DDQ‐mediated Direct C(sp3)?H Cyanation of Benzyl Ethers and 1,3‐Diarylpropenes under Solvent‐ and Metal‐free Conditions

A direct cyanation of benzyl ethers and 1,3‐diarylpropenes with TMSCN was performed under solvent‐ and metal‐free conditions. This oxidative cross dehydrative coupling (CDC) reaction was promoted by 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and provided rapid access to a broad range of nitriles in good to excellent yields.

     

Structure Studies on 6a-Thiathiophthenes and Related Compounds

The results from structure studies on 6a-thiathiophthenes show that different substituent groups perturb the bonding in the three-sulphur sequence to different degrees. Both equal and unequal S? S bonds occur in symmetrically as well as in unsymmetrically substituted derivatives. The specific effect of methyl and phenyl substituents on the sulphur-sulphur bonding may be described by the results from CNDO/2 calculations on mono-methyl and mono-phenyl substituted 6a-thiathiophthenes. Molecular packing and intermolecular close contacts also seem to affect the S? S bonding. The structures of equally substituted 6a-thiathiophthene analogues with and show, when compared with the equivalent 6a-thiathiophthene, that and cause a pronounced change in the S? S bonding, while the perturbation caused by is negligible. In symmetrical 6a-thiathiophthene analogues with and , the average bond length in the linear three-atom sequence is 9 – 12% longer than the respective single bond.     

Thermal decomposition of uranyl chloride hydrate

The thermal decomposition of uranyl chloride hydrate has been investigated by thermal analyses, X-ray diffraction and infrared spectroscopy. From the results it is concluded that uranyl chloride hydrate decomposes thermally as follows: .     

A Palladium‐Catalyzed Domino Approach to 2,3‐Disubstituted Benzofurans via an Intermolecular Carbopalladation/C(sp3)−H Functionalization/Isomerization Sequence

A palladium‐catalyzed domino strategy has been developed for the synthesis of 2,3‐disubstituted benzofuran derivatives. This cascade reaction sequence involves intermolecular carbopalladation and C(sp³)−H functionalization followed by isomerization.

     

N-n-Alkylpyridinium Derivatives of Mica-Type Layer Silicates

This paper deals with the cation exchange of N-n-alkylpyridinium ions against inorganic ions in mica type layer silicates. The arrangements of these ions in the interlayer space is derived from basal spacing measurements.     

Organolithium route to poly(arylsilane)s

Various poly(arylsilane)s The poly(carbosilane)s prepared in this way are of higher molecular weight than when prepared by the Wurtz-type condensation route previously reported. TG shows 40–50% overll weight loss attained at 500–600°C.     

Kinetics and mechanism of the vapour-phase ammoxidation of 4-picoline

The kinetics of the heterogeneous vapour phase ammoxidation of 4-picoline was studied over V₂O₅-Cr₂O₃-Al₂O₃ catalysts in a differential flow reactor between 548 and 598 K and under atmospheric pressure. The rate equation for the conversion of 4-picoline to isonicotinonitrile and the rate equation for the overall conversion of 4-picoline, represented the rate data satisfactorily. The overall conversion of 4-picoline was also tested by the Langmuir-Hinshelwood mechanism.     

A New Heterogenization Technique for Single‐Site Polymerization Catalysts

Summary: Silica‐supported single‐site catalysts show limitations with respect to catalyst homogeneity and maximum metal content. A novel emulsion‐based catalyst heterogenization concept is described, which allows these limitations to be overcome. The method produces catalyst particles with an inherently perfect spherical shape and unique intra‐ and inter‐particle homogeneity. The catalyst particles are very compact and have a low surface area. Video microscopic studies confirm that the improved catalyst homogeneity leads to a more uniform polymerization behavior on a single particle level. The catalysts contain significantly more complex, compared to silica‐supported catalyst systems, which leads to correspondingly higher catalyst activities. No differences, in terms of the mass‐transfer kinetics of these low‐porosity catalysts, compared to porous catalyst systems have been observed.

Electron microscopy image of self‐supported single‐site catalyst prepared by the emulsion‐based method.     

Synthesis of silicon–substituted azonitriles and their use in preparing caulks

A silicon-substituted azonitrile, has been synthesized by the hydrosilation of 5-hexene-2-one azine with methyldichlorosilane in the presence of chloroplatinic acid, followed by hydrocyanation with anhydrous HCN, and subsequent oxidation with chlorine. The azonitrile is an initiator for radical polymerizations. It is especially useful for the preparation of low molecular weight polymers that, after treatment with acetic anhydride, cure at room temperature in the presence of atmospheric moisture. The preparation of a series of room temperature- vulcanizable materials based on a tetrafluoroethylene/methyl vinyl ether copolymer is described.     

Convenient Synthesis of (E)‐5‐Aryl(halo)methylenebicyclo‐ [2.2.2]oct‐2‐enes and ‐[2.2.1]hept‐2‐enes via Lewis Acid‐ Promoted Carbohalogenation of Cyclic 2,6‐Enynols

An efficient synthesis of (E)‐5‐aryl(halo)methylenebicyclo[2.2.2]oct‐2‐enes is reported. Lewis acid‐promoted carbohalogenation of 4‐(3‐arylprop‐2‐ynyl)‐cyclohex‐2‐enols in dichloromethane proceeds rapidly to afford the exo‐methylene‐bridged bicycles in good yields. This method also provides an easy access to (E)‐5‐aryl(halo)methylenebicyclo[2.2.1]hept‐2‐enes from the five‐membered ring 2,6‐enynols. The reactions are procedurally simple and high yielding, producing the aryl(halo)methylene‐bridged bicycles in minutes under air and mild conditions.

     

Base‐Metal Catalysis Marries Utilitarian Aspects with Academic Fascination

No Abstract

     

Chlorierung von substituierten Polyacrylamiden

Preparation and properties of some polymer N-chloroamides of the general formula are described. These polymers are oxidation agents. The oxidation of benzylalcohol with polymer IVa (R?benzyl) was studied in detail. The mechanism is discussed on the basis of results with low-molecular N-halogen amides; it is concluded that chlorine, formed as an intermediate acts as the oxidation agent. The oxidation in the presence of dimethylsulfide, proposed by Corey is also studied with polymer N-chloroamides.     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

Untersuchungen von Polymeren im Massenspektrometer. I. Fragmentierungsreaktionen von oligomeren β-Alaninen

The degradation of poly-β-alanines under mild pyrolytical conditions yields oligomeric amids. Dimeric, trimeric and tetrameric β-lactames were used to study the fragmentation reactions of those degradation products. After ionisation at one of the hetero atoms αN-, keten-, αO- and βO-cleavage (with MC LAFFERTY -rearrangement) were found as main fragmentation reactions.     

Copper‐Catalyzed Monoborylation of Silylalkynes; Regio‐ and Stereoselective Synthesis of (Z)‐β‐(Borylvinyl)silanes

The selective copper‐catalyzed borylation of silylalkynes in the presence of a diboron reagent and methanol produced a variety of (Z)‐β‐(borylvinyl)silanes. The appropriate use of a selective ligand for copper allows the chemo‐, regio‐, and stereoselective monoborylation of silylalkynes. The β‐regioselectivity of an N‐heterocyclic carbene (NHC)‐copper catalyst was investigated by DFT calculations.

     

Iridium(III)‐Catalyzed Direct C?H Sulfonamidation of 2‐Aryl‐1,2,3‐triazole N‐Oxides with Sulfonyl Azides

We have developed a method for the direct sulfonamidation of 2‐aryl‐1,2,3‐triazole N‐oxides using sulfonyl azides as the amino source to release molecular nitrogen as the sole by‐product. This protocol exhibits excellent functional group tolerance and proceeds efficiently under external oxidant‐free conditions. Various 2‐(2‐sulfonamidoaryl)‐1,2,3‐triazoles were prepared in up to 97% yields for 25 examples with excellent regioselectivity.