Study of zinc thiocarbamide chloride,a single-source precursor for zinc sulfide thin films by spray pyrolysis

Thermal decomposition of the title compound, Zn(tu)₂Cl₂ (tu=thiourea), was studied up to 1200°C in dynamic inert (N₂) and oxidative (air) atmospheres using simultaneous TG/DTA techniques. In addition, XRD and IR were employed ex situ to resolve the reaction mechanism and products. Cubic ZnS (sphalerite) is formed below 300°C in both atmospheres and is observed until 760°C, whereafter it transforms in nitrogen to the hexagonal ZnS (wurtzite). EGA by FTIR revealed the complexity of the decomposition reactions involving also the evolution of H₂NCN, which reacts to form hexagonal ZnCN₂ as revealed by an XRD analysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Decomposition of Copper(I) Thiocarbamide Chloride Hemihydrate

Two combinations of simultaneous thermoanalytical techniques (TG+DTA and TG+EGA) were used to study the thermal decomposition of the title compound in order to gain a better insight into the spray pyrolytic processes leading to Cu2-xS and CuInS2 thin films. After dehydration a complex sequence of reactions starts above 220°C leading through several intermediates to the formation of CuO in air at 1000°C. In an inert atmosphere Cu2S is formed which in helium above 800°C partly decomposes to Cu. XRD and FTIR were used to identify the intermediate solid phases which in air included CuCl, Cu2OSO4, Cu2OCl2 and CuSO4. EGA-FTIR confirmed the complex reaction mechanism with NH3, HCl, H2O, COS, CO2 and some HCN as main gaseous products under oxidative conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray crystal structural analysis of dicyclohexylthiocarbamide

The title compound dicyclohexylthiocarbamide has been determined by single crystal X-ray crystal diffraction analysis. The crystals are monoclinic, space group P2(1)/c with a = 12.5908(9), b = 11.2158(9), c = 10.4255(8) Å, α = 90, β = 110.7360(10), γ = 90°, V = 1376.88(18) ų, Z = 4, F(000) = 528, D_c = 1.160 g/cm³, μ = 0.214 mm^?1, the final R = 0.0381 and wR = 0.1030. A total of 6836 reflections were collected, of which 2423 were independent (R_int = 0.0154). In the crystal packing diagram, intermolecular N?H···S hydrogen bonds stabilize the solid state of the title compound.     

The effect of chemisorbed sulfide ions on the gold electrodeposition from acidic thiocarbamide electrolytes

Introducing sodium sulfide (about 10^?5 M) into acidic thiocarbamide solutions reduces the gold reduction overpotential. The reaction rate passes through a maximum at a potential of 0.1 V. The overpotential depends on the sulfide ion concentration and the time of electrode exposure to solution prior to the beginning of scanning. Transients of potential measured on a renewable gold electrode in thiocarbamide electrolytes containing catalytically active species served as the basis for calculations of the coefficient of trapping of sulfide ions by the growing gold deposit. The kinetics of gold electrodeposition at fixed surface coverages with adsorbed sulfide ions θ is studied. It is shown that at θ = const, the dependence of the reaction rate on the overpotential is described by the Tafel equation. It is shown that with an increase in θ, the effective values of exchange current and transfer coefficient increase from i ₀ ≌ 10^?5 A/cm² and α ≌ 0.25 in pure solutions to α ≌ 0.5 and i ₀ ≌ 10^?4 A/cm² at θ ≥ 0.3 and then remains virtually unchanged. The reaction order decreases in the absolute magnitude, remaining negative. Thus for θ ≌ 0, p _k = ?logi/?logc = ?1, whereas for θ ≥ 0.3, p _k = ?0.3. A possible explanation is proposed for the catalytic effect of the sulfide ion adsorption on the mechanism of the gold reduction from acidic thiocarbamide electrolytes.     

A Thermoanalytical Study of Copper(I) Thiocarbamide Compounds

Hydrated isostructural 1:3 complexes of copper(I) chloride and bromide with thiourea were synthesised and their thermal decomposition studied by simultaneous TG/DTA complemented by ex situ FTIR and XRD studies. The decomposition of Cu(tu)₃Cl·H₂O is initiated by dehydration around 100°C, followed by a total multi-step degradation of the structure in the temperature range of 200–600°C. The counter ion has some influence on the temperatures and composition of the solid residue. The results were compared with those obtained with the 1:1 complex Cu(tu)Cl·1/2H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Silver dissolution in acid thiocarbamide solutions containing sulfide ions

Regularities of silver dissolution in acid thiocarbamide electrolytes are studied. The kinetics of the process is shown to be severely affected by the admixture of hydrogen sulfide molecules that form upon inserting sodium sulfide or accumulate in electrolyte with the passage of time elapsed since its preparation. Catalytic effect increases with increasing length of time of the electrode’s contact with solution prior to the beginning of experiment or following an increase in the concentration of sulfide ions. Experiments with the surface renewed in the course of potential scans show that the catalytic effect is connected with the adsorption of sulfide ions on an interface. At large values of the surface coverage with sulfide ions, the dissolution rate increases so much that the dissolution process starts to be limited largely by the process of supply of thiocarbamide molecules toward the electrode surface.     

Synthesis, Crystal Structure and Spectrometry Study of Chiral N-Ethyl-N''''-(2'''',3'''',4'''',6''''-tetra-O-acetyl-β-D-glycosyl)-thiocarbamide

1INTRODUCTIONManynomadicsugarsperformimportantbio-logicalfunctions[1].Theycancontrolvariousgeneexpressionstoadjusttheupgrowth,developmentandreactionoforgans[2].Glycosylisothiocyanateshavebeenwidelyusedasvaluableintermediatesinthesynthesisofglycosylderivatives[3].Theiso-thiocyanatesandglycosylisothiocyanateshavebeenthefocusofsyntheticattentionduringrecentyearsbecauseoftheirpotentialpharmacologicalproperties[4].Theyhavealsoattractedconsiderableinterestduetotheanti-HIVactivityshownby1-deoxy…     

Kinetics and Mechanism of the Electro-oxidation of Gold in Thiocarbamide Solutions

The kinetics and mechanism of the electrooxidation of gold and thiocarbamide in sulfuric acid solutions of thiocarbamide (TC) have been investigated. The potentials for the oxidation of gold in TC solutions to [Au(TC)₂]⁺ _ads and [Au(TC)₃]³⁺ _ads are 0.132 and 0.561 V (relative to the standard silver chloride electrode). The electrooxidation of thiocarbamide in sulfuric acid solution is characterized by two maximums on voltammograms at 0.983 V (formation of formamidine disulfide, FAD) and 1.437 V (oxidation of FAD, sulfides and hydrosulfides of gold(I)). The calculated rate constants for the electrosolution of gold at the maximum current of the voltammogram is k ₁ = 1.15·10^–5 cm/s and at the minimum current is k ₂ = 3.13·10^–6 cm/s in sulfuric solutions of TC. A mechanism is proposed for the electrosolution of gold and TC in sulfuric acid solutions of thiocarbamide.     

Quartz crystal microbalance measurements of kinetic parameters of anodic dissolution of gold in thiocarbamide electrolytes in the presence of sulfide ions

As shown by quartz-crystal microbalance measurements, in the potential range from 0.0 to 0.55 V (NHE), sulfide ions adsorbed on the gold electrode surface accelerate the electrode reaction of anodic dissolution of gold in acidic thiocarbamide solutions. The microbalance determination of kinetic parameters at a constant electrode surface coverage with sulfide ions includes a special procedure developed for the determination of the gold dissolution rate. The conditions (the potential range and the potential scan rate) of independence of the dissolution rate from the diffusion limitations associated with the ligand delivery is determined. Under these conditions, the polarization curve is shown to be linear on semilogarithmic coordinates and correspond to the Tafel equation. In this potential range, the transfer coefficient α and the reaction order with respect to the ligand p are determined at a constant electrode surface coverage θ with adsorbed sulfide ions. It is shown that with the transition from the surface coverage with sulfide ions θ = 0.1 to θ = 0.8, the transfer coefficient α changes from 0.25 to 0.55, the exchange current (i ₀) changes from 10^?5 to 5 × 10^?5 A/cm², and the effective reaction order p with respect to the ligand changes from 0.2 to 1.3. The mentioned changes are associated not only with the acceleration of gold dissolution in the presence of chemisorbed sulfide ions but also with the changeover in the mechanism of this process. Quartz-crystal microbalance data on the gold dissolution rate qualitatively agree with the results of voltammetric measurements of a renewable gold electrode. A possible version of explanation of the catalytic effect of sulfide ion adsorption on the gold dissolution is put forward.     

Microbalance study of gold dissolution in alkaline sulfite-thiocarbamide electrolytes

It is shown that gold does not virtually dissolve in alkaline (pH 12.5) solutions containing either thiocarbamide or sodium sulfite. Gold dissolves in alkaline solutions simultaneously containing thiocarbamide (0.1 M) and sodium sulfite (0.5 M). The gold dissolution rate increases with the increase in the contents of thiocarbamide and sodium sulfite. The methods of microbalance and voltammetry are used in studying the mechanism of gold dissolution in a solution containing 0.5 M sodium sulfite, 0.1 M thiocarbamide, and 0.03 M KOH. The found relationships are explained based on the assumption that the gold dissolution in alkaline sulfite-thiocarbamide electrolytes affords gold sulfite complexes.