Competitive transport of alkali metal ions from aqueous media into toluene solutions of 2-(sym-dibenzo-16-crown-5-oxy)-decanoic acid. A comparative study

Competitive permeation of alkali metal ions from an alkaline source phase into or through a toluene phase facilitated by the lipophilic crown ether carboxylic acid 2-(symdibenzo-16-crown-5-oxy)-decanoic acid is studied in liquid—liquid extraction, bulk liquid membrane transport, and emulsion liquid membrane transport. Most rapid transport was obtained in emulsion liquid membrane experiments. Some differences in selectivity orders for alkali metal permeation were observed for the three separation techniques.     

Crystal structure transformations in ammonium and alkali metal perchlorates

A comparative study of the polymorphic transformations in ammonium and the alkali metal perchlorates has been made using differential thermal analysis. Certain correlations have been attempted between the observed trends in the transformation temperatures and available crystallographic and thermodynamic data. The transformation in the case of sodium perchlorate shows pronounced second-order effects. Considerable hysteresis is observed in the transformations in ammonium, potassium, rubidium and caesium perchlorates. Doping of ammonium perchlorate with ammonium phosphate is seen to result in an upward shift in the transformation temperature and an increase in the thermal hysteresis. Prior mechanical and thermal treatment is also seen to result in a broadening of the hysteresis loops in the case of ammonium and potassium perchlorates. The results are explained in terms of contrapolarization effects and the production of strain in the material as a result of prior treatment.     

Thermal decomposition of alkali metal perchlorates

The effect of past mechanical history on the subsequent thermal decomposition kinetics of sodium, potassium, rubidium and caesium perchlorates, has been investigated. At low temperatures the decomposition of all these salts is significantly sensitized by pre-compression. At high temperatures, however, prior compression results in a lowered decomposition rate in the case of potassium, rubidium and caesium perchlorates and in an increase in the thermal reactivity of sodium perchlorate. The high temperature behaviour is shown to be an indirect consequence of the low temperature behaviour. The difference in behaviour between sodium perchlorate and the other alkali metal perchlorates is explained on the basis of the stability of the respective chlorates, formed during the low temperature decomposition. This is substantiated by experiments which show that the addition of sodium chlorate to sodium perchlorate brings about a sensitization while potassium perchlorate admixed with potassium chlorate results in a desensitization at high temperatures.     

The effect of polyethylene oxide molecular weight on determination of its concentration in aqueous solutions

The influence of the molecular weight of polyethylene oxide (PEO) on the results from several methods for determining its concentration in aqueous solutions has been investigated. Modified versions of the complexation reactions of PEO with molybdophosphoric acid and with tetraiodobismuthate give results that are independent of molecular-weight effects for the range ca. 400-10(6). The reaction with KBiI(4) is the less accurate. Oxidative digestion is also independent of molecular-weight, but impurities easily obscure the measurements. Other methods studied included interferometry, viscometry, and complexation with tannic acid. Interferometry and the reaction with tannic acid were only independent of molecular-weight for M > 4000. With viscometry very poor results were obtained.     

The capacity versus potential dependence of the electrical double layer of the mercury/electrolyte solution of the dicarboxylic ions

The effect of dicarboxylic ions on the capacity hump was investigated by measuring the double layer capacity of the mercury/water electrolyte solution interface. Further experimental evidence was found of the internal rotation effect of the molecule in the double layer electric field. When discussing the effect of dicarboxylic ions on the capacity hump, it is assumed that the latter is due not only to dipole-ion, dipole-electrode and electrode-ion interactions but moreover occurs as the result of intra-ionic electrostatic interaction and the ability of the ion/or its fragment/to reorient in the electric field of the interface.     

Studies on the kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate—II. Mechanistic features in strongly acid solutions

The kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate in 1 M H₂SO₄ have been studied. Ceric ion and thiourea initially form an 1:1 complex which then reacts with uncomplexed ceric ion to form the initiating thiocarbamido radicals. The termination is predominantly biomolecular below an initial ceric concentration of 0.66 × 10^?2 M (depending upon the rate of initiation). At higher initial ceric concentrations, polymer radicals are terminated overwhelmingly by ceric ions. Substituted thioureas reduce the rate of polymerization according to the order of increasing electron density on the sulphur atom. The overall activation energy of polymerization is 12.1 kcal/mol in the region of bimolecular termination and 10.2 kcal/mol in the region of metal ion termination.     

A mechanistic study of the fragmentation of ferrocenyldiarylmethylium ions in aqueous acidic acetonitrile

Ferrocenylcarbocations of the type Fc$\text{c}\text{+}$ArAr′ (Ar, Ar′ = aryl groups) decompose in aqueous acidic acetonitrile liberating the 6,6-diarylpentafulvene ligand. The mechanism of the reaction has been studied by product analysis and by kinetic measurements.     

Fluoride complexes of the alkali metal ions

Measurements by fluoride ion-selective electrode potentiometry on the very weak monofluoride complexes of the alkali metal ions in aqueous solution at 25°C and an ionic strength of 1M indicate their stability constants lie in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ ? Cs⁺. Data at varying ionic strengths and temperatures were used to calculate infinite dilution stability constants and enthalpies and entropies of complexation for LiF and NaF.     

Optical autoionization resonance theory as an approach to electron transfer via adsorbed atoms at metal—solution interfaces

Electron transfer between an ion in solution and an impurity atom adsorbed at a metal electrode is sometimes faster than direct electron transfer between an ion and a metal. This process displays close analogies to Fano autoionization resonances in atoms excited to formally bound states broadened by coupling to continuum states. On the basis of this analogy we have derived current—voltage relationships for electron transfer via adsorbed impurity atoms. The most striking effect is that the current passes through a maximum at overvoltages approximately coinciding with the nuclear reorganization enery, then drops, and rises again at still higher voltages. This pattern is quite different from that of direct electron transfer and is caused by the “interference” of metal and impurity wave functions in certain energy ranges. The effect is generally expected only for activationless process, i.e. for large overvoltages, where the current variation directly reflects the behaviour of the pre-exponential factor in the current expressions.The impurity level also modifies the Gibbs energy of nuclear activation due to the solvent configuration dependence of the electron density at the adatoms. This effect is commonly small and in contrast to the electronic structural effects, leads to smooth current-voltage relations.     

Concentration-dependent transport of gases and vapors in glassy polymers

The transport of gases and vapors in glassy polymers is analyzed on the basis of the “dual-sorption” model with partial immobilization and the assumption that the diffusion coefficient is an exponential function of concentration. Expressions are derived for the effective (apparent) permeability and diffusion coefficients, as well as for the diffusion timelag. These expressions reduce in limiting cases to forms reported by other investigators. The implications of these results to the separation of gas and vapor mixtures by permeation through glassy polymer membranes are discussed.     

Crystal structure and fast ionic conduction of TIZrF5

TlZrF₅ crystallizes in the monoclinic system with unit cell dimensions a = 8.112(1) Å, b = 7.927(3) Å, c = 7.929(1) Å, β = 123.99(1)° and space group P2₁/c (n^o 14); Z = 4. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares techniques to a conventional R of 0.057 (R_ω = 0.063). The structure consists of sheets of (ZrF₅)^? that may be described as edge-shared and corner-shared bicapped trigonal prisms (ZrF₈). The sheets run parallel to the y0z plan and are bonded together by the Tl ions which are surrounded by 12 F^? ions. The ionic conductivity of TlZrF₅ and TlHfF₅ has been investigated by complex impedance measurements and the relationships between structure and fast-ionic conduction are discussed.     

Electrical pumping in carrier-mediated membrane transport

A model of carrier-mediated pumping induced by electrochemical (redox) reactions is presented. The model is compared with published data for the facilitated transport of nitric oxide in a formamide membrane containing dissolved ferrous and ferric chlorides wherein the flux of nitric oxide is augmented by diffusion of the reversible complex, (NO—Fe²⁺. Passing a current through the membrane drives the reduction of ferric ions at the cathode and the oxidation of ferrous ions at the anode, coupling the charge and mass fluxes within the membrane. Our results indicate that this electrically powered, carrier-mediated membrane can pump permeant up to a concentration 0(10) times greater than that in the feed.     

Nernstian and non-Nernstian potential differences at aqueous interfaces

A simplified general formalism of the physics of the charge-potential interdependence of the electrical double layer at ionisable group surfaces is presented. The equilibrium total double layer potential is obtained graphically and analytically for surfaces with acidic and basic sites, with amphoteric sites and with single acid sites. The deviations from Nernstian behaviour are given as a function of the acid ionization constants of the surface groups.     

Acidic and reductive dissolution of magnetite in aqueous sulfuric acid: Site-binding model and experimental results

The open circuit dissolution of ionic metal oxides in mineral acids is modelled assuming that the rate is controlled by the transfer of metal ions in hydrolytic equilibrium with bulk metal ions, from the metal oxide surface to the Stern plane. The site-binding model of the double layer metal oxide/electrolyte solution is used to obtain the pH dependence of surface and Stern potentials. The nature of the active sites is discussed and their surface concentration is assumed to be proportional to suface charge σ₀. Again, the site-binding model is used to detemine the pH dependence of σ₀. It is thus shown that the rate order in c_H⁺ is essentially defined by the potential dependence of the charge transfer process, for oxides with points of zero charge near neutrality that dissolve in mildly or strongly acidic solutions. The role of surface complexation is also discussed in terms of the site-binding model and the difficulties in interpreting dissolution experiments under constant external applied potential are discussed in terms of the complexity of the semiconductor oxide/electrolyte solution interfacial region in magnetite.An experimental study of the open circuit dissolution of magnetite in sulfuric acid is presented and interpreted according to the proposed model.The reductive dissolution of magnetite is modelled by extension of the Valverde-Wagner model of oxide dissolution. Experimental results are presented to demonstrate that the reductive dissolution rate of magnetite in ferrous containing solutions is controlled by the rate of electron transfer from adsorbed Fe(II) to Fe(III) surface states of magnetite.     

A faradaic impedance study of the reduction of oxygen from aqueous alkaline solution at the dropping mercury electrode

The reduction of oxygen to hydrogen peroxide at a dropping mercury electrode in an aqueous solution of 1 M KNO₃+0.04 M KOH (pH=12.35) has been studied by means of impedance measurements as a function of frequency and d.c. potential. The reaction appears to be nearly reversible in the dc sense, but quasi-reversible in the ac sense. The impedance data obey the Randles' equivalent circuit with the following apparent values for the kinetic parameters: standard heterogeneous rate constant k_sh^a=0.035 cm s^?1 and cathodic transfer coefficient α^a_c=0.22. The results are interpreted in terms of a two-step charge transfer mechanism with the step O₂+eO₂^? being rate-determining.     

Spectroscopic and electrochemical studies of transition metal tetrasulfonated phthalocyanines: Part V. Voltammetric studies of adsorbed tetrasulfonated phthalocyanines (MTsPc) in aqueous solutions

Cyclic voltammetric measurements of adsorbed Fe- and Co-tetrasulfonated phthalocyanine (TsPc) and Co-phthalocyanine (Pc) have been carried out on ordinary pyrolytic graphite and silver electrodes at different solution pH ranging from 1 to 13. Many voltammetric peaks were found to be pH dependent with a slope of ?59 mV/ unit pH. In some instances this dependence was observed in alkaline or acid solutions only. The influence of oxygen has been also examined.