The Autocatalytic Reduction of Ferriin by Malonic Acid with Regard to the Ferroin-Catalyzed Belousov-Zhabotinsky Reaction

Mrákavová, Marta; Melicherčík, Milan; Olexová, Anna; Treindl, Ľ.

doi:10.1135/cccc20030023

Cited by 7 publications

(17 citation statements)

References 18 publications

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“…There is a distinct imbedded 1:2:2:1 pattern with hyperfine coupling constants which we could not attribute to any known radical species in literature. The Belousov–Zhabotinskyi reaction mechanism in highly acidic media has established the existence of the bromine dioxide radical as the backbone in the generation of autocatalysis which is the essential nonlinearity for oscillatory behavior: − Oxidation by bromine dioxide radical is via a one-electron transfer: Combining and 2 shows that HBrO 2 is produced autocatalytically via quadratic autocatalysis in which 1 mol of bromous acid, HBrO 2 results in 2 mol of bromous acid, resulting in an ever-increasing reaction rate. The BrO 2 · radical can react with the enol form of DMTU to produce a sulfur-based radical: …”

Section: Resultsmentioning

confidence: 99%

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of 1,3-Dimethylthiourea by Acidic Bromate

Olagunju

Simoyi

2017

J. Phys. Chem. A

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The mechanism of oxidation of the well-known radical scavenger dimethylthiourea, DMTU, by acidic bromate was studied. The stoichiometry of the reaction is 4:3: 4BrO + 3CS(NHMe) + 3HO → 3SO + 3CO(NHMe) + 6H + 4Br. In excess acidic bromate, the reaction stoichiometry is 8:5: 8BrO + 5CS(NHMe) + HO → 5SO + 5CO(NHMe) + 4Br + 2H. In excess bromate, the reaction displays well-defined clock reaction characteristics in which initially there is a quiescent period before formation of bromine. The direct reaction of aqueous bromine with DMTU, with a bimolecular rate constant of k = (1.95 ± 0.15) × 10 M s, is much faster than reactions that form bromine such that formation of bromine indicates complete consumption of DMTU. ESI spectrometry showed evidence for an oxidation pathway that passes through the sulfenic, sulfinic, and sulfonic acids before formation of sulfate. In contrast to the oxidation of tetramethylthiourea, these oxoacid intermediates are not as abundant or as stable. The final product of oxidation was dimethylurea, the desulfurized DMTU. EPR spectroscopy implicates more than one set of radical species. The absence of the dimeric DMTU species, even in excess reductant indicates negligible formation of thiyl radicals. This also precludes substantial formation of the sulfenic acid intermediate which would form the dimer from a condensation-type reaction with unreacted DMTU. A 20-step reaction mechanism network was modeled which gave a reasonable fit with experimental data.

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Section: Resultsmentioning

confidence: 99%

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of 1,3-Dimethylthiourea by Acidic Bromate

Olagunju

Simoyi

2017

J. Phys. Chem. A

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“…Addition of bromide in conditions of excess bromate concentrations accelerated the rate of reaction and decreased the induction periods in Figures a and a. The resulting oxybromine species, HBrO 2 and HOBr carry the bulk of the oxidation . Since rate-determining step is reaction , the overall kinetics would be overall fourth order: rate = italick 0 [ BrO 3 − ] false[ normalH + false] 2 [ Red ] Red, the reductant, could be substrate MESNA or, initially, trace amounts of bromide in the reaction mixture always resident in any standard bromate solutions.…”

Section: Mechanismmentioning

confidence: 99%

“…The mechanism of the generation of radicals from oxybromine chemistry is well-established. This pathway was derived from studies of the Belousov–Zhabotinskyi reaction, with the central species being the autocatalytic bromous acid BrO 3 − + HBrO 2 + normalH + ⇄ 2 BrO 2 • prefix+ normalH 2 normalO BrO 2 • prefix+ RSH ⇄ RS • prefix+ HBrO 2 2 RS • → RSSR RSH is assumed to be the generic thiol, MESNA, and RSSR, the dimeric species at m / e = 280.9294.…”

Section: Mechanismmentioning

confidence: 99%

“…As the reaction proceeds, it is produced autocatalytically (reaction ). Standard Oxybromine Reactions: M4–M6. This is a well-known series of reactions which have been studied extensively in the analysis of the Belousov–Zhabotinsky reaction . Bromate, itself is quite inert, and has to be primed through reaction M4 to generate the reactive oxidizing species; HBrO 2 and HOBr.…”

Section: Mechanismmentioning

confidence: 99%

“…The resulting oxybromine species, HBrO 2 and HOBr carry the bulk of the oxidation. 35 Since ratedetermining step is reaction R7, the overall kinetics would be overall fourth order:…”

Section: ■ Mechanismmentioning

confidence: 99%

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Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Chemoprotectant, Sodium 2-Mercaptoethanesulfonate, MESNA, by Acidic Bromate and Aqueous Bromine

et al. 2014

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The oxidation of a well-known chemoprotectant in anticancer therapies, sodium 2-mercaptoethanesulfonate, MESNA, by acidic bromate and aqueous bromine was studied in acidic medium. Stoichiometry of the reaction is: BrO3(-) + HSCH2CH2SO3H → Br(-) + HO3SCH2CH2SO3H. In excess bromate conditions the stoichiometry was deduced to be: 6BrO3(-) + 5HSCH2CH2SO3H + 6H(+) → 3Br2 + 5HO3SCH2CH2SO3H + 3H2O. The direct reaction of bromine and MESNA gave a stoichiometric ratio of 3:1: 3Br2 + HSCH2CH2SO3H + 3H2O → HO3SCH2CH2SO3H + 6Br(-) + 6H(+). This direct reaction is very fast; within limits of the mixing time of the stopped-flow spectrophotometer and with a bimolecular rate constant of 1.95 ± 0.05 × 10(4) M(-1) s(-1). Despite the strong oxidizing agents utilized, there is no cleavage of the C-S bond and no sulfate production was detected. The ESI-MS data show that the reaction proceeds via a predominantly nonradical pathway of three consecutive 2-electron transfers on the sulfur center to obtain the product 1,2-ethanedisulfonic acid, a well-known medium for the delivery of psychotic drugs. Thiyl radicals were detected but the absence of autocatalytic kinetics indicated that the radical pathway was a minor oxidation route. ESI-MS data showed that the S-oxide, contrary to known behavior of organosulfur compounds, is much more stable than the sulfinic acid. In conditions where the oxidizing equivalents are limited to a 4-electron transfer to only the sulfinic acid, the products obtained are a mixture of the S-oxide and the sulfonic acid with negligible amounts of the sulfinic acid. It appears the S-oxide is the preferred conformation over the sulfenic acid since no sulfenic acids have ever been stabilized without bulky substituent groups. The overall reaction scheme could be described and modeled by a minimal network of 18 reactions in which the major oxidants are HOBr and Br2(aq).

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Oxyhalogen−Sulfur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetylthiourea by Chlorite and Chlorine Dioxide

et al. 2006

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The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).

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The Autocatalytic Reduction of Ferriin by Malonic Acid with Regard to the Ferroin-Catalyzed Belousov-Zhabotinsky Reaction

Cited by 7 publications

References 18 publications

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of 1,3-Dimethylthiourea by Acidic Bromate

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of 1,3-Dimethylthiourea by Acidic Bromate

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Chemoprotectant, Sodium 2-Mercaptoethanesulfonate, MESNA, by Acidic Bromate and Aqueous Bromine

Oxyhalogen−Sulfur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetylthiourea by Chlorite and Chlorine Dioxide

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