Effect of peat humic acids on the kinetics of reduction of anthraquinone dye with sulfur-containing reducing agents

The influence of peat humic acids on the aerobic reduction of Chrome Green Anthraquinone dye with sodium hydroxymethanesulfinate and thiourea dioxide in alkaline solutions was studied.     

Theoretical study on the oxidation mechanism of thiourea by hydrogen peroxide with water and hydroxyl assistance

This article presents a theoretical study on the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions using density functional and ab initio theories. This work also focuses on the analysis of the thermodynamic and kinetic properties of the predicted oxidation mechanism of thiourea using density functional and ab initio theories. The calculated results show that the activation energies, activation enthalpies, and activation Gibbs free energies of the reaction decreased and the releasable reaction energies, enthalpies and Gibbs free energies increased with the cooperation of water or hydroxyl anion. We conclude that the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions was easier and more completed than that in the gas state. The calculated results are consistent with the experiments.     

Effect of Composition and Structure of Aqueous Monoethanolamine Solutions on Carbon Dioxide Sorption and Desorption in Purification of Gas Mixtures

Possibility of raising the efficiency of the monoethanolamine purification of gas mixtures to remove carbon dioxide is demonstrated with consideration for the real intermolecular interactions and the structuring in the absorbent solution. The composition and structure of individual aqueous monoethanolamine solutions with various concentrations and of the same solutions saturated with carbon dioxide were examined. The methods of viscometry and conductometry demonstrated that, at monoethanolamine concentrations exceeding 12 ± 2 wt %, micelles are formed on the background of the existence of associates with intermolecular hydrogen bonds. This necessitates use of high temperatures (120?140°C) in the stage of carbon dioxide desorption. It was found that using a 12 wt % aqueous solution of monoethanolamine in purification of gas mixtures makes it possible to lower the desorption temperature of carbon dioxide to 90°C. This process is more efficient than the standard technology of CO₂ removal from a 30 wt % monoethanolamine solution. This is so because, in addition to a lower expenditure of heat, the extraction of carbon dioxide grows by 16% at a simultaneous decrease in the absorbent expenditure by at least a factor of 2.5.     

A new procedure for the spectrophotometric determination of nitrogen(II) oxide in solutions

A new simple and reliable procedure was developed for the spectrophotometric determination of nitrogen(II) oxide. The procedure is based on the determination of excess oxygen after its reaction with NO. Alkaline solutions of thiourea dioxide were used for the determination of oxygen. It was found that the decomposition of an alkaline solution of thiourea dioxide under aerobic conditions is accompanied by the formation of dithionite, and its concentration is proportional to the concentration of oxygen in the solution. The absorbance of the resulting dithionite was measured at 315 nm. The solutions obeyed Beers law at oxygen concentrations of 1 × 10^–5–1.5 × 10^–3 M. The analytical range for NO was 1 × 10^–5–1.5 × 10^–3 M. The proposed procedure was also used for the determination of nitrogen(II) oxide in aqueous-ethanolic solutions.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 27–29.Original Russian Text Copyright © 2005 by Pukhovskaya, Guseva, Makarov, Naidenko.     

Interfacial potential difference in electromembrane systems with MA-41 anion-exchange membranes and alkaline solutions of glycine

A method for estimating the interfacial potential difference in electromembrane systems with alkaline solutions of amino acids is developed. Systems with MA-41 anion-exchange membranes and aqueous sodium hydroxide solutions with glycine are investigated. It is found that in solutions with alkali concentrations greater than 0.010 M, the interfacial potential difference decreases logarithmically, i.e., in agreement with the Donnan relationship. At the same time, in weakly alkaline solutions of glycine, in which the amino-acid concentration exceeds that of the alkali, an increase in the interfacial potential difference is observed. This may be due to a disturbance of the equilibrium of the protolytic reaction in the membrane on the side where hydroxide ions form.     

Thiourea dioxide promoted efficient organocatalytic one-pot synthesis of a library of novel heterocyclic compounds

The utility of thiourea dioxide as an efficient organocatalyst for the library synthesis of novel heterocyclic compounds via one-pot multicomponent coupling reactions is disclosed. Thiourea dioxide is an inexpensive and readily accessible catalyst, resulting in better product yields as compared to the corresponding thiourea as catalyst. Thiourea dioxide is found to be insoluble in various organic solvents and therefore at the end of the reaction products can be separated by extraction with diethyl ether and the recovered catalyst can be used several times with consistent catalytic activity.     

废水中二氧化硫脲的分光光度法测定

本文提出了分光光度法测定二氧化硫脲的新方法。在ｐＨ１１．３的碱性介质中，二氧化硫脲可将芳香族硝基化合物还原为芳香族伯胺，经重氮化后与萘乙二胺反应生成红色的偶氮染料。其最大吸收波长为５２５ｎｍ，线性范围为２．０￣４０．０ｍｇ／Ｌ，检测限２ｍｇ／Ｌ，回收率９７．０％￣１０２．７％。本法灵敏度高，对二氧化硫脲有较好的选择性，用于为水中微量二氧化硫脲的测定，结果满意。     

酸性和碱性介质中甘氨酸解离吸附和氧化的EQCM研究

用电化学石英晶体微天平(EQCM)研究酸性和碱性介质中甘氨酸在Pt电极上的吸附和氧化过程.结果表明,甘氨酸的解离吸附和氧化行为与溶液的酸碱性密切相关.酸性溶液中甘氨酸吸附较弱,碱性溶液中则产生强吸附物,且当电位低于0V(vs.SCE)时可吸附于Pt电极表面.此外,碱性溶液中甘氨酸还表现出较高的电氧化活性.通过EQCM定量检测上述过程中Pt电极表面的质量变化,测定了不同电位区间(氢区、双电层区和氧区)每传递一个电子所对应的电极表面吸附物种的平均摩尔质量.     

N,N'-Bis(3-triethylsilylpropyl)thiourea S-Dioxide and Poly[N,N'-bis(silsesquioxanylpropyl)thiourea S-Dioxide] as Reductants

The reducing power of organosilicon thiourea S-dioxides, N,N'-bis(3-triethylsilylpropyl)thiourea S-dioxide and poly[N,N'-bis(silsesquioxanylpropyl)thiourea S-dioxide], was studied. The first, monomeric dioxide readily reduces cyclohexanone to cyclohexanol. In its presence, under phase-transfer conditions, dipropyl disulfide reacts with bromobenzene to form propyl phenyl sulfide, and tellurium reacts with ethyl bromide to form diethyl telluride. The reducing power of the polymeric dioxide was demonstrated by the example of reduction of potassium permanganate. Irrespective of the medium (neutral, acidic, or alkaline), this polymer reduces Mn(VII) to Mn(IV).     

Reaction of Thiourea Dioxide and Hydrogen Peroxide with Coumarin

The system thiourea dioxide–hydrogen peroxide is found to effectively hydroxylate coumarin in aqueous solutions. The hydroxyl radical reacting with coumarin is shown to result from decomposition of the complex thiourea dioxide–H₂O₂. The obtained data are compared to the results of investigation of the reactions occurring in the system thiourea dioxide–H₂O₂ with terephthalic acid.     

Permanganate oxidation of glycine: Influence of amino acid on colloidal manganese dioxide

Permanganate ion oxidizes glycine in phosphate buffered solutions, and the product obtained was identified as a soluble form of colloidal manganese dioxide. The influence of glycine on the colloidal product shows glycine concentration changes extinction coefficients of the colloidal product, and only when the influence of glycine has been eliminated, the theoretical and experimental reaction rates coincide. The dependence of the rate of flocculation on several experimental variables was also considered.     

钯铁合金催化剂的稳定性

分别在酸性和碱性溶液中, 结合旋转圆盘电极技术和电化学石英晶体微天平技术原位考察了钯铁合金催化剂对氧还原反应催化活性的稳定性. 发现在酸性溶液中, 钯铁合金催化剂对氧还原反应的催化活性不稳定, 原因是钯铁合金催化剂在酸性溶液中发生电化学/化学溶解; 在碱性溶液中, 覆盖在电极表面的钯铁合金催化剂的质量及电化学活性面积在电化学扫描过程中不发生明显变化, 保持对氧还原反应的催化活性, 证明钯铁合金催化剂在碱性介质中非常稳定.     

Thiourea dioxide in water as a recyclable catalyst for the synthesis of structurally diverse dihydropyrido[2,3-d]pyrimidine-2,4-diones

A series of dihydropyrido[2,3-d]pyrimidine-2,4-diones derivatives were synthesized by the three-component reaction of 6-amino-1,3-dimethyl uracil, aromatic aldehydes, and 1,3-dicarbonyl compound catalyzed by thiourea dioxide in aqueous media. Importantly, the aqueous layer containing thiourea dioxide could be reused for several runs without significant loss in catalytic activity. This method provided several advantages such as inexpensive, recyclable catalyst, easier work-up, milder reaction conditions and environmental benign nature.     

Influence of amines on the change in the spectral properties of alkaline solutions of soda lignin and the transformation of sulfate cellulose on photoirradiation

It has been shown that in the irradiation with light of alkaline solutions of soda lignin and suspensions of sulfate cellulose additions of ethylenediamine, monoethanolamine, and hydrazine lead to a decrease in the optical density in the visible region of the absorption spectra of the samples studied.     

Potentiometric study of end-point detection in the coulometric determination of carbon dioxide

The coulometric determination of carbon dioxide is based on the alkalimetric titration of the product of absorption of carbon dioxide in an organic solution of monoethanolamine. The processes occurring in various solvents have been investigated and optimized for analytical application. The protolytic reactions of 2-hydroxyethylcarbamic acid have been investigated in 2-propanol + 2, 5 and 10% water, dimethylformamide + 2% water, dimethylsulphoxide +5, 10 and 20% water. In coulometric generation of the base, 0.1M solutions of tetraethylammonium bromide in these solvents were used. The course of the titration was followed potentiometrically with glass and antimony indicator electrodes. From the titration curves the autoprotolysis constants of the mixed solvents and protonation constants of monoethanolamine in them were calculated. These constants and the concentration of monoethanolamine influence the size of the end-point break for the titrations. On this basis, optimal conditions for analysis have been selected and the total carbon content in samples of natural waters has been determined.     

Thiourea dioxide catalyzed multi-component coupling reaction for the one step synthesis of naphthopyran derivatives

An aqueous solution of thiourea dioxide was used to catalyze a one-pot three-component coupling reaction of an aromatic aldehyde, malononitrile, and α- or β-naphthol for the synthesis of various naphthopyran derivatives in excellent yields. At the end of the reaction, the product was isolated by filtration or extraction and the remaining aqueous solution of thiourea dioxide was reused as such for several subsequent runs.     

Determination of thiourea and tetramethylthiourea an iodine-arsenite method

Oxidation of thiourea and tetramethylthiourea by alkaline iodine is studied. The reaction is found to proceed quantitatively over a wide range of experimental conditions. A method of estimating thiourea and its tetramethyl derivative is developed, based on the titration of the excess iodine against standard arsenious oxide in a suitable pH range.     

A New Simple Voltammetric Method for Thiourea and Thiourea Dioxide Determinations

Abstract

Linear sweep voltammetry at glassy carbon or other carbon materials is shown to be a simple, highly sensitive, and relatively versatile analytical method for the determination of thiourea and thiourea dioxide. Using the first one-electron oxidation peak occurring at ～0.6V, thiourea can be determined directly in a variety of electrolytes from concentrated acids to solutions of pH ～5. The thiourea dioxide determination is based on the two-electron oxidation peak which appears in a number of electrolytes at ～1.2V.     

Coenzyme B12 model studies: Equilibrium constants for the pH-dependent axial ligation of benzyl(aquo)cobaloxime by various N- and S-donor ligands

Equilibria of the axial ligation of benzyl(aquo)cobaloximes by imidazole, 1-methyl imidazole, histidine, histamine, glycine, ethyl glycine ester, thiourea and urea have been spectrophotometrically measured in aqueous solutions of ionic strength 1.0M (KCl) at 25°C as a function of pH. The equilibrium constants are in the order CN⁻> 1-methyl imidazole > imidazole > histidine > histamine>glycine>ethyl glycine ester > thiourea > urea. The order of stability of benzyl(ligand)cobaloxime is explained based on the basicity of the ligand, Co(III) →>L dπ- pπback bonding and soft-soft and soft-hard interaction. Imidazole, substituted imidazoles, histidine and histamine form more stable complexes than glycine, ethyl glycine ester in contrast to the basicity of the ligands. Benzyl(ligand)cobaloximes were isolated and characterized by elemental analysis, IR and¹H NMR spectra.     

Carbon dioxide absorption by MEA

Biogas generally contains significant quantities of carbon dioxide in addition to methane. A bubbling column reactor operating at atmospheric pressure is proposed for cheap separation and a Mettler RC1 reaction calorimeter was used to build a simplified empirical model for measuring the molar heat of solubility of CO₂ in aqueous solutions of monoethanolamine (MEA). Determinations were performed in 12 mass% MEA solutions regenerated at atmospheric pressure and reflux temperature for 3 h. Flows of CO₂ from 174 to 917 mL min^?1 were used at a reactor temperature of 283 to 353 K.