de outros estudos que verificaram um comportamento de segunda ordem para o íon brometo, bem como um comportamento de primeira ordem para o H + , que levaram a propor a existência de intermediários tais como H 2 Br 2 O 3 e HBr 2 O 3 -. O comportamento de segunda ordem observado para o H + na faixa de concentração 0,005 ≤ [H + ] ≤ 2,77 mol L -1 permite afirmar que o pK a do ácido brômico, HBrO 3 , deve ser menor do que -0,5 a 25 °C, diferentemente de todas as propostas existentes até agora na literatura para o valor deste pK a .The bromate-bromide reaction was investigated in an acidity range not studied yet. The reaction was followed at the Br 2 /Br 3 isosbestic point (λ = 446 nm). It was observed a first-order behavior for bromate and bromide ions and a second-order behavior for H + ion that results in the rate law ν = k[BrO 3 -][Br -][H + ] 2 . This rate law suggests a mechanism involving two successive protonation of bromate followed by the interaction of the intermediate species H 2 BrO 3 + with bromide. These results disagree with the obtained by other authors who observed a second-order behavior for the bromide and first-order for H + , and have proposed intermediate species like H 2 Br 2 O 3 and HBr 2 O 3 -. The second-order for [H + ] observed in the range 0.005 ≤ [H + ] ≤ 2.77 mol L -1 sets down that the pK a of bromic acid, HBrO 3 , must be lower than -0.5 (T = 25 °C), different from all other values for this pK a proposed in the literature.

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Section: Resultssupporting

confidence: 84%

“…al. 10 followed this reaction at the λ max of Br 2 , using UV-Vis spectroscopy. They found a significant increase in the rate constant of this reaction at high values of ionic strength especially when it was controlled by NaClO 4 .…”

Section: Introducionmentioning

confidence: 99%

Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Côrtes

Faria

2001

J. Braz. Chem. Soc.

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“…The explanation is simple; they included trace impurities of bromide ion (5 × 10 –6 M) which is enough to drive the overall reaction via sequence of steps and ; consequently, step was not needed anymore to initiate the reaction. Certainly, the rate-determining step in their kinetic model is therefore step whose rate law is proportional to the square of the hydrogen ion concentration as it was established previously by numerous research groups independently. − Step is a very rapid process that is way out of the timescale of a stopped-flow instrument; therefore, the rate coefficient of this reaction cannot be determined under our experimental condition, so it was fixed at a value of 10 6 M –1 s –1 during the whole calculation procedure. 13 C NMR studies revealed that in excess of TDO after the reaction is completed, again a mixture of urea, cyanamide, and dissolved carbon dioxide may as well be detected (see: Supporting Information, Figure S2).…”

Section: Resultsmentioning

confidence: 98%

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

et al. 2019

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The thiourea dioxide (TDO)–bromate reaction has been reinvestigated spectrophotometrically under acidic conditions using phosphoric acid–dihydrogen-phosphate buffer within the pH range of 1.1–1.8 at 1.0 M ionic strength adjusted by sodium perchlorate and at 25 °C. The title system shows a remarkable resemblance to the classical Landolt reaction, namely, the clock species (bromine) may only appear after the substrate TDO is completely consumed. Thus, the title system can be classified as substrate-depletive clock reaction. Despite the well-known slow rearrangement characteristic of TDO in acidic solution, it is surprisingly found that the Landolt time of the title reaction does not depend at all on the age of TDO solution applied. It is, however, shown experimentally that the inverse of Landolt time linearly depends on the initial bromate concentration as well as on the square of the hydrogen ion concentration. In addition to this, it is also noticed that dihydrogen phosphate markedly affects the Landolt time as well, and this feature may easily be taken into consideration by the H2PO4 – dependence of the rate of bromate–bromide reaction quantitatively. Based on the experiments, a simple three-step kinetic model is proposed from which a complex formula is derived to indicate the exact concentration dependence of the Landolt time.

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“…ionic strength higher than 1 mol dm -3 . The theoretical interpretation of the salt effects on k 3 w can be done by considering the Brönsted equation that relates the variation of the rate constant with the activity coefficients of the reactants and the activated complex and with the activity coefficients being calculated by using the Davies equation or an extended Debye−Hückel equation. , This method has been followed by Burgos et al in the interpretation of salt effects in this reaction in aqueous electrolyte solutions of high ionic strength. Following the same procedure, we obtained a value of 6.9 mol -3 dm 9 s -1 for ( k 3 w ) o , that is, the rate constant extrapolated to I = 0.…”

Section: Resultsmentioning

confidence: 99%

Micellar Effects on the Ionic-Redox Reaction BrO₃^-/Br^- in Acid Medium

Domínguez

Iglesias

1998

Langmuir

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The redox reaction between bromate and bromide ions in aqueous acid medium was studied in the absence and presence of cationic and anionic surfactants. The rate equation in water was found to be v ) k3 w [BrO3 -][Br -][H + ] 2 . The cationic surfactant, tetradecyltrimethylammonium bromide, catalyzes the reaction, using either HBr or HNO3 as the source of H + ; nevertheless, the observed rate constant decreases slightly, goes through a minimum, and increases again as the tetradecyltrimethylammonium nitrate concentration increases. The anionic surfactant, sodium dodecyl sulfate, strongly inhibits the reaction when its concentration is increased, reaching a leveling off at high surfactant concentration; but hydrogen dodecyl sulfate catalyzes the reaction. These micellar effects are quantitatively explained on the basis of the pseudophase ion exchange model: tetradecyltrimethylammonium bromide increases the Brconcentration, while sodium dodecyl sulfate decreases the H + concentration (through the exchange with Na + counterions) in the water phase where the reaction takes place.

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Kinetic salt effects in the bromide oxidation by bromate

Cited by 14 publications

References 12 publications

Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

Micellar Effects on the Ionic-Redox Reaction BrO₃^-/Br^- in Acid Medium

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Kinetic salt effects in the bromide oxidation by bromate

Cited by 14 publications

References 12 publications

Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

Micellar Effects on the Ionic-Redox Reaction BrO3-/Br- in Acid Medium

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Micellar Effects on the Ionic-Redox Reaction BrO₃^-/Br^- in Acid Medium