Search results for "Chloride"
showing 10 items of 1691 documents
Chemoenzymatische „Chiral-Pool”-Synthese von (+)-exo-Brevicomin aus Kohlenhydraten mit Fructose-1,6-diphosphat-Aldolase
1990
Chemoenzymatic “Chiral-Pool” Synthesis of (+)-exo-Brevicomin from Carbohydrates Using Fructose 1,6-Diphosphate Aldolase Fructose-1,6-diphosphate aldolase (EC 4.1.2.13) catalyzes the stereospecific aldol reaction between 1,3-dihydroxyacetone phosphate (4) and 5-oxohexanal (3) or its 5-dithiane-protected analog 8. The products of the aldol reactions are dephosphorylated with acid phosphatase (EC 3.1.3.2). Whereas the aldol adduct of 3 cyclizes spontaneously to give the bicyclic brevicomin precursor 3, the adduct of 8 first has to be deprotected with sulfuryl chloride and wet silica gel. The resulting bicyclic α-hydroxy ketone 3 is reduced with LiAlH4 to form the 1,2-diol 14 which is then deox…
Oxidative halogenation of substituted pyrroles with Cu(II). PartIII. Bromination and chlorination of 2-benzoylpyrrole
1992
The bromination of 2-benzoylpyrrole with copper(II) bromide in the homogeneous and the heterogeneous phase is described, giving 4- and 5-monobromo derivatives whose ratio decreases as the temperature is increased. The same reaction with copper(II) chloride in acetonitrile at 60° produces 5-chloro-2-benzoylpyrrole as the major product. 4,5-Dihalopyrroles in good yields are obtained with an excess of halogenating agent.
Polypyridyl-based Cu(II) coordination polymers: Synthesis, structural and magnetic characterizations
2015
Abstract New Cu(II) coordination polymeric neutral chains of formula [Cu 2 (1,4-tpbd)Cl 2 L 2 ] (1,4-tpbd = N,N,N ′ N ′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine, L = 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet) − ( 1) or 1,1,3,3-tetracyano-2-propoxypropenide (tcnopr) − ( 2 )) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction and magnetic measurements. The crystal structure determinations of 1 and 2 reveal in both cases a one-dimensional structure in which the 1,4-tpbd acts as a bis-chelating ligand and the two chloride anions as asymmetrical bridging ligands. The Cu⋯Cu distances through the bis-chelating 1,4-tpbd ligand (8.194(1) and 8.245(3) A for 1 …
Synthesis of high-surface area CeO2 through silica xerogel template: influence of cerium salt precursor”;
2010
Abstract Ceria nanosized oxides with high surface area were synthesized by means of a templating approach, using a porous silica xerogel with surface area as high as 718 m2/g. After impregnation of the silica template with the cerium salt solution and further calcination at 600 °C, the final ceria oxide was recovered by dissolving the silica framework in NaOH solution. The effect of cerium counteranion, nitrate or chloride, on the textural and reduction properties of the ceria oxide was examined. Characterizations by BET and pore size distribution, XRD, TPR and SEM/EDX techniques were performed. The silica xerogel templated approach resulted in the preparation of ceria with surface area of …
Reprocessing of Poly(Vinyl Chloride), Polycarbonate and Polyethyleneterephthalate
1998
Poly ethyleneterephthalate — PET- and Poly(vinyl chloride) — PVC — are two of the most frequently encountered polymers in post-consumer plastics. In particular, these polymers can be used for manufacturing the same products (bottles, for example) and therefore are often found in the same stream, even when the collection is done with separation. The recycling of PET and PVC is usually carried out by separating them and reprocessing the two homogeneous polymers. Indeed, the heterogeneous recycling of two polymers is at present almost impossible because of many problems: as their melting points are very different, at the processing temperature of PET severe degradation phenomena of PVC take pl…
Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride
1980
Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…
Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride
1980
Melt viscosity and dynamic-mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic-decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.
Preparation and characterization of new hydrogels based on hyaluronic acid and α,β-polyaspartylhydrazide
2007
Abstract Hyaluronic acid (HA) has been crosslinked with α,β-polyaspartylhydrazide (PAHy). The crosslinking reaction has been performed in acidic medium in the presence of various amounts of N-ethyl-N′-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). All obtained samples have been characterized by FT-IR analysis and swelling measurements in double distilled water that have confirmed the occurrence of a chemical linkage between two polymers and the affinity towards aqueous medium of HA–PAHy networks, respectively. In vitro degradation assays have been performed in simulated physiological conditions as well as in the presence of hyaluronidase. Experimental data evidenced that HA–PAHy …
The glass transition behaviour of salted nylon 6
1981
Glass transition measurements of nylon-6/lithium halides mixtures have been carried out in wide range of frequency with the aid of different experimental techniques. The results show an increase of the glass transition temperature when the salt is present and prove the larger effectiveness of lithium chloride with respect of lithium bromide. This effect, in line with the large reduction of the specific volume caused by the salt, is due to the formation of a pseudo-cross-linking between lithium ions and the carbonyl-oxygen groups of the polyamide.
Determination of the conformation of polymers in the amorphous solid state and in concentrated solution by neutron diffraction
1975
Abstract From the coherent neutron scattering on dilute solid solutions of the ordinary polymer within the deuterated polymer, conformation parameters of polymer chains in amorphous solid states can be determined. In this way vitreous poly(methyl methacrylate) (PMMA) has been investigated. The chains form unperturbed coils and the radius of gyration is very near to the corresponding value in dilute solutions of the same polymer in the low molecular θ-solvent butyl chloride. The same principle of measurement has been applied to concentrated solutions of PMMA in D-acetone. The solutions contained 50% polymer, the main part of which (98% and more) was deuterated so that the system was opticall…