Lösungsthermodynamik von FeCl2 und NiCl2 in mischschmelzen aus zwei alkalichloriden oder alkali- und erdalkalichlorid

The excess chemical potential (μ^E) and the partial heat of solution of FeCl₂ and NiCl₂ in molten mixtures of chlorides were determined at 820 and 920°C for diluted solutions by emf-measurements with Galvanic cells of the type

An average cationic potential

is defined and used to fix a common ionic radius and distanceparameter

for the mixed solvent. There exist correlations of the type

and the corresponding constants are tabulated.     

Diffusion potentials and transport numbers in molten alkali chlorides and their binary mixtures

Diffusion potentials at porous asbestos diaphragms separating chloride melts of different cation compositions have been measured as functions of temperature making use of cells with chlorine electrodes. Between individual molten alkali chlorides the diffusion potentials were found to increase with the difference in their cation radii reaching a maximum of ～ 35 mV for

and a minimum of ～ 2 mV for

The melts with smaller alkali cations were more electropositive in all cases. From the experimental data for the systems

where M₁  Cs or K and M_II  Li or Na, transport numbers of those cations were computed as functions of N. They proved to be smaller for Li⁺ and Na⁺ and larger for Cs⁺ and K⁺ as compared with their additive values. The cation mobilities were calculated. For Cs⁺ or K⁺ they are a little higher in the salt mixtures than in their individual chlorides whereas for Li⁺ or Na⁺ they are considerably lower. Such changes in cation transport numbers and mobilities can be explained in terms of autocomplex structure model for molten alkali halides developed recently by M. V. Smirnov.     

Reduction electrochimique a l'electrode de mercure de composes α-hydroxycarbonyles en solution aqueuse - II. Cetols RCOCHOHR′ et aldols (R = H)

In the previous paper, the mechanism of reduction of glyoxals has been discussed. Transfer of two electrons results in hydroxyacetophenone (C₆H₅COCH₂OH) formation. This compound can be reduced in a consecutive step according to two processes in aqueous media of different acidities. In neutral media, the keto grouping is reduced yielding hydroxyphenethylalcohol: C₆H₅CHOH CH₂OH. In acidic media, the COH bond is reductively cleaved, so the whole four electron transfer can be written:

This reaction constitutes an original way of reduction, an aldehyde grouping yielding a methyl grouping.The COH cleavage is exclusive for aliphatic α-hydroxycarbonyl derivatives:

     

Cathodic processes at electrolysis of chloride and chloride-fluoride melts of zirconium

Electrochemical reduction of zirconium from the NaClKClZrCl₄ molten mixture proceeds reversibly in two consequent steps:

With addition of sodium fluoride into the NaClKClZrCl₄ melt and also in the NaClKClK₂ZrF₆ molten mixture, reduction of zirconium occurs reversibly four-electrons step reaction:

     

Interplay between nitronates and nitriles accomplished in a PtIV-mediated reaction

Reaction between the coordinated propanenitriles in trans-[PtCl₄(EtCN)₂] and the cyclic nitronate

(1) gives the N-acylated iminocomplex

(2) which is unstable in wet solvents and undergoes hydrolysis to furnish

(3). The formulation of 2 and 3 was supported by satisfactory C, H, and N elemental analyses, agreeable HRESI⁺-MS, IR, ¹H NMR spectroscopies, and single-crystal X-ray diffraction (for trans-3).     

Mass transfer in fluidised bed electrochemical reactors

Electrochemical mass transfer experiments involving the cathodic deposition of copper from aqueous solutions containing H₂SO₄ have been performed for two distinct cases. (a) Determination of mass transfer rates at a plane wall electrode in the presence of a fluidized bed of inert particles (glass beads). In this work bed height, bed size and fluidization conditions have been varied and a correlating equation:

is suggested as applying over the range

Comparison is made with mass transfer data of several other authors, revealing considerable variance. (b) Determination of mass transfer rates between electrolyte and particles within an active bed of fluidized conducting copper particles. Analysis of the data yields a correlating equation:

in the range

This compares very well with another source for electrolytic fluidized bed mass transfer, but is somewhat lower than other equations for particle to fluid non-electrolytic mass transfer.     

The effect of Cl− on the kinetics of the anodic dissolution of Pd in H2SO4 solutions

The electrodissolution kinetics of palladium have been studied in deoxygenated

solutions at 25°C. The chloride concentration was varied between 0.01 and 0.5 M and the ionic strength was maintained at 1 M. For all the chloride concentrations an anodic Tafel slope of approximately 58 mV decade⁻¹ and an electrochemical anodic reaction order of 1.1 were obtained. The kinetic equation consistent with the experimental results is

which is consistent with the theoretical equation derived from the proposed mechanism, with the assumption that the adsorbed intermediate, (PdCl⁻₂)_ad follows Temkin adsorption behavior.     

Reduction electro-chimique a l'electrode de mercure de composes α hydroxycarbonyles en solution aqueuse—III. composes du type R-CO-C(OH)2-R′, cas de la ninhydrine

At the dme, the first step of the reduction (2F mol^?1) of dihydroxy 2,2 indanedione 1,3 (ninhydrin $\text{1}$) consists in the reduction of the CO group adjacent to the aromatic nucleus in α position and yields tryhydroxy 1,2,2 indanone 3 ($\text{2}$).

$\text{2}$ is furthermore reduced according to an original pathway: the second two electrons transfer implies the cleavage of a C-O bond of the gem-diol group in β position. It results in the formation of the enediol tautomer reversibly oxidized according to the gross reaction:

Cyclic voltammetry enables the determination of ε′^o (ε′^o = ?190 mV at pH = 3.00).A similar process was previously observed in the case of phenyl glyoxal and rhodizonic acid. So it can be concluded that the reduction of organic compounds bearing a —COC(OH)₂— group involves the same process.Whenever introduction of a third carbonyl group (—COC(OH₂CO—) results in change of mechanism. The presence of such a group increases the reactivity of the median carbonyl to nucleophilic addition, in particular to hydration, and then the CO bond cleavage cannot occur.     

Studies on oxygen reduction in molten NaOH

Oxygen reduction in molten NaOH at 623 K has been studied by the use of an Ni rotating disk electrode and a porous O₂ gas electrode. It was clarified that the diffusing species to the electrode surface is molecular oxygen itself, and not an oxygen-containing anion, such as O^2?₂, by limiting current measurements. Kinetic studies show that the following reaction mechanism is more probable:

where the latter is rate determining.Since H₂O transport to the electrode surface is rate determining, pO^2? control is especially important, taking into account the following equilibrium;

     

On the electrolysis of aqueous bromide solutions to bromate

The behaviour of aqueous active bromine solutions prepared by the anodic oxidation of bromide at a Ti/RuO₂ anode has been investigated. Bromate is formed chemically through the oxidation of hypobromite by hypobromous acid and vice versa:

The rate of the first reaction is at least 10 times higher than the second.The electrolytic formation of bromate occurs with the simultaneous evolution of oxygen. The following stoichiometry is suggested:

This is analogous to the anodic chlorate formation. Because the oxidation potential for Br^? is lower than for active bromine, the anodic formation of bromate takes place at current densities lower than the limiting value at Ti/RuO₂ anodes.     

Studies on the mechanism of the hydrogen electrode reaction by means of deuterium tracer—I. the reaction route

The reaction route of the hydrogen electrode reaction on Ni, Rh, Au, and Pt at the reversible potential was investigated through the exchange reaction between deuterium and light water. Various reaction routes involving hydrogen adatom H(a) and adsorbed hydrogen molecule-ion H⁺₂(a) as the reaction intermediates were considered. In order to single out the correct reaction route, these routes were examined, without assuming a priori the existence of a single rate-determining step, for satisfactory interpretation of the isotopic composition of the hydrogen gas during the exchange reaction. It is concluded that the reaction route consists of two consecutive steps,

and

, where B represents H₂O or OH^?.     

Jet break-up and air entrainment by low velocity turbulent water jets

Correlating equations are developed for air entrainment by plunging water jets with velocities in the range between 2 and 5 m/sec. Energy considerations are shown to be a good basis for predictive equations. Two different situations are distinguished depending on whether or not the jet is near its break-up length; for jets produced by nozzles within which turbulence is fully developed the break length is correlated by

Beyond 90% of the total break length the air entrainment produced by vertical jets from 2·85 to 10 mm diameter is given by

For shorter jets which are vertical or inclined, there is a length dependence which leads to the relationship, accurate within 15%, of

     

Stretching and deformation vibrations of CH2, C(CH3) and O(CH3) groups of poly(methyl methacrylate)

Infrared and Raman spectra of atactic PMMA and infrared spectra of stereoregular PMMA and of its four deuterated derivatives

, were measured. They were used to assign the bands of stretching and deformation vibrations of CH₂, CCH₃ and OCH₃ groups in the infrared and Raman spectra and to discuss the effect of stereoregularity on these bands in the infrared spectra.     

Mecanismes de reduction electrochimique de complexes acetylacetonates de metaux de transition

Electroreduction mechanisms of Mn, Fe, Co, Ni, Cu, Ce acetylacetonato complexes have been established in aprotic medium, on mercury electrode, by polarography, cyclic voltammetry and potentiostatic coulometry followed by identification of the reduction products. Two reaction schemes are proposed: (1) E.C. mechanism:

(2) Reversible monoelectronic reduction:

After this reversible reduction, Fe(tfac)₃ leads to iron (0) in a further reduction step. The diffusion coefficients, the Stokes-Einstein radii and the available apparent rate constants of the electrochemical steps are given.     

The aerobic and peroxide-induced coupling of aqueous thiols—II. Reaction mechanisms,model analysis,and a comparison of the model and experimental results

Kinetic results of the preceeding paper are used to formulate the most probable reaction mechanisms for the peroxide-induced and aerobic coupling of aqueous thiols. Parameters in the proposed mechanisms are evaluated for n-propylthiol using the results of independent measurements. A remarkably good agreement is achieved between the model and experimental results.The peroxide reaction, which is not affected by either copper ion or radical scavengers, is shown to be a nucleophilic substitution (S_N 2) reaction which proceeds by a two-step mechanism as follows: RS⁻ + H₂O₂

RSOH + OH⁻ rate-determining RS⁻ + RSOH → RSSR + OH⁻ In the reaction the thiolate anion acts as the nucleophile while hydrogen peroxide and the transient sulfenic acid, RSOH, function as electrophiles.The most plausible mechanism for the copper-catalyzed, aerobic coupling reaction is as follows: Cu⁺ (RSSR)₂⁺ + RS⁻

(RSSR)Cu⁺ (RS⁻) + RSSR (RSSR)Cu⁺ (RS⁻) + RS⁻

(RSSR)Cu⁺ (RS⁻)₂⁻ (RSSR)Cu⁺ (RS⁻)₂⁻ + O₂

Cu⁺(RSSR)₂⁺ + HO₂⁻ rate-determining RS⁻ + H₂O₂

RSOH + OH⁻ rate-determining RS⁻ + RSOH → RSSR + OH⁻ For the n-propylthiol substrate, the pertinent parameters in the mechanism are 1n (K₁) = −11,000 K/T + 33.6, where K₁ is dimensionless, 1n (K₂) = 4270 K/T −10.5, where K₂ is in 1/mol, 1n (k₂) = 30.0 − 5260 K/T, and 1n (k₂) = 26.8 − 6190 K/T, where k₁ and k₂ are in 1/(mol min).     

Thermodynamic studies on liquid AgClKClLiCl solutions

The thermodynamic properties of ternary AgClKClLiCl solutions were determined at various values of

and a different AgCl concentrations, using the formation cell: Ag(s)|AgClKClLiCl(l)|Cl₂(g), graphite. Dilute AgCl solutions were investigated in detail in order to extrapolate in γ_Agcl to X_AgCl å 0. Experimental values of Δ$\text{G}$^E_AgCl were interpreted by the Pelton, Flengas method and compared with Krupkowski's formalism, based only on data from the constituent binaries.     

Ionic mass transfer by free convection with simultaneous heat transfer

Rates of electrochemical mass transfer by free convection under the influence of simultaneous thermal free convection have been measured for upward facing horizontal disc electrodes. The electrode reaction was the cathodic deposition of copper from cupric sulphate solutions containing H₂SO₄ as swamping electrolyte. Results have been correlated by the equations.

and

where GR_m is a combined Grashof number for concentration and thermal buoyancy effects.

.Mass transfer has also been measured for the novel situation of nucleate boiling at the electrode surface and diffusion layer thicknesses as small as 1·7 × 10^?3mm have been obtained.     

Etude des systemes Na3AIF6Ta2O5 et Na3AIF6NaTaO3—I. Leur comportement chimique et leur diagramme d'equilibre

The behaviour of the Na₃AIF₆Ta₂O₅ system, as studied by means of thermal analysis, has been shown to be more complex than the simple binary system. The latter is due to the reaction

forming the sodium tantalate. The equilibrium diagram of the Na₃AIF₆NaTaO₃ system, which behaves as real binary system, was determined by different thermal analysis techniques and microprobe analysis.