On the E.S.R. spectra of intermediates generated during the electrochemical oxidation of triphenylacetic acid in acetonitrile

The acidity level and the fluoride ion activity are evaluated in anhydrous HF and in water+HF mixtures of HF content higher than 70% by means of R(H) and R(F) functions. For both functions, the potentials of the ferrocene/ferricinium or perylene⁺/perylene²⁺ systems are used as reference potentials. A hydrogen electrode is used for acidity level evaluation and it is shown that the R(H) function decreases (acidity increases) when HF content increases in the mixture; the value of R(H) is ?15.5 for anhydrous hydrogen fluoride (+KF 0.1 M). A lanthanum trifluoride monocrystal electrode is built and used for F^? activity evaluations and it is shown that the R(F) function increases (activity of fluoride ion decreases) when HF content increases, up to R(F)=13.6 for basic anhydrous HF (KF 0.1 M solution).     

Photoelectrochemical deposition of thin tellurium films

Effect of polychromatic light on the electrochemical deposition of tellurium(IV) ions on a glass carbon electrode from acid solutions of 0.45 M Na₂SO₄ + 0.05 M H₂SO₄ with pH 2.2 was studied. It is shown that electrochemical reduction of tellurium(IV) is possible in two stages in the potentiodynamic mode at potentials in the range from 0 to ?1000 mV. Elementary tellurium is formed in the first stage (E = ?320 ± 20 mV) and is reduced to telluride ions in the second (E = ?700 ± 50 mV). It is demonstrated that, under potentiodynamic deposition conditions, visible light affects the generation of Te^2? ions at potentials more positive than the electrochemical potential. The chronoamperometric method revealed differences in the behavior of transient currents in the dark and under illumination. The elemental composition and the film surface morphology were studied by electron-probe analysis.     

Extraction studies of antimony bromide into benzene

Antimony(III) can be extracted rapidly and quantitatively into benzene from a 10 M H₂SO₄–0.03 M HBr system. The extracted antimony bromide has an antimony to bromine ratio of 1:3. Under the above optimum conditions for extraction of antimony, the behaviour of 35 other elements was studied; As³⁺, Ge⁴⁺, Se⁴⁺, and Sn²⁺ were extracted almost quantitatively, and the percentage extraction of Hg²⁺, Bi³⁺, and Te⁴⁺ was 74.1%, 10% and 5.5% respectively. The extraction of the elements into benzene from a 5 M H₂SO₄–0.01 M KI system was also investigated, A comparison of the two systems is given.     

The effect of the double layer on the rate of the Fe3+/Fe2+ reaction on a platinum electrode and the contemporary electron transfer theory

The kinetics of the Fe³⁺/Fe²⁺ reaction on a Pt rotating disc electrode was studied in solutions of 0.5 M H₂SO₄ and 0.5 M Na₂SO₄ (pH 2.2). Taking into account formation of sulphate complexes the conclusion was made that the main contribution to the reaction rate is due to FeSO₄⁺ and FeSO₄ complexes. Extended Tafel plots obtained by Randles analysis from experimental current-voltage curves were corrected for the ₂ potential. The latter was evaluated according to the Gouy-Chapman theory by using the surface charge density values deduced from thermodynamic theory and measurements of other authors. Tafel plots were approximated by parabolas and the reorganization energy was calculated as 33 kJ mol^?1 and 51 kJ mol^?1 for Fe³⁺/Fe²⁺ in H₂SO₄ and Na₂SO₄, respectively. The comparison of these values with theoretically predicted ones was made. From the magnitude of the pre-exponential factor of the true rate constant it was concluded that the Fe³⁺/Fe²⁺ electron transfer reaction is non-adiabatic in nature.     

Theoretical Study of the Reactions M++CH3F (M=Ge,As, Se,Sb)

CASSCF–MRMP2 calculations have been carried out to analyze the reactions of the methyl fluoride molecule with the atomic ions Ge⁺, As⁺, Se⁺ and Sb⁺. For these interactions, potential energy curves for the low‐lying electronic states were calculated for different approaching modes of the fragments. Particularly, those channels leading to C? H and C? F oxidative addition products, H₂FC? M? H⁺ and H₃C? M? F⁺, respectively were explored, as well as the paths which evolve to the abstraction (M? F⁺+CH₃) and the elimination (CH₂M⁺+HF) asymptotes. For the reaction Ge⁺+CH₃F the only favorable channel leads to fluorine abstraction by the ion. As⁺ and Sb⁺ can react with CH₃F along pathways yielding stable addition products. However, a viable path joining the oxidative addition product H₃C? M? F⁺ with the elimination asymptote CH₂M⁺+HF was found for the reaction of the fluorocarbon compound with As⁺. No favorable channels were detected for the interaction of fluoromethane with Se⁺. The results discussed herein allow rationalizing some of the experimental data found for these interactions through gas‐phase mass spectrometry.     

The electrochemical Peltier effect observed with electrode reactions of Fe(II)/Fe(III) redox couples at a gold electrode

The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Π_c)_I=0, were determined by analyzing the observed temperature change as a function of current. The values of (Π_c)_I=0 were found to be positive for the Fe(H₂O)₆²⁺/Fe(H₂O)₆³⁺ systems in HClO₄ (1 M), HNO₃ (1 M), H₂SO₄ (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Π_c)_I=0 was obtained in the case of a Fe(CN)₆^4?/Fe(CN)₆^3? couple in a H₂SO₄ (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.     

Trace fluoride determination with specific ion electrode

A method is described for determining 10^-5–10^-4M fluoride in a variety of solutions potentiometrically with a fluoridc-specific electrode, by a standard addition method. Any change of ionic strength or the nature of the solution that might alter activity coefficients or junction potentials is minimized. The relationship between potential and fluoride concentration thus follows the Nernst equation, and the unknown concentration can be calculated. Experimental data are given for solutions of sodium choride, sodium nitrate, acidified sodium silicate and sodium hydroxide, lithium chloride, and phosphoric acid. Metal ions (e.g., Al³⁺, UO₂²⁺, Fe³⁺, Th⁴⁺) that interfere by forming complexes with fluoride can be precomplexed with phosphoric acid. The relative error is estimated at 10%, and the relative standard deviation is less than 5% over the concentration range 10^-5–10^-4M fluoride.     

Sodium-reduced tantalum powders produced from plumbomicrolite raw materials

Effect of various extractive systems (triisoamyl phosphate/HF+H₂SO₄, n-octanol/HF+H₂SO₄, n-octanol/HF+HNO₃) used to obtain potassium heptafluorotantalate from plumbomicrolite-based raw materials on the purity and characteristics of sodium-reduced tantalum powders was studied. Application of the extractive systems provides production of high-purity potassium heptafluorotantalate from raw materials based on products formed in processing of the plumbomicrolite concentrate.     

Investigation of hydrofluorides of the alkaline earth metals by the NMR method

Summary The structure of hydrofluorides with the composition MeF₂ · HF(Me=Sr, Ba) includes two anions: F^– and HF₂ ^– with a linear hydrogen bond. In SrF₂ · HF, the hydrogen bond is characterized by a more asymmetrical position of the proton than in BaF₂ · HF.Increasing the number of added HF molecules leads to the formation of two bifluoride ions in the compounds CaF₂ · 2HF and SrF₂ · 2.5HF. The hydrogen bond in this case is also nonsymmetrical, and the average F–H distance is equal to 1.17 A. Thus, the hydrogen bond in these compounds is of the same order as in KF · 2HF (r_F–F=2.33 A) [12],i.e., weaker than in KF · HF (r_F–F=2.26 A) [13], but stronger than in solid HF (r_F–F=2.49 A) [14].A structure with two polyfluoride anions evidently corresponds to the compound BaF₂ · 3HF.Institute of Inorganic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 9, No. 2, pp. 202–206, March–April, 1968.     

The formation of aryloxenium ion in the reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with strong acids

The reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine (1) with conc. H₂SO₄ affords 4-nitropyrocatechol and that with conc. sulfonic acids (RSO₃H where R = Me, CF₃) affords 2-hydroxy-5-nitrophenyl-R-sulfonates in yields of 80?C85%. These reactions are assumed to proceed through an intermediate (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺, which eliminates the N₂O molecule to form the aryloxenium ion [NO₂C₆H₄O]⁺. The latter reacts with acid anions at the ortho-carbon atom of the phenyl ring. The thermodynamical parameters of the elementary reactions resulting in the formation of the (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺ and aryloxenium ion [NO₂C₆H₄O]⁺ were calculated in the B3LYP/6?311+G(d) study of the combined molecular system (nitrohydroxylamine 1 + [H₃SO₄]⁺). The reaction of nitrohydroxylamine 1 with aqueous solutions of strong acids (??70% H₂SO₄, CF₃SO₃H) affords mainly 4-nitrophenol. It appears that the mechanism of this reaction does not involve the formation of the aryloxenium ion.     

Spectrophotometric and thermal analytical studies on the dehydration of copper(II) sulfate and its double salts

Spectrophotometric (diffuse reflection) and TG-DTA data on the dehydration of CuSO₄ · 5H₂O, Na₂Cu(SO₄)₂ · 2H₂O, M₂Cu(SO₄)₂ · 6H₂O(M⁺ = K⁺, Rb⁺, Cs⁺ and NH⁺₄) and Co₂Cu(SO₄)₃ · 18H₂O are given. Although complete dehydration of CuSO₄ · 5H₂O brings about a striking color change from blue to white, it was found that there is only a slight decrease in the v?_max. of its d-d band in the course of this change, and the total light absorption in the visible-UV region increases at the same time. The dehydration of the alkali metal and ammonium double salts, most of which contain [Cu(OH₂)₆]²⁺ aquo ions (in contrast to the [Cu(OH₂)₄]²⁺ in CuSO₄ · 5H₂O), occurs generally more easily than that of CuSO₄ - 5H₂O, and their v?_max. increases slightly in the change, leading to blue or green anhydrous products, although the formation of a white modification was observed with the potassium salt. It was also found that the v?_max. of the Cu²⁺ ion in the dehydrated cobalt(II) double salt is still lower than that in anhydrous CuSO₄, i.e., the ligand field and/or tetragonality around it is decreased by the presence of Co²⁺ ions.     

Influence of chemisorbed carbon monoxide on the oxidation of molecular hydrogen at smooth platinum in sulfuric acid solution

Potentiostatic current—potential curves of hydrogen oxidation were measured at 0.5 mV s^?1 on two smooth platinum electrodes of different shape in the presence of various coverages with chemisorbed carbon monoxide in 0.5 M H₂SO₄, stirred with molecular hydrogen at 1 cm³ s^?1. Carbon monoxide coverages up to 0.6 have a small influence. The hydrogen oxidation remains controlled by convective diffusion of molecular hydrogen. Above coverages of 0.6, a kinetic step becomes increasingly predominant. The effect of chemisorbed carbon monoxide on the H₂ oxidation is similar to that on hydrogen adsorption, studied previously. The correlation between the rate of the kinetic step and the free energy of hydrogen adsorption in the Temkin model of the surface is established and discussed.     

On the relationship between the structures of CuII complexes and their chemical transformations

The thermal decomposition of the complexes M ₂ ^I Cu(SO₄)₂ · 6 H₂O and M₂Ni(SO₄)₂ · · 6 H₂O (M^I=NH₄, K, Rb, Tl) containing the complex cation M^II(H₂O)₆ ²+ (M^Il = =Cu, Ni) was studied. The values of the experimental activation energyE obtained for the dehydration reactions of both complex cations were found to be influenced in different ways by the outer-sphere cations present. It was therefore concluded that the activation energy of the decomposition of Cu(H₂O)₆ ²⁺ depends on the degree of tetragonal distortion of this cation, which increases with the ionic radius of cation M^I. TheΔH values of the studied reactions depend less on the structures of the coordination polyhedra.     

Pulse polarography: IX. Proton diffusion in aqueous sulphate solution

Average diffusion currents, , of the ions H₃O⁺ and HSO₄^? in the system 0.1 M K₂SO₄+H₂SO₄ (pH=3.1?3.8) have been measured at 25°C both with a dropping mercury and a rotating disk electrode, using pulse techniques. The separate diffusion coefficients D_HSO4 and D_H have been estimated fromand it was found that D_H≤61×10^?6 cm²s^?1, which is definitely less than the value calculated when relaxation and (bulk) viscosity effects are taken into account. This is at variance with all the literature D_H values for non-sulphate systems and also with our experimental result D_H=(84.6±0.2)10^?6 cm²s^?1 for the system 0.1 M KCl+HCl, which is about 7% above the value from Onsager's theory. The peculiar behaviour of D_H in a K₂SO₄ solution is attributed to a strong decrease in rotational freedom of water molecules in such a medium.This paper also gives a critical evaluation of the principle of “independent diffusion” in excess neutral electrolyte if more than one species participates in the diffusion process.     

Effect of the Charge and the Nature of Both Cations and Anions on the Solubility of Zwitterionic Amino Acids,Measurements and Modeling

The effect of the charge and the nature of both the cations and the anions of some electrolytic salts: sodium fluoride (NaF), potassium fluoride (KF), sodium bromide (NaBr), potassium bromide (KBr), sodium iodide (NaI), potassium iodide (KI), sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), calcium chloride (CaCl₂), and barium chloride (BaCl₂), on the solubility of zwitterionic amino acids (glycine, DL-alanine, DL-valine, and DL-serine) in aqueous solutions at 298.15 K are studied and discussed. A salting-in effect is observed for all amino acids under investigation with all electrolytes used in the present study, except for DL-alanine and DL-valine in aqueous solutions containing sodium fluoride where a salting-out effect was observed. The orders of the effect of the nature and the charge of both the anions and the cations are: F^- < Cl^- < Br^- < I^- < NO₃^- < SO₄^2-\mathrm{F}^{-}<{}\mathrm{Cl}^{-}<{}\mathrm{Br}^{-}<{}\mathrm{I}^{-}<\mathrm{NO}_{3}^{-}<{}\mathrm{SO}_{4}^{2-} with both sodium and potassium cations; Na⁺<K⁺<Ca²⁺<Ba²⁺ with chloride anion.     

A thermometric study of the dissolution of copper in acid solutions

The dissolution of Cu in solutions of HNO₃ of different concentrations has been studied by the thermometric method. Starting from the initial temperature, T_i, the temperature—time curves exhibit an induction period followed by a rapid rise in temperature to a maximum value, T_m, attained t min after the start of the reaction. T_m increases and t decreases with increase of the acid concentration, M. ΔT (i.e.T_m ? T_i) and the reaction number (R.N. = (T_m ? T_i)/t) vary with M according to: ΔT = k(M ? M₀) and R.N. = A₁Mⁿ, where k, M₀, A₁ and n are constants.The effect of varying concentrations of HCl, H₂SO₄ and H₃PO₄ on the R.N. of Cu in 3.5 M HNO₃ was examined. Small amounts of these acids lower the R.N. (inhibition) due to the displacement of an active species on the surface of the metal by the anion of the acid. Larger additions of the acids accelerate dissolution. The concentration at which the added acid changes from corrosion-inhibitor to accelerator varies as HCl < H₂SO₄ < H₃PO₄. This sequence is considered to parallel the strength of adsorption of the respective anions. The results of experiments with salt additions confirm this view; all salts act only as dissolution-retardants. Calculations pertaining to the effect of the various ions on the R.N. support the conclusion that the dissolution of Cu in HNO₃ is autocatalytic in nature, and depends on the [H⁺]/[NO₃^?] ratio.Cu does not dissolve in air-free, cold HCl. Attack takes place, however, in the presence of KNO₃. Under these conditions attack is of the pitting- rather than the general type. The temperature rises suddenly after an incubation period, which decreases in length with increase of the amount of the added salt.Proof of the involvement of HNO₂ in the autocatalytic cycle of Cu dissolution in HNO₃ is obtained from the results of urea additions to the solution.     

Host–Guest Chemistry: Oxoanion Recognition Based on Combined Charge‐Assisted C−H or Halogen‐Bonding Interactions and Anion⋅⋅⋅Anion Interactions Mediated by Hydrogen Bonds

Several bis‐triazolium‐based receptors have been synthesized and their anion‐recognition capabilities have been studied. The central chiral 1,1′‐bi‐2‐naphthol (BINOL) core features either two aryl or ferrocenyl end‐capped side arms with central halogen‐ or hydrogen‐bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge‐assisted aliphatic and heteroaromatic C?H noncovalent interactions and combinations of C?H hydrogen and halogen bonding. The receptors are able to selectively interact with HP₂O₇^3?, H₂PO₄^?, and SO₄^2? anions, and the value of the association constant follows the sequence: HP₂O₇^3?>SO₄^2?>H₂PO₄^?. The ferrocenyl end‐capped 7²⁺?2 BF₄ ^? receptor allows recognition and differentiation of H₂PO₄^? and HP₂O₇^3? anions by using different channels: H₂PO₄^? is selectively detected through absorption and emission methods and HP₂O₇^3? by using electrochemical techniques. Significant structural results are the observation of an anion???anion interaction in the solid state (2:2 complex, 6²⁺? [ H₂P₂O₇ ] ^2? ), and a short C?I???O contact is observed in the structure of the complex [ 8 ²⁺][SO₄]_0.5[BF₄].     

Effect of anions on the dissolution of Al in acid solutions

The effect of Cl^?, Br^?, I^?, ClO₄^?, NO₃^?, HSO₄^?, HCrO₄^? and H₂PO₄^? on the of Al in 2 M HCl is studied by the thermometric method. Three sets of experiments are carried out, which allow the variation of the concentration of the various species in a programmed manner. Dissolution promotion is noted in solutions to which HCl, HBr and H₂CrO₄ are added. The way of action of each of these anions is discussed. Additions of HI, HClO₄, H₂SO₄ and H₃PO₄, on the other hand, first retard and later enhance the dissolution of Al in 2 M HCl, as their concentration in solution is increased. This is related to anion adsorption, which is counterbalanced by increase in acidity. HNO₃ differs from the other tested acids in causing only dissolution retardation. Experiments in which LaCl₃ is added to the test solution indicate that the NO₃^? is adsorbed as such on Al₂O₃. The ability of the various anions to retard the dissolution of Al in 2 M HCl decreases in the succession: NO₃^? (strong)>I^?>HSO₄^?>H₂PO₄^?>Br^?, ClO₄^? (weak)