Oxidation Of Thiourea Research Articles

Kinetics of the outer-sphere oxidation of thiourea by heteropoly-α2-17-tungsto-1-vanadodiphosphate anion

Kinetics of the oxidation of thiourea (tu) by heteropoly-α2-17-tungsto-1-vanadodiphosphate anion, α2-[P2VVW17O62]7−, have been studied spectrophotometrically in aqueous acidic medium at 25 °C. At low pH (2.4–3.0), the neutral form of tu is the only reactive species. At higher pH (4.2–4.9), both neutral and deprotonated forms of tu participate in the reaction. The observed mixed-order kinetics suggest two parallel reactions: one in which the order in [tu] is unity, and a second in which it is two. In both cases, the order in [α2-[P2VVW17O62]7−] is unity. Based on the kinetic studies, a mechanism is proposed, in which a second-order proton-coupled electron transfer involving NH2CSNH2 and α2-[P2VVW17O62]7− proceeds through a sequential electron transfer, followed by proton transfer such that the reaction is an “activation-controlled” outer-sphere electron transfer process. By applying the Marcus equation, the self-exchange rate constants for the couples $${\text{NH}}_{2} {\text{CSNH}}_{2}^{ \cdot + }$$ /NH2CSNH2 and α2-[P2VVW17O62]7−/α2-[P2VIVW17O62]8− were evaluated.

Kinetics and mechanism of oxidation of thiourea by a bridging superoxide in the presence of Ellman’s reagent

In aqueous acetate buffer, reaction between the superoxo complex [(dien)(en)CoIII(O2)CoIII(en)(dien)]5+ (1) and thiourea (Tu, SC(NH2)2) proceeds through a complex kinetic pathway and the change of the absorbance of 1 with time follows a sigmoidal trace. Only in the presence of Ellman’s reagent (5,5′-dithio-bis-(2-nitrobenzoic acid), DTNB), the reaction becomes quantitative and Tu reduces the bound superoxo group (––) of 1 to the corresponding peroxo group (––) in [(dien)(en)CoIII(O2)CoIII(en)(dien)]4+ (2). In the presence of DTNB, with large excess of Tu over [1], the reaction follows first-order kinetics and the observed rate constant, ko, increases linearly with the increase in [1], [TTu] ([TTu] is the analytical concentration of Tu), [H+], and the media ionic strength (I). The presence of an intercept in the plot of ko versus [H+] suggests that both tautomeric forms of thiourea, i.e. TuZ and its protonated form TuZH+, are kinetically reactive reductants. The calculated rate constant values for k1 (~102) and k2 (~104) indicate that TuZH+ plays the leading role in the redox reaction. The present work also reveals the prospective involvement of Ellman’s reagent as a radical scavenger.

Electrochemical sensor for the determination of thiourea using a glassy carbon electrode modified with a self-assembled monolayer of an oxadiazole derivative and with silver nanoparticles

This article reports on an electrochemical sensor for thiourea. It is based on a glassy carbon electrode (GCE) modified with a self-assembled monolayer of an oxadiazole derivative and with silver nanoparticles. The modified GCE demonstrated highly catalytic activity in terms of thiourea oxidation. The peak potential is shifted to negative values compared to a GCE coated with silver nanoparticles only. The electrode was characterized by linear sweep voltametry, cyclic voltammetry and chronoamperometry, and thiourea was determined by differential pulse voltammetry in aqueous buffer of pH 7.0 resulting in two linear response ranges of 0.001 − 69.4 and 69.4 − 833.3 μM and the limit of detection of 0.1 nM. The method was applied to the determination of thiourea in copper refinery electrolyte, orange juice and tap water samples. The recoveries ranged from 96.9 to 108.0 %.

Chemisorbed Sulfate-Driven Oscillatory Electro-Oxidation of Thiourea on Gold

The electrochemical oxidation of thiourea in phosphate-buffered solution (PBS, pH 6.0) was studied, and it was shown in the cyclic voltammogram that sulfate addition results in the appearance of a new current peak at ∼0.90 V versus RHE (reversible hydrogen electrode), indicating that the sulfate is chemisorbed. Both current and potential oscillations were observed during the electrochemical oxidation of thiourea in the presence of sulfate under potentiostatic and galvanostatic control, respectively. Potential oscillations occurred in two regions of linear current sweep voltammetry. The presence of adsorbed sulfate gives rise to negative differential resistance (NDR) for the positive feedback of oscillations in the first oscillation region. The bursting and period-doubling oscillations in the second region are caused by oxide formation and adsorbed sulfate acting simultaneously as positive feedbacks. A similar chemisorbed sulfate layer was previously observed with scanning tunneling microscopy and surface ...

Oxidation of thiourea by peroxomonosulfate ion catalyzed by a ruthenium(III) complex: kinetic and mechanistic studies

The complex [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) catalyzes the oxidation of thiourea (TU) by peroxomonosulfate ion (HSO5−). The kinetics of the catalytic oxidation process was studied by using stopped-flow and rapid-scan spectrophotometry as a function of [RuIII(edta)(H2O)−], [HSO5−] and [TU] at a constant pH of 6.2 (phosphate buffer) and temperature of 25 °C. Spectral and kinetic data are suggestive of a catalytic pathway involving rapid formation of a [RuIII(edta)(TU)]− intermediate complex by reaction of [RuIII(edta)(H2O)]− with TU, followed by the oxidation of the coordinated TU in which HSO5− reacts directly with the S atom of TU coordinated to the RuIII(edta) complex. Analysis of the reaction mixture at the end of the reaction revealed the formation of formamidine disulfide (TU2) as a major product; however, thiourea dioxide (TUO2) and sulfate were also observed if the reaction mixture was kept for longer time periods. A detailed mechanism in agreement with the spectral and kinetic data is presented.

ChemInform Abstract: Recent Developments in the Chemistry of Thiourea Oxides

AbstractReview: [83 refs.

Electrocatalytic oxidation of thiourea on graphene nanosheets–Ag nanoparticles hybrid ionic liquid electrode

A simple, selective and sensitive graphene nanosheets–Ag nanoparticles hybrid ionic liquid electrode (GNSs-AgNPs/ILE) was used for the electrochemical determination of thiourea (TU). Cyclic voltammogram of TU showed two well defined oxidation signals at the potentials of −0.2 and 0.1V vs. Ag/AgCl. Amperometric method was used for quantification of TU in the range of 1.0–3000μM. The theoretical detection limit was obtained as 0.7μM. The sensor was successfully applied for TU determination in orange juice and waste water.

Recent developments in the chemistry of thiourea oxides.

Thiourea dioxide is one of the best known, important, and stable products of thiourea oxidation. This compound has long been considered as an effective reducing agent for many years. Traditional areas of its application include the textile and paper industries. In recent years, however, thiourea dioxides and trioxides have been widely used in new fields including organocatalytic, polymerization, and phase-transfer reactions; reduction of graphene and graphite oxides; bitumen modifications; synthesis of guanidines and their derivatives; and studying nonlinear dynamical phenomena in chemical kinetics. The review gives a detailed survey of the latest developments and main trends in the chemistry and application of thiourea mon-, di-, and trioxides.

Redox-Switchable Copper(I) Metallogel: A Metal–Organic Material for Selective and Naked-Eye Sensing of Picric Acid

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

PH Oscillations and Mechanistic Analysis in the Hydrogen Peroxide–Sulfite–Thiourea Reaction System

A new pH oscillator has been constructed by combining the pH clock reaction H2O2-SO3(2-)-H(+) with thiourea (Tu, (NH2)2CS) as a proton-consuming species. The system exhibited oligo-oscillatory behavior in a closed system, and large amplitude oscillations in a continuous-flow stirred tank reactor (CSTR) were observed in a narrow range of input concentrations, flow rate, and temperature. For the purpose of constructing the kinetic model, a reversed-phase ion-pair high-performance liquid chromatography (HPLC) and mass spectrometer (MS) were used to track and determine intermediate species during the oxidation of thiourea by hydrogen peroxide. Experimental results illustrated that the four species: thiourea monoxide (TuO), formamidine disulfide (Tu2(2+)), thiourea dioxide (TuO2), and thiourea trioxide (TuO3) were formed during the oxidation process. A ten-step mechanistic model was proposed, where TuO was another key species participating in two proton feedback loops in addition to bisulfite. Numerical simulations based on this model agreed well with the experimental results.

Synergetic Effect of Thiolacids on the Oxidation of Thiourea by Methylene Blue in Acidic Medium

Thiourea (TU) and methylene blue (MB) react in a molar ratio of 2:1 in acidic medium to give the corresponding disulphide and dihydromethylene blue. The rate of the reaction is considerably enhanced in the presence of 2-mercaptonicotinic acid (MNA) and o-mercaptobenzoic acid (TSA) due to synergetic effect. The order in thiourea is nearly unity in both the cases. The reaction follows a first order kinetics in MB in TU–MNA–MB reaction whereas in TU–TSA–MB reaction, the order in MB varies between zero and one. The rate of reaction increases linearly on increasing [H+] in case of TU–MNA–MB reaction while an insignificant influence has been noticed in TU–TSA–MB reaction. The rate increases linearly on increasing the concentration of total sulphydryl group. The synergetic effect of thiolacids is found to depend appreciably on their structure and it is attributed to the participation of a persulphide-like intermediate or a dithiol as revealed by ESI–MS, 1H-NMR and FT-IR techniques. These studies suggest that the inhibitory effect of thiourea on thyroxine biosynthesis may be minimized through its in situ oxidation assisted by synergetic effect of the thiolacids.

Redox Kinetics and Mechanism of the Oxidation of Thiourea by Diaquotetrakis(2,2’- Bipyridine) - µ - Oxodiruthenium (III) Ion, in Aqueous Perchloric Acid

Redox Kinetics and Mechanism of the Oxidation of Thiourea by Diaquotetrakis(2,2’- Bipyridine) - µ - Oxodiruthenium (III) Ion, in Aqueous Perchloric Acid

Kinetic, Mechanistic and Spectrophotometric Study of Micelle Effects on the Oxidation of Thiourea by Quinolinium Dichromate in Perchloric Acid Medium

The kinetic investigation of oxidation of thiourea by quinolinium dichromate (QDC) in perchloric acid medium at constant ionic strength was studied spectrophotometrically at 440 nm. A stoichiometric ratio of 3:1 with thiourea versus QDC was observed. The reaction was first order with respect to thiourea, monomeric QDC (QMC) and HClO 4. Induced polymerization of acrylonitrile was observed. The mechanism involved the attack of protonated monomeric QDC (QMC) on the substrate in the rate determining step forming the products. Addition of Mn(II) has no effect on the reaction rate. The effect of anionic micelle (SDS) and neutral micelle (TX-100) on the system was studied using Berezin's kinetic model and observed a partial inhibitory effect on the rate of the reaction. The thermodynamic parameters likeEaS andG have been calculated and possible mechanism was proposed.

Oxyhalogen–Sulfur Chemistry: Oxidation of a Thiourea Dimer, Formamidine Disulfide, by Chlorine Dioxide

The oxidation of formamidine disulfide, FDS, the dimer of thiourea, by aqueous chlorine dioxide has been studied in highly acidic and mildly acidic media. FDS is one of the possible oxidation intermediates formed in the oxidation of thiourea by oxyhalogens to urea and sulfate. The reaction is exceedingly slow, giving urea and sulfate with a stoichiometric ratio of 5 : 14 FDS to chlorine dioxide after an incubation period of up to 72 h and only in highly acidic media which discourages the disproportionation of chlorine dioxide to the oxidatively inert chlorate. Mass spectrometric data suggest that the oxidative pathway proceeds predominantly through the sulfinic acid, proceeding next to the products sulfate and urea, while by-passing the sulfonic acid. Transient formation of the unstable sulfenic acid was also not observed.

Selective oxidation of thiourea with H2O2 catalyzed by [RuIII(edta)(H2O)]−: kinetic and mechanistic studies

Reported here is the first example of a ruthenium complex, [Ru(III)(edta)(H(2)O)](-) (edta(4-) = ethylenediaminetetraacetate), that catalyzes the oxidation of thiourea (TU) in the presence of H(2)O(2). The kinetics and mechanism of this reaction were investigated in detail by using rapid-scan spectrophotometry as a function of both the hydrogen peroxide and thiourea concentrations at pH 4.9 and 25 °C. Spectral analyses and kinetic data clearly support a catalytic process in which hydrogen peroxide reacts directly with thiourea coordinated to the Ru(III)(edta) complex. HPLC product analyses revealed the formation of formamidine disulfide (TU(2)) as a major product at the end of the catalytic process, however, formation of other products like thiourea dioxide (TUO(2)), thiourea dioxide (TUO(3)) and sulfate was also observed after longer reaction times. Catalytic intermediates such as [Ru(III)(edta)(OOH)](2-) and [Ru(V)(edta)(O)](-) were evidently found to be non-reactive in catalyzing the oxidation of thiourea by H(2)O(2) under the specified conditions.

Determinación experimental de los parámetros óptimos de operación en el proceso de electrolixiviación y electrodeposición secuencial de oro en soluciones ácidas de tiourea a partir de sulfuros concentrados

Se investigó a nivel de laboratorio las variables de operación (concentración de reactivos, pH y potencial de oxidación) del proceso de lixiviación de piritas auríferas procedentes de río Tablachaca (Ancash Perú) con Tiourea (TU) seguido de electro-deposición de oro. El estudio experimental, se desarrolló en tres etapas: Oxidación de Tiourea, Lixiviación de oro y Electro-deposición de oro. Como una alternativa a los agentes químicos, la oxidación de TU se realizó vía electrólisis para producir Disulfuro Formamidina (FDS), el cual, sirve como oxidante en la disolución de oro. El grado de conversión óptima de tiourea a disulfuro formamidina se obtiene en 2,5 h aplicando una FEM de 4,5 V con un pH igual 1,5. Los compartimientos anódico y catódico del reactor electroquímico fueron separados por una membrana aniónica con la finalidad de eliminar reacciones indeseables en el cátodo. Previo a la etapa de lixiviación, el mineral fue lavado con ácido sulfúrico para eliminar los agentes consumidores de ácido y mantener de este modo un pH constante durante el tiempo que dure la lixiviación. Durante la lixiviación de oro, se estudió las velocidades de disolución en función de las concentraciones de TU, FDS y pH. Finalmente, se efectuó una prueba de lixiviación en tiempos prolongados usando los parámetros óptimos de operación obtenidos en las pruebas anteriores. La prueba de electro-deposición se llevó a cabo usando la técnica de electrodiálisis en una celda de tres compartimentos El bajo consumo de Tiourea (1,76 kg/TM mineral) demuestra que es una alternativa viable desde el punto de vista económico.

The effect of thiourea as a complexing agent on the separation of metallic ions through cation exchange membranes by Donnan dialysis

Donnan dialysis has been investigated in this work in the order to exhibit the influence of the composition of solution on the performance of commercial cation exchange membrane toward metallic ions. Transference fluxes have been determined either as experimental values or calculated according to theoretical models. A good agreement between theoretical and experimental flows has been obtained principally in the case of CMV membrane which presents a lower thickness. It has been demonstrated that addition of thiourea causes an increase of separation properties of membrane. The separation is mainly due to the complex formation between Ag+ and Cu+ ions and thiourea. Monovalent copper ion is obtained after reduction of Cu2+ and oxidation of thiourea and formation of bisulfide of formamidine which constitute a barrier to monovalent complex transference.

Electrochemical Aspects of Silver Sulfosalts Dissolution in Acid Thiourea Solution

Electro-oxidation of synthetic pyrargyrite (Ag3SbS3) and proustite (Ag3AsS3) powders in sulfate acid medium with thiourea has been studied. Two different types of electrodes were used for characterization of dissolution process. On one hand, thiourea oxidation was investigated on a paraffin-impregnated graphite electrode (PIGE) in order to determine the potential range to produce formamidine disulfide (protonated form, FDSH22+). On other hand, electro-oxidized thiourea (FDSH22+) was used to dissolve the sulfosalts particles at the PIGE and carbon paste electrodes (CPEs) surfaces. The chemical bond between sulfur and arsenic or antimony in the crystal structure of sulfosalts has an important role in the dissolution process of the solids. The results obtained herein agree with one previous study on the oxidation of sulfosalts in cyanide media [ChemPhysChem 11 (2010) 2879], and these demonstrate that structural, electronic, and bonding properties of sulfosalts mainly determine their reactivity regulating the extent of the reaction.

Methylene blue sensitized oxidation of ethylene thiourea in cationic micellar medium

Ethylene thiourea (ETU) is relatively stable to hydrolysis but can be rapidly photolysed in the presence of photosensitizers. An aqueous solution of 8.0×10−4M ETU and 5.0×10−5M methylene blue (MB) was photolysed for 90min with halogen lamp both in the presence and absence of cetyltrimethyl ammonium bromide (CTAB). 2-Imidazoline-2-yl-sulphinic acid (ISH) has been identified as the primary product both in the homogeneous and micellar media by chromatographic spectral analysis. The effects of various kinetic parameters were studied to lay down the mechanistic details of the reaction. On the basis of the kinetic studies the participation of singlet oxygen at low ETU concentration is postulated. However, ionic mechanism is suggested at high ETU concentration.

Oxidation of thiourea and substituted thioureas: a review

Thioureas, containing sulfur and nitrogen atoms, are susceptible to oxidation by a large number of oxidants giving rise to various products including ureas, sulfides, oxides of sulfur, and nitrogen. Some novel cyclized products were also obtained during oxidation. The reaction conditions and types of oxidants steer the formation of different products. This review comprises basically the synthetic aspects, and the mechanism/schemes of the reactions discussed in the manuscript are based on stoichiometry and products of the reactions.