Oxidation and Decomposition Kinetics of Thiourea Oxides

Gao, Qingyu; Lu, Bing; Li, Lianhe; Wang, Jichang

doi:10.1021/jp063956q

Cited by 30 publications

(34 citation statements)

References 21 publications

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“…k 5 and k 7 were reasonably adjusted according to pH difference between this work (at pH 2.0) and the reference (at pH 1.5). k 8 and k 9 were determined with HPLC [25]. k 10 were obtained from Rabai et al [26].…”

Section: Mechanistic Analysis and Simulationmentioning

confidence: 99%

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Feng

et al. 2011

Sci. China Chem.

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Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chromatography (HPLC) and mass spectrometry (MS) at 25 °C. By controlling the slow reaction rate and choosing appropriate mobile phase, HPLC provides the unique advantages over other methods (UV-Vis, chemical separation) in species tracking and kinetic study. In addition to thiourea and formamidine sulfinic acid, two unreported products were also detected in the hydrolysis reaction. Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyanogen with mass weights of 92.28 and 116.36, respectively. In the oxidation of formamidine disulfide by hydrogen peroxide, besides thiourea, formamidine sulfenic acid, formamidine sulfinic acid, thiocyanogen and urea, formamidine sulfonic acid and sulfate could be detected. The oxidation reaction was found to be first order in both formamidine disulfide and hydrogen peroxide. The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0. It was found both rate constants are increased with the increasing of pH. Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation, including hydrolysis equilibrium of formamidine disulfide and irreversible hydrolysis of formamidine sulfenic acid.formamidine disulfide, hydrolysis, oxidation, HPLC-MS

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Section: Mechanistic Analysis and Simulationmentioning

confidence: 99%

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Feng

et al. 2011

Sci. China Chem.

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“…[13] Some oxidation reactions of TDO have been controlled in acidic solutions. [14][15][16] The oxidations of TDO with chlorite ions, iodine, and bromine have been performed by Simoyi et al [15][16][17][18] Regrettably, the tautomerization of TDO, which seems to occur relatively slowly from (NH 2 ) 2 CSO 2 to NH 2 NHCSO 2 H [19,20] at low pH values, has so far not been taken into account in these reactions, though the two tautomers may have quite different reactivity towards chlorine dioxide and other chlorine-containing intermediates.…”

Section: Introductionmentioning

confidence: 99%

Mechanism Involving Hydrogen Sulfite Ions, Chlorite Ions, and Hypochlorous Acid as Key Intermediates of the Autocatalytic Chlorine Dioxide–Thiourea Dioxide Reaction

Horváth

Duan

et al. 2015

Eur J Inorg Chem

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The kinetics of the chlorine dioxide–thiourea dioxide reaction was investigated by monitoring absorbance–time profiles at λ = 360 nm. Under acidic conditions, the primary carbon‐containing product is cyanamide, not urea as considered previously for many oxidation reactions of thiourea dioxide. Increase of the rate of the reaction by an increase of pH can be readily explained by the slow pH‐dependent formation of a more reactive form of thiourea dioxide (TDO) that is produced steadily and unavoidably as the stock TDO solution ages. We have also found that the absorbance–time profiles of the chlorine dioxide–TDO reaction are sigmoidal with excess TDO. The addition of methionine as a hypochlorous acid scavenging agent inhibits the reaction significantly, whereas the addition of chlorite ions and trace amounts of hydrogen sulfite ions accelerates the decay of chlorine dioxide. On the basis of these experiments, a sixteen‐step kinetic model involving hypochlorous acid, chlorite ions, and hydrogen sulfite ions as key intermediates that provide an autocatalytic cycle is proposed to account for the overall kinetic behavior observed, including the slow rearrangement of TDO.

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“…Figure 3 also shows that the corresponding curves simulated with the mechanism in Table 1 have all the experimental features. Only the rate constants for R2 and R4 have been fitted; we took k 3 , k 5 and k 6 from a prior HPLC study 14 and k 8 was determined from our experiments on TU 2 hydrolysis, while k 1 and k 7 were obtained from Hoffmann 15 and Rábai et al, 16 respectively. Our value for k 2 differs significantly from the 3000 M -1 s -1 reported by Epstein et al, 2 who note that their model is quite insensitive to this value, but supports the determination of k 2 ) 10 M -1 s -1 by Rábai et al 17 In summary, HPLC can directly identify such species as TU, TU 2 , TUO 2 , TUO 3 , though not the transient sufenyl acid (HOSC(NH)NH 2 ).…”

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Simultaneous Tracking of Sulfur Species in the Oxidation of Thiourea by Hydrogen Peroxide

et al. 2008

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We employ reversed-phase ion-pair high-performance liquid chromatography to quantitatively characterize the oxidation kinetics of thiourea oxidation by hydrogen peroxide. The HPLC technique makes it possible to monitor the concentrations of a variety of sulfur-containing species with different oxidation states and to elucidate the relative phase relations among them. The experimental results are in good agreement with simulations from an 8-step reaction mechanism.Oxidation reactions of sulfur(-II) compounds such as thiourea (TU) can be quite complex, yielding species with oxidation states ranging from -1 to +6. [1][2][3][4] Researchers have investigated the dynamics of these reactions from several perspectives: First, the mechanism of the nonlinear reaction between various oxidants and TU is of considerable interest for explaining such exotic phenomena as oscillations, chaos and spatiotemporal patterning seen in such systems. [5][6][7][8] Secondly, the physiological effects of thiourea oxides have attracted scientists to explore the biofunction of these sulfur species. 9,10 Finally, sulfur abatement is a key technology in alleviating environmental pollution. 4,11 To tackle the above challenges, understanding the basic sulfur chemistry, i.e., the kinetics and mechanism of the changes of sulfur oxidation state, is essential. A major obstacle is the difficulty of tracking the different oxidation states of sulfur during the reaction. Standard methods of chemical analysis, which typically involve multiple steps and intensive experimental efforts, generally fail for most intermediates in these systems. UV-visible spectroscopy cannot quantify the sulfur intermediates, because their absorption spectra overlap.Thiourea (λ max )196 nm and 236 nm, ε ) 11273 and 11048 M -1 cm -1 ), is a typical sulfur(-II) compound that is widely used in industrial production. Its oxidation involves the formation of such reagents as formamidine disulfide (TU 2 , λ max ) 218 nm, ε ) 21523 M -1 cm -1 ), thiourea dioxide (TUO 2 , λ max ) 269 nm, ε ) 489 M -1 cm -1 ), thiourea trioxide (TUO 3 , λ max ) 202 nm, ε ) 7295 M -1 cm -1 ), sulfite (λ max ) 205 nm, ε ) 3548 M -1 cm -1 ) and sulfate. The overlap of the UV-vis absorption spectra prevents simultaneous detection of these intermediates. Using high-performance liquid chromatography (HPLC), Grigorova and Wright 12 separated thiourea, formamidine disulfide and cyanamide from a hydrogen peroxide-thiourea reactive mixture. In this report, we describe a new approach for directly tracking the evolution of multiple sulfur species and performing kinetic analysis.We employ reversed-phase ion-pair high-performance liquid chromatography to quantitatively characterize the oxidation kinetics of TU oxidation by hydrogen peroxide. Indeed, the capability to monitor simultaneously the time evolution of multiple sulfur species allows us not only to study the reaction kinetics but also to characterize the relative phase relations of the different species. Our results demonstrate that HPLC is a unique and effec...

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Oxidation and Decomposition Kinetics of Thiourea Oxides

Cited by 30 publications

References 21 publications

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Mechanism Involving Hydrogen Sulfite Ions, Chlorite Ions, and Hypochlorous Acid as Key Intermediates of the Autocatalytic Chlorine Dioxide–Thiourea Dioxide Reaction

Simultaneous Tracking of Sulfur Species in the Oxidation of Thiourea by Hydrogen Peroxide

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