Voltammetric and chronoamperometric investigation of germanium amalgams: Part I. Properties of the homogenous amalgam

Using cyclic voltammetry and chronoamperometry with several anodic steps the deposition and particularly the oxidation of germanium from a HMDE was investigated within pH range 4–12 at Ge (IV) concentrations ranging from 4×10^?7M to 1×10^?4M in the absence of ligands capable to form the complex compounds with Ge(IV) in a solution. It was found that the initially formed product of electrodeposition is a homogeneous, usually supersaturated amalgam. Germanium from this amalgam oxidizes at about 1 V (vs. mercury sulphate reference electrode) or after some induction period, the length of which depends on concentration of Ge(0) in mercury, it begins to crystallize forming heterogenous germanium amalgam. Germanium from this heterogenous amalgam oxidizes in a separate voltammetric peak at more positive potentials. The solubility of germanium in mercury was evaluated on the basis of the oxidation current of homogenous amalgam and the value obtained is equal to (2±0.5)×10^?7M i.e. (1.1±0.3)×10^?7 wt. %. Applying the Stevens and Shain method the diffusion coefficient of germanium in mercury was found to be (1.32±0.1)×10^?5 cm² s^?1.     

Thermodynamic properties of two metal-rich tantalum sulfides: Ta2S and Ta6S

The incongruent vaporization reactions of Ta₂S and Ta₆S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of P_S(obs) to equilibrium the enthalpies of the reactions $\text{3}\text{2}\text{Ta}{}_2\text{S(s)}\text{=}\text{1}\text{2}\text{Ta}{}_6\text{S(s) + S(g)}$ and Ta₆S = 6 Ta(s) + S(g) were found to be $\text{ΔH}{}^0{}_{298}\text{R}\text{= 53.0(0.3) · 10}{}^3\text{K}$ and $\text{ΔH}{}^0{}_{298}\text{R}\text{= 58.1(0.4) · 10}{}^3\text{K}$, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.     

The elimination of carbon monoxide from molecular ions of phenol and other [C6H6O]+˙ isomers

Phenol and five acyclic isomeric compounds have been investigated using electron impact and field ionization techniques, mass analysed ion kinetic energy spectrometry and collision induced dissociation mass analysed ion kinetic energy spectrometry. The kinetic energy release data corresponding to the elimination of carbon monoxide from the molecular ions show that at least two structures of the reactant ion are involved. The electron impact and field ionization collision induced dissociation mass analysed ion kinetic energy spectra indicate that under electron impact conditions, the phenol ion partially isomerizes to another ion structure. An isomerization of about 40% to the structure of cis-2-hexen-4-yn-1-al is in good accordance with the spectral data.     

Synthesis of an inorganic-organic polymer blend from orthoboric acid and caprolactam

The possibility of modifying boron polyoxide with an oligomeric amide upon thermal dehydration of orthoboric acid and oligomerization of caprolactam in a common melt is shown. The products obtained after thermal pretreatment of the initial blend containing 30 wt % caprolactam are investigated. It is shown that the main processes at T < 200°C are dehydration of orthoboric acid and hydrolysis of caprolactam with the formation of ε-aminocaproic acid. At temperatures of 225–260°C, the predominant process is the formation of boron polyoxide and a caprolactam-based oligomeric product. The data of ¹¹B NMR spectroscopy show that the chemical transformations of caprolactam occur against the background of the N:B donor-acceptor interaction. The two-dimensional [¹¹B-¹H] heteronuclear correlation spectrum indicates that the systems obtained upon thermal treatment are solid solutions.     

The application of triphenylmethane dyes to visualization of selected aliphatic compounds in thin-layer chromatography

Selected triphenylmethane dyes were used as new visualizing agents in thin-layer chromatography of higher fatty acids, higher fatty alcohols, and higher aliphatic amines.     

Tautomerism of xanthine: The second-order MØller-Plesset study

Four 9H and four 7H tautomers of DNA base xanthine were studied by the ab initio LCAO-MO method at the MP2/6-311G^**//HF/6-31G^** and MP2/6-31G^**//HF/6-31G^** approximations. All calculated structures are minima at the HF/6-31G^** potential energy surface with the dioxo 7H tautomer (A1) being the global minimum. The second most stable tautomer, dioxo-9H (B1) is by 9 kcal/mol less stable. For the A1 B1 transition the calculated MP2 energy gap corresponds to the equilibrium constant of 2 × 10^–7. Therefore, only the major tautomeric form A1 is predicted to be detectable in the gas phase. The 7H and 9H groups of tautomers are discussed separately. Within both groups, the dioxo form (A1-7H, B1-9H) is the most stable one and is succeeded by the 2-dihydroxy (A2, B2) form. However, while the energy difference between A1 and A2 is 10 kcal/mol, the energy difference between B1 a B2 is only 2 kcal/mol. The effect of polar environment was estimated by the SCRF method, using a spherical cavity, at the HF/6-31G^** level. These calculations did not change the gas phase stability order of the tautomers. However, the energy difference between A1 and B1 decreased from 9 kcal/mol at the HF/6-31G^** level to 4 kcal/mol at the SCRF HF/6-31G^** level.     

Modification of nonionic adsorbent with eriochrome blue-black R for selective nickel(II) preconcentration in conventional and flow-injection atomic-absorption spectrometry

Chemical modification of nonionic sorbent Amberlite XAD-2 or anion exchanger Amberlyst A-26 with Eriochrome Blue-Black R (EBBR) produces a chelating resin of satisfactory chemical stability and resistance towards mineral acids. Retention of 10 metal ions has been examined for both resins. EBBR loaded XAD-2 was utilized for nickel(II) preconcentration in atomic-absorption spectrometry. In optimal conditions at a preconcentration time not exceeding 1 hr, nickel(II) can be determined at the 0.1 mug/l. level in flow measurements. Retention of metal ions on chelating resin is a convenient method of preconcentration and elimination of matrix interferences.     

Zur synthese von siloxanen: I. Die hydrolyse von chlorsiloxanen

The kinetics of hydrolysis reactions of some chlorodisiloxanes and of the chloropentasiloxanes (Me₃) SiO)₂Si(Me)OSiAr(Cl)OSiMeAr′ (with Ar = Ph and Ar′ = p-ClC₆H₄, C₆H₅ or p-MeC₆H₄; or Ar′ = Ph and Ar = p-ClC₆H₄, C₆H₅ or p-MeC₆H₄ in dioxane were studied by ¹H NMR spectroscopy.Because of their high hydrolysis rate the chlorodisiloxanes can be reacted only with equimolar amounts of H₂O. The formal second order rate constants and also the ? value evaluated can be used only in a tentative way.From hydrolysis reactions of the chloropentasiloxanes with an excess of H₂O and different amounts of HCl or HClO₄ the following results were obtained: hydrolysis is catalysed by HCl and HClO₄. The reaction is of first order with respect to chlorosiloxane. With respect to HCl at a tenfold excess of H₂O the order is in the range 0.5–0.7. Our results indicate, that there is a “non-catalysed” hydrolysis besides the acid catalysed reaction, ?-Values for the variation of Ar (0.7) and Ar′ (0.3) can be derived from the rate constants of the acid catalysed reactions of chloropentasiloxanes with a tenfold amount of water. The results are interpreted in mechanistic terms.     

Novel rhenium(III) complexes with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine: X-ray structures and DFT calculations for [ReCl3(OPPh3)(dppt)] and [ReCl3(PPh3)(dppt)] complexes

The reaction of [ReOCl₃(PPh₃)₂] with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-trazine (dppt) has been examined and [ReCl₃(OPPh₃)(dppt)] has been obtained. The triphenylphosphine oxide can be easily replaced by PPh₃ in the reaction of [ReCl₃(OPPh₃)(dppt)] with an excess of triphenylphosphine. The [ReCl₃(OPPh₃)(dppt)] and [ReCl₃(PPh₃)(dppt)] complexes have been structurally and spectroscopically characterized. Their molecular orbital diagrams have been calculated with the density functional theory (DFT) method, and their electronic spectra have been discussed on the basis of time-dependent DFT calculations. The compound [ReCl₃(OPPh₃)(dppt)] has been studied additionally by magnetic measurement. The magnetic behavior is characteristic of mononuclear complexes with d⁴ low-spin octahedral Re(III) complexes (³T_1g ground state) and arise because of the large spin–orbit coupling (ζ = 2500 cm⁻¹), which gives diamagnetic ground state.     

The two-phase structure of segmented block copoly(ether ester)

The annealing induced morphological changes in isotropic block copoly(etherester)s are investigated by small angle X-ray scattering methods. The observed results are consistent with a lamellar model which is comprised of a crystalline core of thickness 35 to 45 Å, a diffuse boundary zone of width 9 Å, and an amorphous layer which is varying strongly in thickness. The enhanced crystallinity of the samples annealed at higher temperatures is mainly due the lateral growth of the lamellae; the long period increases by not more than 20%. The scattering power of the samples is explained by means of an equivalent two-phase model in which the crystalline phase has the same structure as theα-form of poly(butylene terephthalate), whereas the amorphous phase is a mixture of the uncrystallized ester segments and the ether segments. The crystallinity determined from the scattering power is very much higher than that determined from thermoanalytical investigations.