Untersuchung von Kautschuk

Ohne Zusammenfassung     

Kritische studie über die quantitative bestimmung von sulfat

The gravimetric sulphate determination as barium sulphate works well with the usual precautions and Schleicher & Schuell blue ribbon filters without any agents for increasing crystal size or coagulation effects. Interference by foreign metal ions may be overcome by use of synthetic ion exchange resins.Treatment of filter papers with hydrochloric acid before filtration of barium sulphate precipitates is not necessary. Ignition temperatures should be kept below 600 °C.Smaller amounts of sulphate are preferably determined by volumetric or micro-volumetric methods, by colorimetric methods, or by turbidimetric methods. A turbidimetric titration to maximum of turbidity has been described above.Good results are claimed.     

Harn: Formoltitration

Ohne ZusammenfassungVergl. auch diese Zeitschrift47, 547;49, 66.     

Cyclic (alkyl)(amino)carbene gold(I) complexes: A synthetic and structural investigation

A series of mono- and dicarbene gold(I) complexes of types Au(CAAC)(Cl) [CAAC = cyclic (alkyl)(amino)carbene] (1) and [Au(CAAC)₂]⁺[X]^? (X = Cl, AuCl₂) (2) have been prepared through reaction of AuCl(SMe₂) with free carbenes a–e, and structurally characterized by single X-ray diffraction studies (1a, 1b, 2d, 2e). In addition two new free cyclic (alkyl)(amino)carbenes (c and e) have been synthesized.     

Reagents with a Crystalline Coat

Tetrakis(dimethoxyphenyl)adamantane (TDA) readily forms crystalline inclusion complexes with reactive, toxic, or malodorous reagents, such as benzoyl chloride, acetyl chloride, cyclohexyl isocyanide, phosphorus trichloride, and trimethylsilyl chloride. The crystals are stable and largely free of the problematic properties of the free reagents. When exposed to solvents such as DMSO or MeOH, the reagents react, and a large portion of the TDA precipitates. The TDA‐coated reagents may lead to a safer way of storing, handling, and delivering reagents, and ultimately to synthetic protocols that do not require fume hoods.     

Water-soluble polyesters from long chain alkylesters of citric acid and poly(ethylene glycol)

Long chain aliphatic alcohols have been used as model compounds to develop a preparative method for a water-soluble material, which could be a carrier for triacontanol, a highly hydrophobic plant growth regulator. New polyesters from long chain aliphatic (C = 12, 18 and 22) mono-1-alkyl citrates and poly(ethylene glycol) were synthesized and characterized by NMR spectroscopy. The polyester containing the triacontyl moiety was obtained from mono-1-triacontyl citrate, which was synthesized from the corresponding alcohol extracted from the Agave fourcroydes. The molecular weight of the polyesters depends on experimental conditions during synthesis such as reaction time, atmosphere, catalyst concentration and temperature. The reaction is second order in the early stage of the polyester synthesis. The reaction rate constant is independent of the length of the aliphatic chain, but it decreases with increasing of the poly(ethylene glycol) employed. Turbidity measurements have been used to study the polyester solubility. Solubility characteristics were found to depend on the of poly(ethylene glycol), the aliphatic-chain length and the value of for the polyester. These preparations could potentially be used to release triacontanol.     

Particle Deposition in Porous Media: Analysis of Hydrodynamic and Weak Inertial Effects

We have studied the transport and capture of non-Brownian particles in porous media, when the particles are mainly submitted to hydrodynamic and weak inertial effects. Visualization experiments have been performed using several models of porous media which consist of transparent etched networks of interconnected channels. Typical particle deposits have been observed at the corners of the grains of the porous medium. Their shape and their orientation were dependent on flow rate and on the anisotropy of the flow field. A trajectory analysis model has been applied to a porous medium made of a doubly periodic array of rectangular grains very close to the experimental model. This numerical model has been used to localize particle deposits and to determine particle capture efficiency on the grains over a range of low Stokes numbers, grain aspect ratios and flow-field anisotropy ratios. The results have been interpreted in terms of shape of particle deposits and compared successfully to experimental observations.