Liquid–(Solid + Liquid) Transitions in a Two-Component System of (CH 3 )CCl 3 + CCl 4

Liquid–(solid + liquid) transitions are studied in (CH3)CCl3 + CCl4 by using the Landau phenomelogical model. The Gibbs energy is expanded in terms of the orientational disorder (OD) parameters for the transitions of the liquid–(rhombohedral + liquid) and liquid–(face-centered cubic + liquid) in a two component system of (CH3)CCl3 + CCl4. From the Gibbs energy, the phase line equations are derived for the transitions studied and they are fitted to the observed T–X phase diagram of (CH3)CCl3 + CCl4 for the concentration (X) CCl4. Temperature and concentration dependences of the OD parameters (Ψ and η) and the inverse susceptibility ($$\chi_{\psi }^{ - 1}$$ and $$\chi_{\eta }^{ - 1}$$) for the two transitions of interest, are predicted by using the melting curves of (CH3)CCl3 + CCl4 on the basis of the Landau phenomenological model. Our predictions, which can be compared with the experimental data, indicate that the first order transition of the liquid–(solid + liquid), in particular, for (CH3)CCl3 + CCl4 can be described satisfactorily by the Landau mean field model.     

Physico-Chemical Characterization of Binary and Ternary Mixtures of Imidazolium Based Cation and Common Anion Ionic Liquids with Lactams

Journal of Solution Chemistry - Excess molar volumes, $$V_{{}}^{{\text{E}}}$$ , excess isentropic compressibilities, $$\kappa_{{\text{S}}}^{{\text{E}}}$$ of binary 1-butyl-2,3-dimethylimidazolium...     

Synthesis,Crystal Structures,and Thermal Properties of Protic Metal-Containing Ionic Liquids,Diethanolammonium Halometallates: (HOCH2CH2)2NH2FeCl4 and ((HOCH2CH2)2NH2)2CoCl4

Russian Journal of Coordination Chemistry - Protic metal-containing ionic liquids with the diethanolammonium cation (HO–CH2–CH2)2$${\text{NH}}_{{\text{2}}}^{ + }$$ (DEAH+) and anions...     

Mechanism of the catalyzed by cysteine electroreduction of the insoluble in water cobalt(II) salt as a component of carbon paste electrode

The mechanism of the Co(II) catalytic electroreduction of water insoluble CoR₂ salt in the presence of cysteine was developed. CoR₂ = cobalt(II) cyclohexylbutyrate is the component of a carbon paste electrode. Electrode surface consecutive reactions are: (a) fast (equilibrium) reaction of the complex formation, (b) rate-determining reversible reaction of the promoting process of CoR(Ac⁺) complex formation, (c) rate-determining irreversible reaction of the electroactive complex formation with ligand-induced adsorption, and (d) fast irreversible reaction of the electroreduction. Reactions (a,b) connected with CoR₂ dissolution and reactions (c,d) connected with CoR₂ electroreduction are catalyzed by . Regeneration of (reactions “b,d”) and accumulation of atomic Co(0) (reaction “d”) take place. Experimental data [Sugawara et al., Bioelectrochem Bioenergetics 26:469, 1991]: i _a vs E (i _a is anodic peak, E is cathodic accumulation potential), i _a vs , and i _a vs pH have been quantitatively explained.     

The sources of thermal energy exchange accompanying microbial anabolism

Calculations are made of the thermal energy exchanges accompanying the anabolism of Saccharomyces cerevisiae of four substrates using the equations and . Contrary to a previous postulate cited in the Discussion, the free-energy changes accompanying anabolism are not zero, but can be either positive or negative. However, their magnitude with either sign is small compared to that of catabolism of the same substrates, so that even with free energy changes that are negative it is unlikely anabolism can be considered a spontaneous process.     

Kinetics and mechanism of the oxidation of hydrogen peroxide by the octacyanotungstate(V) ion in alkaline aqueous media

Summary The oxidation of H₂O₂ by [W(CN)₈]^3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law, , strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k _s, given by , involves the formation of [W(CN)₈· H₂O₂]^3–, [W(CN)₈· H₂O₂·W(CN)₈]^6– and [W(CN)₈· HO]^3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)₈·HO]^3– (k _a) and its conjugate base [W(CN)₈·O]^4– (k _b). At 25 °C, I = 0.20 m (NaCl), the rate constant with H _a =40±6kJmol^–1 and S _a =–151±22JK^–1mol^–1; the rate constant with H _b =36±1kJmol^–1 and S _b =–136±2JK^–1mol^–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)₈·HO]^3–, K ₅ =(5.9±1.7)×10^–10 m, with and is the first acid dissociation constant of H₂O₂. The second pathway, with rate constant, k _f, involves the formation of [W(CN)₈· HO₂]^4– and is followed by a formal two-electron redox process with [W(CN)₈]^3–. The pH-dependent rate constant, k _f, is given by . The rate constant k ₇ =23±6m ^–1 s ^–1 with and at 25°C, I = 0.20 m (NaCl).     

Improvement of the electrochemical properties of “as-grown” boron-doped polycrystalline diamond electrodes deposited on tungsten wires using ethanol

The electrochemical properties of boron-doped diamond (BDD) polycrystalline films grown on tungsten wire substrates using ethanol as a precursor are described. The results obtained show that the use of ethanol improves the electrochemistry properties of “as-grown” BDD, as it minimizes the graphitic phase upon the surface of BDD, during the growth process. The BDD electrodes were characterized by Raman spectroscopy, scanning electronic microscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The boron-doping levels of the films were estimated to be ∼10²⁰ B/cm³. The electrochemical behavior was evaluated using the and redox couples and dopamine. Apparent heterogeneous electro-transfer rate constants were determined for these redox systems using the CV and EIS techniques. values in the range of 0.01–0.1 cm s⁻¹ were observed for the and redox couples, while in the special case of dopamine, a lower value of 10⁻⁵ cm s⁻¹ was found. The obtained results showed that the use of CH₃CH₂OH (ethanol) as a carbon source constitutes a promising alternative for manufacturing BDD electrodes for electroanalytical applications.     

Configuration and conformation of substituted 1,3,2-dioxaarsenanes

The configuration and conformations often 2-, 4-, and 5-substituted 1,3,2-dioxaarsenanes were studied from their PMR spectra. Inversion of the shielding constants of protons in the 4, 6, and 5 positions and of methyl groups in the 5 position was established, and the axial orientation of the As-Cl and As-OR bonds, the equatorial orientation of the 4-CH₃ group, and the chair conformation of the six-membered heteroring were proved. The anisotropies of the diamagnetic susceptibility were estimated for the first time: and (dipole approximation); and (nondipole approximation). The cyclic torsion angle (= 58°) as found for 2-chloro-1,3,2-dioxaarsenane by the R-factor method. Conclusions regardiwng the conformation of the ring and substituents were confirmed by a study of the specific effect of an aromatic solvent on the position of the resonance lines.Communication I from the series Investigation of the Stereochemistry of Organic Arsenic Compounds by NMR Spectroscopy.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 457–463, April, 1973.     

Interfacial behavior of sulforhodamine 101 at the polarized water/1,2-dichloroethane interface studied by spectroelectrochemical techniques

The transfer mechanism of an amphoteric rhodamine, sulforhodamine 101 (SR101), across the polarized water/1,2-dichloroethane (DCE) interface was investigated using cyclic voltammetry, differential voltfluorometry and potential-modulated fluorescence (PMF) spectroscopy. The voltammetric response for the ion transfer of SR101 monoanion from water to DCE was observed as the diffusion-controlled transfer process. An unusual voltammetric response was found at 0.15 V more negative than the formal transfer potential of SR101⁻ in the cyclic voltammogram and voltfluorogram. The frequency dependence of the PMF responses confirmed the presence of the adsorption processes at negative potentials. In addition, a further transient adsorption step was uncovered at The interfacial mechanism of SR101 is discussed by comparing the results obtained from each technique.     

Kinetics of the uninhibited and ethanol-inhibited CoO,Co<Subscript>2</Subscript>O<Subscript>3</Subscript> and Ni<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyzed autoxidation of sulfur(IV) in alkaline medium

For getting an insight into the mechanism of atmospheric autoxidation of sulfur(IV), the kinetics of this autoxidation reaction catalyzed by CoO, Co₂O₃ and Ni₂O₃ in buffered alkaline medium has been studied, and found to be defined by Eqs. I and II for catalysis by cobalt oxides and Ni₂O₃, respectively.

Cd(II) and Cd(II)–Eu(III) Complexes with Pentafluorobenzoic Acid Anions and N-Donor Ligands: Synthesis and Structures

Russian Journal of Coordination Chemistry - The reactions of cadmium(II) and europium(III) pentafluorobenzoates ([Cd(Pfbz) $$\left( {{{{\text{H}}}_{{\text{2}}}}{\text{O}}} \right)_{{\text{4}}}^{ +...     

Palladized aluminum as a novel substrate for electrosynthesis of polyaniline in sulfuric acid solutions

The electropolymerization of aniline on a palladized aluminum electrode (Pd/Al) by potentiodynamic as well as potentiostatic methods is described. The effect of the monomer concentration between 0.01 and 0.4 M on the polyaniline (PANI) formation and its growth on the Pd/Al electrode was investigated and a suitable concentration of 0.2 M is suggested. A similar study was carried out to investigate the effect of sulfuric acid concentration and 0.1 M sulfuric acid was chosen. A study on the influence of electropalladization time on the polymer formation and its growth suggested a convenient time of 40 s. The stability of the PANI film on the Pd/Al electrode was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1–0.7 V, the first-order degradation rate constant, k, of PANI film varies between 1×10⁻⁶ and 2×10⁻⁵ s⁻¹, and a relatively low slope (i.e., 2.2) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the PANI-deposited Pd/Al electrode is discussed. The electrocatalytic activity of the PANI-deposited Pd/Al electrode against para-benzoquinone/hydroquinone (Q/H₂Q) and redox systems were investigated and on the basis of of the corresponding cyclic voltammograms and the redox systems were identified as the reversible and quasi-reversible systems, respectively.     

Behavior of (La,Sr)CoO3- and La2NiO4-based ceramic anodes in alkaline media: compositional and microstructural factors

The behavior of dense ceramic anodes made of perovskite-type (x = 0.30–0.70; y = 0–0.05; z = 0–0.20) and K₂NiF₄-type (Me = Co, Cu; x = 0–0.20) indicates significant influence of metal hydroxide formation at the electrode surface on the oxygen evolution reaction (OER) kinetics in alkaline solutions. The overpotential of cobaltite electrodes was found to decrease with time, while cyclic voltammetry shows the appearance of redox peaks characteristic of Co(OH)₂/CoOOH. This is accompanied with increasing effective capacitance estimated from the impedance spectroscopy data, because of roughening of the ceramic surface. The steady-state polarization curves of in the OER range, including the Tafel slope, are very similar to those of model Co(OH)₂–La(OH)₃ composite films where the introduction of lanthanum hydroxide leads to decreasing electrochemical activity. La₂NiO₄-based anodes exhibit a low electrochemical performance and poor stability. The effects of oxygen nonstoichiometry of the perovskite-related phases are rather negligible at high overpotentials but become significant when the polarization decreases, a result of increasing role of oxygen intercalation processes. The maximum electrocatalytic activity to OER was observed for A-site-deficient , where the lanthanum content is relatively low and the Co⁴⁺ concentration determined by thermogravimetric analysis is highest compared to other cobaltites. Applying microporous layers made of template-synthesized nanocrystalline leads to an improved anode performance, although the effects of microstructure and thickness are modest, suggesting a narrow electrochemical reaction zone. Further enhancement of the OER kinetics can be achieved by electrodeposition of cobalt hydroxide- and nickel hydroxide-based films. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

Photoelectrode characteristics of an organic bilayer in water phase containing a redox molecule

We have recently reported that the organic bilayer of 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI, n-type semiconductor) and 29H,31H-phthalocyanine (H₂Pc, p-type semiconductor), which is a part of a photovoltaic cell, acts as a photoanode in the water phase (Abe et al., ChemPhysChem 5:716, [2004]); in that case, the generation of the photocurrent involving an irreversible thiol oxidation at the H₂Pc/water interface took place to be coupled with hole conduction through the H₂Pc layer, based on the photophysical character of the bilayer. In the present work, the photoelectrode characteristics of the bilayer were investigated in the water phase containing a redox molecule , where the photo-induced oxidation and reduction for the couple were found to take place at the bilayer. The photoanodic current involving the oxidation efficiently occurred at the interface of H₂Pc/water, similar to the previous example. In the view of the voltammograms obtained, it was noted that there are pin-holes in the H₂Pc layer of the bilayer, leading to a cathodic reaction with at the PTCBI surface especially in the dark; that is, the band bending at the PTCBI/water interface can essentially be reduced by applying a negative potential [e.g., < ∼ 0 V (vs Ag/AgCl)] to the PTCBI, when the cathodic reaction may take place through the conduction band of the PTCBI. Moreover, under that applied potential condition of irradiation, the photogenerated electron carrier part can move to the PTCBI surface, thus enhancing the reduction of .     

The relationship of conductivity to the morphology and crystallinity of polyaniline controlled by water content via reverse microemulsion

Conducting polyaniline (PANI) with the controllable morphology and crystallinity were successfully synthesized with different water content () in the reverse microemulsion stabilized with sodium bis(2-ethylhexyl)-sulfosuccinate (AOT). In the microemulsion, the systems containing the different amounts of water will show the different phase behaviors and structures. The influence of water content on morphology and crystallinity of conducting PANI was characterized by a number of techniques such as Fourier transform infrared spectra, UV–Visible, scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction and conductivity. In particular, we focus on the understanding of the relationship between the morphology and the crystallinity and the conductivity of PANI powder. With the increasing of the water content (W ₀ = 13.9, 27.8, 55.5, and 111.1) in the microemulsion system, the morphology and the crystallinity obviously changed and the values of relative conductivity are 0.05, 0.11, 2.7, and 1.8 S/cm, respectively.     

Kinetics and mechanism of oxidation of the chromium(III)-DL-aspartic acid complex/periodate reaction. Evidence for iron(II) catalysis

The kinetics of oxidation of the chromium(III)-DL- aspartic acid complex, [CrIIIHL]+ by periodate have been investigated in aqueous medium. In the presence of Fe^II as a catalyst, the following rate law is obeyed:

Kinetics and Mechanism of the Reduction of Enneamolybdonickelate(IV) by Arsenite

The kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by arsenite in aqueous acid solution was studied by spectrophotometry. The reaction rate increases with increasing concentrations of H⁺ and with temperature. The associated rate law is: . The rate constants and activation parameters of the rate-determining step were evaluated. A mechanism related to this reaction was proposed.     

Thermodynamic studies on Pr2TeO6

The standard Gibbs energy of formation of Pr₂TeO₆ $ (\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)) $ was derived from its vapour pressure in the temperature range of 1,400–1,480 K. The vapour pressure of TeO₂ (g) was measured by employing a thermogravimetry-based transpiration method. The temperature dependence of the vapour pressure of TeO₂ over the mixture Pr₂TeO₆ (s) + Pr₂O₃ (s) generated by the incongruent vapourization reaction, Pr₂TeO₆ (s) = Pr₂O₃ (s) + TeO₂ (g) + ½ O₂ (g) could be represented as: $ { \log }\left\{ {{{p\left( {{\text{TeO}}_{ 2} ,\;{\text{g}}} \right)} \mathord{\left/ {\vphantom {{p\left( {{\text{TeO}}_{ 2} ,\;{\text{g}}} \right)} {{\text{Pa}} \pm 0.0 4}}} \right. \kern-0em} {{\text{Pa}} \pm 0.0 4}}} \right\} = 19. 12- 27132\; \left({\rm{{{\text{K}}}}/T} \right) $ . The $ \Updelta_{\text{f}} G^{^\circ } \;\left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} } \right) $ could be represented by the relation $ \left\{ {{{\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)} \mathord{\left/ {\vphantom {{\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}}} \right. \kern-0em} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}} \pm 5.0} \right\} = - 2 4 1 5. 1+ 0. 5 7 9 3\;\left(T/{\text{K}}\right) .$ Enthalpy increments of Pr₂TeO₆ were measured by drop calorimetry in the temperature range of 573–1,273 K and heat capacity, entropy and Gibbs energy functions were derived. The $ \Updelta_{\text{f}} H_{{298\;{\text{K}}}}^{^\circ } \;\left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} } \right) $ was found to be $ {{ - 2, 40 7. 8 \pm 2.0} \mathord{\left/ {\vphantom {{ - 2, 40 7. 8 \pm 2.0} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}}} \right. \kern-0em} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}} $ .     

The standard molar enthalpies of formation of chromone-3-carboxylic acid, 6-methylchromone-2-carboxylic acid,and 6-methyl-4-chromanone determined by micro-combustion calorimetry

The energies of combustion of chromone-3-carboxylic acid (C3CA), 6-methylchromone-2-carboxylic acid (6MCC), and 6-methyl-4-chromanone (6M4C) were determined using an isoperibolic micro-combustion calorimeter. The calorimeter used in the present work has been assembled, calibrated, and tested in our laboratory with the desired results. Prior to the measurement of the energies of combustion, the purities, heat capacities (C _p), fusion temperatures (T _fus), and enthalpies of melting (Δ_fus H) for each compound were determined by differential scanning calorimetry. The values of the energies of combustion were used to derive standard molar enthalpies of combustion ( \( \Delta _{{\text{c}}} H_{{\text{m}}}^{\circ } \) ) and standard molar enthalpies of formation ( \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) ) in the crystalline phase at T = 298.15 K. The values found for the \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) of C3CA, 6MCC, and 6M4C were ?(619.5 ± 2.6), ?(656.2 ± 2.2), and ?(308.9 ± 3.0) kJ mol^?1, respectively.     

Formation,characterization and stabilization of water-soluble colloidal MnO<Subscript>2</Subscript> in the oxidation of methionine,thiourea and thioacetamide by permanganate

Stabilization and characterisation of water soluble colloidal MnO₂ during the oxidation of sulphur-containing organic reductants “thiourea, thioactamide and methionine” by permanganate in aqueous neutral media are reported for the first time. Upon addition of permanganate to a solution of methionine, a transient species appears within the time of mixing, which is stable for several weeks. On the other hand, the transient species is unstable in the presence of thiourea and thioacetamide, respectively. The nature of manganese (IV) species present in the solution was characterized by spectrophotometric and coagulation measurements. On addition of HClO₄, there is a decrease in the absorbance of the reaction mixture. Under pseudo first-order conditions ([reductants] > []), the reduction rate was very fast up to the formation of water soluble colloidal MnO₂. The effect of various parameters, such as hydrogen ion concentration, amount of and concentration of reductants were investigated. Mechanisms consistent with the observed results have been proposed and discussed.