bluuebunny/crossref_metadata_2025_split huggingface dataset:
Untersuchungen an dealuminierten Pentasil‐Katalysatoren
Authors: Öhlmann Gerhard , Jerschkewitz Hans‐Oeorg , Lischke Günter , Parlitz Barbara , Richter Manfred , Eckelt Reinhard 
Published: September 2010

AbstractInvestigations of a ZSM‐5 type zeolite (HS 30, manufactured by VEB CK Bitterfeld without using any template) show that by dealumination various ratios of Si/Alframework can be achieved within a rather broad scale without structural changes of the initial substance. In any case the number of strong acid Brønsted centres of the elementary unit corresponds to the number of Al atoms contained therein.Throughout all investigations the relative catalytic activity of the catalysts has been found to be in a linear relationship to the number of strong acid Brønsted centres (bridged OH groups). With the isomerisation of m‐xylene the initial non‐dealuminated sample already brings about a selectivity of ≈︁80% for the para‐isomere. No influence of dealumination on p‐selectivity could be observed.With the conversion of methanol reduced catalytic activity of dealuminated samples results in an increase of the selectivity of lower olefins at the expense of aromatics for both reaction temperatures. The values obtained at 580°C are in favour of an additional formation of lower olefins due to the cracking of higher olefins. Dealumination gives also rise to an essential growth of the stability (i.e. possible integral charge by CH3OH) of the catalyst. With growing dealumination of the catalyst the attainable time on stream increases and reaches a maximum falling of thereafter.
Citric Acid — Its Natural and Synthetic Derivatives
Authors: Milewska Maria J. 
Published: September 2010

AbstractPhysico‐chemical and chemical properties of citric acid and methods of synthesis of its derivatives, namely esters, amides, 1,3‐dioxolan‐4‐ones etc. are presented. The important group of natural derivatives of this acid belonging to the siderophore family, i.e. compounds fulfilling in nature the function of biocarriers of ferric ions, is described in detail. The recent advances in the total synthesis of natural siderophores — citric acid derivatives, its homologues and analogues of the “retro” type are summarized.
Dithiocarbonsäuren und Dithiocarbonsäureester sowie Thiocarbonsäureamide aus methylenaktiven Chlormethylverbindungen und Schwefel
Authors: Thiel Wilfried , Mayer Roland , Viola Horst 
Published: September 2010

AbstractThe direct sulphurization of chloromethyl compounds with elemental sulphur leads to dithiocarboxylic acids, dithiocarboxylic esters or thioamides. In the presence of a base, the starting products can be oxidized by low‐temperature sulphurization, a reaction of wide application. The conversion of chloroacetic acid and its derivatives to thiooxalic derivatives, activated C2‐building blocks of growing interest in synthetic chemistry, is of special importance. As a rule, the examples described in the review have not been published. They show a new and easy way for the preparation of heterocycles containing activated dithiocarboxylic functions.
Thiophile Reaktionen an Thiocarbonylverbindungen und deren Redoxverhalten
Authors: Viola Horst , Hartenhauer Helge , Mayer Roland 
Published: September 2010

AbstractThe review describes thiophilic reactions of thiocarbonyl compounds with C‐ and S‐nucleophiles. They occur more frequently than has been supposed up to now, especially between vicinal thiocarbonyl systems and S‐nucleophiles. A general relation between thiophilic reactions and the redox behaviour of the system and a possibility to estimate approximately the thiophilic properties are discussed. Some conclusions for the synthesis and the behaviour of thiocarbonyl compounds are drawn.
Quantenchemische Beiträge zur Chemie der Kohlensäurederivate
Authors: Schädler Hans‐Dieter 
Published: September 2010

AbstractQuantum chemical calculations are aible to clarify complex and concurrent mechanisms of the reaction of σ3‐carbonic acid derivatives. MNDO and ab initio calculations have been carried out on alternative transformation mechanisms. It has been shown that under certain circumstances the well believed elimination‐addition transformation is converted in an addition‐elimination manner. Now the kinetic stereoelectronic effect can explain the decomposition direction of the tetraedrical intermediat. Otherwise intermolecular proton transfer is the first step of elimination‐addition process instead of the sometimes formulated intramolecular [1, 3]‐Hydrogen rearrangement.
Mehrdimensionale Varianz‐ und Diskriminanzanalyse sowie Klassifizierungsmethoden zur Auswertung gaschromatographischer Ergebnisse
Authors: Henrion René , Henrion Günter , Michael Günter , Petereit Detlef 
Published: September 2010

AbstractMultivariate data sets are a result of numerous methods of analytical chemistry, for instance like high performance chromatography. In addition to procedures of nonsupervised learning (e.g. cluster analysis) multidimensional analysis of variance, discriminant analysis and classification methods have extraordinary importance for data evaluation. Essential ideas of these methods are described and their application to two data examples by using the BASIC programs VARDIS and CLASS is illustrated. The first example deals with a discrimination of fuel filling stations being provided by the same source. In another example the recognition rate of 10 european brandies is studied. Both data sets were obtained by gas chromatography.
Cobaloxime als Katalysatoren
Authors: Madeja Kurt 
Published: September 2010

AbstractCobaloximes are discussed as catalysts generating highly reactive species like radicals in short catalytic cycles. This general reactivity pattern is demonstrated mainly by means of the reactions of these complexes with hydrogen. It is shown that adduct equilibria with the solvent affect the catalytic activity of these complexes, that their disadvantageous self hydrogenation can be suppressed at least partially and that organocobalt compounds are valuable intermediates for organic syntheses.
Fraktale in der physikalischen Chemie
Authors: Spindler Herbert , Vojta Günter 
Published: September 2010

AbstractThe fractal concept, created by Mandelbrot, has important consequences for the development of physical chemistry. Starting from the idea of the non‐integer Hausdorff dimension fractal mathematics is a powerful tool for the description of irregular structures and processes in physics and chemistry. The fractal dimension D is strictly only defined in the ranges of self‐similarity and normally does not fall below the embedding dimension by more than one. But smaller values of D are possible, too, if subsets of the fractal object are treated (subfractal dimension). Furthermore, a fractal model for porous solids is presented, and it is shown that the value of surface area for fractal objects is a function of measuring approach. The dynamics of atoms and molecules in solids and at surfaces can be described using the fracton dimension Ds < D. Diffusion in a fractal system generally proceeds more slowly than in a normal one. It is stated that percolation is governed by fractal geometry. The formation of many aggregates can be described in terms of fractal geometry. The fractal reaction dimension Dr may help to understand problems in reaction kinetics. For the discussion of dissipative structures and chaotic reactions, too, the fractal concept gains importance.
Quantitative Untersuchungen zur Adsorption von o‐Methylrot an modifizierten Polykieselsäureoberflächen
Authors: Erler Ulrich , Heublein Günther 
Published: September 2010

AbstractQuantitative description of methyl‐red adsorption from benzene solution on surfaces of modified and unmodified silicas is possible with aid of adsorption isothermes of the Langmuir and the Freundlich‐type. Those investigations lead to conclusions about the degree of reaction between silica surfaces and modification reagents like silanes or active polymers.
Neuere Methoden zur quantitativen Auswertung von UV‐VIS‐Remissionsspektren
Authors: Gade Reinhold , Faßler Dieter 
Published: September 2010

AbstractBased on a survey about the applications of diffuse reflectance spectroscopy various methods for quantitative evaluation of these spectra are presented. At first the correction of diffuse reflectance spectra of luminescent samples and the determination of pigment concentrations from reflectance data of powder mixtures are considered in detail. Furthermore a recently suggested method is described enabling the bulk‐absorption coefficients of substrate materials and the molar absorption coefficients of adsorbed molecules respectively to be calculated from diffuse reflectance spectra of powdered adsorbent‐adsorbates.
Cyclometallierende Photodecarboxylierung von Übergangsmetallkomplexen
Authors: Pavlovski Valeri I. , Poznyak Anatoli L. 
Published: September 2010

AbstractPhotodecarboxylation reactions of chelated transition metal carboxylates leading to cyclometallated coordination compounds are considered. The possibilities of such reactions for the synthesis of compounds with three‐, four‐ or five‐membered metallocycles are demonstrated.
Die Reduktion von Bariumsulfat mit Kohlenstoff; Der Reaktionsverlauf
Authors: Kempe Gottfried , Bögel Monika , Meyer Gerhard 
Published: September 2010

AbstractBarium sulphate is reduced by carbon to barium sulphide at higher temperatures. BaCO3, SO2, Sn and COS are found as by‐products in small amounts. It has been confirmed experimentally that barium sulphite is an intermediate of the reduction process. This compound, however, is not stable at temperatures above 500°C and decomposes mainly to BaSO4 and BaS and to a little extent to BaO and SO2. This reactions even take place in the presence of carbon which obviously only attacks the BaSO4 whilst the barium sulphide is enriched in the reaction products. A series of consecutive and side reactions is proposed describing the stepwise reduction of barium sulphate to barium sulphide.
Näherungsverfahren zur Ermittlung von Teilgeschwindigkeitskonstanten eines komplexen, linear abhängigen Reaktionsmodells
Authors: Füllbier Barbara , Haberland Detlef 
Published: September 2010

AbstractA system of linear dependent competitive secondary reactions is regard to, for the kinetical investigation of the synthesis of dimethoate. An analytical solution of this simultane differential equation system is not possible. Various most integral methods of approximation for the solution of this problem are proposed and their usefulness are tested on the basis of experimental data. A complete solution of the differential equations, which is permitted to test the quality of the applied methods of approximations, are obtained by French‐transformation. A good correspondence between experimental and calculated data, is obtained by using a numerical procedure of Range‐Kutta.
Struktur und Aggregation von Dimethylammonium‐dimethylcarbamat (Dimcarb) und analogen Dialkylammonium‐dialkylcarbamaten
Authors: Schroth Werner , Schädler Hans‐Dieter , Andersch Jörg 
Published: September 2010

AbstractIn the wide range of carbamic acid derivatives, dialkylammonium‐dialkylcarbamates receive an exceptional position concerning their structure, molecular aggregation, and thermal behaviour. Among them the first member of this series, dimethylammonium‐dimethylcarbamate, briefly called dimcarb, represents a distillable liquid and claims additional interest in view of preparative utilizations. Its unusual properties have been investigated with regard to other ammonium‐carbamates, resulting in some remarkable conclusions by means of different physical methods. Thus, dimcarb is highly structured in dependence on temperature (viscosimetry, refractometry, cryoscopy). Dimethylamine and carbondioxide are bonded only weakly by binding energies in the order of non‐specific solvation energies (caloric measurements). The ionic species are predominantly involved in contact ion pairs (conductivity) and display a dynamic behaviour along with different prototropic interactions including dimethylcarbamic acid (N M R spectra). Informations about favoured structure combinations are given (quantum chemical calculations, I R and Raman spectra, mass spectra). Altogether, the unusual properties of dimcarb are based on a flexible structure behaviour, sensitively influenced by external factors (temperature, medium, reaction partners).
Rotationsbarrieren exocyclischer, partieller C,N‐Doppelbindungen in aromatischen Verbindungen — Indikatoren der n,π‐Mesomerie
Authors: Kleinpeter Erich 
Published: September 2010

AbstractThe rotational barriers about the exocyclic partial C,N‐double bonds of dimethylamino‐substituted aromatic π‐electron systems, studied so far, have been discussed with respect to the degree of n,π‐mesomerism of the dimethylamino substituent (n‐electrons) and the aromatic system (π‐electrons). Hereby, the possibility arises to estimate the π‐electron deficiency of the heteroaromatic systems studied if the dimethylamino substituent is hold constant. Relevant influences of steric hindrance, of heteroatoms involved, of one positive charge in the aromatic spezies, of further substituents on the same ring system and of the solvent on the dynamic process studied were considered. The parallelism of the rotational barriers to other useful parameters to classify the present degree of n,π‐mesomerisms (1H, 13C and 15N chemical shifts, Hammett substituent constants. C,H coupling constants) is critically estimated.Additionally, special barrier (and adequately the chemistry) determining substructures (vinylogous amides and thioamides, tri‐ and pentamethine cyanines) could be identified.
Aktuelle Aufgaben der chemischen Toxikologie bei der Chemikalienbewertung
Authors: Titephan Ursula 
Published: September 2010

AbstractThe increasing of chemical products and chemical processes in the last years required new concepts for chemical safety. This new laws and governmental regulations based on the knowledge of the chemical, physical and toxicological properties of substances. In the field of safetycodes the chemical toxicology takes a leading part. The risk assessment includes knowledge about chemical reactivity, biotransformation, decomposition and accumulation in the biosphere and the migration of chemicals in water, air and/or soils. Knowledge about the behaviour of chemicals in the biosphere are necessarily for the replacement of toxic chemicals by nontoxic substances demanded by law of poisons or for the waste management. Some topics about the interdependence of progress of chemical toxicology and more chemical safety by laws are discussed.
Elektrochemisches Verhalten von 2,4‐Diamino‐1,3,5‐triazinen und ihren Photolyseprodukten
Authors: Schmidt Silke , Mattusch Jürgen , Werner Gerhard 
Published: September 2010

Abstract2,4‐Diamino‐1,3,5‐triazines are widely applied as herbicides. These compounds are very stable which leads to a accumulation in soil and plants. To detect this group of compounds chromatographic methods (gas chromatography, HPLC, TLC) were employed in the past. The present work was done with the aim to determine electrochemically triazines in flowing systems like HPLC and FIA. Therefore the polarographic and voltammetric behaviour of these compounds was investigated. A sensitive detection was possible on a mercury electrode in the cathodic range and on a glassy carbon electrode pretreated by galvanostatic pulses in the anodic range. The sensitivity can be improved by photochemical derivatization of the triazines in 6‐position to create phenol‐like compounds. The photochemical response of simazine, prometryne, atrazine and ametryne depends on the substitutes in 2‐ and 4‐position and also in 6‐position. The degree of the photochemical conversion was measured with an amperometric detector in a FIA equipment.
Gifte sukkulenter Pflanzen: Cyanogene Glycoside, Glucosinolate, Amine
Authors: Swart Hans 
Published: September 2010

AbstractMany of the about 10,000 succulents are cultivated in Botanical Gardens or amateur collections. Some of them are poisonous plants anl may cause health injuries by careless handling or misuse. Several succulents are used as medicinal, narcotic, or magic plants in their habitats, others are applied for fishing or making poisonous arrows for hunting. Poisoning of livestock may happen due to feeding of special succulents, too. This review mainly describes cyanogenic glycosides of the genus Adenia, glucosinolates in some Moringa species, and phenethylamines of the Cactaceae. As to await, further investigations in this field will get increasing importance, especially for the development of new drugs.
N‐Heterocyclen aus Diaminen
Authors: Kempter Gerhard , Spindler Jürgen 
Published: September 2010

AbstractPesticide chemistry has still a special importance for protection of human food; new pesticides to develop is necessary because of economical and ecological reasons. A description is given of the synthesis of numerous new heterocycles containing triazino‐, triazolino‐ and thiazolo‐condensed quinazolines, benzodiazepines and benzodiazocines. On principle, all of them are in possession of pesticide‐relevant structure elements like cyclic ureas and thioureas and allow correlations between ring‐size and bioactivity. The starting materials are o‐amino‐phenylalkylamines especially aromatic‐aliphatic 1,3‐, 1, 4‐and 1, 5‐diamines; their preparation is also given.
p‐Chinone und p‐Chinonfragmente; „Non‐innocent”︁‐Liganden in elektronenreichen Komplexen der späten d‐Elemente
Authors: Uhlig Egon 
Published: September 2010

AbstractThe coordination behaviour of p‐quinones and p‐quinone fragments in electron‐rich complexes is variable. Considering primarily the nickel triade elements, p‐quinones are bound to palladium(0) or platinum(0) by the CC‐groups (η2‐or η4‐interaction).With nickel(0) the behavior is more complicated. η4(CC)‐coordination is found for Ni(Dch)2 and η2‐coordination for (dipy)Ni(Nch). But because of the stronger oxophilic properties of this element, also an η2(CO)‐coordination is possible, as was shown for (Cy3P)2Ni(Achθ•) · Et2O. In complexes with a low content of phosphine the donors R‐cum or Nch have the function of η2(CC, O)‐bridging ligands.Chloranile with its high half‐wave potential oxidises nickel(0) to nickel(II) and is simultaneously reduced to the dianion of the corresponding hydroquinone. In another case — (Cy3P)Ni(Ach⊖) — the redox process stops at the state of nickel(I) and of the radical anion. It is a general rule, that both 1,5‐cyclooctadiene as a simple diolefine and normal p‐quinones can coordinate to nickel(0) or nickel(I) as n‐acceptor ligands by the CC‐ or in the case of Ach even by the CO‐group. This is not possible with nickel(II) which is only a weak †‐donor.Tertiary phosphines attack Bch, CA, NCh or MSA nucleophilically forming phosphabetaines. Because of the lower nucleophilicity of the phosphine and the lower electrophilicity of the p‐quinone in the coordination sphere of electron‐rich central atoms this reaction does not proceed. The systems of (Cy3P)2Ni(C2H4) with CA, Bch and MSA are exceptional. In these cases the formation of phosphabetaines is connected with an one‐electron transfer. The products are nickel(II)‐species with radical anions as ligands.In general the normal reactions of p‐quinones are hindered in the coordination sphere of electron‐rich complexes. But sometimes other pathways of synthetic use are opend.
Hexacoordinated Complexes of Phosphorus, Arsenic and Antimony Pentafluorides with Oxygen, Nitrogen and Sulphur Containing Ligands
Authors: Buslaev Yuryi , Ilyin Evgenyi , Calov Ursula 
Published: September 2010

AbstractThe paper considers complex formation and structure of phosphorus, arsenic and antimony fluorine‐containing octahedral compounds in organic solvents, aqueous and peroxide solutions, on the basis of results obtained by chemists of the USSR and G.D.R. in the course of recent year scientific cooperation.
Reaktionsverhalten der Kohlenhydrate in wasserfreiem, flüssigem Fluorwasserstoff
Authors: Miethchen Ralf 
Published: September 2010

AbstractThe present review discusses reactions of unprotected and protected carbohydrates in hydrogen fluoride as well as the synthesis of fluorinated carbohydrates by use of anhydrous liquid hydrogen fluoride or Systems containing hydrogen fluoride (e.g. HF/pyridine, triethylamine trishydrofluoride). Our results concerning the stereo‐selective synthesis of kinetically controlled glycosyl fluorides and the micellar aggregation of amphiphilic 3‐0‐(n‐alkyl)‐D‐gluco‐pyranose derivatives in HF are involved. The paper presents a brief introduction in a survey concerning the application of fluorinated carbohydrates. The literature published since the article of Lenard (1969) is summarized.
NMR‐Spektroskopie an phosphororganischen Verbindungen — Beiträge zur Molekülstruktur
Authors: Zschunke Adolf 
Published: September 2010

AbstractThe paper demonstrates the use of N M R‐spectroscopy of organic phosphorus compounds for the detailed description of the molecular structure in the liquid state. It gives special emphasis to the application of 31P‐coupling constants in solving stereochemical problems. An example is the estimation of the conformations and of the relative configuration of phosphorheterocycles.The N M R‐detection of intramolecular mobility is demonstrated on Berry process of (CHs)2N P F4, bond‐fluctuation of Li3P7, phosphorus‐inversion of 1,3‐diphosphorheterocycles and simultaneous processes of allyl‐palladium‐phosphin‐complexes. The autoassociation of organo‐phosphides in different solvents is finally investigated by means of N M R‐spectroscopy.
Nichtklassische Kettenreaktionen
Authors: Eggert Lutz , Kuz'min Michail Georgievič , Ivanov Vladimir Leonidovič 
Published: September 2010

AbstractThe review considers non‐classical mechanisms of chain reactions, which were proposed in recent years. In contrary to classical radical chain mechanisms such mechanisms include electron transfer, heterolytic and other non‐heterolytic elementary propagation steps and a variety of transients (ions, ion‐radicals, biradicals etc.). Most of the known non‐classical chain reactions include electron transfer propagation step. A lot of new speculative chain mechanisms was proposed in literature, but further experimental investigations of short living transient and kinetics of these reactions is necessary to prove their mechanisms. Such investigations will open new possibilities to use chain reactions in chemical and other processes.
Koordinationschemische Stabilisierung „nackter”︁ Elemente der V. Hauptgruppe (außer Stickstoff) — Synthese, Struktur und Bindung
Authors: Scheer Manfred , Herrmann Eckhard 
Published: September 2010

AbstractThe complexchemisty of “nacked” Ex‐unites (E = P, As, Sb, Bi; x = 1–6) has developed rapidly since the end of the seventies. Most of the Ex‐groups, except P4, are unstable in the free state but can be stabilized by complexation with transition metal fragments. They are isolobal to the corresponding (CH)x‐arrangements. This article gives a comprehensive review of this young and dynamic field of chemistry up to 1988. It generalizes methods of synthesis, compares modes of coordination and types of polyeders of these complexes. The article describes the analogies and differences in the coordination behaviour of “nacked” Ex‐groups of phosphorus, arsenic, antimony and bismuth. Thus, there is an anomaly of bismuthine complexes by reason of the metallic character of Bi.