Zur Bestimmung der Bildungsenthalpie von SeCl4 und SeOCl2

Determination of the Enthalpies of Formation of SeCl₄ and SeOCl₂ The enthalpies of formation were derived for SeCl₄ and SeOCl₂ from the enthalpy of solution in NaOH. The determination is based on the enthalpy of formation for SeO₂, NaCl, and NaOH as well as on their enthalpy of solution. Results see ?Inhaltsübersicht”?.     

Thermal degradation of metal novolak precursors for high temperature superconductors: thermogravimetric and mass spectroscopy studies

High temperature superconductor (HTS) materials were prepared from novolak metal precursors in a special annealing process. In the present paper the thermal behaviour of pure cresol novolaks and novolak metal salt (nitrate) precursors was investigated by means of simultaneous thermogravimetric analysis and mass spectroscopy in air. The results show significant differences in thermal stability between the pure novolaks and the novolak metal precursors, with respect to the process as well as the products of decomposition. The main volatile products for the precursors are CO₂, H₂O and NO, thus indicating that the thermal degradation results in the formation of metal oxides at a temperature of about 300 °C.     

Determination of titanium and zirconium wear debris in blood serum by means of HNO3/HF pressurized digestion using ICP – optical emission spectrometry

A ‘one bottle’ method to determine particulate debris of titanium and zirconium in blood serum was developed. Inductively coupled plasma – optical emission spectrometry (ICP-OES) was used to simultaneously detect both elements at concentrations above 50 ng/mL. Pressurized digestion by means of nitric and hydrofluoric acid in PTFE^TM-containers in a specific time-heat-pressure protocol apparatus was applied to assure complete solvation of particles including oxides. Total decomposition of the matrix was achieved and reasonable detection limits were accomplished. The amount of remaining carbon did not cause any matrix problems during measurement. Received: 10 October 1997 / Revised: 5 December 1997 / Accepted: 9 December 1997     

Untersuchungen zum System Te/O/Br

Investigations on the System Te/O/Br The melting point diagram of the system TeBr₄? TeO₂ was obtained by total pressure measurements and DTA measurements. A Congruent melting composition Te₆O₁₁Br₂ exists, the melting point is 570°C. The enthalpy of formation and the standard entropy of the species TeOBr₂,g was derived from measurements of the total pressure over Te₆O₁₁Br₂/TeBr₄ and from the transport behaviour of the TeO₂ with Br₂. From the decomposition-pressure measurements over Te₆O₁₁Br₂/TeO₂ follow the partial pressure. The enthalpy of formation ΔH°(Te₆O₁₁Br₂,f,298) = ?453.5 kcal/Mol was obtained from the enthalpy of solution. The transport-behaviour of TeO₂ with HBr, with Tebr₄ and Br₂ and that of Te₆O₁₁Br₂ is clear with the thermodynamic data of TeObr₂.     

Indirect determination of arsenic by flotation spectrophotometry

An indirect method of arsenic determination in the submicrogram range via the determination of molybdenum is presented here. High sensitivity is achieved by combination of the chemical amplification during formation of dodecamolybdoarsenic acid (arsenic: molybdenum ratio 1 12) with multiplication due to the formation of ion-association complexes during flotation-spectrophotometric molybdenum determination with crystal violet (molar ratio 1 2). Thus, the amplification factor relating to arsenic is 24.Dodecamolybdoarsenic acid is formed in a weakly acidic medium and is quantitatively extracted byn-butanol. Back extraction of the heteropoly acid to the aqueous phase and its simultaneous destruction provides the basis for the reaction of released molybdate ions with thiocyanate ions. The molybdenum-thiocyanate complex forms a sparingly soluble ion-association complex with crystal violet which can be floated with toluene on the phase boundary (film flotation). After separation of the aqueous phase the floated molybdenum compound is dissolved in acetone and the resulting free crystal violet ions are subjected to photometric determination at 590 nm as equivalent of the concentration of arsenic. The molar absorptivity of crystal violet is 3.2 · 10⁵1 · mol^–1 · cm^–1. Beer's law is obeyed in a concentration range from 0.01 to 1 g Mo · ml^–1 (0.001–0.1 g As · ml^–1). The resulting detection limit for arsenic is 1 ng · ml^–1.     

Reactions of (Z)-3-aryl-3-chloropropenals with nucleophiles: stereoselective formation of (E)-vinylogous esters, (E)-vinylogous amides, and vinamidinium salts

The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments.     

Phosphinsubstituierte chelatliganden: XI. NMR-spektroskopische untersuchungen (1H, 13C, 31P, 55Mn) an halogentricarbonylmangan-chelatkomplexen mit phosphino-thioformamid- und -thioformimidoester-liganden

A series of halotricarbonylmanganese chelate complexes, fac-(CO)₃Mn(X)L (X = Cl (a), Br (b), I (c)), with thioformamide (L = Ph₂PC(S)NRMe; R = H (1), Me (2), Ph (3)) and the isomeric thioformimidoester (L = Ph₂PC(NR)SMe; R = Me (4), Ph (5)) ligands were prepared by thermal CO substitution of the pentacarbonylmanganese halides. The IR and NMR data indicate P,S-coordination of the ambidentate ligands and uniform Z configuration in 3–5. Due to the large linewidth of the NMR signals, the ⁴J(PH) and ³J(PC) coupling constants could not be determined for the thioamide complexes 1–3. Coordination of the thioimide 4 causes an increase in ⁴J(PH) whereas ³J(PC) remains unchanged. δ(³¹P) shows a downfield coordination shift as usual for manganese complexes. The broad ⁵⁵Mn NMR signals cover a range of +90 to ?730 ppm (rel. KMnO₄) with the imidoester complexes 4 and 5 at the low-field side. The normal halogen dependence Cl < Br < I is observed for ⁵⁵Mn shielding.     

Domino Reactions with Fluorinated Five-membered Heterocycles – Syntheses of Trifluoromethyl Substituted Butenolides and γ-Ketoacids

Summary. A new approach to trifluoromethyl substituted butenolides and their thioanalogues is described starting from 2-fluoro-3-trifluoromethylfurans and -thiophenes, respectively. The reaction sequence includes three steps – nucleophilic displacement reaction, Claisen, and finally Cope rearrangement – which can be run as domino reaction. A modification of the domino reaction (transesterification instead of Cope rearrangement) provides a concise access to α-trifluoromethyl-γ-ketoacids.     

Density gradient electrophoresis of cells in a reversible gel

Density gradient electrophoresis permits the separation of cell types according to surface charge density with high resolution. Any source of flow compromises the resolving power of density gradient electrophoresis. Although procedures have been devised to successfully counteract electroosmotic and convective flows, the final collection of separands requires that they be pumped out of the electrophoresis column. Experiments were therefore designed to test the hypothesis that this flow could also be eliminated by trapping the separated bands in a gel, from which they could be collected by slicing the gel cylinder. Glutaraldehyde-fixed rat and rabbit erythrocytes were used as test particles in a phosphate-buffered isotonic Ficoll-sucrose density gradient in a 2.2 cm diameter, thermostated vertical glass column that could be opened at both ends. Two types of agarose were used as gel polymers: Electrophoresis grade agarose (J.T. Baker Chemical Co.) at final concentrations of 0.1 to 0.25% and SeaPrep ultralow gelling agarose (Marine Colloids Div., FMC Corp.) at a final concentration of 1.0%. Electrophoretic separability of the test particles and fluid stability were tested independently at 55 degrees C and 32 degrees C at which the two agaroses were, respectively, liquid. The experiments demonstrated that the higher temperatures required and the presence of agarose compromised neither the stability of the density gradient nor the migration properties of the cells, and cells can be separated in a sol at a temperature that is compatible with cell viability.