Cation-exchange chromatography of some metal ions using aqueous NH4SCN-organic solvent mixtures

Summary Systematic cation-exchange studies of 19 metal ions have been made in various concentrations of NH₄SCN in 4060 organic solvent-water mixtures. The exchange behaviour of the ions depends on the solvent employed. Most of the metal ions show decreasing distribution coefficients with increasing concentration of ammonium thiocyanate in the solvent. Based on the variation of distribution coefficients as a function of NH₄SCN concentration, separations could be predicted and subsequently column chromatographic separations involving Zn, Hg(II), Mg, Mn(II), Co(II), Ni(II), Cd(II), Ce(III), Fe(III), La and Th(IV) were achieved.     

Extraction chromatography of common anions in liquid-liquid anion exchange systems. Part. III. Monobasic aliphatic organic acids and their sodium salts as eluants

Summary The chromatographic behaviour of anions on paper strips treated with tri-n-octylamine (TOA) salts or Aliquat 336 and developed with aqueous solutions of acetic, formic, monochloroacetic or trifluoroacetic acids and their sodium salts was investigated. Liquid-liquid extraction of organic acids by 0.1 M solution of TOA in benzene as well as the anion exchange between benzene solutions of TOA salts or Aliquat 336 (in acetate form) in benzene and aqueous solutions of sodium halides was also studied. It was found that extraction increases in the following order of the acids: CH₃COOOH<HCOOH<CH₂CICOOH<CF₃COOH; the relative affinity of organic anions to the quaternary alkyl-ammonium cation also increase in a similar order. The extraction of acid in excess over the amount necessary to neutralize the amine was observed for all four acids. The R_F values of anions investigated depend markedly on the type of organic acids or their salts and their concentration in the mobile phase. Halide ions are more strongly retained on paper treated with Aliquat 336 as compared with TOA salts. The chromatographic systems investigated offer many possibilities to separate various anion mixtures.Parts and II: refs. [1, 2].     

The dynamic behaviour of the silver-silver hexacyanoferrate(II) electrode: coulometric production of hexacyanoferrate(II)

The electrochemical behaviour of the silver-silver hexacyanoferrate(II) elec-trode was studied. The reaction Ag₄[Fe(CN)₆] + 4e^- → 4Ag + [Fe(CN)₆]^4- was shown to be useful for the coulometric production of hexacyanoferrate(II) ions in titrations of zinc(II). Coulometric titrations of organometallic compounds such as R₂Sn(ClO₄)₂, with electrically generated hexacyanoferrate(II) are also reported.     

Kinetics of Hydrogen Peroxide Decomposition in Guaiacol Solution, Catalyzed by Hexacyanoferrate(II)

The kinetics of hydrogen peroxide decomposition in a guaiacol solution, catalyzed by potassium hexacyanoferrate(II), were studied. The reaction mainly follows the pathway of guaiacol hydroxylation. The reaction order is 1 with respect to H₂O₂, 0.5 with respect to hexacyanoferrate, and from 0.4 to 0 with respect to guaiacol (the latter parameter decreases with increasing guaiacol concentration). The apparent activation energy is 105 kJ mol^{- 1}. A kinetic scheme of the process was proposed. An expression consistent with the experiment was obtained for the rate of hydrogen peroxide decomposition in the presence of guaiacol, catalyzed by hexacyanoferrate(II).     

Chelate von β-dicarbonylverbindungen und ihren derivaten: Teil XLVII. Dünnschichtchromatographisches verhalten von metallchelaten mit thiodibenzoylmethan und acetylthioacetaniliden

The thin-layer chromatographic behaviour of thiodibenzoylmethane chelates with cobalt(III), zinc(II), mercury(II), palladium(II), platinum(II) and rhodium(III), and also of acetylthioacetanilide chelates with cobalt(III), nickel(II), zinc(II) and cadmium(II) on alumina is described. Different binary mixtures of eluents are used. The influence of solvent parameters and of the layer material, possible separations and the influence of substituents in the acetylthioacetanilides are discussed.     

Determination of hexacyanoferrate based on its catalytic influence on the oxidation of p-phenylenediamines by iron(III)

Summary Both hexacyanoferrate(III) and hexacyanoferrate(II) catalyze the oxidation of p-phenylenediamines by iron(III)_aq. The rate of this reaction in the presence of a sample with an unknown amount of hexacyanoferrate is compared with the reaction rate of solutions containing well defined concentrations of this substance. In this way, hexacyanoferrate can be determined photometrically down to <10^–9 mol/l. Although this procedure is very sensitive, the analysis can be performed with a simple photometer. Absorbance changes >0.2 can easily be obtained in 1 cm cuvettes, even at extremely small concentrations of hexacyanoferrate, because it is not an absorbance proportional to the concentration of hexacyanoferrate but rather the formation rate of p-semiquinonediimine which enables the quantitative determination of hexacyanoferrate.     

Ion-sensitive behaviour of silver sulphide-based solid-state copper(II) and iodide electrodes in partially aqueous systems

The response of copper(II)- and iodide-selective electrodes was evaluated in various water-organic solvent mixtures. The copper(II) electrode showed an almost Nernstian behaviour in mixtures with ethylene glycol, tert-butanol, propanol, ethanol and methanol. The experimental slopes in buffered water-acetonitrile mixtures were linear but super-Nernstian. The response of this electrode in mixtures with p-dioxane was neither Nernstian nor linear. The interference of mercury(II) in the direct potentiometric titration of copper(II) with EDTA in solution containing acetonitrile was studied. The behaviour of silver sulphide-based iodide electrode hydrophobized by PTFE in mixtures with ethanol, methanol and p-dioxane was poorer than in water. The potential response of the iodide electrode with a homogeneous membrane (Ag₂S + AgI) was satisfactory even after prolonged soaking in p-dioxane.     

Solvatochromism and piezochromism of pentacyanoferrate(II) complexes in binary aqueous solvent media

Summary The solvatochromic behaviour of a number of pentacyano-ferrates (II), [Fe^II(CN)₅L] ^n-, is described, for solutions in H₂O-alcohol, -Me₂CO and -DMSO mixtures. The strong dependence of solvent sensitivity on the nature of the ligand L is particularly fully documented for H₂OMeOH mixtures (0–100% MeOH). The piezochromic behaviour of seven pentacyanoferrates(II) has been established, in aqueous solution. The connection between piezochromism and solvatochromism is detailed, and the solvatochromic results discussed in terms of (preferential) solvation.     

Kinetics of oxidation of iodide by hexacyanoferrate(II) in binary aqueous solvent mixtures

Summary The kinetics of the oxidation of iodide by hexacyanoferrate(III) have been studied in different H₂O-methanol, t-butanol, ethylene glycol glycerol, glucose or sucrose mixtures. Specific solvent effects are found as shown by the different trends in activation parameters and in the variations of the initial state and transition state chemical potentials as observed in different media. From the results of a multiple linear correlation, it is concluded that the kinetics are controlled by the ionizing power of the solvents, their relaxation times and the outer sphere reorganization energies.     

Thin-Layer chromatography of inorganic ions on cellulose phosphate in sulfuric acid-organic solvent media

Summary Thin-layer chromatographic behavior of 49 inorganic ions on cellulose phosphate (P-cellulose) has systematically been surveyed with binary solvent mixtures consisting of sulfuric acid and an organic solvent such as methanol or acetone. The R_f values of many bivalent and monovalent ions as well as Te(VI) decrease on the P-cellulose layer with an increasing concentration of the organic solvent. Polyvalent ions which form strong phosphato-complexes and precipitate insoluble sulfate are strongly retained on P-cellulose. Oxy-anions, Au(III) and Pt(IV) are not adsorbed on the cellulose to any great extent. Feasibilities of the separation of multicomponent mixtures are demonstrated on the P-cellulose layer.     

Solvent effects and correlation with Reichardt'sE T values on charge transfer spectra of bis(2,2′-bipyridyl)biscyanoiron(II)

The solvatochromic behaviour of biscyano-bis(2,2′-bipyridyl)iron(II) in a variety of solvents is described. The frequencies are correlated with Reichardt's solvent parameterE _T . Various trends are indicated, solvatochromic shifts of the title complex in various aqueous mixtures ofDMF and 2-butoxy ethanol are also reported.     

Solid-state ion-selective electrodes for the potentiometric determination of hexacyanoferrate (II)

Hexacyanoferrate(II)-sensing electrodes were prepared by mixing Ag₂S and Ag₄Fe (CN)₆. The 6:1 Ag₂S/Ag₄Fe (CN)₆ provided the best potentiometric response and speed of response. The log concentration vs. potential curves were linear with Nernstian slope (14.8 mV/decade) over the range 10^?1-10^?6 M hexacyanoferrate (II) at pH 7.00 with constant ionic strength. Interferences included iodide, sulfide and bromide. This electrode was used as indicator in potentiometric titrations of hexacyanoferrate (II).     

Kinetic study of ruthenium(VI) -- catalyzed oxidation of 2-methoxy- ethanol by aqueous alkaline hexacyanoferrate(III)

The kinetics of ruthenium(VI) catalyzed oxidation of 2-methoxyethanol by hexacyanoferrate(III) ion in an aqueous alkaline medium at constant ionic strength shows zero order dependence on hexacyanoferrate(III) and first order dependence on Ru(VI). Dependence of substrate concentration shows a Michaelis – Menten type behaviour. The rate increases with the decrease in alkali concentration. A reaction mechanism involves the formation of an intermediate complex between the substrate and ruthenium(VI). This complex decomposes slowly, producing ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in subsequent steps. The theoretical rate law obtained is in complete agreement with the experimental observations.     

Solvent-derived metal oxides in electrospray mass spectrometry of metal salt solutions

The electrospray mass spectra of MX₂and MX₃salts (where X is typically halide or nitrate) in protic and aprotic solvents, and solvent mixtures were examined. Comparisons of species responses with equilibrium aqueous solution concentrations were made. For MX₂salts, a good correlation between MOH⁺ response and MOH⁺ solution concentration was observed under conditions where the collision energy was nominally zero. Cu(II) is easily reduced in acetonitrile to Cu(I); Cu(I) was the principal species observed in the electrospray mass spectrum of Cu(II) in acetonitrile whereas Cu(II) was the principal species observed in that of Cu(II) in dimethyl sulphoxide. Gas-phase reactions between solvated clusters produced by electrospray and a second solvent vapour were examined. M³⁺clusters were the principal ions observed when an aqueous solution of MX₃was sprayed in the presence of aprotic solvent vapours.     

Diagrammes potentiel—niveau d'acidite dans les milieux H2OH3PO4—I Systemes electrochimiques ne faisant pas intervenir le proton

The conditional potentials of redox systems not involving protons have been studied as a function of phosphoric acid concentration (1–14M), with the ferricinium/ferrocene couple as the comparison system. The following systems were considered: Cu(II)/Cu, Cd(II)/Cd, Sn(II)/Sn, Zn(II)/Zn, Ag(I)/Ag, Pb(II)/Pb, Hg(II)/Hg, Bi(III)/Bi and particularly Fe(III)/Fe(II) and Fe(II)/Fe. The hexacyanoferrate(III)/hexacyanoferrate(II) and iodine/iodide couples were also studied. The results are presented as a potential—H₃PO₄ concentration diagram (or potential—acidity level diagram).     

Thin-layer chromatography of tris(1,10-phenanthroline)iron(II) and tris(2,2′-bipyridine)iron(II) on Sephadex G gels

Summary Gel chromatographic behaviour of tris(1, 10-phenanthroline)iron(II), tris(2,2′-bipyridine)iron(II) and tris(glycinato)cobalt(III) on Sephadex G-10 or G-25 was investigated by TLC with 0.001–1.0M NaCl as the eluent. The zone shapes and R_M values of tris(1,10-phenanthroline)iron(II) and tris(2,2′-bipyridine)iron(II) were appreciably dependent on the sample and eluent concentration, while the neutral complex, tris(glycinato) cobalt(III), exhibited the round zones with constant R_M values. The order of R_M values was found to be tris(glycinato)cobalt(III<tris(2,2∔pyridine)iron(II)<tris-(1,10-phenanthroline)iron(II) in all systems studied, although the reverse trend was expected when assuming the chromatographic behaviour of solute compounds to be controlled by the “sieving effect”. The comparison of the behaviour on Sephadex G gels with that on CM-cellulose revealed that the predominant mechanism involved is not the sieving effect, but ion-exchange and/or hydrophobic interaction.     

Kinetics and Mechanism of the Oxidation of Vanillin by Hexacyanoferrate(III) in Aqueous Alkaline Medium

The title reaction was investigated in aqueous alkaline medium. A first-order dependence in hexacyanoferrate(III) concentration and a fractional order in both vanillin and alkali were obtained at the concentrations studied. The added product, hexacyanoferrate(II), had a retarding effect on the rate of reaction. Ionic strength and dielectric constant of the reaction medium have little effect on the reaction rate. The effect of temperature on the rate of reaction has also been studied and activation parameters have been evaluated. A mechanism based on the experimental results is proposed and the rate law is derived. The reaction constants are calculated and used to regenerate the k_obs values, which are compared with the experimental values.     

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.5·7H₂O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.66·9H₂O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.     

Methanolysis of 4-bromobenzenediazonium ions. Effects of acidity, [MeOH] and temperature on the formation and decomposition of diazo ethers that initiate homolytic dediazoniation

We have investigated the effects of solvent composition, acidity and temperature on the dediazoniation of 4-bromobenzenediazonium (4BrBD) ions in MeOH-H(2)O mixtures by employing a combination of spectrometric and chromatographic techniques. The kinetic behaviour is quite complex; in the absence of MeOH, dediazoniations follow first-order kinetics with a half-life t(1/2) approximately 3000 min (T = 45 degrees C), but addition of small concentrations of MeOH lead to more rapid but non-first-order kinetics, suggestive of a radical mechanism, with t(1/2) approximately 125 min at 25% MeOH. Further increases in the MeOH concentration slow down the rate of dediazoniation and reactions progressively revert to first-order behaviour, and at percentages of MeOH higher than 90%, t(1/2) approximately 1080 min. Analyses of reaction mixtures by HPLC indicate that three main dediazoniation products are formed depending on the particular experimental conditions. These are 4-bromophenol (ArOH), 4-bromoanisole (ArOMe), and bromobenzene (ArH). At acidities (defined as -log[HCl]) < 2, the main dediazoniation products are the substitution products ArOH and ArOMe but, upon decreasing the acidity, the reduction product ArH becomes predominant at the expense of ArOH and ArOMe, indicating that a turnover in the reaction mechanism takes place under acidic conditions. At any given MeOH content, the plot of k(obs) or t(1/2) values against acidity is S-shaped, the inflexion point depending upon the MeOH concentration and the temperature. Similar S-shaped variations are found when plotting the dediazoniation product distribution against the acidity. The acid-dependence of the switch between the homolytic and heterolytic mechanisms suggests the homolytic dediazoniation proceeds via transient diazo ethers. The complex kinetic behaviour can be rationalized by assuming two competitive mechanisms: (i) the spontaneous heterolytic dediazoniation of 4BrBD, and (ii) an O-coupling mechanism in which the MeOH molecules capture ArN(2)(+) to yield a highly unstable Z-adduct which undergoes homolytic fragmentation initiating a radical process. Analyses of the effects of temperature on the equilibrium constant for the formation of the diazo ether and on the rate of splitting of the diazo ether allowed, for the first time, estimation of relevant thermodynamic parameters for the formation of diazo ethers under acidic conditions.