Effektive Stofftrennung in Gas‐ und Flüssigphase durch selektive Adsorption

Adsorption is a versatile tool for the separation of low abundant molecules from complex mixtures. The affinity and selectivity of the adsorbents are crucial parameters for the efficiency of the separation process. This work provides an overview of the basic adsorption mechanisms and illustrates their relevance for technical applications based on own experimental data in bioprocess, environmental and safety engineering. Distinctive features between the adsorption from the gas and fluid phase, respectively, the differences between small molecules and interacting biomacromolecules are presented.     

Komplexbildung und selektive Cyclisierung substituierter Oxalamidine

Crystallographic data for the acyclic benzylic substituted oxalamidine 3 and the alkyl substituted oxalamidine 4 reveal different structures for compound 3 (s‐trans(E/E) configuration and intramolecular hydrogen bridges) and compound 4 (s‐cis(E/E) configuration without hydrogen bridges). On the basis of the different configurations of these isomeric oxalamidines, the complexation on a (CO)₄Mo‐fragment varies remarkably: Complex formation of ligand 3 takes place at the sp²‐hybridized nitrogen atoms by rotation of the central C–C‐axis, isomerisation of the C N bonds, and by breaking of the hydrogen bridges. Because of the steric hindrance in 4 , the initiating coordination should occur on the sp³‐nitrogen atoms, followed by a intramolecular proton transfer and rehybridization. This complexation is favoured in the cases of cyclic oxalamidines. The molecular structures of the oxalamidines 3 and 4 , their (CO)₄Mo‐complexes 5 , 6 , and of the coordination compound of the cyclic 2,3‐bis(phenyl‐amino)chinoxaline 8 were unambiguously clarified by X‐ray analysis. The cyclization of the different substituted oxalamidines 3 and 4 by phosgene or thiophosgene in the presence of NaN[Si(CH₃)₃]₂ in THF proceeds regioselectively to the asymmetric 2‐imidazolidinones and ‐thiones 11 and 14 , respectively. In contrast to 3 , 4 cyclizes in toluene selectively to the isomeric symmetric 2‐imidazolidinthione 13 . Furthermore, the cyclization on the coordinated oxalamidines with oxalyl chloride provides exclusively the coordinated 2‐imidazolidinones 12 and 15 , which retain the substituent pattern of the starting complexes 5 and 6 – the (CO)₄Mo‐fragment acts as a protecting group.     

Titanhaltige Molekularsiebe als Katalysatoren für selektive Oxidationsreaktionen mit Wasserstoffperoxid

Titanium Containing Molecular Sieves as Catalysts for Selective Oxidation Reactions with Hydrogen Peroxide Titanium silicalite (TS-1) is known to be a highly-efficient and selective redox molecular sieve that has been found to catalyze a range of synthetically useful oxidation reactions with hydrogen peroxide under mild conditions. Among these reactions which are often influenced also by the shape-selective properties of the Ti-containing molecular sieve are olefin epoxidation, the oxidation of alcohols to carbonyl compounds, aromatic hydroxylations and ammoximation of cyclohexanone to cyclohexanone oxime. A critical review on the present literature on TS-1 catalysts and further Ti-containing molecular sieves is given mainly focused on the questions connected with the identification of the catalytic active titanium species and the mechanism of some of the reactions. Therefore, the procedure of the synthesis of TS-1 as well as the results obtained from the most of the physico-chemical investigations are analyzed. There are no final correlations to realize between the parameters of the synthesis, the results of characterization and the catalytic properties of TS-1.     

Synthese von nitro- und aminosubstituierten Thiobenzamiden durch Thiolierungsreaktionen mit elementarem Schwefel unter milden Bedingungen

Synthesis of Nitro- and Amino-Substituted Thiobenzamides by Thiolation Reactions with Elemental Sulfur at Mild Conditions The Synthesis of thiobenzamides 2 – 7 by basecatalyzed thiolation of nitro-benzyl-halides (type 1 ), especially at low temperatures, and the selective synthesis of p- and m-nitro-thio-benzamides ( 2 , 3 ) or p-and m-amino-thiobenzamides ( 5 , 6 ), respectively, are described. o-Nitro-benzylhalides (→ 4 , 7 ) are less reactive than p- and m-nitro-benzylhalides. The reaction of nitrobenzylhalides (type 1 ) with elemental sulfur and amines occuring at low temperatures to give 2 – 4 leads via structures of the type 11 , 15 and 16 .     

Synthese von 4-Alkoxy- und 3-nitrosubstituierten Isoxazolidinen durch katalysierte 1,3-dipolare Cycloadditionsreaktionen von Nitronen mit Vinylethern und Nitroolefinen

Synthesis of 4-Alkoxy and 3-Nitro Substituted Isoxazolidines by Catalyzed 1,3-Dipolar Cycloaddition Reactionas of Nirtones with Vinyl Ethers and Nitro Alkens 1,3-Dipolar cycloadditions of the C-phenyl-N-alkylnitrones 1,3 and the C,N-diphenylnitrone ( 2 ) with vinyl ethers 5,6 are strongly catalyzed by chiral oxazaborolidines derived form N-arylsulfonyl substituted L -α-amino acids valine and tert-butyl leucine and BH₃·THF complex at −22 °C to room temperature to give predominantly the 3,5-trans-substituted 5-alkoxy-isoxazolidines 8b–12b , but with moderate enantioselectivity. Thermal cycloaddition afforded predominantly the 3,5-cis-substituted 5-alkoxy-isoxazolidines 8a–12a . The cycloaddition of (E)-1-ethyl-2-nitroethene ( 7 ) afforded a mixture of cis- and trans-substituted 4-nitro-isoxazolidines 13 . The ratio depends on reaction temperatute and catalyst. Mild ring cleavage after quarternization of 5-etheoxy-2-methyl-isoxazolidines ( 8 ) yields the corresponding β-amino-esters 27, 28 .