bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inorganic Reactions with Arc‐heated Gases
Authors: Harnisch H. , Heymer G. , Schallus E. 
Published: December 2003

AbstractA novel electric‐arc device, with a torch consuming 100to 240 amps DC has been developed. In previous apparatus of this kind, both reactants passed through the arc together, but now only one component (e.g., hydrogen or nitrogen) is heated in this new‐process. The temperature of this component is raised to a point where it exists in a highly excited state or dissociates into free atoms and then leaves the arc in a stream with supersonic velocity through a hole drilled in the anode, being then mixed with the other reactant. The resultant mixture is then immediately quenched. The design and operation of the torch as well as the mixing and quenching procedures are discussed. The preparation of chlorosilanes, titanium trichloride, titanium nitride, and hydrazine by this method is described.
The Biogenesis of Ergot Alkaloids
Authors: Weygand F. , Floss H.‐G. 
Published: December 2003

AbstractIn this article the biogenesis of the ergoline ring in lysergic acid derivatives and the clavines is discussed. T·yptophan and mevalonic acid are the precursors. The N‐methyl group is supplied by formate or methionine. Concepts and results dealing with the manner in which the compounds are formed are discussed. Finally, the known biogenetic relationships among the ergot alkaloids are discussed in connection with their biogenesis.
Solid‐State Reactions
Authors: Schmalzried H. 
Published: December 2003

AbstractIn the following, solid‐state reactions between ionic crystals are described. The vast field of powder reactions will not be discussed, since various parameters such as particle size distribution and packing density are difficult to determine exactly. The result of this is, that it is almost impossible to establish the mechanisms of solid‐state powder reactions unambiguously and derive general expressions for reaction rates.
The Mössbauer Effect and its Significance in Chemistry
Authors: Fluck E. , Kerler W. , Neuwirth W. 
Published: December 2003

AbstractResonance fluorescence of recoil‐free γ‐rays from atomic nuclei depends on the state of the chemical bonding of the atoms. The latter influences the position of the energy level of the atomic nuclei, so that the energy required for excitation of resonance fluorescence is somewhat smaller or greater than the energy of the γ‐quanta emitted by the radiation source. In order to obtain resonance fluorescence, therefore, the radiation source and absorber have to be kept moving relative to each other. If the intensity of the resonance fluorescence is plotted against this relative velocity, Mössbauer spectra are obtained. The positions of the lines in these spectra make it possible to draw conclusions about the nature of the atom's bonds. The efficiency of this method is demonstrated by illustration with numerous iron compounds. It was shown, for instance, that the iron atoms in “insoluble Prussian Blue” have well‐defined oxidation levels. “Turnbull's Blue” shows the identical spectrum. A structure could be ascribed to tri‐iron dodecacarbonyl that also explains the diamagnetism of the compound.
Base‐Catalysed Reactions of Ketones with Hydrogen Sulfide
Authors: Mayer Roland , Hiller G. , Nitzschke Margot , Jentzsch J. 
Published: December 2003

AbstractMonoketones react with hydrogen sulfide in the presence of basic catalysts to give geminal dithiols or thioketones. β‐Diketones are converted into monothiodiketones. α‐Diketones can be selectively reduced by hydrogen sulfide in the cold in the presence of secondary or tertiary amines to give hydroxy‐or mono‐ketones.
Recent Studies on the Centrally Active Endogenous Amines
Authors: Daly J. W. , Witkop B. 
Published: December 2003

AbstractThe past five years have withnessed significant progress in our knowledge of the metabolism and importance of endogenous, peripherally and centrally active amines. Most of the modern drugs which influence human mood, emotion, or temperament do so by their direct or indirect effect on the biosynthesis, metabolism, storage, or release of endogenous amines in the brain. The relationships discovered in this connection have deepened our understanding of the biochemical basis of acute, chronic, and hereditary mental disorders. The beginnings of a new science “psychochemistry” are discernible at this point.
Syntheses of Heterocyclic Compounds from Aminoguanidine
Authors: Kurzer F. , Godfrey L. E. A. 
Published: December 2003

AbstractDue to its unique structure, aminoguanidine is capable of reacting as a derivative of hydrazine, guanidine or formamidine. Addition and condensation reactions yield products which can be cyclized to heterocyclic compounds. Frequently, heterocyclics are directly accessible from aminoguanidine in one stage.
Modern Methods for the Separation and Continuous Measurement in the Gas Phase of Compounds Labelled with Radiocarbon. Radio and Reaction Gas Chromatography
Authors: Drawert F. , Bachmann O. 
Published: December 2003

AbstractIn biochemical work with isotopic tracers, it is frequently advantageous to investigate samples in the gas phase. In this way, the selectivity of gas‐chromatographic separating columns and the sensitivity of detectors can be utilized for both the detection of gas‐chromatographic fractions and the determination of their radioactive portions. Conversion of materials separated by gas chromatography into a single standard chemical compound prior to measurement of the radioactivity is recommended. Methods suitable for 14C‐labelled compounds can also be applied to those labelled with 3H or 35S.
1,3‐Dipolar Cycloadditions. Past and Future
Authors: Huisgen Rolf 
Published: December 2003

AbstractIn contrast to the very large number of special methods applicable to syntheses in the heterocyclic series, relatively few general methods are available. The 1,3‐dipolar addition offers a remarkably wide range of utility in the synthesis of five‐membered heterocycles. Here the “1,3‐dipole”, which can only be represented by zwitterionic octet resonance structures, combines in a cycloaddition with a multiple bond system – the “dipolarophile” – to form an uncharged five‐membered ring. Although numerous individual examples of this reaction were known, some even back in the nineteenth century, fruitful development of this synthetic principle has been achieved only in recent years.
Nitrenes
Authors: Horner L. , Christmann A. 
Published: December 2003

AbstractNitrens are molecular fragments with six electrons on the nitrogen which are formed thermally or photochemically from hydrazoic acid or organic azides. Kinetics of the cleavage of azides, spectroscopic data, and electron spin resonance measurements constitute proof for a biradical nature of the nitrens studied. As a result of hydrogen shifts, nitrens are capable of isomerization to mines, of hydrogen abstraction from neighbouring molecules affording primary amines, and of ring formation by internal dehydrogenation (insertion reactions). Isomerization and hydrogen shifts are observed primarily with alkylnitrens; however, under favorable structural conditions, hydrogen shifts in arylnitrenes also lead to immines. Arylinitrens dimirize to azo compounds and undergo intra‐ and intermolecular reactions with nucleophilic reactants. Thus, both stable and unstable acylnitrenes, which are formed thermally or photolytically from acyl azides, add on, for example, to dimethyl sulfide or dimethyl sulfoxide, affording sulfimines or sulfoximines, respectively. Nucleophilic reagents, such as alcohols and amines, also react with nitrenes. Besides azides, anil‐N‐oxides also undergo cleavage to give nitrenes. The reaction of N‐chloramines and hydroxylamine‐O‐sulfonic acids with nucleophilic reagents probably does not proceed via a nitrene intermediate, but rathr by an SN mechanism. A crucial experiment differentiating between these two paths is described, and Rashig's hydrazine synthesis is discussed in detail.
An Acylal of Dimethylketene
Authors: Bestian H. , Günther D. 
Published: December 2003

AbstractFree dimethylketene is difficult to handle because of its tendancy to dimerize even at low temperatures and to from explosive peroxides with atmospheric oxygen. In contrast, the dimethylketenacylal of dimethylmalonic acid is simple and safe to use. This compound affords dimethylketene on thermal or catayltic cleavege, hence, it can replace the free ketene in nearly all reaction. The synthesis and reactions of this acylal are described.
Isothiazoles
Authors: Hübenett F. , Flock F. H. , Hansel W. , Heinze H. , Hofmann Hd. 
Published: December 2003

AbstractThe ring system of non‐anellated 1,2‐thiazoles (isothiazoles) has only recently become accessible. Four syntheses and numerous interconversions have opened up new routes to compounds which command interest as intermediates and as analogues of natural products and established pharmaceuticals.
Type and Extent of Isomerization of Straight‐Chain Mono‐olefins during the Koch Carboxylic Acid Synthesis
Authors: Möller K. E. 
Published: December 2003

AbstractWhen straight‐chain mono‐olefins, from pentene to decene, are subjected to the Koch carboxylic acid synthesis by the addition of CO and H2O or CH3OH in the presence of strongly acidic catalysts, not only the expected secondary acids, but also mixtures of a specific type of tertiary acids or their methyl esters are formed. When the catalysts contain boron trifluoride, the secondary acids are formed in ratios of isomers which are, within the scope of this investigation, independent of the experimental conditions and which agree well with the values calculated from the isomer equilibria of the corresponding n‐olefins. Using concentrated sulfuric acid as catalyst, a larger proportion of tertiary acids is obtained than with BF3‐catalysis, and amongst the secondary acids, those isomers predominate in which the COOH group is situated near the centre of the molecule.
Phenol Oxidation Reactions
Authors: Musso H. 
Published: December 2003

AbstractThe use of well‐known phenol oxidation reactions for the preparation of compounds arising from CC and CO coupling has recently received increased attention. A selection from the large number of products obtainable by oxidation of mono‐ and polyhydric phenols and a discussion of the reaction mechanisms indicate the scope of this method. The formation of hydroxyphenylquinones and orceine dyes from resorcinol derivatives is explained. The synthesis of natural products by way of phenol oxidations is briefly discussed.
The Reaction of Oxides with Water at High Pressures and Temperatures
Authors: Wendlandt H. G. , Glemser O. 
Published: December 2003

AbstractThe reactions of the oxides SiO2, MoO3, and WO3 with steam at temperatures between 400 and 700 °C and pressures of 5 to 500 atm were studied by means of the transfer method. The results were evaluated by a new method. In the system Sio2/H2O the formation of gaseous Si(OH)4, Si2O(OH)6, and [SiO2(OH)2]x was found to occur in three different water‐density ranges. In the systems MoO3/H2O and WO3/H2O the gaseous compounds MoO2(OH)2 and WO2(OH)2, which were already known, exist up to densities of approximately 0.05g/cm3. At higher densities, at which the supercritical phase begins to show the properties of a liquid to an ever increasing extent, isopolymolybdic or isopolytungstic acids appear.
Defensive Substances of the Arthropods, Their Isolation and Identification
Authors: Schildknecht H. , Holoubek K. , Weis K. H. , Krämer H. 
Published: December 2003

AbstractNumerous orders of arthropods have organs which produce and store defensive substances. The purpose of our studies was to learn more about the chemical composition of these defensive secretions. In this work, we had to forego a priori many of the possibilities of classical organic‐chemical analysis, since some of the insects were difficult to obtain and operation with substantial amounts of material was precluded. However, the defensive substances of various families of Arthropoda were characterized by using modern chemical and physical analytical procedures and our own methods of separation, purification, and enrichment which we developed specifically for this purpose.
The Mechanism of the Action of Organometallic Catalysts
Authors: Sinn H. , Patat F. 
Published: December 2003

AbstractKinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n‐heptane as solvent indicate the following sequence of reactions: 1. formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, and proof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler‐type catalyst. All the reactions can be formulated in the form of cyclic structures with electron‐deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.
Transformations of Organoboranes at Elevated Temperatures
Authors: Köster R. 
Published: December 2003

AbstractTrialkylboranes with identical or different groups on the boron are stable to alkyl exchange at room temperature. Mixed trialkylboranes only undergo disproportionation in the presence of catalysts such as aluminum trialkyls and boron‐hydrogen compounds. At temperatures above 100 °C, organoboranes such as trialkylboranes and B‐alkylboracyclanes isomerize as a result of migration of the boron along the aliphatic hydrocarbon radical via dehydroboration‐hydroboration equilibria. Alkyl, cycloalkyl, as well as aralkyl and certain arylboranes can be converted irreversibly by pyrolysis at 200–300 °C into other organoboranes (methylboranes and boron‐heterocycles of various structures).
Oxidative Condensation of Quaternary Phenolic Bases
Authors: Franck B. , Blaschke G. , Schlingloff G. 
Published: December 2003

AbstractProvided they contain quaternary nitrogen, simple phenolic bases can undergo oxidative condensation under conditions similar to those of biogenesis to form alkaloids of the isoquinoline series with good yields. By means of such oxidative condensations, more than sixty alkaloids of various structural types have become more easily obtainable. Of the numerous possible condensations of the intermediate mesomeric radicals only those which lead to naturally occurring alkaloids give good yields and few by‐products. The results suggest that oxidative condensations of quaternary bases are also involved in the biosynthesis of alkaloids in the plant cell.
New Methods of Preparative Organic Chemistry IV. Cyclization of Dialdehydes with Nitromethane
Authors: Lichtenthaler F. W. 
Published: December 2003

AbstractCondensation of nitromethane with suitable diadehydes in alkaline medium provides a general method of cyclization, in which the methyl group of the nitromethane is incorporated into the ring. This method leads to 5‐, 6‐, and 7‐membered rings and is equally applicable to aliphatic, aromatic, and sugar dialdehydes. For example, glyoxal is converted into 1,4‐dideoxy‐1,4‐dinitro‐neo‐inositol, and glutaraldehyde into trans‐2‐nitrocyclohexane‐1,3‐diol, while the corresponding cyclization of xylo‐trihydroxyglutaraldehyde leads to deoxy‐nitroinositols having the scyllo, myo‐1, and muco‐3 configurations.‐In the case of aromatic dialdehydes, the cyclization is accompanied by elimination of water. Thus, phthalaldehyde, naphthalene‐2,3‐dicarboxaldehyde, and homophthalaldehyde yield, respectively, 2‐nitroindenol, 2‐nitrobenzindenol, and 2‐nitronaphthalene. ‐Application of the method to sugar dialdehydes (aldehydic diglycol derivatives of monosaccharides formed by periodate oxidation) constitutes an excellent synthesis of 3‐amino sugars, since 3‐deoxy‐3‐nitropyranoses are formed smoothly on cyclization, and the corresponding 3‐amino derivatives are obtained by hydrogenation. Thus, the reaction sequence: periodate oxidation → cyclization with nitromethane → hydrogenation, leads in the case of α‐and β‐D‐pentosides to 3‐amino‐3‐deoxy‐D‐and‐L‐pentosides, respectively, with ribo, xylo, and arabino configurations. α‐D‐hexosides give derivatives with gluco, manno, and galacto configurations. 3‐Amino‐3,6‐dideoxyglucosides of the D‐and L‐series are obtained from 6‐deoxy‐D‐or‐L‐hexosides, respectively, and 3‐aminohexosans with gulo, ido, and altro configurations are obtained from 1,6‐anhydro sugars. Cyclization of the dialdehydes obtained from sedoheptulose and methyl 4,6‐O‐ethylidene‐α‐D‐glucoside by periodate oxidation, leads to 3‐nitro and, after hydrogenation, to 3‐amino derivatives of 3‐deoxyheptopyranoses.
Synthesis of Naturally Occurring Unsaturated Fatty Acids by Sterically Controlled Carbonyl Olefination
Authors: Bergelson L. D. , Shemyakin M. M. 
Published: December 2003

AbstractIt is shown that carbonyl olefination, i.e. the reaction of carbonyl compounds with alkylidene phosphoranes, can be sterically controlled. In some cases cis‐olefins can be obtained by proper choice of the reaction conditions; trans‐olefins are formed only in the presence of suitable structural factors. These cis‐and trans‐olefination reactions have opened new, stereo‐specific routes to unsaturated and polyunsaturated fatty acids with differing positions and sequences of cis‐ and trans‐double bonds and to ω‐hydroxy and branched chain fatty acids.
New Methods of Preparative Organic Chemistry IV
Authors: Wanzlick H. W. , Lehmann‐Horchler M. , Mohrmann S. , Gritzky R. , Heidepriem H. , Pankow B. 
Published: December 2003

AbstractIf catechol or other hydroquinones are dehydrogenated in the presence of a nucleophilic reagent, the latter reacts, usually by Michael addition, with the quinone formed in situ. The wide range of possible variations offered by this synthetic method is comprehensively described in the present paper. procedures are given for carrying out typical reactions.
New Reactive Dyes
Authors: Kleb K. G. , Siegel E. , Sasse K. 
Published: December 2003

AbstractTwo new groups of reactive dyestuffs have been developed. One group (Levafix® dyes) comprises compounds which contain SO2NHCH2CH2OSO3H or CH2N(alkyl)‐CH2CH2OSO3H as reactive groups. The dyes of this group react with cellulose fibers to form cellulose ethers, e.g. RSO2NHCH2CH2Ocellulose. The substances in the second group (Levafix‐E® dyes) consist of the amides formed from 2,3‐dichloroquinoxaline‐6‐carboxylic acid and dyestuffs containing primary or secondary amino groups.
Relations between Structure and Reactivity of Ambifunctional Nucleophilic Compounds
Authors: Gompper R. 
Published: December 2003

AbstractTheoretical considerations and recent experimental results have added greatly to our knowledge of the structures and reactivities of ambifunctional nucleophilic compounds during the last few years. In the present work an attempt is made to present a survey of the theories which have been developed to explain the behavior of these compounds towards electrophilic reagents, and to formulate rules which may serve as guides for carrying out new reactions.
Surface Oxides of Carbon
Authors: Boehm H.‐P. , Diehl E. , Heck W. , Sappok R. 
Published: December 2003

AbstractOn oxidation of graphitic carbon, acidic surface oxides (or hydroxides in the presence of water) are formed at the boundaries of the carbon layers. It was found that the reaction of oxygen with microcrystalline carbon at 400–450°C yields four groups of different acidities. One strongly acidic group and one weakly acidic carboxyl group have been detected, as well as a phenolic hydroxyl group; a carbonyl group is probably also present. With dissolved oxidizing agents, one equivalent of another strongly acidic carboxyl group is formed in addition at room temperature. The possible constitutions of the acidic surface oxides are discussed. Chemically detectable surface oxides are also formed on the surface of diamond. In the presence of oxygen at 800–900°C under reduced pressure, diamond is transformed into black carbon. Surface oxides play a part in this transformation.
Stereospecific Homopolymerization of Cyclopentene
Authors: Natta G. , Dall'Asta G. , Mazzanti G. 
Published: December 2003

AbstractThe polymerization of cyclo‐olefins, like that of olefins with an internal double bond, is sterically hindered. Within recent years it has become possible to prepare copolymers of these compounds with ethylene, with the aid of anionic coordination Ziegler catalysts. This copolymerization always results in cis‐opening of the double bond. Despite the steric hindrance, cyclobutene and cyclopropene have also been homopolymerized, with opening of the double bond. – Rather surprisingly, the best catalysts for homopolymerization of cyclopentene are those which exhibit low activity in the polymerization of ethylene. Ring cleavage occurs with MoCl5/Al(C2H5)3 to give the cis‐polypentenamer, whereas WCl6/Al(C2H5)3 gives the trans‐polypentenamer. Both polypentenamers exhibit elastomeric properties. – Evidence from infrared spectra and oxidative degradation indicates that the monomer units in the trans‐polypentenamer are linked head‐to‐tail. It is presumably the single bond adjacent to the double bond that is broken. Using X‐ray methods at −50 °C, it was possible to determine the crystal structure of the crystalline trans‐polypentenamer at about 400% elongation.
Phosphonium Salt Formation of the Second Kind
Authors: Hoffmann H. , Diehr H. J. 
Published: December 2003

AbstractOrganic compounds containing a positively polarized halogen atom react with tertiary phosphines either with reductive elimination of the halogen or with formation of phosphonium salts and quasi‐phosphonium salts, depending on the solvent. In this reaction, the phosphine first attacks the halogen.
Proton‐Addition Complexes of Aromatic Hydrocarbons
Authors: Perkampus H.‐H. , Baumgarten E. 
Published: December 2003

AbstractThe structures of proton‐addition complexes of aromatic hydrocarbons were hitherto known only with respect to their stoichiometric compositions but can now be clarified by ultraviolet, infrared, and NMR spectroscopic methods. For example, it has been possible to prove by NMR soectroscopy that the expected addition of protons into 9,10‐dimethyl‐[a] benzanthracene actually does take place. Two isomeric proton adducts of toluene have been found by means of infrared spectra. On addition of protons, the ultraviolet spectra of aromatics change considerably; excellent agreement is sometimes observed between the band maxima calculated by quantum mechanics and those found by experiment.
Cyclopropenylium Compounds and Cyclopropenones
Authors: Krebs A. W. 
Published: December 2003

AbstractThe predictions of Hückel's rule gave the incentive to numerous investigations which led ultimately to a new definition of aromatic character, and which have added greatly to our knowledge of the properties and reactivity of aromatic compounds. Increasing use was made of physical measurements as criteria for the aromaticity of a compound. The first member (n = O) in the series of Hückel's (4n + 2) π systems is the cyclopropenylium cation. The predictions regarding the stability of this system have been confirmed at least qualitatively by the synthesis of cyclopropenylium salts. Properties and reactions of cyclopropenylium compounds and cyclopropenones were investigated.
Empirical Parameters of the Polarity of Solvents
Authors: Reichardt C. 
Published: December 2003

AbstractThe empirical parameters of the polarity of solvents which have been determined recently are reviewed: Y‐values (Winstein, Grunwald), X‐values (Gielen, Nasielski), Ω‐values (Berson, Hamlet, Mueller), Z‐values (Kosower), ET‐values (Dimroth, Reichardt, Siepmann, Bohlmann), R‐ and S‐values (Brownstein). Their field of application and interrelationships are discussed. The theoretical principles of the solvent effect on the reaction rate and light absorption of organic compounds are briefly described, and mention is made of attempts to correlate the physical characteristics of the solvent with the empirical parameters.