Bestimmung des Enantiomerenüberschusses von chiralen Ammonium-Ionen mit Hilfe von Flüssigmembranelektroden

Determination of the Enantiomeric Excess of Chiral Ammonium long Using Liquid Membrane Electrodes A cell assembly with two membranes each containing one enantiomer of a chiral ionophore is described. It is suitable for the direct potentiometric determination of the enantiomeric excess of ions. The method is used to determine the enantiomeric excess of ephedronium ions in aqueous solutions.     

Morphometrische Untersuchungen an Leberschnitten von Ratten mit Hilfe eines Fernsehbild-Analysators

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Morphometric measurements of liver sections of rats by an image analysis system

     

Chirale Alkoxytitan(IV)-Komplexe für enantioselektive nucleophile Additionen an Aldehyde und als Lewis-Säuren in Diels-Alder-Reaktionen

Chiral Alkoxytitanium(iv) Complexes for Enantioselective Nucleophilic Additions to Aldehydes and as Lewis Acids in Diels-Alder Reactions A Number of chiral 1,2-1,3 and 1,4-diols were prepared and used as alkoxy ligands on Ti for enantioselective nucleophilic transfer of methyl, butyl, cyclopropyl, allyl, alkinyl, and phenyl groups to aromatic aldehydes, as well as for the enantioselective[4+2]cycloaddition of acrylate to cyclopentadiene. The 1,2-diols were pinane diol 7 and 1,2:5.6-diacetonide-protected mannitol 9 (Scheme 3) and tartrates. The 1,3-diols were obtained from the yeast-reduction products of 2-oxocyclopentane- and 2-oxocyclohexanecarboxylates and excess MeLi, BuLi, or PhLi (or the corresponding Grignard reagents; see 4–6 .) As 1,4-diols, we used the products 2 and 3 from tartrate acetals and methyl or Pheny1 Grignard reagents, the bis(benzaldehyde) acetal 8 of d-mannitol and o,o'-binaphthol (22). These diols were attached to the Ti-atom by azeotropic removal of i-PrOH from a mixture with [TiCi(i-PrO)₃]. Addition of various organometallic reagents R-metal (metal = Li, BR₃, MgX, MnC1, CuLiR) was followed by combination with aldehydes at – 75^., a warm up period, quenching with aqueous KF solution, and workup (for results see Tables 1–6 and Formulae 17–20 ). The enantiomeric excess of the secondary alcohols obtained varies greatly, certain combinations of chiral ligands, nucleophilic groups, and aldehyde substrates give rise to values as high as 90% ee; see e.g. Table 4. The Ti-complexes of the general formula [Ti(R*O)₂Ci₂] or [Ti(R*O)₂(i-PrO)CI] induced the Diels-Alder addition of methyl acrylate to cyclopentadience to take place at –30^.. The best enantioselectivity (50% ee) was observed with the binaphthol derivative (Table 7). The structures of the complexes involved in these reactions are unknown. The substitution on C(2) of the dioxolanes 2 and 3 (derived from tartaric acid) has a pronounced effect on the selectivities of both reactions studied here (Tables 2, 3, and 7). This remote effect (1,6-distance between the stereogenic acetal-C-atom and the Ti-centers) must be caused by conformational changes in the vicinity of the reactive site, i.e. the Ti? C bond in the nucleophilic addition reactions and the Ti-acrylate-oxygen complexation in the Diels-Alder reaction.     

Bestimmung von Methylchlorsilanen in Chlorsilanen mit Hilfe eines Systems Gas-Chromatograph und Massenspektrometer

Zusammenfassung Die Verbindungen (CH₃)₂SiHCl, CH₃SiHCl₂ und (CH₃)₃SiCl wurden in SiHCl₃/SiCl₄-Gemischen gas-chromatographisch analysiert, wobei ein Massenspektrometer mit fester Masseneinstellung als Detektor eingesetzt wurde. Die Nachweisgrenze liegt bei ca. 1 Gew.-ppm für diese Verbindungen.

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Determination of methylchlorosilanes in chlorsilanes with a gas-chromatograph/ mass spectrometer system

Summary The compounds (CH₃)₂SiHCl, CH₃SiHCl₂ and (CH₃)₃SiCl were analyzed in SiHCl₃/SiCl₄ mixtures by gas chromatography using a mass spectrometer being focused on definite peaks as detector. The detection limit was found to be about 1 ppm (wt) of these compounds.

     

Katalytische Reduktion von Stickstoffoxid mit Ammoniak an Vanadiumoxid und Eisen-Chromoxid

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