Über amorphe Festkörper

Zusammenfassung Eisen(III)-Chrom(III)-Mischhydroxyde, die entweder als mechanische Mischungen oder durch Gemeinschaftsfällung hergestellt wurden, zeigten deutliche Unterschiede im H₂O₂-Zerfall, dessen Geschwindigkeit in sämtlichen Fällen einer Reaktion I. Ordnung entspricht. Diese Unterschiede werden noch größer, wenn man auf die Mischhydroxyde das [Fe(CN)₆]^4–-Ion aufträgt, das überdies noch durch eine zeitbedingte optimale Promotorwirkung gekennzeichnet ist.     

Zur Kenntnis der 1-Methylisatine

Ohne ZusammenfassungDer Schmelzpunkt liegt um 145°. Das Krystallisationsvermögen ist ein geringes. Das mikroskopische Bild scheint auf monokline tafelförmige Krystalle zu deuten, welche zum Teil unvollkommen ausgebildet sind. Charakteristisch für die Substanz ist die grüne Fluoreszenz der alkoholischen Lösungen.Die Arbeit wird fortgesetzt.     

Experiments on the analysis of thick, non-conductive metallic oxide layers on sheet using HF-SNMS

First experiments are described for depth profile analytical characterization of non-conducting enamel layers using secondary neutral particle mass spectrometry (SNMS) with HF sputtering technology. The homogeneous distribution of the oxidic components in the enamel layer are examined. The considerable layer thicknesses (> 80 μm) mean that the direct application of HF-SNMS for assessing interface and adhesion mechanisms is not practical at present. To prepare the interface layer from the steel side, the use of different preparation techniques is shown to abrade the sample with simple metallographic techniques down to a residual steel thickness of approx. 1–5 μm.     

Catalytic C(1), C(2)-Bond Cleavage of Long-Chain Aliphatic Alcohols and ω-Phenylalkyl Alcohols

A catalytic one step procedure for the C(1), C(2)-bond cleavage of long-chain aliphatic alcohols and ω-phenyl alcohols has been investigated, using as examples decanol, dodecanol, hexadecanol, benzyl alcohol, 2-phenylethanol and 3-phenyl-propanol. The reactions, which were carried out in a continuous flow tubular reactor using a Ni/Cu catalyst, showed good activity and selectivity with respect to the cleavage products. On the basis of the experimental studies a reaction scheme for the heterogeneous catalytic C(1), C(2)-bond cleavage of the alcohols is suggested.     

Über das unterschiedliche katalytische Verhalten von Harnstoff und Harnsäure

Ohne Zusammenfassung     

Über die Nitrierung der Hemipinsäure und ihrer Ester

Ohne ZusammenfassungHerrn Hofrat V. v. Lang gestatten wir uns, für die Ausführung der in dieser Arbeit mitgeteilten Krystallmessungen bestens zu danken.     

Monitoring Surface Processes During Heterogeneous Asymmetric Hydrogenation of Ketones on a Chirally Modified Platinum Catalyst by Operando Spectroscopy

Surface processes occurring at the catalytic chiral surface of a cinchona‐modified Pt catalyst during the asymmetric hydrogenation of activated ketones have been monitored for the first time using operando ATR‐IR spectroscopy. Fundamental information about this catalytic system could be gained, including the chiral modification process of the catalyst, the surface interaction of reactant ketone with preadsorbed chiral modifier, the role of hydrogen as well as the influence of the product enantiomers in the catalytic cycle. The formation of a diastereomeric transient surface complex between ketone and chiral modifier was found to be related to the ketone consumption. Among the studied activated ketones, a correlation between stereoselection and the strength of the intermolecular hydrogen bond was identified. Dissociated hydrogen from the catalytic surface is found to play a crucial role in the formation of the diastereomeric surface complex.     

Enantioselective hydrogenation over cinchona-modified Pt: the special role of carboxylic acids

The influence of acetic acid (AcOH) and trifluoroacetic acid (TFA) on the hydrogenation of ethyl-4,4,4-trifluoroacetoacetate has been investigated by using Pt/Al(2)O(3) modified by cinchonidine and O-methylcinchonidine. We have shown that the sometimes dramatic changes in enantioselectivity and rate cannot simply be interpreted by protonation of the alkaloid modifier. We propose a new three-step reaction pathway, involving interaction of the carboxylic acid with the reactant and the chiral modifier. The mechanism is supported by IR spectroscopic identification of cyclic TFA-modifier ion pairs. This new approach can rationalise the poorly understood role of acids in the enantioselective hydrogenation of activated ketones over cinchona-modified platinum metals.     

Hydrogen-bonding interactions in cinchonidine-2-methyl-2-hexenoic acid complexes: a combined spectroscopic and theoretical study

Molecular interactions between cinchonidine (CD) and 2-methyl-2-hexenoic acid (MHA) have been studied by means of NMR, ATR-IR MES, DFT, and ab initio molecular dynamics. These interactions are of particular interest due to their pivotal role in the chiral induction occurring in the heterogeneous catalytic asymmetric hydrogenation of alpha,beta-unsaturated acids. The population density of the Open(3) conformer of CD, the most populated one at room temperature in apolar solvents, considerably increased to a maximum by addition of MHA to CD in toluene. The CD-MHA complex showed prominent symmetric and asymmetric carboxylate stretching vibrations in the regions of 1350-1410 and 1520-1580 cm(-1), respectively. DFT calculations revealed that these vibrational frequencies are expected to significantly shift depending on the chemical surrounding of MHA, that is, the hydrogen bond network. Earlier postulated 1:1 binding between CD and MHA was considered unlikely; instead, a dynamic equilibrium involving the MHA monomer and dimer, the 1:3 and possibly 1:2 CD-MHA complexes, were rationalized. Stable CD-MHA structures suggested by DFT calculations are the "1:3, halfN, cyclic" and the "1:3, halfN, cyclic tilted" complexes, where three MHA molecules are connected in wire by hydrogen bonding, two having direct interaction with CD. The confinement of CD's torsional motions in the complexes, leading to a slightly distorted Open(3) conformer via specific hydrogen-bonding interactions, was clearly reproduced by ab initio molecular dynamics, and the stable and flexible nature of the interaction was verified. Theoretical IR spectra of the complexes reproduced the characteristic vibrational frequencies of the complexes observed experimentally, supporting the stability of the 1:3 and implying the possibility of even higher molecular weight CD-MHA complexes.