Unraveling the crystallization mechanism of CoAPO-5 molecular sieves under hydrothermal conditions

The hydrothermal crystallization of CoAPO-5 molecular sieves has been studied using time-resolved in-situ SAXS/WAXS, UV-vis, Raman, and XAS. Data collected during heating to 180 degrees C allowed the observation of different steps occurring during the transformation of the amorphous gel into a crystalline material from a macroscopic and atomic perspective. Raman spectroscopy detected the initial formation of Al-O-P bonds, whereas SAXS showed that these gel particles had a broad size distribution ranging from ca. 7 to 20 nm before crystallization began. WAXS showed that this crystallization was sharp and occurred at around 160 degrees C. Analysis of the crystallization kinetics suggested a one-dimensional growth process. XAS showed that Co(2+) transformed via a two-stage process during heating involving (i) a gradual transformation of octahedral coordination into tetrahedral coordination before the appearance of Bragg peaks corresponding to AFI, suggesting progressive incorporation of Co(2+) into the poorly ordered Al-O-P network up to ca. 150 degrees C, and (ii) a rapid transformation of remaining octahedral Co(2+) at the onset of crystallization. Co(2+) was observed to retard crystallization of AFI but provided valuable information regarding the synthesis process by acting as an internal probe. A three-stage, one-dimensional crystallization mechanism is proposed: (i) an initial reaction between aluminum and phosphate units forming a primary amorphous phase, (ii) progressive condensation of linear Al-O-P chains forming a poorly ordered structure separated by template molecules up to ca. 155 degrees C, and (iii) rapid internal reorganization of the aluminophosphate network leading to crystallization of the AFI crystal structure.     

REALISIS: a medicinal chemistry-oriented reagent selection, library design, and profiling platform

REALISIS is a software system for reagent selection, library design, and profiling, developed to fit the workflow of bench chemists and medicinal chemists. Designed to be portable, the software offers a comprehensive graphical user interface and rapid, integrated functionalities required for reagent retrieval and filtering, product enumeration, and library profiling. REALISIS is component-based, consisting of four main modules: reagent searching; reagent filtering; library enumeration; and library profiling. Each module allows the chemist to access specific functionalities and diverse filtering and profiling mechanisms. By implementing the entire process of reagent selection, library design, and profiling and by integrating all the necessary functionalities for this process, REALISIS cuts the time required to design combinatorial and noncombinatorial libraries from several days to a few hours.     

New dehydration in the pyrrolo[1,2–6-b]isoquinoline series. Preparation and structural identification of 3,5-dihydrobenz[f]indolizin-3-one

3,5-Dihydrobenz[f]indolizin-3-one was prepared by a novel dehydration reaction involving the heating of 1,2,3,5,10,10a-hexahydro[f]indolizine-3,10-dione with polyphosphoric acid. The structure of this new compound was established by X-ray crystallography, by nmr spectroscopy and by reduction to the known products 1,2,3,5-tetrahydrobenz[f]indolizin-3-one and 1,2,3,5,10,10a-hexahydrobenz[f]indolizin-3-one.     

CsMoO2(HO3P–CH2–PO3): a new metallodiphosphonate with a hybrid framework

Crystals of caesium molybdeno­methyl­enedi­phospho­nate, [CsMoO₂(CH₃O₆P₂)], were hydro­thermally synthesized at 473 K. The monoclinic structure, as determined from single‐crystal X‐ray diffraction, is two‐dimensional and consists of stacked mixed layers of corner‐sharing tetrahedral di­phosphon­ate groups and MoO₆ octahedra, between which Cs⁺ cations are intercalated.     

Aldol condensations over reconstructed Mg-Al hydrotalcites: structure-activity relationships related to the rehydration method

Two different rehydration procedures in the liquid or gas phase have been applied to reconstruct mixed oxides derived from calcined hydrotalcite-like materials to be used as catalysts for aldol condensation reactions. The as-synthesized hydrotalcite, its decomposition product, as well as the reconstructed solids upon rehydration were characterized by XRD, N(2) adsorption, He pycnometry, FTIR, SEM, TEM, (27)Al MAS-NMR and CO(2)-TPD (TPD=temperature-programmed desorption). Compared to the Mg-Al mixed oxide rehydrated in the gas phase (HT-rg), that rehydrated in the liquid phase (HT-rl) exhibits a superior catalytic performance with respect to the aldol condensation of citral with ketones to yield pseudoionones and in the self-aldolization of acetone. The textural properties of HT-rl and HT-rg differ strongly and determine the catalytic behavior. A memory effect led to a higher degree of reconstruction of the lamellar structure when the mixed oxide was rehydrated in the gas phase rather than in the liquid phase, although liquid-phase rehydration under fast stirring produced a surface area that was 26 times greater. This contrasts to typical statements in the literature claiming a higher degree of reconstruction in the presence of large amounts of water in the medium. CO(2)-TPD shows that the number of OH(-) groups and their nature are very similar in HT-rg and HT-rl, and cannot explain the markedly different catalytic behavior. Accordingly, only a small fraction of the available basic sites in the rehydrated samples is active in liquid-phase aldol condensations. Our results support the model in which only basic sites near the edges of the hydrotalcite platelets are partaking in aldol reactions. Based on this, reconstructed materials with small crystallites (produced by exfoliation during mechanical stirring), that is, possessing a high external surface area, are beneficial in the reactions compared to larger crystals with a high degree of intraplatelet porosity.     

New developments in the Pd-catalysed cyclisation-coupling reaction of alkene-containing carbonucleophiles with organic halides (and triflates). The first examples of asymmetric catalysis.

The results of our preliminary investigations directed toward asymmetric catalysis of the cyclocarbopalladation of alkenes bearing a proximate nucleophile with organic halides (or triflates) are disclosed. A series of bidentate phosphine ligands were evaluated in intramolecular versions of this reaction using (E)-2-[7-(2-bromophenyl)-hept-4-enyl]-malonic acid dimethyl ester (1) and (Z)-2-[7-(2-trifluoromethanesulfonyloxy-phenyl)-hept-4-enyl]-malonic acid dimethyl ester (9) as model substrates. The highest enantioselective induction was obtained with aryl triflate 9 which produced the corresponding cyclopentylindane as a single diastereomer in 54% chemical yield and 43% ee by using PdCl₂[S-(−)-TolBINAP] as chiral catalyst and K₂CO₃ as base.     

Eine verbesserte Auswertungsmethode für die Röntgenkleinwinkelstreuung von Hochpolymeren

Zusammenfassung Die theoretischen und experimentellen Bedingungen für eine verbesserte Auswertung der Röntgenkleinwinkelstreuung von Hochpolymeren werden untersucht. Es wird gezeigt, daß genaue Messungen des Intensitätsverlaufes bei größeren Winkeln die Trennung der Kleinwinkelstreuung in eine reine Grenzflächenstreuung und eine Komponente der Dichteschwankungen innerhalb der Phasen ermöglicht.Diese Trennung erhöht die Genauigkeit der Bestimmung der Invarianten und gestattet die Berechnung der mittleren Durchschußlänge der kristallinen und amorphen Bereiche.Ein Vergleich dieses Längenparameters mit der Langperiode führt bei Annahme einer Lamellenstruktur zu einer Aussage über die Unebenheit der Grenzflächen.Der Absolutwert der Dichtefluktuation innerhalb der Phasen stellt einen zusätzlichen Strukturparameter dar, der besonders stark vom Unordnungsgrad der amorphen Bereiche abhängt.Ein Vergleich der experimentellen Ergebnisse mit Intensitätsverteilungen im Kleinwinkelbereich, die sich aus der Theorie des Parakristalls ergeben, zeigt, daß es nicht möglich ist, diese Theorie mit den Resultaten der Messungen in Einklang zu bringen.

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Summary The theoretical and experimental conditions for an improved method of evaluating the X-ray small-angle scattering of polymers are studied. It is shown that accurate measurements of the intensity distribution at wide angles makes it possible to decompose the small-angle scattering into a component due to the phase boundaries only and a component related to the density fluctuations within the phases.This separation increases the accuracy of the determination of the invariant and permits the calculation of the average length of segments of the crystalline and the amorphous regions.Assuming a lamellar structure, a comparison of this length parameter with the long period can be used to assess the planarity of the boundaries. The absolute value of the density fluctuations within the phases represents a supplementary structural parameter which is largely determined by the degree of disorder in the amorphous regions.A comparison of the experimental results with calculated intensity distributions in the small-angle region based on the theory of the paracrystal shows that it is impossible to bring this theory into agreement with the experimental results.

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung Berlin 1971 vom 9. bis 13. März des Regionalverbandes Physikalische Gesellschaft zu Berlin.

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Wir danken Herrn Dr.H. Tompa für das Programm zur Berechnung der in Abb. 9 wiedergegebenen Interferenzfunktion, Herrn Prof. Dr.G. Rehage für die Polystyrolpräparate und HerrnJ. P. Pauwels, HerrnJ. Braibant und dem Personal unseres Rechenzentrums für die Mitarbeit.     

Evaluation of an accurate calibration and spectral standardization procedure for Raman spectroscopy

Due to modern developments Raman spectroscopy has evolved into a fast vibrational technique. Detailed fingerprints in combination with non-destructivity and minimal sample preparation has allowed the construction of reference libraries in a variety of research fields. Long-term stability and comparability are important characteristics when developing reference libraries. In addition, small shifts in highly similar spectra of different samples may limit the full potential of Raman spectroscopy. Since libraries often contain a large number of different and/or highly similar spectra, it is important that each data point in all the spectra corresponds to the exact Raman wavenumber. This is often not the case, due to shifts in optical pathway and/or shifts in laser wavelength. This paper describes a complete calibration protocol (wavelength and intensity) and evaluates the procedure for both short and long term stability, by means of 60 randomly selected measurement sessions spread over a period of nine months. A two-step standardization procedure is proposed to deal with spectral shifts.     

Preparation of amphiphilic polyisobutylenes-b-polyethylenamines by mannich reaction. I. Synthesis and characterization of α-phenololigoisobutylenes

The cationic polymerization of isobutylene initiated by 4-(2-hydroxy-2-propyl)phenol/BCl₃ system results mainly in α-phenol-ω-chlorooligoisobutylene; however p-(2-chloro-2,4-dimethyl-4-pentyl)phenol is present in all cases. α-Methyl-ω-chlorooligoisobutylene is formed only when the temperature is below?50°C; it results from initiation by the phenol/BCl₃ system. Thermal dehydrochlorination of α-phenol-ω-chlorooligoisobutylene is quantitative and leads to a mixture of isomeric ω-unsaturated oligoisobutylenes. α-Methyl-ω-phenololigoisobutylene is prepared by the Friedel—Crafts reaction between industrial unsaturated oligoisobutylene and phenol in the presence of SnCl₄ at ?30°C; the reaction is quantitative between ?50 and ?30°C degradation takes place. © 1993 John Wiley & Sons, Inc.     

FeCp]+-induced hexafunctionalization of hexamethylbenzene with dendrons for the direct synthesis of redox-active iron-centered metallodendrimers

Phenol tri- and nonaallyl dendrons (3 and 7, respectively) were functionalized at the focal position to give the new triallyl dendrons 4 and 6 and the nonaallyl dendrons 11 and 13 that contain a iodoalkyl or a bromobenzyl termini. All these dendrons were used for the [FeCp]+-induced hexafunctionalization of hexamethylbenzene in [FeCp(eta6-C6Me6)][PF6] (1) under mild conditions in the presence of KOH. These reactions directly yielded the 18-allyl and 54-allyl dendrimers 9, 10, and 14 with a [FeCp(eta6-arene)]+ unit located at the dendrimer core. Cyclic voltammetry studies were recorded in THF and DMF with these metallodendrimers and compared with those of analogous dendrimers or complexes of smaller size that contain a [FeCp(eta6-arene)]+ unit at the core. The decreased rate of heterogeneous electron transfer when the dendritic size increases first disclosed by Diederich and Gross is confirmed. The variation of the redox potential of the Fe(II/I) redox system with increasing dendritic size is negligible even in a solvent of high dielectric constant such as DMF. This trend is attributed to fact that the involved "redox" orbital is buried on the metal center, well protected by the shell of alkyl chains (electron-reservoir nature), unlike in ferrocene. The chemical irreversibility increases in THF as the dendrimer size increases, due to more facile ligand substitution with THF at the 19-electron level when the chain bulk increases.